Mwd Theory

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Scientific Drilling

MUD PULSE MWD

THEORY MANUAL

Nov. 2000



MWD MUD PULSE MANUAL CONTENTS

Chapter 1 Tool Specifications............................................................... 1

Chapter 2 Tool Operation...................................................................... 6

Introduction.................................................................. 7

Super or Golden EYE .................................................. 9

MWD Controller ........................................................... 13

Gamma ....................................................................... 16

Pulser Driver................................................................ 19

Battery ......................................................................... 23

Power and Communication.......................................... 25

Tool Block Diagram ..................................................... 26

Chapter 3 Pulser Operation................................................................... 28

Overview...................................................................... 29

Detailed Description..................................................... 30

Chapter 4 Surface System..................................................................... 35

Overview...................................................................... 36

Standpipe Pressure Sensor......................................... 38

Pump Position Sensor ................................................. 41Depth Sensor............................................................... 42

Rig Floor Display ......................................................... 44

Tool Communication.................................................... 45

Surface System Hook Up............................................. 46

Chapter 5 Detection Decoding.............................................................. 48

Telecommunications Basics ........................................ 49

Mud Pulse Encoding Scheme...................................... 60

Signal to Noise Ratio ................................................... 69

Chapter 6 Talkdown Scheme ................................................................ 76

Chapter 7 Troubleshooting Flow Diagram........................................... 81

Company Confidential

© 2000 Scientific Drilling International – Revision Nov. 2000

Written by Mike Meadows Toucan Consultancy Inc. (Orig. release Jan. 2000)



TOOL SPECIFICATIONS CHAPTER 1

Contents

CONTENTS .........................................................................................................................................................1

PRODUCT INFORMATION .............. ............. ............. ............. ............. .............. ............. ............. ............. ....... 2

TOOL SPECIFICATION IN PETROLEUM ENGINEER FORMAT................... ............. ............. ............. ..... 3

COMPLETE SENSOR SPECIFICATIONS............. ............. ............. ............. ............. .............. ............. ........... 4

UPDATE RATES.... ............. ............. .............. ............. ............. ............. ............. .............. ............. ............. ......... 4

MAKE-UP TORQUES.............. ............. ............. ............. ............. .............. ............. ............. ............. ............. ..... 5

GAMMA SCALE FACTORS......... ............. .............. ............. ............. ............. ............. .............. ............. ........... 5

Company Confidential© 2000 Scientific Drilling International



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Mud Pulse Theory Manual Chapter 1 – Tool Specifications Page 2Revision Nov. 2000

Product Information



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Tool Specification in Petroleum Engineer Format

GENERAL

Tool OD available, in 4 ¾, 6¼, 6 ½, 6 ¾, 8, 9 ½

Length, ft (tool OD)

Directional Only 16.8 (plus 4.0 pulser sub)

DIR + Gamma Ray 16.8 (plus 4.0 pulser sub)

Maximum dogleg severity

degrees/100ft (tool OD)

Sliding (non-rotating) 12(8"), 20(6¾ "), 28(4 ¾")

Rotating 7(8"), 10(6 ¾ "), 12(4 ¾")

Equivalent bending stiffness 4.66 x 2.25 (4 ¾)

OD x ID, in (tool OD)

Maximum operating temperature 150° (302°)

Degrees C (degrees F)

Power Source Lithium Battery

Operating time, hours 150

Maximum working pressure, psi 20,000

Mud flow rate range, gal/min 100 - 400 (4 ¾- 6 ½)

(Tool OD) 125 -1000 (6 ¾) 125-1500 (8 - 9½)

Lost circulation material Medium nut plug 40 lb/bbl,

maximum size and concentration consult field engineer

Surface mud screen required? Yes

Pressure drop, psi through tool

(tool OD) for water @250 gal/min 40

'@500 gal/min 50

'@1,000 gal/min 75

Pulsation damper required? Recommend charge to 30% of SPP

Transmission trigger Stop pumps, stop rotary, start pumps

Telemetry type Positive

Is tool wireline retrievable? No

Maximum bit pressure, psi No limit

Downlink: Mud flow Yes

Rotary Yes

Wireline Yes

Electromagnetic No

DIRECTIONAL

MTF/GTF switching, inclination degrees 5° increasing, 3°

Tool face update period, seconds 11.2 (fast), 14 secs normal

Survey time, seconds 150 (fast), 172 secs normal

Survey while drilling:

Sliding/Rotating? No/NoDirectional measurement point, ft 14 from pulser bolts

Tool face accuracy, ± degrees 1.4

Azimuth accuracy, ± degrees 0.25

Inclination accuracy, ± degrees 0.15



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GAMMA RAY

Detector type Scintillation

Measurements AAPI GR

Gamma measurement point, ft 10.3 from pulser bolts

Available Real time? Yes

Recorded? YesSpectral GR? No

OTHER

Vibration monitoring? Yes

Downhole weight on bit and torque? No

Other sensors available? Temperature

Electronic caliper? No

Complete Sensor Specifications

Transmitted EYE

Measurement Range Units Bits Resolution Accuracy

Inclination 0 - 180 Degrees 11 0.09 ± 0.15

Azimuth 0 - 360 Degrees 12 0.088 ± 0.25

Tool Face (survey) 0 - 360 Degrees 8 1.4 ± 0.15

Tool Face 0 - 360 Degrees 7 2.81 ± 0.15

Gamma 0 - 64 Counts 7 .5

H-Total 30 - 70 nanoTeslas 9 78

Temperature* 0 - 175 Degrees C 5 5.5c

Battery Voltage 17 - 21 Volts 3 .5v

Peak Vibration VIB 0 - 20 g 7 156mg

DIP -90 - 90 Degrees 10 .18

G-Total 984 – 1016 Mg 5 1mg

* average of Gt & Ht

Update Rates

12 Windows

Measurement Pulse Width 0.76 Pulse Width 1.0

Survey (plus 60 sec delay) 2 min 7 sec 2 min 48 sec

Tool Face 10.6 sec 14 sec

Tool Face with Gamma 21.3 sec 28 sec

Gamma 21.3 sec 28 sec



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Make-up Torques

Connection Pulser SubOD Inches

TopBtm

Collar I/DInches

Torqueftlbs

4.5' Tong ArmLine Pull lbs

4' Tong ArmLine Pull lbs

3.5' Tong ArmLine Pull lbs

Box7-5/8 Regular 9-1/2 Pin 3-1/2 75,000 17,000 19,000 21,000

Box6-5/8 Regular 8 Pin 3-1/2 45,000 10,000 11,000 13,000

Box5-1/2 Full Hole 6-3/4 Pin 3-1/2 25,000 5,500 6,000 7,000

Box4-1/2 Extra Hole(NC46) 6-1/2 Pin 2-13/16 22,000 5,000 5,500 6,000

Box4-1/2 Extra Hole(NC46) 6-1/4 Pin 2-13/16 22,000 5,000 5,500 6,000

Box3-1/2 IF 4-3/4

Box

2-13/16 10,000 2,000 2,500 3,000

Gamma Scale Factors

Collar Size Scale Factor

6-1/2 6.33

4-3/4 4.22



TOOL OPERATION CHAPTER 2

CONTENTS

CONTENTS.............................................................................................................................................6

INTRODUCTION....................... ........................... ........................... ........................... ........................... ..7

EYE.........................................................................................................................................................9

OVERVIEW.......................................................................................................................................................... 9DIRECTIONAL SENSORS..................................................................................................................................... 10

SURVEYS .......................................................................................................................................................... 11

DETERMINING CORRECT SURVEYS .................................................................................................................... 11

EYE POWER AND COMMUNICATION.................................................................................................................. 12

MWD CONTROLLER......................... ........................... ........................... ........................... ..................13

OVERVIEW........................................................................................................................................................ 13FLOW ACCELEROMETER .................................................................................................................................... 13

TOOL OPERATION ............................................................................................................................................. 14

MEMORY .......................................................................................................................................................... 14

VIBRATION DETECTOR ...................................................................................................................................... 15

GAMMA ........................... ........................... ........................... ........................... ........................... .........16

I NTRODUCTION ................................................................................................................................................. 16

SENSOR DESCRIPTION ....................................................................................................................................... 16

PULSER DRIVER..................................................................................................................................19

I NTRODUCTION ................................................................................................................................................. 19

TIMED MODE .................................................................................................................................................... 20SMART MODE ................................................................................................................................................... 21

BATTERY ........................ ........................... ........................... ........................... ........................... .........23

OVERVIEW........................................................................................................................................................ 23

TEMPERATURE.................................................................................................................................................. 23LOADING AND SHELF LIFE................................................................................................................................. 23

BATTERY PACK WIRING.................................................................................................................................... 24

LIFE CYCLE ...................................................................................................................................................... 24

POWER AND COMMUNICATION.........................................................................................................25

TOOL BLOCK DIAGRAM ........................... ........................... ........................... ........................... .........26

DOWNHOLE TOOL OPERATION QUIZ................................................................................................27


© 2000 Scientific Drilling International



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Mud Pulse Theory Manual Chapter 2 – Tool Operation Page 7Revision Nov. 2000

INTRODUCTION

The Mud Pulse MWD tool consists of six major sections:

1. Pulser Sub

2. Pulser3. Pulser Driver4. Battery

5. Controller and Gamma sensors6. Directional sensors



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The pulser subs are similar to standard steering tool orienting subs. They have been bored out toaccept the pulsers, and contain two bolts that are used to secure the tool to the BHA after

alignment of the tool to the mud motor tool face. The pulser sits on a special sleeve called acollar spacer, that in turn sits on a shoulder inside the sub. The purpose of the collar spacer is to

ensure that the pulser is spaced exactly at the right place for the orienting bolts.

The pulser contains a solenoid that drives a pilot valve, which controls the main poppet valvethat creates the positive mud pulses.

Currently there are three different pulser configurations that are optimized for four different flow

rate ranges. The four different pulsers are suitable for operation in six different pulser sub sizesas shown in the chart below.

Pulser Sub Size(inches)

Pulser Used Flow Rate Range(GPM)

9-1/2 1000 GPM or 1500 GPM 125 to 1000 or 200 to 1500

8 1000 GPM or 1500 GPM 125 to 1000 or 200 to 15006-3/4 1000 GPM 125 to 10006-1/2 400 GPM 100 to 400

6-1/4 400 GPM 100 to 400

4-3/4 400 GPM 100 to 400

The pulser driver is an electronic module that controls the solenoid in the pulser.

The battery module contains high-energy batteries that power the whole downhole tool.

The directional and gamma sensors are housed in a barrel that also contains an MWD control

section. The directional and gamma sensors are identical units to those used by ScientificDrilling for steering tool applications. Both the Super EYE and the Golden EYE sensors can beused by the MWD Mud Pulse system.

The pulser driver, the battery, and the directional and gamma sensors are all housed in 1.75”

pressure barrels and connected together by centralizer modules. In addition to these modules, avibration isolator and a bull nose are added to complete the probe assembly that hangs down

from the pulser. The centralizers provide shock and vibration damping and they can beconfigured for use in different drill collar sizes.



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SUPER OR GOLDEN EYE

Overview

The function of the EYE section is to:

1. Measure directional data

2. To communicate these measurements to the MWD controller and the surface equipment

The three primary directional measurements provided are:

1. Azimuth – the directional orientation of the wellbore relative to magnetic north.2. Inclination – a measure of the deviation of the wellbore from vertical.

3. Tool Face – Highside Tool Face (or gravity tool face) and Magnetic Tool Face.

Toolface is a term used in connection with deflection tools or steerable motors, and can beexpressed in two ways.

The place on a deflection tool, usually marked with a scribe line, that is positioned to a particular

orientation while drilling, to determine the future course of the wellbore.

The orientation, expressed as the direction either from north or from the topside of the hole, ofthe navigation sub of a steerable motor.

Toolface orientation then is an angular measurement of the toolface of a deflection tool with

respect to either up (highside) or north (magnetic toolface).

Secondary or quality measurements are:

1. Total Magnetic Field, called H Totals2. Total Gravity Field

3. Magnetic Dip4. Tool Temperature called Ht for magnetometer temperature and Gt for accelerometer

temperature.

Directional data is measured using three accelerometers, three magnetometers, and twotemperature sensors.

This block diagram shows the major parts of the EYE section.



