U.S. patent application number 16/110277 was filed with the patent office on 2019-02-28 for device and method for mitigating annular pressure buildup in a wellbore casing annulus.
This patent application is currently assigned to VALLOUREC TUBE-ALLOY, LLC. The applicant listed for this patent is VALLOUREC TUBE-ALLOY, LLC. Invention is credited to Gabriel ROUSSIE.
Application Number | 20190063191 16/110277 |
Document ID | / |
Family ID | 63364119 |
Filed Date | 2019-02-28 |
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United States Patent
Application |
20190063191 |
Kind Code |
A1 |
ROUSSIE; Gabriel |
February 28, 2019 |
DEVICE AND METHOD FOR MITIGATING ANNULAR PRESSURE BUILDUP IN A
WELLBORE CASING ANNULUS
Abstract
A device and method are provided for mitigating annular pressure
buildup in a wellbore casing annulus of an oil or gas well. The
device includes a tubular member including an outer side, a chamber
secured around the outer side, the chamber having at least one
flexible portion for varying the internal volume of the chamber, at
least one reservoir capable of supplying a gas, and a pressure
compensator connecting the reservoir and the chamber. The reservoir
is able to feed the chamber volume with the gas via the pressure
compensator.
Inventors: |
ROUSSIE; Gabriel;
(Sugarland, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VALLOUREC TUBE-ALLOY, LLC |
Houston |
TX |
US |
|
|
Assignee: |
VALLOUREC TUBE-ALLOY, LLC
Houston
TX
|
Family ID: |
63364119 |
Appl. No.: |
16/110277 |
Filed: |
August 23, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62549315 |
Aug 23, 2017 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 34/063 20130101;
E21B 34/06 20130101; E21B 33/00 20130101; E21B 41/00 20130101 |
International
Class: |
E21B 41/00 20060101
E21B041/00; E21B 34/06 20060101 E21B034/06 |
Claims
1. A device for mitigating annular pressure buildup in a wellbore
casing annulus of an oil or gas well, comprising: a tubular member
comprising an outer side, a chamber secured around said outer side,
said chamber having at least one flexible portion for varying the
internal volume of the chamber, at least one reservoir capable of
supplying a gas, a pressure compensator connecting said at least
one reservoir and said chamber, and wherein said at least one
reservoir is able to feed said chamber with said gas via the
pressure compensator.
2. A device for mitigating annular pressure buildup according to
claim 1, wherein said chamber comprises an envelope disposed around
said outer side, said outer side and said envelope forming said
chamber, and wherein said envelope comprises said at least one
flexible portion.
3. A device for mitigating annular pressure buildup according to
claim 2, wherein said envelope includes a first flange and a second
flange, said flanges being arranged at a distance from one another
along said tubular member, and wherein said flexible portion is an
elastic membrane that is disposed radially around said outer side,
that extends axially along the tubular member and that is fastened
at its axial extremities to said two flanges.
4. A device for mitigating annular pressure buildup according to
claim 3, wherein said elastic membrane is configured to produce a
uniform rise or decrease of said chamber volume.
5. A device for mitigating annular pressure buildup according to
claim 3, wherein said elastic membrane is transversally or
longitudinally lobe-shaped.
6. A device for mitigating annular pressure buildup according to
claim 3, wherein said flanges and said elastic membrane are made of
steel.
7. A device for mitigating annular pressure buildup according to
claim 3, wherein said tubular member comprises reinforcement and
holding means fastening said elastic membrane.
8. A device for mitigating annular pressure buildup according to
claim 1, wherein said chamber includes at least one tube, wherein
said tube comprises said at least one flexible portion.
9. A device for mitigating annular pressure buildup according to
claim 8, wherein said one or more tubes are straight tubes arranged
parallel to said tubular member or tubes wound around said tubular
member.
