Mwd Glosario

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An MWD

G lossary

April, 1996


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Acronyms

AAPI Apparent API unit.API American Petroleum Institute.BHA Bottomhole assemblyBHT Bottom hole temperatureCSG Casing

DOI Depth of investigationDOT Drill-off testDLS Dogleg severityDT Interval transit timeFEWD Formation evaluation while drillingGL Ground levelKB Kelly bushingLCM Lost circulation materialLIH Lost-in-holeLOT Leak-off testLWD Logging while drillingMAD Measurement after drillingMD Measured depth

MSL Mean sea levelMWD Measurement while drillingMTBF Mean time between failuresOBM Oil-based mudOCS Outer continental shelfOD Outside diameterPDM Positive displacement mud motorPOOH Pull out of holeROP Rate of penetrationTD Total depthTF Tool faceTVD True vertical depthUTM Universal Transverse Mercator

WBM Water-based mudWOB Weight-on-bit

International MWD Society (IMS), April 1996 2


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Unit Abbreviations

API American Petroleum Institute unitsC degree (Celsius)cm centimeter(s)cps counts per seconddB decibel(s)F degree (Fahrenheit)

ft foot (feet)FS Full Scaleg gram(s)gal gallon(s)hr hour(s)Hz HertzID inside diameterin inch(es)kg kilogram(s)l litre(s)lb pound(s)m meter(s)MHz megaHertz

min minute(s)mm millimeter(s)mmho millimho(s)msec millisecond(s)mV millivolt(s)sec microsecond (s)nsec nanosecond(s)Ohm-m Ohm-meter(s)Pa Pascal(s)

ppm parts per million psi pounds per square inch p.u. porosity unit(s)s / sec second(s)

V volt(s)



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Glossary

ACCELEROMETERA device for measuring the acceleration of a body in a particular direction. Accelerometers are used in

downhole tools to sense changes of direction of the tool with respect to the Earth's gravity factor.

ACCURACY (of a measurement)

The closeness of the agreement between the result of the measurement and the (conventional) truevalue (of the measurand).

ACOUSTIC LOG

Typically, a measurement of the length of time required for a sound impulse to travel throughrock, usually given in msec/ft. The interval transit time is often used to calculate porosity; it mayalso be used to estimate formation pressure and as an input to seismic data as a velocity control

point in a wellbore.

ACTUATOR A part of the MWD transmitter, it is the hydraulic component that creates the pressure pulse

ANISOTROPY

The property of a rock which allows it to different measurements depending on the axis alongwhich it is measured. In terms of petrophysical measurements, the relationship of the axis ofmeasurement to the bedding plane is often tied to anisotropy.

API GRAVITY

The weight / unit volume of crude oil or other liquid hydrocarbon expressed in degrees API,where a specific gravity of 1.0 is equivalent to 10API. API gravity should always be referencedto temperature. Low API gravity oils (e.g. 10 API @ 80F) are called heavy / thick; high APIgravity oils (e.g. 40 API @ 80F) are called light / thin.

API TEST PITS

Shallow wells located at the University of Houston in Houston, Texas. The wells serve asstandards for a variety of nuclear logging tools. The test pits are currently used primarily as areference/standard for wireline logging tools because most MWD tools are too large a diameter tofit directly into the pits. The API test wells are used to calibrate Gamma Ray (GR), neutron andspectral GR tools.

API UNIT

A unit of measurement in GR logs (previously neutron logs also). For GR tools, one API unit isequivalent to 1/200th of the total deflection observed between zones of high and low radiation inthe test pit. MWD GR tools measure gamma radiation in API units, Counts Per Second (cps) andAAPI (see APPARENT API UNITS). Because MWD GR sensors are housed in thick steel drillcollars, the measurements usually are reduced compared to the same measurement by a wirelineGR tool. GR measurements may vary from one service company to another.

API WELL NUMBER

A unique well identification number consisting of (from left to right) a two digit state code (or pseudo code for offshore), a three digit county code (or pseudo for offshore), a five digit uniquewell code, and if applicable, a two digit sidetrack code as defined in API Bulletin D12A.

APPARENT API UNIT

A unit of measurement of total natural GR tools based on counts/second (cps) and scaled toapproximate standard API units (see API UNIT).



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ATTENUATION

The decrease of a physical quantity. Many high frequency MWD resistivity devices (e.g. 2 MHz)measure the attenuation of the propagated wave and relate this attenuation to resistivity.Conversely, many MWD vendors also measure the shift in phase of the propagated wave andrelate this shift to resistivity. Attenuation is often expressed in decibels (dB).

AVERAGE ANGLE METHOD

A mathematical model, approximating a wellbore, based upon a simple average of adjacent stationinclination angles and adjacent station azimuth angles .