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Magnetometers

& Htemp

Signal Conditioning

Power Processor

Accelerometers

& Gtemp

RS-485

9 Pin MDM Connector

To MWD Controller

Directional Sensors

Accelerometers measure acceleration. Gravity is an acceleration. If we attach a spring to a massand hold it vertically, it will stretch the spring. The amount of stretch will depend upon the

spring, the magnitude of the acceleration, and the mass. The Earth’s acceleration is called “g”.If we could reverse the direction of g, the spring would compress by a similar amount. This is

the principle of the accelerometer. Three accelerometers are used, each aligned at 90 degrees toeach other, and refereed to as the Gx, Gy, and Gz accelerometers.

Magnetometers measure the intensity of the Earth’s magnetic field in a particular direction. A

magnetometer is a device consisting of two identical cores with a primary winding around each

core but in the opposite directions. A secondary winding twists around both cores and the primary winding. An excitation current produces a magnetic field in each core. These fields areof equal intensity, but opposite orientation, and therefore cancel each other out such that no

voltage is induced in the secondary winding. When the magnetometer is placed in an externalmagnetic field, which is aligned with the axis of the magnetometer, an unbalance occurs and a

voltage directly proportional to the external field is produced in the secondary winding.

A measurement of the voltage induced by the external field will provide a precise determinationof the direction and magnitude of the local magnetic field relative to the magnetometer’s

orientation in the borehole. Magnetic field intensity or strength is measured in micro Teslas (ìT)or nano Teslas (nT). A nano Teslas is sometimes referred to as a gamma.

Both accelerometers and magnetometers give voltage outputs that have to be corrected by

applying calibration coefficients. The calibration data corrects for span and bias errors, the effectof temperature, alignment errors, and other slight imperfections in the manufacturing process.

The calibration data are stored in memory in the EYE tool, and updated every time the tool iscalibrated. A temperature sensor is required by the tool in order to apply some of these

corrections when the tool is taking measurements in real time.



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Surveys

Calculations for the survey values are made in the downhole tool.

Inclination calculation uses the three accelerometer sensors only.Azimuth calculations use the three magnetometer sensors and the three accelerometer sensors.Highside Tool Face calculations use the accelerometers only.

Magnetic Tool face calculations use both the accelerometer and magnetometer sensors.Total Magnetic Field calculations use the three magnetometer sensors

Total Gravity Field calculations use the three accelerometer sensorsMagnetic Dip calculations use the three magnetometer sensors and the three accelerometer

sensors.

The downhole tool can transmit Tool Face data in three modes,1. Permanently set to Highside Tool Face

2. Permanently set to Magnetic Tool Face3. Automatically switch from Magnetic to Highside depending upon the inclination.

The automatic tool face switching occurs when inclination increases to a value of 5 degrees, or

decreases to a value of 3 degrees.

Which sensors can be relied upon?1. Inside casing, inclination below the crossover angle. There is magnetic interference and

therefore none of the data that uses the magnetometers can be relied upon. Since inclinationis below the crossover angle, highside tool faces are highly variable. No tool data are

useable.2. Inside casing, inclination above the crossover angle. We can now use the data that uses the

accelerometers, i.e. inclination and highside tool faces.3. H-Total bad. We can rely upon inclination and highside tool face but none of the

magnetometer data.4. Total Gravity Field bad. Question all data.

Determining Correct Surveys

You need to be certain that your survey is correct before giving it to someone else. Check thefollowing:

1. Are the Inclination and Azimuth readings what would be expected?

2. Was the last H-Total transmission correct? There are several programs that can estimate avalue if your longitude and latitude is known.

3. Is the Total Gravity Field correct? It should be around one, and consistent with previoussurveys.

4. Have you entered the correct magnetic and grid declinations?



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5. Is the temperature reading correct? A bad temperature sensor in the tool will result in thewrong calibration calculations and all data will be suspect.

6. Was the pipe moving when the survey was taken?7. Double-check the depth. The survey calculation program must the correct depth to yield

correct section and dogleg results.

EYE Power and Communication

Direct communication with the EYE tool is possible at the surface or with an electric wireline

when downhole. The communication method is the same as that used by Scientific Drilling’sSteering tools, namely Frequency Shift Keying (FSK).

When communicating with the EYE using FSK, power is supplied by the surface system, and is

superimposed on the same wire as the communication line.

The EYE tool passes its data onto the MWD controller using a serial line called RS-485.

In order to save battery life, the EYE tool is only powered up when directional data is required.The MWD controller is responsible for this power switching.



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MWD CONTROLLER

Overview

The purpose of the MWD controller is to:

1. Control the acquisition of data from the EYE tool.2. Measure natural gamma ray radiation

3. Control the timing of data acquisition and transmission by monitoring the flow accelerometerswitch.

4. Format data for output to the pulser driver, which then controls the transmission of data tothe surface.

5. Adjust the pulse width and the data transmission sequence formats according to timed flowon /off or rotation on/off sequences. This reprogramming of the tool from surface is referred

to as Talkdown.6. Measure the battery voltage, and shock and vibration that the tool is experiencing.

7. Store measured data in memory for redundancy and store diagnostic information.8. Provide a communication link for use at the surface to initialize and test the tool.

At the heart of the MWD controller is a microprocessor. The software inside this microprocessor performs the control functions listed above.

The major elements of the controller are shown in this block diagram.

Processor

Flow Accelerometer

PMT/Gamma

Memory 6 MB

(3 X 2MB)

D r i v e L i n e

R e d / B l a c k

From Eye Section

FSK/Power

RS-485

To Other Sections

F S K / P W R

( R E D )

N o t U s e d

( R E D / W h i t e

)

Flow Accelerometer

The tool is designed to actuate the pulser when there is either, flow or rotation on the drill string.

The design uses an accelerometer to detect the slight vibration on the tool caused by either flowor rotation. This has proved to be very reliable and has the added benefit of allowing the

downhole tool to be mode switched (talkdown) by drill string rotation as well as by pump



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pressure. A drawback of this design is that any movement of the tool will cause it to switch onand start transmitting. This means that the tool will be consuming battery energy during trips,

and also increases the chances of unintentional talkdown changes.

One of the set points that the operator can adjust, is the level at which the flow accelerometer

activates the tool. Currently the optimum level is set to 0.050 volts.

The talkdown scheme is described in chapter 6.

Tool Operation

A simplified sequence of the tool operation is as follows:

1. Wait until flow accelerometer detects flow.2. Wait for 60 seconds for the pumps to stabilize.

3. Transmit the survey data, inclination azimuth and tool face.4. Transmit continuously tool face and if selected gamma data.

5. Transmit status data (battery voltage, temperature, and H-total) at times programmed atsurface.

6. Stop transmitting when flow accelerometer has detected flow off for more than 30 seconds.7. Measure next survey data 40 seconds after flow-off initially detected*.

8. Back to step one.

*An exception to this time is during talkdown, when the survey is taken 20 seconds after theflow accelerometer has detected flow off.

Memory

The controller section has two types of memory:

1. Volatile memory (data is lost when power is removed).2. 6 MB of Non-volatile memory (data is retained even when power is removed).

Recorded in the volatile memory is a record of the main activities of the tool with time. Most

surface communications to the tool are recorded such as pulse width changes, clearing ofmemory etc. In addition, when the tool is operating the flow on and flow off times are recorded.

In the main non-volatile memory, more diagnostic data is recorded such as flow accelerometer

voltages. In the future, this memory will also be used to store gamma ray and survey data.

The non-volatile memory does not wrap; i.e. when full, all recording of data ceases. The non-volatile memory stores data in 3 Meg. The remaining 3 MB will be used for storing gamma data.



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Vibration Detector

The MWD controller uses the raw output of the accelerometers to provide two measurements, a peak vibration and an averaged vibration. The range for both measurements is 1 to 16.5 g in 1 g

increments.

The primary use of these measurements is to warn of possible excessive vibration on the BHAand in particular, the relatively delicate MWD tool. If high values are seen, some action must be

taken, such as changing the rotary rpm, or the weight on bit or both, until more normal values areseen.



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GAMMA

Introduction

The gamma ray sensor measures the naturally occurring gamma radiation in the formations.Most naturally occurring radiation comes form potassium which is contained in clay minerals.The gamma ray log is therefore useful for distinguishing shales from non-shales. Some gamma

radiation comes from uranium, (which is most often found in formations through which wateronce flowed), or thorium, (which is found in various clay minerals).

The uses of the gamma ray log are:

1. Distinguish shales from non-shales

2. Estimate clay content in sands and limestones3. Correlation of real-time data with offset logs to determine geological location.

4. Picking casing and coring points.

There are two major limitations to the gamma ray sensor:

1. Gamma measurements are time dependent and are therefore less accurate at high ROPs.2. The drill collar absorbs gamma rays differently to the housing of a wireline tool, making

exact comparison of wireline and MWD gamma ray logs difficult.

Sensor Description

The gamma ray sensor consists of three components, a scintillation crystal, a PhotoMultiplier

Tube (PMT), and power and measurement electronics.

When gamma rays emitted by the formation pass within the crystal lattice, they impart theirenergy to a cascade of secondary electrons, which are finally trapped by impurity atoms. As the

electrons are trapped, visible or near-visible light is emitted. This is called scintillation.

The light flashes are then detected by a PMT tube optically coupled to the crystal andtransformed into an electrical pulse. The PMT tube detects the visible light from the crystal, and

emits two secondary electrons. This multiplying effect of the original gamma ray causes a muchstronger signal to be read by the counter.



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NaI Crystal PMT

gamma ray

photocathode

Electrical pulses

to counter

The sensitivity of the sensor changes when the tool is placed in different collar sizes. To

compensate for this there are several different calibration constants for each drill collar size.These constants are called the Gamma Scale Factor, and are entered into Mfilt.

Two main problems can occur with the gamma sensor. The crystal may crack, causing a markedchange in the sensitivity. This is manifested by a drop in the gamma values on the log. Afterlong period of use and several heat cycles, such as the same tool used over a year or so, the

crystal structure can degrade, which causes a gradual loss in sensitivity. Frequent calibrationchecks can help identify and correct this problem.

Other factors that can affect the gamma response are:

1. Hole diameter, the larger the hole diameter, the less sensitive the response.

2. Mud density, the denser the mud, the less sensitive the response.3. Mud additives, certain mud types such as potassium chloride polymers (KCL) can have an

effect on the response depending upon the levels of concentration.

The absolute radioactivity of a rock varies; however, the relative radioactivity of the rock types isfairly constant.

The various gamma responses in certain rock formations can be seen in the diagram below.



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Sandstone - mostly SiO2 may becontaminated with clays andother K minerals

Siltstone - same as sandstone

Shale - clay minerals, abundant K

Salt - halite, normally pure NaCl,

no K contamination.

Limestone - CaCO3 may be

contaminated with K minerals

Marine Shale - clay minerals, hot

Dolomite - CaMg (CaCO3) same

as limestone

Coal

Granite - large amounts of K, very

hot

low high

Gamma Counts per Second

Salt - sylvite, KCL

Gamma Ray Lithology Response



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PULSER DRIVER

Introduction

The purpose of the pulser driver is to:

1. Accept pulse commands from the MWD Controller.

2. Activate the solenoid in the pulser with a specific current profile.3. Double the voltage from the battery pack to increase the power to the solenoid.

4. Store current and voltage profiles in memory for diagnostic purposes.

The MWD controller simply outputs a signal, whenever it requires the driver to activate the pulser. The width of this signal is the same time as the pulse width that the tool has been set at.

A functional block diagram of the driver section is shown below along with the pulser.

Processor

Driver Capacitors

Memory 2MB

Solenoid PULSER

Wet Connector

F S

K / P W R ( R E D )

F S K / P W R

( R E D )

Tool

Ground

Drive Line

From MWD Controller

PULSER DRIVER

The energizing time for a solenoid to complete a given stroke is measured from the beginning ofthe initial application of power to the seated or energized position. For a given solenoid, this

time is dependent upon the load, duty cycle, input power, stroke, and temperature. When a DCvoltage is applied across the solenoid coil, the current will rise to point (a) as shown on the graph

below.



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a b

c

Time (milliseconds)

C u r r e n t ( a m p s )

This time delay, which occurs before the plunger motion, is a function of the inductance and

resistance of the coil, and the flux required to move the armature against the load. An increase inthe magnetic force is created by closing the air gap as the plunger moves through the stroke,

causing a dip in the current trace. The low point at (b) indicates that the solenoid has completedthe stroke. The current trace then begins to rise to a steady state current value.

If the load on the solenoid increases, more time is required to reach point (c), as shown by thedotted line current trace.

