Abstract:
A method for sealing an annulus defined between an outer casing and an inner casing, the method having steps as follows: fastening a lock ring to an anchor base, wherein the lock ring comprises a threaded fastener of the lock ring to the head; positioning the lock ring and anchor base about the outer casing; fastening a limit clamp to an exterior surface of the outer casing; repositioning the lock ring and anchor base so that the anchor base is in contact with the limit clamp; fastening a head to the lock ring; providing an opening for fluid communication with the annulus through the head; positioning a plug about the inner casing and in contact with the inner casing and the head; positioning a seal fitting clamp about the inner casing and in contact with the plug; positioning a bull cap about the inner casing and in contact with the seal fitting clamp; and fastening the bull cap to the head.

Description:
BACKGROUND  
       [0001]     The present invention relates generally to well head equipment for production wells. In particular, this invention relates to tools and methods for sealing the casing-by-casing annulus at the top of the well bore so that a positive pressure may be applied to the annulus.  
         [0002]     Production wells typically have a surface casing that extends from the top of the well and into the earth to a relatively shallow depth. It is also typical for a production casing to be positioned concentrically within the surface casing and so as to extend from the top of the well to a relatively deep depth. A casing-by-casing annulus is defined between the surface casing and the production casing.  
         [0003]     In certain instances, it is desirable to apply a pressure differential in the annulus relative to atmospheric pressure at the well head. For example, if a reverse circulation cement (RCC) job is to be performed in the annulus, the cement is pumped into the annulus under positive pressure to pump the cement composition down the annulus. Prior to applying the pressure differential in the annulus, steps must be taken to isolate or seal the annulus at the well head. Previously, blow out preventor (BOP) and/or well head equipment has been used to seal the annulus. However, typical blow out preventor and well head equipment do not provide access to the annulus for performing a reverse circulation cement job. Typical blow out preventor and well head equipment limits the use of reverse circulation cementing operations on wells where surface casing is not fitted to accept the wellhead equipment. Further, even where the surface casing is configured to accept the BOP and/or well head equipment, significant hot work is typically required to install BOP flanges or wellhead equipment to the surface casing.  
       SUMMARY  
       [0004]     The present invention is directed to tools and methods for sealing the casing-by-casing annulus at the top of the well bore so that a positive pressure may be applied to the annulus.  
         [0005]     More specifically, one embodiment of the present invention is directed to a seal of an annulus defined between an outer casing and an inner casing, the seal having: an anchor fastened to the outer casing; a head fastened to the anchor, wherein the head comprises an opening for fluid communication with the annulus; and a plug contacting the exterior of the inner casing and the head.  
         [0006]     According to another embodiment of the invention, there is provided a method for sealing an annulus defined between an outer casing and an inner casing, the method having the following steps: fastening an anchor to the outer casing; fastening a head to the anchor; providing an opening for fluid communication with the annulus through the head; and plugging the annulus between the inner casing and the head.  
         [0007]     Still another aspect of the invention provides a method for sealing an annulus defined between an outer casing and an inner casing, the method having steps as follows: fastening a lock ring to an anchor base, wherein the lock ring comprises a threaded fastener of the lock ring to the head; positioning the lock ring and anchor base about the outer casing; fastening a limit clamp to an exterior surface of the outer casing; repositioning the lock ring and anchor base so that the anchor base is in contact with the limit clamp; fastening a head to the lock ring; providing an opening for fluid communication with the annulus through the head; positioning a plug about the inner casing and in contact with the inner casing and the head; positioning a seal fitting clamp about the inner casing and in contact with the plug; positioning a bull cap about the inner casing and in contact with the seal fitting clamp; and fastening the bull cap to the head.  
         [0008]     The features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of the exemplary embodiments, which follows.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings.  
         [0010]      FIG. 1  is a cross-sectional side view of a casing-by-casing seal in a fully assembled configuration for sealing an annulus between a production casing and a surface casing.  