AZIMUTH

Direction, as in a compass direction. The clockwise angle of departure from a reference direction(typically geographic) north, measured in a horizontal plane. In dipmeter and directional surveys,it is the clockwise angle from magnetic north to the tool reference point or electrode. Thismeasurement must be corrected for magnetic declination to compute true azimuth. The azimuth isgenerally expressed in degrees.

Azimuth is the angle between the horizontal component of the borehole direction at a particular point and the direction of north. The angle should always be expressed in the 0-360degree system. The angle may refer to either magnetic, true (geographic), or grid north; whichever

referred to must always be clearly indicated (also known as bearing).

AZIMUTHAL

The characteristic of a logging tool to perform separate measurements in different directions(azimuths) around the axis of the tool. Currently, MWD sensors making azimuthal measurementsare limited to density and tend to give measurements in quadrants around the borehole. SomeMWD GR sensors are shielded on one side so that measurements are taken from only (primarily)the unshielded side. These are oriented measurements rather than true azimuthal measurements.

BARITE

Barium sulfate, a mineral used to increase the weight of drilling mud. The presence of barite canaffect some logging sensors, both wireline and MWD. The measurements most significantlyaffected by barite are spectral gamma-ray and the photoelectric effect (Pe).

BENDING STIFFNESS

The resistance to axial bending of a drill collar (expressed in Nm/Rad or ft-lb/degree ofdeflection). It is equal to the bending moment required to produce a unit deflection of a collarwhen one end is fixed. This value is supplied to drilling engineers for the comparison of the angle

building characteristic of an MWD drill collar to that of a standard API drill collar.

BENTONITE

A type of clay, composed of the mineral montmorillonite. The major area of interest in thismineral is often its tendency to swell when wet. It is a common component of drilling muds.

BIAS

The systematic or persistent distortion of a measurement process which causes errors in onedirection (See SYSTEMATIC ERROR).

BIT BOUNCE

A dynamic axial drillstring motion characterized by the drill bit (bottom hole assembly) periodically lifting off the bottom of the wellbore, in most cases at the naturally resonantfrequency of a drillstring component (e.g. when the BHA axial resonant frequency is three timesthe BHA rpm, when drilling with a tricone bit).



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CAVINGS

Formation falling into the wellbore. Cavings tend to be larger and, in the case of shales, moreelongated than drilled formation. Cavings may pose problems for petrophysical and drillingreasons. In MWD logging, cavings may fall to the low side of the hole and pave the boreholewall with an unnatural layer of material which could confuse estimation of true formation

properties.

CENTRAL MERIDIAN

A longitude passing through the center of a projection. It is generally a straight line about whichthe projection is centered (symmetrically). Usually, the central meridian defines the X-origin ofthe map.

CLAY

A fine-grained aggregate consisting wholly or predominantly of microscopic and submicroscopicmineral particles, derived from the mineral decomposition of rocks. Clays tend to be plastic whenwet and hard when dry. Clays usually exhibit a higher GR-value than most sandstones due to the

presence of radioactive materials such as Potassium and Thorium.

CLOSURE

The distance between two points projected onto a horizontal plane.

COLLARSSee DRILL COLLARS

CORRECTION

A value added to a raw measurement in order to improve the accuracy of the measurement.

COURSE LENGTH

The difference in measured depth or the along hole depth from one station to another .

CURIE

A standard measure of the rate of nuclear transformations or disintegrations: one Curiecorresponds to 3.70 x 10 10 disintegrations/second.

CURVE ID

An identifier for a log curve which, when used in combination with context information for thelogging job, serves to distinguish it from all other log curves. Often this identifier is a code ormnemonic utilized by the logging company.

CURVE TYPE

General classification of log curves, independent of the specific sensor used. Examples aregamma ray, caliper, formation density, resistivity, acoustic, etc.

DATA RATE

The speed at which measurements and data are transmitted and recorded. In MWD, this parameter is important due to its relation to drilling or tripping speeds. If data are recorded slowly by a fast moving sensor, they may be less representative of the environment and difficult toreproduce. See also TRANSMISSION RATE.

DATA STORAGE CAPACITY

The volume of information which may be saved. In MWD, data are usually transmitted to thesurface in real time at a lower rate than the data are stored downhole. The real-time log is oftenreplaced by the higher-density, and better resolution data which are stored downhole and down-



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loaded after the tool is brought to the surface or downlinked from the surface. See alsoDOWNLINK.

DECIBEL

A unit used to express the relationship between two measurements of power as an interval on alogarithmic scale; 20 log 10 of the amplitude ratio or 10 log 10 of the power ratio. An amplituderatio of 2 (power ratio of 4) is approximately 6 dB. 1 dB = 0.1151 Neper.