If the load on the solenoid is larger than the solenoid can handle, then the current in the coil will build to a steady state value and a dip in the trace will not occur since the plunger has not moved.

The driver circuitry provides the initial current for the solenoid to move and reach the steady

state current, and then switches down to a lower current to keep the solenoid energized for therest of the pulse duration. This lower current level is called the hold current, and has the real

benefit of minimizing the energy used from the batteries of the tool.

The driver operates in two modes, timed and smart mode.

Timed Mode

In timed mode, the driver provides two current profiles, a high current to crack open the pilotvalve, and a lower hold current to keep the pilot valve open. The profile of the available current

to the solenoid is shown below.



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Time (milliseconds)

C u r r e n t ( m A )

300

1,000

Min time >40<150

Max time >70<225

Typically set to

40 min, 150 max

Time determined by pulse width - on time

The operator can select the minimum and maximum times that the initial current is provided tothe solenoid.

Smart Mode

In smart mode, the driver automatically controls the current to the solenoid. Up to 1 amp is still provided during the initial open period. However, this high current level is stopped once the

solenoid has reached the steady state level after the solenoid has stopped moving. This results in

a significant current savings compared to the timed mode.

Time (milliseconds)

C u r r e n t ( m A )

300

1,000

Time determined by pulse width - on time

High current

stopped at this

point



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The current required to drive the solenoid is near the limit that the batteries are capable of. Toovercome this problem, energy is slowly stored in capacitors during pulse off times, and

discharged from the capacitors instead of directly from the batteries.

The memory in the driver module stores the current and voltage profiles of each pulse. If there is

a pulsing problem, this diagnostic data can be very useful in the determination of the problem.The memory has a wrap feature, so only the most recent profiles are kept. The memory willtypically store about 24 hours worth of data.



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BATTERY

OverviewThe battery pack consists of 6 lithium thionyl chloride, DD size cells connected in series. The

cells have a lithium anode, a carbon cathode, and a thionyl chloride electrolyte.

Each cell has a nominal voltage of 3.6 volts. The six cells connected together therefore have acombined nominal voltage of 21.6 volts (6 x 3.6). The actual voltages are lower than this due to

various effects discussed later.

The voltages in the downhole tool are normally measured with respect to ground. Ground isconnected directly to the body of the tool through the pressure barrels.

Temperature

The maximum operating temperature of the battery pack is 300° F (150° C). Above this

temperature, the cells may start to swell and become extremely dangerous.

The battery voltage will drop if the battery temperature is allowed to fall below freezing. Once

the batteries are re-warmed, the voltage will recover, but the battery life may have beenshortened. Precautions should be taken to ensure that the batteries are not frozen, even during

transportation.

Loading and Shelf Life

New and unused batteries have a long shelf life of up to ten years.

Before a newly built battery pack can be used it must be activated or loaded down. When

loaded, the voltages in new batteries will be well below the nominal voltage. This is because theelectrolytic reaction within each cell is slowed down by a passivation layer of lithium chloride

crystals around the anode.

Loading down is performed by connecting a 75 ohm resistor across the positive and negative ofthe battery pack. As current flows through the load resistor, the passivation layer is broken

down, the electrolytic reaction speeds up and the voltage gradually rises to the nominal operatinglevel. This process is often referred to as de-passivating. The time taken for the voltage to build

back up to a steady value depends upon the remaining capacity, and the temperature cyclehistory of the batteries.

Before handling these batteries, you must read and understand the SDI Safety Procedures.



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Battery Pack Wiring

Each cell in the battery pack has a diode connected to it to avoid the possibility of one or more ofthe other cells sourcing current into itself. The battery pack also has a 5 amp protective fuse, and

a final protective diode. There will be a small voltage drop across the diode, which will further

reduce the nominal voltage from 21.6 to about 21 volts.

Fuse 5A

Life Cycle

V o l t s

Voltage drops if batteries freeze,rises again on warming

Voltage drops

quickly at end

of life

Time in Hours

Loading brings

voltage up

About 150 hours depending on data rate

21



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POWER AND COMMUNICATION

There are several options that the operator can set that customizes the service to be provided. Inorder to configure the tool for these various options, a method of communicating with the tool is

required. Scientific Drilling uses the same method of communication as used by their wireline

tools, namely Frequency Shift Keying (FSK).

To save battery power in the tool, an external power source is superimposed on the FSK

communication line.

This external power and communication is made through the “wet connect” at the top of the pulser.

A zener diode is used to isolate the battery power, when external power via the surface system is

available. The diagram below shows the general power arrangement in the tool.

Fuse 5A

FSK/PWR (RED)

MWDTOOL

22 volts from MSI

Choke

22 volt

Zener

Diode

21 volts

Communication between the microprocessors in the MWD controller and the EYE tool is via anRS-432 serial line, running at 9600 baud.



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TOOL BLOCK DIAGRAM

For a complete overview of the down hole tool, the following diagram will be useful:

Magnetometers& Htemp

Signal Conditioning

Processor

Flow Accelerometer

PMT/Gamma

Centralizer

Centralizer

Processor

Driver Capacitors

Memory 2MB

Solenoid

Memory 6 MB(3 X 2MB)

D r i v e L i n e

R e d / B l a c k

Power

PULSER

PULSER DRIVER

BATTERY

MWD CONTROLLER

EYE DIRECTIONAL SENSOR

Wet Connector

Fuse 5A

1

234 5 67 8 9

Spring Assy

ConnectorChassis Assy

Tool

Ground

M.M.

1/14/20

MWD TOOL BLOCK DIAGRAMMWD TOOL BLOCK DIAGRAM

F S K / P W R

( R E D )

F S K / P W R ( R E D )

F S K / P W R

( R E D )

Red

Red/wht

Red/blk

D r i v e L i n e

R e d / B l a c k

Red - FSK/Power

Red/black - Solenoid Drive Line

Red/white - not used

1

5

Processor

234 87 6 9

Tool

Ground

Accelerometers & Gtemp

RS-485

9 Pin MDM Connector

9 Pin MDM

9 Pin MDM

FSK/Power

RS-485

N o t U s e d

( R E D / W h i t e )



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DOWNHOLE TOOL OPERATION QUIZ

1. What nominal voltages are provided by the whole battery pack and by a single cell?

2. What is the minimum time that the tool can withstand no flow or movement without shuttingdown?

3. What is the purpose of battery loading?

5. You are checking a tool in the slips after a bit-trip and can hear the pulser clicking at the usualrate, despite no flow. What would you suspect is wrong?

6. List seven steps to determine if a survey is correct.

7. Name four possible sources of magnetic interference.

8. Where are the directional sensor calibration factors stored?

9. The driller takes a survey using the BHA described below. The bit is at a measured depth of

10,112 ft. What is the depth of the survey?

Bit 1.00 Crossover 1.24 Stabilizer 3.12 Crossover 1.68 NMDC 30.24Pulser sub 4.75 Monel 30.11

10. After a few hours of drilling ahead, the directional driller starts to question your surveys.The last H-Total reading is nearly 25% higher than all the previous values. What can you tell

him?



PULSER CHAPTER 3

CONTENTS

CONTENTS ....................................................................................................................................................... 28

OVERVIEW....................... ............. ............. .............. ............. ............. ............. ............. .............. ............. ......... 29

PULSER PRINCIPLE - SIMPLE........ ............. ............. ............. ............. .............. ............. ............. ............. ..... 29

PULSER PRINCIPLE - DETAILED ............. ............. ............. ............. ............. .............. ............. ............. ....... 30

FILTER SCREEN..................... ............. ............. ............. ............. .............. ............. ............. ............. ............. ... 34




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Mud Pulse Theory Manual Chapter 3 – Pulser Page 29Mike Meadows Jan 2000

OVERVIEW

The type of pulser used in the Mud Pulse MWD tool, is a positive one. At its most basic, the pulser consists of a valve that, when actuated, restricts some of the mud flowing down the drill

string. A pressure gauge at the surface will see this temporary restriction as a positive going

pressure pulse.

Actuator

Valve

Mud

time

S t a n d p i p e p r e s s u r e Positive

going pulses

PULSER PRINCIPLE - SIMPLE

The pulser consists of two major sections, a power valve and a pilot valve assembly. The main poppet shaft is attached to a power spring that always acts to try to close the valve. Therefore,

with no flow on the tool, the poppet valve will be in the closed position.

The three diagrams below show a very simplified representation of the pulser operation.

The first drawing shows the situation with no flow through the pulser.

The second drawing shows what happens when there is flow through the pulser, but the actuatoris not creating a pulse. The pressure of the drilling fluid pushes the driving piston down against

the spring, which pulls the main poppet down, allowing mud to flow.



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MainPoppet

Valve

Pilot Valve

Assembly

Main

Spring

NO FLOW

NO PULSE

Main

Orifice

Driving

Piston

FLOW

OFF PULSE

FLOW

ON PULSE

large area

small area

Phigh

Plow

Phigh

Phigh

Plower

Phigh -Plower

Plower

The third drawing shows the status when the tool needs to create a pulse, and the pilot valve isopened.Through the poppet assembly is a small bore that links the pressure at the top of the pulser, to the

back of the driving piston. The cross sectional area of this piston is larger than the crosssectional area of the poppet valve seat. With the pilot valve open, the same pressure across the

main valve is acting on the back of the piston. Force is pressure x area, and because the area onthe piston is larger than the area on poppet seat, the piston assembly will move upward.

PULSER PRINCIPLE - DETAILED

The pulser has two very useful features:1. Controls the pulse height to be nearly constant over a very wide flow range.

2. Very little power is required to operate the pulser, only about 10 watts.

A more detailed look at the pulser operation is required to understand how these two featureswork. Each of the three conditions will be described.



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No Flow, No Pulse

The actuator assembly consists of a

solenoid, pilot valve, relief valve,and a pressure compensator.

The pressure compensator contains

a spring that is changed out for thethree different pulser flow ranges.

The solenoid and pressurecompensator is housed in a pressure

compensated chamber that is oilfilled. A floating piston

compensates for temperature, pressure, and displacement changes.

Solenoid

Main

PoppetValve

Pilot Valve

Assembly

Main

Spring

NO FLOW

NO PULSE

Relief valve

Pilot Valve

Floating Piston

Oil chamber

Main

Orifice

Compensator

DrivingPiston



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Flow and Off Pulse

1. When the pumps are started, the pressure pushes the

poppet down against the main spring (black arrows).2. Flow across the main orifice results in a small pressure

drop across the main valve.3. The pressure on both sides of the driving piston is the

same - P2.4. There is no flow through the main poppet and pilot valve

assemblies.

Solenoid

FLOW

NO PULSE

P1

P1

P2

P2<P1

P2

P2

P2

mud flowmud flow



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Flow and On Pulse

1. When the solenoid is activated, the pilot valves opens, andthe relief valve closes.

2. This applies the same pressure drop that is across the mainvalve, to the back of the driving piston.

3. The pressure area of the driving piston is larger than thearea of the main valve. Therefore the piston will move up

and the main poppet valve will move to the close position.4. There is now flow through the main poppet and pilot

valve assemblies.5. With no pressure control, the main valve would move to

the hard close position. However, the relief valve isspring loaded to maintain a pressure that is defined by the

valve area and the spring force. Once this control pressure is reached, the valve will begin to open to bypass

pilot flow so that the control pressure is maintained at anear constant pressure over a wide flow range. This in

turn, produces a constant force on the driving piston that pushes the poppet closed to produce a near constant

pressure drop across the main valve.

Solenoid

FLOWON PULSE

P1

P1

P2

P2<P1

P2

P1

P1

mud flowmud flow

mud flow



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FILTER SCREEN

A filter screen is incorporated into the main valve to prevent mud particles from blocking the pilot valve assembly. The filter intake screen assembly is situated at the top of the main valve.

If the screen itself becomes plugged, the tool will not pulse.

Filter screen

To prevent the filter screen from becoming caked, the pulser should be flushed with water before

being removed from the pulser sub.



