Field of Invention

The present invention relates to down hole tools for use in drilling operations, and more particularly to down hole plug seals used to isolate zones during drilling operations and other well service.

Background of the Invention

In oil and gas drilling operations, a variety of down hole tools are used for the manufacturing, operation, and maintenance of such drilling systems. One example of a down hole tool is a plug seal, which can be used to seal and isolate certain portions of a drilled well from other portions of the well. A sealing plug that fully isolates one well portion (e.g., a down hole portion) from another well portion (e.g., an up hole portion), wholly blocking flow between the two portions, is commonly referred to as a bridge plug. Other types of plug seals may allow flow in a particular direction (e.g., downstream), but block flow in other directions (e.g., upstream). Plug seals may be permanent, or may be non-permanent dissolving or otherwise removable plug seals.

Hydraulic fracturing (commonly referred to as "fraccing" or "fracking") is becoming a common method of oil and gas drilling, which may employ plug seals to operate different portions of a well. For example, a plug seal may be located within an outer well casing so as to isolate a down hole portion of a well from an up hole portion of the well. In the up hole portion, the well casing may include a plurality of transverse holes that open into a surrounding rock formation. In the hydraulic fracturing process, pressurized fluid is pumped down into the well. At the plug seal, flow is blocked from proceeding from the up hole portion into the down hole portion, pressurizing the well. Under such pressure, the fluid is forced through the holes in the up hole well casing into the adjacent rock formation. The pressurized flow into the rock formation in turn creates cracks through which oil and gas may be extracted.

Conventional plug seals, however, have proven to be deficient in certain respects. It sometimes becomes necessary to remove a plug seal, which typically requires a complex machining and milling process that is costly and time consuming. In addition, conventional plug seals often require sealing elements that seal between the plug seal and the outer well casing. Under the high pressure, the sealing material can extrude along the well casing, which can damage the seal and undermine the sealing efficacy.

Summary of the Invention

The present invention provides an enhanced convertible plug seal assembly that overcomes deficiencies of conventional configurations. During setting, the plug seal assembly of the present invention employs a tapered mandrel that is forced down a tubular housing. As the mandrel is so forced, the tapered configuration of the mandrel expands the housing radially against an inner surface of a well casing bore to press against the well casing. An elastomeric sealing element is provided on a portion of the outer surface of the housing that seals against the well casing. Such a configuration imparts less stress in the elastomeric sealing element than

conventional configurations that axially compress sealing elements to have them bulge radially, and thus the plug seal assembly of the preset invention is less susceptible to damaging extrusion of the sealing element.

The plug seal assembly further incorporates a continuous metallic anti- extrusion ring, offering additional and improved support to the elastomeric sealing element as compared to conventional configurations which use segmented backing rings to prevent extrusion. The lower setting stresses and improved anti-extrusion features allow the sealing element to seal effectively at greater pressures and higher temperatures. In addition, the plug seal assembly of the present invention is substantially shorter than conventional configurations, and the majority of the material used is easily machined, allowing for much shorter milling times if ever it becomes required to remove the plug seal assembly. The plug seal assembly is particularly suitable as a bridge plug, and may be formed as either a dissolving or non-dissolving plug seal depending on the combination of components used. An aspect of the invention, therefore, is a plug seal assembly. In exemplary embodiments, the plug seal assembly includes a tubular housing having a first end and a second end, and defining a hollow bore that extends from the first end to the second, and a mandrel that is moveable within the hollow bore from a first position to a second position in a direction from the first end toward the second end. The housing has a first section adjacent the first end and a second section adjacent the second end, and the first section has a thickness greater than a thickness of the second section. In the first position, the second section has an inner diameter that is smaller than an inner diameter of the first section, and as the mandrel moves from the first position to the second position, the mandrel forces the second section to expand outward such that in the second position, the inner diameters of the first and second sections are substantially the same. The plug seal assembly further may include a sealing element, wherein the housing has an outer diameter including a first groove that is configured to receive the sealing element. The sealing element compresses between the housing and the well casing as the mandrel is moved to the second position to expand the second section of the housing. The plug seal assembly further may include a slip, wherein the outer diameter of the housing has a second groove located toward the second end relative to the first groove, and the second groove is configured to receive the slip. The slip may separate into segments in use and include a plurality of biting teeth that dig into the well casing to grip the well casing as the mandrel is moved to the second position to expand the second section of the housing. In exemplary embodiments of the plug seal assembly, the outer diameter of the housing may have a stress riser in the first section of the housing. The stress riser may be configured as a plurality of pockets milled into the housing or as a third groove. When the mandrel is in the second position, stresses cause the first section of the housing to break away at the stress riser from the remainder of the housing, and the break-away portion of the housing can then be removed.

