U.S. patent number RE29,638 [Application Number 05/707,798] was granted by the patent office on 1978-05-23 for pressure controlled test valve system for offshore wells.
This patent grant is currently assigned to Schlumberger Technology Corporation. Invention is credited to Benjamin P. Nutter.
United States Patent |
RE29,638 |
Nutter |
May 23, 1978 |
Pressure controlled test valve system for offshore wells
Abstract
Methods and apparatus for performing a drill stem test of an
offshore well utilizing a pressure controlled test valve. The test
valve includes a valve element having a transverse pressure area
with the high pressure side exposed to the pressure of fluids in
the well annulus and the low pressure side subject to the pressure
of a compressible fluid medium contained within a chamber in the
test valve. The pressure in the chamber is equalized with the
hydrostatic head of the well fluids so that at test depth the same
pressure is acting on both sides of the transverse pressure area,
whereupon this pressure is confined within the chamber. Then a
fluid pressure in excess of the hydrostatic head is applied to the
well fluids externally of the test valve to develop a pressure
difference across the valve element which causes it to shift from
closed to open position.
Inventors: |
Nutter; Benjamin P. (Bellville,
TX) |
Assignee: |
Schlumberger Technology
Corporation (New York, NY)
|
Family
ID: |
26894895 |
Appl.
No.: |
05/707,798 |
Filed: |
July 22, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
199554 |
Nov 17, 1971 |
03824850 |
Jul 23, 1974 |
|
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Current U.S.
Class: |
73/152.19;
166/128; 73/152.38 |
Current CPC
Class: |
E21B
34/10 (20130101); E21B 49/08 (20130101) |
Current International
Class: |
E21B
34/10 (20060101); E21B 34/00 (20060101); E21B
49/08 (20060101); E21B 49/00 (20060101); E21B
047/00 () |
Field of
Search: |
;73/151,152,155
;166/126,128,148,151 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myracle; Jerry W.
Attorney, Agent or Firm: Moseley; David L. Sherman; William
R. Moore; Stewart F.
Claims
I claim:
1. A fluid pressure controlled well tester apparatus comprising:
housing means adapted for connection to a pipe string and having a
flow passage extending therethrough for conducting formation fluids
from an isolated formation interval; valve means movable from a
position closing said flow passage to a position opening said flow
passage in response to a change in the pressure of fluids in the
well annulus externally of said housing means; chamber means
containing a compressible fluid medium, said valve means having a
transverse, pressure area with one side thereof subject to the
pressure of fluids in said well annulus and the other side subject
to the pressure of said fluid medium; means for equalizing the
pressure of said fluid medium with the hydrostatic head of the well
fluids externally of said housing means; and selectively operable
means for closing said equalizing means, so that pressure applied
to the fluids externally of said housing means subsequent to the
closing of said equalizing means can act on said one side of said
pressure area to move said valve means from closed to open
position.
2. The tester apparatus of claim 1 further including biasing means
for continuously urging said valve means toward closed
position.
3. The well tester apparatus of claim 1 wherein said equalizing
means includes a port through which the hydrostatic head of the
well fluids is communicated to said compressible fluid medium, said
closing means including a valve operable in response to
manipulation of said pipe string for closing off said port.
4. The well tester apparatus of claim 1 wherein said valve means
comprises an annular element that is slidable with respect to said
housing means between longitudinally spaced positions, said annular
element having a piston section providing said transverse pressure
area.
5. The well tester apparatus of claim further including a tube that
is concentrically disposed within said housing means, said chamber
means being defined between an inner wall of said housing means and
an outer wall of said tube, said tube providing a portion of said
flow passage.
6. The well tester apparatus of claim 5 further including a
partition movably mounted at one end of said chamber for providing
a separation between said compressible fluid medium and the well
fluids present in said equalizing means and for transmitting the
pressure of the well fluids to said fluid medium.
7. The well tester apparatus of claim 1 further including a
transverse barrier formed in said housing means, a portion of said
flow passage being formed to extend past said barrier, said valve
means being movably disposed adjacent to said barrier.
8. The well tester apparatus of claim 7 wherein said barrier is
provided by an annular member having a closed upper end and flow
ports extending laterally through the wall thereof, said valve
means being movably received within said annular member and having
a valve head that engages a valve seat located on said annular
member below said flow ports, disengagement of said valve head and
valve seat enabling fluid flow through said flow ports and past
said barrier.
9. The well tester apparatus of claim 7 further including a flow
tube disposed longitudinally of said housing means, said barrier
being formed intermediate the ends of said flow tube, said flow
tube having transverse flow ports extending through the wall
thereof above and below said barrier, said valve means being
constituted by an annular sleeve member that is slidably disposed
on said flow tube adjacent said barrier for movement between one
position closing off said flow ports and another position enabling
communication between said flow ports.
10. A well tester apparatus comprising: upper and lower housing
members adapted to be connected in a pipe string, said housing
members each having a flow passage extending upwardly therein;
pressure responsive first valve means in said upper housing and
movable between positions for opening and closing said flow
passages; chamber means containing a compressible fluid medium,
said first valve means having a transverse pressure area with one
side thereof subject to the pressure of fluids in the well annulus
externally of said upper housing member and the other side thereof
subject to the pressure of said fluid medium; port means for
applying the hydrostatic head of well fluids to said fluid medium
as the apparatus is lowered into a well bore to equalize the
pressures acting on said sides of said transverse pressure area;
and second valve means operable in response to downward movement of
said upper housing member with respect to said lower housing member
for closing off said port means to trap a value of pressure in said
chamber means substantially equal to said hydrostatic head, so that
pressure applied to the fluids externally of said housing members
subsequent to the closing of said port means by said second valve
means can act to develop a pressure differential across said
transverse pressure area to move said first valve means from closed
to open position.
11. The well tester apparatus of claim 10 further including third
valve means operable in response to vertical movement of said upper
housing member with respect to said lower housing member for
opening and closing said flow passage in said lower housing
member.
12. The well tester apparatus of claim 10 further including spring
means for continuously urging said first valve means toward closed
position, and functioning to return said first valve means from
open to closed position upon the release of pressure applied to the
fluids externally of said housing members.