10. A device for mitigating annular pressure buildup according to
claim 1, wherein said pressure compensator allows gas to flow from
said at least one reservoir to said chamber when said external
pressure increases.
11. A device for mitigating annular pressure buildup according to
claim 1, wherein said pressure compensator is an air pressure
regulator adapted to high pressure.
12. A device for mitigating annular pressure buildup according to
claim 1, wherein said reservoir is selected from bottles, cylinders
or any other recipients suitable for containing gas under
pressure.
13. A device for mitigating annular pressure buildup according to
claim 1, wherein said at least one reservoir is a cryogenic storage
dewar.
14. A device for mitigating annular pressure buildup according to
claim 1, wherein said chamber comprises a burst disk to vent supply
gas when the pressure prevailing in the chamber exceeds a
predetermined limit.
15. A device for mitigating annular pressure buildup according to
claim 1, wherein the said tubular member is a casing tube.
16. A method of mitigating pressure buildup within a wellbore
casing annulus of an oil or gas well, wherein said method
comprises: providing at the ground level a device for mitigating
annular pressure buildup according to claim 1, lowering said device
in the wellbore, letting said pressure compensator allow flow of
said gas from the at least one reservoir into the chamber, so as to
at least partially compensate an increase of external pressure due
to the lowering of said device.
17. A method according to claim 16, comprising filling said
reservoir with said gas in pressurized form or in liquid form,
before lowering said device in the wellbore.
18. A method according to claim 17, wherein said gas is inert gas,
such as nitrogen.
19. A method according to claim 16, further comprising filling said
reservoir with a gas generator capable of producing said gas,
before lowering said device in the wellbore.
20. A method according to claim 19, wherein said gas generator is a
propellant and wherein said gas is produced by said propellant.
21. A method according to claim 16, further comprising adjusting
the pressure prevailing in said chamber to a value substantially
equal to ground level pressure before lowering said device in the
wellbore.
22. A method according to claim 16, wherein said pressure
compensator lets said gas flow from the at least one reservoir to
the chamber when the external pressure is above a specified
pressure.
23. A method according to claim 16, wherein said flexible portion
deforms when the pressure difference between the external pressure
and the pressure inside said chamber exceeds a specified value.
Description
[0001] This invention relates generally to mitigation of
temperature-related pressure buildup in the trapped annulus of an
oil or gas well, and specifically to systems and methods for
mitigating such annular pressure buildup, wherein such systems and
methods typically employ production and/or tieback casing having
one or more pressure mitigating chambers.
[0002] Annular Pressure Buildup (APB) is the pressure generated by
the thermal expansion of trapped wellbore fluids as they are
heated. Other terms are also used to describe this occurrence such
as "trapped annular pressure" and "annular fluid expansion."
[0003] Sometimes, a section of formation must be isolated from the
rest of the well with casing to withstand the extreme pressures
prevailing at depth. Casing is run to protect or isolate formations
adjacent to the wellbore. Most land wells and many offshore
platform wells are equipped with wellheads that provide access to
every casing annulus. Any observed pressure increase can be bled
off into atmosphere, thus preventing the damaging effects of
annular pressure buildup from occurring. On the contrary, most
subsea wellhead installations do not have access to each casing
annulus.
[0004] When casing strings are heated by the production of hot
fluid from the lower hotter sections of the wells, the trapped
fluids expand. If one or more annuli are sealed, a steep pressure
increase may result.
[0005] The consequences of an annular pressure buildup without the
benefit of bleed off into atmosphere can lead to collapse the
tubing or rupture the production casing.
[0006] Some methods to mitigate annular pressure buildup have
involved placing of a compressible fluid, such as nitrogen
(N.sub.2), in the trapped annulus during the cement work to limit
the pressure buildup associated with expansion of the trapped fluid
such as described in U.S. Pat. No. 4,109,725. While such methods
can help limiting the pressure in the annulus by liquefying the
compressible fluid, the resulting pressures can still be quite
high.
