Patent Application
20080115928
The invention relates to a packoff nipple and structures supporting packoff nipples and more particular to a non-extruding packoff nipple and arrangement thereof for sealing an annular space in a well pipe.
It is often the case that wells require stimulation to restart or enhance hydrocarbon flow. Such stimulation typically involves pumping stimulation fluid into the hydrocarbon bearing formation under pressure. Stimulation fluid may comprise components such as acid, sand, and energized carbon dioxide and nitrogen gases that, alone and under high pressures, can be damaging to the structural integrity and internal surfaces of a wellhead assembly that is installed at the top of a well casing or tubing. In other instances, it is preferred to localize the effects of elevated pressure in a well.
To protect a wellhead from damage including from high pressures and corrosive or erosive materials used during stimulation of a well, a wellhead isolation tool is used. Such a wellhead isolation tool typically includes a tubular mandrel inserted through the wellhead, blow out preventors (BOP) and the like and into the well tubing or casing therein, such that pressurized stimulation fluids pass through the mandrel without exposure to the wellhead and surface equipment components. To completely seal the wellhead from stimulation fluids during operation, the mandrel has a sealing means, commonly referred to as a sealing nipple or packoff nipple, at its downhole end for achieving a fluid seal against the inside of the tubing or casing while under high stimulating pressure. Such packoff nipples are very well known in the art. For example, U.S. Pat. No. 4,023,814 to Pitts, U.S. Pat. No. 4,111,261 to Oliver, 1978, Canadian Patent 1,169,766 to McLeod and U.S. Pat. No. 5,060,723 to Sutherland and Wenger disclose an annular elastomeric sealing cup attached in a fixed position to a nipple body which expands radially under high fluid pressures to form a friction seal of the annular space between the nipple body and the well tubing or casing. Oliver further discloses an elastomeric packer ring fixedly positioned above the sealing cup as a secondary sealing means. More recently, axially moveable annular elastomeric sealing members have been disclosed whereby stimulation pressures force an elastomeric member to move upwardly and extrude into a narrowing annular space, thereby resulting in an extrusion seal. For example, in U.S. Pat. No. 5,261,487 to McLeod and Roesch, a lower sealing cup expands radially and moves upwardly against an upper packer ring. The packer ring is then forced to extrude between a shoulder section projecting outwardly from the nipple body and the well casing or tubing. In U.S. Pat. No. 6,918,441 to Dallas, rather than using packer ring, a top portion of a sealing cup is extruded. In both cases, however, both a friction seal and an extrusion seal are formed. When pressure is equalized and the nipple is withdrawn from the tubing, the elastomeric members are anticipated to collapse to their original shape thereby allowing safe extraction of the wellhead isolation tool.
To remove the packoff nipple after well stimulation operations are completed, the residual well pressure is equalized above the packoff nipple in the objective of relaxing the elastomeric seals to thereby allow for safe extraction of the packoff nipple.
In general, elastomeric seals of prior art packoff nipples are susceptible to damage during well tubing or casing entry or exit, particularly when the packoff nipple must pass areas of restricted internal diameter. This can be particularly problematic with extruded seals, which typically become permanently deformed when actuated. Prior art packoff nipples are also prone to seal pre-activation during well tubing entry whereby the seals are forced from their protective running-in condition to an actuated condition, thereby increasing the likelihood of seal damage. In any case, damage to the seals does not permit the packoff nipple to be reused and also results in damaged seal material being left in the well, thereby increasing the cost of operations.
Other difficulties encountered by prior art packoff nipples include seal failure due to seal damage by exposure to extreme temperatures associated with CO2 and N2 stimulating fluids, as well as due to misalignment of the packoff nipple in the well tubing.
There is, therefore, a need for an improved packoff nipple.
The invention provides an improved packoff nipple that provides a non-extruding sealing means for sealing an annular space in a well pipe, such as in response to differential pressures across the packoff nipple. Herein, one embodiment of the packoff nipple is described in the context of isolating high pressures downhole of the packoff nipple and orienting terms of downhole and uphole are used and understood to apply in that context, although other orientations are possible and the term downhole would then also refer to the higher pressure side of the packoff nipple.
