Improved Frac Plug

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of United States Provisional Patent Application Serial Number 62/537,448 entitled "Frac Plug" filed on July 26, 2017; and United States Provisional Patent Serial Number 62/670,234 entitled "Frac Plug" filed on May 11, 2018, both of which are incorporated by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR

DEVELOPMENT

[0001] Not applicable.

BACKGROUND

Field

[0002] Embodiments according to the present disclosure relate to flow control devices for use in oil and gas wells, and particularly to flow control devices used for isolating the portion of the well above the device from portions below the device. Such flow control devices may be used to isolate one region of the wellbore, and/or tubing installed in the wellbore, from other portions thereof and are commonly used in the completion of multiple formations accessed by a single well, multiple stage completions of a single formation, or other activities in which it is desirable to prevent fluid communication across a desired location within the well.

Description of Related Art

[0003] Bridge plugs and firac plugs, including plugs made from composite or degradable materials are known in the art. Such plugs are generally set in casing to isolate a previously treated section of a hydrocarbon producing formation from the next section to be treated. By setting such plugs upwell of each treated section, the wellbore can be treated, such as by fracturing or other treatment, in numerous sections. Once all desired sections of the well are treated, the plugs are typically drilled up and the resulting debris flows to the surface with wellbore fluids. The time required to drill or mill out such plugs adds cost to the well's completion and reducing the drill out/ mill out time is desirable to minimize such costs.

[0004] Despite the desire for faster drill out, frac plugs must be amenable to installation in the well, at a desired location, and be able to isolate fluid pressure above the frac plug from the fluid environment below the plug. It is desirable that such frac plugs have sufficient integrity to maintain at least 5,000 psi differential across the plug when fluid is pumped from the surface, more preferably be able to maintain at least 7,500 psi differential across the plug and even more preferably be able to maintain at least 10,000 psi differential across the plug.

[0005] Reducing drill out time typically involves selection of materials that are more machinable (e.g. more easily drilled or milled) and by reducing the total volume of material that must be removed. However, materials that are more machinable can have less material strength, either generally, in one or more key stress planes, and/or in one or more directions. Thus, thicker and/or longer components may be needed when more machinable material (such as commonly used composites) are employed so that the plug may withstand the same forces as a plug or baffle of a less machinable material (e.g. ductile iron or steel). Therefore, it is desirable to optimize frac plug design such that the plugs may be manufactured from composite, or other high machinability, materials while minimizing the volume of material in the plug.

[0006] One component of frac plugs that receives relatively high loads are the slip bodies, though forming slip bodies of composite or other easily machinable materials remains desirable. Some composite slip bodies may need a mandrel or other structure around and over which they are assembled and which help to maintain their generally tubular configuration as the slip bodies move to their expanded, set state. This requirement for a mandrel inside the slip bodies increases the total material volume, and total length, of the frac plug in its set position, both of which increase the drill out or mill out time of the tool. Such mandrels also increase the amount of material released to move within the well following mill out of the lowest slips. Certain embodiments of the present disclosure reduce and/or eliminate the need for a mandrel to extend through the slips in the unset state, helping to minimize the volume of material in and the length of the firac plug, thereby minimizing drill out/mill out time.

[0007] Additionally, current frac plugs designed to be milled or drilled out typically contain a clutch system of some type to facilitate complete drill out/mill out of the plug. The clutch is necessary because a portion of each frac plug is typically released to freely spin and move down the well once the lowest slip bodies are milled or drilled away. A clutch element at the bottom of the lower end mates with a corresponding clutch at the upper end of the next downwell plug. Engagement of these two clutch elements allows the mill or bit to work through the remaining portion of the upper plug before beginning on the next one. In some circumstances, an upper clutch element may not be available because the next lower plug is degradable or there is no next lower plug. An improved plug requiring little or no mill out/drill out of components below the lowest slips or slip bodies is therefore desirable.

Brief Description

[0008] Embodiments according to the present disclosure strike a balance of the various requirements and forces needed for operation of the frac plug. Embodiments herein provide for a short tool with relatively thin walls so that the volume of material to drill out is reduced. Further, embodiments herein avoid or limit tensile forces and in favor of compressive forces and friction.

[0009] Embodiment plugs may include a floating key system to positionally maintain the slip bodies in a desired configuration while the tool is the run-in state without requiring a mandrel around and over which the slip bodies may slide. Such floating key system may engage the bottom section of an embodiment plug to prevent axial skewing while permitting the slip to expand radially outward when moving to the set position.

[0010] Embodiment plugs may have an angular surface for expansion of the element ring and the slips. Such angular surface may be shallow, such as between about four degrees and about fifteen degrees. Such shallow angle reduces the tendency of the angular surface to be pushed out of the slip bodies and reduces the shear forces applied to the material at the angular surface.

[0011] Further embodiments of the present disclosure may contain an element system in which movement of the slip bodies applies longitudinal force into the element, increasing the pack off force of the rubber, elastomer, or other element. Elements may have a profile that fits into a recess, in the outer surface of the plug's mandrel, permitting the element to include a greater volume of rubber and providing resistance to movement of the element while the plug is run into the well. Such element systems may provide a fluid seal against both the plug and the casing in a single piece of rubber, elastomer, or other appropriate material and permit a uniform sealing force between the plug and casing. Use of an element whose body is made of an extrudable material such as rubber may also facilitate a stronger seal between the element and each of the casing and plug mandrel respectively as well as facilitate the use of a single size plug in casing sizes having varying inner diameters.

