Grace Robert. Advanced Blowout and Well Control
Подождите немного. Документ загружается.
276
Advanced
Blowout
and
Well
Control
4ll
fr
=
112.36
3
P
A
=
0.1305
ft2
t3
q
=
0.5307
f
L
sec
q
=5.7bbVmin
The foregoing example
is
only
one simple example
of
the use of
the Momentum
Kill
technology. The momentum
of
the wellbore fluids
is
more difficult to calculate when
in
multiphase
flow.
However, the
momentum
of
each
component
of
the
flow
stream
is
calculated
and
the
total momentum
is
the
sum
of
the momentum
of
each component.
FIuid
Llynarnics
in
Well
Control
277
References
1.
Grace,
Robert
D., "Fluid Dynamics Kill Wyoming Icicle." World Oil,
April
1987,
page
45.
2.
Blount, E.
M.
and Soeiinah, E., "Dynamic Kill: Controlling Wild
Wells a
New
Way," World
Oil,
October
1981,
page
109.
3.
Kouba,
G.
E., et al. "Advancements in Dynamic Kill Calculations for
Blowout Wells," SPE DrillinP and Comdetion,
September
1993,
page
189.
4.
Courtesy
of
P.
D.
Storts and Williford Energy.
5.
Orkiszewski,
J.,
"Predicting Two-Phase Pressure Drops in Vertical
Pipe,"
Journal
of
Petroleum Technolopv,
June
1967,
page
829.
CHAPTER
SIX
SPECIAL SERVICES
IN
WELL CONTROL
SNUBBING
Snubbing is the process of running or pulling tubing, drillpipe or
other tubulars in the presence
of
sufficient surface pressure present to
cause the tubular to be forced out of the hole.
That
is,
in
snubbing the
force due to formation pressure’s acting to eject the tubular exceeds the
buoyed weight of the tubular.
As
illustrated in Figure
6.1
,
the well force,
F,,
is greater than the weight of the pipe. The well force,
F,,
is a
combination of the pressure force, buoyant force and friction force.
Stripping is similar
to
snubbing in that the tubular is being
run
into or pulled out
of
the hole under pressure; however, in stripping
operations the force resulting from the surfixe pressure is insufficient to
overcome the weight of the
string
and force the tubular out
of
the hole
(Figure
6.2).
Snubbing or stripping operations through rams can be performed
at any pressure. Snubbing or stripping operations through
a
good quality
annular preventer are generally limited
to
pressures less
than
2000 psi.
Operations conducted through a stripper rubber or rotating head should be
limited to pressures less than
250 psi. Although slower, ram-to-ram is the
safest procedure for conducting operations under pressure.
Some of the more cormnon snubbing applications are
as
follows:
Tripping tubulars under pressure
Pressure controVwel1 killing operations
0
Completion operations under pressure
Fishing, milling or drilling under pressure
278
Special Services
in
Well
Control
279
:Ai
M
iiM
:I:
u
iiu
..
iR:
D
::D
i
wpi
iJ.:
..
‘...
.-*
+
Fw
MUD
u
Wp
<
Fw
Where:
Fw
-
Ff
+
PsAcs
+
Fb
Wp
-
Nomind
pipe
weight.
Ib/ft
I
M
M
:R:
u
i:u
D
..
’.....’
.p
Fw
MUD
u
PIA
+
Fb
Ff
-
Fw
(
WpL
Figure
ti2
-
Stnpping
There are some significant advantages to snubbing operations.
Snubbing may be the only option in critical well control operations. In
general,
high
pressure operations are conducted more safely. For
completion operations, the procedures can be performed without kill
fluids, thereby eliminating the potential for formation damage.
There are, however, some disadvantages and risks associated
with
snubbing. Usually,
the
procedures and operations are more complex.
Snubbing
is
slower than stripping or conventional tripping.
Finally,
during snubbing
operations
there
is
always
pressure
and
usually
gas at
the
surface.
280
Advanced
Blowout
and
Well
Control
EQUIPMENT
AND
PROCEDURES
The
Snubbing
Stack
There are many acceptable snubbing stack arrangements. The
basic snubbing stack is illustrated in Figure
6.3.
As
illustrated, the
lowermost
rams
are blind safety
rams.
Above the blind safety rams are
the pipe safety
rams.
Above the pipe safety rams is the bottom snubbing
ram, followed by a spacer spool and the upper snubbing
ram.
Since a
ram
preventer should not be operated with
a
pressure differential across the
ram,
an
equalizing loop is required
to
equalize the pressure across the
snubbing rams during the snubbing operation. The pipe safety ram are
used only when the snubbing
rams
become worn and require changing.
When
a
snubbing
ram
begins
to
leak, the upper safety
ram is closed and the pressure
above the upper safkty ram is
released through the bleed-off
line. The snubbing ram is then
repaired. The pump in line
can
be used to equalize the pressure
across the safkty
ram
and the
snubbing operation continued.