13. The well tester apparatus of claim 10 wherein said first valve
means comprises a tubular mandrel open from one end to the other
and having a piston section presenting said transverse pressure
area, said valve mandrel having further transverse cross-sectional
areas sized so that the pressure of fluids within said flow
passages act with equal force in opposite longitudinal
directions.
14. The well tester of claim 13 further including a barrier sleeve
within said first housing member, said barrier sleeve having a
closed upper end and flow ports through the side walls thereof, an
upper portion of said tubular mandrel being sealingly and slidably
received within said barrier sleeve and having a valve head that is
coengageable with a valve seat on said upper housing member below
said flow ports.
15. The well tester apparatus of claim 14 further including a
second valve head on said tubular mandrel below said first
mentioned valve head, said second valve head being coengageable
with a second valve seat on said upper housing member, the annular
space externally of said tubular mandrel between said valve seats
defining a flow-through sample chamber adapted to confine a sample
of formation fluids upon simultaneous engagement of said valve
heads with said valve seats.
16. The well tester apparatus of claim 10 wherein said compressible
fluid medium is nitrogen gas, and further including a movable
partition sealingly received at one end of said chamber means for
providing separation between said nitrogen gas and the well fluids
entering said port means, said partition additionally functioning
to transmit the hydrostatic head of the well fluids to said
compressible fluid medium.
17. The well tester apparatus of claim 16 wherein said port means
opens outwardly to the well annulus intermediate the ends of a
reduced diameter section of the lower end portion of said upper
housing member, said second valve means being formed in part by a
valve seat inside the upper end of said lower housing member
adapted to receive said reduced diameter section.
18. A pressure controlled well tester apparatus comprising: an
elongated tubular housing member adapted for connection to a pipe
string and to be lowered into a fluid filled well bore; said
housing member having at its upper portion an internal annular
valve seat; barrier means located above said valve seat, said
barrier means being an annular member with a closed upper end and
having flow ports extending laterally through the wall thereof; a
valve mandrel having its upper end portion slidably received within
said barrier means and including an annular valve head engageable
with said valve seat to prohibit fluid flow through said flow
ports; said valve member being movable downwardly to a position
where said valve head is disengaged from said valve seat to enable
fluid flow through said flow ports; said valve mandrel having a
piston section that is sealingly slidable with respect to said
housing member and provides a transverse pressure area with an
upper side and a lower side; first port means for subjecting the
upper side of said piston section to the pressure of fluids in the
well annulus externally of said housing member; spring means
pressing upwardly on the lower side of said piston section; a
chamber of substantial volume defined between an inner wall of said
housing member and the outer wall of a flow tube concentrically
disposed within said housing member, said chamber containing a
compressible fluid medium, the lower side of said piston section
being subjected to the pressure of said fluid medium; second port
means for applying the hydrostatic head of the well fluids
externally of said housing member to said compressible fluid medium
so that pressure of said fluid medium is substantially equal to
said hydrostatic head; and a valve selectively operable at test
depth for closing off said second port means, so that pressure
applied to the well fluids externally of said housing can act via
said first port means on said upper side of said piston section to
develop a pressure difference thereacross and force said valve
mandrel downwardly to a position where said valve head is
disengaged from said valve seat.
19. The well tester apparatus of claim 18 further including a
second valve seat on said housing member and a second valve head on
said valve mandrel located below said first mentioned valve head
and seat, the space between said housing member and said valve
mandrel and between said valve seats providing a flow through
sample chamber adapted to trap a sample of formation fluids when
said valve heads are simultaneously engaged with said valve
seats.
20. The well tester apparatus of claim 19 further including
separable coupling means in said housing member below said lower
valve seat and in said valve mandrel below said lower valve head,
separation of said coupling means enabling that portion of the
apparatus defining the sample chamber to be disconnected from the
balance of the apparatus.
21. The well tester apparatus of claim 18 wherein said second port
means extends between the lower end of said chamber and a side
opening in the wall of reduced diameter lower section of said
housing member, said lower section being adapted for telescopic
reception within the upper end of a second housing member located
therebelow, said second housing member having an inner wall surface
adapted to span and close off said side opening.
22. The well tester apparatus of claim 21 further including a
movable partition sealingly received in the lower end of said
chamber and functioning to separate said compressible fluid medium
from the well fluids entering said second port means and to
transmit the hydrostatic head of said well fluids to said fluid
medium.
23. A pressure controlled well tester apparatus comprising: an
elongated housing member having a flow tube disposed concentrically
therein, said flow tube having a transverse barrier intermediate
the ends thereof; port means through the wall of said flow tube
above and below said barrier, said port means and the bores in said
flow tube extending respectively above and below said barrier
providing a flow passage; sleeve valve means slidable on said flow
tube adjacent said barrier between a closed position blocking
communication between said port means and an open position
permitting communication between said port means; chamber means
within said housing member and containing a compressible fluid
medium, a portion of said sleeve valve means providing a piston
section having a transverse pressure area with one side subject to
the pressure of fluids in the well annulus externally of said
housing member and the opposite side subject to the pressure of
said fluid medium; a pressure transmitting channel for applying the
hydrostatic head of the fluids in a well bore to said fluid medium
as the apparatus is lowered into a well bore so that substantially
the same fluid pressure acts on both sides of said transverse
pressure area; and a valve structure operable at test depth for
closing off said channel to trap the hydrostatic head of the well
fluids within said chamber means, so that pressure applied to the
well fluids externally of said housing member subsequent to the
closing of said channel by said valve structure can act on said one
side of said pressure area and develop a pressure differential
thereacross to move said sleeve valve means from closed to open
position.
24. The well tester apparatus of claim 23 further including spring
means pressing between one end of said sleeve valve means and an
outwardly directed shoulder on said flow tube for continuously
urging said sleeve valve means toward closed position.
25. The well tester apparatus of claim 24 wherein said sleeve valve
means comprises a sleeve member having an internal recess for
communicating said port means with one another in the open position
of said valve means and a valve head section for closing off at
least one of said port means in the closed position of said valve
means.
26. The well tester apparatus of claim 24 wherein said chamber
means is located within said housing member above said sleeve valve
means, said spring means being located within said chamber means,
and further including a movable partition at the upper end of said
chamber means for transmitting the pressure of fluids in said
channel to said fluid medium.