Another aspect of the invention is a setting process for a plug seal assembly. In exemplary embodiments, the setting process includes the steps of: providing a plug seal assembly in accordance with any of the embodiments, connecting the plug seal assembly to a setting tool and locating the plug seal assembly at a desired position within a well casing, and moving the mandrel from the first position to the second position. The movement of the mandrel forces the second section of the housing to expand outward against the well casing, such that in the second position, the inner diameters of the first and second sections are substantially the same. As the mandrel moves from the first position to the second position, the sealing element compresses within the first groove between the housing and the well casing to form a seal. Also as the mandrel moves from the first position to the second position, the slip expands outward against the well casing and the biting teeth grip the well casing. The setting process further may include breaking the first section of the housing at the stress riser away from the remainder of the housing, and removing the broken away portion of the first section of the housing from the well casing.

These and further features of the present invention will be apparent with reference to the following description and attached drawings. In the description and drawings, particular embodiments of the invention have been disclosed in detail as being indicative of some of the ways in which the principles of the invention may be employed, but it is understood that the invention is not limited correspondingly in scope. Rather, the invention includes all changes, modifications and equivalents coming within the spirit and terms of the claims appended hereto. Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in

combination with or instead of the features of the other embodiments.

Brief Description of the Drawings

Fig. 1 is a drawing depicting a side cross-sectional view of an exemplary convertible plug seal assembly in accordance with embodiments of the present invention, with a mandrel in an initial or first position.

Fig. 2 is a drawing depicting a side cross-sectional view of the exemplary convertible plug seal assembly of Fig. 1 , with the mandrel in a second or set position.

Fig. 3 is a drawing depicting a side cross-sectional view of the exemplary convertible plug seal assembly of Fig. 2, with a housing portion removed up hole of the mandrel.

Fig. 4 is a drawing depicting an isometric side view of an alternative

configuration of an exemplary convertible plug seal assembly in accordance with embodiments of the present invention. Detailed Description

Embodiments of the present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. It will be understood that the figures are not necessarily to scale. Fig. 1 is a drawing depicting a side view of an exemplary convertible plug seal assembly 10 in accordance with embodiments of the present invention. The convertible plug seal assembly 10 includes a tubular housing or sleeve 12, a mandrel 14, a sealing element 16, and a slip 18. The plug seal assembly 10 may be installed by attaching the plug seal assembly to a setting tool (not shown) at a first end 20 of the housing or sleeve 12. The first end 20 is opposite to a second end 22 of the housing or sleeve 12, and the housing or sleeve 12 defines a hollow bore 21 that extends from the first end to the second end. With the plug seal assembly attached to the setting tool, the tool is manipulated to move the plug seal assembly down the bore of an outer well casing (not shown) to a desired position where the plug seal assembly is to be set or anchored. Once in a position to be set, the mandrel is moveable within the hollow bore 21 from a first position to a second position in a direction from the first end 20 toward the second end 22.

