kick tolerance

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WELL CONTROL for the Rig-Site Drilling Team

SECTION 5 : METHODS OF WELL CONTROL

5.10 KICK TOLERANCE

When a gas influx has entered a well there are 2 critical locations for the influx:-

a) When the influx is at the bottom of the well. In this case the SICP must notexceed the MAASP, if the formation is not fractured at the casing shoe.

b) When the influx has been circulated up to the casing shoe, by a constantbottom hole pressure method. In this case, the pressure at the choke mustnot exceed the MAASP.

KICK TOLERANCE DEPENDS UPON:-

Formation strength, fracture pressure or fracture gradient.

Mud density or gradient.

Gas influx density or gradient.

Formation pore pressure, gradient or SIDPP.

Drill string and wellbore geometries.

The maximum tolerable length of gas influx in the annulus at any positionbetween bottom hole and the casing shoe is:-

H (Max) = MAASP - SIDPP (Eqn1) Gm - Gi

Where:- GM = mud gradient (psi/ft)

GI = influx gradient (psi/ft)

MAASP = (Gfrac - Gm) x Ds (psi)

Gfrac = formation fracture gradient at the shoe (psi/ft)

DS = TVD to the shoe (ft)

SIDPP = shut-in drillpipe pressure (psi)



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BDE = pressure profile in annulus atshut-in.

BD = initial gas influx height = H1

BMFKL = pressure profile in annuluswhen top of gas is circulated tocasing shoe, by 'drillers method'.

SK = fracture pressure at shoe.

FK = maximum tolerable length ofexpanded gas influx at shoe= HMAX.

∆le FKN = ∆le BDM.

Hence HMAX = MAASP - SIDPP GM - GI

MAASP

SICP

0 E L PRESSURE

KICK TOLERANCE : DRILLED KICK

SIDPP

Phyd PporeC

AM

B

D

H1(gas)

H max (gas)

N KSShoe

F

Mud G

radient/Preffure Line

DE

PT

H (

TV

D)

Fracture Line

NB. Well geometry assumed to be constant

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DEFINITION 1: for a kick taken while drilling into a high pressure formation.

Kick Tolerance is the maximum allowable influx volume, for a known or assumedSIDPP, which will not cause the formation to fracture when either the influx is atthe bottom of the annulus or when it is circulated and expanded to the casing shoeby a constant bottom-hole pressure method. (Usually the Driller's method).

Thus the kick tolerance is either

a) V1g = H x Vdca bbl (If H is <Ldc) Ldc

or V1g = Vdca + (H - Ldc) bbl (if H is >Ldc) Cdpa

where H is calculated from Eqn 1

OR

b) V1g = Pfrac x (MAASP - SIDPP) bbl Ppore x (GM - GI) x Csa

The Lower value of V1g calculated from a) and b) is the Kick Tolerance.

Where:- Vdca = Volume of DC/OH annulus, (bbl)

Ldc = (Vertical) length of drill collars, (ft)

Cdca = Capacity of DC/OH annulus (ft/bbl)

Cdpa = Capacity of DP/OH annulus (ft/bbl)

Csa = Capacity of annulus (ft/bbl) at the casing shoe - thiswill probably = Cdpa, but on occasion it may = Cdca

Pfrac = fracture pressure at shoe (psi)

Ppore = pore pressure at bottom of hole (psi)



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DEFINITION 2: for a kick taken while tripping out of the hole.

Kick tolerance for a swabbed kick is the maximum allowable influx volume whichmay be swabbed into the bottom of a well, without fracturing the formation whenthe well is closed in, and when the mud gradient is at the least equal to theformation pore pressure gradient.

It is assumed that prior to tripping, the mud weight was correct. In this case, whenthe bit is eventually back at bottom SIDPP=0, although initially SIDPP should =SICP (no float) when the well is closed in and the bit is above the influx.

In this case Hmax = MAASP ft GM - GI

and the kick tolerance is either

V1g = H x VdcaLdc

or V1g = Vdca + (H - Ldc)Cdpa

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KICK TOLERANCE EXERCISE 1

A well has a TVD of 14500 ft with the casing shoe at 13200 ft TVD. The fracturegradient is 0.87 psi/ft and the current mud is 15.3 ppg. There is 700 ft of 6 1/2"OD drill collar and the open hole diameter is 8 1/2", with 5" drill pipe.

The annular capacities are:-

DC/OH = 34.314 ft/bbl

DP/OH = 21.787 ft/bbl

1) Calculate the kick tolerance if the well is shut-in with thecurrent mud and a SIDPP of 570 psi.

The gas gradient is 0.1 psi/ft.

2) Calculate the kick tolerance for a swabbed kick when the mudweight is equivalent to the formation pore pressure.

The mud gradient is 0.835 psi/ft.



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SOLUTION

1) MAASP = (Gfrac - GM) x DShoe GM = 15.3 x 0.052 = 0.7956 psi/ft

= (0.87 - 0.7956) x 13200

= 982 psi

Then H1 max = MAASP - SIDPP GM - GI

= 982 - 570 .0.7956 - 0.1

= 592.3 ft

a) For influx at the bottom of the well, influx is still within the DC/OH annulus,at its maximum.

Volume of DC/OH annulus= 700 = 20.40 bbl 34.314

Therefore: Kick tolerance (a) = 592.3 x 20.40 = 17.3 bbl 700

b) For kick at casing shoe,

Kick tolerance (b) = Pfrac x (MAASP - SIDPP)Ppore x Cdpa x (GM - GI)

= Gfrac x (MAASP - SIDPP) x DshoeGpore x Cdpa x (GM - GI) x TVD

Gpore = 15.3 x 0.052 x 14500 + 570 = 0.835 psi/ft14500

Therefore: kick tolerance (b) = 0.87 x (982 - 570) x 13200 = 25.8 bbl 0.835 x 21.787 x (0.7956 - 0.1) x 14500

conclusion: The smaller of those 2 values is the (a) valuetherefore kick tolerance = 17.3 bbl when the kick isin the DC/OH annulus. This is usually the case inshort open-hole sections.

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2) For a swabbed kick, maximum allowable (SIDPP = 0) influx height is:

Hmax = MAASP ft GM - GI

New MAASP = (0.87 - 0.835) x 13200

= 462 psi

Therefore H1 max = 462 = 628.6 ft 0.735

Therefore swabbed kick tolerance with 0.835 psi/ft mud.

= 628.6 x 20.4 700

= 18.3 bbl

kick tolerance

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