27. The well tester apparatus of claim 23 wherein said valve
structure includes an annular member adapted for connection to a
pipe string and telescopically received over an upper reduced
diameter section of said housing member, said pressure transmitting
channel having an opening to the exterior of said housing member
intermediate the ends of said reduced diameter section, said
annular member being selectively movable with respect to said
section to a position closing off said opening.
28. A method of operating a test valve that is positioned in a
fluid-filled well bore in order selectively to conduct fluids from
an isolated formation interval, said test valve including a
normally closed valve element having pressure responsive areas one
of which is subject to the pressure of fluids in the well bore
externally of said test valve and the other of which is subject to
the pressure of a compressible fluid medium contained within a
chamber in said test valve, comprising the steps of: equalizing the
pressure of said fluid medium with the hydrostatic head of the well
fluids externally of said test valve to establish within said
chamber a value of pressure peculiar to the depth of the well bore
where said test valve is positioned; closing said chamber to
confine therein said value of pressure; and then while maintaining
said chamber in a closed condition, moving the valve element from
said normally closed position to an open position by applying
pressure to the well bore at the surface to increase the pressure
of the well fluids externally of said test valve to a value in
excess of the value of pressure confined within said chamber, the
difference in pressure acting across said areas to develop a force
that is effective to move said valve element to said open position
to permit a flow of formation fluids from said isolated formation
interval through said test valve.
29. The method of claim 28 including the further steps of releasing
the increase in pressure and returning the valve element from open
position to closed position while continuing to maintain said
chamber in a closed condition.
30. The method of claim 28 including the further steps of
precharging the chamber containing said fluid medium to an intial
pressure that is less than the hydrostatic head of the well fluids
at test depth, and then lowering the test valve into the well
bore.
31. The method of claim 30 wherein the precharge pressure is
approximately 500 psi less than the hydrostatic head of the well
fluids at test depth.
32. A method of operating a pressure controlled test valve that is
disposed in a fluid-filled well bore in order selectively to
conduct formation fluids from an isolated formation interval, said
test valve having a normally closed valve element with a transverse
pressure area that is subject on one side to the pressure of fluids
in a well bore and on the other side to the pressure of a
compressible fluid medium contained within a chamber in the test
valve, the application of pressure to said one side shifting the
valve element from closed to open position, comprising the steps
of: charging the chamber containing said fluid medium to an initial
pressure that is less than the hydrostatic head of the well fluids
at test depth; lowering the test valve into the well bore; from the
point in the well bore where the hydrostatic head is equal to the
charge pressure in said chamber on downward to test depth,
equalizing the pressure of said fluid medium with the hydrostatic
head of the well fluids so that the same pressure acts on both
sides of said transverse area; closing the chamber at test depth in
order to confine therein a value of pressure substantially equal to
the hydrostatic head at test depth; and then while maintaining said
chamber in a closed condition, applying pressure to the well fluids
externally of said test valve to increase the external pressure to
a value in excess of said hydrostatic head so that a pressure
difference is developed across said transverse area effective to
shift the valve element from closed to open position, thereby to
permit a flow of formation fluids from an isolated formation
interval. .Iadd. 33. A fluid pressure controlled well apparatus
comprising: housing means adapted to be connected to a pipe string
and having a flow passage extending therethrough for conducting
formation fluids from an isolated formation interval; valve
actuator means including a tubular member defining a portion of
said flow passage and movable with respect to said housing means
between longitudinally spaced positions in response to a change in
the pressure of fluids in the well annulus externally of said
housing means; chamber means for containing a compressible fluid
medium, said tubular member having a transverse pressure area with
one said thereof subject to the pressure of fluids in said well
annulus and the other side thereof subject to the pressure of said
fluid medium; means for equalizing the pressure of said fluid
medium with the pressure of well fluids externally of said housing
means; and selectively operable means for closing said equalizing
means, so that pressure applied to the fluids externally of said
housing means subsequent to the closing of said equalizing means
can act on said one side of said pressure area to move said valve
actuator means from one of said longitudinally spaced positions to
another of said longitudinally spaced positions. .Iaddend. .Iadd.
34. The apparatus of claim 33 further including spring means
reacting between said housing means and said tubular member for
continuously urging said tubular member toward said one
longitudinally spaced position. .Iaddend..Iadd. 35. The apparatus
of claim 34 further including a partition movably mounted at one
end of said chamber means for providing a separation between said
compressible fluid medium and the well fluids present in said
equalizing means and for transmitting the pressure of the well
fluids to said fluid medium. .Iaddend. .Iadd. 36. The apparatus of
claim 33 wherein said tubular member has an outwardly directed
shoulder defining a piston section which provides said transverse
pressure area, said piston section being sealingly slidable with
respect to said housing means. .Iaddend..Iadd. 37. The apparatus of
claim 33 wherein said equalizing means includes fluid inlet means
through which the pressure of the well fluids is communicated to
said compressible fluid medium, said closing means including a
valve element movable relative to said housing means for opening
and closing said fluid inlet means. .Iaddend. .Iadd. 38. A fluid
pressure controlled well apparatus comprising: housing means
adapted to be connected to a pipe string, said housing means having
an inwardly directed shoulder and cylinder means adjacent said
shoulder; valve actuator means including a tubular mandrel having a
reduced diameter portion sealingly slidable with respect to said
shoulder and an enlarged diameter piston section sealingly slidable
with respect to said cylinder means, said mandrel being movable
with respect to said housing means between longitudinally spaced
positions in response to a change in the pressure of fluids in the
well annulus externally of said housing means; chamber means within
said housing means for containing a compressible fluid medium, said
piston section having one side thereof subject to the pressure of
fluids in said well annulus and the other side thereof subject to
the pressure of said fluid medium; means for transmitting the
pressure of fluids in said well annulus to said compressible fluid
medium whereby said pressure initially acts on both sides of said
piston section; and selectively operable valve means for preventing
transmission of the pressure of fluids in said well annulus to said
compressible fluid medium, so that pressure subsequently applied to
the fluids in the well annulus externally of said housing means can
act on said one side of said piston section to move said tubular
mandrel from one to another of said longitudinally spaced
positions. .Iaddend. .Iadd. 39. The apparatus of claim 38 further
including spring means reacting between said housing means and said
valve actuator means for continuously urging said valve actuator
means toward said one position. .Iaddend..Iadd. 40. The apparatus
of claim 38 wherein said transmitting means includes a partition
movably mounted at one end of said chamber means for providing a
separation between said compressible fluid medium and fluids in
said well annulus. .Iaddend. .Iadd. 41. The apparatus of claim 40
wherein said transmitting means further includes fluid inlet means
through which the pressure of well fluids is communicated to the
interior of said housing means, said valve means including a valve
element movable relative to said housing means for opening and
closing said fluid inlet means. .Iaddend..Iadd. 42. The apparatus
of claim 40 wherein said transmitting means includes a port through
which the pressure of well fluids in said annulus is communicated
to said compressible fluid medium, said valve means including a
valve element that is operable in response to manipulation of the
pipe string for closing off said port. .Iaddend. .Iadd. 43. The
apparatus of claim 38 further including a tube that is
concentrically disposed within said housing means, said chamber
means being defined in part between an inner wall of said housing
means and an outer wall of said tube, said tube providing a portion
of said flow passage. .Iaddend.