Since all rams hold pressure
from below,
an
inverted ram
must be included below the stack
if the snubbing
stack
is
to
be
tested
to
pressures greater
than
well pressure.
The
Snubbing
nocedure
The snubbing procedure
is illustrated beginning
with
Figure 6.4.
As
illustrated
in
Figure 6.4 when snubbing into
the
hole,
the tool
joint
or
~~ ~
Figure
63
-
Basic
Snubbing
Stack
connection is above the uppermost snubbing
ram
which is closed.
Therefore, the well pressure
is
confined
below the upper snubbing ram.
Special Services in Well Control
281
Figure
44
-
Snubbing into
the
hole
When the tool joint reachcs
the upper snubbing ram, the
lower snubbing ram and
equalizing loop are closed,
which confines the well
pressure below the lower
snubbing ram. The pressure
above the lower snubbing
ram
is released through the bleed-
off
line as
shown
in
Figure
6.5.
After the pressure
is released above the lower
snubbing ram, the upper
snubbing ram is opened, the
blecd-off line is closed and the
connection
is
lowered to
a
position immediately above
the
closed lower snubbing
ram
as
illustrated
in
Figure
6.6.
The upper snubbing ram
is then closed and the
equalizing loop is opened,
which equalizes the pressure
across the lower snubbing
ram (Figure
6.7).
The lower
snubbing ram is then opened
and the pipe is lowered
through the closed upper
snubbing ram until the next
connection is immediately
above the upper snubbing ram. With the next connection above the upper
snubbing ram, the procedure is repeated.
Snubbing
Equipment
If
a rig is on the hole, it can be used to snub the pipe into the hole.
The rig-assisted snubbing equipment is illustrated in Figure
6.8.
With the
stationary slips released and the traveling slips engaged, the traveling
block
is
raised and the pipe is forced into the hole. At the bottom
of
the
282
stroke, the stationary slips are engaged and the traveling slips
are
released.
The counterbalance weights raise the traveling slips
as
the traveling block
is lowered. At the top
of
the stroke, the traveling slips are engaged, the
stationary slips are released and the procedure is repeated. The
conventional snubbing system moves
the
pipe.
If
drilling operations under
pressure are required,
a
power swivel must
be
included.
Advanced
Blowout
and
Well
Control
Figure
65
-
Snubbing
into the
Hole
Figure
66
-
Snubbing into
the Hole
In
the absence
of
a rig, a hydraulic snubbing
unit
can be used.
A
hydraulic snubbing unit is illustrated in Figure
6.9.
With
a
hydraulic
snubbing unit,
all
work is done from the work basket
with
the hydraulic
Special Services in Well Control
283
system replacing
the
rig.
The
hydraulic system
has
the capability to
circulate
and
rotate for cleaning out
or drilling.
Figure
6
7
-
Snubbing into the Hole
Figure
6
8
-
Conventional
or
Rig
Assisted Snubbing Unit
Theoretical considerations
As
shown
in
Figure
6.1,
snubbing is required
when
the well force,
F,,
exceeds the total weight of the tubular. The snubbing force is equal
to the net upward force
as
illustrated
in
Equation
6.1
and Figure
6.1
:
284
Advanced
Blowout
and
Well
Control
Where:
Wp
=
Nominal
weight of
the
pipe,
#/e
L
=
Length
of pipe, feet
Fr
=
Friction force,
Zbf
FB
=
Buoyant
force,
Zbf
Fwp
=
Well pressure force,
lbf
Figure
6
9
S’cial Services
in
Well
Control
285
The well pressure force,
FV
,
is given by Equation 6.2:
Fv
=
0.7854Dp2P,
(6.2)
Where:
pS
=
Surface
pressure, psi
Dp
=
Outside diameter
of
tubular
exposed
to
P,,
inches
As
shown
in Equation 6.2,
the
diameter
of
the pipe
within
the seal
element must be considered. When running pipe
through
an
annular or
stripper,
the
outside diameter of
the
connection is the determining
variable. When stripping
or
snubbing pipe
from
ram
to
ram, only the pipe
body
is
contained
within
the
seal
elements; therefore, the outside diameter
of
the tube
will
detennine
the
force
required
to
push
the
pipe
into the well.
With
drillpipe, there is
a
significant difference
between
the diameter
of
the
pipe body
and
the tool joint. Example 6.1 illustrates
the
calculation
of
the
wellhead pressure force:
Example
6.
I
Given:
Surface pressure,
Work
string
Pipe
OD,
DP
Connection
OD,
4
=
1500psi
=
4.5
-inch drillpipe
=
4.5
inches
=
6.5 inches
Required:
The well pressure
force
when the
annular
is
closed
on
1. The tube (Figure 6.10)
2.
The
connection (Figure 6.11)