Note: Descriptions are shown in the official language in which they were submitted.
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PISTON ASSEMBLY TO REDUCE ANNULAR PRESSURE BUILDUP
Technical Field
[0001] A wellbore can include multiple annuli having
trapped fluids. Pressure can build up in the annuli because of
heating of these fluids, which can cause damage to wellbore
components if the pressure is not reduced. A piston assembly
can be used to reduce the amount of pressure in the annuli.
Brief Description of the Figures
[0002] The features and advantages of certain
embodiments will be more readily appreciated when considered in
conjunction with the accompanying figures. The figures are not
to be construed as limiting any of the preferred embodiments.
[0003] Fig. 1 is cross-sectional view of a well system
showing multiple annuli and a piston assembly.
[0004] Fig. 2A is an enlarged cross-sectional view of
the piston assembly prior to movement of the piston.
[0005] Fig. 2B is an enlarged cross-sectional view of
the piston assembly after movement of the piston.
Detailed Description
[0006] Oil and gas hydrocarbons are naturally occurring
in some subterranean formations. In the oil and gas industry, a
subterranean formation containing oil and/or gas is referred to
as a reservoir. A reservoir can be located under land or off
shore. Reservoirs are typically located in the range of a few
hundred feet (shallow reservoirs) to a few tens of thousands of
feet (ultra-deep reservoirs). In order to produce oil or gas, a
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wellbore is drilled into a reservoir or adjacent to a reservoir.
The oil, gas, or water produced from a reservoir is called a
reservoir fluid.
[0007] As used herein, a "fluid" is a substance having a
continuous phase that tends to flow and to conform to the
outline of its container when the substance is tested at a
temperature of 71 F (22 C) and a pressure of one atmosphere
"atm" (0.1 megapascals "MPa"). A fluid can be a liquid or gas.
[0008] A well can include, without limitation, an oil,
gas, or water production well, or an injection well. As used
herein, a "well" includes at least one wellbore. A wellbore can
include vertical, inclined, and horizontal portions, and it can
be straight, curved, or branched. As used herein, the term
"wellbore" includes any cased, and any uncased, open-hole
portion of the wellbore. A near-wellbore region is the
subterranean material and rock of the subterranean formation
surrounding the wellbore. As used herein, a "well" also
includes the near-wellbore region. The near-wellbore region is
generally considered to be the region within approximately 100
feet radially of the wellbore. As used herein, "into a well"
means and includes into any portion of the well, including into
the wellbore or into the near-wellbore region via the wellbore.
[0009] A portion of a wellbore can be an open hole or
cased hole. In an open-hole wellbore portion, a tubing string
can be placed into the wellbore. The tubing string allows
fluids to be introduced into or flowed from a remote portion of
the wellbore. In a cased-hole wellbore portion, a casing is
placed into the wellbore that can also contain a tubing string.
It is also common for more than one casing and tubing string to
be installed within a wellbore. The multiple casings can be
placed inside of one another and may not extend the same
distance within the wellbore. A wellbore can contain an
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annulus. Examples of an annulus include, but are not limited
to: the space between the wellbore and the outside of a tubing
string in an open-hole wellbore; the space between the wellbore
and the outside of a casing in a cased-hole wellbore; and the
space between the inside of a casing and the outside of a tubing
string in a cased-hole wellbore. When there are multiple
casings and/or tubing strings, there can also be multiple
annuli.
[0010] A wellbore can be separated into one or more
wellbore intervals. One way to create wellbore intervals is by
bringing the top of a cement column from a subsequent tubing
string up inside the annulus above the previous casing shoe.
However, annular pressure buildup can occur. Annular Pressure
Buildup (APB) is one of many challenging issues in the oil and
gas industry. APB occurs when annular fluids that are trapped
between the column of cement and the surface of the land become
heated due to production or higher formation temperatures. The
annular fluids then expand and can exert pressure on the casing.
This condition is present in all producing wells, but is most
evident in deep water wells. Deep water wells are likely to be
vulnerable to annular pressure buildup because of the cold
temperature of the displaced fluid, in contrast to elevated
temperature of the production fluid during production. This big
change in temperature during production can increase the
pressure in the annulus rather rapidly. Sometimes the pressure
can become so great as to collapse the inner string or even
rupture the outer string or casings, thereby destroying the
well.
[0011] A wellhead can provide access to some or all of
the wellbore annuli, and an observed pressure increase can be
quickly bled off via the wellhead. However, most subsea
wellhead installations do not have access to each wellbore
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annulus. In order to overcome the lack of access to each
annulus, other attempts to solve the problem of annular pressure
build up include: use of a syntactic crushable foam wrap;
leaving the cement column short of previous casings; providing a
leak path or bleed port; use of a compressible fluid in the
inaccessible annulus; different casing designs; and full column
height cementing. However, these attempts have some
shortcomings, for example, cement channeling can occur due to
poor mud displacement in the case of cement column short of
previous casings, very high costs can be incurred in the case of
enhanced casing design and full column height cementing, and a
foam wrap can only be used one time to bleed off the excess
pressure.
