Patent Application
20070039759
None
Not Applicable
Not Applicable
1. Field of Invention
The present invention relates to internal blowout preventers used on oil and gas drilling rigs. More particularly, the present invention relates to a mud-saver valve that can be used in connection with internal blowout preventers on drilling rigs. More particularly still, the present invention relates to a mud-saver valve that can be used in connection with top drive units.
2. Description of Related Art
Drilling rigs, such as those used to explore for oil and gas, are typically comprised of a supportive rig floor, a derrick extending vertically above said rig floor, and a traveling block which can be raised and lowered within said derrick. A wellbore typically extends downward beneath the derrick into subterranean strata. During drilling operations, such drilling rig equipment is used to move tubular goods into and out of said wellbore.
Frequently, boring drill bits and/or other equipment are lowered into wellbores, and manipulated within said wellbores, via tubular drill pipe. For example, oil and gas wells are usually drilled by rotating a boring bit located at the bottom of a length of tubular components known as a drill string. Rotation of the drill bit is typically accomplished by applying torque to the drill string at the drilling rig and transmitting such torque via the drill string to the subsurface boring bit located within the wellbore. Such torque may be generated at the drilling rig by a rotary table and kelly or, alternatively, by a large motor known as a top drive unit.
Top drive units, which are typically movable vertically within the derricks of drilling rigs, generally include a pipe gripping apparatus having at least one set of toothed inserts for gripping the outer surface of a section of pipe. Top drive units also typically include means for connecting to a section of pipe, as well as a motor for rotating or spinning such pipe about its longitudinal axis. In most cases, fluid can be communicated through such top drive units and into the inner flow path of pipe sections connected to such top drive units.
During drilling operations, a fluid known as drilling mud is normally pumped down the longitudinally extending bore of the tubular drill string, and circulated up the annular space which is formed between the external surface of said drill string and the internal surface of the wellbore. In order for drilling mud to accomplish its intended objectives, it is often necessary to adjust or control certain characteristics of such drilling mud. Thus, chemicals and/or other additives are often mixed into such drilling mud. Common drilling mud additives include gelling agents (e.g., colloidal solids and/or emulsified liquids), weighting materials, and other chemicals which are used to maintain mud properties within desired parameters. On a rig equipped with a top drive unit, mud is often pumped through the top drive unit and into the drill string situated below the top drive unit.
Many drilling muds, and/or drilling mud additives can be environmentally damaging. Further, exposure to such muds and/or additives can have a harmful effect on the health of rig personnel. Thus, it is often undesirable, and in many cases a violation of applicable environmental regulations, to release such muds and/or additives directly into the surrounding environment. As such, it is generally beneficial to limit or restrict spillage of drilling mud and mud additives on a rig.
In the course of drilling, it is often necessary to disconnect and separate various components of the drill string, usually at or near the level of the drilling rig floor. When such components are disconnected and separated, drilling mud and/or other fluids situated within the drill string above the point of separation may spill out into the surrounding area. Such spillage is highly undesirable because it can have harmful effects on the environment, as well as the health of rig personnel working in the area.
On “standard” drilling rigs utilizing a rotary table and kelly to rotate a drill string, a discrete mud-saver valve may be used to prevent such spillage of drilling mud and/or other fluids. On such rigs, mud-saver valves are typically installed between the kelly and drill string. On rigs employing top drive units, existing mud-saver valves have proven to be ineffective and/or unusable. In such cases, a device known as an internal blowout preventer (“IBOP”) is commonly used to prevent spillage of drilling mud and other fluids. However, use of IBOP's for this purpose is generally not desirable.
In many cases, upper and lower IBOP's are installed as tubular components of the drill string within the structure of the top-drive unit itself. In such cases, the upper IBOP is typically actuated by an external hydraulic cylinder and linkage arrangement, while the lower IBOP is typically manually operated and includes a short tubular saver-sub at the lower threaded connection. The overall length and outside diameter of the upper IBOP/lower IBOP/saver-sub assembly cannot be increased because it must be positioned within the structure of the top-drive unit. As a result, there is no room to add an existing prior art mud-saver valve to the top drive unit or attached drill string.
Due to such length restrictions, a common practice is to actuate an IBOP to control the spillage of drilling mud on top drive rigs when the top drive unit is separated from the drill string. However, IBOP's must control the flow of the well in the event of a blowout. Thus, IBOP's must be tested frequently and must not leak. If the IBOP's are repeatedly actuated in order to prevent mud spillage (that is, if the IBOP's are being used as mud-saver valves), the life and reliability of such IBOP's can be significantly reduced. Moreover, the position of the IBOP's within a top drive assembly makes such valves very difficult and time-consuming to replace.