Fig. 1 depicts the plug assembly 10 with the mandrel 14 being located in the initial or first position. The housing 12 is configured as a tubular sleeve. The housing 12 has a first or thick section 24 on an up hole side adjacent the first end 20, and a second or thin section 26 on a down hole side adjacent the second end 22 that is a thin section relative to the first or thick section 24. In other words, referring to a wall thickness of the housing 12, the first section 24 has a thickness greater than a thickness of the second section 26. In the state of the plug seal assembly depicted in Fig. 1 with the mandrel in the first position, the second (thin) section 26 has an inner diameter that is smaller than an inner diameter of the first (thick) section 24. When the mandrel is in such first position, the first (thick) section 24 and the second (thin) section 26 are connected by an inward tapered section 25 that slopes radially inward from the thick section 24 to the thin section 26. The inner diameter of the thick section 24 may have coupling features machined therein, such as threads, which allow the plug seal assembly to attach to the setting tool. With the mandrel in the first position as depicted in Fig. 1 , the thin section 26 defines a reduced inner diameter of the housing 12 as compared to the inner diameter defined by the thick section 24. As further described below, the thin nature of the thin section 26 relative to the thick section 24 permits the housing material to expand and grow in diameter during the setting process. In particular, as the mandrel moves from the first position to the second position during the setting process, the mandrel forces the second section to expand outward such that when the mandrel is in the section position, the inner diameters of the first and second sections are substantially the same.

In exemplary embodiments, the housing 12 is made from a ductile material that is preferably metallic. The housing 12 may have two grooves machined out on an outer diameter. In particular, a first groove 28 on the outer diameter of the housing is configured to receive the sealing element 16, and a second groove 30 on the outer diameter of the housing is configured to receive the slip 18. In exemplary embodients as seen in Fig. 1 , the second groove is located toward the second end of the housing relative to the first groove. The first and second grooves 28 and 30 are separated by a ring 32 that extends from the outer diameter of the housing 12 and between the first and second grooves. This ring 32 supports the sealing element 16 and transfers loads developed by fluid pressure from the sealing element 16 to the slip 18. The mandrel 14 is configured as a cylindrical plug of material that fits into the inner diameter of the housing 12. The mandrel may be made of any suitable material that has good compressive strength, a low coefficient of friction relative to the housing material, and is easily machined as are known in the art for down hole tool plug components. Examples of suitable materials for use in the mandrel include cast iron, Garolite, Torlon, and Peek. The coefficient of friction between the mandrel and the housing can be reduced through the use of coatings or lubricants at the mandrel/housing interface in the inner diameter. The mandrel can be alternatively made from a dissolving material as also are known in the art for down hole tool plug components, such that the mandrel is a non-permanent element. Examples of suitable dissolvable materials for use in the mandrel include degradable aluminum alloys, degradable magnesium alloys, and similar materials. Using a dissolvable material permits the plug seal assembly to temporarily isolate sections of a well casing to allow fracturing treatment as described above. With the dissolvable mandrel, the plug seal assembly would then ultimately open up to permit flow without any additional intervention.

The down hole side of the mandrel 14 is configured to have a taper 34 that is sloped relative to the up hole side of the mandrel 14, and sloped commensurately with the tapered section 25 of the housing. In exemplary embodiments, the taper may be configured to have a rounded shape. In the initial state of the plug seal assembly as depicted in Fig.1 with the mandrel in the first position, the mandrel 14 is located within the housing 12 with the taper 34 of the mandrel positioned against the commensurately sloped tapered section 25 of the housing 12. The tapered nature of the mandrel facilitates the expansion of the housing at the thin section 26 during the setting process of the plug seal assembly. As the mandrel moves from the first position to the second position, the taper of the mandrel is forced against the tapered section of the housing to expand the second section of the housing outward. The mandrel is non-permeable and configured to seal fluid tight against the bore of the housing for the duration of the fracturing well treatment.

The sealing element 16 may be made of any suitable elastomeric material as are known in the art, which permits the sealing element to expand easily in the radial direction. In exemplary embodiments particularly suitable for drilling operations, the material of the sealing element 16 is chemically resistant and resilient under exposures to temperatures as high as approximately 400°F. The material of the sealing element 16 also has a high shear strength to resist being extruded under the forces generated by fluid pressure. Two example materials that are suitable for the sealing element 16 are hydrogenated nitrile butadiene rubber (HNBR) and various fluoroelastomers such as VITON®. To enhance the sealing functionality, the sealing element 16 may include a plurality of ribbed features 36 that are compressible in use to enhance the seal and prevent extrusion.