Description
This invention relates generally to earth formation testing, and
more particularly to a new and improved method and apparatus for
conducting a drill stem test of an offshore well utilizing a test
valve that is remotely controlled by the application of pressure to
the well fluids at the surface.
To conduct what is commonly known as a drill stem test, a packer
and a tester valve are lowered into a well on a pipe string, and
the packer is set to isolate the formation interval to be tested
from the hydrostatic pressure of fluids thereabove. The test valve
is then opened and closed to alternately flow and shut-in the
formations, while pressure recorders make a record of the pressures
as a function of time. From the pressure record, many useful
formation parameters or characteristics can be determined. Usually,
a sample of the produced formation fluids is recovered.
For drill stem tests of land based wells, it is typical practice to
provide a test valve that can be opened and closed in response to
manipulation of the pipe string at the surface. The surface
manipulations may either be rotation, longitudinal movement or a
combination of the two. However, for offshore wells, which are
becoming more and numerous as exploration for oil extends to and
beyond the continental shelf, it is generally considered to be
undesirable to have to manipulate the pipe string during a drill
stem test, particularly for tests conducted from a floating rig
that is subject to vertical movement due to the action of waves and
tides. This is because there are certain hazards involved in
manipulating a pipe string that is under pressure, and operators
would prefer to keep the blowout prevents closed against the pipe
string at all times during a test. All such precautions are taken,
of course, to the view of eliminating the causes which might lead
to a fire or blowout with the consequent loss of highly expensive
drilling equipment, and to pollution of the waters.
For drill stem testing in the offshore environment, a test system
has been developed which does not require pipe manipulation for
operation, but rather includes a test valve that moves between open
and closed positions in response to the application and release of
pressure to the well annulus between the pipe string and the well
bore wall. This system utilizes a housing with a slidable inner
valve mandrel having a piston with a precharged gas pressure acting
on one side and with the other side exposed to annulus pressures.
To open the valve, applied annulus pressure compresses the gas and
acts to move the valve mandrel to open position. A release of the
applied annulus pressure enables the gas pressure to shift the
valve mandrel back to closed condition. However, the principle
disadvantage of this approach is that the gas must be precharged at
the surface to a value that will maintain the valve mandrel in
closed condition during lowering into the well. This is because the
hydrostatic pressure increases with depth, and of course the
pressure is tending to force the valve mandrel to open position.
Accordingly, extensive calculations are necessary in preparation
for a test to determine the gas pressure required for precharging
the tool. A large amount of well data is needed including mud
weight, testing depth, and temperature at that depth. Corrections
must be calculated for temperature difference due to precharging
the gas at the surface. All of this is quite burdensome and is
based upon data which is not always available.
It is the principle object of this invention to provide a new and
improved drill stem testing system that can be operated by applied
annulus pressures and without the necessity for a critical gas
precharge and the elaborate surface calculations required in the
prior art.
This and other objects are attained in accordance with the concepts
of the present invention which from a method or process standpoint
comprises the steps of lowering into a fluid-filled well bore and
to test depth a pressure controlled test valve including a valve
element with a transverse pressure area that is subject on one side
to the pressure of the fluids in the well bore and on the other
side to the pressure of a compressible fluid medium such as
nitrogen gas contained within a chamber in the test valve. As the
test valve is lowered, the pressure of the fluid medium is
equalized with the hydrostatic head of the fluids externally of the
test valve so that the same pressure acts on both sides of the
transverse area of the valve element. Thus the valve element is not
moved at all as the test valve is lowered. At test depth, the
method is further practiced by confining the hydrostatic head of
the well fluids at such depth within the chamber, and then applying
fluid pressure to the well bore at the surface which results in an
excess of fluid pressure at the test valve over and above the
normal hydrostatic head that is confined within the chamber. The
applied pressure acts across the transverse area of the valve
element to move it from its normal position prohibiting fluid flow
from the formations being tested to its open position where the
formation fluds can flow via the test valve into the pipe string
thereabove. To shut-in the formations for the recordal of pressure
build-up information, the applied pressure is released at the
surface and the valve element is returned to the closed position.
Preferably, the chamber containing the compressible fluid medium is
precharged in preparation for lowering into the well to a pressure
that is somewhat less than the hydrostatic pressure expected at
test depth, however the actual precharge pressure valve is not
critical because the pressure in the chamber is balanced with the
hydrostatic head and is maintained at whatever value that may be as
the applied pressure is used to control the valve element.
From an apparatus standpoint, the concepts of the present invention
are attained through the provision of an elongated housing member
adapted for connection to a pipe string and having a flow passage
extending longitudinally therethrough. A valve element is movable
within the housing member between positions closing and opening the
flow passage, and is spring biased toward closed position. The
valve has oppositely facing pressure surfaces that are arranged
such that one face is selectively subjected to the pressure of
fluids externally of the housing body through the medium of a
compressible fluid such as nitrogen gas, while the other face is
always subject to the pressure of fluids externally of the housing
body. Thus during lowering into a fluid filled well bore the valve
is balanced with respect to hydrostatic pressure, and the pressure
of the compressible medium precisely reflects the value of
hydrostatic pressure externally of the housing body.
