Patent Application
20140311752
The present invention relates to downhole tools and methods of removing such tools from wellbores. More particularly, the present invention relates to downhole tools designed to be comprised of dissolvable materials or frangible materials and methods for dissolving or fragmenting such downhole tools in situ.
A wide variety of downhole tools may be used within a wellbore in connection with producing hydrocarbons or reworking a well that extends into a hydrocarbon formation. Downhole tools such as frac plugs, bridge plugs, and packers, for example, may be used to seal a component against casing along the wellbore wall or to isolate one pressure zone of the formation from another. Such downhole tools are well known in the art.
After the production or reworking operation is complete, these downhole tools must be removed from the wellbore. Tool removal has conventionally been accomplished by complex retrieval operations, or by milling or drilling the tool out of the wellbore mechanically. Thus, downhole tools are either retrievable or disposable. Disposable downhole tools have traditionally been formed of drillable metal materials such as cast iron, brass and aluminum. To reduce the milling or drilling time, the next generation of downhole tools was formed from composites and other non-metallic materials, such as engineering grade plastics. Nevertheless, milling and drilling continues to be a time consuming and expensive operation. Therefore, a need exists for disposable downhole tools that are removable without being milled or drilled out of the wellbore, and for methods of removing disposable downhole tools without tripping a significant quantity of equipment into the wellbore.
In accordance with one embodiment of the invention there is provided a downhole apparatus for use in a wellbore. The apparatus comprises a center mandrel, a slip assembly, a cup shaped sealing element, a ring element and a sleeve. The slip assembly is disposed on the mandrel. The slip assembly grippingly engages the wellbore when the downhole apparatus is in a set position. The cup shaped sealing element is disposed on the mandrel. The sealing element sealingly engages the wellbore when the downhole apparatus is in the set position. The ring element is disposed on the mandrel and operationally engages the sealing element and the slip assembly such that, when a setting force is applied to the ring element, the ring element outwardly expands thus transferring the setting force to the sealing element such that the sealing element sealing engages the wellbore and the ring element axially transfers the setting force to the slip assembly such that the slip assembly grippingly engages the wellbore. The sleeve is disposed on the mandrel. The sleeve transfers the setting force from a setting tool to the ring element when the downhole apparatus is changed from an unset position to the set position.
In accordance with another embodiment of the invention there is provided a downhole apparatus for use in a wellbore. The apparatus comprises a central mandrel, and a sealing element. The central mandrel is comprised of frangible material that breaks apart under impact or pressure wave. The sealing element is disposed about the mandrel wherein the sealing element sealingly engages the wellbore when the downhole apparatus is in a set position.
In accordance with yet another embodiment of the invention there is provided a method of performing a downhole operation wherein a downhole tool is disposed within a wellbore. The method comprises:
Referring to the drawings,
Within wellbore 12 is downhole tool 18. In the embodiment of the invention illustrated in
In
A slip assembly 40 is positioned on and/or disposed about mandrel 20. Upward facing shoulder 30 provides an abutment, which serves to axially retain slip assembly 40 from downward movement. When downhole tool 18 is in its set position, slip assembly 40 provides anchoring for downhole tool 18 by grippingly engaging wellbore 12, which is by grippingly engaging casing 14 if it is present. Slip assembly 40 includes a slip ring 42 and a slip wedge 44. Slip ring 42 has an inclined/wedge-shaped first surface 46 positioned proximate to an inclined/wedge-shaped complementary second surface 48 of slip wedge 44. Slip ring 42 can have wickers or buttons 50 positioned on its outer surface. Buttons 50 bite into wellbore 12 or casing 14 when downhole tool 18 is placed in its set position, thus anchoring downhole tool 18. Slip ring 42 can be an integral unit of frangiblely connected slip segments or can comprise slip segments held in place by retaining bands 52, as is known in the art.
At its upper end 54, slip wedge 44 abuts retaining ring 56 and cup-shaped sealing element 60. Sealing element 60 and retaining ring 56 are disposed about mandrel 20. Sealing element 60 is generally cup-shaped in that it forms a first chamber 62 and a second chamber 64 separated by radially extending portion 66. Second chamber 64 houses retaining ring 56 and first chamber 62 houses ring element 68, which is disposed about mandrel 20. Accordingly, at upper end 58, retaining ring 56 abuts radially extending portion 66, which is sandwiched between retaining ring 56 and ring element 68. At its upper end 70, ring element 68 abuts ratcheted sleeve 72, which is disposed about mandrel 20. Ratcheted sleeve 72 has a generally axial-extending cylindrical shape with ratcheting teeth 74 on its inner surface that mate with ratcheting teeth 38 on setting tool connector 32.