         [0011]      FIG. 2A  is a cross-sectional, side view of a quick latch head, a quick latch lock ring and a limit clamp assembled to a surface casing.  
         [0012]      FIG. 2B  is a cross-sectional, side view of the wellbore and casings shown in  FIG. 2A , wherein a seal gasket and quick latch head are assembled to the surface casing.  
         [0013]      FIG. 2C  is a cross-sectional, side view of the wellbore and casings shown in  FIGS. 2A and 2B , wherein a head/hinge plug, a seal fitting clamp, and a bull cap are assembled to the production casing and quick latch head.  
         [0014]      FIG. 2D  is a cross-sectional, top view of the quick latch head and production casing wherein the quick latch head has two nipple connectors.  
         [0015]      FIG. 3  is a cross-sectional, side view of a wellbore and casings with a fully assembled casing-by-casing seal.  
         [0016]      FIG. 4A  is a cross-sectional, side view of a wellbore and casings with a quick latch lock ring, a quick latch anchor base, and a limit clamp assembled to the surface casing.  
         [0017]      FIG. 4B  is a cross-sectional, side view of the wellbore and casings shown in  FIG. 4A , wherein a seal gasket and a quick latch head are assembled to the surface casing.  
         [0018]      FIG. 4C  is a cross-sectional, side view of the wellbore and casings shown in  FIGS. 4A and 4B , wherein a washer plug, a seal fitting clamp, and a bull cap are assembled to the production casing and the quick latch head.  
     
    
     DETAILED DESCRIPTION  
       [0019]     The details of the present invention will now be described with reference to the accompanying drawings. This specification discloses various types of tools and methods to install the tools to pack-off or seal the casing-by-casing annulus such that a positive pressure can be applied to the casing annulus. This is in conjunction with, but not limited to, performing a reverse circulation cement (RCC) job. These tools require little, if any, hot work to install. As used herein, the term “casing” refers to any casing, tubing, pipe, rods, or any other similar devices used in wellbores and known to persons of skill in the art.  
         [0020]     Referring to  FIG. 1 , a cross-sectional, side view of an embodiment of a casing-by-casing annulus seal  1  is illustrated. A surface casing  2  extends from a well bore  3  above the surface of the ground  4 . A production casing  5  is positioned concentrically within the surface casing  2  to define a casing-by-casing annulus  6 . The production casing  5  extends further out of the well bore  3  than does the surface casing  2 .  
         [0021]     The casing-by-casing annulus seal  1  comprises several components. A limit clamp  7  is attached to the exterior of the surface casing  2  above the surface  4  of the ground. A quick latch  10  surrounds the limit clamp  7  and engages the surface casing  2  below the limit clamp  7  to provide a nippled head for fluid communication with the annulus  6 . A bull cap  21  and seal fitting clamp  20  secure the production casing  5  to the head to close off the top of the annulus  6  above the head. These components and others are described more fully.  
         [0022]     The limit clamp  7  is attached to the exterior of the surface casing  2  near its distal end protruding from the wellbore  3 , as  FIG. 1  illustrates. The quick latch  10  is also attached to the surface casing  2  and comprises three major components: a quick latch anchor base  13 , a quick latch lock ring  12 , and a quick latch head  11 . The quick latch anchor base  13  has a lower interior flange that defines a hole through the center of the anchor only slightly larger than the outside diameter of the surface casing  2 . The quick latch lock ring  12  is received into the opposite end of the quick latch anchor base  13  from the lower flange. A relatively smaller flange at the upper end of the quick latch anchor base  13  mates with a corresponding recess in the quick latch lock ring  12  to connect the components. The quick latch lock ring  12  has a female threaded end for receiving male threads on the quick latch head  11 . The quick latch head  11  mates with the quick latch lock ring  12  via these threads. A seal gasket  14  seals the quick latch head  11  to the distal end of the surface casing  2 . The seal gasket  14  has a casing/gasket seal  15  that extends between the surface casing  2  and the seal gasket  14 . The seal gasket  14  also has a channel in its outer surface in which a head/gasket seal  16  is received. The head/gasket seal  16  seals the gap between the seal gasket  14  and the quick latch head  11 .  