SURFACE SYSTEM CHAPTER 4

CONTENTS

CONTENTS ....................................................................................................................................................... 35

SURFACE SYSTEM OVERVIEW ............. .............. ............. ............. ............. ............. .............. ............. ......... 36

STANDPIPE PRESSURE......... ............. ............. ............. ............. .............. ............. ............. ............. ............. ... 38

PUMP POSITION SENSOR.................... ............. ............. .............. ............. ............. ............. ............. .............. 41

DEPTH SENSOR............................................................................................................................................... 42

RIG FLOOR DISPLAY......... .............. ............. ............. ............. ............. .............. ............. ............. ............. ..... 44

TOOL COMMUNICATION ............................................................................................................................. 45

SURFACE SYSTEM HOOK UP............... ............. .............. ............. ............. ............. ............. .............. ........... 46

SURFACE SYSTEM QUIZ............ ............. .............. ............. ............. ............. ............. .............. ............. ......... 47


© Scientific Drilling International 2000



Confidential

Mud Pulse Theory Manual Chapter 4 – Surface System Page 36Revision Nov. 2000

SURFACE SYSTEM OVERVIEW

The main function of the surface system is to convert pressure pulses to directional data.

In more detail, the surface system:

1. Provides signal conditioning for the Input sensorsStandpipe Pressure

Pump Position Sensor (for noise subtraction)Depth Encoder (for gamma depth)

MWD Tool Memory

2. Detects Pulses byRemoving dc pressure component

Filtering out unwanted frequenciesSubtracting pump noise

Correlating pressure transitions to pulse transitions

3. Decodes the pulse data into final measured parameters

4. Stores data into files

5. Outputs data to:Rig Floor Display (RFD)

Computer ScreenPrinter

Plotter

The two major components of the surface system are the Multi System Interface (MSI) and alaptop PC.

All of the signal conditioning functions are carried out by the MSI. The MSI is basically a

computer with various specialized boards to perform data acquisition and output controlfunctions.

The main functions of the MSI are therefore:

1. Power and measure the signal transmitted by the downhole tool from the standpipe

transducer and pass this onto the PC2. Power and measure the pump position transducer and pass this onto the PC

Surface System

Inputs:

Standpipe pressure

Pump positionDepth

Outputs:

Inc, Azi, Toolface, Htot

GammaVibration



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3. Power and measure the depth encoder and pass this onto the PC4. Output processed information from the PC to the rig floor display

5. Provide direct communication to the tool for setup and retrieving memory data

Standpipe Pressure

Pump Position

Depth Encoder

Tool Memory

Rig Floor Display

Depth Display

Multi System InterfaceMSI

Laptop PC Printer/Plotter



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STANDPIPE PRESSURE

The standpipe pressure sensor operates in a similar manner to a strain gauge. It contains voltageregulator circuits, current measurement, and precision detection circuits. The pressure in the

standpipe causes a diaphragm to deflect. This deflection is detected by a semiconductor bridge

and amplifier. The bridge amplifier outputs to a current control circuit that sends the outputsignals to the MSI.

The transducer has an operating range of 10 to 40 volts dc, but is supplied with approximately 24volts dc from the MSI. The standpipe sensor outputs a current of between 4 and 20 mA to the

MSI, which represents 0 to 3,000 psi or 0 to 5,000 psi depending upon which transducer you areusing.

This 4-20 mA signal is converted to a voltage of 0 to 10 volts before being digitized by the

Analog to Digital Converter in the MSI.

The chart above shows the relationship between pressure and current output for each of the two

sensors used.

To determine the current output for a particular pressure use the following equation

Current (in mA) = (16/ pressure range x pressure) + 4

For example, what is the current output when the standpipe pressure is 2,500 psi. when using a5,000 psi sensor?

Current (in mA) = (16/5,000 x 2,500) + 4

The answer is 12 mA

0

4

8

12

16

20

24

0 1,000 2,000 3,000 4,000 5,000 6,000

Pressure (psi)

C u r r e n t ( m A m p s )

3,000 psi Sensor 5,000 psi Sensor



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The diagram below shows the complete routing of the standpipe pressure signal and will beuseful for troubleshooting.

A

B

C

D

E

F

GH

Standpipe

PressureSensor

RedBlack

Male

8 pin

Female

8 pin

Multi System Interface

4-20 mA

Current toVoltage

Analog to Digital

Converter

Processor

Serial Output

Laptop Computer

Standpipe Pressure Signal RoutingStandpipe Pressure Signal Routing

A

B

C

D

E

F

GH

A

B

C

D

E

F

GH

A

B

C

D

E

F

GH

Male

8 pin

Female

8 pin

A

B

C

D

E

F

G

H

Female

8 pin

Female

11 pin

Male

11 pin

A

B

C

D

E

FG

H

J

K

L

A

B

C

D

E

FG

H

J

K

L

MWD Y CableReadout Cable

For Pump Position Sensor

Pressure Sensor Assy

Troubleshooting:

1. Unplug readout cables at Y Connector and confirm voltage

across H&L and K&L are approx. 24 volts. If not, swap out MSI

boxes

2. If voltages OK, check cables all the way up to pressure

transducer (across G&H)

3. Short pins G&H at female connector that transducer plugs

into. Mfilt should show about 3,000 or 5,000 psi. If not, replace

transducer.



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The pressure transducer and the pump position sensor can be plugged into either of the two Yconnectors.

The transducer should be installed as close to the main mudflow as possible, and the transducer

body parallel to the ground.

The pressure transducer has zero and span adjustment capability. When back at the shop,connect the sensor to an MSI, and adjust the zero by turning the zero screw on the sensor while

watching the Mfilt screen. Attach an Enerpac to the transducer and carefully pressure up toeither 3,000 or 5,000 psi as appropriate. Adjust the span screw until the Mfilt screen reads 3,000

or 5,000 psi.

Do not press or touch the diaphragm as you may damage or alter its calibration.



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PUMP POSITION SENSOR

The purpose of the pump position sensor is to measure the motion of the pump piston shaft inorder to determine a pressure signature of the pump noise. This signature is then subtracted form

the raw standpipe pressure and usually all that will remain is the MWD pulses. A secondary

purpose of this sensor is to measure the stroke rate of the pump.

The sensor consists of a single chip accelerometer and signal conditioning circuitry mounted on a

printed circuit board. The sensor assembly is mounted on one of the piston shafts on the pump.The accelerometer outputs a voltage that is proportional to the vibration on the shaft. Circuitry

inside the sensor covert this voltage to a 4-20 mA signal. If the pump is running, the output ofthe sensor will be a sine wave. The frequency of this sine wave will be the pump stroke rate.

The surface system uses this signal to remove the noise due to the pump.

By telling the surface equipment the barrels per stroke for the pump, the flow rate in gallons perminute can be computed and displayed.

The diagram below shows the complete routing of the pump position signal and will be useful

for troubleshooting.

A

B

C

D

E

F

G

H

Pump Position Sensor

Green

Male

8 pin

Female

8 pin

Pump Position Signal RoutingPump Position Signal Routing

A

B

C

D

E

F

G

H

A

B

C

D

E

F

G

H

Male8 pin

Readout Cable

4-20 mA signal P1

-12 volts P4

+12 volts P2

ground P3

White

Blue

Red

Black

For Standpipe Sensor


Current toVoltage

Analog to DigitalConverter

Processor

Serial Output

Laptop Computer

A

B

C

D

E

F

G

H

Female

8 pin

A

B

C

D

E

F

G

H

Female8 pin

Female11 pin

Male11 pin

A

B

C

D

E

F

G

HJ

K

L

A

B

C

D

E

F

G

HJ

K

L

MWD Y Cable

Troubleshooting:

1. Unplug Y Connector at MSI and confirm voltage across E&C

and E&D is approx. -12 volts, and +12. If not, swap out MSI

boxes.

2. If voltage OK, check cables all the way up to pressure

transducer (E&C and E&D).

3. If voltages at female connector that transducer plugs into

are correct then replace sensor.



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DEPTH SENSOR

The depth sensor monitors the position of the kelly indirectly by measuring the movement of thecable connected to the rig’s Geolograph.

The actual transducer is an optical shaft encoder that translates rotary shaft movement to a seriesof square waves. The shaft encoder is attached to the bushing of a wheel that is connected to theGeolograph cable.

Geolograph Cable

Shaft Encoder Wheel

The sensor requires between 5 and 24 volts for its supply voltage. The MSI actually supplies

12volts.

The sensor outputs the following signal to the MSI.

A

B

1 Cycle

90º



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By counting the number of pulses and the frequency of the two signals, it is possible to compute

the distance and speed moved by the sensor wheel and therefore the position of the kelly.Direction of movement, depth increasing or decreasing, is determined by measuring the phase

shift between the two signals.

By entering a calibration factor of 133.3 counts per foot into the Mlink software, each turn of thewheel, will result in 3 feet of depth change. For metric operation, enter 437.4 counts per meter.

In addition to the sensor, a local display of depth and rate of penetration can be connected to the

MSI.

The diagram below shows the complete routing of the depth encoder signal and will be useful fortroubleshooting.

AB

C

DE

FG


AB

C

DE

FG

AB

C

DE

FG

Male7 pin

Female

7 pinMale7 pin

AB

C

DE

FG

Female7 pin

AB

C

DE

F

Male6 pin

AB

C

DE

F

Female

6 pin

A

Power V+

Ground

Not Used

AB

C

D

EF

AB

CD

EF

AB

C

D

EF

Pigtail

Encoder Adapter

Encoder

Local Display

Local Display

Depth Encoder Signal RoutingDepth Encoder Signal Routing

Optical Shaft

Encoder

Shield

Not Used

B

Female

6 pinMale

6 pin

Optional2nd

LocalDisplay

Processor

Serial Output

Laptop Computer

Troubleshooting:

1. Unplug adapter cables at MSI Connector and confirm

voltage across D&F is approx. 12 volts. If not, swap out MSI

boxes

2. If voltage is OK, use back-up sensor to test each cable by

rotating the wheel one turn and noting a three foot change in

the depth display.

3. If all cables check out, replace depth sensor.

Depth Cable



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RIG FLOOR DISPLAY

The rig floor display consists of a circular Liquid Crystal Display (LCD) divided into 120segments and 2 alphanumeric LCD displays of 8 characters each. Each segment on the circular

display represents 3 degrees of Tool Face data. Data is transmitted to the display via a standard

RS-232 serial interface. The minimum input voltage is 7.5 volts with a minimum current of 20mA.

When first powered up, the rig floor display runs through a self-test.1. All the digits of the alphanumeric displays are sequenced from 0 to 9.

2. Each segment of the circular display is sequentially turned on3. Each segment of the circular display is sequentially turned off

4. The internal firmware version number is shown on the alphanumeric displays

This self-test takes about six seconds. The display is then ready to receive and display data.

The display requires three lines, supply voltage, RS-232 serial data, and ground. The serial datais sent at 1200 baud, eight data bits, no parity and one stop bit (8N1).

The display is not currently certified for Intrinsically Safe use.

A

B

C

D

E

F

G

H

A

B

C


A

B

C

D

E

F

G

H

A

B

C

D

E

F

G

H

RS-232

Intercom1

Not Used

Power V+

Ground

Intercom 2

Not Used

Intercom 3

male female male

A

B

C

D

E

F

G

H

female

A

B

C

D

E

F

G

H

male

A

B

C

D

E

F

G

H

female

RS-232

Intercom1

Not Used

Power V+

Ground

Intercom 2

Not Used

Intercom 3

A

B

C

D

E

F

G

H

female

Intercom 2

Intercom 3

Intercom 1

Intercom1

Ground

Intercom 2

Intercom 3

Optional Splitter Cable

Rig Floor Display Signal RoutingRig Floor Display Signal Routing

Rig Floor Display Readout Cable

Processor

Serial Input

Laptop Computer

Troubleshooting:

1. Unplug display on the drill floor, and

reconnect to check the self-test sequence. If

fails test, replace display.

2. Unplug readout cables at splitter or MSI

and confirm voltage across D&E is approx.

7.5 volts, and serial line has approx. -8.4

volts. If not, swap out MSI boxes.

3. If voltages OK, use back-up display to

test the cables each in turn up to the drill

floor.



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TOOL COMMUNICATION

Direct communication with the tool through the wet connect is facilitated by using a technique

called Frequency Shift Keying (FSK).

FSK modulation sends digital signals over a power line by using two or more separatefrequencies that are in a fairly narrow band. This is the technique used by modems to connect

computers via telephone lines.

Two distinct frequencies represent binary 1s and 0s. The center frequency is 1820 KHz.

To reduce the number of wires and connectors, the supply power is superimposed with thecommunication signal.

This diagram shows the two frequencies superimposed on top of the dc power line.