The slip 18 is intended to anchor the plug seal assembly at a specific location within the bore of the outer well casing. To achieve this anchoring function, an outer diameter of the slip 18 may include a plurality of biting teeth 38. The slip 18 anchors to the casing by biting into the casing via the teeth 38, and using the casing material's shear strength to resist movement under the axial load developed by fluid pressure. As seen in Fig. 1 , one exemplary configuration of the teeth 38 is formed by machining a saw tooth pattern on the surface of the slip with the teeth 38 oriented in a direction of expected movement of the plug seal assembly under the fluid pressure. Accordingly, the slip 18 may be made from a rigid material that is hard enough to bite into the casing's wall and yet still remain millable. An example of a suitable material of the slip 18 is grey cast iron, which has a hardened outer surface or case. The case of the slip material may be formed through induction hardening or nitriding. Other materials that are suitable for the slip 18 include steel, ceramic, and tungsten carbide. The slip 18 may be configured having a body that is a ring and cut axially into segments, or the slip 18 may have features that allow a monolithic ring to fracture into equal axial segments during setting. Segmenting allows the slip to grow outward with the housing groove during the setting process.

In use, the plug seal assembly 10 is provided, and then is connected to a setting tool, such as by threading the housing onto a setting tool on the up hole side 20 of the plug seal assembly. The setting tool with the attached plug seal assembly are then located at a desired position within a well casing of a drilling operation. An inner diameter of the thick section 24 of the housing attaches to the setting tool as referenced above. The combined plug seal assembly 10 attached to the setting tool assembly is pumped down the well using fluid pressure and is tethered to a wire line or coiled tubing. When the plug seal assembly reaches its desired position, the wire or tubing stops the down-well movement of plug seal assembly and setting tool by applying tension. This position of the plug seal assembly corresponds to the configuration of the initial position that is shown in Fig. 1.

Fig. 2 is a drawing depicting a side view of the exemplary convertible plug seal assembly 10 of Fig. 1 , showing the plug seal assembly configuration in the set state with the mandrel in the second or set position within an outer well casing (well casing not shown). The setting process occurs as follows. As referenced above, a setting process includes connecting the plug seal assembly to a setting tool, and locating the plug seal assembly at a desired position within a well casing. The setting process further includes moving the mandrel from the first position to the second position, which is the set position of Fig. 2. The movement of the mandrel forces the second section of the housing to expand outward against the well casing, such that in the second position, the inner diameters of the first and second sections are substantially the same. By "substantially the same", it is noted that a small portion of the bore in the zone where the slips are located may have a diameter that is slightly smaller due to the tapers on the slips and mandrel. This smaller bore diameter will have grown from its initial diameter, but not necessarily to the full size of the bore in the first section. This difference between the smaller bore diameter and the bore diameter of the first section is defined as "overlap" and may act to prevent the fluid pressure from forcing the mandrel to push completely through the housing. Aside from such small overlap portion that may occur, the inner diameters of the first and second sections are essentially the same.

To achieve the set position of Fig. 2, the plug seal assembly is activated by extending a plunger (not shown) into the housing first section 24 at the up hole end 20. The plunger presses against the mandrel 14 to move the mandrel from the first position to the second position. The plunger forces the mandrel through the housing 16 to move the mandrel down hole until the mandrel is approximately adjacent the down hole side 22 of the housing. As the mandrel 14 is forced through the housing from the first position to the second position, the mandrel forces the second section 26 of the housing to expand outward such that in the second position of the mandrel, the inner diameters of the first and second sections 24 and 26 are substantially the same. The relative thinness of the second section 26 permits such expansion. In particular, as the mandrel 14 is forced through the housing from the first position to the second position, the taper 34 of the mandrel is forced against the tapered section 25 of the housing. Such force expands the inner diameter of the first (thin) section 26 of the housing as the mandrel is forced down hole. By having a relatively thin wall thickness, the expansion is readily achieved is as the mandrel moves further down hole with the mandrel continually forcing expansion along the thin section 26 of the housing where the taper 34 of the mandrel is forced against the tapered section 25 of the housing.