[0012] Still further embodiments of the present disclosure may be installed in casing or other host tubing such that the annulus between the upper end of the plug and the host tubing act as a thimble for an element ring of the plug. The characteristics of the element ring in such embodiments may be configured to cooperate with the annulus size in order to limit extrusion or other movement of the element between the plug and host tubing.

[0013] Further embodiments of the present disclosure may include plugs whose components below the slip bodies are comprised of degradable materials— that is materials that retain structural integrity as needed for a given component's function, but dissolve, disintegrate or otherwise are substantially reduced in size over a relatively short time without intervention such as fishing, mill out or drill out. The reduced length of the mandrel in such embodiments, e.g. the mandrel does not run through the slip bodies in the unset position, may facilitate the creation of such a hybrid tool. Hybrid plug embodiments may permit drill out of the plug through the slip bodies with sufficiently small debris and without needing to drill out components below the slip bodies. Such embodiments obviate the need for an adjacent lower plug with a corresponding clutch.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0014] Fig. 1 is a sectional elevation of an embodiment plug according to the disclosure herein.

[0015] Fig. 2 is a sectional elevation of another embodiment plug and connected WLAK according to the disclosure herein.

[0016] Fig. 3 A is an external elevation of one embodiment retainer ring which may be used in certain embodiment plugs according to the disclosure herein.

[0017] Fig. 3B is a sectional elevation of one embodiment retainer ring which may be used in certain embodiment plugs according to the disclosure herein.

[0018] Fig. 4A is a top view of one embodiment slip body which may be used in certain embodiment plugs to the disclosure herein.

[0019] Fig. 4B is an orthogonal view of one embodiment slip body which be used with certain embodiment plugs according to the disclosure herein.

[0020] Fig. 5 is cross sectional view through the bottom portion of one embodiment plug in the unset or run-in state.

[0021] Fig. 6 is a cross sectional view through the bottom portion of one embodiment plug in the set state.

[0022] Fig. 7 is a sectional view of another embodiment plug according to the present disclosure.

[0023] Fig. 8 is an orthogonal view of one embodiment mandrel according to the present disclosure.

[0024] Fig. 9 is a sectional view of an embodiment plug connected to one embodiment wireline adaptor kit.

[0025] Fig. 10 is a sectional view of an embodiment plug set inside a tubular.

[0026] Fig. 11 is an embodiment retainer ring according to the present disclosure.

[0027] Fig. 12 is a plurality of slip bodies arranged in an embodiment retainer ring.

[0028] Fig. 13 is a series of plugs arranged along a host tubular.

[0029] Fig. 14 is a sectional view of an embodiment plug according to the present disclosure.

[0030] Fig. 15 is an orthogonal view of one embodiment retainer ring according to the present disclosure. [0031] Fig. 16 is an orthogonal view of one embodiment shear ring according to the present disclosure.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

[0032] When used with reference to the figures, unless otherwise specified, the terms "upwell," "above," "top," "upper," "downwell," "below," "bottom," "lower," and like terms are used relative to the direction of normal production and/or flow of fluids and or gas through the tool and wellbore. Thus, normal production results in migration through the wellbore and production string from the downwell to upwell direction without regard to whether the tubing string is disposed in a vertical wellbore, a horizontal wellbore, or some combination of both. Similarly, during the fracing process, fracing fluids and/or gasses move from the surface in the downwell direction to the portion of the tubing string within the formation.

[0033] Figure 1 shows an embodiment frac plug 100 according to the present disclosure. The embodiment of Figure 1 comprises a mandrel 110, backup ring 120, element 130, expansion ring 140, slip bodies 150, bottom section 160 and retainer ring 170 (see Figures 3A and 3B). In Figure 1, one finger 172 of retainer ring 170 is visible. Back up ring 120 and expansion ring 140 may be made of suitable materials known in the art such as commercially available nylons while the element may be made of rubber or other suitable materials. The other components may be preferably made of millable materials such as wound composites or other non-metallic materials, though frac plugs of any suitable material are within the scope of the present disclosure. Mandrel 110 comprises a conical or angular outer surface 111 and crenels 112 which may serve as the upper clutch for assisting in drill out/mill out of the lower sections of an upwell plug. Lower section 160 may also contain crenels as the corresponding clutch element for adjacent plugs. Mandrel 110 also has an inner surface which may have a seat 118— such as a shoulder, a generally conical surface, or other feature— for receiving a flapper, ball, dart or other element to seal the interior of the mandrel 110 against flow therethrough. The embodiment of Figure 1 is illustrated with a flapper 180 and associated seat 118 but embodiments of the present disclosure are not limited to flappers and flapper seats for sealing the passage through the mandrel 110.

[0034] Outer surface 111 of mandrel 110 may have a recessed section 115 for receiving a portion of the element 130, the backup ring 120, or both. Such recessed section allows for the volume of the element 130 and/or backup ring 120 to be increased without lengthening the element 130 and/or back up ring 120 and without increasing their outer diameter. Further, engagement of element 130 and/or back up ring 120 in the recessed section may assist to prevent the element and back up ring from swabbing over the mandrel 110 when the plug 100 is being pumped or otherwise run into a well.