         [0023]     A hinge plug  17  is positioned at the top of the quick latch head  11  and extends from the quick latch head  11  to the production casing  5 . The hinge plug  17  has a casing/hinge plug  18  that extends between the hinge plug  17  and the production casing  5 . The hinge plug  17  also has a head/hinge plug  19  that extends between the hinge plug  17  and the quick latch head  11 . A seal fitting clamp  20  is positioned above the hinge plug  17  around the production casing  5 . A clamp/hinge seal  25  is positioned between the hinge plug  17  and the seal fitting clamp  20 . A bull cap  21  completes the assembly and is positioned above the seal fitting clamp  20  to sandwich the seal fitting clamp  20  and hinge plug  17  between the bull cap  21  and the quick latch head  11 . A clamp/cap seal  26  is positioned between the seal fitting clamp  20  and the bull cap  21 . Female threads at the lower end of the bull cap  21  mate with male threads on the quick latch head  11 .  
         [0024]     As shown in  FIG. 1 , the casing-by-casing seal  1  uses a modified quick latch coupling and a modified limit clamp attached to the surface casing or riser  2 . The casing-by-casing seal  1  also uses a properly selected cement head to fit the surface casing  2  for a conventional cement job. The Quick Latch coupling may need to be modified to fit the inside and outside diameters of the surface casing, rather than the diameters of the casing collars. The casing-by-casing seal  1  uses a modified cement head cap or bull cap  21  that has a bore in the top with a rubber seal (clamp/cap seal  26 ) under the cap. The bore in the cap should slightly exceed the largest possible production casing  5  that could be set in the surface casing  2 . In some embodiments of the invention, the quick latch  10  components, the seal gasket  14 , and the bull cap  21  may be one-size-fits-all for a range of casing sizes, while the limit clamp  7 , the hinge plug  17 , and the seal fitting clamp  20  are precisely sized for individual casing sizes.  
         [0025]     The casing-by-casing seal  1 , illustrated in  FIG. 1 , may be assembled in step wise fashion. Referring to  FIG. 2A , the quick latch lock ring  12  and quick latch anchor base  13  are made up to each other so that a flange of the anchor base  13  mates with a recess of the lock ring  12 . The quick latch lock ring  12  and quick latch lock anchor base  13  are then positioned over the distal end of the surface casing  2 , with the threaded end of the lock ring  12  at the top. Because the inner diameter of the hole through the lower flange of the quick latch anchor base  13  is slightly larger of the outside diameter of the surface casing  2 , the quick latch anchor base  13  easily slides over the end of the surface casing  2 . The quick latch lock ring  12  and quick latch anchor base  13  are lowered to a position well below the distal end of the surface casing  2 . A crane or air hoist may be used to lower the quick latch lock ring  12  and quick latch lock anchor base  13  over the production casing  5  and surface casing  2 . The limit clamp  7  is then attached to the exterior of the surface casing  2  by any means known to persons of skill. For example, the limit clamp  7  may comprise two semicircular segments that are fastened together, an annular ring that is welded to the surface casing, and annular ring that is bolted or otherwise fastened to the casing, etc. In some embodiments of the invention, the limit clamp  7  may be a casing collar or a welded collar previously made part of the surface casing  2 . In these cases, the quick latch anchor base  13  may be split in pieces for later assembly around the surface casing  2  below the limit clamp  7 . With the limit clamp  7  fixed to the surface casing  2 , the quick latch lock ring  12  and quick latch anchor base  13  are pulled upwardly until the flange of the quick latch anchor base  13  rests snugly against the lower edge of the limit clamp  7 . Thus, the limit clamp  7  creates a shoulder that prevents further upward movement of the quick latch anchor base  13  relative to the surface casing  2 .  
