04 directional

1

1

Trajectory Designand

Directional Drilling

2

Directional Drilling

• What is Directional Drilling?

“Intentional, controlled deflection of a wellbore to intersect pre-determined targets.”

• Topics:– Terminology– Drivers for directional drilling– Directional tools and techniques– Measuring trajectories – Calculations– Potential problems

2

3

Trajectory Components

True

Ver

tical

Dep

th

Horizontal Departure

Kickoff Point (KOP)

Tangent

Lateral

2nd Kick

off Point

Build Section

2nd Build Section

Measured Depth

4

Trajectory Measurements

Inclination: the measure in degrees of the angle of the wellbore from vertical

Azimuth: the measure of the direction of the wellbore in:

45°

0° / 360°

90°

180°

270°

45° = N 45°E

200° = S20°W155° = S25°E

295° = N65°W

(1) degrees from North between 0° and 360°, or

(2) degrees from North or South to the East or West

3

5

6

Drivers for Directional Drilling• Access to remote reservoirs from a central

platform, template, or pad.– Avoid or defer capital expenditures – fewer

platforms, fewer subsea installations– Monetize otherwise uneconomic reserves –

offshore reserves from onshore facilities• Access to otherwise inaccessible reserves.

– Environmental restrictions– Other exclusions, e.g. lakes, cities, shipping lanes

4

7

Directional Drilling Applications

8

Industry Directional Capabilities

5

9

Potentially high contact force in build (torque, casing wear)

Simple; Long reaches achievable Low tangent angle

Build and hold: Constant BR to tangent angle, hold constant tangent angle

Limited intervention and stimulation scenarios

Increased exposure to reservoir, reduced drawdown, fewer surface facilities

Multi-Lateral: branched well bores from mother bore through various junction styles

More curvature means more torque and drag, limited reach

Flexibility to handle anti-collision and multiple target requirements

3-D: Any of the above with significant azimuth changes

Theoretical benefits not cost-effective in implementation; Limited reach

Lowest contact force (torque, casing wear) of any trajectory

Catenary: Continuously increasing build rate (BR) with depth, no tangent

High tangent angleMuch longer reach than catenary; Lower torque/drag

Multiple build: BR increases with depth in several discrete steps to tangent angle, hold constant tangent angle

Higher tangent angle for given reach; Potentially high contact force in build (torque, casing wear)

Allows lower angle reservoir entry, possibly easier intervention

S-shaped: Includes angle drop section

Requires deep steering; High angle in second tangent

Very long reaches possible with lower contact forces in upper build

Double build: Build-hold-build-hold trajectory, can use two different BRs in curves.

High tangent angle; Reduced reach

Lower contact force in build sectionUndersection: Build and hold with deep KOP

DisadvantagesAdvantagesOption

Trajectory Options

10

Trajectory Options

6

11

Trajectory Design Criteria

• Targets

• Drillability

• Cost

• Intervention

12

Trajectory Design Criteria• Targets

– Specifications• Horizontal departure• Size• Shape• Orientation

– Stacked targets– Natural Drift Predictability

7

13

Horizontal Departure

14

Stacked Targets

Final tangent angle may vary widely depending upon Horizontal Departure required to reach targets.

8

15

Walk Tendencies

Angle Building• Normal Force into the high

side of the hole = ↑ Inclination• With RH rotation of bit, walk

tendency is to the left.

Angle Dropping• Normal Force into the low

side of the hole = ↓ Inclination• With RH rotation of bit, walk

tendency is to the right.

16

Natural Drift

• As directional tendencies become known for local combinations of:

FormationsBitsBHAs

• Rig locations can be optimized to minimize expensive directional control techniques in favor of natural drift.

