U.S. patent application number 10/558452 was filed with the patent office on 2007-01-18 for inflatable packer.
Invention is credited to Scott R. Clingman, Mark C. Gentry, Steven B. Lonnes, William A. Sorem.
Application Number | 20070012437 10/558452 |
Document ID | / |
Family ID | 34079351 |
Filed Date | 2007-01-18 |
United States Patent
Application |
20070012437 |
Kind Code |
A1 |
Clingman; Scott R. ; et
al. |
January 18, 2007 |
Inflatable packer
Abstract
An improved inflatable packer is provided. In one embodiment,
the improved packer has a tubular mandrel with an outer diameter
essentially equal to the deflated inner diameter of an inflatable
element surrounding the mandrel and has fluid flow passages that
are adapted to cause at least a portion of pressurized fluid for
inflating the element to be introduced into the annular space
between the packer and the mandrel in a direction substantially
parallel to the longitudinal axis of the tubular mandrel.
Inventors: |
Clingman; Scott R.;
(Houston, TX) ; Gentry; Mark C.; (Woodlands,
TX) ; Lonnes; Steven B.; (Pearland, TX) ;
Sorem; William A.; (Katy, TX) |
Correspondence
Address: |
Brent R Knight (CORP-URC-SW 337);ExxonMobil Upstream Research Company
P O Box 2189
Houston
TX
77252-2189
US
|
Family ID: |
34079351 |
Appl. No.: |
10/558452 |
Filed: |
June 24, 2004 |
PCT Filed: |
June 24, 2004 |
PCT NO: |
PCT/US04/20533 |
371 Date: |
November 28, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60487185 |
Jul 14, 2003 |
|
|
|
Current U.S.
Class: |
166/187 |
Current CPC
Class: |
E21B 33/1277
20130101 |
Class at
Publication: |
166/187 |
International
Class: |
E21B 33/12 20060101
E21B033/12 |
Claims
1. An inflatable packer comprising: (a) a tubular mandrel having a
longitudinal axis; (b) an inflatable element substantially
concentrically disposed around said tubular mandrel, said
inflatable element having a first end and a second end with each
said end being sealingly attached to said tubular mandrel, and said
inflatable element being adapted (i) to be inflated by introduction
of pressurized fluid into an annular space between said inflatable
element and said tubular mandrel and (ii) to be deflated by removal
of said pressurized fluid from said annular space; and (c) one or
more fluid flow passages positioned substantially longitudinally
along said tubular mandrel and extending through said annular space
between said inflatable element and said tubular mandrel, which
fluid flow passages are adapted to cause at least a portion of said
pressurized fluid to be introduced into said annular space in a
direction substantially parallel to said longitudinal axis of said
tubular mandrel.
2. The inflatable packer of claim 1 wherein said tubular mandrel
has an outer diameter that is substantially equal to the inner
diameter of said inflatable element prior to inflation.
3. The inflatable packer of claim 1 wherein at least one of said
fluid flow passages is formed by two or more grooves in said
tubular mandrel.
4. The inflatable packer of claim 1 wherein said inflatable element
comprises an outer elastomeric cover and a plurality of
interconnected inner slats and, further, wherein at least a portion
of said outer elastomeric cover has been removed such that at least
a portion of said plurality of interconnected inner slats are
exposed.
5. An inflatable packer suitable for use under a pre-selected
compressive load, said inflatable packer comprising: (a) a tubular
mandrel having a longitudinal axis, and (b) an inflatable element
substantially concentrically disposed around said tubular mandrel
and adapted to provide pressure seals above and below said
inflatable packer when inflated, and further said tubular mandrel
having an outer diameter configured to prevent bending and buckling
of said tubular mandrel under said pre-selected compressive load
that results in failure of either of said pressure seals or of said
inflatable packer and said tubular mandrel having one or more fluid
flow passages positioned substantially longitudinally along said
tubular mandrel and extending through an annular space between said
inflatable element and said tubular mandrel.
6. An inflatable packer suitable for use under a pre-selected
external pressure, said inflatable packer comprising: (a) a tubular
mandrel having a longitudinal axis; (b) an inflatable element
comprising an inner bladder and an outer elastomeric cover and
being substantially concentrically disposed around said tubular
mandrel, said inflatable element having a first end and a second
end with each said end being sealingly attached to said tubular
mandrel, and said inflatable element being adapted (i) to be
inflated by introduction of pressurized fluid into an annular space
between said inflatable element and said tubular mandrel and (ii)
to be deflated by removal of said pressurized fluid from said
annular space; (c) one or more fluid flow passages positioned
substantially longitudinally along said tubular mandrel and
extending through said annular space between said inflatable
element and said tubular mandrel, wherein fluid flow passages are
adapted to cause at least a portion of said pressurized fluid to be
introduced into said annular space in a direction substantially
parallel to said longitudinal axis of said tubular mandrel, and
further said tubular mandrel having an outer diameter configured to
prevent extrusion of said inner bladder into one or more of said
fluid flow passages in said direction substantially parallel to
said longitudinal axis of said tubular mandrel when said inflatable
packer is subjected to said pre-selected external pressure.
7. An inflatable packer comprising: (a) a tubular mandrel having a
longitudinal axis and one or more fluid flow passages positioned
substantially longitudinally along said tubular mandrel, and (b) an
inflatable element comprising an inner bladder and an outer
elastomeric cover and being substantially concentrically disposed
around said tubular mandrel, said inflatable element having a first
end and a second end with each said end being sealingly attached to
said tubular mandrel, and said inflatable element being adapted (i)
to be inflated by introduction of pressurized fluid into an annular
space between said inflatable element and said tubular mandrel and
(ii) to be deflated by removal of said pressurized fluid from said
annular space, and further said tubular mandrel having an outer
diameter configured to prevent folding of said inner bladder within
said annular space between said inflatable element and said tubular
mandrel.