[0007] Insulating fluid has sometimes been placed in the casing
annuli in an effort to limit the transfer of heat due to convection
from the wellbore to the fluids in the trapped casing annuli.
[0008] In document U.S. Pat. No. 7,096,944, annular pressure
buildup mitigation efforts have involved strapping a compressible
solid material, such as foam or hollow particles, to the outside of
the inner casing string to accommodate expansion of the fluids in
the annulus by effectively increasing the volume in the annulus as
the solid material compresses.
[0009] However, this system is not reversible. If the fluids
contracts when the well cools down, a vacuum is created on the
outside of the casing. Thus, compensation is reduced between
internal and external pressure.
[0010] Another approach described in US 20070114033 for mitigating
annular pressure buildup is to place a fluid or other material such
as methyl methacrylate in the annulus that will shrink when
activated by heat.
[0011] Burst disks also have been employed to act as a pressure
relief means and to allow the heated fluid in the annulus to vent
through the disc. In U.S. Pat. No. 8,066,074, burst disks are used
in combination with expandable chambers comprising pistons along
with highly pressurized neutral gas. However, the pistons have to
be strongly pre-stressed at the surface, which request prudence
during manipulations, and may be unsafe. Moreover, efficiency of
piston chambers is limited by hydrostatic pressure when
deployed.
[0012] Therefore, it is an object of the invention to provide a
device for mitigating annular pressure buildup in a wellbore casing
annulus of an oil or gas well. In one embodiment, the device for
mitigating annular pressure buildup comprises: [0013] a tubular
member comprising an outer side, [0014] a chamber secured around
said outer side,
[0015] wherein [0016] said chamber has at least one flexible
portion for varying the internal volume (V1) of the chamber.
[0017] The chamber is intended to be immersed in an external fluid,
and to be sealed and filled with gas.
[0018] The flexible portion of the chamber may deform under the
effect of the pressure difference between the external pressure
(Pe) and the chamber pressure (P1). The deformation of the flexible
portion accommodates, at least partially, the remaining difference
between external pressure (Pe) and chamber pressure (P1).
Furthermore, when the deformation of the flexible portion is
inward, so that the internal volume (V1) of the chamber diminishes,
the space available in the surrounding annulus increases and the
external pressure decreases.
[0019] In a preferred embodiment, the chamber comprises an envelope
disposed around the outer side of the tubular member and the
envelope comprises the at least one flexible portion. The outer
side of the tubular member and the envelope form said chamber. More
specifically, the envelope covers a portion of the outer side of
the tubular member and the internal volume (V1) of the chamber is
defined by this portion and the envelope.
[0020] In such an embodiment, the envelope may include a first
flange and a second flange and the flanges are arranged at a
distance from one another along the tubular member. The flexible
portion may be an elastic membrane that is disposed radially around
the outer side, that extends axially along the tubular member and
that is fastened at its axial extremities to the two flanges. The
elastic membrane is preferably fastened in a leak-tight manner. The
flanges may be made of steel. Advantageously, the elastic membrane
is configured to produce a uniform rise or decrease of said chamber
volume. In particular, the elastic membrane may have a shape that
is geometrically adapted to achieve this effect.
[0021] Advantageously, the elastic membrane is transversally or
longitudinally lobe-shaped. When the membrane has longitudinal
lobes, the number of said lobes is advantageously between 3 and
10.
[0022] In a preferred embodiment, the elastic membrane is made of
steel.
[0023] The tubular member may comprise reinforcement and holding
means fastening said elastic membrane.
[0024] Optionally or in combination, said chamber may also include
one or more tubes, such as straight tubes arranged parallel to the
tubular member or tubes wound around the tubular member, wherein
said at least one of tubes comprises said at least one flexible
portion.
[0025] The device further comprises: [0026] at least one reservoir
capable of supplying a gas, [0027] a pressure compensator
connecting said at least one reservoir and said chamber, and
[0028] wherein said at least one reservoir is able to feed said
chamber with said gas via the pressure compensator.