0 volts

22 volts



21

20

22

IPL751 Mud Pulse MWD Instrumentation

and Surface Equipment

15

12

17

16

18

8

13

ENCODER MWD AUX COMPUTER POWER

LINEIN115/230TOOLSUPPLY

TRANSMIT

RECEIVE

REMOTE

DISPLAYS

M S Iu l t i ys tem n ter face

WIRELINE

9

5

4

6

33

10

10

10

7

13A-E

SPI UP/DWN Load

26

14

11

1923

24

25

SURFACE SYSTEM HOOK UP

Connecting the system is straightforward. The diagram below shows all the connections to be made.

Confidentia

Mud Pulse Theory Manual Chapter 4 - Surface SystemRevision Nov. 2000

Page 4



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SURFACE SYSTEM QUIZ

1. What is the normal voltage on the pressure transducer line?

2. What is the normal range of currents on the pressure transducer line?

3. How many turns on the depth sensor wheel will be required to display an additional 9 feet?

4. What is the normal voltage supplied to the pump position sensor?

5. What is the normal range of currents on the pump position line?

6. The computer screen does not show the correct strokes per minute, what do you suspect is the

problem?

7. What safety precaution would you take before installing or removing a pressure transducer?

8. What safety precautions would you observe while installing the pump position sensor?

9. If your laptop is reading zero psi with the pumps running, what actions would you take?

10. What is the normal voltage supplied to the depth-tracking sensor?

11. Convert the following, 1536 psi on a 5,000 psi transducer to mA, and 9.33 mA. to psi using a

3,000 psi transducer.

12. What is the normal voltage supplied to the rig floor display?



DETECTION DECODING CHAPTER 5

CONTENTS

CONTENTS ....................................................................................................................................................... 48

TELECOMMUNICATIONS BASICS ............. ............. ............. ............. .............. ............. ............. ............. ..... 49

CHARACTERISTICS OF A SIGNAL ......................................................................................................................... 49

TIME DOMAIN AND FREQUENCY DOMAIN .......................................................................................................... 50FOURIER ’S EXPANSION...................................................................................................................................... 53

FILTERS ............................................................................................................................................................ 55

TIME CONSTANTS ............................................................................................................................................. 57

MUD PULSE ENCODING SCHEME.............. ............. ............. ............. .............. ............. ............. ............. ..... 60

SURVEY DATA .................................................................................................................................................. 61MAIN SYNC ...................................................................................................................................................... 61

SUB SYNC......................................................................................................................................................... 61DATA FORMATS................................................................................................................................................ 62

UPDATE TIMES ................................................................................................................................................. 64

DETECTION DECODING...................................................................................................................................... 65

PUMP SUBTRACTION ......................................................................................................................................... 66

CORRELATION DETECTOR ................................................................................................................................. 66

SIGNAL TO NOISE RATIO............ .............. ............. ............. ............. ............. .............. ............. ............. ....... 69

SIGNAL STRENGTH............................................................................................................................................ 69

NOISE STRENGTH.............................................................................................................................................. 72

DETECTION DECODING QUIZ............... .............. ............. ............. ............. ............. .............. ............. ......... 75




Confidential

Mud Pulse Theory Manual Chapter 5 – Detection Decoding Page 49Revision Nov. 2000

TELECOMMUNICATIONS BASICS

Characteristics of a signal

A signal is any physical parameter that changes with time. The real world is full of manydifferent kinds of signals. There are electrical signals, radio signals, pressure signals, thermalsignals, and mechanical signals. The beat of one’s heart produces a signal which doctors

measure and call the pulse. Speaking into a telephone creates acoustic and electrical signals thatcarry sound from one telephone to another through miles of connected wires. The pulsing of the

mud pulse valve produces a signal by creating changes in the standpipe pressure.

The rate and magnitude of the changes in the physical parameter give the signal itscharacteristics. Two main categories of signals exist: periodic signals and aperiodic signals. A

periodic signal is a signal that repeats itself regularly and exactly over a specific interval of time.A sine wave, as shown below, is the simplest example of a periodic signal. Another periodic

signal is a square wave. The square pulses in the sync sequence of a mud pulse message are periodic signals. An aperiodic signal, however, is a totally random non-repeating signal. A truly

aperiodic signal will never repeat itself.

Period Period

Sine WaveSquare Wave

As mentioned, periodic signals repeat regularly at determinable intervals. The time duration fora signal to complete a full repetition or cycle of an up pulse and down pulse (or a down and up

pulse) is called its period. The measure of how many cycles occur in a specific block of time isits frequency. Frequency is expressed mathematically in units of cycles per second or Hertz and

is equivalent to the inverse of the signal’s period.

Frequency (Hertz) = # of cycles / time (seconds)

Frequency (Hertz) = 1 / period of the signal (time to complete one cycle)

A signal’s amplitude describes the strength or energy within a signal. The amplitude of a mud

pulse signal is the height of the pressure pulse.

Periodic signals are often described in terms of their amplitude and frequency. A standard walloutlet in the U.S. provides a periodic A.C. voltage signal that has a frequency of 60 Hz and

amplitude of 120 Volts. In the UK the outlet signal is 240 Volt periodic signal at 50 Hz.



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This figure shows a sine wave with a period of 5 seconds and a frequency of 0.2 Hertz.

Period T = 5 seconds

Time Domain

A m p l i t u d e

Frequency = 1/T = 1/5 = 0.2 Hz

Pulse width is the time for one half of a signal’s period. The period is the total time for the full

up and down pulse. There are two pulse widths currently in use by the Mud Pulse MWD tool,0.8 and 1.0 seconds.

To calculate the frequency of these pulse widths use the following equation:

Frequency = 1/pulse width x 2

For example, for 0.8 pulse widths,

Frequency = 1/0.8 x 2 = 0.625

For a 1 second pulse width, the frequency is 0.5 Hz

Time Domain and Frequency Domain

Recall that any physical parameter that changes produces a signal. This signal can be expressed

graphically in either the time domain or the frequency domain.

In the time domain a signal is drawn as a change in the amplitude of the physical parameter

versus time. This is the domain used to draw the pulse data on the Mfilt screen.

In the frequency domain a signal is portrayed as a change in energy versus frequency where the

graph produced is referred to as a Power Spectral Density (PSD) plot. The frequency domain issimply a different perspective to view the characteristics of a signal. All the information found

in the time domain also exists in a frequency domain representation, only the way we view it haschanged.



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The diagram below shows a sine wave with a period of five seconds and a frequency of 0.2 Hertz

in both the time and the frequency domains.

Period T = 5 seconds

Time Domain

A m p l i t u d e

Frequency = 1/T = 1/5 = 0.2 Hz

E n e r g y

Frequency

(Hz)

0.1 0.2 0.3 0.4 0.5 0.6

To understand the importance of analyzing signals in both the time and the frequency domains,let us first consider a relationship established by Fourier over one hundred years ago. Fourier

proved that any signal that exists in nature can be uniquely expressed as the sum of sine (and/orcosine) waves of different frequencies and amplitudes.

Simply put, this concept means that any signal, no matter how random, can be created by adding

specific sinusoidal signals together and conversely, that same signal can be broken down andrepresented as the sum of its sinusoidal parts. This allows us to take a signal, like the standpipe

pressure signal, and break it down by frequency into its individual components for analysis.

For instance, the total change in pressure observed in the standpipe has many different sources.

The mud pulse valve, the mud pumps, the drillpipe rotation, and bit torque all produce vibrationsthat combine to create the total standpipe pressure signal transmitted to the decoder. This rawdata signal is sorted in the frequency domain into its different components.

Then the decoder isolates the part of the signal that contains the mud pulse data and discards therest.

This chart is a time domain plot of the raw signal. The time domain plot demonstrates the

amplitude and shape of the signal. What you can not see is the various frequencies that form thesignal.



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The next chart, however, is the same standpipe pressure signal shown in the frequency domain.This figure shows the frequencies from 0.1Hz to 10Hz that form the signal, as well as, the energy

contained in each frequency.



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Fourier’s Expansion

To help understand Fourier’s theorem, that any signal can be expressed as the sum of a series ofsine (and/or cosine) waves, let us take the example of a square wave signal. Fourier states that asquare wave of a known frequency, say 0.2 Hz, can be created by summing together sine waves

in the following expansion series.

0.2Hz square wave = sin(0.2kt) + 1/3 sin(3x0.2kt) + 1/5 sin(5x0.2kt) + 1/7 sin(7x0.2kt) + ...

where:k = 2ð

t = time

All periodic waveforms consist of a fundamental frequency and its harmonically relatedcomponents. The expansion above starts with a sine wave that has the same frequency as the

square wave. This frequency is the lowest and strongest frequency component in the signal andit is called the fundamental frequency. Added to the fundamental are successively higher

frequency sine waves that are odd integral multiples of the fundamental frequency. These sinewaves at the odd integral multiples are termed the odd harmonics of the signal.

The next diagram illustrates the step by step addition of the components in the Fourier expansion

of a square wave. As each higher harmonic is added, note that the shape of the signal is broughtcloser and closer to a square wave.



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If the expansion were continued to infinity, the shape of the signal would approach a perfectsquare wave.

The next diagram illustrates an ideal square wave in the time and frequency domains. Note that

the number of harmonic frequencies that form the square wave continue into infinity.

Period T

Time Domain

A m p l i t u d e

Frequency = 1/T

E n e r g y

Frequency

(Hz)

1

T

3

T

5

T

The decoder isolates the frequencies that are part of the mud pulse by invoking one or more

filters.



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Filters

Filters are signal processing tools that are designed in the frequency domain and work in the time

domain, filters isolate and act on a specific range of frequencies within a signal by applying a

varying gain to all the frequencies of a signal. The gain applied may be either greater or lessthan one depending on the filter’s function and design. A gain greater than one is referred to asamplification whereas a gain less than one is called attenuation. Applying a gain of one or

greater than one to some frequencies in a signal results in those frequencies being passed (saved) by the filter. Applying a gain of less than one to the remainder of the frequencies in the same

signal results in those frequencies being rejected by the filter. The signal that remains after thefilter is the sum of all the frequencies that have been passed.

The following text lists several categories of filters and a general description of their function.

The filters are described graphically by plotting the gain they apply verses frequency.

Lowpass Filter

A lowpass filter passes the lower frequencies within a signal while rejecting the higher

frequencies. The filter usually achieves this by attenuating the higher frequencies.

Frequency

S i g n a l S i z e

Low Pass Filter

Low High

Signals passed Signals rejected

Highpass Filter

A highpass filter passes the higher frequencies within a signal while rejecting the lowerfrequencies. The filter usually achieves this by attenuating the lower frequencies.



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S i g n a l S i z e

Frequency

Low High

High Pass Filter

Signals passedSignals rejected

Bandpass Filter

A bandpass filter passes a specific range or band of frequencies within the signal while rejectingthe frequencies within the signal that arc outside the band. The filter usually achieves this goal

by attenuating the frequencies outside the band. This passed band of frequencies is called the passband.

S i g n

a l S i z e

Frequency

Low High

Band Pass Filter

Signals passedSignals rejected Signals rejected

Notch filters

Notch filters isolate a much narrower band or notch of frequencies within the signal. They then

act by either amplifying or attenuating the frequency within the notch.



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Time Constants

A Time Constant (TC) is defined as the time it takes for any system to reach about 60% of its

final steady state value.

If an input to a system, is a square wave, then the rise and fall characteristics of the output will bedetermined by the time constant of the filter. For this example, the time constant of the system is

1.0 second.

Input

0

10

20

30

4050

60

70

80

90

100

110

-1 0 1 2 3 4 5 6 7 8 9 10

Time

P r e s s u r e

The shape of the system output to the rising edge will look like,

Rising

0

10

20

30

40

50

60

70

80

90100

110

0 1 2 3 4 5

Time

P r e s s u r e

Time constant

and the shape of the falling output will look like:



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Falling

0

10

20

30

40

5060

70

8090

100

110

4 5 6 7 8 9 10

Time

P r e s s u r e

Time constant

The time constant for this particular system is 1.0 second. It takes 1 second for the output to riseto 63% of its final value, and 1 second to drop from 100 psi to 37 psi (a 63% drop).

The drawing below shows the effect of increasing the time constants.

Increaing time

constant

The diagram below shows the response of a system with a slow time constant, to a narrow squareinput pulse. The output signal never reaches the height of the input signal.



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This shows two important factors to remember:

1. Systems or filters with longer time constants give smaller pulses because it takes longer for pressure transitions to reach steady state.

2. The faster the data rate the smaller the pulse height. This is because it is time constantdependent and at faster data rates, the pressure has less time to reach steady state value.