[0035] A plurality of slip bodies 150 are arranged with slip body ends adjacent to the expansion ring 140 and surrounding a portion of the mandrel 110. In the embodiment of Figure 1, an assembly ring 152 connects mandrel 110 with the upper end of slip bodies 150. Other components for connecting slip bodies 150 to the lower end of mandrel 110, including but not limited to brass or nylon screws, dowels or other connectors, may be used for such engagement. Buttons 156 are installed in the slip bodies 150 for penetrating into the casing or tubing into which the frac plug is being installed. Such buttons may be of carbide, aluminum oxide, or other materials know in the art.

[0036] It will be appreciated that other forms of slip bodies may be used with embodiment frac plugs. Such slip bodies may include sections or complete slips that break apart as the frac plug transitions from the run in state to the set state. Gripping elements other than buttons, such as teeth, wickers, abrasives and others may be used and are within the scope of the present disclosure.

[0037] The slip bodies 150 may further comprise a ring 154 which may be made of elastomeric or other suitable materials. Such ring may assist in retaining the plurality of slip bodies 150 in the retracted position until the desired location in the well is reached. [0038] Bottom section 160 and retainer ring 170 are connected via shear pins 162. Retainer ring 170 may also have a circular base 174 which fits into a recess of bottom section 160. Slip bodies 150 may have an extension or key 158 extending into and engaging the bottom section 160 and/or the retainer ring 170.

[0039] In operation, embodiments of the present disclosure may be run into a well on wireline using a setting tool such as a conventional Baker 10, Baker 20, or Go-Shorty hydraulic setting tool or other setting tool. Such setting tools are known in the art and may include a suitable or custom wireline adaptor kit (WLAK) for the specific embodiment frac plug, may be connected to the device via setting shear pins 162 connecting a setting mandrel to the bottom of the baffle. Setting tools for plugs conveyed downwell and set using tubing instead of wireline are also know in the art. Assemblies for wireline conveyed plug installation and tubing conveyed plug installation may be referred to collectively as setting assemblies.

[0040] Figure 2 illustrates an embodiment frac plug assembled on a corresponding WLAK. Setting mandrel 260 is connected to the setting tool (not shown) via one or more crossovers 210, and to frac plug 100 at lower section 160 and retainer ring 170 through setting shear pins 162. Shear retainer 270 may be connected to end of shear mandrel 260 to secure shear mandrel to the plurality of shear pins 162 and be configured to capture the ends of shear pins following the setting operation. Setting piston 240 may be connected to the setting tool via crossover 230 and to the firac plug 100 via the upper end of mandrel 110. Mandrel 110 may have a shoulder machined into its upper end for receiving a lip of setting piston 240. Further, setting piston 240 may have an inner surface 250 configured to receive crenels (112 inf Fig. 1) or the upper end of crenels. During such run in, the upper section of mandrel 110 and the bottom section 160 may serve as gauge rings, each having a larger outer diameter than that of the slip bodies 150, element 130, back up ring 120 and expansion ring 140.

[0041] When the setting tool is actuated, force is applied to the setting piston 240 forcing the setting piston 240 and shear pins 162 toward one another. The force of the setting piston 240 is transferred to the mandrel 110 such that the crenels 112 are forced towards the bottom section 160 and retainer ring 170. Movement of the bottom section 160 and retainer ring 170 towards the mandrel pushes the slip bodies 150, and thereby the expansion ring 140, element 130 and retainer ring 120 along the angular outer surface 111 of mandrel 110, causing each to radially expand.

[0042] As the slip bodies 150 and element 130 expand, they come into contact with the casing or other tubing in which the frac plug is being installed. As mandrel 110 continues to move into element 130 and slip bodies 150, thereby forcing element 130 and slip bodies 150 into such casing or tubing, buttons 156 of slip bodies 150 penetrate the casing to mechanically anchor the firac plug. Expansion of the element 130 causes it to seal against both the outer surface of mandrel 110, both on and above the angular outer surface 1 11, and the tubing or casing, substantially preventing fluid communication around the frac plug 100.

[0043] It will be appreciated that element systems of certain embodiments herein provide greater pack off force than other element systems using separate pieces to seal against the mandrel and against the casing respectively. As the element 130 back up ring 120, and expansion ring 140 move over the mandrel, the frictional and compressive mechanical forces increase and resist movement of the back up ring 120 and element 130 over the mandrel's conical outer surface 111.. More energy is required to continue movement of the back up ring 120 and element 130 over the mandrel as the outer diameter 111 of the mandrel 110 increases. Elements made of rubber or other sufficiently elastic materials will absorb that energy and may begin to extrude, including extrusion radially outward, increasing the outer diameter of the element. Such extrusion is in addition to an increase, if any, in the element's outer diameter from movement along the mandrel's angular outer surface 111. When the element extrudes sufficiently to contact the host casing, friction between the element and host casing further resists movement of the element over the mandrel surface. The back up ring 120 and the decreasing annular space between the mandrel outer surface 111 and the host casing limit the ability of the element 130 to extrude longitudinally. Thus, the element 130 becomes constrained in all directions by the back up ring 120, the mandrel outer surface 111, the expansion ring 140 and the host casing. Because of these constraints, the element may store setting energy applied from the slip segment via the expansion ring, increasing the pack off of element 130 against both the mandrel 110 and the host casing. This increase in energy stored by an elastomeric element allows the element to more readily resist the pressure differential the plug experiences during treatment operations.