[0029] The pressure compensator allows gas to flow from the
reservoir to the chamber when an external pressure (Pe) increases.
Typically, the pressure compensator allows gas to flow into the
chamber when the external pressure is above a specified pressure.
The pressure compensator may be an air pressure regulator adapted
to handle external pressure.
[0030] The reservoir is configured to be filled with said gas or a
generator of said gas.
[0031] The reservoir is capable of supplying a specified quantity
of said gas in use.
[0032] The reservoir is preferable capable of withstanding inner
pressures up to at least 5 ksi (34.5 MPa).
[0033] The reservoir may be a bottle, a cylinder or any other
recipient suitable for containing gas under pressure.
[0034] The gas supplied by the reservoir may be inert gas, such as
nitrogen (N.sub.2).
[0035] In an alternative embodiment, the reservoir is a cryogenic
storage dewar. Such a reservoir is suitable for containing liquid
nitrogen.
[0036] In another alternative embodiment, the reservoir is capable
of containing a gas generator, such as a liquid or solid
propellant.
[0037] The chamber may comprise a burst disk to vent supply gas
when the pressure (P1) prevailing in the chamber exceeds a
predetermined limit.
[0038] The tubular member may be a casing tube, such as a
production or tieback casing tube.
[0039] The external fluid may be brine.
[0040] It is a further object of the invention to provide a method
of mitigating pressure buildup within a wellbore casing annulus of
an oil or gas well. Such a method comprises: [0041] providing at
ground level a device for mitigating annular pressure buildup as
defined above, [0042] preferably adjusting the pressure prevailing
in said chamber to a value substantially equal to ground level
pressure before lowering said device in the wellbore, [0043]
lowering said device in the wellbore, [0044] letting the pressure
compensator allow flow of said gas from the at least one reservoir
into the chamber, so as to at least partially compensate an
increase of external pressure (Pe) due to the lowering of said
device.
[0045] Before lowering the device in the wellbore, the reservoir is
filled with said gas in pressurized form or in liquid form, or with
a gas generator capable of producing said gas.
[0046] Advantageously, the reservoir is filled with said gas or
said gas generator so as to allow the supply of a specified
quantity of said gas in use, preferably at least during
production.
[0047] The gas may be inert gas, such as nitrogen. The gas pressure
in the reservoir is may be between 3 and 6 ksi (20.7 and 41.4 MPa)
when the reservoir is filled with gas under pressure. The gas
pressure is much lower, and may be close to atmospheric pressure,
when the reservoir is a dewar containing liquid inert gas, such as
nitrogen.
[0048] The gas generator may be a propellant and said gas is
produced by said propellant. The propellant may be solid, such as
sodium azide with potassium nitrate or an ammonium perchlorate
composite, or liquid, such as hydrogen peroxide, hydrazine or
nitrous oxide, or any combination thereof. The propellant may
mechanically be activated to release gas during the lowering
operation.
[0049] The pressure prevailing in said chamber at ground level is
deemed to be substantially equal to ground level pressure when it
departs from the latter by less than a factor of 2.
[0050] The device mitigates the increase of external pressure (Pe)
caused by its lowering in the wellbore. This mitigation is obtained
by at least partial compensation of the increase in internal
pressure. The mitigation is more specifically obtained by the flow
of said gas from the reservoir into the chamber that
counter-balances the increase in external pressure.
[0051] Typically, the pressure compensator lets said gas flow from
the reservoir to the chamber when the external pressure increases
above ground level values.
[0052] In a possible embodiment of the invention, the reservoir
initially contains a quantity of gas such that the gas provided by
the reservoir continues to flow from the reservoir to the chamber
during production if the external pressure increases further in the
wellbore casing annulus due to the high temperature reached during
production. In this manner, the device extends the mitigation of
the difference between external pressure and chamber pressure. Some
of the gas contained in the chamber may advantageously be allowed
to flow back in the reservoir if the external pressure increases
even further.