[0012] Therefore, there is a need for improved means to
reduce the amount of pressure that builds up in wellbore annuli.
It has been discovered that a piston assembly can be used to
bleed off the excess pressure from one or more wellbore annuli.
The one or more annuli can be connected via a common tubular
that is connected to the piston assembly. Any excess pressure
would be exerted on a piston of the piston assembly to prevent
the pressure from building up within the annuli.
[0013] According to certain embodiments, a system for
preventing annular pressure buildup comprises: a wellbore; two
or more annuli located within the wellbore; a piston assembly
located adjacent to a wellhead of the wellbore; and a pipe
system that connects the two or more annuli in parallel to the
piston assembly, wherein when the amount of pressure in the pipe
system exceeds a predetermined amount, then a piston of the
piston assembly moves whereby the movement reduces the amount of
pressure in the two or more annuli.
[0014] According to other embodiments, a method of
reducing the amount of pressure in two or more annuli of a
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wellbore comprises: connecting the two or more annuli in
parallel to a piston assembly via a pipe system, wherein the
piston assembly is located adjacent to a wellhead of the
wellbore; and allowing a piston of the piston assembly to move
when the amount of pressure in the pipe system exceeds a
predetermined amount, wherein the movement reduces the amount of
pressure in the two or more annuli.
[0015] Any discussion of the embodiments regarding the
well system or any component related to the well system is
intended to apply to all of the apparatus, system, and method
embodiments.
[0016] Turning to the Figures, Fig. 1 depicts a well
system 10. The well system 10 can include at least one wellbore
21. The wellbore 21 can penetrate a subterranean formation 20.
The subterranean formation 20 can be a portion of a reservoir or
adjacent to a reservoir. The well system 10 can be an off-shore
system. The off-shore system can include, for example, an off-
shore platform 100 that is located within a body of water 11.
The well system 10 can include a wellhead 13 that is located on
the sea floor 12. In off-shore drilling, a production tubing 22
is inserted into the body of water 11 and extends through the
water to the sea floor 12 of the body of water. The sea floor
12 is the surface of the sub-water land. The body of water and
the wellbore can be several hundred to several thousands of feet
deep. As used herein, the term "body of water" includes,
without limitation, either formed by nature or man-made, a
river, a pond, a lake, a gulf, a canal, a reservoir, a retention
pond, or an ocean. As used herein, the term "water" means the
water located within the body of water. The water can be
freshwater, salt water, effluent, produced or flowback water, or
brackish water. The well system 10 can also include other
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components not depicted in the drawings or described herein that
are commonly included in an off-shore drilling system.
[0017] The wellbore 21 can include one or more wellbore
intervals. The wellbore intervals can correspond to one or more
zones of the subterranean formation 20. The wellbore intervals
can be formed via the use of isolation devices, for example,
packers 24, cement 31, balls and seats, etc. (not shown).
[0018] The well system 10 also includes two or more
annuli. The well system 10 can include two or more casing
strings 23 installed within the wellbore 21. The casing strings
23, for example as depicted in Fig. 1, can be various lengths.
The well system 10 can include a first annulus 25 located
between the outside of the tubing string 22 and the inside of a
first casing string. A second annulus 26 can be located between
the outside of the first casing string and the inside of a
second casing string. A third annulus 27 can be located between
the outside of the second casing string and the inside of a
third casing string. Of course there can be more than three
annuli in the well system as well as a multitude of casing
strings or tubing strings. The casing strings 23 can be
partially or wholly cemented in the wellbore 21 via cement 31.
Partially cemented means that the cement composition does not
completely fill the annulus in which the cement is placed;
whereas, wholly cemented means that the cement composition does
completely fill the annulus in which the cement is placed.
According to certain embodiments, at least two annuli are not
completely filled with the cement 31.
[0019] Some or all of the two or more annuli (e.g., the
first, second, and third annuli 25, 26, 27) can contain a
wellbore fluid 32. The two or more annuli can contain the
wellbore fluid 32 in addition to the cement 31. The wellbore
fluid 32 can be a fluid that is introduced by an operator or a
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reservoir fluid. According to certain embodiments, the wellbore
fluid 32 can exert a certain amount of pressure within the two
or more annuli. The amount of pressure can be exerted on the
outside and inside of the casing strings 23 and/or tubing string
22 making up the annuli. The amount of pressure can also
increase over time. By way of example, the amount of pressure
can increase due to an increase in temperature of the wellbore
fluid 32 via production of a reservoir fluid or the surrounding
subterranean formation temperature.