In light of the foregoing, it is evident that there exists a significant need for a mud-saver valve that can be used on top-drive rigs. Such a mud-saver valve should preserve the life and integrity of the upper and lower IBOP's, without adding to the combined length of said existing upper and lower IBOP's. Further, the mud-saver valve should be automatically actuated by change of pressure within the drill string, such as when mud pumps are turned off prior to disconnecting a top drive unit from a section of pipe.
Ideally, a mud-saver valve for top-drive rigs should be integral to the lower IBOP, and operation of the mud-saver valve should not wear or damage the IBOP, or otherwise reduce or compromise the reliability or integrity of such IBOP. Furthermore, because the mud-saver valve must be positioned near the top of the drill string, the structure of the valve must be capable of transmitting the maximum loads that may be applied to the drill string. Such loads include internal hydraulic pressure, applied torsion, and axial loading from the weight of the drill string. In other words, inclusion of the mud-saver valve members should not significantly reduce the capacity of the system to handle loads commonly observed in the drilling process.
Several objects and advantages of the present invention include, but are not necessarily limited to, the following:
The mud-saver valve of the present invention comprises an independent means for blocking the flow of fluid through the inner bore of an IBOP, such as an IBOP attached to a top-drive unit. The mud-saver valve of the present invention generally comprises a tubular body having a central through-bore, a rotatable ball having a through-bore, and right and left rotating concave cup members. The ball is rotatably disposed within the through-bore of the body such that the ball may be rotated from an open to a closed position. When the ball is in the open position the through-bore of the ball is axially aligned with the through-bore of the body, thereby permitting the flow of fluid through the aligned bores of said ball and body. When the ball is in the closed position, the through-bore of the ball is oriented perpendicular to the through-bore of the body, thereby preventing fluid flow through the through-bore of such ball. When the ball is rotated, the mud-saver valve of the present invention operates much like existing ball valves or IBOP's which are generally known in the art.
The rotating concave cup members of the present invention are rotatably disposed about the periphery of said ball valve. When the ball is in the open position, said concave cup members may be rotated from an open to a closed position along the outer surface of the ball, thereby obstructing and sealing the through-bore of said ball. Such concave cup members rotate in a manner similar to the closing of eyelids about an eyeball. In the closed position, such concave cup members block the flow of mud or other fluids through the body of the mud-saver valve regardless of the position of the ball. In the preferred embodiment, such concave rotating cup members are actuated by a spring-biased piston.
Ball 108 is rotatably disposed within through-bore 166 of body 100. In a first position, as depicted in
Referring back to
Seat 106 is disposed above ball 108 and is biased downward against the outer surface of ball 108 by wave spring 104. Seat 106 has a concave surface 160 that sealingly engages against the outer surface of ball 108. Spacer 102 is disposed between wave spring 104 and internal shoulder 164 of body 100. As depicted in
Actuating piston 116 is slidably disposed within through-bore 166 of body 100, and translates axially within sleeve 120. Piston seal 144 and lower piston seal 140 are disposed between the outer surface of actuating piston 116 and the inner surface of sleeve 120. Upper sleeve seal 139 and lower sleeve seal 138 are disposed between the outer surface of sleeve 120 and inner surface of body 100. Sleeve 120 is coaxial to body 100 and is prevented from movement by sleeve retaining pin 118. Spring 122 biases actuating piston 116 upward toward ball 108.
Saver sub 124 is attached to the lower end of body 100. Body 100 has lower threads 134 that engage upper threaded member 132 of saver sub 124. Saver sub seal 136 is disposed between the outer surface of upper threaded member 132 of saver sub 124 and the inner surface of body 100. Saver sub 124 has lower threads 130 that can engage an adjacent threaded component, such as a component of the drill string. In the event of a problem with lower threads 130, saver sub 124 can be easily repaired or replaced without affecting the other components of mud-saver valve 10 of the present invention.
Referring to
Application of downward vertical force to levers 214 will cause rotating cup members 114 and 115 to rotate to an open position, while upward vertical force applied to of levers 214 will cause rotating cup members 114 and 115 to rotate to a closed position. Lever 214 depicted in
Spherical shell member 222 of each rotating cup member 114 and 115 has a forward sealing edge 230. In a closed position, sealing edge 230 of right rotating cup member 115 bears against sealing edge 230 of left rotating cup member 114. In the preferred embodiment, sealing edge 230 of left rotating cup member 114 has a circumferential recess 232 at outer spherical surface 226. Sealing edge 230 of right rotating cup member 115 has a circumferential recess 228 at inner spherical surface 224. In a closed position, sealing edge 230 of left rotating cup member 114 overlaps sealing edge 230 of right rotating cup 115.
