Patent Application
20060113501
The present invention relates to ram-type blowout preventers (“BOPs”) used in oil and gas operations for well control including preventing a well blowout. In particular, the present invention relates to the design and use of an improved shear/seal ram assembly used in ram-type BOPs.
In the drilling of an oil and/or gas well, a specially formulated fluid known as “drilling mud” is circulated through the wellbore. During rotary drilling operations, the drilling mud serves multiple functions, including protecting against blowouts by holding back subsurface pressures of formation fluids. As long as the bore hole contains a sufficient volume of drilling mud of a sufficient density, the pressure created by the weight of the column of drilling mud is typically sufficient to prevent formation fluids from entering the bore hole. If a formation having higher pressure than expected is encountered during drilling operations, however, the potential for formation fluids including gas, to enter the borehole and migrate toward the surface is present.
When formation fluids enter the bore hole, a pressure spike, or “kick” as they are commonly referred to in the industry, can occur. Ram-type BOPs are part of a pressure control system used in oil and gas drilling operations to control these unexpected well bore pressure “kicks.” The BOPs are designed to close off the well to prevent a blowout by sealing the well against the fluid pressure from below. By sealing the well, the BOP prevents gas (and other well fluids) from migrating past the BOP stack to the drill floor of a rig where numerous potential ignition sources exist that could ignite the gas and thereby cause a blowout. A BOP can also be used to seal off the well around the drill string in normal drilling operations involving positive downhole pressure.
BOPs are typically included in the surface assembly at a wellhead when drilling or completing a well. Typically, multiple BOP rams are assembled in a vertical stack that is positioned over and connected to the wellhead.
The BOP has a central valve body with a vertical bore running through it. Wellbore tubulars, such as the drill string or coiled tubing, extend up through the center, vertical bore of the BOP stack. Similarly, during wireline logging operations, wireline extends up through the center, vertical bore of the BOP stack. Depending on the operations being conducted on the well, other wellbore equipment may be within the vertical bore of the BOP stack at a particular time.
A typical BOP has a plurality of laterally disposed, opposing actuator assemblies fastened to the valve body. Each actuator assembly includes a piston that is laterally moveable within an actuator body by pressurized hydraulic fluid (during normal operation) or by manual force (in the event of a failure of the hydraulic control system). Each piston has a stem threadably engaged or otherwise connected to it. The stem extends laterally toward the bore of the valve body and has a ram body attached to the end of the stem nearest the bore of the valve body.
Replaceable sealing elements are mounted within or on the ram bodies that extend into the vertical bore of the valve body of the BOP. When the pistons of the BOPs are moved to a closed position, commonly referred to as “closing the rams,” the vertical bore of the BOP is sealed and the well bore pressure is contained. The sealing elements mounted within or on the ram bodies are available in a variety of configurations designed to seal the vertical bore of the BOP valve body when the opposing rains and pistons are moved to their closed position.
Several types of ram and seal assemblies are used in the actuator assemblies of a BOP stack. One type of ram and seal assembly known as a “pipe ram” utilizes seals designed to seal around the wellbore tubulars within the BOP's vertical bore when the BOP is closed. Each seal of a pipe ram typically has a semicircular opening in its front face to form a seal around half of the outer periphery of the tubular. When the pipe rams are closed, the opposing pipe rams engage each other and seal the entire periphery of the tubular, thereby closing off the annulus between the tubular and the well bore surface.
Another type of ram and seal assembly, known as a “blind ram,” seals across the entire wellbore when no tubular is located in the vertical bore at the location of the blind rams. Like pipe rams, the blind rams are designed to engage each other when the BOP is closed. Blind rams, however, typically utilize seals with no opening in the face of the seals such that the blind rams form a complete seal through the vertical bore of the BOP.
BOP stacks typically also include shear, or cutting, rams that shear the tubular (or wireline) when the rams are driven toward each other as the BOP is closed. In operation, the shear rains are typically used as a last resort measure to contain wellbore pressure from causing a blowout. A BOP with shear rams is typically the top section of a ram-type BOP stack, while various pipe rams and blind rams are typically located below the shear rams. In operation, the pipe rams will be closed first to try to contain the wellbore pressure and prevent a potential blowout. In the event the pipe rams (and/or the blind rams) do not contain the “kick,” the shear rams are actuated to try and contain the “kick” and prevent a potential blowout.
The shear ram assemblies must be sealed to prevent wellbore fluids from migrating through or around the shear blades after the tubular or other item within the valve body of the BOP is sheared. Various prior art patents disclose shear rams with integral sealing means disposed on or within the shear blades and/or within the shear ram bodies. Such prior art patents include U.S. Pat. Nos. 4,580,626; 4,646,825; 6,244,336; and 6,719,042. Each of these patents energize the seal between the shear blades in different ways. However, the designs of the sealing mechanisms of each of these prior art patents have certain drawbacks that limit the amount of squeeze that may be placed on the seals and/or that make replacement of the sealing components difficult.