8. An inflatable packer comprising: (a) a tubular mandrel having a
longitudinal axis and one or more fluid flow passages positioned
substantially longitudinally along said tubular mandrel, and (b) an
inflatable element comprising an outer elastomeric cover and a
plurality of interconnected inner slats and being substantially
concentrically disposed around said tubular mandrel, said
inflatable element having a first end and a second end with each
said end being sealingly attached to said tubular mandrel, and said
inflatable element being adapted (i) to be inflated by introduction
of pressurized fluid into an annular space between said inflatable
element and said tubular mandrel and (ii) to be deflated by removal
of said pressurized fluid from said annular space, and further
wherein at least a portion of said elastomeric cover has been
removed such that an appropriate length of said plurality of
interconnected inner slats are exposed to minimize the deflated
diameter of said inflatable element and to prevent loss of said
outer elastomeric cover when said inflatable packer undergoes a
plurality of inflation/deflation cycles.
9. An inflatable packer suitable for use under a pre-selected
internal pressure, said inflatable packer comprising: (a) a tubular
mandrel having a longitudinal axis and one or more fluid flow
passages positioned substantially longitudinally along said tubular
mandrel, and (b) an inflatable element comprising an outer
elastomeric cover, an inner bladder, and a plurality of
interconnected inner slats and being substantially concentrically
disposed around said tubular mandrel, said inflatable element
having a first end and a second end with each said end being
sealingly attached to said tubular mandrel, and said inflatable
element being adapted (i) to be inflated by introduction of
pressurized fluid into an annular space between said inflatable
element and said tubular mandrel and (ii) to be deflated by removal
of said pressurized fluid from said annular space, and further,
wherein a portion of said outer elastomeric cover has been removed
such that an appropriate length of said plurality of interconnected
inner slats are exposed to prevent said exposed plurality of
interconnected inner slats from damaging said inner bladder when
said inflatable packer is subjected to said pre-selected internal
pressure.
10. An inflatable packer suitable for use under a pre-selected
external pressure, said inflatable packer comprising: (a) a tubular
mandrel having a longitudinal axis; (b) an inflatable element
comprising an inner bladder and an outer elastomeric cover and
being substantially concentrically disposed around said tubular
mandrel, said inflatable element having a first end and a second
end with each said end being sealingly attached to said tubular
mandrel, and said inflatable element being adapted (i) to be
inflated by introduction of pressurized fluid into an annular space
between said inflatable element and said tubular mandrel and (ii)
to be deflated by removal of said pressurized fluid from said
annular space; (c) one or more fluid flow passages positioned
substantially longitudinally along said tubular mandrel and
extending through said annular space between said inflatable
element and said tubular mandrel, wherein fluid flow passages are
adapted to cause at least a portion of said pressurized fluid to be
introduced into said annular space in a direction substantially
parallel to said longitudinal axis of said tubular mandrel, and
wherein at least one of said fluid flow passages has at least one
edge that is chamfered at an angle of about 40 degrees to about 50
degrees.
11. An inflatable packer suitable for use under a pre-selected
external pressure, said inflatable packer having a fixed end and a
floating end and comprising: (a) a tubular mandrel having a
longitudinal axis; (b) an inflatable element comprising an inner
bladder and an outer elastomeric cover and being substantially
concentrically disposed around said tubular mandrel, said
inflatable element having a first end and a second end with each
said end being sealingly attached to said tubular mandrel, and said
inflatable element being adapted (i) to be inflated by introduction
of pressurized fluid into an annular space between said inflatable
element and said tubular mandrel and (ii) to be deflated by removal
of said pressurized fluid from said annular space; (c) one or more
fluid flow passages positioned substantially longitudinally along
said tubular mandrel and extending through the annular space
between said inflatable element and said tubular mandrel, which
fluid flow passages are adapted to cause at least a portion of said
pressurized fluid to be introduced into said annular space in a
direction substantially parallel to said longitudinal axis of said
tubular mandrel; and (d) at least one device adjacent said fixed
end, said device being adapted to prevent extrusion of said inner
bladder into one or more of said fluid flow passages in a direction
substantially parallel to said longitudinal axis of said tubular
mandrel when said packer is subjected to said pre-selected external
pressure.
12. The inflatable packer of claim 3, further comprising a screen
in the form of a cylindrical sleeve sized to fit around said
tubular mandrel, said screen having holes to allow fluid flow but
prevent extrusion of said inflatable element during deflation of
said inflatable packer.
13. The inflatable packer of claim 12, wherein said screen sleeve
is confined on said tubular mandrel axially by a diameter upset on
said tubular mandrel at one end, and a removable securing device at
the other end.
14. A method comprising: providing an inflatable packer comprising
a tubular mandrel having a longitudinal axis and one or more fluid
flow passages positioned substantially longitudinally along said
tubular mandrel, and an inflatable element substantially
concentrically disposed around said tubular mandrel, said
inflatable element having a first end and a second end with each
said end being sealingly attached to said tubular mandrel, and said
inflatable element being adapted (i) to be inflated by introduction
of pressurized fluid into an annular space between said inflatable
element and said tubular mandrel and (ii) to be deflated by removal
of said pressurized fluid from said annular space; and disposing
said inflatable packer into a wellbore.
15. The method of claim 14, wherein said one or more fluid flow
passages are adapted to cause at least a portion of said
pressurized fluid to be introduced into said annular space in a
direction substantially parallel to said longitudinal axis of said
tubular mandrel.
16. The method of claim 14 wherein said tubular mandrel has an
outer diameter that is substantially equal to the inner diameter of
said inflatable element prior to inflation.
17. The method of claim 14 comprising defining at least one of said
fluid flow passages to be formed by two or more grooves in said
tubular mandrel.
18. The method of claim 14 wherein said inflatable element
comprises an outer elastomeric cover and a plurality of
interconnected inner slats and, further, wherein at least a portion
of said outer elastomeric cover has been removed such that at least
a portion of said plurality of interconnected inner slats are
exposed.
19. The method of claim 18 comprising configuring a portion of said
outer elastomeric cover has been removed such that an appropriate
length of said plurality of interconnected inner slats are exposed
to prevent said exposed plurality of interconnected inner slats
from damaging said inner bladder when said inflatable packer is
subjected to said pre-selected internal pressure.