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MUD PULSE ENCODING SCHEME

The tool typically transmits the following data sequences:

Main Sync

Survey Sub Sync

Survey Data

Main Sync

Sub Sync

Tool Face

Tool Face

Tool Face

Tool Face

Tool Face

Main Sync

STAT sub sync

Tool Status

Directional OnlyTool Face (Auto, HS or M)

Main Sync

Survey Sub Sync

Survey Data

Main Sync

Tool Face

Tool Face

Directional GammaTool Face (Auto, HS or M)

Gamma

Gamma

Gamma

Tool Face

Gamma

Tool Face

8 Word sequence

9 Word sequence

Tool Face

Periodic Messages

(Time Starts @ Beginning of Survey)

Main Sync

VIB Inc. /Az.

Inc./Az. Sub Sync

Data

Data

Data

The transmission system is very flexible and many of the transmitted items can be customized.The sequences shown above represent defaults in use at the time of writing.

All transmissions (words) are 14 pulse widths long.



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Survey Data

The survey takes 12 transmissions (words) the format is shown below. Inclination and azimuth

require two words each because greater accuracy is required for these values.

12 words

1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 Word 5 Word 6

INC (11 bits) Azimuth (12 bits) Tool Face GTotal

Word 1 Word 2 Word 3 Word 4 Sur sync Main sync

BATV

1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7

DIP HTotal Temp Checkson

Word 7 Word 8 Word 9 Word 10

I H V

12 words

The status bits are defined as:I = Tool Face Mode 0 is HS, 1 is MTF

H = H-Total beyond limitV = Vibration beyond limit.

Main Sync

The main sync fulfills two functions, to keep track of the start of a transmission and also toimpart information as to what type of tool faces will follow. So there are two types of main

sync, a high side sync and a magnetic tool face sync.

The two main sync patterns are:

HTF

MTF

Sub Sync

A sub sync is primarily used to tell the surface system what type(s) of data will follow. There

are 8 different sub syncs:

GYSUR - for Gyro SurveyMSUR - for Magnetic Survey

Inc./Az. - for Inclination and Azimuth with pumps on.

3

4

2

2

1.5

1.5

3

3

2

4

1

1



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GYTF_Gamma – for Gyro Tool Face with Gamma

GYTF - for Gyro Tool FaceMTF - for Magnetic Tool Face

HTF - for High Side Tool FaceHTF_GAMMA - for Gamma

MTF_GAMMA - for Gamma combined with vibrationVIBS - for vibration data, average and maximum

ERR - for error messagesHTOT is a special sync for a magnetic ranging product.

GAMMA - for Gamma onlyRANGE - for Ranging

Data Formats

128 unique patterns of pulses are available for each data word transmission. Each of these patterns represents a number for the data value being transmitted.

These 128 patterns have been carefully chosen for maximum probability of successful decoding.

One rule adopted in picking the patterns was that the off time after a pulse must be at least aslong as the on-time of the pulse. This reduces the chances of pulses running into each other, and

disturbing the clock tracking routines.

The tool can transmit eleven different data items. These are shown below along with the rangeof values.

Measurement Range Units

Inclination 0 – 180 Degrees

Azimuth 0 – 360 Degrees

Tool Face (in survey) 0 – 360 Degrees

Tool Face 0 – 360 Degrees

Gamma Raw 0 – 64 Counts

H-Total 30k – 70,000 nanoTeslas

Temperature* 0 - 175 Degrees C

Battery Voltage 17 - 21 Volts

Peak Vibration 0 - 20 g

The table below shows the number of words (14 pulse widths each) and the number of bits used

to transmit each data item.



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Data Item Words Bits

Inclination 2 11

Azimuth 2 12

Tool Face (in survey) 1 8

Tool Face 1 7

Gamma 1 7

H-Total 1 9

Temperature 1 5

Battery Voltage 1 3

Peak Vibration 1 7

The transmitted resolution for each measurement can be calculated by

Resolution = Range ÷ 2#bits

For example, the resolution for normal tool face is

=360/27 = 360/128 = 2.81

The transmitted resolution for all the measurements is shown below.

Transmitted EYE

Measurement Range Units Bits Resolution Accuracy

Inclination 0 - 180 Degrees 11 0.09 ± 0.15 Azimuth 0 - 360 Degrees 12 0.088 ± 0.25

Tool Face (survey) 0 - 360 Degrees 8 1.4 ± 0.15

Tool Face 0 - 360 Degrees 7 2.81 ± 0.15

Gamma 0 - 64 Counts 7 .5

H-Total 30k – 70,000 nanoTeslas 9 78

Temperature* 0 - 175 Degrees C 5 0.996

Battery Voltage 17 - 21 Volts 3 .5v

Peak Vibration 0 - 20 g 7 156mg

DIP -90 – 90 Degrees 10 .18

G-Total 984 – 1016 Mg 5 1mg



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Update Times

The data update times are easy to calculate. Since tool face data are one word long, and one

word is 14 pulse widths, the update rate for ½second pulses is 14 x 0.5 = 7 seconds. For 1

second pulse widths, the update rate is 14 seconds.

The transmission time for a survey is 8 words x 14 pulse widths. For ½second pulse widths this

results in 56 seconds, for 1 second pulse widths, a transmission time of 1 minute 52 seconds.

Measurement Pulse Width 0.76 Pulse Width 1.0

Survey 2 min 7 sec 2 min 48 sec

Tool Face 10.6 sec 14 sec

Tool Face with Gamma 21.3 sec 28 sec

Gamma 21.3 sec 28 sec



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Detection Decoding

This diagram provides an overview of the signal detection and decoding process.

Remove DC

component

Low pass

Filter

Sync

Detector

Matched Filter

Pump

Subtraction

DataDecode

Raw A/D Input

Match Patterns

Detector Decoder PrincipleDetector Decoder Principle

Digital pressure data is provided by the MSI to the decoding program called Mfilt. The first stepis to remove the high background pressure. A pump subtraction routine removes the signalscaused by the mud pumps. A low pass filter is then used to remove the remaining high



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frequency noise from the signal. Finally a matched filter, or correlation filter, performs the main

task of identifying pulses and decoding the data.

Pump Subtraction

The pump subtraction routine runs at two different rates. The downhole tool does not transmit

any pulses for the first 60 seconds after the pumps have been turned on. This provides anopportunity for the surface system to measure the signature of the pumps without the

complication of having pulses present.

The user can make three adjustments to the pump subtraction routine; the low and upper bound pump periods and the graph adaptation time constant. The pump periods give the software an

initial guess as to the periods of the pump noise. The two numbers should be kept to a ratio offour. For example, if the low bound is set to 0.3, the upper bound should be set to 1.2. Setting

the upper bound pump period to zero effectively turns off pump subtraction.

Sometimes the pump subtraction can do more harm than good, especially with a pump that has poor speed control. The graph adaptation time constant is the update time for the pump

subtraction routine after the tool has started pulsing. The long default of 70 seconds is usuallysufficient to allow for slowly changing pump characteristics.

Correlation Detector

The next stage is the correlation or matched filter detector. Correlation detection is similar to

decoding by eye, and is accomplished by matching the pulse shapes received, with the idealshapes for the 128 patterns of ones and zeros, and determining a best fit. The correlation

detector displays a measure of how close a fit it has found and shows it as a percentage.

The program automatically adjusts three set points after detection has started. They are the lowerand upper bound pulse time constants and the RMS amplitude. The default values will suffice

for most jobs running at 1 second pulse widths.



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Remove DC

component

Low pass

Filter

Matched

Filter

Pump

Subtraction

DataDecode

Raw A/D Input

Detector Decoder SettingsDetector Decoder Settings

Freq (rel.corner) = 1.00

Damping Ratio = 1.00

TC 4 Activation Calc. = 2.0

Lower Bound Pump Period = 0.3

Upper Bound Pump Period = 2.5

Graph Adaptation TC = 70

Lower Bound TC = 0.500

Upper Bound TC = 1.500

Downslope Time = 0.100

Time for Upslope = 0.050

Expected Sync ID (0=None) = 0

Amplitude (RMS) = 5.000

Fraction Rand/Rand+Sys = 0.500

Base RMS Noise/Signal = 0.80

TC Signal Loss = 10.0

Delay to Comm Start = 4

Lower TC Lock 2 Synch = 1.0

Mean Cancellation TC = 4.00

The Mfilt quick guide shows the values that all of the parameters should be set to at the start of arun.



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1. Pulses

Lower Bound TC = 0.500

Upper Bound TC = 1.500

Downslope Time = 0.100

Time for Upslope = 0.050

2. Noise Filter

Freq (rel.corner) = 1.00

Damping Ratio = 1.00

Mean Cancellation TC = 4.00

Lower Bound Pump Period = 0.3

Upper Bound Pump Period = 2.5

Activation Amplitude = 500.0

TC 4 Activation Calc. = 2.0

Graph Adaptation TC = 70

Value to Clip to (PSI) = -300

5. Initialization

Load

Write

Defaults

3. Calculations

Offset for Toolface = 000.00

E.Longitude = 200.00

Latitude = -123.0

Altitude (ft) = 34.0

Interference along Axis = 1000

Cross-axis Interference = 100

Horiz Fld. Uncertainty = 100

Vert Fld. Uncertainty = 100

Total Fld. Uncertainty = 100

Gamma Scale Factor = 1.00

Mag field Declination = XX.X

4. Sync/Decode

Expected Sync ID (0=None) = 0

Amplitude (RMS) = 5.000

Fraction Rand/Rand+Sys = 0.500

Base RMS Noise/Signal = 0.80

TC Signal Loss = 10.0

Delay to Comm Start = 4

Lower TC Lock 2 Synch = 1.0

Low pass filter settings

relative to pulse width

Pump subtraction

Low pass filter TC determines if pressure high sufficient for pulsing, leave at 2.0

Program automatically changes this value, start job at 1/2 pulse width

Program automatically changes this value, start job with 1-1/2 pulse width

Not for wellsite use


Program automatically changes this value, start at 5

MfiltMfilt Quick GuideQuick Guide

Adjust to remove noise, start at 1.00

Leave at 1.00

Change only if sync problems (20004 for HTF, 20006 for MTF)


Start at 0.8, increase if sync problems to 1.2max, decrease if false syncs

Time after program starts before searching for sync, leave at 4

Removes the changes in baseline pump pressure

Set high enough to allow pump(s) to stabilize, lower when shallow testing

Pump signature update time, leave at 70 seconds

For removing pulse echoes, set to -100 to disable, call office if echoes

Time program waits before declaring signal lost, and stops looking for pulses?

Enter Offset Toolface between pulser and EYE

Enter longitude, East is negative (North America)

Enter latitude, North of equator is positive (North America)

Enter altitude in feet above sea level

Leave as is

Leave as is

Leave as is

Leave as is

Leave as is

Terms used for

azimuth correction

Enter value shown on well plan chart (positive for most of North America)

For 6.5” collars, use 6.33

Reads all values from file filter1m.ini

Stores all values into file filter1m.ini

Loads all values from file filter1m.ini

Set to 0.0 if not installed

M.M. 1/20/00

Time program waits before declaring best pattern match, set to 1 - 1.5 pw



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SIGNAL TO NOISE RATIO

For successful MWD data decoding, we want to maximize our signal to noise ratio.

Signal to noise ratio = Signal strength Noise strength

Signal Strength

The MWD signal strength is the pulse height of the signal measured at the standpipe. Two

factors, the initial size of the pulse at the transmitter and the damping (reduction) the pulsessuffer along its path, determine the pulse height seen at the transducer. Therefore to improve the

pulse height, you must either increase the initial pulse size at the pulser, or reduce the amount ofdampening, or both.

Signal Strength at the PulserThe pulse height in the SDI tool is self-regulating and keeps a fixed pulse height. Therefore,nothing needs to be done by the field hand to increase the pulse height.

Damping FactorsAnother way to increase the pulse height is to reduce the influence of the damping factors thatact upon the signal. The damping factors are any physical parameters that rob energy from all or part of the signal. The first step in reducing these influences is to identify them. You must be

aware of the sources of signal damping and alert for any adjustments that might be made toimprove decoding. Depth, mud weight, viscosity, pulsation dampeners, flow restrictors, mud

motors, and mud aeration are all sources that can steal energy from our signal.

FrequencyThe smaller the pulse width (faster tool frequency), the smaller the pulse height. In marginal

decoding conditions, the largest pulse width will produce the best decoding.