[0044] When the strength of shear pins 162 is exceeded by the force required to further move the mandrel 110 into back up ring 120, element 130, expansion ring 140 and slip bodies 150, the shear pins 162 can break and release the WLAK from the frac plug 100, leaving frac plug 100 installed in the tubing or casing.

[0045] For the embodiment of Figure 1, removal of the WLAK, and specifically of setting mandrel 260, permits flapper 180 to close against its seat 118 via a spring connected to the hinge of the flapper 180. Fluid pressure, such as may be applied from pumps at the surface, against flapper 180 may complete or reinforce the seal of flapper 180 against seat 118 and operations for treating sections of the well above the frac plug may begin immediately. [0046] For embodiment frac plugs configured to receive balls, darts or other elements introduced into the well from surface, a seat configured to receive such element may be included in the plug. The mandrel of such plug may have an entry section at an angle of about 5 to 10 degrees, and preferably about 6 degrees, leading to a seat 118 having an angle between 25 and 40 degrees, preferably about 30 degrees. In some embodiments, such seat section 118 may be longitudinally below the element 130 when the frac plug 100 is in the set state. In some embodiments, the diameter of a ball used to seal the interior of the frac plug 100 may be between .035 and .250 inches larger than the largest diameter of the seat section, preferably between .08 and .20 inches larger. In one embodiment, made entirely of wound composite materials with aluminum oxide buttons, a 3.25 inch diameter ball seated in a frac plug having a largest seat section diameter of 3.09 inches held 10,000 psi in a pressure test without any movement of the plug within the test casing.

[0047] Tools according to the present disclosure may incorporate a floating key assembly comprising keys and non-restrictive keyways to permit the tool to operate without the mandrel 110 extending through the slip bodies 150 in the run-in position. Such floating key assembly may assist in maintaining the location and orientation of the slip bodies during assembly and run-in while permitting the slip bodies freedom of movement during the setting process.

[0048] Figures 3 A and 3B show external views of retainer ring 170. As discussed with respect to Figure 1, retainer ring 170 may be connected to bottom section 160 through shear pins 162and engagement of circular base 174 of the retainer ring 170 with a groove in bottom section 160. Retainer ring 170 has a plurality of fingers 172 defining key ways between each finger pair. Key ways may include slots 178, which may be adjacent to the base ring 174 of retainer ring 170. The fingers 172 may be configured such that the gap between fingers at the interior diameter of the fingers is smaller than the gap at the outer diameter.

[0049] Figures 4A and 4B show external views of certain embodiment slip bodies 150 according to the present disclosure. Slip body 150 has a generally rectangular profile with an inner surface and an outer surface. Holes 157 for buttons and one or more taps 159 for shear pins may be machined into the outer surface of or through slip bodies 150, respectively. The outer surface may also have a channel 155 for receiving ring 154 (described with respect to Figure 1, above). Slip bodies 150 according to the present disclosure may also have key section 158 extending from the generally rectangular profile. Such key section 158 may be manufactured as a single piece with the rectangular body or may be a separate piece connected to the rectangular body via threaded connections, adhesives, or other fastening during assembly. [0050] Key section 158 may be complimentary to the key ways between fingers 172 of retainer ring 170. For example, the enlarged end of key section 158 may be wider than the gap between the fingers but fit into slots 178. Further, the sides of key section 158 may be tapered such that the inner surface of key section 158 is narrower than the outer surface of key section 158, permitting an elongated or shaft portion of key section 158 to fit between fingers 172 while reducing the contact between key section 158 and fingers 172.

[0051] During assembly of the frac plug 100, key section 158 of each of the plurality of slip bodies 150 may placed into the key way between two fingers 172 of retainer ring 170. The engagement of the key sections 158 with the key ways of retainer ring 170 may postion the plurality of slip bodies 150 in a generally tubular arrangement. The retainer ring 170 with associated slip bodies 150 may then be placed inside the bottom section 160. Bottom section 160 may then be connected to fingers 172 via shear pins 162.

[0052] Figure 5 shows a cross section of the assembled retainer ring 170, bottom section 160, and plurality of slip bodies 150 at a location just below the shear pins. In this arrangement, movement of slip bodies 150 is constrained circumferentially by the placement of of key sections 158 in keyways between fingers 172. The slip bodies 150 are constrained longitudinally by the insertion of the enlarged end of key section 158 into slots 178 as well as engagement of rectangular section of the slip bodies 150 against the opposing end of both fingers 172 and, in some embodiments, bottom section 160. Ring 154 may be placed into groove (155 in Fig. 4A and 4B), generally prior to connecting the slip bodiesl50 with the mandrel 110.

[0053] The upper portion of the firac plug may be assembled by sliding the back up ring 120, element 130 and expansion ring 140 onto the lower end of mandrel 110 and seating the element 130 and/or back up ring 120 into the recessed area 115 in the angular outer surface 111. If present, assembly ring 152 may be installed after the expansion ring 140. The upper end of slip bodies 150 may then be installed over the lower end of mandrel 110 and the slip bodies connected to the mandrel by assembly ring 152 or by other connecters. The WLAK may then be installed through the mandrel 110, slip bodies 150, and bottom section 160 and connected to the shear pins 162 via the shear retainer 270.

