Deviation Control

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PETR 5315 – Lecture 9

Deviation Control

S. H. Emadi, Ph.D.

PETR 5315 - S. H. Emadi, Ph.D. - Spring 2016 1

Deviation Control

• Whipstocks• Retrievable• Fixed

• Hydraulic Jetting• BHA Configurations• Downhole Motor• Rotary Steerable System (RSS)


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Whipstocks


Whipstocks


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Mills


Starting Mill Window Mill

Watermelon Mill Tapered Mill

Hydraulic Jetting


• Fast & Economical• Soft Formation• One Large & Two Small Nozzles• Orient Large Nozzle• No Rotation at First (3 – 6 ft)• Conventional Drilling for 20 – 25 ft

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Bottom Hole Assembly (BHA)

• Drill Collar (DC)• Stabilizer• MWD• LWD• Drilling Jars• Mud Motor• Heavy Weight Drill Pipe (HWDP)


Mechanics of BHAs• Slick Assembly in an Inclined Hole

• Assumptions: • 2D Wellbore• Drill Bit Rotation• Inertia• Drilling-Fluid Flow Effects• Drilling String Lies Down on the Low Side

• Drop (Pendulum Effect)

• Hold

• Build (Fulcrum Effect)


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Mechanics of BHAs


Fundamental of Drilling Engineering, R. F. Mitchel

Mechanics of BHAs• Drilling Anisotropy Index (h): the relative difference of drillabilities

parallel and perpendicular to bedding planes.

1

and

tan Φ

Where

: Equilibrium hole inclination angle

: Formation dip angle

Φ: Resultant force angle

: Bit-Displacement DirectionPETR 5315 - S. H. Emadi, Ph.D. - Spring 2016 10

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Mechanics of BHAs



Mechanics of BHAs

If ≫


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Mechanics of BHAs

X

,

, 0.5 ,

64

,


Mechanics of BHAs

1 cos1 cossin

sin 0.5

tan tan


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Mechanics of BHAs

• Example: Inc. 25deg, 8.5 , : 6.25 ,2.25 , 91 /

10 , 30,000 ,

a. 0, 0b. 0.1, 40


Mechanics of BHAs

•Slick Assembly in a Curved Hole•Assumptions:• DC lies down on the low side of the borehole for some

finite length just above the Tangency Point (TP).• DC’s are under constant compression between bit and TP. • Borehole has a constant curvature (R: Constant).

• is small compared with the WOB.

• Bit is at the center of wellbore.• No bending moment at the bit.


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Mechanics of BHAs



Mechanics of BHAs

• sin ))S

• Boundary Conditions (BC):• @ Bit

• S=0, U=0• @ TP

• S=L, U(L)= , 0, and " 0

• EI

• No bending moment @ bit, so

• , S s, , ,


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Mechanics of BHAs

,

, , tan

12 sin

tan2

WhereR: Wellbore Radius of Curvature


Mechanics of BHAs

1

11

sin


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Mechanics of BHAs


Types of stabilizers: (a) Welded-blade; (b) Integral-blade; (c) Sleeve; (d) nonrotating sleeve (Inglis 1987)

Mechanics of BHAs


Adjustable-diameter stabilizer (AGS Tool 2010)

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Mechanics of BHAs

• Stabilizers• Effective use of stabilizer begun in 1953• Effects of position and size of DC’s• Pendulum Effect• Fulcrum Effect



Mechanics of BHAs



• BHA with One Stabilizer in an Inclined Hole

• Length of Stabilizer is not considered• DC’s do not contact the wall of the

hole between the bit and the stabilizer.

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Mechanics of BHAs

• wsinφ

Which is valid for 0

• wsinφ

Which is valid for


Mechanics of BHAs

sin cos cot 1 cos0.5 0

Where

1 0.5 cos sin

cos sin 0.5 1sin


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Mechanics of BHAs

•Where

0.5 /

l /


Mechanics of BHAs



• BHA with One Stabilizer in a Curved Hole

• Length of Stabilizer is not considered• DC’s do not contact the wall of the

hole between the bit and the stabilizer.

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Mechanics of BHAs

sin cos 0

Where

1 ∓ 0.5 cos sinsin

11∓ 0.5 cos sin


Mechanics of BHAs

• Where

1 1/ cos sin

sin l∓ .


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Mechanics of BHAs

• Complex BHA’s• Two or three stabilizers


Typical build, hold, and drop BHA’s (Fundamental of Drilling Engineering, R. F. Mitchel

Downhole Drilling Motors


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• Turbine type (turbodrill or dynamic motors)

• Positive-Displacement Motor (PDM)


Turbodrill with bent housing (Beaton et al. 2004)

Bent Sub & Bent Housing


Turbodrill with bent housing (Beaton et al. 2004)Mud Motor with bent sub (Bourgoyne et al. 1986)

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Schematic of drilling fluid flow through a turbine (Beaton et al. 2004)Bent Housing



Typical torque and HP curves at 500 gpm and MW=10 ppg(Beaton et al. 2004)

1

260

301

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Components of PDM with adjustable bent housing (Underwood and Payne 1997)

• Dump Valve• Power Assembly• Connecting Rod• Bearing and Drive

Shaft• Bit Sub


•∆

•


WhereA: Cross-Sectional Area of Flow Path

: Rotor Pitch: No. of lubes in the rotor

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Typical PDM Performance Characteristic Curves (Underwood and Payne 1997)

Steerable Motors


Bent sub above the motor (Bourgoyne et al. 1986)

• Position of bent sub• Vertical wellbore• Kickoff Assembly• No more than 20

degrees

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Steerable Motors


Schematic of bent-housing motor with stabilizers (Stefan Miska, 2011 )

• Bend angle 0 to 3 degrees• Usually run with MWD• Tool-face angle• Rotating or Sliding Mode• Type of formation• Field experience• Inexpensive• Disadvantages

Steerable Motors


• Disadvantages• Poor Control on Directional Drilling• Drilling Overgauge hole• Poor Well Trajectory (Not very Smooth Well Path)• Poor Axial Force Transfer to the Drill Bit• Poor Hole Cleaning• Wellbore Stability Problem (e.g. Differential Sticking)• Long Tool-Face Adjustment Time

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Steerable Motors


A series of slide-rotate sequences for a 500 –ft wellbore section (Lesso et al. 2001)

Rotary Steerable System (RSS)


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•First Commercially Available in 1995•No Sliding•Bit Steering while Rotating•High ROP•Better Hole Cleaning•Less Wellbore Stability Problems•Drill more Complex Well Trajectories

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Deviation Control

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