Ring element 68 and sealing element 60 are generally comprised of material that can hold a pressure seal. For example, ring element 68 and sealing element 60 can be made from materials including, but not limited to, fluorocarbon elastomer or nitrile rubber. While the other portions of downhole tool 18 can be made from metal or composite material, in one embodiment of the inventions at least some of them will be made from material selected from the group comprising frangible materials or dissolvable materials and combinations thereof. In one embodiment of the invention at least mandrel 20 is made from a frangible material or a dissolvable material. Typically, at least mandrel 20 and slip wedge 44 will be made from frangible material or dissolvable material. Additionally, other components such as slip ring 42 can be made from frangible material or dissolvable material.
By frangible materials it is meant materials that can hold up to the downhole environment for the period of time the plug is needed in the wellbore but which can be readily broken up into fragments by impact or application of pressure waves and without resorting to drilling or other severe techniques. The components may be formed of any frangible material that is suitable for service in a downhole environment and that provides adequate strength to enable proper operation of downhole tool 18. Suitable frangible materials include materials made from glass or glass ceramics. Suitable glass materials can be selected from the group consisting of borosilicate, aluminosilicate, soda lime, sapphire, fused quartz/silica and combinations thereof. The frangible material can be chemically or thermally treated to increase its strength, as is known in the art. When frangible materials are used in the components of the downhole tool, it generally becomes necessary to use lower setting force than is used with traditional downhole tools. Downhole tool 18 described above advantageously utilizes such lower setting force and, thus, is well suited for the use of frangible materials. In downhole tool 18 the setting force is applied to the mandrel 20 and ratchet sleeve 72 and then directly transferred into the sealing element 60 and the slip assembly 40. The cup-shaped sealing element 60 serves to reduce the force required to set the downhole tool.
By dissolvable materials it is meant materials that dissolve when exposed to a chemical solution, an ultraviolet light, a nuclear source or a combination thereof. The components may be formed of any dissolvable material that is suitable for service in a downhole environment and that provides adequate strength to enable proper operation of downhole tool 18. By way of example only, one such material is an epoxy resin that dissolves when exposed to a caustic fluid. Another such material is a fiberglass that dissolves when exposed to an acid. Still another such material is a binding agent, such as an epoxy resin, for example, with glass reinforcement that dissolves when exposed to a chemical solution of caustic fluid or acidic fluid. Other such materials include various dissolvable metals. Any of these exemplary materials could also degrade when exposed to an ultraviolet light or a nuclear source. Thus, the materials may dissolve from exposure to a chemical solution, or from exposure to an ultraviolet light or a nuclear source, or by a combination thereof. The particular material matrix used to form the dissolvable components of the downhole tool 18 are customizable for operation in a particular pressure and temperature range, or to control the dissolution rate of the downhole tool 18 when exposed to a chemical solution, an ultraviolet light, a nuclear source, or a combination thereof. Thus, a dissolvable downhole tool 18 may operate as a 30-minute plug, a three-hour plug, or a three-day plug, for example, or any other timeframe desired by the operator. Alternatively, the chemical solution may be customized, and/or operating parameters of the ultraviolet light source or nuclear source may be altered, to control the dissolution rate of the plug comprising a certain material matrix.
In operation, downhole tool 18 may be used in well operations such as stimulation/fracturing operations to isolate the zone of the formation below the downhole tool 18. Referring now to
Downhole tool 18 is then lowered by a cable 79 to the desired depth within the wellbore 12. Once in the desire location, downhole tool 18 is changed from its unset position to its set position by engaging a setting tool (not shown) with the setting tool connector 32 at upper end 36. The setting tool applies axial force to ratcheted sleeve 72 causing it to move axially toward ring element 68 from a first position to a second position and thereby asserting axial force on ring element 68. The interaction of ratcheting teeth 38 and 74 prevent sleeve 72 from moving axially away from ring element 68. Thus, even if the setting tool is disengaged, sleeve 72 will remain in the second position and maintain its pressure on ring element 68.
Ring element 68 transfers axial force to retaining ring 56 through radial extending portion 66. Retaining ring 56 moves axially and, in turn, transfers the axial force to slip wedge 44 of slip assembly 40. This causes slip wedge 44 to move axially with first surface 46 and second surface 48 sliding over one another so that slip wedge 44 moves further underneath slip ring 42; that is, between slip ring 42 and mandrel 20. The movement of slip wedge 44 exerts a radially outward force on slip ring 42 so that it grippingly engages the wellbore 12, generally the inner wall 16 of casing 14. As slip ring 12 grippingly engages wellbore 12, the axial force on ring element 68 causes compression; thus, ring element 68 not only transfers axial force to retaining ring 56 through radial extending portion 66, but also expands radially outwardly because of the compression. Thus, ring element 68 exerts an outward radial force on sealing element 60 causing it to sealingly engage the wellbore 12, generally the inner wall 16 of casing 14. Thus, the sealing element 60 is set against the wellbore 12 and the downhole tool 18 has been placed in its set position, thereby isolating zone A as depicted in
After the downhole tool 18 is set into position as shown in
After the fluid recovery operations are complete, the downhole tool 18 must be removed from the wellbore 12. In this context, as stated above, at least some of the components of downhole tool 18 are frangible, dissolvable or both. Generally, the components will be either frangible or dissolvable. This nature of the components eliminates the need to mill or drill downhole tool 18 out of the wellbore 12. Thus, when at least some of the components are frangible, they can be fragmented by use of a fragmenter, which fragments the components by impact, pressure wave or a combination thereof causing the downhole tool 18 to release from the wellbore 12 and the fragmented components, along with the unfragmented components, fall to the bottom of the wellbore 12. Similarly, where at least some of the components are dissolvable, the can be dissolved by exposing downhole tool 18 to a chemical solution, an ultraviolet light, a nuclear source, or a combination thereof, and at least some of its components will dissolve, causing the downhole tool 18 to release from the wellbore 12, and the undissolved components of downhole tool 18 to fall to the bottom of the wellbore 12.