The compressible medium is contained in a chamber within the
housing member, and the hydrostatic head is applied to the chamber
by way of a pressure channel that is adapted to be closed at test
depth and prior to initiation of the test. Upon closing of the
pressure channel, the hydrostatic pressure value is "memorized" in
the chamber. With the chamber closed, the application of pressure
to the fluid in the annulus will develop a pressure differential
across the oppositely facing pressure surfaces of the valve to
force it against the bias of the spring to open position, and
release of applied pressure will enable the valve to return to
closed position. The displacement volume due to movement of the
valve is proportioned with respect to the volume of the chamber
such that movement of the valve from closed to open position has a
negligible effect on the memorized fluid pressure in the chamber.
Thus the pressure that is applied to the well annulus to operate
the valve is a substantially fixed value for any test depth. The
chamber may be precharged at the surface with a pressure that is
less than the expected hydrostatic pressure of the well fluids at
test depth, however, as previously mentioned this pressure is not
critical and there is no need for any elaborate surface
calculations in this regard.
The present invention has other objects and advantages which will
become more readily apparent in connection with the following
detailed description of preferred embodiments, taken in conjunction
with the appended drawings in which:
FIG. 1 illustrates somewhat schematically a drill stem testing
being conducted in an offshore well from a floating rig;
FIGS. 2A and 2B are detailed cross-sectional views of one
embodiment of the present invention with parts in position for
running into the well and with the control valve closed FIG. 2B
forming a lower continuation of FIG. 2A;
FIG. 3 is a view similar to FIG. 2 except with the parts in the
positions occupied during a portion of a test where the test valve
is open;
FIG. 4 is a detailed cross-sectional view of a releasable
connection between the upper and lower sections of the test valve
assembly shown in FIGS. 2A and 2B; and
FIGS. 5A and 5B are cross-sectional views to illustrate a second
embodiment of the present invention;
Referring initially to FIG. 1, a drill stem test using equipment
constructed in accordance with the principles of the present
invention is shown being conducted in an offshore well. Although
the well may be open hole, it is usually cased at 10 as shown. A
riser 11 normally extends from a subsea well head assembly 12
upward to the floating drilling rig or vessel 13 which is anchored
or otherwise moored on location. A pipe string 14 extends from the
vessel 13 downward into the well and is used to lower the test
tools to test depth. The pipe string 14 can include a sub sea
control valve assembly 15 of typical design and providing a landing
shoulder 16 that is seated in the well head assembly 12 so that the
pipe string and test tools therebelow are suspended from a fixed
point not subject to vertical motion which the vessel 13
experiences under the influence of wave and tide action. A major
string of pipe 17, such as a suitable length drill pipe, is
connected to a minor string of pipe 18, such as drill collars
having a preselected weight, by a slip joint and safety valve
combination tool 19 of the type disclosed in U.S. Pat. application
Ser. No. 42,372, Kisling, filed June 1, 1970 now U.S. Pat.
3,652,439 and assigned to the assignee of this invention. The lower
end of the minor string 18 may be connected to a reversing valve 20
which is in turn connected to a choke assembly 21, the reversing
valve and choke assembly being conventional items of equipment
whose details form no part of the present invention. Of course the
choke assembly 21 limits the rate of upward flow of formation
fluids during a test, and the reversing valve 20 can be operated in
such a manner as to enable fluids that are produced into the pipe
string during a test to be recovered at the surface before the test
equipment is retrieved.
A pressure controlled test valve 22 that is constructed in
accordance with the principles of this invention is next connected
in the string of tools and will be described in detail herebelow.
The test valve 22 may be coupled to the upper end of a flow control
valve 23 of the type shown in my U.S. Pat. No. 3,308,887, also
assigned to the assignee of this invention, the valve 23 being
operated in response to only vertical motion of the pipe string.
For purposes of isolating the well interval to be tested from the
hydrostatic head of fluids thereabove, a well packer 24 is provided
and includes packing elements 25 to seal off the well bore and
slips 26 to anchor at the proper level above the well interval to
be tested. The packer 24 can be of the type shown in U.S. Pat. No.
3,399,727, McGill, assigned to the assignee of the invention, and
includes an integral fluid bypass arrangement that enables well
fluid to bypass through the packing element 25 during lowering, but
is closed off when the packer is set. The elements 25 seal off the
cross-section of the well bore to isolate the zone to be tested
from the fluid in the annulus thereabove, and of course at the end
of the test the bypass referred to above is opened to equalize
pressure and enable release of the packer 24 and retrieval of the
tools to the surface. Suspended below the packer 24 is a perforated
nipple 27 to enable fluid entry during the test, and of course
suitable pressure recorders 28 are provided to make a record of the
pressures of fluids versus time as the test proceeds. Other typical
equipment such as a safety joint 29 and a jar 30 can be connected
between the control valve 23 and the packer 24 but as shown only
schematically to simplify this disclosure.
In general terms, a formation test amounts to a temporary
completion of the well, in that the isolated formations are allowed
to produce fluids into the pipe string. The formation is then
shut-in and the pressure allowed to bluid up over a period of time.
A record of the pressure build-up curve can be analyzed by known
techniques to determine formation permeability and the initial or
virgin formation pressure, plus other parameters that are
invaluable aids to a reservoir engineer in coming to a decision on
whether to recommend a permanent completion of the well. Several
flow and shut-in pressure records can be obtained for additional
information.
Turning now to FIGS. 2A and 2B, one embodiment of a pressure
operated test valve assembly 22 that is constructed in accordance
with the principles of the present invention will be described. The
valve assembly 22 includes, in general, an upper sampler and valve
section 35 and a lower valve operating section 35'. The sections
are formed by tubular housing member 36 having its upper end
adapted as shown for connection to a pipe string and with its
through bore closed by a barrier 37 located above an annular valve
seat 38. The outer side walls 39 of the barrier 37 are spaced
laterally inwardly with respect to the surrounding internal walls
40 of the adjacent housing section to provide a space 41 for fluid
passage. One or more side ports 42 in the walls of the barrier 37
communicate the bore thereof with the space 41. A vertically
movable valve mandrel 44 has its upper end portion slidably
received within the bore of the barrier 37, and a valve head 45
carries seal elements 46 which engage the valve seat 38 when the
valve mandrel is in its upper or closed position. A second valve
head 47 is provided on the valve mandrel 44 in spaced relation to
the upper valve head 45 and also carries seal elements 48 which
normally engage a lower annular valve seat 49. The annular space 50
surrounding the valve mandrel 44 between the seats 38 and 49
provides a sample chamber for trapping the last flowing sample of
formation fluids as will be described further below. The center
bore 54 of the valve mandrel 44 is open from one end to the other
so that fluid pressures are free to act on the upper end surface 51
thereof, however the uppermost end of the mandrel is sealed with
respect to the barrier 37 by a suitable seal ring 52. One or more
ports 53 extend through the wall of the valve mandrel 44 below the
lower valve head 47 to communicate the bore 54 with the interior of
the housing section below the valve seat 49. The lower end portion
of the housing section 36 has an inwardly directed shoulder 55
through which an intermediate portion of the valve mandrel 44 is
sealingly slidable. Fluid leakage is prohibited by a seal ring
56.