The present invention offers an improved sealing mechanism that “energizes” the sealing element between the shear blades in a unique way and that offers a design that allows for easy replacement of the seal assembly. Thus, the sealing mechanism of the present invention overcomes many of the drawbacks of the prior art.
An improved shear/seal ram assembly used in ram-type BOPs is disclosed. The disclosed invention is a unique shear/seal ram assembly in which rail seal actuators attached to or integrally formed in a planar surface of one shear blade mate with and slide within corresponding rail guide grooves formed in a planar surface of a second shear blade. As the shear blades move over each other, the rail seal actuators slide within the rail guide grooves, eventually coming into contact with a seal actuator plate of a unique blade-to-blade seal assembly placed within a shear blade seal groove. Continued movement of the shear blades over each other causes the rail seal actuators to compress, or “energize,” the blade-to-blade seal, thereby providing a pressure tight seal between the shear blade assemblies.
The following figures form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these figures in combination with the detailed description of specific embodiments presented herein.
The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.
Referring to
Pipe ram actuator assemblies 30 are the lowermost actuator assemblies connected to valve body 20. Each pipe ram actuator assembly 30 comprises actuator body 31, piston 32, stem 34, ram body 36, and ram packer 38. Stem 34 operatively connects piston 32 with ram body 36.
Proceeding upwardly along BOP stack 10, pipe ram actuator assemblies 40 are the next level of rams connected to valve body 20. Each pipe ram actuator assembly 40 comprises actuator body 41, piston 42, stem 44, ram body 46, and ram packer 48. Stem 44 operatively connects piston 42 with ram body 46. Pipe ram actuator assemblies 40 are substantially identical to pipe ram actuator assemblies 30.
Shear seal ram actuator assemblies 80 are connected to valve body 20 above pipe ram actuator assemblies 40. Each shear/seal ram actuator assembly 80 comprises actuator body 82, piston 84, stem 86, and ram body 90. Stem 86 operatively connects piston 84 with ram body 90. As will be discussed in more detail below with reference to
In operation, when a well experiences a “kick,” the pistons 32 within the lowermost pipe ram actuator bodies 31 will be activated via hydraulic pressure (in normal operation) or manually (in the event of a failure of the hydraulic control system) such that the ram packers 38 will be driven laterally inwardly toward the vertical bore 25 running through valve body 20. Eventually, the ram packers 38 of ram bodies 36 will be forced together such that the ram packers 38 will form a seal around the entire circumference of a wellbore tubular passing through vertical bore 25. In this way, ram packers 38 are designed to prevent wellbore fluids from migrating upwardly through vertical bore 25. Similarly, the pistons 42 within ram actuator bodies 41 may be activated as a redundant sealing mechanism or may be necessary in the event of a failure of the lowermost pipe rams to contain the kick.
In the event the pipe rams of BOP stack 10 fail to adequately contain the wellbore pressure, the shear/seal rams of shear/seal actuator assemblies 80 will be activated. As with the pipe rams, the pistons 84 within the actuator bodies 82 will be activated via hydraulic pressure such that the ram bodies 90 will be driven laterally inwardly toward the vertical bore 25 running through valve body 20. Eventually, the shear blades (numbers 100 and 150 in
To seal the area between the upper and lower shear blades 100 and 150 and the ram bodies 90, each shear blade 100 and 150 has a rear seal groove 101 formed in the back portion of the shear blade. Rear seal grooves 101 are shaped to receive a blade-to-ram seal 102. When the shear/seal ram assemblies of the present invention are assembled, the blade-to-ram seal 102 is compressed between the ram body 90 and the shear blade 100 or 150 to form a seal (as shown in
One of skill in the art will appreciate that the seals 96 and 102 and the blade-to-blade seal assemblies 175 of the present invention are designed such that they are easy to assemble onto and within the shear/seal ram assemblies. Unlike some prior art shear/seal assemblies, the seals 96 and 102 and the blade-to-blade seal assemblies 175 of the present invention provide for easy removal and replacement when the seals become worn.
The unique sealing mechanism of the present invention will now be discussed with reference to
As shown in
As the seal actuator plate 176 is driven axially backward in shear blade seal groove 170 by the continued movement of rail seal actuators 182, blade-to-blade seal 177 is “squeezed” such that a seal between the upper and lower shear blades 100 and 150 is created. The rail seal actuators 182 are sized so that the optimal “squeeze” on blade-to-blade seal 177 is reached after the wellbore tubular (or other member) is sheared and the upper cutting edges 110 and 160 of upper and lower shear blades 100 and 150 have traveled past the blade-to-blade seal 177.
Blade-to-blade seal 177 is formed with or has connected to it an integral solid retainer 178 (shown in
While the apparatus, compositions and methods of this invention have been described in terms of preferred or illustrative embodiments, it will be apparent to those of skill in the art that variations may be applied to the process described herein without departing from the concept and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the scope and concept of the invention as it is set out in the following claims.