In one embodiment, the packoff nipple provides one or more elastomeric sealing rings adapted to seal the annular space in response to an actuating mechanical force, preferably pressure-induced, exerted against each sealing ring. Furthermore, the packoff nipple is adapted to axially compress the sealing rings in response to increasing pressure. Upon equalization of the pressure differential across the packoff nipple, the sealing rings substantially return to their pre-actuated shape, thereby permitting the packoff nipple to be safely extracted from the well pipe without incurring damage to the sealing rings. The packoff nipple can be used for any operations that introduce elevated pressure into a well where it is desired to isolate the annular space. For example, one or more packoff nipples can be fit on the end of a mandrel of a wellhead isolation tool to isolate an uphole wellhead from high pressures and corrosive materials used downhole of the packoff nipples during well stimulation.
In further detail, an embodiment of the packoff nipple comprises a tubular body adapted to be positioned within a bore of a well pipe, with an annular space being formed between the tubular body and the well pipe. A sealing ring assembly comprising at least one elastomeric sealing ring is positioned to be axially moveable around the tubular body. Each sealing ring includes a downhole face having a circumferential groove formed therein and an expansion portion adjacent the circumferential groove. The packoff nipple further comprises an uphole stop positioned around the tubular body and uphole of the sealing ring assembly to substantially extend across the annular space, and an actuator positioned axially moveably around the tubular body and downhole of the sealing ring assembly. In operation, the actuator is caused to move uphole, such as by elevated pressure in the annular space below the actuator, and forcibly engage the sealing ring assembly. Mechanical force is therefore applied against or transferred to the downhole face of each sealing ring causing at least the expansion portion of each sealing ring to expand radially to seal the annular space and the sealing ring assembly to move uphole until it contacts the uphole stop. Upon contact with the uphole stop, the sealing ring or rings are axially compressed between the actuator causing further radial expansion of the sealing rings to further accentuate the sealing of the annular space. Notably, the sealing rings adjacent the uphole stop are encouraged not to extrude past the uphole stop or otherwise become permanently destroyed when actuated, thereby allowing the packoff nipple to be used repeatedly in the same or other operations in a cost-effective manner.
The sealing ring assembly preferably includes a plurality of stacked sealing rings to provide a redundancy in sealing. The sealing ring assembly can further include rigid spacers positioned between the actuator and an adjacent sealing ring and between adjacent sealing rings. The rigid spacers may assist in keeping the sealing rings perpendicular to the tubular body for tripping in and out of the well pipe and in equalizing actuating forces exerted across the downhole face of a sealing ring.
Preferably, the actuator is an elastomeric packer cup positioned downhole of the sealing ring assembly and being moveable on the tubular body, in which case the packer cup provides a primary seal, with the sealing ring assembly providing a secondary seal.
The sealing rings and the packer cup of the packoff nipple can also be adapted in various ways to avoid pre-activation, whereby the sealing rings and packer cup are forced from their protective running-in condition to an actuated condition and consequently damaged or destroyed as they enter the restrictive annular space.
Further adaptations to the packoff nipple that provide functional and structural advantages for any packoff nipple are also described. For example, the uphole stop can have a concave stop surface that urges or constrains a top of an adjacent sealing ring or any other suitable sealing member radially inwardly to avoid extrusion. In addition, an improved sleeve suitable for use with any sealing member, such as a packer cup, intended to be slidably fit around a tubular body is also provided, whereby the sleeve includes an upper radial compression surface to form a supplemental seal between the radial compression surface and the tubular body.
In drawings which are intended to illustrate embodiments of the invention and which are not intended to limit the scope of the invention:
With reference to
In principle, elevated fluid pressures in the annular sealing space 24 downhole of the packoff nipple 10, such as from well stimulation operations, cause the packer cup 30 to actuate and move axially along the tubular body then to engage and actuate the sealing ring assembly 26, thereby reversibly sealing the annular sealing space 24 with the packer cup 30 and each sealing ring 28.
