1. Field of the Invention
The present invention is generally directed to the field of offshore well drilling, and, more particularly, to a lightweight, reusable temporary abandonment cap that can be placed on and retrieved from an open pipe of a subsea well.
2. Description of the Related Art
Drilling of offshore oil and gas wells is a very expensive and time-consuming activity. Moreover, when drilling and/or completing such wells, there may be many occasions, both planned and unexpected, where it is desirable to temporarily suspend drilling or completion activities at a well. As part of this process, a temporary abandonment cap is installed to aid in protecting the wellhead during this period of inactivity. Typically, a portion of the well bore will be filled with a liquid corrosion inhibitor to displace the seawater within the bore such that certain surfaces, e.g., sealing surfaces, are not corroded by the seawater or otherwise subjected to the formation of undesirable marine growth, e.g., algae. The temporary cap is used in an effort to keep the corrosion inhibitor fluid in the bore until such time as it is desired to resume drilling and/or completion activities at the well.
Some prior art temporary caps were locked to the wellhead by a plurality of sacrificial pins. See, for example, U.S. Pat. No. 5,107,931 (Valka et al.) for an example of such a temporary cap. Some prior art temporary abandonment caps were comprised of a relatively heavy steel body and they were deployed from a surface vessel or rig via a drill string. The cap 12 depicted in FIG. 4 of the Valka patent weighed approximately 600 pounds. A running and retrieve tool 42 was attached to the end of a drill string and the running and retrieve tool 42 included a plurality of pins 48 for holding the temporary cap 12 during transit to the well. In this position, the temporary abandonment cap 12 was secured to the well by a plurality of spring-loaded, sacrificial pins 32. An upward force was exerted on the drill string once the cap 12 was properly positioned over the wellhead to shear the pins 48. To remove the cap 12, the running and retrieve tool 42 was run from the surface to the temporary cap 12 and coupled to the cap 12 by spring-loaded pins 50. Thereafter, an upward force was exerted by the drill string to shear the sacrificial pins 32 to thereby release the temporary cap 12 from engagement with the wellhead.
FIGS. 1A-1C are various views of an illustrative prior art running and retrieve tool 10 for use with the temporary abandonment cap 12 depicted in the Valka patent. FIGS. 1A and 1B are, respectively, side and plan views of the tool 10. The running and retrieve tool 10 is generally comprised of a body 11 having a conical portion 13 that defines an opening 14. A threaded connection 11A is provided to secure the tool 10 to a drill string. The tool 10 further comprises a plurality of ROV (remotely operated vehicle) handle assemblies 15. Each of the handle assemblies 15 is comprised of a gripper block 15A, a rod 17, a housing 18, and a set screw 16. FIG. 1C is an enlarged view of a helical groove 19 formed in each of the rods 17. The running and retrieve tool 10 is generally comprised of various carbon steel materials, and it has an approximate weight of 100-150 pounds.
In operation, to run the temporary cap 12 down to the well, the tool 10 is secured to the temporary cap 12 of the Valka patent by positioning the stem 22 (see FIG. 4 of the Valka patent) in the opening 14 in the running and retrieve tool 10. The ROV handles 15 are then manually rotated in a clockwise direction to advance the ends 17A of the rods 17 into the grooves 28 of the stem 22 shown in FIG. 4 of the Valka patent. The rods 17 are advanced by virtue of the camming action achieved as the helical groove 19 in the rod 17 engages the set screw 16. The combined assembly of the running and retrieve tool 10 and the temporary cap 12 is then secured to the drill string via threaded connection 11A. Thereafter, the temporary cap 12 is run down to the well and coupled thereto by the techniques described in the Valka patent. An ROV is then used to rotate the handles 15 on the tool 10 in a counter-clockwise direction to disengage the ends 17A of the rods 17 from the groove 28 in the stem 22 of the temporary cap 12. The running and retrieve tool 10 is then retrieved to the surface. To remove the temporary cap 12, the tool 10 is secured to the drill string and run down to the wellhead. Using the conical opening 14, the tool 10 is maneuvered until such time as the stem 22 of the temporary cap 12 is positioned in the tool 10. An ROV is then used to rotate the handles 15 in a clockwise direction such that the ends 17A of the rods 17 engage the groove 28 on the stem 22. A pulling force is then generated to shear the pins 32, thereby releasing the temporary cap 12 from the well.