DECLINATION The angular difference in azimuth readings of magnetic north and true north. The magneticdeclination varies with time and place. The magnetic declination is by definition positive whenmagnetic north lies east of true north, and negative when magnetic north lies west of true north

DENSITY

The mass of some material divided by its volume. In petrophysics, formations and drilling fluiddensities are measured, primarily as input to equations to derive the porosity of the rock. Mostlogging tools actually measure bulk density ( b), and express the density in g/cm

3. The equationused for determining porosity ( ) from bulk density is:

= (ma - b)/(ma - mf )

where ma is the assumed density of the matrix (formation) and mf is the assumed density of thefluid in the pore spaces.

DEPARTURE

Horizontal displacement of one station from another in the horizontal plane. Departure is oftenexpressed as two components - east/west and north/south.

DEPTH DATUM

The zero-depth reference for logging. A location on or above the surface (land or water) at whichan elevation can be determined for depth reference. The elevation of this datum is the referencefor all depth measurements made in the wellbore. Usually, the top of the kelly bushing is used asdepth datum in drilling wells, but it could be ground level, derrick floor, or some other specific

depth reference.

DEPTH ENCODER

A device that is generally affixed to the rig drawworks and that generates electric pulses as thedrum rotates. After calibration the output of the encoder is converted to depth.

DEPTH OF INVASION

The radial depth from the borehole wall to which mud filtrate has invaded porous and permeablerock. It is usually measured in inches.

DEPTH OF INVESTIGATION

The radial distance from the measure point on a sensor to a circle, usually within the formation,where the predominant tool-measured response may be considered to be centered. It varies fromone type of device to another because of different designs, and techniques of compensation andfocusing. It also varies from formation to formation due to changes in formation properties. For a

better understanding of the volume of investigation of a logging tool, it is recommended to knowthe depths of investigation corresponding to 10%, 50% and 90% of the cumulative GEOMETRICFACTOR. See also RADIUS OF INVESTIGATION.

DEPTH POLICY

A set of procedures defined by a data vendor to obtain a consistent depth.



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DEPTH SHIFT

(1) Amount of change to a core or log depth scale to align that scale to another log depth scaleused as a depth reference.

(2) Amount of change to the depth produced by the MWD depth system to match the driller'sdepth.

DETECTION RADIUS

The distance at which an MWD sensor in one formation can detect another formation parallel to

the borehole, measured from the center of the MWD tool. For resistivity or conductivity tools,this is defined as the distance where the log response changes by 25% of its value in the currentformation. For nuclear measurements, it is defined as the distance where the log response changes

by at least two standard deviations from the value in the current formation.

DIAMETER OF INVESTIGATION

Geometrical specification that characterizes a logging measurement. It is equal to twice the radiusof investigation or twice the depth of investigation plus the tool diameter. See GEOMETRICFACTOR.

DIELECTRIC CONSTANT

The ratio of a the observed DIELECTRIC PERMITTIVITY of a formation or material to that of avacuum.

DIELECTRIC EFFECT

Systematic shift observed on resistivities when the actual formation dielectric permittivity differsfrom the assumed dielectric permittivity value. This effect is larger when resistivities aremeasured with a high frequency (MHz range) electric field. See also DIELECTRICPERMITTIVITY.

DIELECTRIC PERMITTIVITY

A measure of the ability of a material to store electrical energy or to be electrically polarized whensubmitted to an electric field. Dielectric permittivity is frequency dependent.

DIFFERENTIAL PRESSURE

The difference between off-bottom pressure and stall pressure of a mud motor .

DIP DIRECTION

The direction of dip (maximum slope in a plane) perpendicular to the DIP STRIKE, expressedrelative to compass directions.

DIP STRIKE

The direction or bearing of a horizontal line drawn on the plane of a structural surface. The strikeis perpendicular to the DIP DIRECTION.

DIRECTIONAL DRILLING

Intentional drilling of an off-vertical well at a closely controlled, predetermined angle anddirection through the use of special equipment .

DIRECTIONAL SURVEY

A well survey that measures the degree of departure of a borehole from vertical and the directionof departure. Measurements are made of azimuth and inclination of the borehole.



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DOGLEG

The total angular change between the tangent to the bore hole at one point and the tangent to the borehole at another point. A dogleg may result from changes of inclination and/or azimuth.

DOGLEG SEVERITY

The rate of angular change of hole angle and/or direction evaluated between the current survey point and the next shallowest survey point. It is expressed in degrees per course length, and is

significantly influenced by the course length over which it is calculated.