As the mandrel moves from the first position to the second position, the sealing element compresses within the first groove between the housing and the well casing to form a seal. The expansion of the housing inner diameter of the thin section 26 in turn moves the sealing element 16 outward until the sealing element contacts the bore of the outer well casing and compresses. In use, the sealing element is compressed radially between the casing bore and the expanded diameter of the housing at the groove 28 to seal against both the housing and casing surfaces. The ribbed features 36 reduce the load required to radially compress the sealing element during the setting process. Once the sealing element comes into contact with bore of the well casing, the sealing element compresses radially and bulges in the axial direction under the radial compressing force. The ribbed features 36 permit the material of the sealing element to bulge into the spaces between the ribbed features and cause them to narrow or become filled (compare Fig. 2 to Fig. 1 ). The result is an effective seal with reduced tendency for axial extrusion of the sealing element material.

As the mandrel is forced further down the housing beyond the ring 32, the portion of the thin section 26 of the housing also expands the housing inner diameter in the area of the ring 32 and slip 18. As the mandrel moves from the first position to the second position, the slip expands outward against the well casing, and the plurality of biting teeth grip the well casing when the slip expands against the well casing.

The expansion that forces the ring 32 and slip 18 outward can cause the slip 18 to fracture or separate into multiple separate segments, each segment including a portion of the biting teeth. The ring 32 expands toward the bore of the well casing, which minimizes the clearance between the ring's outer diameter and the well casing inner diameter. As referenced above, the slip 18 also moves radially outward by such expansion and may separate along axial longitudinal lines into segments 18a, 18b, and 18c (the segmenting is not visible in Figs. 2 and 3, but see Fig. 4), each segment including a portion of the biting teeth 38. Although three segments are shown in Fig. 4 as an illustrative example, the actual number of segments can vary. In addition, although as described the segments may form when the mandrel is moved, the segments alternatively may be pre-formed when the plug seal assembly is initially manufactured and assembled before use. The slip segments eventually come into contact with the well casing, and the biting teeth 38 engage with the inner diameter of the well casing to provide the anchoring function to restrict any further movement of the plug seal assembly.

The teeth 38 of the outer surface of the slip segments bite into the casing bore to grip and anchor the slip segments to the well casing, achieving an effective anchoring which requires a substantial increase in force. This also increases the compressive load on the taper 34 of the mandrel 14. Accordingly, once anchoring forces are significant, the mandrel cannot readily translate any further toward the down hole end 22 of the housing without a substantial increase in force. At this point, any increase in force on the mandrel translates into a deeper bite of the slip's teeth into the bore of the well casing.

When such a compressive force is applied to the mandrel to move it down hole, an equal load in tension is generated between the setting tool attachment point at end 20 and the point where the housing cross section 26 is pinched between the taper 34 of the mandrel 14 and the slip segments 18. The housing may have a third groove 40 machined into the outer diameter of the first section 24 of the housing to act as a stress riser. Eventually, when the mandrel is in the second position, the tension load increases to a level of stresses that causes the material at the third groove 40 to shear, separating the up hole end 20 of the plug seal assembly housing from the down hole end 22, with the third groove 40 being the separation point. In this manner, when the mandrel is in the second position, stresses cause the first section of the housing to break at the third groove 40 away from the remainder of the housing. Upon setting, therefore, the plug seal assembly down hole from the groove 40 detaches from the setting tool by shearing the housing at the groove 40. The setting tool is then pulled back to the surface with the break-away portion of the housing 12 up hole from the groove 40 still attached to the setting tool. The down hole portion of the plug seal assembly that has detached from the tool remains in position and isolates the portion of the well that is down hole from the plug seal assembly from the portion of the well casing that is up hole from the plug seal assembly. With the detached portion removed, the remaining portion is shorter as compared to conventional configurations, which makes milling and removing the plug seal assembly easier than typical if needed. Fig. 3 is a drawing depicting a side view of the exemplary convertible plug seal assembly 10 of Fig. 2, with the up hole portion of the housing removed. As shown in the progression of Fig. 2 to Fig 3, the part of the housing between the groove 40 and the up hole end 20 had remained attached to the setting tool and is retrieved to the surface. The part of the housing between the groove 40 and the down hole end 22 remains anchored in the casing by the slip 18. The sealing element 16 seals the outer portion of the housing to the well casing, and the mandrel 14 seals the inner portion of the housing from any downstream flow. The mandrel thus serves a secondary role of keeping the slip segments loaded against the casing bore. Any increase in pressure on the upstream side of the plug seal creates a load on the mandrel to force it toward the down hole side. This load transfers through the taper 34 of the mandrel 14 into the slip 18, which creates a higher contact load between the slip segments and the casing bore. In other words, higher fluid pressures on the upstream side generated during fraccing are countered by a greater resistance to movement of the plug seal assembly by the biting force of the slip segments.

