Schlum Kick Tol Presentation

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COPYRIGHT 2001, NExT. All Rights Reserved

HUSSAIN RABIA

KICK TOLERANCE

2 COPYRIGHT 2001, All Rights Reserved

Course Title: Course Title: KICK TOLERANCEKICK TOLERANCEObjectivesAt the end of this module, YOU will be able to:

1. List variables affecting kick tolerance.

2. List situations when to calculate KT

3. Calculate kick tolerance

4. List situations when to increase KT

5. Describe influence of FG on KT


Kick ToleranceKick Tolerance

DEFINITION

For practical purposes, kick tolerance may be defined as the maximum kick size which can be tolerated without fracturing the previous casing shoe.

Kick tolerance may also be defined in the terms of the maximum allowable pore pressure at next TD or maximum allowable mud weight which can be tolerated without fracturing the previous casing shoe


Kick Tolerance Elements

1. Pore pressure from next TD2. Frac Gradient at current casing shoe3. Design influx volume that can be

safely circulated out of hole4. Type of well: exploration or

development


Pore Pressure & Type of Well

1. For Exploration wells, an overpressured zone may be penetrated. The pore pressure gradient is assumed to be 0.5 ppg greater than the maximum mud gradient.

2. For Development wells, assume that an influx enters from swabbing the well. Pore pressure gradient is assumed to be equal to current mud gradient.


When to Calculate Kick Tolerance

1. After a leak-off test

2. Prior to drilling ahead

3. If a factor such as mud weight or drillstring geometry is changed

4. When drilling into areas of overpressure with rapid pore pressure increase, and increasing mud weight to compensate, kick tolerance, limited by formation strength at the previous casing shoe, will be rapidly reduced


Boyles Law

PV= constant

P1 V1 = P2 V2

Gas Behaviour

Gas is highly compressible. Its volume depends on both pressure and temperature


Gas

0

Gas

Open

Gas

Gas

00


2

22

1

11

TVP

TVP

=

46060

27.14

460240

15000++

=

xVx

P1 = 5000 psi

T1= 240 F

V1 = 1 bbl (Assumed values)

P2 = 14.7 psi

T2= 60 F

V2 = ?

V2 = 253 bbls & pressure reduces from 5000 psi to 14.7 psi

Gas

0

Gas

Open

Gas

Gas

00


When the tube is closed , gas rises up the tube without expansion carrying its pressure with it all the way up the tube.

Gas

Gas

Mud hydrostatic = 5000 psi

Gas pressure = 5000 psi

Gas

Closed

Mud = 9.6 ppg

Depth= 10000

0 5000?


Bottom Hole Pressure (Igore gas head)

BHP= surface pressure + Hydrostatic heads= 0 +5000 = 5000 psi

Gas

50000

Gas

Closed

Mud = 9.6 ppg

Depth= 10000 Gas

?

BHP= surface pressure + Hydrostatic heads=5000 +5000 = 10,000 psi

In a real well, the hole will fracture when gas is at surface


Gas

Gas

Hence gas expansion must be allowed to reduce wellbore pressures. This is the basis of well kill methods.


Pa

Mud

Gas

Pf

DPSIP

Yf

Before circulation


Gas half-way up the hole

CSDPx

Pa1

H

TDPf

Gas Bubble

m


Pamax

Gas at surface


Position Of Gas Bubble During Circulation Using The Drillers Method

C) Gas at surface

Pa

Mud

Gas

Pf

A) Before circulation

DPSIP

Yf

B) Gas half-way up the hole

CSDPx

Pa1X

H

TD

Pamax



Px = Pf - Pg - (TD - H - CSD) x pm x 0.052CSDPx

Pa1 X

H

TDPf

Gas BubblePf =formation pressure at next TD, psiPg =hydrostatic pressure in gas bubble = H x GH =height of gas bubble at casing shoe, ftG =gradient of gas = 0.05 to 0.15 psi/ftTD =next hole total depth, ftCSD =casing setting depth, ftpm =maximum mud weight for next hole section, ppg



Px = Pf - Pg - (TD - H - CSD) x pmx 0.052

CSDPx

Pa1 X

H

TDPf

Gas Bubble

Px = FG x CSD x 0.052

Pg = H (ft) x 0.1 psi/ft


H = 0.052 x pm (TD - CSD) + (FG x CSD x 0.052 - Pf)0.052 x pm - G

Where FG is the fracture gradient at the casing shoe in ppg


H = 0.052 x m (TD - CSD) + (FG x CSD x 0.052 - Pf)0.052 x pm - G

Where FG is the fracture gradient at the casing shoe in ppg

The volume of influx at the casing shoe is

V1 = H x Ca bbl

Where Ca = capacity between pipe and hole, bbl/ft CSDPx

Pa1 X

H

TDPf

Gas Bubble

Remember pressure at shoe is FG (fixed)


At bottom hole conditions the volume of influx (V2) is given by

P2 V2 = P1 V1

(The effects of T and Z are ignored)

V2 = V1 x P1 bblP2

Where P1 = fracture pressure at shoe, psiP2 = Pf, psi

The value of V2 is the circulation kick tolerance in bbls.

