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Understanding Kick Tolerance

and Its

Significance

in

rilling Planning and Execution

K.P. Redmann Jr. SPE Chevron U.S.A. Inc.

Summary. Kick tolerance is a drilling parameter that has prompted both confusion and misunderstanding in the drilling industry,

yet its importance to drilling engineers may be increasing exponentially. The increasing number

of

worldwide drilling catastrophes

may spur government agencies to tighten controls on casing-setting-depth criteria, requiring pipe to be set once minimal kick tolerance

values are reached. A thorough understanding of kick tolerance is necessary in both drilling operations and casing program design.

Confusion involving kick tolerance may be attributed to the concept of zero gain, which is commonly referred to in many accepted

definitions of kick tolerance. This paper presents an innovative approach to determining true kick tolerance that not only incorporates

the conditions of an influx within the well bore but also considers the possible reductions in kick tolerance caused by the circulation

of

that influx from the wellbore. New techniques are available for hand-held calculators, which are now more accurate in determining

influx pressure and volume anywhere within the wellbore. A typical well example with illustrations describes kick tolerance and empha

sizes the influence of other drilling parameters. Integration of kick-tolerance considerations into the well planning process also is dem

onstrated.

Introduction

The concept

of

kick tolerance has been controversial in the drilling

industry. Many say it fosters a false sense of security.

1

Much con

fusion can be credited to the term

zero gain,

which is used in

this commonly accepted definition: kick tolerance is the maximum

increase

in

mud weight allowed by the pressure integrity test

of

the casing shoe with no influx (zero gain) in the wellbore. To the

drilling hand on the rig, this means, How much I can weight up

to kill the well without breaking down the shoe, assuming zero pit

gain? All too often, the zero-gain condition is either misunder

stood or omitted entirely.

Previously published papers have defined kick tolerance

in

terms

of

a particular field or operation, developing equations that include

safety factors, trip margins, and pit gains common to that environ

ment.

2,3

Although interesting and discernible to the drilling engi

neer, this may add to the confusion of the average field drilling

hand. In addition, governmental regulations may lead to further

misunderstanding when improperly interpreted. Minerals Manage

ment Service 250.

54

a)

6)

states, A safe margin, as approved by

the District Supervisor, shall be maintained between the mud weight

in use and the equivalent mud weight

at

the casing shoe as deter

mined in the pressure integrity test. 4

Although each well should be considered individually in the de

termination of such a safe margin, many contend that the future

will see a standard value for this parameter defined as 0.5 Ibm/gal.

This requirement could mislead many drillers into believing that

they can continue to drill until the mud weight equals exactly

0.5

Ibm/gal less than their shoe test.

For

a better understanding of kick tolerance, the derivation of

the kick tolerance equation, based on the above definition,

is

present

ed. This equation encompasses the effects of an influx in the well

bore at initial shut-in conditions. And, of course, no examination

of

kick tolerance would be complete without consideration

of

the

effects as the influx

is

circulated from the wellbore.

It is likely that government regulatory agencies may soon dictate

not only a minimum value for kick tolerance, but also the method

of determining that value. A thorough understanding of kick toler

ance and how to calculate it while drilling are very important for

the drilling representative at the rigsite.

The drilling engineer in the office also must consider kick toler

ance during the well design. Pore pressure and fracture gradient

information, if available, are excellent when used effectively to

select casing setting points. However, kick tolerance must also be

incorporated, especially in the case oflong, openhole sections. Other

factors, such as hole stability, may require an increase in mud

weight. Should this occur, the minimum allowable kick tolerance

Copyright 99 Society of Petroleum Engineers

SPE Drilling Engineering, December 1991

may be experienced earlier than anticipated, and governmental regu

lations may require casing setting.

Studies have shown an increase in the number

of

blowouts world

wide,5 resulting in escalating costs and increasing liability. The

drilling program may soon come under close scrutiny by the vari

ous government agencies, which will undoubtedly set stricter guide

lines for the drilling

of

all wells, possibly including kick tolerance.

Background

The derivation of kick tolerance (based on the accepted definition)

must be understood.