In detail and with further reference to
While the packoff nipple 10 can include a single sealing ring 28, it may be desired to use a stack of two or more sealing rings 28 to provide a redundancy in sealing.
The packer cup 30 comprises an elongated elastomeric member having a mounting portion 48 and a downwardly depending skirt 50 that is open at its bottom end 52. In operation, upon elevated pressure, the skirt 50 flares, i.e. expands outwardly, to seal against the well pipe 22 thereby providing a primary seal. The pressure contained in the skirt 50 then causes the packer cup 30 to slide axially on the tubular body 12 towards low pressure and forcibly engage the sealing ring assembly 26. The resulting mechanical force exerted on the downhole face 40 of each sealing ring 28, either by forcible contact of the packer cup 30, a top 54 of another sealing ring 28, or rigid spacer 32, causes the lower expansion portion 44 to expand radially to seal the annular sealing space 24 (
To release the packoff nipple 10 from its actuated condition, stimulation pressure is removed and equalizing pressure corresponding to the residual well pressure is applied above the packoff nipple 10. The equalizing pressure migrates downwardly past the sealing rings 28, and further migrates to the packer cup 30 to thereby release the packer cup 30 from the tubular body 12. If necessary, the packoff nipple 10 can be stroked up and down to encourage the equalizing pressure to migrate past any sealing rings 28 and the packer cup 30. Since the sealing rings 28 and packer cup 30 are not extruded or otherwise permanently deformed, they substantially instantaneously and reversibly return to their pre-activated state when the packoff nipple 10 is released from its actuated condition. Consequently, the packoff nipple 10 can be used repeatedly in the same or other operations.
To restrict downward slippage of the packer cup 30 during extraction of the packoff nipple 10 from the well pipe, the downhole stop 38, provides an outwardly projecting shoulder formed from the tubular body 12 against which a bottom surface 60 of the mounting portion 48 of the packer cup 30 can abut. The downhole stop 38 should be positioned sufficiently far from the bullnose 20 to prevent the skirt 50 of the packer cup 30 from lodging between the well pipe 22 and the bullnose 20 as the skirt 50 becomes elongated when the packoff nipple 10 is extracted.
While it is preferred that the sealing ring assembly 26 be moveably positioned around the tubular body 12 to reduce the likelihood of pre-activation of sealing rings 28 upon entry into restricted areas of the well pipe 22, the sealing ring assembly 26 can also be adapted to resist upward axial movement. For example, the sealing ring assembly 26 can frictionally engage the tubular body or be positioned to abut against the uphole stop 36 when in the non-actuated position.
The sealing rings 28 and packer cup 30 can be of any suitable fabrication and construction as would be apparent to one skilled in the art. For example, the elastomeric material can be any suitable urethane. Preferably, the sealing rings 28 are made of a material having a durometer value in the order of about 80A-95A, and most preferably 95A, whereby the material is soft enough to be expandable under typical operating conditions, while being hard enough to not be undesirably deformed. Generally, the packer cup 30 is made of softer material than the sealing rings 28. Further preferably, elastomeric material is resistant to degradation by intense pressure, chemical and extreme hot or cold temperatures conditions encountered in well stimulation operations, such as the proprietary “hybrid” urethane provided by HiTek Urethane Ltd (Nisku, Alberta). Applicant has noted that while stimulation operations intend that stimulation fluids be pumped at temperatures of about 80-100° F., temperatures often have exceeded 200° F. Consequently, conventional urethane sealing rings, which tend to break down at temperatures exceeding 180° F., may be unsuitable in some cases. The urethane should also be manufactured under known standards and conditions with respect to cleanliness and curing temperatures and times that are important for maintaining the strength of the urethane, such as those for 95A urethane. Further, the urethane may also be manufactured with an integrated lubricant additive to reduced the chance of pre-activation of the sealing rings 28 and packer cup 30.