20. The method of claim 14 comprising configuring said inflatable
packer to have an outer diameter suitably large to prevent bending
and buckling of said tubular mandrel under said pre-selected
compressive load that results in failure of either of said pressure
seals or of said inflatable packer.
21. The method of claim 14 comprising configuring said tubular
mandrel to have having an outer diameter suitably large to prevent
extrusion of said inner bladder into said one or more of said fluid
flow passages in said direction substantially parallel to said
longitudinal axis of said tubular mandrel when said inflatable
packer is subjected to said pre-selected external pressure.
22. The method of claim 14 wherein at least one of said fluid flow
passages has at least one edge chamfered at an angle of about 40
degrees to about 50 degrees.
23. The method of claim 14 comprising expanding said inflatable
packer to seal a portion of said wellbore.
24. The method of claim 23 comprising producing hydrocarbons from
said wellbore by utilizing said expanded inflatable packer.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to an improved inflatable
packer useful for restricting flow of fluids in a wellbore during
the perforating and treating of a subterranean formation to
increase the production of oil and gas therefrom. More
particularly, this invention relates to an inflatable packer having
a tubular mandrel with an outer diameter essentially equal to the
deflated inner diameter of an inflatable element surrounding the
mandrel and further having fluid flow passages that direct the flow
of fluid for inflating the element into and through the annular
space between the mandrel and the element. Preferably, the fluid
flow passages direct the flow of fluid for inflating the element in
a direction substantially parallel to the longitudinal axis of the
mandrel.
BACKGROUND OF THE INVENTION
[0002] When a hydrocarbon-bearing, subterranean reservoir formation
does not have enough permeability or flow capacity for the
hydrocarbons to flow to the surface in economic quantities or at
optimum rates, hydraulic fracturing or chemical stimulation is
often used to increase the flow capacity. A wellbore penetrating a
subterranean formation typically includes a metal casing cemented
into the original drill hole. Perforations are made to penetrate
through the casing and the cement sheath surrounding the casing to
allow hydrocarbon flow into the wellbore and, if necessary, to
allow treatment fluids to flow from the wellbore into the
formation.
[0003] Hydraulic fracturing comprises injecting fluids (usually
viscous shear thinning, non-Newtonian gels or emulsions) into a
formation at pressures and rates high enough to cause the reservoir
rock to fail and to form a planar, typically vertical, fracture (or
fracture network) much like the fracture that extends through a
wooden log as a wedge is driven into it. Granular proppant
materials, such as sand, ceramic beads, or other materials, are
generally injected with the later portion of the fracturing fluid
to hold the fracture(s) open after the fluid pressure is released.
Increased flow capacity from the reservoir results from the flow
path left between grains of the proppant material within the
fracture(s). In chemical stimulation treatments, flow capacity is
improved by dissolving materials in the formation or otherwise
changing formation properties.
[0004] Application of hydraulic fracturing as described above is a
routine part of petroleum industry operations as applied to
individual target zones of up to about 60 meters (200 feet) of
gross, vertical thickness of subterranean formation. When there are
multiple or layered reservoirs to be hydraulically fractured, or a
very thick hydrocarbon-bearing formation (over about 60 meters),
then alternate treatment techniques are required to obtain
treatment of the entire target zone.
[0005] When multiple hydrocarbon-bearing zones are stimulated by
hydraulic fracturing or chemical stimulation treatments, economic
and technical gains are realized by injecting multiple treatment
stages that can be diverted (or separated) by various means,
including mechanical devices such as bridge plugs, packers,
downhole valves, sliding sleeves, and baffle/plug combinations;
ball sealers; particulates such as sand, ceramic material,
proppant, salt, waxes, resins, or other compounds; or by
alternative fluid systems such as viscosified fluids, gelled
fluids, foams, or other chemically formulated fluids; or using
limited entry methods.
[0006] In mechanical bridge plug diversion, for example, the
deepest interval is first perforated and fracture stimulated, then
the interval is typically isolated by a wireline-set bridge plug,
and the process is repeated in the next interval up. Assuming ten
target perforation intervals, treating 300 meters (1,000 feet) of
formation in this manner would typically require ten jobs over a
time interval of ten days to two weeks with not only multiple
fracture treatments, but also multiple perforating and bridge plug
running operations. At the end of the treatment process, a wellbore
clean-out operation would be required to remove the bridge plugs
and put the well on production. The major advantage of using bridge
plugs or other mechanical diversion agents is high confidence that
only the target zone is treated, and the stimulation is diverted
from previously treated zones. The major disadvantages are the high
cost of treatment resulting from multiple trips into and out of the
wellbore and the risk of complications resulting from so many
operations in the well. For example, a bridge plug can become stuck
in the casing and need to be drilled out at great expense. A
further disadvantage is that the required wellbore clean-out
operation may damage some of the successfully fractured
intervals.
[0007] To overcome some of the limitations associated with
completion operations that require multiple trips of hardware into
and out of the wellbore to perforate and stimulate subterranean
formations, methods and apparatus have been proposed for
"single-trip" deployment of a downhole tool string to allow for
fracture and chemical stimulation of zones in conjunction with
perforating. Specifically, these methods and apparatus allow
operations that minimize the number of required wellbore operations
and time required to complete these operations, thereby reducing
the stimulation treatment cost. Frequently, an inflatable packer
assembly is included in a tool string used for these types of
applications.
[0008] Referring now to FIG. 1 (PRIOR ART), a standard inflatable
packer assembly 10 comprises several separate parts, including an
inflatable element 14, a tubular mandrel 12, two end-caps 13, and
two ends 16 and 18. Often, end 16 is fixed and end 18 is sliding,
i.e., adapted to slide along mandrel 12 as element 14 is inflated
and/or deflated, as will be familiar to those skilled in the art.
The packer assembly is typically attached to tubing 17. There are
three categories of commercially-available, inflatable elements:
metal-slat reinforced, metal-cable reinforced, and polymer
composite reinforced. An inflatable packer can be assembled using
any type of inflatable element, including the three described
above, by inserting a mandrel through the center of the element and
using two end-caps to attach the element to the mandrel.