[0020] The well system 10 includes a pipe system that
connects the two or more annuli in parallel to a piston assembly
200. The pipe system can include two or more pipes that are
connected to a common pipe 40. The two or more pipes can
correspond to the two or more annuli. According to certain
embodiments, the two or more annuli are accessible from the sea
floor 12 for being able to connect a pipe to the accessible
annulus. By way of example, a first pipe 41 can be connected to
the first annulus 25, a second pipe 42 can be connected to the
second annulus 26, and a third pipe 43 can be connected to the
third annulus 27. The pipes can be connected to each annulus in
any manner that is known to those skilled in the art. It is to
be understood that as used herein, reference to a pipe means any
tubular object that allows fluids to flow through the object and
does not imply a particular shape. A pipe can be any shape so
long as fluids are able to flow through the pipe. The pipes of
the pipe system can also be made out of a variety of materials
including, but not limited to, metals, metal alloys, plastics,
non-corrodible materials, etc.
[0021] The amount of pressure in each annulus of the
well system can be the same or different. The initial amount of
pressure from each of the pipes is the initial amount of
pressure from the respective annuli that are connected to the
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pipes. By way of example and as depicted in Fig. 1, the initial
amount of pressure in the first pipe 41 will be the amount of
pressure from the first annulus 25, the initial amount of
pressure in the second pipe 42 will be the amount of pressure
from the second annulus 26, etc. Each of these pressures in the
pipes of the pipe system will feed into the common pipe 40. By
connecting the annuli with the common pipe 40, the pressure will
become the same in the annuli 25, 26, 27, corresponding pipes
41, 42, 43, and the common pipe 40 of the network because of the
continuity of fluids.
[0022] The well
system 10 can also include one or more
annuli that are inaccessible (not shown) from the sea floor.
Any of the annuli can include a rupture disk 28 or other fluid
flow restriction device that restricts fluid flow past the
device but fails above a certain pressure rating. The rupture
disk can block fluid flow past the disk when the pressure of the
wellbore fluid 32 is below a certain value. Then, when the
pressure equals or exceeds the certain value, the disk can
rupture, thus allowing the wellbore fluid to flow out of the
annulus and into an adjacent annulus. Generally, the pressure
at which the disk ruptures is below the pressure at which damage
to the casing strings or tubing strings forming the annulus
would occur. In this manner, the strings do not become damaged
by the pressure from the wellbore fluid. Preferably, any
inaccessible annuli contain the rupture disk 28 or similar
device. When the pressure in the inaccessible annulus equals or
exceeds the pressure rating of the rupture disk, then the disk
will rupture and allow the fluid within that annulus to flow
into an adjacent annulus. The amount of pressure in the
inaccessible annulus will then decrease as the fluid flows into
the adjacent annulus. The adjacent annulus can be an accessible
annulus that is connected to a pipe of the pipe system.
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[0023] The common pipe 40 of the pipe system is
connected to the piston assembly 200. The piston assembly 200
is located adjacent to the wellhead 13 of the wellbore.
Accordingly, the piston assembly 200 can be located on the sea
floor 12. Turning to Figs. 2A and 2B, the piston assembly 200
includes a housing 201. The housing 201 can be made of a
variety of materials and can be a variety of shapes. For
example, the housing 201 can be made out of metals, metal
alloys, plastics, non-corrodible materials, etc. The piston
assembly 200 also includes a piston 202. The piston 202 can
define two chambers within the housing 201. The common pipe 40
can feed into a first chamber 204 on one side of the piston 202.
A second chamber 205 can be located on the other side of the
piston 202 opposite of the first chamber. The second chamber
205 can be filled with a compressible gas 203 or mixtures of
compressible gases. Compressibility is a measure of the
relative volume change of a fluid or solid as a response to a
pressure (or mean stress) change. The compressibility of a gas
or mixture is dependent on the pressure, temperature, and molar
volume. The compressible gas 203 or mixture can be selected
from air (which generally comprises about 80% nitrogen and about
20% oxygen), oxidizer gases such as oxygen, or inert gases such
as helium, and combinations thereof. Preferably the
compressible gas does not include a flammable gas.
[0024] The piston 202 can move within the housing 201.
Movement of the piston 202 can inversely change the dimensions
of the first and second chambers 204/205. As the piston
movement increases the dimensions of the first chamber 204 the
dimensions of the second chamber 205 are reduced and vice versa.
The compressible gas 203 within the second chamber 205 will
compress as the piston moves to reduce the dimensions of the
second chamber 205, for example as depicted in Fig. 2B.