For a given mud weight, the casing-shoe pressure-integrity test

will define the maximum allowable shut-in casing pressure that will

fracture the formation at the shoe p

cmax)'

This relationship is

Pcmax

= s

W

e

,, 0.052D

· (1)

The casing-shoe pressure-integrity test, or shoe test, may be deter

mined by one

oftwo

different methods, each lithologically depend

ent. In either case, a surface pressure is obtained during the testing

procedure and is added to the existing hydrostatic pressure at the

casing shoe. The shoe test

is

the sum of these pressures in mud

weight equivalent (pounds per gallon) and identifies that pressure

to which the casing shoe was exposed.

To avoid fracturing exposed formations, which will not heal when

pressure is reduced (such

as

in hard rock drilling), a simple pres

sure test may be incorporated. After a minimum of

10

ft is drilled

below the casing shoe, the bit is pulled into the casing; the blowout

preventer

is closed around the drillpipe; and the casing and exposed

formations at the casing shoe are slowly pressured to some pre

determined value, which is based on the maximum mud weight re

quired to drill the next section

of

hole. Additionally, this value is

sufficiently below the estimated fracture pressure at the casing shoe

to prevent fracture. This pressure (to which the casing shoe and

drilled formations have been exposed) may be converted to equiva

lent mud weight in pounds per gallon and represents the shoe-test

value.

In softer areas (the offshore environment) where formations will

heal when pressure is reduced, a different type of casing-shoe

pressure-integrity test is performed. Called the leakoff test, it deter

mines the pressure, in mud-weight equivalent, at which the drill

ing fluid initiates small, vertical fractures in the exposed formations.

This test is similar to the above test, except no predetermined pres

sure is used. The casing shoe and exposed formations are pressured

by the pumping of equal increments (usually

\4

to

z

bbl in volume)

of drilling fluid. Surface pressures are recorded for each increment

pumped until the incremental pressure begins to decrease. The last

recorded surface pressure before the observed decrease is added

245



to the existing hydrostatic pressure at the casing shoe and repre

sents the formation fracture pressure. When converted to mud

weight equivalent, this value

is

called the leakoff test or shoe test.

For any given depth, and assuming no wellbore influx, the max

imum formation pressure allowable by the pressure integrity test is

Pfmax =Pemax

+Phex

2)

f

he required

or

new mud weight, W

n

,

to balance this maximum

formation pressure

is

incorporated, then

Pfmax=0.052W

n

D

h

·

(3)

Likewise, the existing or old mud weight

ex

will define the ex

isting hydrostatic pressure:

Phex=0.052W

ex

D

h

. (4)

Combining Eqs. 2 through 4 yields

0.052WnDh

=Pemax +0.052W

ex

D

h

. (5)

Eq. 5 may be simplified to

n - ex

=Pcmax/(0.052D

h

) 6)

Eq. 6, which assumes no influx

in

the wellbore (zero pit gain), de

fines kick tolerance because the quantity

(Wn

-

W

ex

) is

the maxi

mum increase in mud weight allowed by the pressure-integrity test.

Therefore,

Ko =Pcmaxf(0.052D

h

)· 7)

Including

Influx

Eq. 7 can be developed further to include the effects of an influx

in the wellbore. The following conditions, common to the worst

case well-control scenario, are assumed: the influx enters the bot

tom

of

the wellbore as a slug; the influx remains as a slug during

circulation; and the influx

is

gas. (Commonly, 0.1 psi/ft

is

used

as the gradient, unless a more accurate figure

is

known.)

Any annular influx

of

a lesser gradient than the drilling fluid will

cause a reduction

of

the hydrostatic pressure in the annulus and

a corresponding increase in the casing pressure at the surface. Based

on the above conditions, this increase

is

Peine =

[(0.052W

ex

gd

i· (8)

For a given influx size,

Pcmax

will be reduced by an amount

equal to that in Eq. 8, and kick tolerance may be calculated to in

clude the effects

of an

influx in the wellbore at initial shut-in con

ditions:

Kin

= (Pcmax - {[(0.052W

ex

gi 1

L

d)/0.052D

h

· (9)

Worst-case scenarios are used in well-control design to ensure

that the surface equipment, casing, and exposed formations are com

petent to withstand and contain any pressures encountered. To de

sign on a less stringent criterion would risk the integrity of the

wellbore and would require extensive risk analysis using very ac-

246

4000'