Fig. 4 is a drawing depicting an isometric side view of an alternative

configuration of an exemplary convertible plug seal assembly 50 in accordance with embodiments of the present invention. As plug seal assembly 50 is comparable in many respects to the plug seal assembly 10, like structures are identified with like reference numerals. In addition, because Fig. 4 is an isometric view showing the plug seal assembly in three dimensions, only the outward visible portions of the plug seal assembly are shown. As in the previous embodiment, the plug seal assembly 50 includes a tubular housing or sleeve 12 that extends from the up hole end 20 to the down hole end 22. The embodiment of Fig. 4 further includes the sealing element 16 and the slip 18 that are configured and function comparably as in the embodiment of Figs. 1 -3. In the isometric view of Fig. 4, the specific slips segments 18a, 18b, and 18c are visible, the slip 18 having split into such segments along the longitudinal lines 52 and 54.

The embodiment of Fig. 4 further includes an enhanced stress riser

configuration. In the plug seal assembly 50, the stress riser may be configured as a plurality of pockets 56 milled into the housing. When the mandrel is in the second position, stresses cause the first section of the housing to break away at the pockets from the remainder of the housing, and the break-away portion of the housing can then be removed. Configuring the stress riser as pockets milled in the housing has advantages. The fractured surface of the pockets takes on the shape of tines which can couple with the castellations of a milled remnant, for example from a bridge plug up stream, to allow complete milling. Examples of such castellations 58 are depicted as also being present on the down hole end 22, as the various drilling segments would include such castellations for interaction between segments. The plug seal assembly 10/50, therefore, provides enhanced performance in isolating portions of a drilling well as compared to conventional configurations.

Conventional bridge plugs may be pressure activated, but to a lesser degree as compared to the configuration of the present invention. The shallow taper 34 and the large area of the mandrel 14 generate a high load at the teeth 38. In addition, the lower setting stresses and improved anti-extrusion features allow the sealing element to seal effectively at greater pressures and higher temperatures. In addition, the plug seal assembly of the present invention is substantially shorter than conventional configurations, and the majority of the material used is easily machined, allowing for much shorter milling times if ever it becomes required to remove the plug seal assembly.

An aspect of the invention, therefore, is a plug seal assembly. In exemplary embodiments, the plug seal assembly includes a tubular housing having a first end and a second end, and defining a hollow bore that extends from the first end to the second; and a mandrel that is moveable within the hollow bore from a first position to a second position in a direction from the first end toward the second end. The housing has a first section adjacent the first end and a second section adjacent the second end, and the first section has a thickness greater than a thickness of the second section. In the first position, the second section has an inner diameter that is smaller than an inner diameter of the first section, and as the mandrel moves from the first position to the second position, the mandrel forces the second section to expand outward such that in the second position, the inner diameters of the first and second sections are substantially the same. The plug seal assembly further may include one or more of the following features, either individually or in combination. In an exemplary embodiment of the plug seal assembly, when the mandrel is in the first position, the first and second sections of the housing are connected by an inward tapered section that slopes radially inward from the first section to the second section.

In an exemplary embodiment of the plug seal assembly, the mandrel has a taper that is sloped commensurately with the tapered section of the housing when the mandrel is in the first position, and as the mandrel moves from the first position to the second position, the taper of the mandrel is forced against the tapered section to expand the second section of the housing outward. In an exemplary embodiment of the plug seal assembly, the assembly further includes a sealing element, wherein the housing has an outer diameter including a first groove that is configured to receive the sealing element.