The valve mandrel 44 has a stepped diameter outer wall surface to
provide a piston section 57 whose outer periphery is sealed against
the adjacent cylinder wall 58 by a seal ring 59. A plurality of
ports 60 extend laterally through the wall of the housing 36 below
the shoulder 55 so that the upwardly facing transverse surface 61
of the piston section 57 is subjected to the pressure of fluids in
the well annulus outside the housing. The lower face 62 of the
piston section 57 is engaged by a coil spring 63 whose lower end
rests on an inwardly directed shoulder 64 on the housing 36. The
outer surface of the lower portion 65 of the valve mandrel 44 is
sealed with respect to the shoulder 64 by a seal ring 66.
An elongated chamber 67 of substantial volume is formed in a lower
portion of the housing 36. The chamber 67 is defined between the
outer surface of a tube 70 whose upper end is connected to the
shoulder 64, and the surrounding inner wall surface 71 of the
housing, the lower end of the tube 70 being sealed against the
housing by a suitable seal ring 72. An annular floating piston 73
normally is disposed at the lower end of the chamber 67 and is
provided with internal and external seats 74 and 75. The chamber 67
is adapted to be filled through a suitable valve port (not shown)
with a compressible fluid medium such as nitrogen gas, and a
suitable communication path 76 extends upwardly through the
shoulder 64 so that the pressure of the nitrogen can act upwardly
on the downwardly facing transverse surface 62 of the piston
section 57 on the valve mandrel 44. The interior space 77 of the
housing 36 below the floating piston 73 is placed in communication
with the well annulus by a pressure channel that is constituted by
a vertically extending port 78 which terminates in a side opening
79. Thus it will be readily appreciated that as the tester valve
assembly 22 is lowered into a fluid filled well bore, the
hydrostatic head of the well fluids is communicated by the ports
79, 78 and transmitted by the floating piston 73 to the nitrogen
within the chamber 67. Inasmuch as the upper and lower surfaces 61
and 62 of the piston section 57 can be subjected to the same
pressure, the hydrostatic head of the well fluids does not tend to
move the valve mandrel 44 toward open position. Moreover, the
pressure of any fluids present within the bore 54 of the valve
mandrel 44 acts upwardly on the lower end surface 80 thereof,
downwardly on the upper end surface 51 thereof, and on the lower
transverse surface of the lower valve head 47 via the ports 53. It
can be demonstrated that the fluid pressures are acting with equal
force in opposite longitudinal directions, so that the valve
mandrel 44 is balanced with respect to fluid pressures as the
equipment is lowered to setting depth. This being the case, the
valve mandrel 44 does not move vertically as the hydrostatic head
increases.
The lower end of the housing 36 has a reduced diameter portion 82
which is connected by threads 83 to the mandrel 84 of the flow
control valve assembly 23. The mandrel 84 is telescopically
received within a housing 85 and is movable between extended and
contracted positions with respect thereto. As the equipment is
being lowered into the well, the mandrel 84 is in the extended
position as shown so that the port 79 is open. However, when the
packer 25 is set as will be subsequently described, the mandrel 84
moves downwardly with respect to the housing 85 to a position where
seal rings 86 and 87 located respectively above and below the port
79 engage the inner wall 88 of a counterbore in the housing 85 to
close off the port from communication with the well annulus. In
this manner the hydrostatic head of the well fluids at test depth
is trapped or "memorized" in the chamber 67 and does not change to
any appreciable extent during operation of the valve as will become
more readily apparent herebelow.
The structural details of the flow control valve assembly 23 will
not be set forth at length here since reference may be had to the
aforementioned U.S. Pat. No. 3,308,887. In general, however, the
valve assembly 23 includes an index section 90, a hydraulic delay
section 91 and a valve section 92. The index section 90 has a
sleeve 93 which is mounted for rotation relative to both the
housing 85 and the mandrel 84, and carries an index pin 94 which
engages in an external channel configuration 95 on the mandrel. The
hydraulic delay section 91 is constituted by a metering sleeve 97
that works within a fluid filled chamber 98 and functions to retard
downward movement of the mandrel 84 within the housing 85, but on
the other hand enables free upward movement. The valve section 92
is somewhat similar to that previously described, in that a valve
head 99 on the mandrel 84 engages an annular valve seat 100 to
close off fluid flow past a transverse barrier 101. When the
mandrel 84 moves downwardly, however, a flow path including ports
102 and 103 and the space 104 externally of the mandrel is placed
in communication with the bore 105 of the mandrel above the barrier
101.
In operation, the pressure operated test valve assembly 22 is
prepared at the surface by injecting a charge of nitrogen gas into
the chamber 67 and the chamber can be pressurized to an initial
pressure that is not critical and for most tests should be about
2,500 psi. A guide that can be used is to charge the chamber to a
pressure about 500 psi less than the hydrostatic pressure at test
depth. Of course at the surface and during the initial stages of
descent into the well bore, the nitrogen pressure is well in excess
of the hydrostatic head of the well fluids and thus biases the
valve mandrel 44 in the closed position. The string of tools is
lowered from the vessel 13 into the well casing 10 until the packer
24 is located at the proper point above the formation interval to
be tested. At a location well above the setting point, the
hydrostatic head will have become in excess of the precharge
pressure of the nitrogen within the chamber 67, and when this
occurs the floating piston 73 will begin to move upwardly somewhat
as it transmits the hydrostatic head to the compressible medium
within the chamber. In any event, the valve mandrel 44 remains
stationary because the same pressure is acting on the opposite
sides 61 and 62 of the piston section 57. Due to the fact that the
medium in the chamber 67 is compressible, however, the piston
section 57 can move readily downwardly when a pressure difference
is imposed in a downward direction thereacross.