10,000'

TVD

:

10,000'

Mud Wt:

10

ppg

Shoe

Test:

13 ppge

Hole Size : 8 112

Drill Pipe

: 4

112

16.60 ppf

Drill Collars

: 1 x 2

13/16

(200')

Casing: 9 5/8 (Assume 8 112 10)

Influx Gradient: 0.1

psi

1ft

Fig. 1 Well schematic.

curate formation data on those formations to be drilled. Such ac

curacy

is

often unobtainable. A departure from the worst-case

scenario typically reduces the risk to wellbore integrity. One ex

ample

is

the stringing out

of

the influx, which increases the ef

fective gradient of the influx, thus minimizing the reduction

of

annular hydrostatic pressure. A second example includes the gra

dient of the influx itself. As with the previous case, if the forma

tion fluid gradient

is unknown and 0.1 psi/ft is used, the reduction

of

annular hydrostatic pressure will be lessened

if

the true influx

gradient exceeds 0.1 psi/ft.

No discussion

of

increasing formation pressure has been attempt

ed. Under certain conditions, such

as

swabbing,

an

influx may enter

the wellbore even though the mud weight is sufficient for the ex

posed formation pressures. Formation pressure has been omitted

to gain a basic understanding

of

kick tolerance.

Under most conditions and for most well geometries, Eq. 9 may

be used to determine kick tolerance. In some cases, such

as

an un

usually large influx or a tight hole geometry, 6 expansion of the

influx during circulation will cause the true vertical length

of

the

influx at the casing shoe to exceed greatly the true vertical length

of

the influx at initial shut-in conditions. Expansion of the influx

during circulation is necessary to reduce the pressure of the influx

and to maintain constant bottomhole pressure. However, this ex

pansion

is

accompanied by a reduction in the hydrostatic head

of

the annulus and a corresponding increase in surface and casing

shoe pressures. Modern well-control procedures consider this ex

pansion and calculate its effects on surface and casing-shoe pres

sures. Therefore,

it is

necessary to examine this condition as

it

pertains to kick tolerance.

Influx at

Casing

Shoe

Pressure within the influx when

it

has been circulated to the casing

shoe is calculated by considering the

driller's

method of well

control, which uses the existing mud weight to remove the influx

from the wellbore. This method

is

preferred for this analysis be

cause higher casing-shoe pressures will be experienced (in keep

ing with the worst-case scenario) and because occasionally neither

time nor weighting material (barite)

is

available for use

of

the

en-

gineer 's or wai t and weight method. Therefore, the maximum

shoe pressure will be realized when the top

of

the influx has been

circulated to the casing shoe and will equal the pressure of the influx.

It

is

desirable to calculate the pressure

of

the influx when

it

reaches

the casing shoe. Advances

in

hand-held programmable calculators

efficiently solve the formerly time-consuming, iterative, pres

sure/volume equations. 7 Because the pressure and volume

of

the

influx are known at initial shut-in conditions, the drilling engineer

or representative can use these programs (see the Appendix)

to

predict the pressure and volume

of

the influx at the casing shoe.

The equivalent mud weight, W

eq

, at the shoe may then be deter

mined and a new value for kick tolerance computed:

Kc=s- Weq (10)

4000'

8514'

10,000'

69.5 Bbl

Gain

For

either

case,

Max

slep

has been reached without

drilling into

pressure.

6 4

104.3

Bbl Gain

Fig, 2 Signlficance of influx pit gain).

8514'

10,000'




11.5 r-r---I • Kick Tolerance Decreases With

True

Vertical Depth

•

Kick

Tolerance Decreases With Increasing Pit Gain

• Kick Tolerance

Decreases With

longer DC lengths

11.0

10.5

0.5

10.0

50 69.5 bbls

100

Pil Gain

Fig. 3-Kick tolerance at initial shut-in conditions.

The value for kick tolerance computed from Eq. 10 is now com

pared with that calculated by Eq.

9.

The lesser

of

the two is con

sidered the actual kick tolerance.

xample

Fig. 1 shows a well schematic and gives some pertinent informa

tion. Because the true influx gradient is unknown, the worst-case

scenario

of

a gas influx is used, and 0.1 psilft is approximated as

the influx gradient.