DepthObviously the longer the path the signal must travel, the more energy it will lose. However this

influence by itself it has less effect on the signal than one might expect.

Valve ObstructionSelf-explanatory, use of pipe screens can reduce the occurrence.

Air in MudGas or air in the mud will severely attenuate our pulses. This can occur when the pre-charger onthe pump fails and there is not enough hydrostatic head on the suction side of the mud pump.



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Gas or air in the mud can be recognized by a severe unexplained reduction of the pulse height

with the high frequency (narrow pulse width) pulses smaller than the low frequency (wide pulsewidth) pulses.

During the initial Sync pattern, it is possible to determine if some form of damping is actingupon the signal. Look for reduced pulse height in the narrow pulses compared to the wide pulse

widths.

Pulsation DampenersThe mud pumps create a surging flow rate that rises and falls periodically with the action of their

pistons. The standpipe pressure sees this rise and fall in the flow rate as a sinusoidal change in pressure at either the stroke frequency and the piston frequency (number of pistons X the stroke

rate). To smooth out and to reduce the pressure fluctuations, pulsation dampeners (also calledaccumulators or desurgers) are attached to the discharge side of the mud pumps. Their purpose

is to reduce the mechanical vibrations and fatigue failures of the pump components such asvalves, fluid cylinders, pipe and fittings.

The dampers consist of large metal spheres attached directly to the discharge line of the mud

pumps. In the upper portion of the sphere, there is a flexible bladder, which is filled withnitrogen at a set pressure. This bladder is exposed to the lower portion of the dampener to thesurging flow and it works to absorb and stabilize the changing flow and pressure. It functions

much like a pressure shock absorber or capacitor as it attempts to damp out any sudden changesin flow rate or pressure.



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The main problem that the pulsation dampener creates for us is that it treats the pressure pulse

created by MWD tools in the same manner as pump pressure changes i.e. it smoothes them out.Often the amount of energy taken by the pulsation dampener is not significant enough to cause

decoding problems. However, when small pulse height is already a problem, it is important to properly set the pre-charge on the pulsation dampener. Under marginal decoding conditions,

success of the job can hinge on a properly adjusted pulsation dampener.

Rule of thumb: The pulsation dampener pre-charge should be set to 1/4 to 1/3 of the standpipe pressure e.g. with a standpipe pressure of 3,000 psi, the dampeners should be charged to

between 750 and 1,000 psi.

Two dampeners act as very efficient pulse dampeners, especially if only one pump is in use andthe other pump, with its dampener, is not isolated.

If only one pump is being used, always isolate the other pump.

Suction Pulsation Stabilizers

Without suction stabilization, pumps cannot function smoothly or efficiently. In extreme

decoding problems, it is worth having the rig crew check the operation of the suction stabilizers,especially on rigs where there is little drop down from the mud pits to the pumps.

Pressure TransducerThe position of the transducer in the flow system can be significant in low signal to noise

conditions. Try to position the transducer as close to the main flow as possible. Avoid being atthe end of a side pipe that has several valves and other transducers.

Always try to position the transducer horizontally. This is a compromise that reduces the chance

of mud cake building up, and reduces the chance of trapping air. Including a bleed valve in thetransducer assembly, and pre-packing with grease, are useful improvements.

Finally, try to reduce the number of 90-degree bends in the run to the transducer.



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Noise Strength

It is imperative that the field hand knows the frequency that tool is operating. The frequency of

other noise sources, only become significant when they become close to the tool frequency.

Pulse Width(secs)

Tool Frequency(Hz)

0.8 0.625

1.0 0.5

Pump Noise Normally with a mud pump in good condition two signals will exist in the standpipe due to the

mud pumps. The first and weaker signal will be at the overall stroke rate or drive rate of the pump. The second, and stronger signal, will be at the piston frequency. For example a single

acting triplex pump at 55 spm, will create a signal at

55 spm X 3 pistons per stroke/ 60 seconds = 2.75 Hz

Most of the time, these frequencies are well above the tool frequency, and are removed by thelow pass filter.

Many problems with a pump can cause problems such as bad valves, unbalanced chambers,

malfunctioning prechargers, cavitation, and seal failures. An alert MWD hand can often spot a problem developing well before the motorman notices. Having hard copies of pump noisesignatures before and after a problem develops can really help to convince a toolpusher to have

someone check out a suspect pump.

If two pumps are being used at different stroke rates, it is possible to create a beat frequency.This occurs at a frequency that is the difference between the stroke rates of the two pumps. If

two triplex pumps are operating at 60 spm and 50 spm, a low frequency beat signal might beseen at either of the following frequencies:

(50 spm - 60 spm)/60 secs = 0.167 Hz or

(50 spm - 60 spm) X 3 pistons/60 secs = 0.5 Hz

The tables below show a selection of possible pump frequencies.



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Single Triplex Pump

SPM Frequency(Hz)

Piston Frequency(Hz)

20 0.33 130 0.50 1.5

40 0.67 2

50 0.83 2.5

60 1.00 3

70 1.17 3.5

80 1.33 4

90 1.50 4.5

100 1.67 5

110 1.83 5.5

120 2.00 6

Two Triplex Pumps

Delta SPM Frequency(Hz)

Piston Frequency(Hz)

2 0.03 0.1

3 0.05 0.15

4 0.07 0.2

5 0.08 0.25

10 0.17 0.5

15 0.25 0.75

20 0.33 1

25 0.42 1.2530 0.50 1.5

Torque NoiseThe easiest way to identify torque noise is to look for noise that disappears as soon as drillpipe

rotation stops. Toque noise can exist on or off bottom depending upon the source. If the cuttingaction of the bit is the main source of torque, then it should disappear as the bit is pulled off

bottom even before rotation is stopped. However, if the stabilizer configuration is supplyingsignificant torque then the interference will not disappear until rotation is stopped, regardless of

bit location.

Torque noise is formation related. Harder rock formations, high angles, PDC bits, and packedassemblies all increase the chances of suffering from torque noise. The frequency is often

between 0.1 to 0.3 Hz.

What can be done? The first attempt is to try to filter it out with a high pass filter, being carefulnot to filter out the pulses. The next step is to try to alter the drilling parameters to move the

frequency away from the MWD signals, or to reduce the level of the torque noise. Changes in



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WOB and rpm will have the biggest effect. Try decreasing the WOB and increasing the rpm.

Another possibility is to reprogram the tool to a faster data rate in order to move away from thenoise frequency. If none of these changes work, then the only remedy is to persuade the

company man to change the BHA; rock bit instead of PDC, undergauge stabilizers, etc.

Mud Motor NoiseThe frequency of the mud motor noise can be determined if three properties of the motor are

known.

1. The number of lobes2. The rpm for each gpm

3. The minimum on flow rate

Frequency = (Flow rate – min flow on) X rpm/gpm X # of lobes60

Usually mud motor noise is much higher than the tool frequency and can be ignored.Stalling of the mud motor will cause a loss of sync. The motor stalls when the resistance to

rotation exerted by the formation on the bit is greater than the maximum torque the motor can produce. When this occurs, the standpipe pressure increases suddenly as the rotor in the motor

stalls and the mud flow forces a breakdown in the rotor to stator seal in the motor. Drilling withtoo much WOB causes motor stalls because the resistance to the bit increases with an increase in

WOB. Drilling with a constant differential pressure will give the best decoding conditions.

In addition to actually stalling, poor drilling practices can cause decoding problems. If the drillerfails to keep a relatively constant WOB, abrupt changes in the standpipe pressure will be seen.The driller needs to avoid the practice of slacking off on the pipe and allowing the motor to drill

off the weight. If there is an automatic driller on the rig, then try to persuade them to use it, if,

and only if, it has been adjusted correctly. The automatic driller usually makes very smallchanges on the brake, which allows the decoding software to maintain sync.

Swab/SurgeSwab and surge effects are sudden changes in the standpipe pressure that occur when the pipe is

abruptly worked up and down. Moving the pipe suddenly will cause a sharp increase in pressureand abruptly lifting the pipe will cause a sharp drop in pressure. If there is an automatic driller

on the rig, then try to persuade them to use it, if, and only if, it has been adjusted correctly. Theautomatic driller usually makes very small changes on the brake, which allows the decoding

software to maintain sync.

Electrical NoiseThis occurs due to pick up from cables adjacent to the standpipe cable. SDI uses shielded cables,

so this should not be a problem.



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DETECTION DECODING QUIZ

1. What is the frequency when using a pulse width of 0.8 seconds?

2. Gas or air in the mud severely reduces our signal. Will the effect of air in the mud be greateror smaller on the wider pulses than the normal pulses (e.g. the 3 pulse width pulses of the main

sync)?

3. What is the recommended pulsation dampener charge?

4. What are the frequencies of the pump noise for two triplex pumps operating at 60 spm? Whatwould be the beat frequency if one pump were slowed to 40 spm?

5. When is it important to bleed the pressure transducer?

6. What setting on Mfilt would you change to turn off pump subtraction?

7. What is the update rate for tool face when also transmitting gamma ray?

8. How long after the pumps are started does it take to obtain a survey?

9. On the Mfilt screen, what does the correlation number mean?

10. You are having trouble detecting data and the directional driller is getting impatient with theloss of tool faces. You are on 0.5 second pulse widths. What can you do to improve the

situation?



TALKDOWN SCHEME CHAPTER 6

CONTENTS

CONTENTS ....................................................................................................................................................... 76

OVERVIEW....................... ............. ............. .............. ............. ............. ............. ............. .............. ............. ......... 77

TALKDOWN MESSAGES............... .............. ............. ............. ............. ............. .............. ............. ............. ....... 77

USER DEFINED TALKDOWN MESSAGES................... .............. ............. ............. ............. ............. .............. 78

PULSE WIDTH ................................................................................................................................................. 79

INCLINATION MESSAGE SWITCHING...... ............. ............. ............. .............. ............. ............. ............. ..... 80

TALKDOWN PATTERNS............. ............. .............. ............. ............. ............. ............. .............. ............. ......... 80


© 2000Scientific Drilling International



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Mud Pulse Theory Manual Chapter 6 – Talkdown Scheme Page 77Revision Nov. 2000

OVERVIEW

Talkdown is the method by which transmission modes of the downhole tool can be remotelymodified from the surface.

Communication down to the tool is accomplished by the flow accelerometer and the MWDcontroller. The controller constantly looks for specific patterns of on and off times measured bythe accelerometer. When a match is found, the tool switches to a different mode of operation.

TALKDOWN MESSAGES

There are several mode options, currently 10 different ones. What these modes do is governed by a “talkdown table”. Two of these modes are fixed, while the remaining eight can be

configured by the operator before running the tool downhole. The modes are referred to as“talkdown messages”.

A talkdown table is a simple text file that can be viewed and changed by any text editor.

This extract from the talkdown table lists the 10 different messages.

[**************************************************************************][ POPPET Talkdown Table Created 01/06/00 12:30:12 ][**************************************************************************][ Talkdown Message Structure ][ ======================================================================== ][ TDMess1 - Survey then Auto Tool Face (System Defined) ][ TDMess2 - Toggle Pulse Width (System Defined) ][ TDMess3 - User defined message 1 ]

[ TDMess4 - User defined message 2 ][ TDMess5 - User defined message 3 ][ TDMess6 - User defined message 4 ][ TDMess7 - User defined message 5 ][ TDMess8 - User defined message 6 ][ TDMess9 - User defined message 7 ][ TDMess10- User defined message 8 ][--------------------------------------------------------------------------]

Talkdown Messages 1 and 2 are the hard coded ones.

Message 1 sets the tool to transmit a survey on pressure up, and then continuous tool faces that

automatically switch from magnetic to highside depending upon the inclination taken during thesurvey. In addition, every 15 minutes, a tool status sequence will be transmitted up. The tool

status sequence is H-Total, battery voltage and the tool temperature.

Message 2 sets the data rate of the tool by changing the pulse width from high to low. The actualvalues for the pulse width can be changed, but only by creating a new talkdown table and storing

it in both the downhole tool and the surface equipment. At the time of writing, the two default pulse widths are set to 0.8 and 1.0 seconds.



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USER DEFINED TALKDOWN MESSAGES

The User Defined messages must be configured by creating a new talkdown table. This extractshows the format for creating your own user messages.

