Grace Robert. Advanced Blowout and Well Control
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246
Advanced
Blouout
and Well
Control
h,
=
1,477
feet
Determine the margin for pressure increase at the casing
shoe
using Equation
5.10:
Ph
=
0.012(1042)
+
5
13
+
0.6084
(12097
-
1042
-
1477)
+
(0.052)( 12.8)( 1477)
pShw
=
7336
psi
The
maximum
permissible pressure at
shoe,
Equation 5.2
is
equal
to 8492 psi.
pp~~,
from
The maximum increase
in
surface pressure and hydrostatic,
Ut,
that
will
not result in
fracturing
at the
shoe
is given by
Equation
5.3:
Ut
=
8492
-
7336
Ut
=
1156
psi
The volume of the kill-weight mud,
5,
with density,
p,,
to
achieve,
Mt,
is
given
by
Equations 5.4 and
5.5:
Fluid
mamics in
Well
Control
241
0.667(27.5)
+
0.0264(5 13
+
1
156)
2(0.667)
XI
=
XI
=
46.780
1
1 156(0.0264)(27.5)
1:
0.667
1
5
=
16.3
bbls
Determine the effect
of
pumping
16
bbls
of
kill mud
with
density
p,
=
12.8 ppg. The resulting additional hydrostatic,
Myd,
is
given by Equation 5.6:
Myd
=
0.052p1
Mjd
=
(0.052)(12.8)
-
(0.
iz64)
Myd
=
404
psi
Additional surface pressure resulting
from
compressing
the
bubble at the surface with 16 bbls
of
kill mud
is
248
Advanced Blowout
and
Well
Control
(513)(27.5)
pz=
(27.5-
16)
pZ
=
1227
psi
Additional surface pressure,
us
is
given by Equation
5.7:
Ms=1227-513
Ms
=
714
psi
Total
pressure increase,
Mtotal,
is given by Equation 5.8:
MtotO,
=
404
+
7
14
qotal
=
1118
psi
Since
Mtohl
is
less
than
the
maximum permissible pressure
increase,
Ut,
calculated using Equation
5.3,
pump
16
bbls
of
12.8-ppg mud at
1
bpm and shut in
to
permit the
gas
to migrate to
the surface.
In
2 to
4
hours shut-in
p2
=
1227
psi.
Fluid DyMmics
in
Well
Control
249
The surface pressure,
e,
may now
be
reduced
by
bleeding
ONLY GAS
from
P2
to
P,,
=
Pa
-
Myd
P,,
=
5
13
-
404
P,,
=109psi
However, the new surface pressure must be used to determine the
effective hydrostatic pressure
at
13,913
feet to insure no
additional influx.
Pursuant to Equation
5.9:
27.5- 16
h=
0.0264
h
=436feet
250
Advanced Blowout and Well
Control
55
0.0264
h,
=-
h,
=2,O83feet
(0.6)(109)
pr
=
(53.3)(0.984)(540)
Py
=
0.0023
psilft
pb
=
109
+
(0.6084)( 139 13
-
436
-
2083)
+
(0.0
1
1)(436)
+
(0.667)(2083)
pb
=
8431
psi
However, the shut-in pressure
is
8442
psi. Therefore, since the
effective
hydrostatic
cannot
be
less
than
the reservoir pressure,
the surface pressure
can
only
be
bled
to
Pa
=
109
+
(8442
-
843 1)
P,
=
120
psi
The surface pressure must be bled to only
120
psi to ensure no
additional influx by bleeding only dry gas through the choke
manifold. Important!
No
mud can be bled from the annulus.
Fluid
Dynamics
in
Well
Control
251
If
the well begins to
flow
mud from the annulus, it must
be
shut in until the
gas
and
mud separate.
Now
the procedure
is
repeated for the
final
increment:
(0.6)(
120)
pf
=
53.3(0.983)(540)
Pf
=
0.0025
psi/&
Now
solving
for
h
,
use
27.5- 16.0
h=
0.0264
h
=436feet
Similarly
solving
for
h,
:
55
0.0264
h,=-
252
Advanced
Blowout
and
Well
Control
h,
=
2,083
feet
Determine the margin for pressure increase at the casing shoe
using Equation
5.10:
pshw
=
0.0025(436)
+
120
+
0.6084
(12097
-
436- 2083)
+
(0.052)(12.8)(2083)
p,h,
=
7338
psi
The
maximum
permissible pressure
at
shoe,
pfi~~,
from Equation
5.2
is equal
to
8489
psi.
The
maximum
increase
in
surface pressure and hydrostatic,
Mt,
that
will
not result
in
fracturing
at
the shoe is given by
Equation
5.3:
Wt
=
8492
-
7338
Mt
=
1154
psi
The volume
of
the kill-weight mud,
Y;,
with density,
ply
to
achieve,
Ut
,
is given by Equations
5.4
and
5.5
:
Fluid
Dynamics in Well Control
253
0.667(11.5)+0.0264(120+1154)
2(
0.667)
x1
=
XI
=
30.963
r
1
154(0.0264)(11.5)
6
1
=
30.963 30.9632
-
-1
0.667
=
10.14
bbls
Determine the effect
of
pumping
10
bbls
of
kill mud with density
pl
=
12.8 ppg. The resulting additional hydrostatic,
AHyd,
is
given by
Equation
5.6:
Myd
=
(0.052)(12.8)
-
(0.
ii64)
AHyd
=
252
psi
Additional surfixe pressure resulting from compressing the
bubble
at
the surface with
10
bbls
of
kill mud
is
254
Advanced Blowout
and
Well
Cmtrol
(120)(11.5)
Pz
=
(11.5-10)
P2
=92Opsi
Additional sufice pressure,
Ds
is given
as
Us
=
920-
120
Us
=
800
psi
Total
pressure increase,
UtotaI,
is given
as
dpbtaI
=
252
+
800
Ptotal
=
1052
psi
Since
dphml
is
less
than
the maximum permissible pressure
increase,
Pt,
calculated using Equation
5.3,
pump
10
bbls
of
12.8-ppg mud at
1
bpm and shut
in
to permit the gas
to
migrate to
the surface.
In
2
to
4
hours shut-in
pZ
=
920
psi.
Fluid Llynamics in Well
Control
255
The surface pressure,
Po,
may
now
be
reduced by bleeding
ONLY
GAS
from
pZ
to
Pmo
=
120
-
252
P,,
=Opsi
and the hole filled and observed.
The well is killed.
Summary
By following
this
schedule, the well can be killed safely without
violating the casing seat and losing more mud and without permitting
any
additional
influx
of
formation gas into the wellbore.
In
summary,
the well
is
controlled by pumping kill-weight mud
into the annulus and bleeding
dry
gas out
of
the annulus. The volume
of
kill
fluid that can be pumped without fracturing the casing seat
is
determined
from
Equation
5.3.
Logically, the surface pressure should be
reduced
from
the value prior to lubricating kill mud by the additional
hydrostatic contributed
by
the kill-weight
mud.
However, for obvious