Before determining kick tolerance for this example problem, we

consider the significance

of

an influx

in

the wellbore, with no

in

crease in formation pressure.

From Eq. 1, Pemax is found to be 624 psi.

If

the bit is on or near

the bottom

of

the hole and a full column

of

mud exists within the

drillstring, the shut-in drillpipe pressure is zero. Knowledge of the

hole geometry allows us to calculate the influx length and size that

will correspond to a shut-in casing pressure

of

624 psi. Using the

information given, we determine that for a O.l-psilft influx gra

dient, an influx length

of

1,486

ft

69.5 bbl) would produce 624-

psi shut-in casing pressure. Therefore, the casing-shoe integrity is

compromised

by

a 69.5-bbl kick, without drilling into pressure.

A second consideration involves the bit having been pulled uphole,

as on a trip, and an influx being swabbed in. The influx length to

broach the casing shoe remains the same 1,486 ft). In this exam

ple, however, the influx must fill the 8V2-in. hole, not just the

8V x4V2-in. annulus, requiring 104.3 bbl to reach the same length.

Also, shut-in casing and drillpipe pressures will be 624 psi, unless

a drillpipe float is used and is holding pressure. Understanding the

significance

of

an influx in the wellbore Fig. 2 is essential if kick

tolerance as a drilling tool is to be used to its full potential. Armed

with this insight, let us now consider kick tolerance for this exam

ple problem.

Again, using the information given and applying Eq. 9, we can

now determine kick tolerance for any given influx size at initial

1.5 r g r = . ~ K : i C ~ k ~ T : O I = e r = a = n c = e : D : : e c : : : r = e a = s e = s ~ W : i t = h ~ T = r u = e = Y : : e r t = i c a : I :De=p:th:l

•

Kick

Tolerance

Decreases

With

Increasing

Pit

Gain

•

Kick

Tolerance

Decreases With longer

D

lengths

o ~ ~ ~ L ~ ~ ~ · ~ ~ ~ ~ ~ ~ L ~ ~ ~ ~

o 14.5 2$ 39 50

53J

bbl.

bbl. bbl.

Pil Gain

11.5

bbl.

100

Fig. 5-Kick tolerance at initial shut-in conditions. Drilling

at

10,000

ft.

SPE Drilling Engineering, December

1991

13.0

12.5

12.0

11.5

1.5.--r--- -=-=-:---::----::::::-:::--:-:-:--:-::--:I

• Kick Tolerance

Decreases

With True Vertical

Depth

• Kick Tolerance Decreases With Increasing

Pit Gain

• Kick Tolerance

Decreases

With longer DC

lengths

50

Pit

Gain

bbls

_8 . 000

_10 .000

_12 .000

c:::J

14,000'

100

Fig. 4-Kick tolerance at initial shut-in conditions mud weight

increased

to

11.5 Ibm/gal).

shut-in conditions. Plotting kick tolerance vs. pit gain Fig. 3

is

simple for different drilling depths these values are based on the

use

of

the existing or current mud

weight-in

this case, 10.0

Ibm/gal).

Any of

the hand-held programmable calculators avail

able today can easily provide the same information once pro

grammed with Eq. 9.

Should the mud weight be increased, new kick-tolerance values

must be calculated because

of

the reduction inPcmax Fig. 4 shows

that kick tolerance does indeed decrease with an increase in mud

weight. Also notice that the maximum kick size has now dropped

to 26 bbl. The ability

of

the rig crew to shut in the well efficiently

is now an even greater concern.

Figs. 3 and 4 also portray, on the far left axes, the maximum

formation pressure that may be drilled, given the existing shoe test,

depth, mud weight, and anticipated pit gain. Recall that Eq. 2,

when divided by 0.052

h

relates the maximum formation pres

sure to kick tolerance and existing mud weight.) Variations

of

these

diagrams are helpful to the drilling engineer and the drilling repre

sentative when discussing the current drilling situation. Fig. 5 rep

resents the relationship between kick tolerance and pit gain at 10,000

ft

for different mud weights at initial shut-in conditions. It is in

teresting to note that, if 0.5 Ibm/gal is determined to be the mini

mum kick tolerance and a horizontal line is drawn across Fig. 5

at 0.5 Ibm/gal, the use

of

mud weights greater than 11.0 Ibm/gal

cannot be recommended, to the dismay of those who felt comfort

able with a 13.0-lbm/gal shoe test.