DOLOMITE

Rock mostly composed of the mineral CaMg(CO 3)2.

DOWNLINK

The capability to retrieve data from, and send instructions to the tool when it is located downhole.Four principles are currently used for downlink communications: mechanical (wireline), electrical(inductive coupling), hydraulic (mud pulse) and electromagnetic propagation.

DRIFT ANGLE

The deviation of a section of the borehole from vertical.

DRILL BIT PENETRATION RATE

The average or instantaneous distance drilled per unit of time (see also RATE OFPENETRATION.

DRILL COLLAR

Heavy, thick-walled tube, usually steel, employed between the drill pipe and the bit in the drillstring to provide weight on the bit in order to improve its performance.

DRILLING FLUID TYPE

The type of mud present in the drilling media, such as chemical gel mud, crude oil, caustic (high pH), gypsum mud, native mud, etc.

DRILLING LOG

A log of drilling parameters such as penetration rate, rotary speed, weight on the bit, pump pressure, pump strokes, etc.

DRILL-OFF TEST (DOT)

A drilling procedure whereby additional weight is applied to the bit, and the drilling brake lockeddown at various rates of rotation (rpm), and the drilling rate of penetration observed as the weightdrills off. This technique is commonly used to determine optimal drilling control parameters.

DROP ANGLE

The average rate of angular decrease at which a deviated hole departs from the hold angle in adirectional well.

ELECTROMAGNETIC PROPAGATION

The passing of electromagnetic energy through a medium. Most MWD resistivity logs are basedon electromagnetic propagation and typically operate at high frequencies (typically betweenhundreds of kHz and a couple of Mhz). They are used for correlation and to determine formationelectrical properties or invasion characteristics. MWD tools record the phase shift and attenuationof electromagnetic energy through the formation near the borehole, which are then converted intoresistivities and dielectric properties.



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FORMATION WATER RESISTIVITY

The resistivity of the in-situ water contained in a formation, usually referred to as R w.. It should be referenced to a temperature.

FRACTURE GRADIENT

The mechanical strength of a formation that represents the maximum borehole fluid pressure thatcan be sustained without fracturing the formation, and losing borehole fluid. This gradient islargely dependent upon lithology, the formation pore pressure, and the weight of overlayingsediments (see also LEAK-OFF TEST).

FUNNEL VISCOSITY

Viscosity, equal to the time(in integer seconds) it takes one U.S. quart of mud to flow through aMarsh funnel. The measuring unit is seconds.

GALLING

Abrasion to unprotected metal surfaces. When drill collar threads are galled, they must be recut, ordamage to a mating connection will result.

GAMMA-RAY LOG

A log of the formation natural radioactivity level. It is typically used as an indicator of formationshaliness. It is also used extensively for well-to-well correlation and to correlate cased-hole logswith open-hole logs.

GEOLOGRAPH

A brand name commonly used to refer to a drilling recorder that records particular drilling eventsas a function of time. Depth and rate of penetration are two drilling parameters derived from itsrecording.

GEOMETRIC FACTOR

The contribution of a small geometrical region to the total response of a sensor. Geometric factorsare used to provide insight as to the spatial response characteristics of a measuring device.Geometric factors are usually integrated and cumulated over spatial volumes.

GEOSTEERING

A technique in which one or more geologically sensitive parameters, measured downhole andtransmitted to the surface, are used to guide the well path and keep it in the desired location. InGEOMETRICAL STEERING, the measurements are limited to azimuth and inclination, and thewell is steered toward a pre-determined geometrical target. In GEO(logical)STEERING,formation sensitive measurements are used to steer the wellbore in relation to adjacent geologicalfeatures.

GRAVITY TOOL FACE

The angle between a tool reference axis and a line perpendicular to the hole axis and lying in thevertical plane. Also commonly referred to as HIGHSIDE TOOL FACE.

GRID CORRECTION

The angular correction converting azimuth readings of true north and grid north. The grid correction is by definition positive when true north lies east of grid north, and negative when true north lies west ofgrid north.



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GRID NORTH (GN)

Within a rectangular grid system, the direction which is parallel to the central meridian of longitudethrough the grid origin.

GYROSCOPE

Comprises a spinning mass mounted within a gimbal system. In absence of friction and unbalance thespinning mass would remain stationary in inertial space and ideally act as a portable referencedirection.

GYRO SURVEY INSTRUMENT

A survey instrument which uses an oriented gyroscope to determine the azimuth angle at the survey point.

HEAVE

The vertical motion of a mobile offshore drilling rig. Logging depth systems need to track the righeave in order to accurately calculate the drillbit position.

HIGHSIDE TOOL FACE

See GRAVITY TOOL FACE.

