Patent Application
20080196889
Typically, after a well for the production of oil or gas has been drilled, casing is lowered and cemented into the well bore. Normal primary cementing of the casing string in the well bore includes lowering the casing to a desired depth and displacing a desired volume of cement down the inner diameter of the casing. Cement is displaced downward into the casing until it exits the bottom of the casing into the annular space between the outer diameter of the casing and the well bore apparatus. This method may present numerous challenges, including difficulty getting circulation inside of the annular space due to weak formations. Not only does the hydrostatic weight of the cement exert pressure against formations, but additional pressure is applied to formations due to the friction of the fluid that must be overcome.
One method to help reduce the formation pressure is to pump fluids down the annulus and back up through the casing, often called “reverse circulation” or “reverse cementing.” The reverse-cementing method comprises displacing conventionally mixed cement into the annulus between the casing string and the annulus between an existing string, or an open hole section of the well bore. As the cement is pumped down the annular space, drilling fluids ahead of the cement are displaced around the lower ends of the casing string and up the inner diameter of the casing string and out at the surface. The fluids ahead of the cement may also be displaced upwardly through a work string that has been run into the inner diameter of the casing string and sealed off at its lower end. Because the work string has a smaller inner diameter, fluid velocities in the work string will be higher and will more efficiently transfer the cuttings washed out of the annulus during cementing operations. To ensure that a good quality cement job has been performed, a small amount of cement will be pumped into the casing and the work string. As soon as a desired amount of cement has been pumped into the annulus, the work string may be pulled out of its seal receptacle and excess cement that has entered the work string can be reverse-circulated out the lower end of the work string to the surface.
Reverse cementing, as opposed to the conventional method, provides a number of advantages. For example, cement may be pumped until a desired quality of cement is obtained at the casing shoe. Furthermore, cementing pressures are much lower than those experienced with conventional methods and cement introduced in the annulus free-falls down the annulus, producing little or no pressure on the formation. Oil or gas in the well bore ahead of the cement may be bled off through the casing at the surface. Finally, when the reverse-cementing method is used, less fluid is required to be handled at the surface and cement retarders may be utilized more efficiently.
While reverse-cementing can greatly reduce the total pressure applied to the formation, it has some drawbacks. First, it is difficult to know exactly when the cement has been circulated into the casing. In some instances a wire line tool is placed downhole to determine when radioactive tracers or changes in fluid properties occur, thus providing an indication of when the cement has completely filled the annulus and begun to enter the casing. Another technique is to use a volumetric method involving the monitoring of fluid volumes returning to the surface and estimating when the cement has filled the annulus. If, however, this method is attempted while cementing an annulus between the casing and formation that been drilled out, there can be a large uncertainty about the actual annular hole volume. This may result in incomplete filling of the annulus with cement, or it may result in overfilling the annulus and getting cement back up inside the casing string. This cement inside the casing string may cover potential productive zones and/or require additional rig time to drill out. Another challenge to reverse circulation is the problem of effective float equipment that keeps the typically heavier cement from flowing inside the casing due to U-Tubing. Because the fluids are pumped reverse, conventional float equipment cannot be used. This means that after a reverse cement job, pressure must be held on the inside of the casing until the cement has sufficiently set to prevent this U-Tubing. This can cause a micro-annulus to form between the cement sheath and casing, which makes it difficult to bond log the casing to evaluate the quality of the cement job and determine if the annulus is properly sealed.
The present invention relates generally to reverse cementing. More specifically, the present invention is directed to a valve that may be used in reverse cementing operations.
In one embodiment of the present invention, a method for reverse cementing comprises: providing a valve comprising a sliding sleeve, an outer sleeve situated about at least a portion of the sliding sleeve and connected to a casing string, and a spring configured to position the valve in an open position. The method of this embodiment further comprises: running the casing string and valve into a well bore while the valve is in an open position; reverse cementing, while the valve is in an open position; and closing the valve after reverse cementing by allowing the valve to contact the well bore.
In another embodiment of the present invention, a valve for reverse cementing comprises: a sliding sleeve having one or more openings; a nose attached to sliding sleeve; an outer sleeve situated about at least a portion of the sliding sleeve; and a spring configured to position the sliding sleeve such that fluid may pass through the openings.
In still another embodiment of the present invention, a method for reverse cementing comprises: providing a valve comprising a sliding sleeve, an outer sleeve situated about at least a portion of the sliding sleeve and connected to a casing string. The method of this embodiment further comprises: running the casing string and valve into a well bore while the valve is in a closed position; opening the valve after running the casing string by allowing the valve to contact the well bore; reverse cementing, while the valve is in an open position; and closing the valve after reverse cementing.
Referring now to
Valve 100 may include outer sleeve 118, which may have threads 130 near an upper end for securing outer sleeve 118 to casing string 102. Outer sleeve 118 and threads 130 may be sized such that valve 100 may fit any of a number of different casing strings, depending on the specific circumstances of the site. Therefore valve 100 may be a shoe.
Additionally, valve 100 may include sliding sleeve 108 situated at least partially within outer sleeve 118. Sliding sleeve 108 may be moveable longitudinally with respect to outer sleeve 118. Sliding sleeve 108 may include nose 110 at an end opposite outer sleeve 118. Nose 110 may be constructed such that it guides valve 100 into well bore 106, without activating, yet easily activates valve 100 when reaching the bottom of well bore 106. For example, nose 110 may have a conical, rounded or other suitable shape. Since drilling of the well bore 106 does not necessarily stop at the exact point where casing string 102 ends, it may be desirable to construct at least a portion of valve 100 of drillable materials. For example sliding sleeve 108, including nose 110 may be made of drillable materials, such as composites, phenolics, metallics, or plastics, or any other drillable material. While drillable materials may be desirable in certain applications, they would not be necessary when drilling stops at the bottom of the casing string 102.