Additionally, a frangible downhole tool can be fragmented by traditional drill out methods. The use of a drill bit can provide impact and break up of the frangible material. Advantageously, a frangible downhole tool has a significantly shortened drill-out time than traditional downhole tools.
As depicted in
As will be readily apparent, there are a number of other ways to dissolve the dissolvable components. For example, a pumpable dart may be used to release the chemical solution onto the downhole tool 18. The pumpable dart engages and seals against the casing within the wellbore. Therefore, fluid must be pumped into the wellbore behind the pumpable dart to force the dart to move within the wellbore and contact downhole tool 18. In another example, an enclosure is provided on the downhole tool for storing the chemical solution. An activation mechanism, such as a slideable valve, for example, may be provided to release the chemical solution from the enclosure onto the downhole tool. This activation mechanism may be timer-controlled or operated mechanically, hydraulically, electrically, or via communication means, such as a wireless signal, for example. This embodiment would be advantageous for fluid recovery operations using more than one downhole tool, since the activation mechanism for each downhole tool could be actuated as desired to release the chemical solution from the enclosure and dissolve each downhole tool at the appropriate time with respect to the fluid recovery operations. In a further example, a wire line or slick line 86 could be used to lower an ultraviolet light source or a nuclear source in the vicinity of the downhole tool. Exposure to one of these sources will dissolve at least some components of the downhole tool, thereby causing the downhole tool to release from the wellbore, and the undissolved components of the downhole tool to fall to the bottom of the wellbore.
If additional well stimulation/fracturing operations will be performed, such as recovering hydrocarbons from zone C, additional downhole tools 18 may be installed within the wellbore 12 to isolate each zone in accordance with the procedure outline above.
Turning now to
Downhole tool 92 has first extrusion limiter 100 and second extrusion limter 102, which support first end 96 and second end 98, respectively, of sealing element 94 during setting of downhole tool 92. In setting downhole 92, a setting tool (not shown) engages with the setting tool connector 32 at upper end 36. The setting tool applies axial force to ratcheted sleeve 72 causing it to move axially towards extrusion limiter 100 from a first position to a second position and thereby asserting axial force on extrusion limiter 100. The interaction of ratcheting teeth 38 and 74 prevent sleeve 72 from moving axially away from extrusion limiter 100. Thus, even if the setting tool is disengaged, sleeve 72 will remain in the second position and maintain its pressure on extrusion limiter 100.
Extrusion limiter 100 transfers axial force to extrusion limiter 102 through sealing element 94. Extrusion limiter 102 abuts slip assembly 40 and moves axially so that it, in turn, transfers the axial force to slip wedge 44 of slip assembly 40. This causes slip wedge 44 to move axially with first surface 46 and second surface 48 sliding over one another so that slip wedge 44 moves further underneath slip ring 42; that is, between slip ring 42 and mandrel 20. The movement of slip wedge 44 exerts a radially outward force on slip ring 42 so that it grippingly engages the wellbore 12, generally the inner wall 16 of casing 14. As slip ring 42 grippingly engages wellbore 12, the axial force on sealing element 94 causes compression; thus, sealing element 94 expands radially outwardly and causing it to sealingly engage the wellbore 12, generally the inner wall 16 of casing 14. Removal of downhole tool 92 can be by the methods described above for downhole tool 18.
Removing a downhole tool, such as described above, from the wellbore is more cost effective and less time consuming than removing conventional downhole tools, which requires making one or more trips into the wellbore with a mill or drill to gradually grind or cut the tool away. The foregoing descriptions of specific embodiments of a frangible tool and dissolvable tool, and the systems and methods for removing such tools from the wellbore have been presented for purposes of illustration and description and are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many other modifications and variations are possible. In particular, the type of downhole tool, or the particular components that make up the downhole tool could be varied.
While various embodiments of the invention have been shown and described herein, modifications may be made by one skilled in the art without departing from the spirit and the teachings of the invention. The embodiments described here are exemplary only, and are not intended to be limiting. Many variations, combinations, and modifications of the invention disclosed herein are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is defined by the claims, which follow. The scope includes all equivalents of the subject matter of the claims.