[0053] The compliance and stiffness of the flexible portion are
selected to allow a variation in the internal volume (V1) of the
chamber according to the difference between the pressure (P1)
inside the chamber and the pressure (Pe) outside the chamber.
[0054] The flexible portion deforms when chamber internal pressure
(P1) significantly differs from the external pressure (Pe). Part of
the pressure difference is compensated by the change in internal
volume (V1) resulting from the deformation of the flexible portion
and the remaining pressure difference is mechanically absorbed by
the deformation of the flexible portion.
[0055] The deformation adds a mechanical contribution to the
compensation effect of the gas provided by the reservoir. The
pressure-balancing effect of the gas from the reservoir and the
mechanical pressure-balancing effect of the deformation combine to
mitigate the pressure exerted on said tubular member.
[0056] In a possible embodiment, the flexible portion of the
chamber deforms when the pressure difference between the external
pressure (Pe) and the pressure (P1) inside the chamber exceeds a
specified value.
[0057] When the external pressure increases in the wellbore casing
annulus due to the high temperature reached during production, said
flexible portion deforms to partially balance the difference
between external pressure (Pe) and chamber pressure (P1).
[0058] When the external pressure decreases in the wellbore casing
annulus due to the decrease in temperature reached during
production interruption, said flexible portion deforms again to
partially balance the difference between external pressure (Pe) and
chamber pressure (P1).
[0059] The deformation of said flexible portion is typically
inwards, that is towards the tubular member, when the external
pressure increases and outwards, that is away of the tubular
member, when the external pressure decreases.
[0060] Other advantages and features of the invention will emerge
upon examining the detailed description of embodiments, which are
in no way limiting, and in view of the appended drawings
wherein:
[0061] FIG. 1 is a sectional side view of a wellbore including
crushable foams according to prior art to mitigate annular pressure
buildup,
[0062] FIG. 2 is a side view of a tubular member provided with a
device for mitigating annular pressure buildup according to the
invention,
[0063] FIGS. 3A and 3B are side view and sectional front view,
respectively, of a tubular member and a part of a device according
to one embodiment of the invention, and
[0064] FIG. 4A is a graph of external pressure Pe and external
temperature Te in a wellbore annulus, and chamber pressure P1 and
reservoir inner pressure P2 in a device for mitigating annular
pressure buildup according to the invention, during deployment and
production.
[0065] FIG. 4B is a graph of external pressure Pe in a wellbore
annulus, and chamber volume V1, chamber pressure P1 and reservoir
inner pressure P2 in a device for mitigating annular pressure
buildup according to the invention, during deployment and
production.
[0066] FIG. 1 shows a sectional side view of a wellbore according
to the state of the art having several coaxial annuli. As shown in
FIG. 1, wellbore 1 penetrates subterranean formation 2. Within
wellbore 1, concentrically placed casing strings 30 define annuli
3A, 3B and 3C. The casing strings are made of one or more casing
tubes and are usually much longer than their diameter. Concrete 31
is inserted in the outer annuli 3B and 3C and close them at their
bottom end. A production tubing 4 is inserted in the arrangement of
casing strings. While shown with two concentric annuli, depending
on the length of wellbore 1, any number of concentric annuli may be
present. Annulus 3A, which is defined between the innermost casing
surface and production tubing 4, extends through most of the length
of wellbore 1 and maintains fluid communication with the head of
wellbore 1. Although FIG. 1 shows wellbore 1 as having a vertical
section, it is to be recognized that any wellbore orientation may
be possible.
[0067] In the process of drilling and servicing wellbore 1, fluids,
such as drilling fluid or any fluid from the formation, such as
brine, may accumulate within annuli 3B and 3C.