The length of the minor pipe string 18 is selected to provide the
proper amount of weight to set the packer 24, and the landing sub
16 is located in the major string 17 at the proper spacing such
that when the packer 25 is anchored at setting depth and the string
17 is suspended in the sub sea well head 12, the slip joint 19 is
in its closed or contracted condition to enable the weight of the
minor string 18 to be applied via the test tools to the packer. Of
course this weight compresses and expands the packing elements 25
to seal off the test interval, and moves the tester housing 36 and
the mandrel 84 downwardly to cause the control valve 23 to open,
admitting fluids into the interior of the pressure operated test
valve 22. Downward movement of the housing 36 with respect to the
control valve housing 85 positions the housing portion 82 within
the valve seat 88 to close off the port 79 from communication with
the well annulus as shown in FIG. 3. The result is to trap or
"memorize" the hydrostatic head of fluids within the chamber 67 so
that a substantially constant pressure acts upon the lower surface
62 of the piston section 57 at all times during operation of the
tester assembly 22.
With the blowout preventers closed in a typical fashion at the
surface so that the well is completely under control, a formation
test can be conducted without resort to manipulation of the pipe
strings 17 or 18 in the following manner. Fluid pressure is applied
by suitable surface pumps and control lines (not shown) to the well
annulus 106 between the pipe strings 17, 18 and the surrounding
casing 10. The pressure acts through the housing ports 60 on the
upper surface 61 of the piston section 57 of the valve mandrel 44
to force the mandrel downwardly against the bias of the coil spring
63. In a typical example, an applied annulus pressure of 600 psi
will start the valve mandrel 44 moving downwardly, and an applied
pressure of 1,200 psi will cause the valve mandrel 44 to move
completely downwardly to its open position as shown in FIG. 3. In
this position, a fluid flow path is opened upwardly through the
tester assembly so that produced formation fluids can enter the
pipe string 18, the flow path being through the tube 70, the bore
50 of the valve mandrel 44, the lower mandrel and sleeve ports 53
and 53', the sample chamber 50, the upper sleeve ports 42', the
barrier wall ports 42 and the annular space 41 between the barrier
37 and the adjacent housing wall 40. The valve is left open for a
relatively short flow period of time sufficient to draw down the
pressures in the isolated formation interval below the packer 24
and enable connate fluids within the formation to be produced into
the well bore. Then the applied annulus pressure is bled off at the
surface to enable the coil spring 63 to force the valve mandrel 44
upwardly to its closed or shut-in position shown in FIG. 2A. The
valve mandrel 44 is left in closed position for a shut-in period of
time during which the pressure recorders 28 make a record of the
pressure build-up data. If desired, the valve mandrel 44 can be
shifted between closed and open position repetitively by
alternately applying and then releasing fluid pressure in the
annulus 106.
As previously mentioned, the valve mandrel 44 is balanced aganist
any opening movement due to hydrostatic fluid pressures during
running, and the changes in fluid pressure that occur within the
tester assembly 22 during the actual test do not affect the
vertical position of the valve mandrel for the same reasons, that
is, the pressures at any instant act with equal force in opposite
longitudinal directions. Moreover, the parts are sized such that
the volume of the chamber 67 that contains the compressed nitrogen
gas is quite large in relation to the volume of displacement of the
piston section 57 as it moves downwardly against the bias of the
coil spring 63. For example the ratio of the chamber volume to
displacement volume at test depth may be in the order of 100 to 1.
Consequently, there is a negligible increase in pressure within the
chamber 67 as the valve mandrel 44 is shifted downwardly, and for
practical purposes the magnitude of the annulus pressure that is
applied to operate the valve is a function only of the modulus or
rate of the coil spring 63, which is of course quite predictable.
This feature is important because it provides for a substantially
constant value of the applied annulus pressure that is necessry to
operate the valve, without regard to test depth and the hydrostatic
head of the fluids pesent in the well bore at such depth. As a
consequence, there are no elaborate calculations as required in the
prior art for a critical precharge pressure for the nitrogen within
the chamber 67, and the annulus pressure that is applied at the
surface to operate the valve mandrel 44 is always a substantially
constant amount, independent of test depth.
To terminate the test, it is only necessary to lift straight
upwardly on the pipe strings 17 and 18 at the surface, thereby
extending the slip joint 19 causing the control valve 23 to close
as the mandrel 84 moves upwardly. The bypass associated with the
packer 24 is opened to equalize pressures across the packer
elements 25 so that they can retract, which is then accomplished by
further lifting of the packer mandrel. Of course it will be
appreciated that the reversing valve 20 can be operated in a
typical fashion if it is desired to remove the fluids that have
been produced into the pipe string before the tools are recovered
to the surface.
As the housing 36 is elevated with respect to the control valve
housing 85, the ports 79 are exposed to the well annulus, so that
the pressure of the nitrogen within the chamber 67 experiences a
gradual decrease as the hydrostatic head is reduced during
withdrawal of the tools from the well. At the surface the chamber
67 will have the initial precharge pressure. A sample of the last
porton of flowing fluids is trapped within the sample chamber 50
upon simultaneous closure of the valve heads 45 and 47, and can be
removed for inspection and analysis at the surface.
A form of the present invention which enables a readily
accomplished disconnection of the sampler and valve section 35 of
the tester assembly 22 is shown in FIG. 4. The valve mandrel 144 is
constituted by an upper section 120 and a lower section 121 coupled
together by a releasable connection 122. The connection comprises a
sleeve 123 that is longitudinally slotted from its upper end to
provide a plurality of upwardly extending fingers 124 having
internal threads 125 that normally mesh with external threads 126
on the lower end portion of the upper mandrel section 120. In order
to corotatively couple the upper mandrel section 120 to the
surrounding housing 135, a cross-pin 127 extends through elongated,
diagonally opposed slots 128 through the wall of the mandrel
section 120, and the ends of the pin 127 are fixed to the lower end
of the valve seat sleeve 129. The slots 128 are long enough to
enable the valve mandrel to move vertically during pressure
actuation thereof as previously described without interference with
the cross pin 127. The lower section 121 of the valve mandrel 144
is corotatively coupled to the surrounding section 133 of the
housing 136 by a pin 130 which projects into an elongated groove
131 formed in the exterior of the mandrel section 121. Finally the
upper and lower sections 132 and 133 of the housing are joined
together by thread 134.
