Drilling and Completion

Objectives• Identify the major components of a drilling rig• Explain the purpose of the drilling mud system• Calculate the appropriate mud weight for

drilling a well• Identify common drilling bits and their uses • Identify the major components of a blow-out

prevention system• List six types of offshore drilling rigs and state

where each is used

Objectives• Describe common drilling problems• Describe common completion techniques• Describe common completion equipment • List three perforation methods and their

advantages and disadvantages• Describe two stimulation techniques and

their appropriate uses

Outline• Rotary drilling rig• The fluid circulation

system• The drillstring• Bits• Blow-out preventors

• People on the rig• Types of rigs• Drilling problems• Completions• Well stimulation

Components of the Drilling Rig

Main Drilling Rig Equipment Systems

Hoisting System

1

2

5

Crown Block

Deadline

Traveling Block

Drum

Deadline Anchor

Storage Reel

Fast Line

Drawworks

6

710

9

7

3

8

46

Wireline

Pipe elevators

9

11

Drum Brake

The Drill String

Drill Pipe

Drill Collars

Bit

SwivelKelly

Kelly BushingK.B. ElevationRotary Table

Top Drive System

Topdriv

e

Rig floor Drill pipe

‘A’ frame

Guiderails

CirculationSystem

Drill Collar

Mud House

BoreholeShaleslide

Mud pit

Shale shaker

Chemical tankMud return

line

Discharge

Mudpump

Swivel

Kelly

Drill pipe

Annulus

Reservepit Bit

Standpipe

Rotary hose

Drilling Fluids

• Control flow of gas and fluid from the formation (hydrostatic pressure)

Purposes of Drilling Mud

• Cool bit

• Lubricate drill string

• Clean drill cuttings from hole

Preparation of Drilling Mud

• Treated with other chemicals to prevent formation damage

• Water- or oil-based fluid

• Thickened with polymers to lift formation cuttings from well

• Weighted with clays and other materials to increase density for well control

Hydrostatic Pressure of Mud (Fluid) Column

• A force in the wellbore that controls formation pressure

hydrostatic pressure, psi= mud weight, ppgx depth, ft x 0.052

mud

Example 1Calculate the hydrostatic pressure exerted by a 10.3 ppg mud at 8,000 ft.

Hydrostatic Pressure= 10.3 ppg x 8,000 ft x 0.052

hydrostatic pressure, psi= mud weight, ppg x depth, ft x 0.052

= 4,285 psi

Overbalanced Drilling

• Prevents oil, gas and/or water from flowing into well

• Usually, 200 to 300 psi of excess pressure is desired

mudHydrostatic pressure exerted by column of fluid is greater than formation pressure

Drilling mud filtrate invasion can damage the formation !

Balanced Drilling

Increases risk of flow into wellbore (kick)

mudHydrostatic pressure exerted by column of fluid is approximately equal to formation pressure

• Reduces chances of drilling mud damage

Underbalanced DrillingHydrostatic pressure exerted by column of fluid is less than formation pressure

mud

• Formation flows oil, gas and/or water during drilling

Can be a safety hazard (controlled blowout) without proper control equipment

Formation Fracture PressurePressure at which a formation will crack or fracture mud

During drilling, the hydrostatic pressureshould be less than the fracture pressure, or significant mud loss can occur into the formation. The well could blow out.

Calculating Mud WeightReservoir pressure, depthFracture gradient

depthpressure formationThe fracture gradient is derived

from measurements,

Fracture pressure = depth x formation pressureFracture pressure

Needed hydrostatic pressureReservoir pressure < Hydrostatic pressure < Fracture pressure

depth 052.0pressure chydrostatiweight mud

×=

Example 2What mud weight (density) should be used to control a formation at 9000 ft?

Reservoir pressure = 5000 psiFracture gradient = 0.58 psi/ft

Fracture pressure

Fracture pressure = depth x fracture gradient= 9000 ft x 0.58 psi/ft = 5220 psi

Depthx0.052PressurecHydrostatiWeightMud =

Example 2 Solution

In this case, we allow 100 psi over reservoir pressure.

