138704541 00019991 Understanding Kick Tolerance
-
Upload
florentin-zamfirache -
Category
Documents
-
view
218 -
download
0
Transcript of 138704541 00019991 Understanding Kick Tolerance
8/20/2019 138704541 00019991 Understanding Kick Tolerance
http://slidepdf.com/reader/full/138704541-00019991-understanding-kick-tolerance 1/5
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
8/20/2019 138704541 00019991 Understanding Kick Tolerance
http://slidepdf.com/reader/full/138704541-00019991-understanding-kick-tolerance 2/5
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'
SPE Drilling Engineering, December 1991
8/20/2019 138704541 00019991 Understanding Kick Tolerance
http://slidepdf.com/reader/full/138704541-00019991-understanding-kick-tolerance 3/5
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
8/20/2019 138704541 00019991 Understanding Kick Tolerance
http://slidepdf.com/reader/full/138704541-00019991-understanding-kick-tolerance 4/5
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.
SPE Drilling Engineering, December 1991
8/20/2019 138704541 00019991 Understanding Kick Tolerance
http://slidepdf.com/reader/full/138704541-00019991-understanding-kick-tolerance 5/5
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