[0054] Figure 6 shows the same cross section as Figure 5, but with respect to a firac plug in the set position. Key sections 158 have expanded outward between fingers 172, but the key ways are configured such that the sides 159 of key sections 158 no longer engage fingers 172. It will be appreciated that some limited contact between key sections 158 and fingers 172 may occur, but the wider key way between fingers 178 limits such contact and allows the slip bodies 150 to expand and set against the host casing without substantial interference from the key sections 158.

[0055] Figure 7 shows an embodiment frac plug 300 according to the present disclosure. The embodiment of Figure 7 comprises a mandrel 310, element 330, expansion ring 340, slip bodies 350, bottom section 360 and retainer ring 370 (see Figure 11) as reflected by the location of finger 372. Mandrel 310 comprises a conical outer surface 311, and crenels 312 which may serve as the upper clutch for assisting in drill out/mill of the lower sections of an upwell plug. Lower section 360 may also contain crenels as the corresponding clutch element for adjacent plugs. Mandrel 310 also has an inner surface which may have a seat 318— such as a shoulder, a generally conical surface, or other feature— for receiving a flapper, ball, dart or other element to seal the interior of the mandrel 310 against flow therethrough. In some embodiments, the seat 318 may be on the inner diameter generally adjacent to the apex 317 on the outer diameter.

[0056] As can be seen more clearly in Fig. 8, the conical outer surface 311 of mandrel 310 may have a generally continuous angular profile with a recessed section 315 which may engage a portion of the element 330. The engagement of element 330 in recess 315 is illustrated in Fig. 7. Such recessed section allows for the volume of the element 330 to be increased by increasing its radial cross-section without increasing the element's 330 length or outer diameter. Further, engagement of element 330 in the recessed section may assist to prevent the element 330 swabbing over the mandrel 310 when the plug 300 is being pumped or otherwise run into a well. Shear pin taps 353 may be included for pinning slip bodies 350 to mandrel 310.

[0057] Some embodiment elements, such as element 330 may be run without a back up ring, e.g. back up ring 120 in Fig.1, or the element may be extended such that the back up ring function is at least partially incorporated into the element itself. It will be appreciated that element 330 is elongated on the side closer to the seat 318 compared with element 130 in Fig. 1. It is preferred, though not required, that the leading edge of the elongated portion be at least thick enough, from inner diameter to outer diameter, to fill the annular space between the casing and the upper portion 319, between apex 317 and crenels 312, and conical outer surface 311. In some embodiments, the leading edge may be configured to fill the annular space based on the published nominal inner diameter for the host casing. Thus, for a firac plug whose upper end has an outer diameter of 4.375 inches and is settable in casing having a 5.5 inch outer diameter and a weight to length ratio of 20 pounds per foot, the leading edge of the element may be about 0.21 to 0.22 inches thick. However, elements with a leading edge both smaller and larger than the annular space at the apex 317 of the conical outer surface 311 of the mandrel 310 are within the scope of the present disclosure, including the use of an element with a 0.21 to 0.22 inch thick leading edge in an annular space that is, based on nominal casing inner diameter, about 0.15 inches.

[0058] The recess has an entry section leading to the recess's reduced diameter. The leading section may have an angle of about 13 degrees. The entry section reduces the outer diameter of the mandrel in order to accommodate the extra thickness of the element. The recess may also have an exit section, at an angle of about 20 degrees leading out of the recess' s reduced diameter and adjacent to the expansion ring. The exit section may help define the reduced diameter and aid in firmly positioning the element along the outer conical surface. Further, the exit section may assist in preventing the element from swabbing over the mandrel, and off of the tool, during run in.

[0059] Referring to Fig. 7, a plurality of slip bodies 350 are each positioned about the end of mandrel 310 adjacent to the expansion ring 340. Screws, such as brass shear pins, may connect each slip body 350 to the mandrel 310. Such screws or other connector may serve as an anti-preset device in addition to fixing the upper end of slip bodies 350 in place with respect to mandrel 310. Other components for connecting slip bodies 350 to the lower end of mandrel 310, including but not limited to nylon screws, dowels, elastic rings or other connectors, may be used for such engagement. Buttons 356 may be installed in the slip bodies 350 for penetrating into the casing or tubing into which the frac plug is being set. Such buttons may be of carbide, aluminum oxide, or other materials known or which become known in the art and other gripping elements such as teeth, wickers or others may be used in lieu of such buttons.

[0060] The slip bodies may be engaged by a ring 354 which may be made of elastomeric or other suitable materials. Such ring 354 may assist in retaining the plurality of slip bodies 350 in the retracted position until the desired location with the well is reached.

[0061] Bottom section 360 and retainer ring 370 may be threadedly connected by complimentary threads on the interior surface of the bottom section 360 and the outer surface of fingers 372. Shear ring 374 may be positioned between bottom section 360 and retainer ring 370. Slip bodies 350 may have an extension or key 358 extending into and engaging the retainer ring 370 within the interior of bottom section 360.