Hydrostatic pressureReservoir pressure

Fracture pressure

= 5000 psi

= 5220 psi

Mud weight

ppgx

9.109000052.01005000WeightMud =

+=

The Drill String and Bit

Basic Bottomhole Drilling Assembly

• Provides rotation to bit

• Provide weight on bit

• Grinds layers of rock to make hole

Common Types of Drill Bits

• Insert• Mill tooth

• Polycrystalline diamond compact (PDC)

Insert BitRadial seal

Roller bearing or bushingThrust face

Grease reservoirReservoir cap

Diaphragm

Carbide tooth

Bit leg

Shank

Bit information(size, type, serial number)

Cone

Shirttail

Grease reservoir cap

Jet nozzle

Milled-Tooth Bit

Polycrystalline Diamond Compact (PDC) Bit

Junk slot

PDC cutter

Breaker slot

Interchangeablenozzle

The Blow-Out Prevention System

Blow-Out PreventersBell nipple

Flow lineFill line

Annularpreventer

Pipe ramShear/blind ram

Kill line Choke

Pipe ram

Emergency kill line Emergency choke

BOP riser

Drilling spool

Casing head

People on the Rig

Drilling Personnel

Company Man

Service Company

Tool Pusher

Geologists Service Company

Geologists

Drilling Personnel

Service CompanyGeologists

Cementing Service Crews

Mud Engineer

Casing Crews

Mud Loggers

Drilling Personnel

Company Man

Service Company

Tool Pusher

Geologists Tool Pusher

Drilling Personnel

Tool Pusher

Rig Mechanic

MotormanCrane Operator

Rig Electrician

Driller

RoustaboutsRotary Helpers(Roughnecks)

Derrickman

Types of Drilling Rigs

Offshore Rig Types

Swampbarge

Jacketwith

tender Jack-upSemi-sub

FixedPlatform Drillship

SemisubmersiblesLake/Swamp BargesLand Rigs

Drill ShipJack Ups Monohull

Tenders

Drilling Rigs

Land Rig

Sedco 702 in TAD-mode offshore New Zealand

Semisubmersible

Semisubmersible

Types of Wells

Perforations

Casing

Tubing

To production equipmentWellhead

Vertical Well

HydrocarbonsPacker

S-shape Tangent

Horizontal

Deviated Well Projectories

Downhole Assembly for Building Hole

Angle

String stabilizer

Kickoff sub

Bent sub

Low-speed,high-torque motor

Upper bearinghousing with stabilizer Bit

Hole Orientation Surveys• Single shot (basic)

– Run every 400 - 500 ft and at bit trips to record hole angle

• Magnetic multi-shot– Tool run before bit trip– Records hole angle while pulling out

of hole• Gyroscope

– Electronic survey of hole angle and direction

Horizontal Well Completions

20-40 ft radius1.5°-3°/ft

125-700 ft radius 8°-20°/100 ft

Short radius

Medium radius

1000-3000 ft radius2°-6°/100 ft

2000-5000 ft

Long radius1500-3000 ft

300-750 ft

Slimhole Drilling• Advantages

– Less site preparation– Easier equipment mobilization– Reduction in the amount of consumables (drill

bits, cement, muds, fuel)– Less cuttings disposal– Smaller, lighter equipment

• Disadvantages– Plugs and packers required– More crowded annular space – Tubular corrosion and loss of mechanical

integrity

Multilateral Well Completions

Stacked Lateral,Multiple Layers

Planar Lateral,Single Layer

Planar Opposed Lateral,Single Layer

Choosing Well ProjectoriesVertical wells

Thick, permeable formations

Horizontal wells

Thick, low-permeabilty

formations

Hydraulic fracture

Thin, permeable formations

Thin zones overlain by gas or underlain by water

Naturally fractured reservoirs

Multilaterals

Drilling Problems• Stuck pipe

• Fishing

• Lost circulation

Causes of Stuck Pipe

Drillpipe

Pressure differential between borehole and formationPbh > Pf

Borehole

PbhPf

Causes of Stuck Pipe

Drillpipe

Borehole

Clays absorb water, swell, reduce size of borehole

Causes of Stuck Pipe

Drillpipe

ProposedBorehole

Unstable formations, badly worn bits result in undergauged hole

Causes of Stuck Pipe

Drillpipe

ProposedBorehole

Tectonic stresses cause borehole to collapse

Causes of Stuck Pipe

Drillpipe

ProposedBorehole

Dogleg in trajectory snags pipe

Reasons for Fishing

Stuck Drillpipe(twisted off, backed off, cemented)