         [0026]     As shown in  FIG. 2B , the seal gasket  14  is then placed over the end of the production casing  5  and allowed to rest on the top of the surface casing  2 . In particular, the seal gasket  14  has a casing/gasket seal  15  that rests on the extreme distal end of the surface casing  2 . A crane or air hoist may be used to raise the quick latch lock ring  12  and quick latch anchor base  13  until they engage the lower shoulder of the limit clamp  7 . Note that the limit clamp  7  was attached to the surface casing  2  at a precise location so as to allow the seal gasket  14  to be positioned concentrically inside the threaded portion of the quick latch lock ring  12 . A crane or air hoist may be used to lower the quick latch head  11  over the production casing  5  and around the seal gasket  14 . With the seal gasket  14  and quick latch lock ring  12  appropriately positioned, the quick latch head  11  is threaded into the quick latch lock ring  12 . As these members are threaded together, an interior shoulder of the quick latch head  11  rests firmly on the top of the seal gasket  14  to drive the seal gasket  14  downwardly onto the extreme distal end of the surface casing  2 . The quick latch head  11  also engages a head/gasket seal  16  around the periphery of the seal gasket  14 . Because the quick latch anchor base  13  is held firmly in place by the limit clamp  7 , the threading procedure firmly attaches the quick latch head  11  to the top of the surface casing  2 . The casing/gasket seal  15  and the head/gasket seal  16  completely seal the connection between the quick latch head  11  and the surface casing  2 .  
         [0027]     Referring to  FIG. 2C , the annulus  6  is closed by assembling the hinge plug  17  to the top of the quick latch head  11 . This may be done by placing the hinge plug  17  over the distal end of the production casing  5 . The hinge plug  17  is lowered relative to the production casing  5  until it rests on the top of the quick latch head  11 . This may be done with a crane or air hoist. Properly positioned, the head/hinge plug  19  rests on the top of the quick latch head  11 . Also, the casing/hinge plug  18  of the hinge plug  17  firmly engages the production casing  5  because the parts are sized so as to squeeze the casing/hinge plug  18  between the production casing  5  and the hinge plug  17  when the parts are assembled. A crane or air hoist may then be used to place a seal fitting clamp  20  over the distal end of the production casing  5  and to lower it until it rest on the top of the hinge plug  17 . A clamp/hinge seal  25  is positioned between the hinge plug  17  and the seal fitting clamp  20 . Depending on the particular embodiment of the invention, a crane, air hoist, or drilling rig may then be used to lift up the production casing  5  so that the production casing  5  moves upward slightly relative to the stationary seal fitting clamp  20 . The seal fitting clamp  20  is then fixed to the production casing  5 . In some embodiments, the seal fitting clamp  20  comprises two, semi-circular parts that mate with each other to tighten a metal-to-metal seal with the production casing  5 . The production casing  5  is then lowered so that the weight of the production casing  5  squeezes the hinge plug  17  between the seal fitting clamp  20  and the quick latch head  11 . The production casing  5  may be lowered until the desired amount of weight is placed onto quick latch head  11  as measured with the weight indicator. A bull cap  21  is placed over the seal fitting clamp  20  and lowered relative to the assembly. A clamp/cap seal  26  is positioned between the bull cap  21  and the seal fitting clamp  20 . In the embodiment shown, the seals are counter-sunk in the seal fitting clamp  20 , but in alternative embodiments, any seal configuration known to persons of skill may be implemented. Female threads of the bull cap  21  are mated with male threads at the top of the quick latch head  11  so as to fasten the bull cap  21  to the quick latch head  11 . As these members are threaded together, the hinge plug  17  and seal fitting clamp  20  are squeezed between the quick latch head  11  and the bull cap  21  to insure a complete seal of the annulus  6 .  
         [0028]      FIG. 2D  is a cross-sectional, top view of the quick latch head  11 . The quick latch head  11  has two nipple connectors  24  to which pipe and/or hose fittings are attached for fluid communication with the annulus  6 . The annulus  6  is defined between the production casing  5  and the quick latch head  11 .  
