Patent Application
20080110639
When a well is drilled to intersect a hydrocarbon-producing formation, it is often necessary to stimulate the formation to enhance the flow of hydrocarbons. Stimulation treatments generally include pumping of fluids under high pressure into a well and into a formation. The stimulation fluid may be, for example, an acid or a proppant containing fluid utilized for fracturing a formation. The stimulation fluids are in many instances corrosive and/or abrasive and can cause damage, sometimes irreparable damage, to wellhead equipment if the fluids are pumped directly through the wellhead into a well. To prevent, or at least limit damage to the wellhead, wellhead isolation tools are used. Wellhead isolation tools are designed to isolate the wellhead from the pressure, and corrosive/abrasive fluids.
Known wellhead isolation tools generally utilize a mandrel that is inserted through the various valves and spools of the wellhead. The mandrel will isolate the wellhead from the elevated pressures and from the stimulation fluids utilized during the stimulation process. The mandrel of the wellhead isolation tool is typically connected to a valve through which stimulation fluids will be pumped, and a bottom end of the mandrel is configured with a pack-off assembly so that a seal is provided between the lower end of the mandrel and either the production tubing or casing.
Typically, if other operations are to be conducted in the well, the wellhead isolation tool must be removed to allow the passage of service tools. For example, if it is desired to set a packer or bridge plug in the well above or below a previously perforated formation and perforate an additional formation in the well, the wellhead isolation tool must be removed and the bridge plug, or packer, along with the perforating device can be lowered into the well on a tubing or wire line. Once the bridge plug is set and the additional formation perforated, the service tools must be removed and the wellhead isolation tool reinserted for any stimulation of the formation. The process of removing the wellhead isolation tool, and then reinserting must be repeated any time tools must be lowered into the well to conduct downhole operations. The following U.S. published applications are examples of wellhead isolation tools: U.S. 2005/0217868 A1; U.S. 2003/0192698 A1; U.S. 2003/0221323 A1; U.S. 2003/0221838 A1.
There is a need for a wellhead isolation tool that will provide a proper seal to prevent damage to the wellhead and that will also allow for the passage of other service tools therethrough.
The wellhead isolation tool of the current invention is a self-aligning wellhead isolation tool that sealingly engages the production casing. The self-aligning wellhead isolation tool has a tubular mandrel with a centralizing device slidably mounted thereto. The tubular mandrel has a sealing system at or near the lower end thereof. The wellhead isolation tool may be inserted into the wellhead so that the tubular mandrel extends into the production casing and seals against the production casing. Thus, zones or formations intersected by the well may be stimulated by conducting stimulation fluid through the wellhead isolation tool into the desired formations. The seal between the wellhead isolation tool and the production casing will be such that the wellhead is protected against any abrasive and/or chemical damage since the stimulation fluid will not contact the wellhead.
The centralizing device and tubular mandrel comprise a centralizing apparatus. The centralizing device may comprise a plurality of bow springs slidably disposed about the mandrel and adapted to engage a wellhead interior thereby centralizing the tubular mandrel. Because the tubular mandrel is centralized, it may be efficiently inserted into the production casing. The tubular mandrel thus may be a relatively thin-walled mandrel that defines an open tubular bore through which service tools may be passed.
One or more zones may be stimulated through the wellhead isolation tool and thereafter service tools such as perforating devices and plugging devices (for example, packers, bridge plugs and other plugging devices) may be inserted therethrough so that other operations such as plugging and/or perforating in the well may be conducted. The service tools may be withdrawn through the wellhead isolation tool and stimulation procedures may then be conducted again.
Referring to the drawings,
Referring now to
Wellhead isolation tool 68, which includes a centralizer apparatus 70 may be shown and described with reference to
Centralizing device 74 comprises an upper collar 96 and a lower collar 100 and includes a plurality of bow springs 98 extending between and connected to collars 96 and 100, respectively. Collars 96 and 100 may be attached to bow springs 98 by any means known in the art as well, such as fastening, or spot welding. Any desired number of bow springs may be included and in one embodiment, six bow springs 98 are equally spaced around the circumference of collars 96 and 100.