9

17

Trajectory Design Criteria• Drillability

– Normal force • Curvature + Tension = Normal Force• Torque / drag: ↑ normal force = ↑ torque / drag• Casing / drill string wear: ↑ normal force = ↑ wear rates

– Wellbore stability• Orientation of wellbore in the in-situ tectonic stress field will

effect stresses, and therefore, stability of wellbore wall.– Hole Cleaning

• Cuttings transport efficiency affected by hole inclination– Anti-collision

• Constraints imposed by nearby wellbores

18

Trajectory Design Criteria• Cost

– Tool selection• Availability• Familiarity / Support• Track record• Logistics

– Cost-effectiveness• Cost (including Lost in Hole charges)• Time• Efficiency• Impact on other drilling systems

– Failure likelihood• Failure modes – trip or fish• Recovery plans – back up plan

10

19

Trajectory Design Criteria• Intervention

– Wireline– Coiled Tubing

• Critical Angle (α)– Ability of tools to slide under their own

weight without being pushed from above– α = Tan-1(1/µ)– Function of Coefficient of Friction (µ)– Ex. Where µ=0.2, α= 78.7°

20

Achieving Directional Control• Two Primary Approaches:

– Push the bit: side force > side cutting– Point the bit: bit tilt

• Push the bit– Traditional rotary BHAs– Bent sub motor assemblies– Rotary steerable – BHI Autotrak /

Schlumberger Powerdrive• Point the Bit

– Bent housing motor BHAs– Rotary steerable – Halliburton GeoPilot

11

21

Bit Side Force• All BHAs cause a side force at the bit • This side force may make the bit

– build angle– hold angle– drop angle– turn right– turn left

• The key is to control the direction and magnitude of the force.

22

Rotary BHA Configurations90 ft 30 ft

60 ft 30 ft

45 ft 30 ft

10-20 ft30 ft 30 ft

30 ft 30 ft

UG

10-20 ft

30 ft 30 ft30 ft

45 ft 30 ft

90 ft 30 ft

60 ft 30 ft

60-90 ft 30 ft

UG

UG - UndergaugeStabilizer Optional Stabilizer

Strong angle building tendency

Moderate angle building tendency

Slight angle building tendency

Strong holding tendency (little incl. and azim. change)shorter stab. spacing gives better holding capability

Moderate holding tendency - highly UG 2nd stab. may provide some building tendency

Slight holding tendency - formation tendencies to build or drop angle often overpower this assembly

Strongest angle dropping tendency

Weakest angle dropping tendency

(Optional stabs. make behavior more predictableand increase dropping tendencies)

UG near-bit stab. may moderate dropping tendency

12

23

Directional Motor BHA Configurations

ADJ - AdjustableStabilizer Optional Stabilizer

Simple motor with bent sub - prior to 1980higher side load and less bit tilt - sliding mode only

Bent housing motor - early ‘80’s higher bit tilt and less side load - sliding mode only

Bent housing motor with bent sub above - lower deflections allowed string rotation and “steerability”

Adjustable bent housing deflection angle (some downhole adjustable)

Downhole adjustable stabilizer allows 2-D steerability (inclination only) in rotary mode (e.g. TRACS)

Rotary steerable tools allow downhole 3-D (inclination and azimuth) steerability in rotary mode (e.g. Autotrack)

BSmotor

DTU motor

BH motor

AKO motor

BH motorBS

RST

Double tilted u-joint motor - mid ‘80’s very high bit tilt - limited string rotation

ADJ

24

Rotary Steerable Systems

• Push-the-bit– BakerHughes INTEQ Autotrak– Schlumberger Powerdrive

• Oversize hole can reduce build rate

High Side

Orientation

MagnitudeBit Side Force

13

25

Rotary Steerable Systems

• Point-the-bit– Halliburton SperrySun Geopilot

• Pair of eccentric rings • Controls orientation and magnitude of deflection

Zero deflection

Maximum deflection

Intermediatedeflection

26

• Measurement Types:• Inclination Only• Inclination and Azimuth• Single Shot• Multi-Shot

• Tool Types:• Gravity• Magnetic• Gyroscopic

• Deployment Mechanisms:• Wireline• MWD – telemetry or memory• Pipe - conveyed• Dropped

• Measurement Errors• Position Uncertainty

• Collision Avoidance

Trajectory Measurement - Surveying

14

27

Magnetic Instrument

1. Pendulum2. Circular Glass3. Compass4. Pressure equalization5. Cover glass

Inclination = 5°Direction = N 45°E or Azimuth = 45°

28

Raw Reading:Inclin. = 5.5°

Dir. = N35°W

Must be corrected for Declination

Magnetic Instrument Film

15

29

• Inertial effects keep it pointing in the same direction.• Not affected by the earth’s magnetic field, or by steel in the wellbore• Single shot or multi-shot tools available