         [0029]     Referring to  FIG. 3 , a cross-sectional side view of an alternative embodiment of a casing-by-casing seal  1  is illustrated. In this embodiment, a trapezoidal-shaped washer plug  22  is positioned around the production casing  5  above the quick latch head  11 . In one embodiment, the washer plug  22  is an annular ring having a trapezoidal shape in cross-section. The inside diameter of the interior hole through the center of the annular washer plug  22  is slightly smaller than the outside diameter of the production casing  5  so that the seal  22  fits snugly around the production casing  5 . Further, the washer plug  22  has a beveled surface  23  that engages the top of the quick latch head  11 . In an alternative embodiment, the washer plug  22  is cut into segments so that the segments may be easily placed around the production casing  5  as opposed to the annular embodiment which is placed over the end of the production casing  5 . Once assembled, the several seal segments mate and engage with each other to form a complete annular seal.  FIG. 3  illustrates a seal fitting clamp  20  resting on top of the washer plug  22 . A bull cap  21  engages a top surface of the seal fitting clamp  20 . A clamp/cap seal  26  is positioned between the bull cap  21  and the seal fitting clamp  20 . The bull cap  21  has a female thread for engaging the male threads on the top of the quick latch head  11 .  
         [0030]     As shown in  FIG. 3 , the casing-by-casing seal  1  uses a modified Quick Latch coupling and a modified limit clamp attached to the surface casing or riser  2 . The casing-by-casing seal  1  also uses a properly selected cement head to fit the surface casing  2  for a conventional cement job. The casing-by-casing seal  1  uses a modified cement head cap or bull cap  21  that has a bore in the top with a rubber seal (washer plug  22 ) under the cap. The bore in the cap should slightly exceed the largest possible production casing  5  that could be set in the surface casing  2 . The bore in the cap should slightly exceed the largest possible production casing  5  that could be set in the surface casing  2 . In some embodiments of the invention, the quick latch  10  components, the seal gasket  14 , and the bull cap  21  may be one-size-fits-all for a range of casing sizes, while the limit clamp  7 , the washer plug  22 , and the seal fitting clamp  20  are precisely sized for individual casing sizes.  
         [0031]     In various embodiments of the casing-by-casing seal, different sealing mechanism may be used to achieve the casing-by-casing seal. In some embodiments, the seal uses the assistance of the seal fitting clamp  20  to help give a pressure seal using some of the weight of the production casing  5 . In other embodiments, the seal fitting clamp  20  is not fixed to the production casing  5 , such that the seal uses the bull cap  21  to tighten the washer plug  22  (rubber gasket) between the seal fitting clamp  20  and the quick latch head  11 . Those embodiments that do not fix the seal fitting clamp to the production casing may be better suited for lower pressure needs or smaller rigs.  
         [0032]     Referring to  FIG. 4A , the quick latch lock ring  12  and quick latch anchor base  13  are made up to each other so that the flange of the anchor  13  mates with a recess of the lock ring  12 . The quick latch lock ring  12  and quick latch anchor base  13  are then positioned over the distal end of the surface casing  2 . Because the inner diameter of the hole through the lower flange of the quick latch anchor base  13  is slightly larger of the outside diameter of the surface casing  2 , the quick latch anchor base  13  easily slides over the end of the surface casing. The limit clamp  7  is then attached to the exterior of the surface casing by any means known to persons of skill. For example, the limit clamp  7  may comprise two semicircular segments that are fastened together, an annular ring that is welded to the surface casing, and annular ring that is bolted or otherwise fastened to the casing, etc. With the limit clamp  7  in place, the quick latch lock ring  12  and quick latch anchor base  13  are pulled upwardly until the flange of the quick latch anchor base  13  rests snugly against the lower edge of the limit clamp  7 . Thus, the limit clamp  7  creates a shoulder that prevents further upward movement of the quick latch anchor base  13  relative to the surface casing  2 .  