[0009] Currently, the elements that have the most desirable
properties in terms of absolute pressure resistance and internal
differential-pressure resistance, comprise an outer elastomeric
cover (which, when inflated and sealingly engaged with the wall or
casing of the wellbore, provides pressure seals above and below the
packer), a reinforcement structure (which provides adequate
mechanical strength to withstand stresses induced by inflation),
and an internal elastomeric bladder (which provides a pressure seal
between the fluids inside and outside the element). The combination
of high pressure resistance, sufficient thermal stability, and thin
cross-section has allowed these cover-reinforcement-bladder
composite elements to essentially dominate the oil-field
market.
[0010] As each type of reinforced element has different strengths
and weaknesses, each type is generally best suited for particular
types of applications. Commercially available polymer-reinforced
packers are most often used in low temperature and/or low pressure
water well applications and can typically survive many
inflation/deflation cycles under lower pressure conditions.
Metal-cable reinforced packers have also been optimized to maximize
fatigue life (and hence the number of inflation/deflation cycles),
and while testing has shown that currently available varieties may
not handle as many cycles as the polymer-reinforced variety, they
are currently able to handle relatively high temperatures. Lastly,
metal-slat reinforced elements have been optimized for
high-pressure, high-temperature service at the cost of shorter
fatigue life.
[0011] All three varieties of packers are typically exposed to
service conditions that place the mandrel of the packer in tension.
Recent extension of these packers to newly developed completion
techniques, for example, as described in U.S. Pat. Nos. 6,394,184
and 6,520,255, and in U.S. Publication No. 2003/0051876, which deal
with a technology known as "Annular Coiled Tubing Fracturing" or
"ACT-Frac", require that the packers withstand much higher
compressive loads than currently available packers can withstand
without buckling the mandrel. Existing partial solutions to large
compressive loads include the use of a larger diameter inflatable
element with a correspondingly larger mandrel, the use of cement as
an inflation fluid, and alternate designs to the tool-string to
reduce the effective compressive loads, such as by adjusting the
position of the element within the tool-string. Each of these
partial solutions introduces additional drawbacks. The use of a
larger diameter element reduces the clearance between the outer
diameter of the element and the inner diameter of the casing, which
decreases the cross-sectional area between the element and the
casing. This reduces the maximum running speeds and increases the
chance for damaging the element or sticking the tool downhole.
Inflating the element with cement or other hardening material
supports compressive loads extremely well but does not allow for
the multiple inflation/deflation cycles required by some
applications. Lastly, placing the element in a different position
within a string of tools to reduce compressive loading may be
detrimental in several ways, including shifting the higher
compressive loads to other tools, exposing other downhole tools to
flows/environments otherwise protected by the packer, making the
tool-string more complex, or changing the functionality of the
tool-string itself.
[0012] Using a larger mandrel without increasing the diameter of
the inflatable element is also an option, but raises other
concerns. In packer designs that use the gap between the mandrel
and the element to inflate or deflate the element, increasing the
diameter of the mandrel results in a smaller inflation/deflation
pathway and increases the likelihood that the rubber interior of
the element will pinch off flow to the inflation chamber.
Operational problems will arise if the flow blockage results in
either a partial inflation (e.g., lack of pressure isolation in the
wellbore) or partial deflation (e.g., the packer is more likely to
become stuck in the wellbore, the outer cover is more likely to
experience additional wear, and the element is more likely to
experience pinching failures). Despite these problems, however,
larger mandrels are occasionally used for either their mechanical
strength/buckling resistance, or to allow for a larger passageway
through the interior of the mandrel. Towards this end, two
techniques have arisen to alleviate flow restrictions through the
mandrel-element gap.
[0013] One technique utilizes a plurality of holes drilled through
the entire covered length of the mandrel thereby affording multiple
fluid pathways between an energized fluid source within the mandrel
and the inflation chamber. Unfortunately, for several tool designs
and completion procedures, it is undesirable to have the inflation
fluid pathway include the interior of the mandrel (which may be
required to contain electric lines or serve as a passageway for a
separate fluid system). In addition, the holes can result in
internal-bladder failure initiation sites due to either external
pressure extrusion through the holes or jet-impingement onto the
bladder during inflation. A second technique, which does not use
the interior of the mandrel in the inflation fluid pathway,
requires a second, concentric, perforated tube between the element
and a solid mandrel (see U.S. Pat. No. 5,495,892). The inflation
pathway is then shifted to between the mandrel and the concentric
tube, effectively preventing the element from pinching off the
inflation/deflation fluid pathway. However, this design is not
applicable in situations where the mandrel is placed under larger
compressive stresses, as the additional tube can not be load
bearing when used in floating head packers (i.e., inflatable
packers that use one fixed end and one floating end, i.e., an end
that is allowed to travel during inflation (the predominant packer
design in the oil-field)). Moreover, the perforated concentric tube
requires additional space which must translate into either a larger
element diameter (less wellbore-element clearance), a smaller
mandrel diameter (less buckling resistance), or a thinner element
design (lower pressure resistance).
[0014] Inner-bladder failures are the most common failure mechanism
in composite packers. This is not surprising as these bladders tend
to be constructed of thin elastomeric tubes (necessary to allow
expansion during inflation) and they are typically the only
pressure seal around the inflatable chamber. Two of the most common
inner-bladder failure mechanisms are pinching failures and
extrusion failures. Pinching failures initiate during deflation
when the thin elastomeric bladder, having just been stretched
during the inflation stage, is now quickly forced into its initial
deflated dimensions without giving the elastomer enough time to
relax. To accommodate a smaller diameter in less time than the
elastomer requires to relax, the still distended bladder can fold
over itself given enough radial clearance. If a large external or
internal pressure is applied to the packer element while a fold is
present, the pressure can act to squeeze the fold together and
split the bladder along the fold line. Once the bladder splits, the
element no longer possesses pressure integrity and the packer has
failed. A smaller clearance between the mandrel and the element
would alleviate this problem, but can result in other problems as
stated above.
