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1. Field of the Invention
The present invention relates to a downhole tool for isolating zones in a wellbore. More particularly, the present invention relates to a millable bridge plug system.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
A bridge plug is a downhole tool that is lowered into a wellbore. At a particular distance through the wellbore, the bridge plug is activated. The bridge plug locks and opens to seal the bridge plug to the walls of the wellbore. The bridge plug separates the wellbore into two sides. The upper portion can be cemented and tested, separate from the sealed lower portion of the wellbore. Sometimes the bridge plugs are permanent, and they seal an entire portion of the wellbore. Other times, the bridge plugs must be removed, and still other times, the bridge plugs must be removed and retrieved. These removable bridge plugs are millable or drillable, so that a drill string can grind through the bridge plug, making remnants of the destroyed bridge plug to remain at the bottom of a wellbore or to be retrieved to the surface by drilling mud flow.
Bridge plugs generally include a mandrel, a sealing member placed around the mandrel, ring members adjacent the end of the sealing member and around the mandrel, upper and lower slip devices at opposite ends of the mandrel, and respective upper and lower cone assemblies engaged to the upper and lower slip devices.
The activation of the bridge plug requires advancement for a more efficient and stable seal in the wellbore. The ramming portion provide the force needed to form the seal on the wellbore, and this force is directed by those stack structures, the sealing member, ring members, cone assemblies, and slip devices, of the bridge plug. The interactions between these stack structures are important for efficiency and consistency of the forming the seal and locking the seal on the wellbore. The pressure is exerted directly on the sealing member by ring members in some arrangements of the stack structures. The interface between the sealing member and the ring members of the prior art has a constant taper angle between the sealing member and the ring members. The amount of pressure against the sealing member does not vary as the pressure of the positioning assembly is exerted through the ring members. The expansion of the sealing member to the wall of the wellbore is steady, yet possibly insufficient for an adequate seal. The lack of a threshold amount of pressure for setting the seal may result in a sealing member that is not expanded enough to form a good seal or extrusion of the sealing member beyond the ring members due to too much pressure. The exerted pressure on the sealing member may also be too much, causing extrusion and degradation of the seal member. There is a need for resistance to excess pressure after the seal is formed.
Conventional materials of the millable bridge plug, like all downhole tools, must withstand the range of wellbore conditions, including high temperatures and/or high pressures. High temperatures are generally defined as downhole temperatures generally in the range of 200-450 degrees F.; and high pressures are generally defined as downhole pressures in the range of 7,500-15,000 psi. Other conditions include pH environments, generally ranging from less than 6.0 or more than 8.0. Conventional sealing elements have evolved to withstand these wellbore conditions so as to maintain effective seals and resist degradation.
Metallic components have the durability to withstand the wellbore conditions, including high temperatures and high pressures. However, these metallic components are difficult to remove. De-activating and retrieving the bridge plug to the surface is costly and complicated. Milling metallic components takes time, and there is a substantial risk of requiring multiple drilling elements due to the metallic components wearing or damaging a drilling element of a removal assembly.
Non-metallic components are substituted for metallic components as often as possible to avoid having so much metal to be milled for removal of the bridge plug. However, these non-metallic components still must effectively seal an annulus at high temperatures and high pressures. Composite materials are known to be used to make non-metallic components of the bridge plug. These composite materials combine constituent materials to form a composite material with physical properties of each composite material. For example, a polymer or epoxy can be reinforced by a continuous fiber such as glass, carbon, or aramid. The polymer is easily millable and withstands the wellbore conditions, while the fibers also withstand the wellbore conditions and resist degradation. Resin-coated glass is another known composite material with downhole tool applications. Composite materials have different constituent materials and different ways of combining constituent materials.
It is an object of the present invention to provide an embodiment of a millable bridge plug system.
It is another object of the present invention to provide an embodiment of the millable bridge plug system with improved stack structures, including a sealing means.
It is still another object of the present invention to provide an embodiment of the millable bridge plug system with a sealing means with controlled deformation by pressure.