Dropped Items(floor tools, drill string parts)

Logging tools

Lost Circulation

BoreholeFissures information

Add plugging materials such as cellulose chips to circulating mud

Completion Methods

Well Completion Techniques

• Cased hole

• Liner (cemented, slotted or perforated)

• Openhole

• Tubingless or slimhole

• Gravel pack (special case required for control of formation sand)

Surface

Conductor/stovepipe

Surfacecasing

Immediatecasing

Productioncasing

Productionliner

Casing Scheme

Cementing

gas zone

oil zone

Hole

Casing

Cement

l Provides zonal isolation.

l Supports axial load of casing.

l Protects casing against corrosion and erosion

l Provides support to borehole in plastic or unconsolidated formations

Casing/Cementing Procedure

Drill bit

Mud

Mudcirculating

Casing

Float shoe

Top plug

Cement

Bottom plug

Cement

Displacement

Bottom plug

Top plugDrill pipe

New hole

Set Cement

Continue Drilling

Cementing Problems

• Contamination of cement by mud

• Reduction in cement bonding to formation caused by mud cake, solids

• Channeling caused by laminar flow in annulus

• Lost circulation caused by additional hydrostatic head of high-density cement

Casing Shoe

CasingCement

Openhole Completion

OilSand

Casing

Cement

Casing Shoe

Hanger(usually with a packer)

Slotted Liner

Liner ShoeOilSand

Slotted Liner Completion

Casing Shoe

Casing

Cement

Hanger(usually with a packer)

Cemented Liner

Liner ShoeOilSand

Cemented Liner Completion

Gravel Pack

GP PackerCrossover

Gravel (sand)

Fracture created,sometimes propped

Washpipe

Screens

Blank Pipe

Sump Packer

Completion Type Advantages DisadvantagesCased Hole - Pressure control

- Isolation of zones- Control of stimulation- Wellbore Stability

- More expensive- Limited communication

to reservoir- Possible cement damage

Liner - Less expensive thancasing entire hole

- Pressure andstimulation control(when cemented)

- Wellbore stability

- Cementing more difficult- No control of flow if not

cemented- Slots plugged w/formation- Limited control of

stimulationOpen Hole - Maximum flow area

- Minimize damage- No control of flow- Limited or no control of

stimulation- Hole collapse in weak

formationsSlimhole - Lower Cost - Limited workover

capability due to smallhole

- Limited stimulation rate- No zone isolation

Comparison of Completions

Perforating

• Establishes communication with the reservoir by “shooting” holes through the casing

Perforated Casing

Wellbore Conditions While Perforating

• Overbalanced

• Underbalanced

Overbalanced Perforating

Completion fluidin wellbore

Oil or gasreservoir

Casing

Cement

Pres< phyd > pres

Perforating gun

Perforations can be plugged with debris in wellbore

Pressure controls well during completion

Underbalanced Perforating

Completion fluidin wellbore

Oil or gasreservoir

Casing

Cement

Pres> phyd < pres

Perforating gun

Perforations will be clean from surge in wellbore

Well will be ‘live’ and need

control after perforating

Completion Equipment• Wellhead

• Tubing

• Packers

• Bridge plugs

• Seating nipples

Perforations

Packer Casing

Casing headTubing headCasing valveMaster valveTee

Pressure gaugeWing valve

Choke

Components of a Typical Well

To productionequipment

Tubing

WellheadWing valve

Chokeassembly

Dualmastervalves

Casinghead

Bradenhead

Casingstrings Tubing

Tubing hanger

Tubinghead

Perforations

Packers Casing

Tubing

Well Components

‘Christmas tree’

‘Angel’Wellhead monitors and controls well pressures

Casing head

Tubing head

Wellhead

Suspend casing and tubing in well

Master valve

Wellhead

Stops fluid flow, shutting in well

Casing valve

Wing valveControls production line

To productionequipment

Pressure gauges

Choke

Wellhead

Tee

To productionequipment

Tubing

Producingperforations

Tubing

Fluids flow into tubing

• Type and size depend on well conditions

• Diameter must be designed for expected flow rate

Casing

Pressure drop in tubing can restrict flow/injection rate.