To reduce the likelihood of pre-activation and damage to the sealing ring 28 upon entering restricted well pipe diameter, an outer diameter 62 of the sealing ring 28 can be marginally less than an outer diameter 64 of the packer cup 30.
As is particularly shown in
Preferably, an outer sidewall 72 of each sealing ring 28 has a generally V-shaped, radially outwardly tapered profile, with a lower portion 74 of sealing ring 28 being tapered upwardly and radially outwardly to an apex and an upper portion 76 of the sealing ring 28 being tapered upwardly and radially inwardly from the apex. The V-shaped profile assists in actuation of the sealing rings 28. In particular, as the apex of the actuated sealing ring 28 is axially compacted between the packer cup 30 and the uphole stop 36, compressive forces cause a reactive expansion of the lower portion 74. The V-shaped profile also assists in minimizing damage to any sealing rings 28 upon entry into the well pipe 22 by reducing the outer cross-sectional diameter of the downhole face 40 of the sealing rings 28 and permitting the sealing rings 28 to compress radially inwardly when entering restricted well diameters.
Referring now to
With additional reference to FIGS. 6A-C and 7-10, the uphole stop 36 is generally positioned around the tubular body 12 and includes an annular stop surface 80 extending substantially across the annulus 24 against which a top 54 of an adjacent sealing ring 28 can abut or contact. The uphole stop 36 may be formed, for example, from a sizing ring positioned around the tubular body 12 (FIGS. 1A-C, 2A, 2B, 5, 8-10) or from the lower box end of the mandrel 16 (
With particular reference to FIGS. 1A-C, 2A, 2B, 5 and 6A-C and 12, the uphole stop 36 preferably forms a downwardly depending lip 86 spaced radially and outwardly from the tubular body 12 for constraining the top 54 of the adjacent sealing ring 28 radially inward to the tubular body 12. The lip 86 thereby helps to ensure the adjacent sealing ring 28 does not extrude into the annular space 55 uphole of the stop 28.
The annular surface 80 of the uphole stop 36 may be flat, as shown in
To assist in the entry of the sealing ring 28 into the annular cup space 88, the stop surface 80 may have an extended radially inwardly profiled portion 89, as seen in
With additional reference to
With particular reference to
In the embodiments shown, the expansion ring 90 is integrally formed with the uphole stop 36, although the expansion ring 90 can be separate from the uphole stop 36.
In an arrangement of lower and upper packoff nipple 10a, 10b, as shown in
The outer sidewall 92 of the expansion ring 90 can be parallel to the tubular body 12, (
Where the outer sidewall 72 of the sealing ring 28 has a V-shaped profile, as described previously, the cross-sectional width of each of the expansion ring 90 and the top 54 of the sealing ring 28 are preferably sized to prevent substantial radial expansion of the top 54 of the sealing ring 28. At the same time, more significant compressive force is exerted on the upper portion 76 of the sealing ring, thereby directing the expansion portion 44 to expand radially and further improve the seal. In other words, the cross-sectional width of the annular surface of the stop 36 substantially corresponds to the cross-sectional width of the top 54 of the sealing ring 28.
Where rigid spacers 32 are used, as described previously, the rigid spacers 32 can be, for example, high durometer thrust washers, steel washers, or axially elongated steel rings. In general, the rigid spacers 32 assist in keep the sealing rings 28 generally perpendicular to the tubular body 12, which reduces the likelihood of seal pre-activation. Further, the rigid spacers 32 assist in equalizing force exerted across the downhole face 40 of the sealing ring 28. This may be particularly important if there has been damage to the downhole face 40 of the sealing ring 28. The spacers 32 may also help ensure that equalization pressure migrates to the packer cup 30.
