Patent Application
20070044976
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 ram inner seal assembly used in ram-type BOPs.
Wireline BOPs are typically included in the surface assembly at a wellhead when conducting well intervention services. The wireline BOP is typically installed below a grease injection head. In use, grease is pumped into the lower end of the grease injection head at some pressure above well bore pressure. Often, the grease is pumped into the grease injection head at 1.2 times well bore pressure.
By pumping grease into the grease injection head at a pressure above well bore pressure, the grease prevents well bore pressure from migrating past the lower end of the grease injection head. Additionally, because the grease surrounds the wireline that passes through the grease injection head, the grease prevents hydrocarbons from the well bore from flowing into and around the wireline and, thus, prevents migration of well fluids past the grease injection head.
While grease injection heads have proven very successful at holding back well bore pressure while conducting well intervention services, grease injection heads have sometimes failed to maintain an effective “grease seal” adequate to hold back well bore pressure. The grease seal can fail for any number of reasons, including the well experiencing a pressure spike while the intervention services are being performed and/or the grease thinning due to exposure to increased temperatures or well chemicals. On the rare occasions that a grease injection head fails to maintain an adequate grease seal, the rams of the wireline BOP are actuated to seal around the wireline and hold back well bore pressure.
Typically, a wireline BOP is equipped with multiple BOP rams that 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. 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 wireline 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 rams 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. A BOP stack typically includes one type of ram and seal assembly known as a “blind ram” that seals across the entire wellbore when no wireline (or other tubular) is located in the vertical bore at the location of the blind rams. The blind rams are designed to engage each other when the BOP is closed. Blind rams 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.
Another type of ram and seal assembly, known as a “wireline ram” (or “pipe ram” for BOPs used with other types of wellbore tubulars) utilizes seals designed to seal around the wireline (or other wellbore tubulars) within the BOP's vertical bore. Like blind rams, the wireline rams are designed to engage each other when the BOP is closed. Each seal of a wireline ram, however, typically has a semicircular opening in its front face to form a seal around half of the outer periphery of the wireline. When the wireline rams are closed, the opposing wireline rams engage each other and seal the entire periphery of the wireline, thereby closing off the annulus between the wireline and the well bore surface.
A third type of ram known as a shear, or cutting, ram is designed to shear the wireline (or other tubular) when the shear rams are driven toward each other as the BOP is closed. In operation, the shear rams 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.
Should it become necessary to actuate a wireline BOP, it is desirable for the wireline rams to guide the wireline (or other tubular) to the center of the vertical bore of the BOP as the rams close to ensure that the ram bodies and/or the metal bodies of the inner seals do not damage the wireline within the bore. Given the high cost of wireline, centering the wireline to prevent damage or loss is very important. For example, if wireline is damaged or severed as the ram bodies close and seal around the wireline, the replacement cost of such wireline can amount to nearly $300,000 per 30,000 feet of wireline.
Prior art U.S. Pat. No. 6,676,103 (“the '103 patent”) discloses a guide system for centering wireline (or other tubular) in the vertical bore of the BOP when a set of wireline rams (or pipe rams) is closed. However, the guide system of the '103 patent has certain drawbacks, including the inability to replace the “guides” that guide the wireline (or other tubular) to the center of the vertical bore of the BOP without replacing the entire ram body, the distance between the guides and the seal assembly, and the potential for damaging the ram body in the event excessive “squeezing” force is imparted on the inner seal elements. Further, replacement of the sealing elements of such prior art pipe ram assemblies is more difficult, and requires extra expense, when compared to the inner guide seal assembly of the present invention.
The present invention offers an improved inner guide seal assembly that guides a wireline (or other tubular) to the center of the well bore and “energizes” the sealing elements of the assembly. The present invention helps prevent damage to the wireline due to misalignment and prevents the potential for excessive force building up in the inner seal elements such that they may deform or damage the ram bodies. Additionally, the inner guide seal assembly of the present invention allows for easy replacement of the entire seal assembly or, alternatively, replacement of the sealing element itself. Thus, the inner guide seal assembly of the present invention overcomes many of the drawbacks of the prior art.
An improved seal assembly used in ram-type BOPs is disclosed. The disclosed invention is a unique inner guide seal assembly that comprises a guide body and specially shaped sealing element. When a ram-type BOP is closed, two opposing rams move toward one another, causing the inner guide seal assembly of the present invention to guide a wireline (or other tubular) located in the vertical bore of the BOP to the center of the bore. By centralizing the wireline, the inner guide seal of the present invention helps ensure a positive seal around the wireline and helps prevent potential damage to the wireline.
In the preferred embodiment, the body of the inner guide seal assembly comprises a one-piece body having an upper plate and a lower plate integrally connected by multiple posts. This design feature prevents the body of the inner guide seal assembly from “expanding” during the sealing process, thereby preventing potential damage to the ram body.