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[0025] When the pressure in the pipe system via the
pressure from the two or more annuli increases and exceeds a
predetermined amount, then the piston 202 of the piston assembly
200 moves. The pressure moves the piston 202 to reduce the
dimensions of the second chamber 205 via compression of the
compressible gas 203. This movement of the piston 202 reduces
the amount of pressure in the common pipe 40, each of the pipes
making up the pipe system, and each annulus connected to a pipe
of the pipe system. In this manner, movement of the piston
reduces the total amount of pressure in the two or more annuli.
[0026] The predetermined amount of pressure at which the
piston 202 moves within the housing 201 can be based on
anticipated conditions of the oil and gas operation. By way of
example, the casing strings 23 can have a pressure rating at
which above that pressure then damage could occur to the casing
strings. In this example, the predetermined amount of pressure
can be less than the pressure rating of the casing strings so
the piston would move to reduce the pressure in the annuli prior
to the casing strings becoming damaged. The predetermined
amount of pressure can also be a pressure less than the amount
of pressure at which wellbore components become damaged.
[0027] The amount of movement of the piston, thereby
increasing the dimensions of the first chamber 204, causes a
certain amount of pressure in the pipe assembly and the two or
more annuli to decrease. The amount of reduction in the
pressure in the two or more annuli can be calculated based on a
variety of factors including, but not limited to, the
temperature of the wellbore fluid 32 within the annuli, the size
of the piston assembly 200 including the size of the housing 201
making up the first chamber 204 and second chamber 205, the
compressibility of the compressible gas 203, and the initial
amount of pressure in the two or more annuli prior to reduction.
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The size of the housing 201 and the second chamber 205 can be
adjusted to provide a desired pressure decrease in the two or
more annuli. By way of example, the larger the dimensions of
the housing 201 and second chamber 205 prior to movement of the
piston 202, the greater amount of pressure decrease will occur
in the two or more annuli. The type of compressible gas 203 can
also be selected to provide the desired pressure decrease in the
two or more annuli. According to certain embodiments, the
desired pressure decrease is at least sufficient such that
damage to wellbore components, such as the casing or tubing
strings, does not occur. In this manner, the excess pressure
within the annuli of the wellbore can be bled off into the
piston assembly before any damage can occur.
[0028] After the amount of pressure in the two or more
annuli is reduced or decreased, the piston 202 can move back
towards the inlet into the first chamber 204. This movement
decreases the dimensions of the first chamber 204 and increases
the dimensions of the second chamber 205. Should the pressure
in the pipe system increase again above the predetermined
amount, then the piston 202 would move again to reduce the
pressure in the two or more annuli.
[0029] It should be noted that the well system 10 is
illustrated in the drawings and is described herein as merely
one example of a wide variety of well systems in which the
principles of this disclosure can be utilized. It should be
clearly understood that the principles of this disclosure are
not limited to any of the details of the well system 10, or
components thereof, depicted in the drawings or described
herein. Furthermore, the well system 10 can include other
components not depicted in the drawing.
[0030] Therefore, the present system is well adapted to
attain the ends and advantages mentioned as well as those that
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are inherent therein. The particular embodiments disclosed
above are illustrative only, as the principles of the present
disclosure can be modified and practiced in different but
equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. Furthermore, no
limitations are intended to the details of construction or
design herein shown, other than as described in the claims
below. It is, therefore, evident that the particular
illustrative embodiments disclosed above can be altered or
modified and all such variations are considered within the scope
and spirit of the principles of the present disclosure.
[0031] As used herein, the words "comprise," "have,"
"include," and all grammatical variations thereof are each
intended to have an open, non-limiting meaning that does not
exclude additional elements or steps. While compositions and
methods are described in terms of "comprising," "containing," or
"including" various components or steps, the compositions and
methods also can "consist essentially of" or "consist of" the
various components and steps. It should be understood that, as
used herein, "first," "second," "third," etc., are arbitrarily
assigned and are merely intended to differentiate between two or
more annuli, casing strings, wellbore intervals, etc., as the
case may be, and does not indicate any particular orientation or
sequence. Furthermore, it is to be understood that the mere use
of the term "first" does not require that there be any "second,"
and the mere use of the term "second" does not require that
there be any "third," etc. Whenever a numerical range with a
lower limit and an upper limit is disclosed, any number and any
included range falling within the range is specifically
disclosed. In particular, every range of values (of the form,
"from about a to about b," or, equivalently, "from approximately
a to b") disclosed herein is to be understood to set forth every
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number and range encompassed within the broader range of values.
Also, the terms in the claims have their plain, ordinary meaning
unless otherwise explicitly and clearly defined by the patentee.
Moreover, the indefinite articles "a" or "an," as used in the
claims, are defined herein to mean one or more than one of the
element that it introduces. If there is any conflict in the
usages of a word or term in this specification and one or more
patent(s) or other documents that can be incorporated herein by
reference, the definitions that are consistent with this
specification should be adopted.
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