[0062] In operation, embodiments of the present disclosure may be run in on wireline using a setting tool such as a conventional Baker 10, Baker 20, or Go-Shorty hydraulic setting tool or other setting tool. Such setting tools are known in the art. Such setting tool, which may also include a suitable or custom wireline adaptor kit (WLAK) for the specific embodiment frac plug, may be connected to the device via setting shear pins connecting a setting mandrel to the bottom of the baffle. [0063] Figure 9 illustrates an embodiment frac plug assembled on a corresponding WLAK. Setting mandrel 460 is connected to the setting tool (not shown) via one or more crossovers 410, and to frac plug 300 at shear ring 374 positioned between lower section 360 and retainer ring 370. Shear ring 374 may be preferred over shear pins in embodiments made of certain materials, such as wound composites, due to the avoidance of point loads where the shear pin is pulled or pushed against another component as the frac plug is being set. ... Shear retainer 470 may be connected to end of shear mandrel 460 to secure shear mandrel 460 to the shear ring 374 and be configured to capture the section of shear ring 374 broken away during the setting procedure. Setting piston 430 may be connected to the setting tool via setting nut 405 and to the frac plug 300 via the upper end of mandrel 310. Mandrel 310 may have a shoulder machined into its upper end for receiving a lip of setting piston 430. Further, setting piston 430 may have an inner surface configured to receive crenels 362, or the upper end of crenels 362.

[0064] When the setting tool is actuated, force is applied to the setting piston 430 to force the setting piston 430 towards the shear mandrel 460 and shear ring 374. The force of the setting piston 430 is transferred to the mandrel 310 such that the crenels 362 are forced towards the bottom section 360 and retainer ring 370. Force from the shear mandrel 460 is transferred to the retainer ring 370 via the shear ring 374. Movement of retainer ring 370 towards the mandrel 310 (or the mandrel towards the retainer ring) causes the plurality of slip bodies 350, and thereby the expansion ring 340 and element 330 to be moved relative to the angular outer surface 311 of mandrel 310, each of which then radially expands.

[0065] As the slip bodies 350 and element 330 expand, they come into contact with the casing or other tubing in which the frac plug is being installed. As mandrel 310 continues to move into element 330 and slip bodies 350, thereby forcing element 330 and slip bodies 350 into such casing or tubing, buttons 356 of slip bodies 350 penetrate the casing to mechanically anchor the frac plug 300. Expansion of the element 330 causes it to seal against both the outer surface of mandrel 310 (including conical outer surface 311) and the tubing or casing, substantially preventing fluid communication around the frac plug 300.

[0066] It will be appreciated that element systems of certain embodiments provide greater pack off force than element systems having separate components which seal against the mandrel and against the casing respectively. The increased pack off force results from the force of slip bodies 350, applied through the expansion ring 340, which longitudinally compresses element 330. More particularly, the transition of frac plug 300 from the unset to the set position moves element 330 over the mandrel 310 across the increasing diameter of outer conical surface 311. Such movement progressively increases frictional forces resisting movement. Further, the elasticity of rubber or other elastomer from which the element 330 may be made may cause such element to resist movement along the conical outer surface's progressively larger outer diameter. Elements of sufficiently elastic materials will absorb that energy and may begin to extrude, including extrusion radially outward, increasing the outer diameter of the element. When the element extrudes sufficiently to contact the host casing, friction between the element and host casing further resist movement of the element over the mandrel surface. Further, as the element reaches and or passes apex 317 at the upper end of outer conical surface 311, the element 330 becomes constrained, or substantially constrained, in all directions— by the annular space between the plug and the casing, the mandrel outer surface 311, the expansion ring 340, and the host casing— and the element 330 may receive and store the setting energy applied from the slip bodies 350 via the expansion ring 340. Such stored energy increases the pack off of element 330 against both the mandrel 310 and the host casing.

[0067] When the strength of shear ring 374 is exceeded by the force required to further move the mandrel 310 into element 330, expansion ring 340 and slip bodies 350, the shear ring 374 can break and release the WLAK from the firac plug 300, leaving frac plug 300 installed in the host tubing or casing.

[0068] Figure 10 illustrates an embodiment frac plug set inside a host tubing or casing 500. Mandrel 310, element 330, expansion ring 340 slip bodies 350, bottom section 360 and retainer ring 370 are as generally described with respect to Figure 7. However, each slip body is engaged with a side or section of mandrel 310 along at least most of the slip body and the element 330 and expansion ring 340 have moved along the mandrel 310 so they are positioned adjacent to the apex of the conical outer diameter 311 and become expanded to contact and grip the casing. Element 330 may be partially extruded in the annulus between the upper end of frac plug 310 and the casing 500. The length of the upper end of frac plug 300, between apex 317 and the crenels 362, may be selected to prevent such element 330 from extruding onto and or between the crenels 362. In one embodiment, such arrangement positions the element 330, around the exterior of the mandrel 310, adjacent to the seat 318 on the interior of the of mandrel 310 and may prevent the formation of a pressure differential across the mandrel wall when a ball or other plug are engaged on the seat. 318

[0069] Referring to Figure 11, embodiment retainer rings may be constructed in various configurations. While the retainer 170 of Figures 1, 3 A and 3B extend from a circular base, the retainer 370 of Figures 7 and 11 has fingers 372 inscribed into a tubular structure. As shown in Fig. 12, keys 358 of slip bodies 350 are positioned between the fingers 372 and ring 354 may be installed around the slip bodies 350 to maintain the slip bodies' 350 arrangement in the retainer ring 370. Further, shear spins may be connected to slip bodies 350 and mandrel 310 through shear pins in shear pin taps 355 and 353 in the slip bodies 350 and mandrel 310 respectively. It will be appreciated in such embodiment, keys 358 may rest on the outer surface of the tubular structure between fingers 372, rather than resting against both walls of adjacent fingers 172, as shown in Fig. 5.

