PTRL 4017 Well Technology Unit a Well Design Directional Ch5 Directional Control

PTRL 4017 Well Technology – Part A Directional Drilling – Directional Control

School of Petroleum Engineering, UNSWSchool of Petroleum Engineering, UNSW

Directional Control

1



Introduction

Inclination and azimuth of the wellbore are determined by the yderivation of bit which is controlled through BHA. The configuration of BHA is defined by:o Physical dimensions of the collaro Physical dimensions of the collaro Type of materials usedo Number of stabilisers and their position on the stringo Size of the bit and the stabilisers

Multi-stabiliser BHAs are effective in directional drilling and deviation control.

2



Introduction

Deviation of the bit results from:o Flexibility (bending) of the drillstring, which is a function of collar

material and geometryo Weight on bito e g t o b to Hole geometryo Formation characteristics

Changing BHA configuration and WOB can lead to:o Build up

H ldo Holdo Drop-off

The size, position and number of stablisers play an important role in the deviation control of bit.

3



Introduction

In general, BHAs are treated as elastic columns.g ,

Designing a BHA involves calculations of:o Side force at the bit and stabilisers,,o Deformed shape of the BHA ando Bit tilt angle.

4



Forces at Bit

Forces acting on bit includes:go Weight on bit,o Side force (resulted from lateral forces).

αI li ti

The tendency of the bit to build or drop an angle depends on the direction of the resultant force at the bit.

Bending force Fb

Inclination

Stabiliser side force

Side force Fs

L side force Fc

Pendulum force Fp

Resultant force FR

Bit tilt angle β

L

WOB Fa

β

5



Forces at BitAxial force Fa

o F is the weight on bit (WOB)o Fa is the weight on bit (WOB),o Fa is perpendicular to bit face,o Fa tends to direct the bit to drill ahead,

[ ]

αI li ti

o Fa is from the weight of drill collar.

o Bit tilt angle β = angle between bit axis and borehole axis

[ ] )cos()cos(LWF tca β⋅α⋅⋅=

Bending force Fb

Inclination

Lt

o Bit tilt angle β is affected by the deflection of the collar above the bit.


Side force Fs L

Lt

side force Fc

Pendulum force Fp

Resultant force FR

Bit tilt angle β

WOB Fa

β

6



Forces at BitLateral forces:o Pendulum force Fo Pendulum force Fp –

due to gravity and acts toward the low side of the well,It tends to push the bit toward vertical (dropping).

Bending force F

αI li ti

o Bending force Fb –due to bending moment produced at the near-bit stabiliser,It tends to push the bit upward If the bending produced is convex upward

Bending force Fb

Inclinationconvex upward,It tends to push the bit downward If the bending produced is convex downward.


Side force Fs

L side force Fc

Pendulum force Fp

Resultant force FR

Bit tilt angle β

L

)sin(LW21F cp α⋅⋅⋅=

WOB Fa

β

7



Forces at BitLateral forces:o Bending force Fo Bending force Fb –

due to bending moment produced at the near-bit stabiliser,It tends to push the bit upward If the bending produced is convex upward,It tends to push the bit downward If the bending produced is convex downwardIt tends to push the bit downward If the bending produced is convex downward.

8



Forces at Bit

Side force Fs:o The resultant of the two lateral forces (bending and pendulum),o If the side force tends build up then it is positive, pointing to high

side of the wellbore,

αI li ti

o If the side force tends drop off then it is negative , pointing to low side of the wellbore.

Bending force Fb

Inclination


Side force Fs

L side force Fc

Pendulum force Fp

Resultant force FR

Bit tilt angle β

L

WOB Fa

β

9



Forces at Bit

Resultant force FR:o The resultant of the WOB and side force.

Bending force

αInclination

Bending force Fb

Side forceStabiliser side force

FcPendulum force

Side force Fs

Resultant force FR

L

Fp

WOB Fa

Bit tilt angle β

a

10



Forces at Bit

Resultant force FR:o The resultant force controls the drilling direction.

11



Forces at Bit

Drilling direction:o Most drill bit are designed to drill perpendicular to the bit face.o However bit is pushed in the direction of the resultant force.o As a result, the bit usually drills in a direction which is

αInclination

o As a result, the bit usually drills in a direction which is somewhere between the direction of the resultant force and bit axis.

o The angle between

Bending force Fb

the resultant force and drilling direction (θ) depends on bit tilt angle bit type and


Side force Fs

R lt t fL

angle, bit type and formation drillability.

FcPendulum force

Fp

Resultant force FR

WOB

Bit tilt angle β

θ

WOB Fa

β

12



Deformation of BHA

BHA is a Tubular Column.

Beam Column Theory:q(x)

P O P

x

ydx

q

M V qydPydEI =+24

M+dM

P

V+dV

Pdydx

nq

dxP

dxEI + 24

( )44π13

dx

( )4i

4o dd

64I −

π=



Deformation of BHA

Slick BHA:

o A slick BHA consists of drillpipes, drill collars and bit, but no stabiliser.

o A simple pendulum assembly.

o It may be used to minimise the inclination angle when drilling a vertical well, but the weight on bit should be limited to very small values.

greater (Fa)axial force (Fa)

14weaker (Fp)

pendulum force(Fp)



Deformation of BHA

Slick BHA:

( )t

tccatccS Ll θLBW. - Fθ LBW. - F cos50sin50 +=

xy

Fa

Lt

Ra

θ

FS = bit side force (lbf)Wc = air weight of the collar (lbm/ft)B = buoyancy correction factor a

