Grace Robert. Advanced Blowout and Well Control
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236
Advanced
BIowout
and
Well
Control
(1
420)(
66.5)
pz’
(66.5
-
20)
Pz
=
2031 psi
Additional surface pressure,
Ws
,
is
given
as:
APs=pz-Pa
Us
=
2031- 1420
CIP,
=
611 psi
Total
pressure increase,
ptoh1,
is
given
as:
(5.7)
AProlal
=
504
+
611
=
1115
psi
Since is less
than
the maximum permissible pressure
increase,
Mt,
calculated using Equation 5.3, pump 20 bbls
of
12.8-ppg mud at
1
bpm
and
shut
in
to
permit the gas to migrate
to
the
surface.
Observe initial
Pz
after pumping
=
1950 psi.
Observe 2-hour shut-in
Pz
=
203
1
psi.
Fluid
Qwarnics
in
Well
Control
237
The surface pressure,
P,,
may
now
be reduced by bleeding
ONLY
GAS
from
Pz
to
P,,
=
1420-504
P,,
=
916
psi
However, the new surface pressure must be used to determine the
effective hydrostatic pressure
at
13,913 feet to ensure no
additional influx.
Equation
2.7
expands
to
Equation 5.9:
Where:
Y,
=
Remaining
volume
of
influx, bbls
66.5-
20
h=
0.0264
h
=
1,762
feet
238
Advanced Blowout and Well
Control
h,
=758feet
(0.6)(9 16)
pf
=
(53.3)(0.866)(540)
Pf
=
0.022
psi/ft
e
=
916
+
(0.6084)(13913
-
1762
-
758)
+(0.022)(1762)+(0.667)(758)
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
=
916+(8442-8392)
Pa
=
966 psi
Important! The pressure cannot be reduced by bleeding mud.
If mud
is
bled from the annulus, the well must be shut in for a
longer period to allow the gas to migrate to the surface.
Fluid
Dynamics
in
Well
Control
239
Now,
the
procedure
must
be
repeated
until
the
influx
is
lubricated
from
the
annulus
and
replaced
by
mud
s*P,
pf
=
53.32,T
(0.6)(966)
”
=
53.3(0.866)(540)
Pf
=
0.023
psi/fi
Now
solving
for
h
,
use
h
=
1,762
feet
Similarly
solving
for
4
:
h,
=
758
feet
240
Advanced
Blowout
and
Well
Control
Determine
the
margin
for pressure increase
at
the casing
shoe
using Equation
5.10,
which
is
Equation
5.1
modified
for inclusion
of kill mud,
p,
:
pshw
=
0.023( 1762)
+
966
+
0.6087
(12097- 1762
-
758)
+
(0.052)(12.8)(758)
pShm
=
7339
psi
The
maximum
permissible pressure at
shoe,
pfim,
from
Equation
5.2
is equal
to
8492
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:
Ut
=
8492
-
7339
Ut
=
1153
psi
The volume of the kill-weight mud,
5,
with density,
p,,
to
achieve
is given by Equations
5.4
and
5.5:
FIuidDynamics
in
Well
Control
241
0.667(46.5)
-k
0.0264(966+
1
153)
2(0.667)
x,
=
X,
=
65.185
r
1
153(0.0264)(46.5)
d
0.667
1
&
=
65.185
65.185’
-
-1
=
19.1
bbls
Determine
the
effect
of
pumping
19
bbls
of
kill
mud
with
density
p,
=
12.8
ppg.
The
resulting additional
hydrostatic,
Myd,
is
Myd
=
(O.O52Xp,
-
AH’
=
(0.052)(12.8)
-
(0.
AHyd
=
480
psi
Additional
surface
pressure
resulting
from compressing
the
bubble
at
the
surface
with
19
bbls
of
kill
mud
is
242
Advanced
Blowout
and Well
Control
(966)(46.5)
P2
=
(46.5- 19)
=
1633
psi
Additional surface pressure,
us,
is given
as
Ms
=
1633
-
966
Ms
=
667
psi
Total
pressure increase,
MmtaI,
is
given by Equation
5.8:
MtotaI
=
480+667
Mhtd
=
1147
psi
Since
Dhm,
is less
than
the maximum permissible pressure
increase,
4,
calculated using Equation
5.3,
pump
19
bbls
of
12.8-ppg mud at
1
bpm
and
shut in
to
permit the gas to migrate to
the surface.
Observe initial
P2
after pumping
=
1550
psi.
Fluid
Dynamics
in
Well
Control
243
Observe 2-hour shut-in
Pz
=
1633 psi.
The
surface pressure,
Pa,
may now be reduced by bleeding
ONLY
GAS
from
.pZ
to
P,,,
=
966
-
480
Prima
=486psi
However,
the
new surfice pressure must
be
used to determine
the
effiive
hydrostatic
pressure at 13,913
feet
to ensure no
additional influx.
The bottomhole pressure is given by Equation 5.9:
46.5
-
19
h=
0.0264
h
=
1,042
feet
244
Advanced
Blowout
and
Well
Control
4
=
1,477
feet
(0.6)(486)
”
=
(53.3)(0.930)(540)
Pf
=
0.011
psi/ft
pb
=
486+(0.6084)(13913-1042- 1477)
+
(0.01 1)(1042)
+
(0.667)(1477)
pb
=8415psi
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
P,
=
486
+
(8442
-
84
15)
Pa
=
513 psi
The surface pressure must be bled to only 513 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
245
If the well begins to flow mud from the annulus, it must
be
shut in until the
gas
and mud separate.
Again,
the procedure
must
be repeated:
s*P,
pf
=
53.3zsT,
(0.6)(
5
13)
Pf
=
5
3.3(
0.926)
(540)
Pf
=
0.012
psi/&
Now
solving
for
h
,
use
46.5
-
19.0
h=
0.0264
h
=l,042feet
Similarly
solving
for
h,
:
39
0.0264
4
=-