It is yet another object of the present invention to provide an embodiment of the millable bridge plug system with a sealing means having an active surface interface with respective ring members.
It is another object of the present invention to provide an embodiment of the millable bridge plug system with improved ring members.
It is still another object of the present invention to provide an embodiment of the millable bridge plug system with ring members with an active ring surface interface with cone assemblies.
These and other objectives and advantages of the present invention will become apparent from a reading of the attached specifications and appended claims.
A millable bridge plug system comprises a mandrel, a sealing means positioned around the mandrel, a plurality of ring members, a plurality of cone assemblies, and a plurality of slip devices. The sealing means has an upper end and a lower end. A first ring member is placed adjacent the upper end of the sealing means, and a second ring member is adjacent the lower end of the sealing means. A first cone assembly is proximate to the first ring member, and a second cone assembly is proximate to the second ring member. The slip means extend radially outward and engage an inner surface of a surrounding borehole to lock the position of the bridge plug. A first slip means is mounted around the mandrel and engages the first cone assembly, and a second slip means is mounted around the mandrel and engages the second cone assembly.
The sealing means further comprises a first means for resisting pressure by the first ring member when in contact with the first ring member, and a second means for resisting pressure by the second ring member when in contact with the second ring member. The first means is on the upper end and the second means is on the lower end. In one embodiment, the first and second means for resisting pressure are comprised of surface interfaces with curvatures. In another embodiment, the first and second means for resisting pressure are comprised of double radiused surfaces. When pressures are exerted by the ring members on the upper end and the lower end of the sealing means, the sealing means is deformed to spread radially towards the borehole at a rate dependent upon location of the pressures on the curvatures of the surface interfaces or the double radiused surfaces. The sealing means also has an inner cavity curved from the upper end and the lower end towards an indentation in a middle of the sealing means.
The first ring member may also have a first ring means to resist pressure when in contact with the first cone assembly, and the second ring member may also have a second ring means to resist pressure when in contact with the second cone assembly. Similar to the first and second means for resisting pressure, the first and second ring means for resisting pressure are comprised of ring surface interfaces with ring curvatures. Alternatively, the first and second ring means for resisting pressure are comprised of single radiused surfaces. When pressures are exerted by the cone assemblies on the ring members, the ring members are deformed and pass pressure through to the sealing means at a rate dependent upon location of the pressures on the curvatures of the surface interfaces or the single radiused surfaces.
The method of installing a millable bridge plug system comprises the steps of: placing a bridge plug in a wellbore, the wellbore having inner walls surrounding the bridge plug, forming a seal against the inner walls by exerting pressure on the bridge plug, and fixing position of the bridge plug by exerting additional pressure on the bridge plug. The bridge plug includes a mandrel having an upper portion and a lower portion, a sealing means positioned around the mandrel, a plurality of ring members, a plurality of cone assemblies, and a plurality of slip means for extending radially outward and engaging the inner walls. The step of forming a seal involves the sealing member being compressed to radially extend outward to seal against the inner walls, the ring members pushing the sealing member to expand, the cone assemblies pushing the ring members. The step of fixing position of the bridge plug involves the cone assemblies pushing the slip means to extend radially outward to fixedly engage the inner walls. The sealing means and the ring means can have means for resisting pressure so that the compression is controlled according to the means for resisting. The means for resisting can be surface interfaces with curvatures or single or double radiused surfaces.
Referring to
The mandrel 112 of the system 100 is a generally tubular member formed of a material to withstand the heat and pressure of the borehole conditions. The mandrel 112 is also millable. The mandrel 112 may have a bridge 134, which seals the zone above the system 100 from the zone below the system 100. The sealing means 114 is positioned around the mandrel 112. The sealing means 114 has an upper end 136 and lower end 138 as shown in
The system 100 also includes the plurality of cone assemblies, 120, 122.