[0015] Extrusion failures occur when applied pressure forces the
thin elastomeric bladder through a gap or hole in either the
surrounding reinforcement structure or the mandrel/mandrel-end-cap
junction. To help prevent internal-pressure related extrusion
failures, element design has focused on minimizing the gap-sizes in
the element reinforcing structures wrapped around the inner
bladder. How effective the design is in minimizing the
reinforcement gap size, coupled with the strength of the
reinforcement, generally determines the maximum internal pressure
differential that the element will be able to resist without
failure. However, the same degree of care has not been extended to
preventing extrusion failures caused by large applied external
pressures. This is in part due to the relatively low frequency of
events with large applied external pressures. Large external
pressures can arise inadvertently (e.g., well control events,
greater than anticipated reservoir pressures, human or mechanical
error, etc.) or be applied on purpose (e.g., standard wellbore or
lubricator pressure tests, stimulation procedures, production, well
tests, etc.). With the extension of inflatable packers to high
pressure stimulation operations, the likelihood that packers will
experience higher external pressures is increased; thereby
requiring packers with improved external pressure resistance.
Improved external pressure resistance will permit application of
inflatable packers to a wider range of newly developed completion
operations, allow the packers to be present in the wellbore or
lubricator during pressure testing, and allow the packer to remain
in service after an unexpected external pressure event. The
inner-bladders are especially susceptible to external pressure
extrusion failures when the element is in a deflated, non-sealing
state because the inner-bladder is in direct contact with any holes
or gaps in the mandrel assembly.
[0016] Inflatable packers are rarely used in conjunction with
proppant fracturing operations due to their propensity to become
damaged or stuck downhole when exposed to particulate-laden
environments. Current designs generally rely on single o-ring seals
to provide both static and dynamic pressure seals at the
mandrel/end-cap junction to isolate the pressurized, inflatable
chamber from the wellbore. Through testing, we have found that,
under both particulate-free and particulate-laden environments,
more robust pressure seals would be advantageous. In addition to
seal design, the design of the outer elastomeric cover used in
currently available packers also can led to poor performance in
particulate-laden environments. The ability of the packer to return
to its original outer diameter after each inflation maximizes the
cross-sectional area in the annulus between the packer and the
wellbore. This large annular area increases the ability of
particulate-laden fluid to flow past the packer after each set,
consequently reducing the likelihood of not being able to move the
packer in the wellbore.
[0017] Extensive testing of commercially available, inflatable
packers revealed several limitations in existing packer designs,
including the inability of these packers to resist bending and
buckling under applied compressive loads, to resist extrusion and
pinching failures of the element bladders, to perform in
particulate-laden environments, and to have large annular clearance
when deflated. With the development of the above-referenced
completion technologies, there is now a need for an improved
inflatable packer that possesses high buckling resistance, improved
inner-bladder failure resistance, improved inflation-cycle
repeatability, better resistance to particulate damage, a large
tubular mandrel inner diameter through which fluids and electrical
conduits can be passed, and a minimal deflated outer diameter to
minimize the restriction to annular flow.
[0018] Therefore, an object of this invention is to provide such
improved inflatable packers. Other objects of this invention will
be made apparent by the following description of the invention.
SUMMARY OF THE INVENTION
[0019] An inflatable packer is provided that comprises: (a) a
tubular mandrel having a longitudinal axis; (b) an inflatable
element substantially concentrically disposed around said mandrel,
said element having a first end and a second end with each said end
being sealingly attached to the mandrel, and said element being
adapted (i) to be inflated by introduction of pressurized fluid
into an annular space between said element and the mandrel and (ii)
to be deflated by removal of said pressurized fluid from said
annular space; and (c) one or more fluid flow passages extending
through the annular space between the element and the mandrel,
which fluid flow passages are adapted to cause at least a portion
of said pressurized fluid to be introduced into said annular space
in a direction substantially parallel to said longitudinal axis of
said tubular mandrel. In one embodiment, each of said fluid flow
passages is in fluid communication with each of the other said
fluid flow passages. In one embodiment, the mandrel has an outer
diameter that is substantially equal to the inner diameter of the
element prior to inflation. In one embodiment, at least one of the
fluid flow passages is formed by two or more grooves in the
mandrel. In another embodiment, the element comprises an outer
elastomeric cover and a plurality of interconnected inner slats
and, further, at least a portion of said elastomeric cover has been
removed such that at least a portion of the interconnected inner
slats are exposed.
[0020] In another embodiment, an inflatable packer suitable for use
under a pre-selected compressive load is provided, wherein the
inflatable packer comprises: (a) a tubular mandrel having a
longitudinal axis, and (b) an inflatable element substantially
concentrically disposed around said mandrel and adapted to provide
pressure seals above and below said inflatable packer when
inflated, and further said mandrel has an outer diameter suitably
large to prevent bending and buckling of the mandrel under said
pre-selected compressive load that results in failure of either of
said pressure seals or of said inflatable packer.
[0021] In another embodiment, an inflatable packer suitable for use
under a pre-selected external pressure is provided, wherein said
inflatable packer comprises: (a) a tubular mandrel having a
longitudinal axis; (b) an inflatable element comprising an inner
bladder and an outer elastomeric cover and being substantially
concentrically disposed around said mandrel, said element having a
first end and a second end with each said end being sealingly
attached to the mandrel, and said element being adapted (i) to be
inflated by introduction of pressurized fluid into an annular space
between said element and the mandrel and (ii) to be deflated by
removal of said pressurized fluid from said annular space; (c) one
or more fluid flow passages extending through the annular space
between the element and the mandrel, which fluid flow passages are
adapted to cause at least a portion of said pressurized fluid to be
introduced into said annular space in a direction substantially
parallel to said longitudinal axis of said tubular mandrel, and
further wherein said mandrel has an outer diameter suitably large
to prevent extrusion of said inner bladder into one or more of said
fluid flow passages in a direction substantially parallel to said
longitudinal axis of said tubular mandrel when said packer is
subjected to said pre-selected external pressure. In one
embodiment, each of said fluid flow passages is in fluid
communication with each of the other said fluid flow passages.