HORIZONTAL DISPLACEMENT

The horizontal distance from a vertical line through the well head to a selected point along the well bore.

IMPULSE RESPONSE

The theoretical sensor response when logging past an infinitely thin formation of infinite contrastto its shoulder beds. See GEOMETRIC FACTOR.

INCLINATION

The angle as measured between the well bore and vertical.

INTERVAL TRANSIT TIME

The travel time of a compressional (usually) wave over a unit distance. It is proportional to thereciprocal of the wave velocity. Also called SLOWNESS. It is usually expressed in the unit ofsec (microseconds) per unit length.

INVADED ZONE

The portion of formation surrounding a wellbore into which drilling fluid (typically mud filtrate)has penetrated, displacing some of the native fluids.

ISOGONIC CHART

A chart showing lines of equal magnetic declination super-imposed on a geographical map.

JETTING

Through some soft formations, more than adequate deviation and penetration rates can be achieved byusing one large bit nozzle and the rest small or blank. The large nozzle is oriented in the desireddirection, the rotary locked, and the pumps turned on. The washing action creates a pocket into whichthe bit is spudded. Alternate periods of jetting and drilling ahead, using the same BHA, establish thedesired inclination and azimuth angles.



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MAGNETIC DECLINATION

The angle between geographic north and magnetic north. It can be either a negative or positivenumber. It is used to transform data referenced to magnetic north to data referenced to geographicnorth.

MAGNETIC INCLINATION

Vertical angle between the direction of the magnetic field and the horizontal plane. Commonlycalled magnetic dip angle.

MAGNETIC INTERFERENCEThat condition which occurs when extraneous (not due to the earth) magnetic forces affect amagnetically sensitive instrument. Proximity to magnetized casing, magnetized drillstringcomponents, and certain magnetic minerals are potential sources of interference.

MAGNETIC NORTH (MN)The direction of the horizontal component of the Earth's magnetic field at a particular point on the

Earth's surface. A compass will align itself in the direction of the field with the positive pole of thecompass pointing to the magnetic north

MAGNETIC PERMEABILITY

The property of a substance that determines to what degree it modifies the magnetic flux in a

magnetic field - assumed to equal unity in most oilfield geological formations. Magnetic permeability is frequency dependent. See also DIELECTRIC PERMITTIVITY.

MAGNETIC TOOLFACE

The angle between magnetic north and the projection of the tools reference axis onto a horizontal plane. See RELATIVE BEARING.

MAGNETOMETER

A geophysical instrument used to measure the intensity, in both the horizontal and verticaldirections, of the earth magnetic field.

MAXIMUM OPERATING TEMPERATURE

The published temperature above which a tool is not designed or expected to operate within its performance tolerances.

MAXIMUM RECORDED TEMPERATURE

The maximum (highest) temperature measured in the borehole during a logging operation. Thistemperature is a function of several parameters (e.g. formation temerature, depth, mud flow rate,and time since circulation).

MEAN TIME BETWEEN FAILURE (MTBF)

Average elapsed time between failures. It is calculated by dividing the number of MWDoperating hours by the number of failures. Industry standard practice (see SPE paper #19862) hasestablished two measures of MTBF, one for circulating hours (real-time transmission), and thesecond for total hours of operation below rotary (while the tool operating and recording data).

MTBF statistics are recorded for individual components, for whole MWD systems, and bygeographical area. Operators are also interested in the number of times MWD failures interferewith drilling operations and require tripping for the MWD tool. MTBF is significantly affected bythe drilling environment (e.g. SHOCK, VIBRATION, mud solids and flow rate) and by MWDmaintenance schedules.

MEASURED DEPTH

The actual distance measured along the axis of the borehole from the zero depth reference point tothe depth of interest. Sometimes referred to as the Along Hole Depth (AHD).



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MEASUREMENT AFTER DRILLING (MAD)

Measurements taken in a borehole after the initial drilling has taken place. MAD is the commonacronym for this operation.

MEASUREMENT ERROR

The difference between the true value and that which is reported from a measurement.

MEASUREMENT WHILE DRILLING (MWD)

A technique of making downhole measurements of azimuth, inclination, tool orientation, naturalradioactivity, resistivity, porosity, temperature, vibration, weight, torque, etc. Thesemeasurements are made while drilling by sensors located in the bottomhole assembly close to thedrill bit, and can be recorded downhole and/or telemetered to the surface.

MEASURING RANGE

Range of values for a quantity subjected to a measurement, for which the error of a measuringinstrument is intended to lie within specified limits. Sometimes called operating range.

MEMORY DUMP TIME

Elapsed time required to retrieve the data stored (recorded) in an MWD tool, once it is returned tothe surface. See TURN-AROUND TIME.