Diameter 88 has a magnitude such that it may be slidably received in production casing 20. The portion of mandrel 72 with outer diameter 88 may be referred to as lower portion 102. A sealing system 104 is operably associated with mandrel 72 such that when mandrel 72 is inserted into top casing 54 of production casing 20, a seal is created therebetween. Sealing system 104 is preferably positioned in a groove 106 on lower portion 102. Sealing system 104 comprises an annular ring 108 disposed in groove 106. Annular ring 108 has one or more sealing rings thereon, adapted and sized to sealingly engage inner surface 53 of production casing 20.
In the embodiment of
The operation of the isolation tool 68 is as follows. After well 10 has been drilled and production casing 20 has been installed in wellbore 15, casing 20 will be perforated to create perforations 30 in a manner known in the art, so that formation 25 is communicated with casing interior 22. Formation 25 may then be stimulated by a treatment process such as acidizing or fracturing. If desired, wellhead isolation tool 68 can be installed prior to perforating formation 25, or between the initial perforating step and the stimulating process. Generally, prior to perforating, a plug, packer or other well sealing device will be set in the well below the producing formation 25.
When wellhead isolation tool 68 is inserted into the wellhead 40, it will be inserted so that sealing system 104 is received in top casing 54. Sealing system 104 shown in the preferred embodiment includes two sealing rings or seals 110 and 112 of increasing diameter from the lower end 78 toward the upper end 76 of mandrel 72. If desired, more or less than the two sealing rings may be used and one seal only may be used as well. Sealing system 104, and thus seals 110 and 112 are preferably an elastomeric material. Seals 110 and 112 may be swellable elastomeric materials which swell when exposed to a triggering fluid such as water, salt water, hydrocarbons, diesel fuel, kerosene or other chemical materials. Such materials are known and used for example in Halliburton Easywell™ Swellable Technology. Once mandrel 72 is sealingly inserted into production casing 20, stimulation procedures may be conducted. Because mandrel 72 seals inside production casing 20 below bit guide 44, the high pressure experienced during the stimulation procedures does not act upon any components of wellhead 40. Thus, wellhead 40 is protected from not only the high pressure but from the corrosive and/or abrasive effects of the fluids that might be utilized in acidizing or fracturing processes. After the initial formation 25 has been stimulated, it may then be desirable to perforate, stimulate and produce hydrocarbons from one or more additional formations intersected by well 10. The separate locations treated in the well may be referred to as zones, which may be separate formations intersected by the well, or which may be different zones of a single formation.
Because wellhead isolation tool 68 has a relatively thin-walled mandrel and because it has an open mandrel bore 82, wellhead isolation tool 68 does not have to be removed from wellhead 40 prior to passing service tools therethrough. Service tools such as, for example, perforating device 34 which may be a perforating gun lowered on a wire line, or a jetting apparatus lowered on a tubing and sealing device 32 may be passed through wellhead isolation tool 68 into production casing 20. Sealing device 32 and perforating device 34 are shown lowered into well 10 as a single tool string on a wire line 36. It is understood that such devices may be lowered separately, and may be lowered on tubing, coiled or jointed, as opposed to wire line 36. Sealing device 32, which may be any number of sealing devices known in the art such as bridge plugs, or packers, is set in well 10 below formation 38 and above formation 25. Perforating device 34 may then be utilized to perforate the additional formation 38 in well 10. Perforating device 34 may then be retrieved and formation 38 may be stimulated with an acidizing or fracturing fluid as known in the art. Such operations can be conducted sequentially in well 10 as many times as desired without the need for removal of the wellhead isolation tool which is more economical and efficient than prior methods. Thus, any desired number of formations may be perforated and treated as described herein without removing wellhead isolation tool 68. While the downhole operation described herein involves sealing the well and perforating at a plurality of locations, it is to be understood that equipment for performing other downhole operations, such as, for example, frac plugs, packers, coil tubing and coil tubing mud motors, drop darts and perforating balls may be lowered through mandrel 72 of wellhead isolation tool 68.