[0068] Annuli are often sealed at their upper ends as well, thereby
trapping the annular fluid within a confined space. As explained
above, when annuli 3B and 3C are sealed at both their upper and
lower ends, a pressure increase can occur upon the trapped annular
fluid undergoing thermal expansion due to exposure to
high-temperature production fluids. Through this phenomenon, the
accumulated annular fluid can possibly lead to annular pressure
buildup.
[0069] Known pressure-collapsible materials such as hollow spheres
and syntactic foam, shown by the numerical reference 5 in FIG. 1,
can mitigate annular pressure buildup by providing available space
for the annular fluid upon their collapse. Such materials are
limited, however, in that they are only effective for one
pressurization cycle. That is, once they have collapsed in response
to a pressure increase, they are no longer effective to further
mitigate the pressure increase. Additionally, the pressure for
initiating their collapse may be above a threshold pressure at
which casing damage begins to occur. Additionally, when temperature
decreases, trapped fluid volume decreases accordingly. Pressure
will decrease to the point that a vacuum cap may form in place of
the collapsed volume of material. This vacuum may be detrimental to
the well integrity.
[0070] Referring to FIG. 2, a device for mitigating annular
pressure buildup according to a preferred embodiment of the
invention is represented. The device is secured to a tubular member
6, such as a wellbore casing section made of pipe body. In use, the
device is mainly immersed in wellbore fluids, such as brine, having
an external pressure Pe.
[0071] In this embodiment, an elastic membrane 7 is mounted around
the tubular member 6 and at a specified distance from the surface
of the tubular member 6. This elastic membrane 7 is preferably
disposed radially around the outer side of the tubular member 6,
and extends axially along the tubular member 6. The device further
includes a first flange 8A and a second flange 8B at a distance
from one another and secured to the tubular member 6 in a
leak-tight manner. Said flanges are preferably made of steel and
welded to the tubular member 6. The elastic membrane 7 is attached
in a leak-tight manner to the two flanges 8A and 8B at its axial
extremities. The space located between the elastic membrane 7, the
tubular member 6, and the two flanges 8A and 8B forms a sealed
chamber 8, having a chamber volume V1. Said chamber 8 has an
internal pressure P1 in use.
[0072] At least one reservoir 9, having a volume V2, capable of
containing a specified quantity of gas, such as inert gas such as
nitrogen (N.sub.2), or of a gas generator, is rigidly connected to
a pressure compensator 10. In one embodiment of the invention, the
pressure compensator 10 may be an air pressure regulator adapted to
handle the external pressure, which typically varies between 3 ksi
(20.7 MPa) and 20 ksi (137.9 MPa), and more typically between 5 ksi
(34.5 MPa) and 15 ksi (103.4 MPa). This reservoir 9 is able to let
gas flow into the chamber 8 through the pressure compensator
10.
[0073] In another embodiment, liquid state of nitrogen is used in
the reservoir, which therefore may be a dewar flask. Volume needed
is advantageously less than one liter and generates much more
volume compensation capacity. After installation, gas would slowly
vaporize and flow in the chamber 8. This embodiment advantageously
includes a heat exchanger sized to absorb heat at a relevant pace
from the environment. Moreover, this embodiment advantageously
allows to reduce the size of the reservoir.
[0074] In an alternative embodiment, the reservoir may contain a
gas generator cartridge using solid propellant such as sodium azide
(NaN.sub.3) with potassium nitrate (KNO.sub.3) or ammonium
perchlorate composite propellant. An alternative to solid
propellant could be liquid propellant selected among hydrogen
peroxide, hydrazine, or nitrous oxide, or any combination thereof,
that may mechanically be activated to release gas during the
lowering operation.