Typical Gyroscope

Outer Gimbal

Inner Gimbal(Spin Motor)

Spin Axis

Inner Gimbal Axis

Outer Gimbal Axis

30

Sources of Survey Errors

• Instrument measurement limitations• Depth Error• North Reference Error • Magnetic Interference • Gyro Drift Errors• Instrument Alignment Errors

16

31

Magnetic Declination• Declination is the angle a freely turning magnetic

needle makes with the imaginary line pointing to True North.

True North

MagneticNorth

Declination Angle

32

Magnetic Declination Correction

+

-+

-+

- +

-

West Declination(Subtract from Azimuth)

East Declination(Add to Azimuth)

BUT, when using oilfield direction nomenclature, declination must be added or subtracted from the magnetic compass reading, depending upon whether

it is East or West declination and in what quadrant the raw heading lies.

17

33


ExampleDeclination = 5o WestMAGNETIC READING= S65oE = 115o Magnetic

Corrected Azimuth = 115o - 5o = 110o True

True North

MagneticNorth

115o

65o

110o

5o

34


203°200°S23°WS20°W168°165°S12°ES15°E293°290°N67°WN70°W38°35°N 38°EN 35°E

CorrectedAzimuthCorrectedDirection

+

-+

-

West Declination(Subtract from Azimuth)

East Declination(Add to Azimuth)

35° = N 35°E

3° East Declination Corrects CW:

290° = N70°W

165° = S15°E200° = S20°W

+

- +

-35° = N 35°E

290° = N70°W

165° = S15°E200° = S20°W

3° West Declination Corrects CCW:

197°200°S17°WS20°W162°165°S18°ES15°E287°290°N73°WN70°W32°35°N 32°EN 35°E

CorrectedAzimuthCorrectedDirection

18

35

Isogonic chart for the U.S.

I

Isogonic: lines of equal magnetic declination

36

Isogonic Chart for the World (2000)

I

Measures may change a few minutes per year.

19

37

Earth’s

Magneti

c

Field Lines

Steel Colla

r

Bit Sub

Compass Interference Field Lines

Magnetic Interference.

Non-magnetic Collar

38

• Field intensity varies geographically. • Length of the nonmagnetic drill collars required in a BHA will vary

(1) from area to area and (2) as wellbore inclination & azimuth vary.

Earth’s Magnetic Field Intensity

20

39

Direction Angle from magnetic N or S

Incl

inat

i on

Thailand is inZone I

Directional Plan:Azim: N40°WIncl: 55°

Required Length of Non-Mag DC:43 ft

40


Incl

inat

i on

UK is in Zone II



21

41

Incl

inat

i on


North Slope is inZone III



42

Wellbore Position Uncertainty

• Uncertainty in surveys results in uncertainty in wellbore position.

• Common to have higher magnitude of uncertainty in azimuth orientation (L-R) than inclination orientation.

• Calculated uncertainty shows boundaries of EoUs.

• EoU Separation guidelines should be agreed beforehand

22

43

Ellipse of Uncertainty Separation

• EoU’s should never overlap• EoU Separation guidelines

should be agreed beforehand

44

“Christmas Tree”of Survey Errors

• Magnetic surveys like EMS and MWD typically have larger errors, and therefore larger EoUs.

• Gyro surveys at casing points reduce the errors and provide smaller EoUs.