Fig.

6

displays the same example problem with some additional

pump information and an influx circulated to the casing shoe. To

complete our investigation

of

kick tolerance for this problem, we

must consider the pressure

of

the influx when its top reaches the

shoe. Using the pressure/volume calculator program previously

mentioned see the Appendix), we plot the data obtained from Eq.

10

with that information gained from Eq.

9

Fig.

7).

We find that

above about 37 -bbl initial gain, expansion

of

the influx will cause

4000'

10,000'

TVD :

10,000'

Mud

Wt

: 10 ppg

Shoe Test: 13

ppge

Hole Size

: 8

112

Drill Pipe : 4 112 16.60

ppf

Drill Collars : 7 x 2 13/16 (200')

Casing: 9 5/8 (Assume 8 112 10

Pumps

: 7 x

12 Triplex @ 95%

Pump Rate :

45

spm

Assumptions

:

No

Migration, Influx

Remains

as

a Slug

Fig.

6-Circulating out

influx.

247



1 . 5 r - - - g - - r : . - K ; ; i : : ; C k ; - : T ; : o ~ 1 8 : : : r a : n c : : 8 : - ; D ; : 8 : : c r : : 8 a : : S : : 8 S ; - : W ; ; ; i ; ; ; l h ~ l ; : n f ; ; : l u : I - ; E I : : p : a n : : S : ; : i o : n l

...

During

Circulation

~

Fig.

7-Kick

tolerance with Influx at shoe. Drilling at 10,000

ft; mud weight 10.0 Ibm/gal.)

0

2

A \

~

4

e

0

=

ca

I )

I I )

6

ID

...

~

..

?

ID

c

8

Q..

.c

-

a..

ID

Q

-

=

,)

C

e

C

ID

C

>-

::::

ID

=

10

12

14

10 12 14 16 18

Mud Weight Equivalent (ppg)

Fig. B-Choosing casing pOints.

the shoe pressure experienced when the influx is circulated to the

shoe to exceed considerably that experienced initially. It is addi

tionally shown that the maximum pit gain

of

69.S bbl discussed

earlier could not have been circulated out with the drille r's method

of well control without breaking down the shoe.

Diagrams like Figs. 3 through Sand 7 are useful to illustrate the

effects

of

other drilling parameters on kick tolerance. As previ

ously shown, drilling personnel can easily develop these, not only

to perform their job responsibilities better, but also to emphasize

to the rig crew the importance

of

minimizing the influx. The failure

of

the rig crew to react to the warning signs of a kick

is

a signifi

cant factor in many blowouts.

It

is

also the principal reason behind

the tremendous amounts

of

time and effort invested in the training

of

personnel.

8

It benefits the drilling representative to train his rig

crew and thus improve the efficiency

of

the drilling operation.

248

.c

-

a

ID

Q

-

=

,)

C

:e

C

ID

C

>-

.....

-

D

2

0

2

A \

~

4

~

ID

ID

~

..

( , )

ca

c

I I )

E

I)

6

ID

ID

...

0

~

..

t-

ID

?

c

8

Q..

10

12

14

~ ~ n

Mud

Weight

Equivalent

(ppg)

Fig. 9-Chooslng casing points.

BLOWOUTS/ I

) )

WELLS

US

GULF OF MEXICO-OCS

0.5

0.395

0.4

0.3

0.2

0.1

0.06

1950

1960 1970

1980

SURVEY FOR 25 YEARS

0.5

0.4

0.3

0.2

0.1

Fig.

10-Blowouts:

exploration, development, production af

ter Hammett and DUdley 5).

Well Planning

When designing a well, the drilling engineer must consider kick

tolerance, especially when long, openhole sections are anticipated.

Commonly, O.S-lbm/gal kick and trip margins are plotted on the

diagrams

of

pore pressure/fracture gradient and are used to select

casing setting depths.