MINIMUM CURVATURE (CIRCULAR ARC)

The mathematical method recommended to calculate horizontal and vertical coordinate out of themeasured values of along hole depth (ADH), inclination (I), and azimuth (A).

MODULARITY

The ability to interchange components of an MWD tool string at the wellsite, either when onecomponent fails, or in order to conform to desired (directional) drilling characteristics.

MUD

A liquid circulated through the wellbore during drilling and workover operations. One purpose ofthe mud is to remove rock cuttings produced by drilling. The mud also helps cool the bit, it

prevents the borehole walls from caving in, constrains high-pressure formation fluids, and provides a medium for MWD mud-pulse transmission signals. See DRILLING FLUID.

MUD CAKE

The sheath of mud solids which forms on the borehole wall opposite permeable formations whenthe mud filtrate seeps into the formation.

MUD FILTRATE

The liquid portion of the mud that is able to flow into permeable formations.

MUD MOTOR

A hydromechanical device utilizing drilling fluids to rotate the bit without rotating the drill string.

MUD MOTOR CAPACITY

The actual stalling pressure of a mud motor for a given flowrate, divided by its stalling pressure atthe same flowrate when originally manufactured.

MUD MOTOR DRILLING EFFICIENCY

The actual maximum mechanical horsepower of a mud motor divided by its maximum mechanicalhorsepower when originally manufactured.



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OVERSHOT

Grapple device used to retrieve a survey instrument which has been go-deviled into the hole.

PERMANENT DATUM

The permanent elevation reference entity, independent of any equipment at the location.Generally, mean sea level (MSL) or ground level (GL) is used.

PERMEABILITY

A property of rock denoting its ability to pass fluids, and commonly used by the oil industry todistinguish between rocks which will give up no pore fluids and those which will produce oil, gas,and/or water. See also MAGNETIC PERMEABILITY.

PERMITTIVITY

See DIELECTRIC CONSTANT.

PHASE SHIFT

The phase angle between two different signals, typically measured in degrees (e.g. betweenelectromagnetic propagation receivers).

POLARIZATION HORN

A localized (in true vertical depth), high resistivity deflection anomaly on some propagationresistivity logs, caused by a combination of high relative dip and a large, sharp resistivity contrastat two adjacent formations.

POPPET VALVE A conical shaped device which extends on the end of the actuator. It extends or retracts, restrictingthe flow of mud, thus creating the pressure pulse

PORE PRESSURE

The pressure of fluids within a porous formation. MWD services are used in certain areas toestimate the formation pore pressure.

PORE SPACE

The open space, or voids, between the individual grains of a rock mass, available for fluidaccumulation.

POROSITY

The percentage of bulk rock volume that consists of interstitial spaces or voids, whether isolatedor connected. Porosity can be measured, calculated, or inferred. The common unit for porosity isthe p.u. (porosity unit). One p.u. is equivalent to 1% porosity.

PRECISION

The closeness of agreement between the results obtained by applying a measurement procedure

several times on identical materials and under prescribed measurement conditions. The smallerthe random part of experimental error, the more precise the measurement procedure.

PRESSURE

Force per unit area applied to a body (e.g. hydrostatic, flow and pump pressures). It may be gaugeor absolute. The kPa (kiloPascal) unit is used in physics. The more common related oilfield unitis the pound per square inch (psi).

PRESSURE PULSE



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The MWD downhole assembly generates pressure pulses in the drilling mud by retracting andextending the poppet valve. The type of pulse (zero or one) is determined by the time the plungeris allowed to remain in the extended position

PRINCIPAL MERIDIAN

A meridian line accurately located and used as a basis from which to construct interior lines ofmonuments, called meridians, for use by surveyors.

PROPOSED DIRECTION

The direction referenced to magnetic north that a well bore must follow to reach its target.

PROTRACTOR

Angle measured device designed to fit against curve of drill pipe body. Used to measure adjustmentsof tool face direction.

P.U.

A unit of porosity. One percent by volume of porosity is one p.u.

PULSE RATE

The number of variations caused by mud pulses per unit of time.

QUALITATIVE

Relates to a parameter that can be characterized by a relation, not a value.

QUALITY ASSURANCE

An integrated system of management activities involving planning, quality control, qualityassessment, reporting and quality improvement to ensure that a product or service meets definedstandards of quality with a stated level of confidence.

QUALITY PARAMETERS

Quantitative parameters that provide an indication of the quality of a measurement (e.g. static

error, observed error, resolution, signal to noise and hole size).

QUANTITATIVE

Relates to a parameter that can be characterized by a value, not a relation.

RANDOM ERROR

Random error is a non-reproducible error that is generally imputable to the physics of themeasurement.