In an exemplary embodiment of the plug seal assembly, the assembly further includes a slip, wherein the outer diameter of the housing has a second groove located toward the second end relative to the first groove, and the second groove is configured to receive the slip.

In an exemplary embodiment of the plug seal assembly, the housing further comprises a ring that extends from the outer diameter, and the ring separates the first and second grooves.

In an exemplary embodiment of the plug seal assembly, the sealing element has a plurality of ribs, and the ribs are compressible within the first groove when the mandrel is moved from the first position to the second position.

In an exemplary embodiment of the plug seal assembly, the sealing element is made of an elastomeric material.

In an exemplary embodiment of the plug seal assembly, an outer diameter of the slip includes a plurality of biting teeth.

In an exemplary embodiment of the plug seal assembly, the biting teeth have a saw tooth pattern. In an exemplary embodiment of the plug seal assembly, the slip comprises a plurality of segments, each segment having a portion of the biting teeth.

In an exemplary embodiment of the plug seal assembly, as the mandrel moves from the first position to the second position, the slip separates into the plurality of segments. In an exemplary embodiment of the plug seal assembly, the slip is made of a rigid material.

In an exemplary embodiment of the plug seal assembly, the outer diameter of the housing has a stress riser in the first section of the housing, such that when the mandrel is in the second position, stresses cause the first section of the housing to break at the stress riser away from the remainder of the housing. In an exemplary embodiment of the plug seal assembly, the stress riser comprises a plurality of blind pockets milled into the housing.

In an exemplary embodiment of the plug seal assembly, the mandrel is made of a dissolving material. In an exemplary embodiment of the plug seal assembly, the mandrel is made of a non-dissolving material.

Another aspect of the invention is a setting process for a plug seal assembly. In exemplary embodiments, the setting process includes the steps of: providing a plug seal assembly, the plug seal assembly comprising: a tubular housing having a first end and a second end and defining a hollow bore; and a mandrel that is moveable within the hollow bore from a first position to a second position in a direction from the first end toward the second end; wherein the housing has a first section adjacent the first end and a second section adjacent the second end, and the first section has a thickness greater than a thickness of the second section; and wherein in the first position, the second section has an inner diameter that is smaller than an inner diameter of the first section; connecting the plug seal assembly to a setting tool and locating the plug seal assembly at a desired position within a well casing; and moving the mandrel from the first position to the second position, the movement of the mandrel forcing the second section of the housing to expand outward against the well casing, such that in the second position, the inner diameters of the first and second sections are substantially the same. The setting process further may include one or more of the following features, either individually or in combination.

In an exemplary embodiment of the setting process: when the mandrel is in the first position, the first and second sections of the housing are connected by an inward tapered section that slopes radially inward from the first section to the section; the mandrel has a taper that is sloped commensurately with the tapered section of housing when the mandrel is in the first position; and as the mandrel moves from the first position to the second position, the taper of the mandrel is forced against the tapered section to expand the second section of the housing outward. In an exemplary embodiment of the setting process, the plug assembly further comprises a sealing element located in a first groove of an outer diameter of the housing, and as the mandrel moves from the first position to the second position, the sealing element compresses within the first groove between the housing and the well casing to form a seal.

In an exemplary embodiment of the setting process, the plug assembly further comprises a slip located in a second groove of the outer diameter of the housing, and as the mandrel moves from the first position to the second position, the slip expands outward against the well casing. In an exemplary embodiment of the setting process, the slip includes a plurality of biting teeth that grip the well casing when the slip expands against the well casing.

In an exemplary embodiment of the setting process, the setting process further includes separating the slip into a plurality of segments, each segment having a portion of the biting teeth.

In an exemplary embodiment of the setting process, as the mandrel moves from the first position to the second position, the slip separates into the plurality of segments.

In an exemplary embodiment of the setting process, the outer diameter of the housing has a stress riser in the first section of the housing, the setting process further comprising, when the mandrel is in the second position, breaking the first section of the housing at the stress riser away from the remainder of the housing; and removing the break-away portion of the first section of the housing from the well casing. Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and

understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.