Packers

Producingperforations

Packers

Fluids flow into tubing

• Protect annulus from fluid flow

• Provide seal in well to isolate formation for production or stimulation

• May be permanent or retrievable

Packers

Producingperforations

Isolatedperforations

Packers

Fluids flow into tubing

Straddle Packers

• Used in gas zones, cases of excess water production

• Prevent fluid from entering tubing

Single Packer

Sealing or packing element

Slips

Hold downbuttons

Frictionblocks

0

• Most common retrievable packer in use

• Commonly made of elastomers

prevent movement of the packer

expands against the casing either hydraulically or mechanically

Dual Packer

Unidirectional slips

Sealing or packing element

Dual tubing strings• Prevents commingling

of produced fluids

Bridge Plug• Isolates intervals above and

below or plugs off formation

• Retrievable plugs– safety valves to plug well

during repairs or abandonment

– can be repeatedly set and released without coming out of hole

• Permanent plugs– commonly used for zone

abandonment – must be drilled out of hole

Standard Seating Nipple• Provides a place to ‘set’ tools or

equipment in well – Temporary plugs, downhole pumps,

pressure gauges, etc.• Prevents unwanted passage of

certain diameter tools • Isolates zone to control pressure• Serves as a safety device for

logging tools not to exit the end of tubing– Equipment normally run on slick line

(small, non-electric wireline)

Well Stimulation

Reasons to Stimulate• Increase production efficiency or flow

capacity – Overcome formation damage– Enhance production from

low­permeability wells• Connect with natural fracture system• Increase effective drainage area• Produce complex reservoirs (e.g.,

discontinuous sand bars)• Increase wellbore stability (minimize

drawdown)

Stimulation Treatments• Matrix treatments

– Near-wellbore region

– Chemicals such as acids, surfactants and inhibitors

• Hydraulic fracturing

– Acid fracturing

– Proppant fracturing

Matrix Treatments• Acids remove damage

Reservoir

Wellbore

Damagedregion

rd

Sandstone, ±1 ft

• Other chemicals plug excess water or gas production

Carbonates, a few feet

Distance from wellbore

Pressure

Matrix Acidizing

Wellbore

After stimulationBefore stimulation

Pressure distribution forsame production rate Matrix stimulation

results inradial flow

Stimulated zone

CoiledTubing

Pump

ProductionTubing

Casing

Perforations

Circulatingacid down

Squeezingacid away

(a)(b)

Acid

Acid Fracturing

• No proppant

• Acid injection above the formation parting pressure

Shale

Water

Shale

Hydraulic FracturingHigh­conductivity pathway for reservoir fluids

(low-permeability formation)Pack with sand or other proppants

Fractured zone between rock barriers

Fracture Zone

Lf(May be several feet)

Width may be mm’s

Flow Patterns

Lf

rw

Fracture

Shale

Water

Shale

Good Stimulation CandidatesDamaged wells

Tight reservoirs with economic potential

Naturally fractured

reservoirs(sometimes)

Unconsolidated, high­permeability

reservoirs (sometimes)

Shale

Water

Shale

Poor Stimulation Candidates

Reservoirs with limited reserves

Low-pressure reservoirs where cleanup of

hydraulic fracture fluid is difficult

Reservoirs where stimulation fluid reaction with reservoir

fluid leads to severe damage

Reservoirs where stimulation can penetrate water zones and cause excess water production

Effect of Reservoir Permeability on Overall Pressure Drop

Flow Rate Fixed

Distance From Well

Pressure

rw re

pe

Low Permeabilitypwf

High Permeability

Effect of Skin Factor on Pressure

pwf(Skin = 0)

pwf(Positive

Skin)