Valve 100 may also include spring 120, which may be a standard spring or any other type of compression member tending to bias sliding sleeve 108 out of outer sleeve 118. Spring 120 may be constructed of materials suitable for use in a typical downhole environment. In the embodiment shown in
Valve 100 may also include one or more seals 126 to reduce or eliminate leakage through the valve. Seals 126 may be o-rings or any other type of seal used in a downhole environment.
Since well bore 106 is not cased until after valve 100 has passed through, valve 100 may include centralizer 128. Centralizer 128 may prevent nose 110 from catching on the formation prior to reaching the bottom. Thus, centralizer 128 may help to prevent premature activation.
Valve 100 also includes one or more ports 116 configured to selectively allow fluid to flow from annulus 104 into casing string 102. In the embodiment of
In the embodiments shown, ports 116 are closed when spring 120 is compressed, such that at least a portion of sliding sleeve 108 moves into outer sleeve 118. As this happens, ports 116 close. In the embodiment of
Referring now to
When pin 122 and groove 124 are used, ports 116 may be reopened by applying pressure on the inside of casing string 102. This pressure will push downward on sliding sleeve 108 relative to outer sleeve 118. While pin 122 and groove 124 may have a tendency to prevent movement, sufficient pressure may cause pin 122 to retract from groove 124, and thus allow sliding sleeve 108 to move relative to outer sleeve 118, until ports 116 are reopened. Therefore, pin 122 may be rounded or otherwise shaped such that it does not completely and irreversibly engage groove 124. Likewise, any other latch mechanism used may be constructed such that it can be released without damage.
When casing string 102 and attached valve 100 are being run into well bore 106, ports 116 may be held in an open position by spring 120, allowing mud or other fluid to flow freely from annulus 104 into and through casing string 102. This is known as “auto flow” and prevents casing string 102 from floating in the mud.
In some instances, it may be useful to reopen ports 116 that have inadvertently closed. This may occur in any number of cases. For example, nose 110 may “catch” on well bore 106 at a point above the bottom. In one embodiment, ports 116 may be reopened by simply removing weight from casing string 102. In another embodiment, reopening ports 116 involves the application of pressure to the inside of casing string 102.
After valve 100 reaches the bottom of well bore 106, weight on casing string 102 may cause ports 116 to close, verifying that valve 100 has reached the bottom. After ports 116 have closed as a result of valve 100 reaching the bottom of well bore 106, ports 116 may be reopened. Fluids may be circulated in either the conventional or reverse directions when ports 116 are open. Ports 116 may remain open until cement is reverse circulated in place. At the end of the circulation of cement, casing string 102 and valve 100 may again be lowered until spring 120 compresses and ports 116 are closed. In one embodiment, pin 122 then engages groove 124 such that ports 116 remain closed. This may allow for optimum bonding of the cement to casing string 102. Additionally, it may allow normal surface operations to take place while waiting for the cement to set.
One of ordinary skill in the art will appreciate that the elements for use in the embodiments described above may be used in a manner that allows weight on casing string 104 to cause ports 116 to open. In other words, weight may cause sliding sleeve 108 to move, such that ports 116 are open. Optional pins (not shown) may be used to keep the ports 116 open. Ports 116 may then be closed by removing the weight of casing string 102. Alternatively, ports 116 may be closed by doing a weight shift cycle on and off. Yet another alternative is to close ports 116 with a “bomb” that is dropped allowing for a pressuring up. Thus, a method for reverse cementing may include: providing valve 100 including sliding sleeve 108, outer sleeve 118 situated about at least a portion of sliding sleeve 108 and connected to casing string 102, and spring 120 configured to position valve 100 in an open position. This method may also include: running casing string 102 and valve 100 into well bore 106 while valve 100 is in an open position; reverse cementing, while valve 100 is in an open position; and closing valve 100 after reverse cementing by one of several methods. The methods of closing valve 100 may include, for example, setting weight down on casing string 102 to close ports 116 or dropping a weighted plug (not shown) that then can have pressure applied to close ports 116.
An alternative method for reverse cementing may include: providing valve 100 including sliding sleeve 108, outer sleeve 118 situated about at least a portion of sliding sleeve 108 and connected to casing string 102. This method may also include: running casing string 102 and valve 100 into well bore 106 while valve 100 is in an open position; reverse cementing, while valve 100 is in an open position; and closing valve 100 after reverse cementing by dropping a weighted dart/bomb (not shown) that can engage a closing mechanism (not shown) and then applying pressure to move sliding sleeve 108 downward and close valve 100.
Valve 100 may be used in conjunction with wire line tools and various fluid tags. Valve 100 may also be used by pumping a tracer fluid ahead of the cement job. The tracer fluid can be identified at the surface to determine when cement slurry, some distance behind the leading edge of the tracer, will be entering casing string 102. Valve 100 may also be used with a simple volumetric method of pumping a predetermined amount of fluid and stopping.
A variation of valve 100 may also be placed some distance above the bottom of a tubing string assembly, allowing for circulation of cement to a predetermined depth, and leaving well bore 106 below free of cement.
One may also drill well bore 106 past a target production zone, set casing below the target production zone, and then allow for cement to circulate up into the casing, but not up across production zones. This may reduce or eliminate the need to drill out cement at the bottom for the casing string, if the method were used on a final production casing cement job.
Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.