23

45

Position Errors by Survey Tool Type

After SPE 56702 / 67616 - 1999

46

Calculate position of the wellbore based upon survey dataPosition: TVD

N-S / E-W departure (Rectangular Coordinates)Closure: Drift (HD) and Direction (Azimuth) (Polar Coordinates)

Survey Data at each survey station:Measured Depth (MD)InclinationAzimuth

Calculation Methods:Minimum Curvature Radius of CurvatureMany others…

Dogleg Severity (DLS) – Total rate of curvature (°/100 ft or °/30m)

Survey Calculations

24

47

Arc Length to Angle Change Relationship

Length of arc of circle (S)Radius of Curvature (R)Angle Change (α)

∆S = R∆α

Smaller Radius

Larger Radius

r

r

R

R

α1

α2

S1

S2

NOTE: All angles in radians

48

Survey Calculation Methods

• Minimum Curvature• Radius of Curvature• Tangential• Balanced Tangential (Acceleration Method)• Trapezoidal (Vector Averaging)• Average Angle• Mercury (Combined Method)• Simpson’s Rule Method

25

49

Minimum Curvature Method

• This method assumes that the wellbore follows the smoothest possible circular arc from one survey station to the next.

• Knowns: Location of first survey point, ∆MD between surveys, and inclination and azimuth at both survey points.

Ref: API Bulletin D20 (1985)

50

Minimum Curvature Method

P

r

O

r

RDL

Q

DL2

S

PQR ArcSRPSRF +

=

( )DLr2

DLtanr2

DLtanr

+

=

2DLtan

DL2RF =

))A-(Acos1(IsinIsin)I(Icos(DL) cos 122112 −−−=


RF = Ratio FactorDL = Dogleg Angle

26

51

[ ]

[ ]

[ ] RF)cos(I)cos(I2

∆MD∆Vert

RF)sin(A)sin(I)sin(A)sin(I2

∆MD∆East

RF)cos(A)sin(I)cos(A)sin(I2

∆MD∆North

21

2211

2211

•+=

••+•=

••+•=

Minimum Curvature Method - Equations

2DLtan

DL2RF =

))A-(Acos1(IsinIsin)I(Icos(DL) cos 122112 −−−=

Ref: API Bulletin D20 (1985)

Where:


52

Radius of Curvature Method

• This method assumes the wellbore follows a smooth, spherical arc between survey points and passes through the measured angles at both ends. (tangent to inclination and azimuth at both survey points).

• Knowns: Location of first survey point, ∆MD between surveys, and inclination and azimuth at both survey points.

27

53

Radius of Curvature Method - Equations

[ ] [ ]

[ ] [ ]

[ ])I(I

)sin(I)sin(I∆MD∆Vert

)A(A)I(I)cos(A)cos(A)cos(I)cos(I∆MD∆East

)A(A)I(I)sin(A)sin(A)cos(I)cos(I∆MD∆North

12

12

1212

2121

1212

1221

−−•

=

−•−−•−•

=

−•−−•−•

=

Ref: API Bulletin D20 (1985) NOTE: All angles in radians

54

• Poor response of directional tools• Industry going for more “science” and less “art”• Directional driller dependent on computer control

• Tool failure / system failure• MTBF of rotary steerables and other tools• Unable to steer in sliding mode

• Tortuosity• Unplanned curvature in wellbore• Increased torque, drag, casing wear

Directional Problems

28

55

Sliding with Bent Housing PDMs

Drag force reduced once pipe moves

Dra

g Fo

rce

Time

Dynamic Friction

Static Friction

25%

Pipe movement

Dyn Drag = 50,000 lbs

Static = 67,000 lbs

WOB = 10,000 lbs

Total = 77,000 lbs

Pipe moves ===>WOB = 27,000 lbs,not…...10,000 lbs.

56

Sliding with Bent Housing PDMs

0

1000

2000

3000

4000

5000

0 10 20 30 40 50

Weight-on-Bit, 1000 lb

Torq

ue, f

t-lb

Typical max torque for6-1/2” slow-speed motor

Series M121PDC bit

Series M332

Series 517Rollercone

29

57

Tortuosity – Unsurveyed Curvature

Apparent Dogleg

Actual Dogleg

Survey Station (n)

Survey Station (n+1)

• Survey intervals may not allow correct representation of curvature.

• Calculation method assumes smoother curve than actually exists locally.

• Result is higher normal force, higher torque / drag, higher casing wear.

• Lower drillability, higher cost

Notes: __________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

04 directional

Documents

higher tangent angle

catenary high tangent

targets final tangent

normal force torque

high normal force

trajectory measurements

trajectory effective

tendencies angle buildingangle