Flow Rate Fixed

pe

Damage Zone

∆Pskin

rw rd re r

Pressure

Distance From Well

Reading AssignmentDrilling and Completion

• SPE/IADC 37613, “The Evolution of Profitable Drilling in Prudhoe Bay: A Case of Adapting to Survive”

• SPE 26596, “An Evaluation of Prudhoe Bay Horizontal and High-Angle Wells After 5 Years of Production”

SummaryWell Stimulation

• Reasons to stimulate

• Stimulation treatments

– Matrix acidizing

– Hydraulic fracturing

• Stimulation candidates

• Effects of skin factor on pressure

SummaryDrilling and Completion

• Rotary drilling rig• Drilling fluids• Types of drilling rigs• Deviated wells• Drilling problems• Completion methods• Well stimulation

ExercisesDrilling and Completion

10

97

1

2

3

8

54

11

6

• Identify the major components of the hoisting system

Exercise 1

Exercise 2a

• Identify the parts of the circulation system

Circulation System

Mud House

5

6

7

Shaleslide

Mud pit

8

9

10

Discharge11

12

13

1

2

3

4

Reservepit

Exercise 2b

• Assuming a pressure gradient of 0.465 psi/ft to a depth of 5000 ft, and a pressure gradient of 0.5 psi/ft from 5000 ft to 10,000 ft, how deep can one drill with a mud weighing 9.0 ppg, without allowing formation fluids to enter the wellbore?

Exercise 3

• Name and describe the three common bits used in rotary drilling

• What are they used for?

Exercise 4

• Identify six types of offshore drilling rigs and what they are used for.

• List different well types and their uses.

Exercise 4Identify Offshore Rig Types

(Cont’d)

Exercise 5

• Describe common drilling problems and the conditions that cause them.

Exercise 6

• What are some of the functions of casing?

• Give four reasons why casing is cemented into the well.

• Describe gravel packing.

Exercise 7

• Describe possible wellbore and formation pressure while perforating, and explain the advantages and disadvantages of each.

• List and describe the equipment commonly used in completing a well.

Exercise 8• Choose the word(s) that complete the

following sentences correctly:

– (Matrix acidizing/acid fracturing) is a near-wellbore treatment

– In acid fracturing, the injection pressure is (below/above) the formation parting pressure

– We (use/don’t use) proppant in acid fracturing.

Exercise 9

• Describe two stimulation techniques.

• What kinds of wells are good candidates for stimulation?

• What kinds of wells are poor candidates?

Exercise 1Solution

• Identify the major components of the hoisting system

Drum Brake

Draw -Works Storage

Reel

CrownBlock

DeadLine

Wire Line(8 Lines are Strung)

Drum

Dead LineAnchor

Traveling Block

FastLine

Pipe Elevators

Hoisting System

Exercise 2a Solution

Mud House

5

6

7

Shaleslide

Mud pit

8

9

10

Discharge11

12

13

1

2

3

4

Reservepit

Exercise 2bSolution

• Assuming a pressure gradient of 0.465 psi/ft to a depth of 5000 ft, and a pressure gradient of 0.5 psi/ft from 5000 ft to 10,000 ft, how deep can one drill with a mud weighing 9.0 ppg, without allowing formation fluids to enter the wellbore?

Exercise 3Solution

• Name and describe the three common bits used in rotary drilling

• What are they used for?

Exercise 4Solution

• Identify six types of offshore drilling rigs and what they are used for.

• List different well types and their uses.

Exercise 5Solution

• Describe common drilling problems and the conditions that cause them.

Exercise 6Solution

• What are some of the functions of casing?

• Give four reasons why casing is cemented into the well.

• Describe gravel packing.

Exercise 7Solution

• Describe possible wellbore and formation pressure while perforating, and explain the advantages and disadvantages of each.

• List and describe the equipment commonly used in completing a well.

Exercise 8Solution

• Choose the word(s) that complete the following sentences correctly:

– (Matrix acidizing/acid fracturing) is a near-wellbore treatment

– In acid fracturing, the injection pressure is (below/above) the formation parting pressure

– We (use/don’t use) proppant in acid fracturing.

Exercise 9Solution

• Describe two stimulation techniques.

• What kinds of wells are good candidatesfor stimulation?

• What kinds of wells are poor candidates?