RATE OF PENETRATION (ROP)

The interval drilled per unit of time, either averaged over an interval or instantaneous. Also calledROP.

REACTIVE TORQUE

When a mud motor is running, two basic sets of forces are involved. One set causes the shaft to turn.The other acts in the opposite direction and tries to turn the body of the mud motor. These latter forcesare the reactive torque. Since reactive torque has an effect on MWD high side readings, an effortshould be made to survey while the bit is off-bottom, thus avoiding the effects of reactive torque.



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REAL-TIME DATA

(1) Data transmitted to the surface while a drilling operation is in progress.

(2) Data acquired during the time that a new borehole section is first being drilled.

REAMING

The process of circulating and rotating drillpipe down (or up) a wellbore section that has been previously drilled.

RECORDED WHILE DRILLING (RWD)Data which were recorded in the logging tool while drilling, stored in downhole electronicmemory, and later retrieved - sometimes referred to as RWD. Because recorded mode data arenot sent by mud pulse transmission, the data are generally of higher resolution, more complete,and of greater precision than real-time data.

REFERENCE POINT

(1) Measure point: a mark or position on the MWD tool to which all measurements are related - atool zero.

(2) A depth datum.

REGULARIZATION

A filtering process that shifts unevenly spaced data onto an evenly spaced grid - commonly performed when converting evenly time sampled data onto an even depth grid.

RELATIVE BEARING

The clockwise angle (looking downhole) from the upper side of the survey tool to the sensor face.See also MAGNETIC TOOLFACE.

REPEAT SECTION

Another set of measurements run over a short section of hole, usually run to enable comparisonwith the main survey and document instrument stability and repeatability.

REPEATABILITY

(1) Qualitatively: The closeness of agreement between independent results obtained in the normaland correct operation of the same method on identical test material, in a short interval of time, andunder the same test conditions (same operator, same apparatus and same laboratory).

(2) Qualitatively: The representative parameters of the dispersion of the population which may beassociated with the results are qualified by the term "repeatability", for example repeatabilitystandard deviation, repeatability variance.

(3) Quantitatively: The value equal to, or below which, the absolute difference between twosingle test results obtained in the above conditions may be expected to lie with a probability of95%.

REPLACEABILITY

The ability to retrieve and replace a portion of an MWD device (such as a failed electronicscomponent) from the bottom hole assembly, without tripping the drillpipe, and then continueoperating the MWD tool.

REPRODUCIBILITY

(1) Qualitatively: The closeness of agreement between individual results obtained in the normaland correct operation of the same method on identical test material, but under different testconditions (different operators, different apparatus and different laboratories).



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no progress as weight is applied, and conversely makes hole with no apparent movement of the pipe at the surface. Screwing out is the reverse technique when there is drag in the borehole, andthe driller pulls the drillstring, and then rotates until the amount of pull has reduced.

SCRIBE LINE

A line marked on various drillstring components that relates to the orientation of the bend in amotor or orientation of the azimuthally sensitive sensors.

SENSOR FACEThe orientation of a sensor in the borehole when the drillpipe is not rotating (zero by conventionis defined as the gravitational top side of a borehole). See also MAGNETIC TOOLFACE andRELATIVE BEARING.

SHALE

A fine grained, thinly laminated sedimentary rock formed by the compaction and consolidation ofclay, silt and mud.

SHOCKSLarge and sudden, instantaneous forces applied to the BHA, and characterized by a relativelywide frequency band. Shocks are often associated with either resonant vibrations (accumulating

large amounts of energy) or chaotic motion of the BHA. Accelerometer sensors are often used tomonitor the severity and frequency of axial, lateral and tangential shock loading on an MWD toolin order to help the driller adjust surface drilling control parameters (e.g. rpm and hookload) toreduce the magnitude and frequency of destructive shocks. See also VIBRATION.

SIDETRACK

The drilling of a new and different hole from an existing wellbore.

SILT

A sedimentary particle with a diameter less than 1/128 mm, based upon the Wentworth scale ofmeasurement.

SINGLE SHOT SURVEY DEVICE

A survey device which utilizes either a magnetic compass on a gyroscope to measure theinclination and direction of the well bore. The device takes a photograph of the compass or gyroafter being positioned in the well bore. The photograph is developed once the tool is removed andthe survey is read

SLIDING

The process of drilling without rotating the drillstring.

SPECIFICATIONS

A set of values that characterize a measurement or define the design operating limits for a system.Typical measurement specifications are accuracy, precision, depth of investigation and resolution.Typical operating limits include flow rate, mud sand content, dogleg severity and temperature.

SPECTRAL GAMMA-RAY LOG

See NATURAL GAMMA-RAY SPECTROSCOPY.