[0022] In another embodiment, an inflatable packer is provided that
comprises: (a) a tubular mandrel having a longitudinal axis, and
(b) an inflatable element comprising an inner bladder and an outer
elastomeric cover and being substantially concentrically disposed
around said mandrel, said element having a first end and a second
end with each said end being sealingly attached to the mandrel, and
said element being adapted (i) to be inflated by introduction of
pressurized fluid into an annular space between said element and
the mandrel and (ii) to be deflated by removal of said pressurized
fluid from said annular space, and further wherein said mandrel has
an outer diameter suitably large to prevent folding of said inner
bladder within said annular space between said element and said
mandrel.
[0023] In another embodiment, an inflatable packer is provided that
comprises: (a) a tubular mandrel having a longitudinal axis, and
(b) an inflatable element comprising an outer elastomeric cover and
a plurality of interconnected inner slats and being substantially
concentrically disposed around said mandrel, said element having a
first end and a second end with each said end being sealingly
attached to the mandrel, and said element being adapted (i) to be
inflated by introduction of pressurized fluid into an annular space
between said element and the mandrel and (ii) to be deflated by
removal of said pressurized fluid from said annular space, and
further wherein at least a portion of said elastomeric cover has
been removed such that an appropriate length of said interconnected
inner slats are exposed to minimize the deflated diameter of said
element and to prevent loss of said outer elastomeric cover when
said packer undergoes a plurality of inflation/deflation cycles. In
one embodiment, a plurality is meant to include two or more
inflation/deflation cycles. In another embodiment, a plurality is
meant to include three or more inflation/deflation cycles. In yet
another embodiment, a plurality is meant to include five or more
inflation/deflation cycles.
[0024] In another embodiment, an inflatable packer suitable for use
under a pre-selected internal pressure is provided, wherein said
inflatable packer comprises: (a) a tubular mandrel having a
longitudinal axis, and (b) an inflatable element comprising an
outer elastomeric cover, an inner bladder, and a plurality of
interconnected inner slats and being substantially concentrically
disposed around said mandrel, said element having a first end and a
second end with each said end being sealingly attached to the
mandrel, and said element being adapted (i) to be inflated by
introduction of pressurized fluid into an annular space between
said element and the mandrel and (ii) to be deflated by removal of
said pressurized fluid from said annular space, and further,
wherein a portion of said elastomeric cover has been removed such
that an appropriate length of said interconnected inner slats are
exposed to prevent said exposed slats from damaging said inner
bladder when said packer is subjected to said pre-selected internal
pressure.
[0025] In another embodiment, an inflatable packer suitable for use
under a pre-selected external pressure is provided, wherein said
packer comprises: (a) a tubular mandrel having a longitudinal axis;
(b) an inflatable element comprising an inner bladder and an outer
elastomeric cover and being substantially concentrically disposed
around said mandrel, said element having a first end and a second
end with each said end being sealingly attached to the mandrel, and
said element being adapted (i) to be inflated by introduction of
pressurized fluid into an annular space between said element and
the mandrel and (ii) to be deflated by removal of said pressurized
fluid from said annular space; and (c) one or more fluid flow
passages extending through the annular space between the element
and the mandrel, which fluid flow passages are adapted to cause at
least a portion of said pressurized fluid to be introduced into
said annular space in a direction substantially parallel to said
longitudinal axis of said tubular mandrel, and wherein at least one
of said fluid flow passages has at least one edge that is chamfered
at an angle of about 40 degrees to about 50 degrees. In one
embodiment, said at least one edge is chamfered at an angle of
about 45 degrees.
[0026] In another embodiment, an inflatable packer suitable for use
under a pre-selected external pressure is provided, wherein said
inflatable packer has a fixed end and a floating end and comprises:
(a) a tubular mandrel having a longitudinal axis; (b) an inflatable
element comprising an inner bladder and an outer elastomeric cover
and being substantially concentrically disposed around said
mandrel, said element having a first end and a second end with each
said end being sealingly attached to the mandrel, and said element
being adapted (i) to be inflated by introduction of pressurized
fluid into an annular space between said element and the mandrel
and (ii) to be deflated by removal of said pressurized fluid from
said annular space; (c) one or more fluid flow passages extending
through the annular space between the element and the mandrel,
which fluid flow passages are adapted to cause at least a portion
of said pressurized fluid to be introduced into said annular space
in a direction substantially parallel to said longitudinal axis of
said tubular mandrel; and (d) at least one device adjacent said
fixed end, said device being adapted to prevent extrusion of said
inner bladder into one or more of said fluid flow passages in a
direction substantially parallel to said longitudinal axis of said
tubular mandrel when said packer is subjected to said pre-selected
external pressure. Said device that is adapted to prevent extrusion
of said inner bladder when said packer is subjected to said
pre-selected external pressure may comprise a filter, a screen, or
any other device capable of preventing such extrusion, as will be
familiar to those skilled in the art.
DESCRIPTION OF THE DRAWINGS
[0027] The advantages of the present invention will be better
understood by referring to the following detailed description and
the attached drawings in which:
[0028] FIG. 1 (PRIOR ART) is a sketch of a standard inflatable
packer assembly;
[0029] FIG. 2A is a cut-away view of an inflatable packer according
to this invention;
[0030] FIG. 2B is a plan view at section 24 of the inflatable
packer illustrated in FIG. 2A (looking down at the top);
[0031] FIG. 2C is a plan view at section 34 of the inflatable
packer illustrated in FIG. 2A (looking down at the top);
[0032] FIG. 2D is a detailed sketch of groove 33 shown in FIG.
2C;
[0033] FIG. 3 is a sketch of an element useful in the present
invention; and
[0034] FIG. 4 is a graphical representation of data showing the
benefits of use in the present invention of the element illustrated
in FIG. 3;
[0035] While the invention will be described in connection with its
preferred embodiments, it will be understood that the invention is
not limited thereto. On the contrary, the invention is intended to
cover all alternatives, modifications, and equivalents which may be
included within the spirit and scope of the present disclosure, as
defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
[0036] This invention comprises several improvements to an
inflatable packer assembly to address performance limitations in
existing packer designs. These improvements allow the assembly to
operate more reliably when (1) large compressive loads are applied
to the packer, (2) large external pressures are applied to the
packer, and/or (3) the packer is placed in a particulate-laden
environment.