         [0033]     Referring to  FIG. 4B , the seal gasket  14  is then placed over the end of the production casing  5  and allowed to rest on the top of the surface casing  2 . In particular, the casing/gasket seal  15  rests on the extreme distal end of the surface casing  2 . Note that the limit clamp  7  was attached to the surface casing  2  at a precise location so as to allow the seal gasket  14  to be positioned concentrically inside the threaded portion of the quick latch lock ring  12 . With the seal gasket  14  and quick latch lock ring  12  so positioned, the quick latch head  11  is threaded into the quick latch lock ring  12 . As these members are threaded together, an interior shoulder of the quick latch head  11  rests firmly on the top of the seal gasket  14  to drive the seal gasket  14  down onto the extreme distal end of the surface casing  2 . Because the quick latch anchor base  13  is held firmly in place by the limit clamp  7 , the threading procedure firmly attaches the quick latch head  11  to the top of the surface casing  2 .  
         [0034]     Referring to  FIG. 4C , the washer plug  22  is positioned around the outside of the production casing  5  in a manner depending upon the particular embodiment of the washer plug  22 . For washer plugs  22  that are annular in construction, the washer plug  22  is placed over the end of the production casing  5 . The washer plug  22  is then translated down the length of the production casing  5  until it engages the top of the quick latch head  11 . For embodiments of the washer plug  22  that are segmented, the individual segments are simply placed around the production casing  5  at the top of the quick latch head  11 . With the washer plug  22  in place, a seal fitting clamp  20  is positioned over the top of the production casing  5  and translated down the production casing  5  until it rests on the top of the washer plug  22 . In the illustrated embodiment, the seal fitting clamp  20  is not fixed to the production casing  5 , rather the seal fitting clamp  20  is allowed to freely move relative to the production casing  5 . The bull cap  21  is then positioned over the end of the production casing  5  and translated down the length of the production casing until it rests on top of the seal fitting clamp  20 . The bull cap  21  engages a top surface of the seal fitting clamp  20  and surrounds at least a portion of the seal fitting clamp  20  and the washer plug  22 . The bull cap  21  has female threads which engage the male threads at the top of the quick latch head  11 . The relative sizes of the washer plug  22 , the seal fitting clamp  20 , and the bull cap  21  are such that when the bull cap  21  is threaded on to the quick latch head  11 , the bull cap  21  and seal fitting clamp  20  bear down on the washer plug  22  so as to squeeze the washer plug  22  between the quick latch head  11  and the seal fitting clamp  20 . Further, because the washer plug  22  has a beveled surface  23 , when the bull cap  21  and the seal fitting clamp  20  bear down on the washer plug  22 , the washer plug  22  is squeezed radially inward toward the production casing  5  to produce a complete seal of the annulus  6 . The washer plug  22  forms a sealed contact with the production casing  5  and the quick latch head  11 .  
         [0035]     Once a casing-by-casing seal  1  is properly installed, a reverse circulation cement job may be commenced and executed in a safe and effective way. The cement composition may be injected under pressure into the annulus  6  through one of the nipple connectors  24 . Clearly, if only one nipple connector  24  is used for the injection step, all other nipple connectors  24  must be capped off before pressure will build in the annulus. After the cement composition is set in the annulus  6 , the casing-by-casing seal  1  may be removed from the wellhead and repaired as needed for other jobs.  
         [0036]     Therefore, the present invention is well-adapted to carry out the objects and attain the ends and advantages mentioned as well as those which are inherent therein. While the invention has been depicted, described, and is defined by reference to exemplary embodiments of the invention, such a reference does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent arts and having the benefit of this disclosure. The depicted and described embodiments of the invention are exemplary only, and are not exhaustive of the scope of the invention. Consequently, the invention is intended to be limited only by the spirit and scope of the appended claims, giving full cognizance to equivalents in all respects.