The rate of deformation is controlled by the location of the pressures on curvatures of the surface interfaces of the upper end 136 and the lower end 138 of the sealing means 114. The ring members 116, 118 do not provide steady or even pressure on the sealing member 114 to deform at a constant rate. Because of the curvature, the pressure along the curvature can build until a fulcrum is reached, wherein the tangential pressure to the curvature is sufficient to start the deformation of the sealing member 114. The present invention reduces the risk of insufficient pressure to deform the sealing member 114, causing extrusion instead of a seal on the wellbore. In prior art systems, the amount of pressure may be a gradual conical taper. The control of the pressure on the sealing member 114 cannot be controlled. A threshold of pressure at the fulcrum on the curvature of the present invention improves the seal formed on the inner walls of the borehole or casing 130. There is more surface area on the means for resisting pressure 140, 142 than the conventional tapers, wedges and conical surfaces. More even spread of the sealing member 114 can be achieved with embodiments of the present invention.
In an alternate embodiment, the first means 140 for resisting pressure is comprised of a double radiused surface with a curvature and double curvature, as shown in
The first ring means 144 for resisting pressure is comprised of a ring surface interface with a ring curvature, and the second ring means 146 for resisting pressure is comprised of a ring surface interface with a ring curvature. Pressures exerted by the cone assemblies 120, 122 on the ring members 116, 118 cause deformations of the ring members 116, 118 and affect the amount of pressure passed through to the sealing means 114, which forms the actual seal to the wellbore. The ring surface interfaces with ring curvatures control the deformation of the ring members 116, 118 and the amount of pressure passed through to the sealing means 114. Because of the ring curvatures, the pressure along each ring curvature can also build until a fulcrum is reached, wherein the tangential pressure to the ring curvature is sufficient to start the deformation of the ring members 116, 118 and pass pressure through to the sealing means 114. The ring curvatures of the first ring means 144 and the second ring means 146 prevent extrusion by controlling the amount of pressure passed through to the sealing means 114. The sealing means 114 is protected from too much pressure. Pressure builds to the fulcrum of the ring curvatures to finally release pressure to the sealing means 114. The first and second ring means 144, 146 are structures that may also extend radially to further seal against the wellbore.
In combination with the first means 140, the second means 142 on the sealing means 114 and the first ring means 144 and the second ring means 146 on the ring members 116, 118, the present invention controls pressure and reduces the risk of insufficient pressure to deform the sealing member 114, causing extrusion instead of a seal on the wellbore. These structures of the stack structures have interactions and interrelationships not present in the prior art. In prior art systems, the amount of pressure may be a gradual conical taper. The control of the pressure on the sealing member 114 cannot be controlled as disclosed by the present invention.
The method of installing a millable bridge plug system 100 comprises the steps of placing a bridge plug system 100 in a wellbore, forming the seal on the wellbore, and locking the system 100 in position within the wellbore. With the millable bridge plug system 100 of the present invention, system 100 is lowered into the wellbore having inner walls, such as a casing 130, using a setting tool on a positioning assembly. The mandrel is held in place as the stack structures 114, 116, 118, 120, 122, 124, and 126 are hammered by a ram portion of the setting tool. Pressure on the bridge plug system 110 forms a seal, when the sealing means 114 is compressed to radially extend outward to seal against the inner walls of the borehole. The ring members 116, 118 push the sealing means 114 to expand, and the cone assemblies 120, 122 push the ring members 116, 118. The cone assemblies 120, 122 also push the slip means 124, 126 to extend radially outward to fixedly engage the inner walls, locking the system 100 in position within the wellbore. At least one slip means 124, 126 is activated, so that stack structures are locked in the sealed position. The exerted pressure through the system 100 is controlled by the first means 140 and second means 142 on the sealing means 114, and sometimes in conjunction with the first ring means 144 and the second ring means 146 on the ring members 116, 118.
The present invention provides an embodiment of the millable bridge plug system with an innovative sealing means. The sealing means has a controlled deformation to create the seal under more known and predictable conditions, resulting in a more consistent and stronger seal. The pressure exerted on the millable bridge plug is more regulated by active surface interfaces and curvatures, including a double radiused surface in one embodiment. The improved control of the deformation is further facilitated by active ring surface interfaces and ring curvatures on the ring members.
The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated structures, construction and method can be made without departing from the true spirit of the invention.