Pa

Mud

Gas

Pf

DPSIP

Yf


CSDPx

Pa1X

H

TD

Pa

Mud

Gas

Pf

DPSIP

Yf


Increasing Kick Tolerance

KT values may be increased when:

1. drilling extremely high porous and permeable zones ( 1-3 darcies)

2. using low tech kick detection equipment

3. several transition zones in same open hole section are encountered

4. drilling from a semi-sumbersible rig


Example: Calculate the Kick Tolerance for

9 5/8 = 14,500 ft

Next Hole TD = 17000 ft

FG at 9 5/8 shoe = 16 ppg

Temperature gradient = 0.02 F /ft

Max. mud weight for next hole =14.5 ppg

Max formation pressure at next hole = 14 ppg

Assume next hole 8

5 drillpipe from surface to TD


H = 0.052 x pm (TD - CSD) + (FG x CSD x 0.052 - Pf)0.052 x pm - G

H = 0.052 x 14.5 (17000-14500) + (16x14500x0.052 14x17000x0.052)0.052 x 14.5 0.1

CSDPx

Pa1 X

H

TDPf

Gas

Bubble

= 14500 ft

= 17000 ft= 14 ppg

Mud = 14.5 ppg

H = 2405 ft


Volume at shoe = H x capacity between hole/DP

Capacity = ( 8.52 52) ___1____

4 x 144

= 0.2577 ft3/ft

5.62 bbl/ft

= 0.0459 bbl/ft

V1 = 0.0459 x 2405

= 110.4 bbl (volume of bubble at shoe)


P1 V1 = P2 V2

16 x 14500x 0.052 x 110.4 = 14x17000x 0.052 x V2

V2 = 107.8 bbls


Temperature Effects

T = surface temp + temperature gradient + 460

T1 ( at shoe) = 60 + 0.02(F /ft) x 14500 (ft) + 460 = 810

V1 x P1T1

= V2 x P2T2

110x16x14500x0.52810

= V2 x14x17000x0.052860

V2 =115 bbl (compared to 108 bbl without temperature effects)

T2 (at TD) = 60 + 0.02 x 17000 + 460 = 860


Exercise 1 : Repeat previous example if FG= 15.2 ppg

H = 1482.87 ft

V1 = 68 bbl

V2 = 63 bbl ( without temperature effects)

V2 = 67 bbls

68x15.2x14500x0.52810

= V2 x14x17000x0.052860

With temperature effects


Influence of FG on Kick Tolerance

(i) If the actual FG is greater than the design value, then open hole section below the casing shoe can be drilled further than planned if desired. In other words , the well is actually stronger than planned.

(ii) If the actual FG is less than the planned, then the reverse of the above is true. The open hole section can not be drilled to it planned depth. The section may then be drilled to a shallower depth with less pore pressure or a cement plug is placed at the shoe to artificially strength the shoe. The last practice was actually performed by the author and was found successful in areas with FG less than 15 ppg.


Table : Kick Tolerances for exploration Wells

HOLE SIZE (inch) KICK VOLUME (bbl)

6 and smaller 258.5 25-5012 50-10017.5 100


Exercise 2: Exploration WellSemisubmersible

Calculate KT for 12 hole

133/8 casing is set at 7000 ft.

FIT results:

Mud in hole = 13 ppg , surface pressure 1000 psi

5 drillpipe

Temperature 0.015 F /100 ft

Pore pressure unknown ? Maximum mud weight to be used is 14 ppg.


Exercise 1: Exploration WellSemisubmersible

Answer:

FG = 15.75 from FIT

Pore pressure = 14 ppg = maximum mud weight

H =

KT =


Now , YOU should be able to:

1. List variables affecting kick tolerance.

2. List situations when to calculate KT

3. Calculate kick tolerance

4. List situations when to increase KT

5. Influence of FG on KT

Documents

Schlum Kick Tol Presentation