Having now described various embodiments of the sealing assembly, the packer cup will now be described in detail. As previously described, the packer cup 30 comprises an elastomeric mounting portion 48 and a downwardly depending elastomeric skirt 50. The packer cup can also include further features, including a rigid sleeve 96 securely inset within the mounting portion 46 and adjacent the tubular body 12, and which is slidably positioned on the tubular body 12. Preferably, the sleeve 96 is made of steel and the mounting portion 48 is bonded to the sleeve 96. Typically, the sleeve 96 includes a groove 98 in its inner periphery into which an elastomeric O-ring 100 is mounted, thereby creating a moveable seal between the packer cup 30 and the tubular body 12. The O-ring 100 also helps to ensure that stimulation fluid does not leak between the tubular body 12 and the packer cup 30.
The sleeve 96 can be configured in a variety of ways to enhance operation of the packer cup 30. As shown, for example, in
While it is particularly contemplated to use a sleeve 96 having a radial compression surface 102 with the packer cup 30, such a sleeve could be used for any type of sealing member including a sleeve to be fit on any tubular body, such as some sealing rings.
In another embodiment, and with reference to
With particular reference to
In another embodiment and as best seen in FIGS. 1A-C, a backup sleeve seal can be provided to reduce or eliminate load on the sleeve bond and thereby prevent seal failure. In particular, elastomeric material of the mounting portion of the packer cup 30 extends radially inwardly below the sleeve, thereby providing for improved seal of the mounting portion and sleeve when the packer cup 30 moves up the tubular body 12.
While a conventional packer cup 30 can be used, and as shown in greater detail in
an elastomeric and annular skirt extending axially from the annular mounting portion and adapted to engage the well pipe to seal the annular space, wherein an outer diameter of the skirt is greater than an inner diameter of the well pipe and wherein an inner side wall of the annular skirt has a radially outwardly, generally V-shaped profile which deflects inwardly when engaged with the well pipe.
While it is preferable to use a packer cup 30 as the sealing ring assembly 26 actuator, other suitable actuators can be used as would be understood by one skilled in the art. For example, the actuator 30 could be an axially moveable ring (not shown) positioned around the tubular body 12 and below the sealing rings 28 which could be mechanically pulled upward to forcibly engage the downhole face 40 of a sealing ring 28.
As previously mentioned, the bullnose 20 guides and centralizes the packoff nipple 10 as it enters the well pipe 22. With further reference to
Preferably, the bullnose 20 is an exchangeable ring which can then be replaced if damaged. In addition, exchangeable bullnoses 20 of various outer diameters can be fit on a tubular body 12 to provide closer tolerances to the well pipe, thereby optimizing centralization of the packoff nipple and optimizing protection of the sealing rings 28 and packer cup 30 when entering the well pipe 22. Even further, where all components on the tubular body 12 are exchangeable, the same tubular body 12 can be used with well pipe 22 of various inner diameter, thereby providing a potential cost savings. As an additional convenience, the packer cup 30 and sealing rings 28 sized to a well pipe can be mounted on adapter sleeves (not shown) of various sizes which fit over the tubular body 12, rather than being mounted directly on tubular bodies 12 of varying sizes.
With reference to
While the packoff nipple 10 has been described for sealing the annular sealing space 24 from upwardly directed pressures, one skilled in the art would appreciate that the packoff nipple 10 can also be oriented to seal annular sealing space 24 from downwardly directed pressures. In this case, all designated uphole and downhole orientations in the foregoing description would be reversed. Further, as one would understand that opposing orientation of two packoff nipples would constrain pressure therebetween.
The following exemplifies the outer diameters of various components of a packoff nipple 10 according to the present invention installed in well pipe 22 of an inner diameter of 2.441 inches.
The following exemplifies the outer diameters of a various components for a packoff nipple 10 according to the present invention installed in well pipe of an inner diameter of 4.892 inches.
Although preferred embodiments of the invention have been described in some detail herein above, those skilled in the art will recognize that various substitutions and modifications of the invention may be made without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2487533 | Nov 2004 | CA | national |
| 2488794 | Dec 2004 | CA | national |
| 2503790 | Apr 2005 | CA | national |
This application is a divisional application of U.S. application Ser. No. 11/164,126, filed Nov. 10, 2005, the entirety of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11164126 | Nov 2005 | US |
| Child | 12020914 | Jan 2008 | US |