Additionally, the upper and lower plates of the guide body include the guide surfaces that help guide the wireline (or other tubular) to the center of the vertical bore of the BOP when the rams are closed. By placing the guides on the inner seal assembly itself, the guides are closer to the centerline of the ram bodies, thereby maximizing the chances that the guides will be the first element to contact the wireline or tubular in the vertical bore of the BOP. Additionally, by keeping the guides as close to the centerline of the ram body as possible, it substantially reduces the possibility of the wireline laying angled or horizontally across the ram assembly, thereby helping prevent potential damage to the wireline. Further, by placing the guides on the inner seal assembly, the inner seals of existing ram bodies that currently do not have such guides can be replaced with the inner guide seal assembly of the present invention to provide such guides without having to replace the entire ram body.
The sealing element of the inner guide seal assembly is separate from the guide body and is formed as one piece with splits in the rear and center of the sealing element. This design feature allows the sealing element to be easily “opened” for placement onto (and removal from) the guide body. This feature facilitates replacement of the sealing elements without having to replace the entire inner guide seal assembly. Additionally, the inner guide seal assembly is not integral to the ram body and, thus, the assembly can be easily replaced without replacing the entire ram body.
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
Ram actuator assemblies 30 are the lowermost actuator assemblies connected to valve body 20. Each 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.
Ram actuator assemblies 40 are connected to valve body 20 above ram actuator assemblies 30. Each 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. Ram actuator assemblies 40 are substantially identical to ram actuator assemblies 30. Ram actuator assemblies 30 and 40 may differ in the type of ram seal employed in the assemblies. For example, ram actuator assemblies 30 may employ a set of blind rams, while ram actuator assemblies 40 may employ a set of wireline rams (or vice versa).
During well intervention operations, if the grease seal of a grease injection head fails, the pistons 32 within the lowermost 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. As ram packers 38 are driven laterally and inwardly, the guide assembly will guide a wireline (or other tubular) within the vertical bore 25 to the center of the vertical bore 25. 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 the wireline (or other tubular) passing through vertical bore 25. In this way, ram packers 38 are designed to hold back well pressure and 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 rams to hold back well pressure.
Turning to
As can be seen in
As seen in
The specially-shaped guide body 110 can be seen in more detail with reference to
As shown in
The use of posts 119 and 120 to connect top guide plate 112 and bottom guide plate 113 prevents guide body 110 from being deformed, and thereby potentially damaging ram body 50, in the event guide body 110 is exposed to excessive forces created by the expansion of sealing element 130 as ram bodies 50 are closed around a wireline (or other tubular). Specifically, as the ram bodies 50 move inwardly, front seal face 134 of the sealing elements 130 (refer to
In prior art guide seal assemblies that lack posts 119 and 120, if these outwardly directed forces are great enough, they can cause the top and bottom plates of the seal assembly to exert forces on the ram bodies that can deform the ram bodies and/or cause the seal assemblies to become stuck in the ram bodies. Unlike the prior art seal assemblies, the posts 119 and 120 of the present invention maintain the top and bottom guide plates 112 and 113 a set distance apart from each other and prevent them from exerting a potentially deforming force on the ram bodies. While the preferred embodiment of the present invention uses two posts, one of skill in the art will appreciate that one, two, three, or even more posts between the top and bottom guide plates can be used.
Referring to
Sealing element 130 is designed to be easily inserted into and removed from guide body 110 for easy and cost effective replacement of such seal. Specifically, as shown in
In operation, when the ram bodies 50 are driven laterally inward, the guide surface 116 of guide nose 115 and the guide surface 117 of guide nose 114 will contact a wireline (or other tubular) in the vertical bore of the BOP and force it along the guide noses 114 and 115 toward center notch 118 in the center of the guide body 110 and center notch 137 of the sealing element 130. Ultimately, the wireline (or other tubular) is received and held in center notch 137 in the sealing element 130. When the ram bodies 50 are completely closed, the contact between the front seal surface 134 of opposing sealing elements 130 (as well as the mating of center notches 137 around the circumference of the wireline) forms a seal in the annulus between the wireline (or other tubular) and the vertical bore of the BOP.
By utilizing guide noses 114 and 115 that are integrally formed with the top and bottom guide plates 112 and 113, the guide noses 114 and 115 are closer to the centerline of the ram body 50, thereby maximizing the chances that the guide surfaces 116 and 117 will be the first element to contact the wireline (or other tubular) in the vertical bore of the BOP. This helps to substantially reduce the possibility for the wireline to lay angled or horizontal across the ram face and helps ensure no damage is caused to the wireline. Further, by placing the guide noses 114 and 115 on the inner guide seal assembly 100, the inner seals of existing ram bodies that currently do not have such guides can be replaced with the inner guide seal assembly 100 of the present invention to provide such guides without having to replace the entire ram body.
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.