In other cases, the running and retrieve tool 10 shown in FIGS. 1A-1C may be used to deploy the temporary cap 12 by means of an ROV. In that case, a sub (not shown) is threadingly coupled to the tool 10 via the threaded connection 11A. The sub may be used to provide a means to inject fluid into the well via a hot stab manifold. A shackle (not shown) is secured to the top of the sub. A cable is connected to the shackle and the combination of the tool 10 and the temporary cap 12 is lowered into the sea until such time as an ROV can grasp the assembly and position it on the wellhead. After the cap 12 is secured to the wellhead by the sacrificial pins 32, the ROV rotates the handles 15 such that the rod ends 17A are in their retracted position, and the retrieve tool 10 may be removed leaving the cap 12 on the well.
FIG. 2 is a cross-sectional view of an alternative temporary abandonment cap 20 that employs a plurality of ROV-operated handles 15 for locking and unlocking the temporary cap 20 to and from the wellhead. In FIG. 2, the same references numbers will be used to describe parts that function in a similar manner to those described previously in connection with FIGS. 1A-1C. The temporary cap 20 is generally comprised of a cylindrical body 21, a conical portion 23, a top portion 25, a stem 22A and a groove 28A. The cap 20 further comprises a plurality of check valves 27A, 27B positioned on the top portion 25 of the cap 20. The cap 20 is generally made from carbon steel material, and its weight is approximately 600 pounds. A running and retrieve tool (not shown) may be used to position the cap 20 over the well (not shown). Thereafter, an ROV is used to rotate the handle 15A such that the end portions 17A of the rod 17 engages a recess or groove in the well. To remove the cap 20, the running and retrieve tool is landed on the stem 22A, and an ROV is used to rotate the handles 15A on the cap 20 such that the ends 17A of the rods 17 are disengaged from the well. The cap 20 may then be retrieved to the surface.
U.S. patent application Ser. No. 2002/0000322A1 (Bartlett et al., Jan. 3, 2002) depicts a situation in which a debris cap 460 is used in conjunction with an internal tree cap 458. See, e.g., FIGS. 13, 16 and 17 and the associated discussion thereof The debris cap performs a variety of functions. For example, the debris cap 460 is used to protect various sealing surfaces on the exposed end of the Christmas tree. The debris cap 460 also serves to prevent debris from collecting in the annular area between the internal tree cap and the tree bore.
FIGS. 3A-3B are, respectively, plan and side views of an illustrative debris cap 30 that may be employed with an inner tree cap similar to that depicted in the Bartlett application. The debris cap 30 is comprised of a body 31, a conical portion 32, a top, circular portion 33, an O-ring seal 34 and an O-ring seal 35. The top, circular portion 33 of the debris cap 30 defines an opening 36 therein. The debris cap 30 is further comprised of two locking pins 37 that are coupled to a handle 38. A cam pin 39 is coupled to the locking pin 37 and it is adapted to move within the helical groove 40 formed in the housing 41 for the lock pins 37 when the handle 38 is raised or lowered. More specifically, in the position shown in FIGS. 3A and 3B, the ends 37A of the lock pins 37 are in a position to engage a groove on a wellhead (not shown). The O-ring seal 34 engages and seals against the outside diameter of the well. The O-ring 35 is adapted to seal against a tree cap that is to be subsequently installed. The handle 38 of the debris cap 30 may be operated by an ROV. With the handle 38 in the vertical position, the lock pins 37 are in their retracted, non-engaged position. In this position, the debris cap 30 may be positioned over the well by an ROV. Once properly positioned, the ROV may rotate the handle 38 to the position shown in FIGS. 3A-3B to thereby cause the lock pins 37 to move to their engaged position by virtue of the cam pins 39 moving within the groove 41 as the handle 38 is moved to its locked position. To remove the debris cap 30, the process is reversed.
Despite prior efforts, there still exists a need for temporary abandonment caps that may be readily deployed by means of an ROV. Moreover, such a temporary cap should provide means for supplying desired fluids to the well bore in a timely and efficient manner.
The present invention is directed to an apparatus for solving, or at least reducing the effects of, some or all of the aforementioned problems.