9

From the previously discussed example

problem, pore pressure and fracture gradient data were obtained

to develop Fig. 8. On the basis

of

the 0.5-lbm/gal margins, inter

mediate casing would be set at a depth of 11,700 ft. However, at

11,700 ft, the mud weight will exceed 12.0 Ibm/gal

if

the pore

pressure information

is

accurate. The earlier example indicated that

this mud weight offered little kick tolerance at 10,000 ft. Further

more, Fig. 5 shows only O.S-lbm/gal kick tolerance available to

11.

7S-lbm/gal mud at 10,000 ft with zero pit gain. From a safe

drilling standpoint, this should be considered absolute minimal stan

dards at 10,000 ft.




Once again, an examination

of

Fig. 5 shows that 11.0 Ibm/gal

is the maximum allowable mud weight at 10,000

ft

for a 1O-bbl

influx and a 0.5-lbm/gal kick tolerance in this example. With this

mud weight, a

1O-bbl

influx, and K=0.5 Ibm/gal, Eq. 9 indicates

that the well can be drilled to only 10,400 ft. Because this depth

is

substantially shallower than the casing point proposed

by

Fig.

8, a lighter mud weight may be considered.

Returning to Eq. 9, the same conditions are applied for a 10.9-

Ibm/gal drilling fluid. The maximum allowable drill depth with this

fluid weight is found to be 11,261 ft. Fig. 9 incorporates this mud

weight with the margins previously discussed and depicts the in

termediate casing setting depth at 10,900 ft. Although this casing

point

is

800 ft shallower, the well can still be drilled to the planned

total depth. The prudent drilling engineer will continue this analy

sis until convinced that the casing point chosen does conform to

minimal kick-tolerance specifications.

Kick tolerance, in this respect, is offered as an additional tool

for the well-design engineer to incorporate.

It

is not to be looked

upon as the only casing-design criterion but should be considered

when this analysis is undertaken. Also, from both safety and eco

nomic standpoints, wells should be designed to reach total depth.

The practice

of

setting casing

as

deep as possible is often un

necessary, usually more expensive, and certainly risky because kick

tolerances are reduced to the point that any influx taken, even that

swabbed in, will compromise the integrity

of

the former casing shoe.

onclusions

Current statistics (Fig. 10) point to an increasing trend

in

blowouts.

5

Discussions with well-control experts and blowout

specialists confirm this trend. The future will hold stricter govern

ment and company regulations regarding the drilling of wells to

provide the utmost in safety and security for the drilling personnel

and the environment.

The significance of kick tolerance in drilling planning and exe

cution cannot be underestimated. Safe drilling practices will de

mand that minimal kick-tolerance standards be considered on a

per-well basis. Regulatory bodies soon may hold all drilling per

sonnel responsible for a working knowledge

of

kick tolerance.

It

is

hoped that through these simple but effective methods, a thorough

understanding has been achieved.

Nomenclature

Dh

= true vertical depth

of

hole,

ft

DR = reservoir depth, ft

Ds

= true vertical depth

of

casing shoe, ft

gi = gradient

of

influx, psi/ft

K = kick tolerance, Ibm/gal

Kc

= kick tolerance during circulation, Ibm/gal

Kin

= kick tolerance including effects

of

influx, Ibm/gal

Ko = kick tolerance with zero pit gain, Ibm/gal

Lex

= length

of

existing mud

Lg

= length of gas

Li

= true vertical length

of

influx, ft

Pcinc

= increased casing pressure caused by influx, psi

Pcrnax = maximum allowable shut-in casing pressure, psi

Pfmax

= maximum formation pressure, psi

Phex

= existing hydrostatic pressure, psi

PR

= reservoir pressure, psi

= surface pressure, psi

Psidp

= shut-in drillpipe pressure, psi

Ptob

= pressure at top

of

bubble or influx, psi

s = shoe test, Ibm/gal

Vg = volume

of

gas

Weq

= equivalent mud weight, psi

Wex

= existing or current mud weight, Ibm/gal

Wn = new or required mud weight, Ibm/gal

g

= density

of

gas influx, Ibm/gal

Acknowledgment

I express my appreciation to Chevron U.S.A. Inc. for permission

to publish this paper.