STABILIZER

A bladed device that is used to eliminate vibration, centralize and prevent differential sticking ofthe bottom hole assembly, and to control the directional tendencies of the drilling process. Thediameter of some stabilizers can be controlled by adjusting surface drilling parameters.



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TRIPPING

The process of moving drillpipe down (or up) a previously drilled wellbore section withoutcirculating mud or rotating the drillpipe.

TRUE VERTICAL DEPTH (TVD)

The vertical, straight line, distance from a reference elevation to a subsurface point of interest.

TRUE VERTICAL DEPTH LOG

A well log from deviated borehole that has been rescaled from measured depth onto a vertical plane with true vertical depths.

TURBINE

An axial mud flow device which converts linear hydraulic mud flow to rotary mechanical power. This powers the transmitter and electronics in the MWD tool.

TURBO DRILL

Downhole mud motor based on the turbine principal .

TURN-AROUND TIMEThe time required to prepare an MWD system for lowering back into the borehole after tripping itto the surface. This will include such operations as dumping memory, replacing batteries and

performing diagnostic operational checks.

TWO-WAY COMMUNICATION

A system that allows a downhole tool to transmit and receive information from the operator toeither query the MWD tool or change some operating parameters such as data sampling times,transmitted data sequence and quality control checks.

UPHOLE MUD FILTER

The uphole mud filter is placed in the joint of drill pipe directly below the kelly and is designed tocapture any sizeable debris which could block or damage the downhole turbine or the poppet valveaperture.

UTM COORDINATE SYSTEM

The UTM (Universal Transverse Mercator) system is a convention for transforming a portion ofthe curved surface of the earth onto a flat plane surface of grid rectangular (x-y) coordinates. Thegrid system is designed for the identification of locations between the latitudes of 80 degreessouth and 84 degrees north.

VALIDATION

A procedure performed after the calibration of a sensor which confirms that the calibration

parameters truly produce measurements within a specified accuracy over a range of measurement.

VERIFICATION

A check performed at the rigsite that establishes whether a sensor electronics are operating withintheir design specification See also OPERATIONAL CHECK.

VERTICAL SECTIONHorizontal distance drilled towards the target, measured in the plane of the proposed direction.



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VIBRATION

Repeatable (quasi-harmonic) motion of the drillstring, MWD tool or other drillstring components,characterized by relatively narrow frequency bands. Vibration is often caused by resonant

phenomena or driven energy sources (e.g. mud motors). See also SHOCKS.

VISCOSITY

The property of a substance offering internal resistance to flow; a measure of the degree offluidity. Viscosity is defined as the ratio of the shear stress applied to a fluid divided by the shearrate resulting from the shear stress application. If the shear stress is expressed in dynes/cm 2 andthe shear rate is expressed in reciprocal seconds, the viscosity would be calculated in poise.

WALK

(1) Of the bit: The action of a drill bit that causes the direction of the wellbore to tend to driftaway from its projected path.

(2) Of the hole: The tendency of a wellbore to deviate in the horizontal plane; generally thoughtto be caused by the bit rotating preferentially into the side of the hole and/or the anisotropic natureof the formation.

WASHING

The process of moving drillpipe down (or up) a wellbore section that has been previously drilled,

while circulating mud, but without rotating the drillpipe pipe.

WATER SATURATION

The percentage of the rock pore volume that is filled with water.

WHIRL

An excentered rotation of the center axis of the drillstring in the borehole, induced most usually by either the compressive bending or the rotational mass imbalance of drill collars. Dependingupon the frictional forces acting at the borehole wall, and upon the severity of the bending forces,whirl may manifest itself in the same direction as (forward whirl), or in the opposite direction asthe rotation of the drillstring (backward whirl). Whirl can also be instable, transitioning betweenforward whirl and backward whirl states in a chaotic manner.

WIPER RUN The process of moving drillpipe down (or up) a wellbore section that has been previously drilled,while circulating mud and rotating the drillpipe pipe - also referred to as a wiper trip or short trip.

WIRELINE STEERING TOOL

Steering tools used close to the bit which measure and transmit survey data to the surface via awireline.

WHIPSTOCK

A wedge-shaped steel tool having a tapered concave groove down one side to guide the whipstock bitinto the wall of the hole.

YIELD POINT

An additional thixotropic measurement of the mud, which is the resistance to internal fluid flowmeasured as stress.

ZERO DEPTH REFERENCE

The elevation reference from which depths are measured. Frequently used reference points arederrick floor (DF) or kelly bushing (KB).



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Date post:	02-Jun-2018
Category:	Documents
Author:	nichole-johnson
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Mwd Glosario

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