[0070] Another advantage of the embodiments herein is that different sections of the tool experience significantly different forces and may be readily constructed from different materials. For example, the key section (158, 358) of slip bodies (150, 350) retainer ring (170,370) bottom section 160 and shear element (shear pins 162, shear ring 374 or other shear element) primarily functionally serve during run in and setting of the frac plug. Thus, it is possible to make a hybrid tool in which the mandrel (110, 310) and the general portions of the slip bodies (150, 350) which engage and support the engagement with the casing when in the set position may be manufactured with wound composites, or other highly machinable materials, while portions of the slip bodies and components below the slip bodies— the key sections (158, 358) bottom section (160, 360) and retainer ring (170, 370)— may be made from materials such as magnesium and/or aluminum alloys or other materials— that efficiently degrade in the wellbore without further intervention. After installation, the mandrel 110, back up ring 120, element 130 expansion ring 150 and slip bodies 150 remain functional even after the lower elements (e.g. key section 158, 358 bottom section 160, 360 and retainer ring 170, 370) degrade away. Key section, bottom section and retainer ring may be referred to as a lower setting ring assembly as these components are assembled together below the slip bodies 150, 350 and are used to transfer setting force from the setting tool to the slip bodies and element. A hybrid plug, such as the described plug with components of the lower setting assembly manufactured from degradable materials, could be placed at the bottom of the well or as the bottom most plug above fully degradable plugs, sliding sleeves, large bore plugs or other toe section completion. Positioned thus, the hybrid plug could provide the clutch needed to drill out/mill out the bottom portions of the plug(s) upwell after which the mandrel 110, slip bodies 150 and other upper elements of the hybrid plug may be milled out and the bottom portions degrade away.

[0071] Referring to Figure 13, such a hybrid plug 700 may be used as a transition between plugs 600, such as fully composite plugs, intended for drill out and fully degradable plugs 800. In some embodiments, at least one plug 600 intended to be fully drilled out, such as a fully composite firac plug, is installed in host casing upwell of hybrid plug 700. The bottom section, retaining ring and keys of certain embodiment plugs, such as can be seen in Figure 10, do not expand during setting and therefore are not held against the walls of the casing, but are held in place via the keys' connection to their respective slip bodies. During drillout, these components become free or loose in the well after the slip bodies have been drilled away. The drill bit or mill may push these components of plug 600 downwell until they engage the hybrid plug 700. The crenels of bottom section in the fully drillable plug 600 (e.g. Fig. 7, crenels 364) can then engage upper crenels (Fig. 7, upper crenels 312) to facilitate drillout of these remaining portions of plug 600.

[0072] With respect to the drillout of hybrid plug 700, the mandrel, element, expansion ring and slip bodies may be comprised primarily of wound composite or other readily millable materials while the keys, retaining ring and bottom section are comprised of degradable material such as magnesium, magnesium and/or aluminum alloys or other degradable materials. The readily millable components may be drilled out, which releases the keys, retainer ring, shear ring and bottom section from the host casing. Because these components are comprised of degradable materials, they may have already degraded away or may be left in the well to degrade following drillout of the components above them. Because the entirety of lower plug 800 is made of degradable components, there is no need to drill out any portion of it. Therefore, the drillout assembly may be removed from the well once the upper portions of hybrid plug 700 are milled out.

[0073] While it may be desirable that the upper section of hybrid plug 700 mate with the bottom section of plug 600, the other components of hybrid plug 700 are not required to match with plug 600, provided that the components below the slip bodies or slip bodies of hybrid plug 700 are made of degradable material. Further, fully degradable plug 800 may be of any configuration that meets the performance requirements— such as pressure rating and degradation time— of the treatment application for which it is installed. One example of a fully degradable plug which my be used below a hybrid plug is the Kronos™ Plug sold by Applicant.

[0074] Other features may be incorporated into the slip bodies themselves to facilitate the formation of such a hybrid firac plug. For example, it may be desirable to utilize hybrid slip bodies, e.g. slip bodies in which the slip bodies are manufactured from drillable materials to a point past the lowest button or other gripping element which is then joined with a degradable material. Alternatively, the gripping elements may be positioned in the slip bodies such that debris from drillout of the slip body is small enough for efficient removal from the well.

[0075] Degradable materials are known in the art. Some degradable materials include alloys of magnesium and/or aluminum, but other degradable materials for use in hybrid plugs are within the scope of the present disclosure provided such materials retain structural integrity until the hybrid plug is set. In some embodiments, the degradable material will permit loss of mass, over 30 days, for the particular component(s) such that the largest remaining piece will be less than about 20% of the mass of the original component.. Degradable materials that allow for the largest remaining pieces to be less than about 10% of the mass of the original component after 30 days are preferred and materials allowing degradation such that the largest remaining piece is less than about 5% of the components mass after 30 days are more preferred. However, materials with faster and slower degradation times, provided they may be efficiently removed from the well without intervention, are within the scope the present disclosure.

[0076] Fig 14 is another embodiment plug according to the present disclosure. Mandrel 910 with angular surface 911, element 950 in recess, expansion ring 940, slip bodies 950 with shear pins 952, ring 954 and buttons 956, lower section 960, retainer ring 970 and shear ring 974 are generally arranged as described with respect to Fig. 7.