SPE Drilling Engineering, December

1991

Author

K.P. Redmann is

a senior drilling en·

gineer in Chevron U.S.A. s Central Profit

Center in New Orleans. Since joining

Chevron in 1981, he has held positions

in drilling and production engineering

and has worked both on· and offshore

in the Gulf of Mexico and in west Africa.

Before 1981, Redmann worked with Mul·

lins and Prichard Oil Producers in New

Orleans.

He

holds an MS degree in pe·

troleum engineering from Louisiana

State U. and is the current national president of the Ameri·

can Assn. of Drilling Engineers.

References

1.

Pilkington, P.E. and Niehaus H.A.: Exploding the Myths About Kick

Tolerance, World Oil (June 1985) 59-62.

2. Wilkie, D.l. and Bernard, W.F.: Abnormal Pressure Detection and

Control in Beaufort Sea Wells, Ocean Industry (March 1981) 33-36.

3.

Wilkie, D.l. and Bernard, W.F. : Detect ing and Controlling Abnor

mal Pressure, World Oil (July 1981)129-144.

4. MMS 250. 54(a)(6)

,

Rules and Regu lationsfor Drilling, Completion,

and

Workover Operations in

All

OCS Waters, Minerals Management Service.

5. Hammett, D.S. and Dudley, W.O.:

Day

Rates Affect Rig Safety and

Training , paper SPE 18680 presented at the 1989 SPE/IADC Drilling

Conference, New Orleans, Feb. 28-March 3.

6. Nance, G.W.: Annular Geometry - Its Effect on Kick Tolerance,

paper presented at the 1978 ASME Energy Technology Conference,

Houston, November.

7. Brewton, J., Rau, W.E., and Dearing, H.L. : Development and Use

of a Drilling Applications Module for a Programmable Hand-Held Cal

cula tor , paper SPE 16657 presented at the 1987 SPE Annual Techni

cal Conference and Exhibition, Dallas, Sept. 27-30.

8.

Redmann, K.P.: Flow Characteristics of Commercially Available Drill

ing Chokes Used in Well Control Operations,

MS

thesis, Louisiana

State U., Baton Rouge,

LA

(1982).

9. Bourgoyne, A.T. et al.: Applied Drilling Engineering, Textbook Series,

SPE, Richardson, TX (1986) 2, 330.

Appendix Gas Pressure

at

Depth Calculation

The calculation

is

as follows.

PR = 0.052D

R

W

ex

) +Psidp

(A-I)

Initialize surface pressure for iterative solution:

Ptob(i) =P

r

(A-2)

and

czt(r) =4.03 -0.38 In Ptob(i)

A-3)

Solve iteratively for

Ptob:

Pg(i+ I =0.037 In Ptob i) -0.219

A-4)

Ptob(i+I) =Pr-0.052[ DR -Dtob-Lex

g

)P

g

2 +Lex W

ex

]-LgP

g

.

(A-5)

czt(i+

I

=4.03 -0.38 In Ptob(i+ I )

A-6)

Then,

Vg(i+

I

=CztrPR V;lCzt(i+ l)Ptob(i+

I )

(A-7)

Eqs. A-4 through A-7 are repeated until

Ptob(i+ I)

and

Vg(i+l)

con

verge within

10

psi.

Weq =Ptobl(0.052Dtob)

(A-8)

and

Ps =Ptob

- 0.052W

ex

D

tob

)·

(A-9)

SI Metric onversion Factors

bbl

x

1.589873

E-Ol

m

3

ft

x

3.048*

E-Ol

m

gal

x 3.785412

E-03

m

3

in.

x

2.54*

E OO

cm

Ibm

x 4.535924

E-Ol

kg

psi

x

6.894757 E OO

kPa

• Conve,sion factor

is

exact.

SPEDE

Original SPE manuscript received for review Feb. 27, 1990. Paper accepted for publica

tion Sept. 3, 1991. Revised manuscript received Aug.

7

1991. Paper (SPE 19991) first

presented at the 1990 IADC/SPE Drilling Conference held in Houston, Feb. 27-March 2.

249

138704541 00019991 understanding kick tolerance

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