Patent Application
20140174754
This disclosure relates in general to offshore blowout preventer equipment for well drilling, and in particular to an annular blowout preventer and lower marine riser package connector unit.
A blowout preventer assembly is employed for offshore well drilling operations. The blowout preventer assembly includes a blowout preventer stack (BOP stack) that includes several ram preventers. The BOP stank lands on and corrects to a wellhead housing at the sea floor. A lower marine riser package (LMRP) connects to a tubular mandrel on the upper end of the BOP stack. The LMRP secures to a lower end of the riser and has control pods that control various functions of the BOP stack and LMRP. The LMRP also has one or more annular blowout preventers, which can seal around pipe of a variety of sizes as well as completely close the passage.
The LMRP has a connector that is hydraulically actuated and will releasably connect the LMRP to the mandrel of the BOP stack. The annular BOP is located directly above the LMRP and connected by an external bolted flange.
The LMRP and BOP stack are large pieces of equipment, quite tall. It would be desirable to reduce the overall height of the BOP assembly because of height restrictions when the equipment is stowed on the rig. A reduced height LMRP would allow the use of the equipment on rigs with a lower deck height. A reduced height LMRP would allow for smaller rig designs. It would also allow for the installation of an additional ram BOP preventer in the BOP stack without adding the full height of the additional ram to the assembled BOP stack and LMRP. A reduced height LMRP would also allow replacement of shorter height annular BOPs, if desired, for taller height annular BOPs.
An annular blowout preventer assembly includes a single-piece annular element housing having a central cavity containing an elastomeric annular element and an annular element piston that strokes axially, relative to an axis of the annular element housing, to deform the annular element radially. The overall height of the annular blowout preventer assembly is reduced by employing a single-piece connector housing that abuts and is secured to a lower end of annular element housing. The connector housing contains a locking element and a locking dement piston that axially strokes a cam ring to move the locking element radially inward into engagement with a mandrel of a blowout preventer stack. The overall height of the unit that makes of the annular BOP and LMRP connector is less than those employing an external bolted flange on the lower end of the annular BOP.
An axial distance from the lower end of the annular element housing to the central cavity is less than an axial distance from a lower end of the connector housing to the lower end of the annular element housing. A radial wall thickness of the annular element housing at any point from the central cavity to the lower end of the annular element housing is at least equal to the radial wall thickness of the annular element housing at the lower end of the annular element housing. The annular element housing has an exterior surface from the lower end to the central cavity that is free of any upward-facing surfaces. A maximum outer diameter of the connector housing is less than art outer diameter of the annular element housing at any point along the annular element housing.
An external flange on the connector housing defines an upward-facing surface and a downward-facing surface, the upward-facing surface of the external flange being in abutment with the lower end of the annular element housing. Bolts extends through holes provided in the external flange into threaded holes provided in the annular element housing. The bolts have heads that engage the downward-facing surface of the external flange.
Referring to
A cap 45 secures to the upper end of annular element housing 31 with a locking member 47. The upper end of annular element 41 engages a lower side of cap 45. Cap 45 has a concentric upper opening 49 with a diameter the same as the diameter of annular element passage 43 when annular element 41 is not being deformed. A concentric lower opening 51 is located at a lower end 53 of annular element housing 31 and is the same diameter as upper opening 49. Lower end 53 has at its outer periphery a downward extending cylindrical collar 55.
A connector 57 secures to annular BOP 29 for connecting to BOP stack 11 (
Connector 57 has a locking element, preferably a number of dogs 67 spaced circumferentially around connector 57. Dogs 67 have grooves on an inner side for engaging a grooved profile of a tubular mandrel 69 located at the upper end of BOP stack 11 (
Annular BOP 29 and connector 57 provide an assembly or unit with less height than similar components of the prior art. Axial distance 77 indicated in
Referring to
A wear bushing 83 is optionally configured to fit closely in counterbore 81. Wear bushing 83 is a metal, sacrificial member that may suffer some damage from landing on BOP stack mandrel 69, but can readily be replaced when LMRP 13 (
Wear bushing 83 also has a cylindrical lower extension 83e that extends downward from lower end 83d into connector housing 59. Lower extension 83e has an outer diameter less than wear bushing outer surface 83c so that lower extension 83e will insert between cam ring 71 and mandrel 69. The portion of lower end 83d outward from lower extension 83e is closely spaced to or in substantial contact with the upper side of cam ring 71. The inner diameter of wear bushing 83 is the same as the inner diameter of opening 51 and has a downward-flaring tapered surface 83f.
Seals 85 are located on both the wear bushing cylindrical outer surfaces 83b, 83c for sealing to counterbore outer diameter walls 81b and 81c. Also, a seal 87 on the inner diameter of lower extension 83e seals to the outer surface of mandrel 69. A metal seal gasket 89 seals between wear bushing 83 and the inner diameter of mandrel 69. Seal gasket 89 has an upper tapered surface 89a on its outer side that seals to wear bushing tapered inner diameter portion 83f. Seal gasket 89 has a lower tapered surface 89b on its inner side that seals to a conical surface on the inner diameter of mandrel 69 near its rim. Seal gasket 89 is thus located in lower opening 51 of annular element housing 31 directly below central cavity 35.
In operation, connector 57 is secured to lower end 53 of annular element housing 31 by bolts 63. The operator lands LMRP 13 on mandrel 69 of BOP stack 11. Wear bushing 83 will land on the rim of mandrel 69. The operator supplies hydraulic fluid pressure to connector piston 73 to stroke cam ring 71 downward, which pushes dogs 67 radially inward into engagement with the exterior profile on mandrel 69. Once installed, the lower end of annular element housing collar 55 will be below the upper end of mandrel 69.
The disclosure has several advantages. By bolting connector housing 59 directly to the lower end 53 of annular element housing 31, an external flange with an upward-facing shoulder between the connector housing and the annular element housing is eliminated. The elimination of such a flange allows a reduction in overall height of the LMRP 13, which is an advantage when the LMRP 13 is positioned on the vessel for maintenance or transport. The sacrificial wear bushing 83 absorbs damage that might occur due to landing on the mandrel 69 of the BOP stack. If damaged significantly, the wear bushing can be replaced when the LMRP is retrieved.
While the disclosure has been shown in only two of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the disclosure.