[ ======================================================================== ]

[ User Message Definition Area ][ ][ Definitions: <Msg> = <MsgType>[-<MsgType>...] ][ ][ Message Format: <Msg>[,<time>][;]<Msg>[;]<Msg>[,<delay>,...] ][ \____________/ \___/ \_________________/ ][ | | | ][ Sent Once Sent Continuously Sent Periodically ][ ][ Where: <time> = Time to wait in minutes before sending Msg again, ][ even if the pumps cycle before <time> has elapsed. ][ <delay> = Delay in minutes for periodic message ][ ; = Mmessage section separator ]

[ <MsgType> = Defined in table below... ][ ][ ============================== <MsgType> =============================== ][ AutoTF - Auto Toolface MSur - Magnetic Survey ][ Gam - Gamma Counts HTOT - H-Total Message ][ HsTF - Highside Toolface IncAz - Inclination and Azimuth ][ MTF - Magnetic Toolface Vib - Vibration ][ GyroTF - Gyro Tool GySur - Gyro Survey ][ GMSur - Gyro-Magnetic Survey Range - Ranging Message ][ ======================================================================== ][ Example1: ][ TDMsg3 = MSur; HsTF-Gam; IncAz,15 ][ In this example, send the survey once each time pumps are cycled ][ followed by high-side tool-face continuously. Every 15 minutes send ]

[ the inclination and azimuth. ][ ][ Example2: ][ TDMsg3 = GySur,15; GyroTF-Gam; Vib,10 ][ Send the gyro survey once, but only if 15 minutes have passed since the ][ last gyro survey was sent. Then send both gyro tool-face and gamma ][ continuously. Send vibrations every 10 minutes. ][ ]

Another important example is = Msur; AutoTF-Gam; Vib,10

This will cause the tool to transmit auto tool faces and gamma data (standard resolution), along

with tool vibration data every 10 minutes.

It is prudent to test any talkdown messages you create, with a simulator box at the surface, beforeever running it downhole. Some messages just do not work, even though they obey all the rules,

for example,

Msur; Gam; Vib,15

Sends up a sequence of one magnetic tool face and then a STOP sub synch.



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This is the area of the talkdown table where the user talkdown messages are changed. Note theabsence of square brackets in the lines that can be changed.

[**************************************************************************][ Message Definition ][ TDMsg1 = MSur; AutoTF;Vib,15 >>> REFERENCE ONLY, System Defined ]

[ TDMsg2 = (Pulse Width Toggle) >>> REFERENCE ONLY, System Defined ]TDMsg3 = GSur; GyroTF-Gam; Vib,15TDMsg4 = MSur; MTF-Gam;Vib,15TDMsg5 = MSur; AutoTF;Vib,15TDMsg6 = MSur; AutoTF;Vib,15TDMsg7 = MSur; AutoTF;Vib,15TDMsg8 = MSur; AutoTF;Vib,15TDMsg9 = MSur; AutoTF;Vib,15TDMsg10 = MSur; AutoTF;Vib,15

Occasionally the tool may be accidentally switched to another talkdown mode. This could

happen during tripping in the hole. If you are sure that you only wish to transmit one particularmessage sequence, then you should adjust the talkdown table so that all the user messages are the

same. This will reduce the odds of your having to perform talkdowns to switch to tool back tothe desired message format.

It is possible to disable talkdown completely. This is done in Mlink.

PULSE WIDTH

The pulse width section of the talkdown table is shown below:

[--------------------------------------------------------------------------]

[Pulse Width Settings for Toggle between Low and High (Seconds)]PulseWidthLow = 0.80PulseWidthHigh = 1.00TDPulseWidth = 30[--------------------------------------------------------------------------]

This is where the absolute pulse widths may be changed. If you do want to change the pulsewidth, you have to pick a number that is divisible by 0.02. A pulse width of 0.75 will not work,

the nearest number that will work is 0.76.

In addition to the pulse widths concerning data rate, the window size for the patterns of on andoff times can also be changed. It is set to 30 seconds in the above example, and there must be a

good reason to have to change it.



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INCLINATION MESSAGE SWITCHING

[ Inclination Message Switching ][ ======================================================================== ][ Inclination message switching allows the operator to switch between two ][ messages based on the current inclination. When the inclination of a ]

[ survey is above the GyroToMagIncl TDMsg3 will be sent. When below, ][ TDMsg4 will be sent. This feature is only enabled when a Gyro message ][ is seen in either TDMsg3 or TDMsg4 (or both). ][ ]GyroToMagIncl = 10.00

TALKDOWN PATTERNS

The actual patterns for on and off times are hard coded and are also shown in the talkdown table:

[--------------------------------------------------------------------------]

[ ________________________________________________________________ ][ _______| Come up in Default Mode ][ ][ | 30sec | 30sec | 30sec | 30sec | 30sec | 30sec | 30sec | ][ _______ _______ _______ Msg 01 ][ _______| |_______| |_______________________| |________ ][ ][ _______ _______ _______ Msg 02 ][ _______| |_______| |_______________| |________________ ][ ][ _______ _______ _______________ Msg 03 ][ _______| |_______| |_______________| |________ ][ ][ _______ _______ _______ Msg 04 ]

[ _______| |_______| |_______| |________________________ ][ ][ _______ _______ _______________ Msg 05 ][ _______| |_______| |_______| |________________ ][ ][ _______ _______ _______________________ Msg 06 ][ _______| |_______| |_______| |________ ][ ][ _______ _______________ _______ Msg 07 ][ _______| |_______| |_______________| |________ ][ ][ _______ _______________ _______ Msg 08 ][ _______| |_______| |_______| |________________ ]

[ ][ _______ _______________ _______________ Msg 09 ][ _______| |_______| |_______| |________ ][ ][ _______ _______________________ _______ Msg 10 ][ _______| |_______| |_______| |________ ][ ]



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For example, to change from user message 3 (or any other message), to the default message 1,

The pumps and the rotary table must be off for at least 30 seconds before starting the talkdowncycles.

1. Turn on the pumps and/or rotate the drillstring for 30 seconds.2. Turn off the pumps and/or stop rotating for 30 seconds.3. Turn on the pumps and/or rotate the drillstring for 30 seconds.

4. Turn off the pumps and/or stop rotating for 90 seconds.5. Turn on the pumps and/or rotate the drillstring for 30 seconds.

6. Turn off the pumps and/or stop rotating for greater than 45 seconds.7. Turn on the pumps and the first survey will be transmitted in 60 seconds.



TROUBLESHOOTING CHAPTER 7

CONTENTS

CONTENTS ....................................................................................................................................................... 81

OVERVIEW....................... ............. ............. .............. ............. ............. ............. ............. .............. ............. ......... 82

TROUBLESHOOTING CABLES............... .............. ............. ............. ............. ............. .............. ............. ......... 83

FINDING AN OPEN CIRCUIT................................................................................................................................ 83

ISOLATION & CONTINUITY ................................................................................................................................ 83

TROUBLESHOOTING CHART ............ ............. ............. .............. ............. ............. ............. ............. .............. 85

Company Confidential© 2000Scientific Drilling International



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Mud Pulse Theory Manual Chapter 7 – Troubleshooting Page 82Mike Meadows Jan 2000

OVERVIEW

A major difference between an average MWD operator and a top hand, is in their ability totroubleshoot problems quickly and efficiently. The two old adages “an ounce of prevention is

worth a pound of cure”, and “if it ain’t broke don’t fix it”, both apply to MWD systems. Do as

much testing and checking out of your tools and equipment as possible before running in thehole. Check the mud pumps and dampener settings, be firm on you transducer location. Keep agood eye and ear on activities around the rig for any actions that may cause you a problem such

as mixing of mud additives, traffic around your cables, broken de-sander etc. However, once thesystem is in the hole and working, do not fiddle with anything!

The first step in fault finding is to decide where to begin investigations. Sometimes this is

obvious, but on other occasions, a little detective work will be necessary. The field operator whomakes a dozen haphazard adjustments or replacements may be successful in fixing a problem,

but he will be none the wiser if the problem recurs and he may well have spent more time andmoney than was necessary. A calm and logical approach is more satisfactory in the long run. A

good understanding of how the MWD tool and software works will really help.

Some general points to remember:

• Always take into account any warning signs or abnormalities that may have been noticed before the problem. For example, have the vibration readings been slowly increasing? Hasanyone been talking about lost returns?

• Verify the fault. Be sure that you know what the symptoms are before starting to

troubleshoot, and especially before calling the office for help.

•

Don’t overlook the obvious. For example, have they just switched pumps?

• Cure the disease not the symptom. Don’t adjust the decoder settings when the pressuretransducer just needs bleeding.

• Don’t take anything for granted. Just because the office sent you a “new” part do not assumethat it works or that it is configured the same way the rest of your kit is, check it out yourself.



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TROUBLESHOOTING CABLES

Most electronic and electrical faults are due to wiring and connectors. You should know how touse a multimeter.

Finding an Open Circuit

Testing with a voltmeter.1. Set the meter to handle 24 volts dc.

2. Starting at the MSI, disconnect the appropriate cable and test the voltage across the powerlines. If no voltage is present, replace the MSI.

3. If the voltage was good in step two, reconnect the cable to the MSI, and work your way up tothe next connector. Test the power lines again. If no voltage here, then you have found the

bad cable/connector. The open circuit is somewhere between the connector in your hand andthe last connector that passed the test.

Using the MSI for Standpipe Pressure Cables.1. For circuits that use 4-20 mA, a direct short circuit will read maximum values e.g. for the

standpipe pressure sensor 3,000 or 5,000-psi. Unplug the Y connector at the MSI and use a paper clip to short the appropriate pins. The mfilt screen should show maximum pressure, if

it doesn’t, replace the MSI.2. Reconnect the Y connector and unplug the readout cable going to the pressure sensor. Use

the paper clip again. If full pressure is not seen, the problem is in the Y cable.3. Repeat this test all the way up to the sensor until you isolate the problem.

Isolation & Continuity

Testing for isolation and continuity is done with the multimeter set to the ohms position.Isolation testing is for finding shorts and continuity testing for finding short opens.

Isolation1. Disconnect both ends of the cable.

2. Set the multimeter to the maximum ohms setting.3. Measure the resistance across the all combinations of pins.

4. The resistance should read the maximum reading on the meter, usually Meg ohms.5. If the meter shows any resistances less than 1 meg ohm, there is a short in the line. A dead

short will read close to zero ohms, and a partial short will read a higher resistance.



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Continuity1. Normally this test is performed with both ends of the cable within reach of the meter’s leads.

If you can not connect both meter leads to both ends of the cable, you will have to use a jumper such as a paper clip.

2. Touch the leads to the same pins at each end of the cable, i.e., pin A to pin A. If you used a

jumper, touch the leads across A and B on the connector without the jumper. The resistanceof a 200 foot cable is about 5 ohms.



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TROUBLESHOOTING CHART

Start

Does Mfilt see pressure?

YES

Short MWD G & H on MSI

Full scale pressure?

Are pulses visible?

NO

YES

Are pulses visible on Rig Floor?

NO

YESNO

MSI Problem

YES

Short G & H at Transducer

Full scale pressure?

YES

NO

Cable Problem

Transducer Problem

NO

Is pulse width correct?

YES

Set correct pulse width

Surge pipe, rotate, cycle

pumps drill a few feet etc.

Any pulses visible?

NO

Any changes to mud recently?

eg viscosity, LCM

YES

NO

Are pulses small &

rounded?

YES

Some form of damping is present,check:

Pumps are isolated

No open surface valves

Transducer locationNo trapped air in transducer

Dampeners are charged correctly

Motor hand to check pumps

Pumps jacking off (air lock, fluid

starvation) NO

Problem Found?

NO

Change tool pulse widthto highest

Set all Mfilt settings todefault

YES

Noisy signal?

NO

YES Pumps near tool

frequency?

NO

YES

Change strokes and/or

liner, or install pump

position sensor.If using 1 pump, try

swapping pumps

Detection OK off bottom?

YES

Some form of drilling problem is

Downhole Tool Failure

NO

YES Circulate until

flushed through

Check transducer, bleed,

valve position etc

Syncs Problems?Try:

Activation amplitude sufficient

Turning off pump subtraction

Changing Expected Sync ID

Increase Base Noise/signal

Check:

Filter Freq set to pulse width.

Trylower setting, 0.1 increments

Identify noise source:

Bit torqueMud motor status

Weight on bit

RPM near pulse frequency

Pump noise, eg valve springs

Problem Found?

NO

Change tool pulse width

to highest/different

Detection TroubleshootingDetection Troubleshooting

NO

YES

Are the pumps on?YES

NO

Check with office before

declaring failure

Talkdown Enabled?

Has PW switched?

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