[0037] In the current invention, the compressive load capability is
optimized by maximizing the outer tubular diameter of the mandrel
with respect to the inner diameter of the element. To facilitate
load transfer through the large-diameter tubular mandrel, the
threads at both ends are oriented so as to compress at one quarter
of the buckling load thereby allowing the shoulders above and below
the threads to shoulder with the adjacent female sub. This feature
substantially ensures that the entire load-bearing cross-sectional
area is in contact when the tool is subjected to large compressive
load.
[0038] The tubular mandrel is constructed to be effectively flush
with the inner diameter of the element, i.e., the outer diameter of
the mandrel is substantially equal to the inner diameter of the
element. In one embodiment, the tubular mandrel has one or more
passages therethrough for the passage of fluid, electrical wires,
or other devices though the interior thereof. Fluid flow passages,
e.g., comprising a plurality of metal runners to form slots or
"flutes", are provided down the sides of the mandrel and/or on the
inner-bladder of the element to allow fluid flow along the length
of the element while retaining the large outer diameter required
for high resistance to buckling and bending loads. As used herein,
the term "fluid flow passages" includes any passage formed in any
way in the annulus between the mandrel and the inner-bladder, such
as flutes in the mandrel or inserted tubes, but is not intended to
refer to an annular region between the mandrel and the inner
bladder. Passages may comprise holes, perforations, grooves, slots,
or other continuous openings. To reduce the likelihood of damage to
the inner-bladder, the fluid entrance to the flutes are preferably
oriented parallel to the longitudinal axis of the mandrel to avoid
any fluid-jet impingement on the inner-bladder. Fluid flow through
the flutes and annulus is preferably substantially parallel to the
longitudinal axis of the mandrel; however, some or all of the fluid
flow may be oriented to flow in a helical path around the outer
surface of the mandrel, or in some other path.
[0039] When flutes are used to provide the fluid flow passages, the
flutes are designed to accommodate external pressure loading
without damaging the thin inner-bladder. This is accomplished, for
example without limiting this invention, through the use of
chamfered and beveled edges, a slow run-out at the end of the
flutes, and/or the installation of a suitable filter or screen at
the entrance to, throughout and/or covering the flutes. A suitable
filter or screen may comprise, for example, a shaped load-bearing,
porous material, sintered metal filters, machined screens, and
other suitable filters or screens as will be familiar to those
skilled in the art. The combination of these features minimizes the
chance to cut the inner-bladder in the event external pressure
forces the bladder into the mandrel and mandrel/end-cap
junctions.
[0040] In addition to resisting higher compressive loads without
buckling, the new, larger mandrel design improves packer
performance in other ways; 1) the smaller resultant clearance
between the mandrel and the element minimizes the opportunity for
occurrence of inner-bladder pinching failures, 2) the design of the
mandrel's outer diameter profile mitigates element inner-bladder
extrusion failures caused by the application of external-pressure,
and 3) the proportionately larger inner diameter allows for both
significant fluid flow for rapid pressure equalization across the
packer and the passage of secondary conduits for additional
communication (pressure, flow, electrical) with the wellbore and
remaining bottomhole assembly below the packer.
[0041] In one embodiment of the present invention, numerous fine
holes are drilled (via mechanical means, by laser, etc) through the
tubular mandrel, each hole preferably having no greater than a 0.8
mm ( 1/32 inch) diameter. The hole diameter is then small enough to
prevent extrusion failures. In this embodiment, enough holes are
drilled to allow for adequate inflation and deflation times, as
will be familiar to those skilled in the art.
[0042] Referring now to FIG. 2A, in one embodiment of this
invention a mandrel 20 has an upper end 25 having threads 26, for
connection to tubing or an end-cap, and sealant ring glands 42 and
44 to assist in sealing. Neither tubing or an end-cap is shown in
any of FIG. 2A-FIG. 2D; any tubing or end-cap that is suitable for
the application at hand may be used, although same may require
modification to fit mandrel upper end 25, all as will be familiar
to those skilled in the art. Further, in this embodiment mandrel 20
in section 24 has an outer edge 20c and an outer diameter 22 of
about 5.05 cm. (1.99 inches). Referring to FIG. 2B, mandrel 20 at
section 24 has outer edge 20c and a plurality of flutes or grooves
23 having outer edge 20a, each having a width 21 of about 0.64 cm.
(0.25 inches) and a depth 27 of about 0.25 cm. (0.1 inch) and being
substantially evenly spaced at an angle 29 of about 45 degrees
along the circumference of mandrel 20. Referring again to FIG. 2A,
mandrel 20 has a lower end 35 having threads 36, for connection to
an end-cap, and sealant ring glands 52 and 54 to assist in sealing,
as will be familiar to those skilled in the art. The end-cap is not
shown in any of FIG. 2A-2D and may be any end-cap that is suitable
for the application at hand, although same may require modification
to fit mandrel lower end 35, as will be familiar to those skilled
in the art. Further, mandrel 20 in section 34 has outer edge 20b
and an outer diameter 32 of about 4.92 cm. (1.937 inches).
Referring to FIG. 2C, mandrel 20 at section 34 has outer edge 20b
and a plurality of flutes or grooves 33 having outer edge 20a, each
having a width 31 of about 0.64 cm. (0.25 inches) and a depth 37 of
about 0.188 cm. (0.074 inch) and being substantially evenly spaced
at an angle 39 of about 45 degrees along the circumference of
mandrel 20. Referring now to FIG. 2D, grooves 33 in section 34 are
manufactured with chamfers 40 at an angle of about 45 degrees and
are beveled to minimize damage to the inner bladder of the
inflatable element circumferentially disposed over mandrel 20 when
exposed to external pressure. Preferably, grooves 23 in section 24
(see FIG. 2B) are similarly chamfered and beveled. This embodiment
may include screen sleeves that are disposed axially over the
length of the fluted region and are supported against radial
external loading by the non-fluted portion 20b of mandrel 20
outside diameter. The screen sleeves could be confined axially
through a diameter upset on the mandrel at one end and a removable
securing device on the other end, for example, a threaded sleeve
that screws onto mandrel 20 and axially presses the screen sleeves
against the mandrel diameter upset. The screen sleeves would
contain numerous radial holes sized to prevent extrusion of the
inner bladder when external pressure is applied, the numerous
radial holes having diameters of about 0.2 mm (0.008'') and
numbering in the thousands. It may be preferable to make the screen
sleeve in two or more sections in order to reduce the longitudinal
dimension over which tight radial tolerances must be maintained and
to facilitate cleaning and inspection. Reference to a screen herein
will be understood to include embodiments having such multiple
sections. The inflatable element is not shown in any of FIG.