Actuating piston 116 is sealably disposed within sleeve 120. Actuating piston 116 has an upper piston seal 144 and a lower piston seal 140. The outside diameter of upper piston seal 144 is larger than the outside diameter of lower piston seal 140. As such, a cylindrical volume 240 is defined by the differential area between upper piston seal 144 and lower piston seal 140 and the axial length between upper piston seal 144 and lower piston seal 140. Sleeve 120 has radial bore 242 disposed between upper sleeve seal 139 and lower sleeve seal 138. Similarly, body 100 has radial bore 244. In the preferred embodiment, cylindrical volume 240 between upper piston seal 144 and lower piston seal 140 communication with pressure observed outside of body 100.
Actuating piston 116 has a concave upper surface 248. The radius of curvature of concave upper surface 248 is approximately equal to the radius of curvature of outer spherical surfaces 226 of rotating cup members 114 and 115. Two elongated extension arms 218 extend upward from the upper surface of actuating piston 116 (although only one such extension arm 218 is visible in
Operation
During drilling operations, fluid such as drilling mud is pumped through the bore of a top drive unit (including the mud-saver valve of the present invention) and drill string. Restriction to the flow of such fluid results in a higher pressure within the drill string and mud-saver valve 10 of the present invention compared to pressure observed on the outside of such components. When it is desired to disconnect or break-out a connection between components of the drill string at or near the rig floor, mud pumps are typically shut off, and pressure within the drill string and mud-saver valve 10 decreases to static head pressure; such static head pressure results from the vertical length of the fluid column within the drill string above the rig floor (i.e., the point where such drill string components are to be disconnected). On many rigs, this height may be 90 feet or more.
As described previously, actuating piston 116 has a larger diameter at upper piston seal 144 than at lower piston seal 140. Cylindrical volume 240 between upper piston seal 144 and lower piston seal 140 communicates with pressure observed outside body 100 via radial bore 244. Actuating piston 116 is upwardly biased by spring 122. When mud is being pumped, both the top and the bottom of actuating piston 116 are exposed to high internal pump pressure. As such, downward force is exerted by such internal pressure acting against the area of the larger upper piston seal 144. A lesser upward force is exerted by the same internal pump pressure acting against the area of smaller lower piston seal 140. The differential area between the larger upper piston seal 144 and the smaller lower piston seal 140 is acted upon by pressure communicated through radial hole 242 of sleeve 120 and radial hole 244 of body 100. Spring 122 also exerts an upward force on actuating piston 116.
Compression spring 122 is designed such that internal pressure (such as, for example, internal pressure resulting from rig mud pumps) greater than a predetermined trip pressure overcomes the upward bias of spring 122. Actuating piston 116 is held in a lower position, with extension arms 218 exerting downward force on levers 214 of rotating cup members 114 and 115, thereby holding rotating cup members 114 and 115 in their open position.
When such internal pressure drops, such as when rig mud pumps are shut off, pressure observed within mud-saver valve 10 drops below such predetermined trip pressure. Under this scenario, upward bias of spring 122 overcomes the net downward force of the internal pressure acting against the differential area between larger upper piston seal 144 and small lower piston seal 140. Actuating piston 116 moves upward by the force exerted by spring 122. As such, extension arms 218 exert upward force on levers 214 of rotating cup members 114 and 115, thereby moving rotating cup members 114 and 115 into their closed Ooined) position.
The net upward force applied to actuating piston 116 exerts upward force on lever 214 of rotating cup members 114 and 115, causing sealing edges 230 of rotating cup members 114 and 115 to seal against each other. The net upward force of spring 122 also forces concave surface 248 of actuation piston 116 against outer surface 226 of shell members 222 of rotating cup members 114 and 115, thereby creating a seal between rotating cup members 114 and 115 and actuating piston 116. In the closed position, head pressure above mud-saver valve 10 is completely sealed, and fluid contained within the assembly is prevented from draining out of the assembly and on the rig floor or surrounding environment.
The above disclosed invention has a number of particular features which should preferably be employed in combination, although each is useful separately without departure from the scope of the invention. While the preferred embodiment of the present invention is shown and described herein, it will be understood that the invention may be embodied otherwise than herein specifically illustrated or described, and that certain changes in form and arrangement of parts and the specific manner of practicing the invention may be made within the underlying idea or principles of the invention.