To disconnect the valve and sampler section 135 from the valve
operator section 136, so that the sample of fluids in the sample
chamber 150 can be taken to a laboratory or the like for inspection
and analysis, the upper housing section 132 is rotated with respect
to the lower housing section 133 to disconnect the thread 134.
Rotation of the housing section 32 causes corresponding rotation of
the upper mandrel section 120 with respect to the lower mandrel
section 121, since the mandrel section 120 is corotatively coupled
to the housing section 132 by the cross pin 127, and since the
lower mandrel section 121 is held stationary by the pin projection
130. The threads 125 and 126 are of the same lead and hand as the
housing threads 134, whereby the members are simultaneously
unthreaded. To reconnect the two sections, it is only necessary
again to thread the two housing sections together. The purpose of
the laterally flexible fingers 124 is to enable a thread slippage
or ratcheting action of the mandrel threads 126 within the sleeve
threads 125 in case these threads are fully engaged before the
housing threads 134 are tightly made up.
Turning now to FIGS. 5A and 5B, a second embodiment of the present
invention is illustrated. In this example, the housing member 200
has a flow tube 201 disposed and fixed concentrically therein, the
flow tube 201 having upper and lower bores 202 and 203 extending
above and below a transverse barrier section 204. Flow ports 205
and 206 extend through the wall of the tube 201 above and below the
barrier 204. An annular valve sleeve 207 is sealingly slidable on
the flow tube 201 adjacent the barrier section 204, and is provided
with an internal annular recess 208 of sufficient length to span
the ports 205 and 206 and place them in communication when the
valve sleeve is in its upper position. In its lower or closed
position as shown in FIG. 5A, the valve sleeve 207 has an upper
portion 210 with seal rings 211 and 212 that function to close off
the ports 205. A lower portion 214 of the valve sleeve 207 has
internal and external seals 215 and 216 which engage respectively
the outer wall 217 of the tube 201 and the inner wall 218 on an
inwardly thickened portion 219 of the housing 200 to provide an
annular piston effect. The lower transverse face of the piston 214
is placed in communication with the well annulus by one or more
ports 220 that extand through the wall of the housing 200.
A coil spring 222 surrounds the flow tube 201 and has its lower end
pressing downwardly against the upper end of the valve sleeve 207,
and its upper end engaging an outwardly directed shoulder 223 on
the flow tube 201. Of course the spring 22 forces the valve sleeve
207 toward its lower or closed position. The annular cavity 224
between the flow tube 201 and the housing 200 provides a large
volume chamber that is, as in the case of the first embodiment,
filled with a compressible fluid medium such as nitrogen by way of
a valved port (not shown). An annular floating piston 225 having
inner and outer seal rings 226 and 227 segregates the upper end of
the chamber 224 from a hydrostatic pressure input channel 228 which
terminates in a side port 229.
A valve assembly 230 for trapping the hydrostatic pressure of the
well fluids within the chamber 224 is comprised of an outer member
231 adapted by threads 232 for connection in the pipe string and
telescopically disposed over an inner member 233 that is provided
by a reduced diameter upper section of the housing 200. The members
231 and 233 are coupled together by coengaging splines 234 and 235,
the inner spline grooves having circumferential offsets at their
upper portions which are engaged by the outer spline ribs 234 to
prevent downward relative movement of the outer member 231 during
running. The lower portion 236 of the outer member 231 has upper
and lower seal rings 237 and 238, and can span and seal off the
side port 229 when the outer member is rotated a part turn to the
right and then lowered with respect to the inner member 233 as
shown in FIG. 5B.
The operation of the above-described device is essentially similar
to the embodiment shown in FIGS. 2A and 2B in that the valve is
prepared for use by injecting a precharge of nitrogen gas into the
chamber 224. The gas pressure and the force of the coil spring 22
maintain the valve sleeve 207 in its lower or closed position.
Inasmuch as the seal rings 211, 212 and 215 are all engaging the
same seal diameter of the flow tube 201, the valve sleeve is
balanced with respect to the pressures of fluids within the flow
tube. Moreover, during lowering the hydrostatic head of fluids is
transmitted via the ports 229 and 228 and the floating piston 225
to the chamber 224 and is offset or balanced by the same pressure
acting through the annulus ports 226 over the same cross-sectional
area of the piston 214. As a consequence, the valve sleeve 207 is
completely balanced and does not tend to move vertically as the
apparatus is lowered into a fluid filled well bore.
A test depth the packer is set as previously described, and the
pipe string is manipulated to cause the outer member 231 to
telescope downwardly with respect to the inner member 233, closing
off the port 229 and trapping or memorizing the hydrostatic head
within the chamber 224. Pressure is applied to the annulus to open
the valve and acts through the annulus ports 220 on the lower end
surface of the piston 24, shifting the valve sleeve upwardly
against the bias of the coil spring 22 to open position where the
ports 205 and 206 are in communication via the valve sleeve recess
208 as shown in FIG. 2B. Hereagain, the volume of the chamber 224
is quite large in relation to the displacement volume due to
movement of the valve sleeve 207, so that there is practically no
increase in pressure within the chamber 224 as the valve sleeve
moves upwardly. To close the valve, the applied annulus pressure is
bled off, enabling the coil spring 222 assisted by gas pressure to
force the valve sleeve 207 downwardly to its closed position as
shown in FIG. 5A.
It will now be apparent that a new and improved pressure controlled
tester valve has been disclosed, the valve being operable in
response to a substantially fixed value of applied annulus pressure
without regard to test depth. The valve element is balanced with
respect to hydrostatic pressure in the well bore, so that neither
elaborate calculations nor myriads of well data are necessary for
successful operation of the tester valve.
Since certain changes or modifications may be made in the disclosed
embodiments without departing from the inventive concepts involved,
it is the aim of the appended claims to cover all such changes or
modifications falling within the true spirit and scope of the
present invention.
* * * * *