2A-FIG. 2D and may be any inflatable element that is suitable for
the application at hand, as will be familiar to those skilled in
the art. The specific description of this embodiment of the
invention in no way limits this invention. As is familiar to those
skilled in the art, dimensions of parts are adjusted as needed for
the application at hand.
[0043] In order to accommodate operation of the inflatable packer
assembly according to this invention in a particulate-laden fluid,
wipers are preferably added to the floating end to remove
particulates as the packer is inflated and deflated. In addition to
the wipers, redundant o-rings seals with back-up rings to prevent
extrusion preferably replace the single o-ring seals commonly used
in existing designs. A POLY-PAK, pressure-energized seal is
preferably used in the floating end for improved sealing and a more
robust seal for use in particulate-laden environments.
[0044] Referring again to FIG. 2A, upper end 25 of tubular mandrel
20 comprises a blunt nose 43 and threads 26, which threads 26 are
oriented so as to compress at one quarter of the buckling load
thereby allowing the shoulders above and below the threads to
shoulder with the female sub above, as will be familiar to those
skilled in the art. In this embodiment, threads 26 are oriented at
an angle 41 of about 30 degrees. Also, the seal system comprises
VITON o-rings (not shown in the FIG.) in ring glands 44 with PARBAK
backup rings (not shown in the FIG.) in ring glands 42. The tubular
or end-cap to which upper end 25 is connected may require
modification to ensure a tight fit, as will be familiar to those
skilled in the art.
[0045] Lower end 35 of tubular mandrel 20 comprises a blunt nose 53
and threads 36, which threads 36 are oriented so as to compress at
one quarter of the buckling load thereby allowing the shoulders
above and below the threads to shoulder with the female sub below,
as will be familiar to those skilled in the art. In this
embodiment, threads 36 are oriented at an angle 51 of about 30
degrees. Also, the seal system comprises VITON o-rings (not shown
in the FIG.) in ring glands 54 with PARBAK backup rings (not shown
in the FIG.) in ring glands 52. The end-cap to which lower end 35
is connected may require modification to ensure a tight fit, as
will be familiar to those skilled in the art. When mandrel lower
end 35 is attached to a floating end (end not shown in the FIG.)
the floating end preferably comprises a TEFLON wiper ring and a
poly-pack pressure energized seal, both as will be familiar to
those skilled in the art.
[0046] Additionally, when a packer assembly according to this
invention is used in a particulate-laden fluid, a metal-slat
reinforced element is preferred. Referring now to FIG. 3, one end
of a preferred element 60 for use in a packer assembly according to
this invention is illustrated as attached to an end-cap 66. Prior
to inflation, the outer elastomer cover 64 has a length 62 of
exposed slats 63 of about 7.62 cm. (3.0 inches) with a taper 65 of
about 15 degrees. Preferably element 60 has such exposed slats at
both ends.
[0047] In an experimental testing program conducted to evaluate the
performance of existing packer/mandrel assemblies and assemblies
according to this invention, conventional packer/mandrel assemblies
buckled and failed under a compressive load of 378.1 kN (85,000
lbs.) or 34,474 kPa (5000 psi) differential. The modified, larger
diameter mandrel according to this invention withstood 458.2 kN
(103,000 lbs.) or 41,369 kPa (6000 psi) differential with no
buckling, and up to 685 kN (154,000 lbs.) or 62,053 kPa (9000 psi)
differential with slightly bending but no pressure containment
failure of the packer element.
[0048] FIG. 4 compares the deflated outer diameter of a packer
according to this invention without exposure of 3 inches of the
slats at each end to the deflated outer diameter of a packer
according to this invention with exposure of 3 inches of slats (as
illustrated in FIG. 3) at each end. Each packer was tested within
casing having an inner diameter of about 11.86 cm (4.67 inches).
The element on each packer had an outer diameter of about 9.53 cm
(3.75 inches) and a rubber outer cover with a thickness of about
0.95 cm (3/8 inch). Referring again to FIG. 4, abscissa 70
indicates axial position of the packers during testing, with the
numerals 2, 4, 6, . . . 32 indicating inches from the rubber edge
nearest the top end. Ordinate 71 indicates the measured outer
diameter of the element in inches, area 72 shows measurement data
from the original element before the first inflation, area 73 shows
measurement data about the element as modified with the exposed
slats after 30 inflation/deflation cycles, and area 74 shows
measurement data about the original element (unmodified) after 20
inflation/deflation cycles. The maximum final outer diameter of the
packer with the exposed slats was about 10.62 cm. (4.182 inches)
after 30 cycles compared to a maximum final outer diameter of about
11.30 cm. (4.45 inches) after 20 cycles for the packer without
exposed slats. This reduction in outer diameter increased the
annular flow area by 115% from about 10.2 cm.sup.2 (1.58
inches.sup.2) for the original outer cover to about 21.9 cm.sup.2
(3.39 inches.sup.2) for the modified outer cover. The modified
packer/mandrel assembly was tested successfully in 20/40 proppant,
as will be familiar to those skilled in the art, at pressures up to
about 55,159 kPa (8,000 psi) without failing. During this
experiment, the wiper and improved seal designs discussed herein
were found to operate successfully in particulate-laden fluid.
[0049] While the present invention has been described in terms of
one or more preferred embodiments, it is to be understood that
other modifications may be made without departing from the scope of
the invention, which is set forth in the claims below.
* * * * *