[0077] Slip bodies 950 may have scores or grooves 955 on their outer surface (e.g. the surface that contacts the host casing when installed). Such grooves may assist the outer surface of slip bodies 950 to conform to the inner surface of the casing in which the frac plug is installed and thereby improve the slip body's engagement with and holding power against the casing. In some installations, the drill bit or mill may not effectively remove the outermost layer one or more of the slip bodies or portions thereof because the bit or mill is smaller than the inner diameter of the host casing. The grooves 956, when present, may be machined to ensure that the bit or mill can be selected to remove the slip bodies 950 to at least the depth of such grooves 956, Thus, any fragments of the slip bodies that remain by mill out may be limited to the spaces between grooves 956 that our outside the diameter of the mill that is used. Further, in certain embodiment hybrid tools, the grooves may reduce the size of debris from drill out of the portion of the slips below the buttons or other gripping elements, which may be particularly useful in hybrid plugs.

[0078] As shown in Fig. 15, retainer ring 970 may have a setting shoulder 973 positioned between the setting ring 974 and fingers 972 as shown in Figure 15. Such setting shoulder 973 facilitates more even loading around the circumference of the shear ring's 974 face during setting of the plug.

[0079] Figure 16 illustrates one embodiment shear ring 974 according to the present disclosure. Such shear ring 974 may be made from magnesium, an alloy or magnesium or other degradable materials with suitable shear properties. Shear ring 974 may have a tab or shoulder, such as tab 975 for engaging a slot, recess or shoulder to prevent shear ring 974 from spinning, and acting as a thrust washer, during mill out or drill out. Shear ring 974 may also have a shear plane 976, which may be configured empirically for a given batch of raw material, so that it shears at a desired force, such as at or about 25,000 pounds of force.

[0080] The advantages of the present embodiments become readily apparent, allowing for a tool that minimizes the amount of required material and permitting highly machinable materials, such as wound composite material or degradable material to be used. Some embodiment plugs may be formed using Lamitex G-13 wound composite material, obtained from Franklin Fibre-Lamitex Corp in Wilmington Delaware. In some embodiments, slip bodies may be formed from Lamitex G-13 with a varying wind angle that is shallower nearer the innder diameter (e.g. the fibers generally run more circumferentially under the buttons) and the angle of the wind becomes steeper moving towards the outer diameter. This arrangement assists in preventing the buttons from pushing through the slip bodies as the casing is engaged while helping prevent shear of the slip bodies due to longitudinal force against the shaft of the buttons. Further, the use of wound composites may also increase the friction forces between the conical outer surface and each of the element and the slip bodies, helping to hold the firac plug in the set state.

[0081] Embodiment plugs have may an outer conical surface with a shallow angle, such as about five degrees. Such shallow angle provides for a longer outer conical surface and therefore longer slip bodies. Such additional length may increase the frictional forces between the slip bodies and the outer conical surface. Further, the length between the seat, such as seat 318, and the lower end of the mandrel may be increased, providing additional strength against the shear forces applied to the seat by the ball, dart, flapper or other sealing device for which the seat is configured.

[0082] In one embodiment the recessed section in such outer surface may have a minimum outer diameter that is decreased relative to the angular outer surface of mandrel by about 0.1 inches. The element may have an inner diameter that is complimentary to the recess and .0625 to .125 inches diametrically smaller than the outer surface of the recess to reduce swabbing of the element off of the plug during run in. While the embodiment recesses (e.g. 11 specifically disclosed with respect to the drawings herein have particular configurations, any recess including grooves, scallops, reduced o.d. and shoulder, indentations or other structure are within the scope of the present disclosure provided that such recess enables, in comparison with a continuation of the angular outer surface, a greater volume of element material without requiring increased element length or outer diameter.

[0083] In some embodiments shown to operate successfully downhole and to maintain pressure differentials of at least 10,000 psi in shop tests, the element was comprised of rubber having a durometer of at least 80 and more preferably of at least 84, and elements made of rubber or other elastomers or extrudable materials and having durometers lower than 80 and higher than 84 are within the scope of the present disclosure, s Use of higher durometer materials may reduce extrusion of element in the annular space between the upper section of the mandrel and the host casing, thereby assisting the thimble effect of such annulus while use of lower durometer elements may increase extrusion and permit use of a single size plug across a wider range of host casing internal diameters.

[0084] Further embodiment plugs may have a shear ring whose shear surface is configured smaller than the inner diameter of the mandrel. For example, one embodiment plug may have a mandrel with a minimum internal diameter 2.78 inches. In order for the sheared off portion of shear ring, such as shear ring 974, to fit through the mandrel without pulling the mandrel out of the slip bodies, the shear section 976 of shear ring 974 may have a maximum outer diameter of 2.5 inches, providing sufficient clearance for removal of the sheared portion of shear ring without interfering with mandrel positioning and therefore tool operation.

[0085] In some embodiments, the expansion ring may be configured with a longer surface extending over the upper end of slips. Such longer surface may limit the ability of slip bodies to pivot such that the upper end of slip body (e.g. adjacent to shear taps 355 in Fig. 7) rises away from the mandrel. Such pivoting may prevent the slips from properly engaging the inner surface of the casing and prevent the frac plug from holding its designed pressure and possibly cause plug failure.

[0086] Devices according to the present disclosure are described with reference to specific embodiments. Alternatives to the described arrangements will be apparent from a review of the embodiments of the disclosure and such alternatives are within the scope of the invention as claimed. Further, while the embodiments may be described as being made of particular materials or particular types of materials, the invention as claimed is not limited to embodiments so constructed.