WcBcLt FB

Bc buoyancy correction factorLt = length between the bit and the first point of tangency (ft)θ = inclination angleF = axial load on the bit (lbf)

15

c c t

RB

FBFa axial load on the bit (lbf)l = clearance radius of the drill collars (in.) = 0.5(db – dc)



Deformation of BHA

Slick BHA: ( )tccatccS LlθLBW.- Fθ LBW.- F cos50sin50 += ( )t

tccatccS L

WOB (lbf) F (lbf) L (ft)

Effect of WOB on side forces and tangency Lengths of Slick BHA

WOB (lbf) FS (lbf) Lt (ft)

≈ 0 -167 47.310000 -154 46.420000 -136 45.330000 -117 45.360000 -58 41.280000 -15 39.490000 +7 38.5

density of the metal (ρm) 491 lbm/cuftdrill bit diameter (db) 8.5"collar outside diameter (dc) 7.0"collar inside diameter (di) 2.1875"

16

mud weight (ρf) 9.5 lbm/galinclination (θ) 4o



Deformation of BHA

Single-Stabiliser BHA:

o Adding a stabiliser to the collars moves the point of tangency further away from the bit. This increases the negative side force at the bit (higher pendulum force).at the bit (higher pendulum force).

17



xDeformation of BHA


y

x

Fa

Ltm

1

θ

Rs

WcBcLt FB( ) 11cos50sin50ml

θLBW-FθLBWF −⎟⎟⎞

⎜⎜⎛

+−= c c t

RB

B( )11

1111 cos50sin50LL

θLBW.-F θLBW.F ccaccS ⎟⎟⎠

⎜⎜⎝

+=

( )⎤⎡ θθ 32 llEI6lEI6LsinBWLsinBW1 ( )⎥⎥⎦

⎤

⎢⎢⎣

⎡ −++χ

⋅θ−χ

⋅θ−

⎟⎟⎠

⎞⎜⎜⎝

⎛Λ+Λ

=21

21121

112

21

2c2c1

1c1c

221

121

1 LLllEI6

LlEI6

IL4LsinBW

4LsinBW

ILIL

2

1m

18



Deformation of BHA


Effect of stabiliser distance L1 and WOB on side forces of Slick BHA

F (lbf)FS (lbf)WOB (lbf) L1 = 5 ft L1 = 20 ft L1 = 35 ft L1 = 50 ft L1 = 65 ft

10000 728.17 88.00 -38.78 -110.78 -166.0520000 736.42 89.91 -38.18 -110.04 -163.4030000 745.80 91.87 -37.60 -109.27 -159.9060000 770.67 98.10 -36.08 -106.73 -131.4980000 788.53 102.54 -35.40 -105.6990000 770 17 105 85 35 24 103 42

density of the metal (ρm) 491 lbm/cuftd ill bit di t (d ) 8 5“

90000 770.17 105.85 -35.24 -103.42

drill bit diameter (db) 8.5“stabiliser diameter (dS1) 8.46875"collar outside diameter (dc) 7.0"collar inside diameter (di) 2.1875"m d eight ( ) 9 5 lbm/gal

19

mud weight (ρf) 9.5 lbm/galinclination (θ) 4o



Deformation of BHA

Single-Stabiliser BHA:Effect of stabiliser distance L1 on side forces of Slick BHA

o The stabiliser near the bit causeso The stabiliser near the bit causes the drillstring to bend in a way that pushes the bit against the high side of the borehole wall. The BHA will, therefore, have a positive side force t e e o e, a e a pos t e s de o ceand a tendency to build angle.

o Increase in the distance between the stabiliser and the bit leads to an increase in pendulum force, and the BHA will have a negative side force and a tendency to drop-off.

20



Deformation of BHA

Multi-Stabiliser BHA:

L4

m3

m

L2

L3

m1

m2

Fs

21L1 FB



Deformation of BHA

Multi-Stabiliser BHA:

22



Deformation of BHA

Multi-Stabiliser BHA: Effect of Stabiliser Position on the Side Force

23

BHA configuration



Deformation of BHA

Multi-Stabiliser BHA: Effect of Stabiliser Position on the Side Forceo First Stabiliser (varying L1 while L2 and L3 kept unchanged)

The effect of first stabiliser position on the side force.

The effect of first stabiliser position on the deflection of collar.

As the first stabiliser moves away from the bit the side force at the bit decreases: the increase in tangency length decreases the bending force and increases the pendulum force. The assembly becomes a pendulum assembly.

24

y y



Deformation of BHA

Multi-Stabiliser BHA: Effect of Stabiliser Position on the Side Forceo Second Stabiliser (varying L2 while L1=3 ft and L3 kept unchanged)

The effect of second stabiliser position on the side force.

The effect of second stabiliser position on the deflection of collar.

Since the first stabiliser is placed close to the bit (3 ft) the pendulum force is at its minimum;As the second stabiliser moves away from the first one the lateral component of the weight of the collar section (L2) increases which, in turn, increases the bending moment at the first stabiliser, therefore the bending force at the bit

25

therefore, the bending force at the bit.For pendulum assembly however, due to the large pendulum force, effect on side force is insignificant.



Deformation of BHA

Multi-Stabiliser BHA: Effect of Stabiliser Position on the Side Forceo Third Stabiliser (varying L3 while L1 and L2 kept unchanged)

The effect of third stabiliser position on the side force.

The effect of third stabiliser position on the deflection of collar.

As the third stabiliser moves away from the second one, the side force starts to decrease gradually.For pendulum assembly, the effect on side force is insignificant.

26

y g

PTRL 4017 Well Technology Unit a Well Design Directional Ch5 Directional Control

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