[0075] FIG. 3A illustrates a side view of a section of a tubular
member 6 partially covered by parts of a device according to the
invention. The parts of device shown include an elastic membrane 7,
the first flange 8A and the second flange 8B. FIG. 3B shows a view
through section III of the elastic membrane 7. In the embodiment of
the invention illustrated in FIGS. 3A and 3B, the elastic membrane
7 includes four lobes. The transversally lobe-shaped membrane is
advantageously adapted for reinforcement and holding means (not
represented) used in the fastening of the elastic membrane 7 to the
tubular member 6. The shape of the elastic membrane 7 is designed
according to the compliance needs in volume, and allows a uniform
radial deformation when submitted to a differential pressure
between chamber internal pressure P1 and external pressure Pe. The
compliance needs in volume may be between 0.5 gal/foot (6.2
liter/m) and 4 gal/foot (49.7 liter/m). It also allows having a
higher chamber pressure P1 than external pressure Pe when
installed. The elastic membrane has a stiffness that allows having
a lower chamber internal pressure P1 than external pressure Pe at
the nominal external temperature when maximal compensation is
needed. In this manner, the pressure exerted on the tubular member
is lower than the external pressure and thereby reduces the risk of
deformation or collapse of the tubular member.
[0076] The flanges and the elastic membrane are preferably made of
steel so as to achieve high values of resistance to pressure. In
that case, the thickness of the elastic membrane may be between
1/16 inch and 3/16 inch to provide resistance to pressure and
flexibility.
[0077] FIGS. 4A and 4B provide example values for external pressure
Pe, external temperature Te, chamber pressure P1 and volume V1, and
reservoir pressure P2. The evolutions of these parameters have been
represented during two stages, using an arbitrary time scale
numbered from 1 to 20. The first stage starts at the ground level.
Time 1 to time 9 illustrate the progressive lowering of the device
in the wellbore, i.e., its installation. The second stage starts
when the device is in its final position. Time 10 to time 20
represent a period of production in the wellbore.
[0078] During the installation (times 1 to 9), external pressure Pe
significantly rises due to hydrostatic pressure. At the same time,
the reservoir fills the chamber volume V1, thus simultaneously
raising internal chamber pressure P1 and lowering reservoir
pressure P2, until around 4.5 ksi (31 MPa) each at the end of the
stage.
[0079] As illustrated in FIG. 4B, the internal chamber volume V1
increases significantly, i.e., from 5 L up to 8.4 L in this
example, and as a consequence, provides more expansion compensation
ability once the annulus is closed. However, depending on the
pressure difference, the internal chamber volume V1 does not
necessarily increase during the installation.
[0080] While producing (times 10 to 20), external temperature
dramatically increase from 20.degree. C. to 80.degree. C.,
classically expanding the volume of trapped fluids, typically
including brine, within the external annulus, following the annular
pressure buildup phenomenon above described. The elastic membrane,
which closes the chamber 8 having the internal pressure P1,
compresses under the effect of external pressure Pe, thus,
resulting in the slight increase of internal pressure P1, combined
with a steep fall of the internal chamber volume V1. Space has
advantageously rose in the external annulus, which also
advantageously reduces the external pressure Pe elevation, and
finally mitigates the annular pressure buildup.
[0081] In the example of FIGS. 4A and 4B, the internal chamber
volume V1 increases during the installation stage and decreases
during the operation stage.
[0082] The proposed device and method are reversible since chamber
volume V1 springs back to its installation bottom hole capacity
when external temperature drops. In case the device needs to be
recovered back to the surface and gas vented out during the
process, the device may be reconditioned and the reservoir may be
refilled in order to re-use the device just as if it was for the
first time.
[0083] Safety may advantageously be improved by using a robust gas
container for the transportation and manipulation of pressurized
gas in steel bottles.
[0084] In an alternative embodiment, several devices of the
invention may be used along the casing string, typically 50 to 200,
to accommodate the whole annulus volume.
[0085] In such an embodiment, reservoirs could be connected
together in series and fed from ground level. Thus, they would
advantageously provide more gas supply for deepest chambers.
* * * * *