The wellhead isolation tool 68 described herein is a self-aligning isolation tool that is insertable in casing 20 without causing damage to the mandrel 72 or to sealing system 104. As isolation tool 68 is inserted through wellhead 40 and into production casing 20, bow springs 98 will engage wellhead interior 42 and will centralize mandrel 72 so that it will be received in production casing 20 with little or no damage to sealing system 104 and mandrel 72. Prior apparatus which do not utilize a centralizer require a much heavier wall to prevent damage to the mandrel. As such, a more restrictive bore, which does not provide for the passage of service tools, must be used. Tools that seal above top casing 54 do not adequately protect the wellhead. The current invention resolves both issues. Sealing system 104 will sealingly engage inner bore or inner surface 53 of top casing 54 to provide preferably a pressure and fluid tight seal between isolation tool 68 and production casing 20. Because the thin-walled mandrel 72 is centralized, there is little or no risk of damage to the mandrel or the wellhead. Stimulation operations may then be performed as described hereinabove. After stimulation of the well 10, any number of service operations such as setting plugs, perforating and other operations may be conducted with the wellhead isolation tool 68 in place in wellhead 40. The process of stimulating and conducting downhole operations can be repeated as often as necessary, thus alleviating the need for removal of wellhead isolation tools.
Referring to
Centralizing device 154 comprises an upper collar 176 and a lower collar 180 and includes a plurality of bow springs 178 extending between and connected to collars 176 and 180, respectively. Bow springs 178 may have first and second end rings 182 and 184, respectively, at the ends thereof. End rings 182 and 184 may be utilized to connect the bow springs to upper and lower collars 176 and 180, respectively. End ring 182 may be spot-welded through openings 186 in upper collar 176. Collar 176 may be attached to bow springs 178 by other means known in the art as well. Likewise, bow springs 178 may be attached by any means known in the art to lower collar 180. Upper collar 176 may comprise a collet that includes a plurality of collet fingers 188. While the centralizing device described herein includes upper and lower collars, other configurations that utilize bow springs may be used, for example, bow springs attached to a collar at only one end.
A sealing system 190 is operably associated with mandrel 152 such that when mandrel 152 is inserted into top casing 54 a seal is created therebetween. Sealing system 190 preferably comprises three separate seals, namely a first or upper seal 192, a second or intermediate seal 194 and a third or lower seal 196. Seals 192, 194 and 196 have outer diameters 198, 200 and 202, respectively. Preferably, diameter 202 is smaller than diameter 200 and diameter 200 is smaller than diameter 198 such that the seals are progressively larger in diameter from the lower end 158 of mandrel 152 in a direction upwardly toward upper end 156 of mandrel 152. Seals 192, 194 and 196 are preferably made of an elastomeric material and may be a swellable material as described herein.
When wellhead isolation tool 68a is inserted into the wellhead 40, it will be inserted so that sealing system 190 is received in top casing 54. While sealing system 190 includes three seals 192, 194 and 196 of increasing diameter from the lower end 158 toward the upper end 156 of mandrel 152, more or less than three seals may be used and one seal only may be used as well. Shoulder 168 and groove 164 define the limits of axial movement of centralizing device 154. Lower groove 166 is configured so that collet fingers 188 will be received therein and will prevent any further downward movement relative to mandrel 152. Lower groove 166 therefore is lower limit of axial movement for centralizing device 154. Grooves 166 and 168 are configured to allow collet fingers 188 to move upwardly, and upward travel relative to mandrel 152 stops when collar 180 engages shoulder 168.
Bow springs 178 will engage wellhead 40 in wellhead interior 42 to centralize and align mandrel 152 with production casing 20. Mandrel 152 may therefore be inserted in production casing 20 without prematurely engaging any other surfaces in wellhead interior 42. Mandrel 152 will not be damaged in the insertion process, and because the mandrel defines an open bore, and has a thin wall, service tools will pass therethrough. Just as described with respect to tool 68, tool 68a, when inserted in production casing 20 protects wellhead 40 from not only the high pressure but from the corrosive and/or abrasive effects of the fluids that might be utilized in acidizing or fracturing processes. After the initial formation 25 has been stimulated, it may then be desirable to perforate, stimulate and produce hydrocarbons from one or more additional formations intersected by well 10. The operation described can be performed without the removal of isolation tool 68a.
Thus, it is seen that the apparatus and methods of the present invention readily achieve the ends and advantages mentioned as well as those inherent therein. While certain preferred embodiments of the invention have been illustrated and described for purposes of the present disclosure, numerous changes in the arrangement and construction of parts and steps may be made by those skilled in the art, which changes are encompassed within the scope and spirit of the present invention as defined by the appended claims.
