Antirotation device for subsea wellheads

A subsea well assembly, comprising in combination:

• an outer wellhead housing located at a sea floor, the outer wellhead housing having an axis and an axial bore containing an internal landing shoulder, the outer wellhead housing having a circular rim on its upper end;
• a lock ring protruding upward from the rim;
• a plurality of slots formed in and spaced apart from each other around the lock ring, each of the slots having an open upper end at an upper edge of the lock ring;
• an inner wellhead housing located in the outer wellhead housing, the inner wellhead housing having an external landing shoulder which engages the internal landing shoulder as the inner wellhead housing is lowered into the outer wellhead housing on a string of conduit from a drilling vessel;
• and
• a plurality of pins secured to the inner wellhead housing, each of the pins being received in one of the slots to prevent rotation of the inner wellhead housing in the outer wellhead housing.

In a subsea well assembly having an outer wellhead housing located at a sea floor and having an axial bore, the subsea well assembly having an inner wellhead housing which is lowered from a drilling vessel on a string of conduit into and lands in the bore of the outer wellhead housing, the inner wellhead housing having a lower end secured to a string of casing, an improved antirotation means for preventing rotation of the inner wellhead housing in the outer wellhead housing due to swinging movement of the drilling vessel, comprising in combination:

• a plurality of slots formed in and spaced apart from each other around the rim, each of the slots having an open upper end and opposed sidewalls, at least a portion of each sidewall extending axially;
• a pair of guide surfaces extending downward and converging toward each other into each of the slots, the guide surfaces between each of the slots intersecting each other in a triangular apex;
• and
• a plurality of pins rigidly secured to the inner wellhead housing and protruding radially therefrom, each of the pins being received in one of the slots to prevent rotation of the inner wellhead housing in the outer wellhead housing.

An improved method for preventing rotation of an inner wellhead housing in an outer wellhead housing due to swinging movement of a drilling vessel, the outer wellhead housing being located at a sea floor and having an axial bore and an internal landing shoulder, the inner wellhead housing being secured to a string of conduit toward from the drilling vessel for reception int he outer wellhead housing and having an external landing shoulder, the method comprising:

• providing at least one slot in the outer wellhead housing with opposed sidewalls which are circumferentially spaced apart from each other;
• securing at least one pin to the inner wellhead housing;
• then
• lowering the inner wellhead housing from the drilling vessel on the string of conduit into the outer wellhead housing, causing the inner wellhead housing to rotate a limited amount if necessary until the pin registers with the slot, then locating the pin in the slot, and causing the external landing should to engage the internal landing shoulder, the circumferential spacing of the sidewalls of the slot restraining the inner wellhead housing from all rotation relative to the outer wellhead housing.

An improved method for mounting an inner wellhead housing in an axial bore of an outer wellhead housing of a subsea well, comprising:

• providing the outer wellhead housing with an upper rim, a lock ring protruding upward from the rim, the lock ring having a plurality of slots spaced circumferentially around the rim, each slot having an open upper end;
• providing each of the slots with at least one guide surface inclining downward into the open upper end of each slot;
• rigidly securing a plurality of pins to the inner wellhead housing, and spacing the pins circumferentially apart from each other and protruding radially from the inner wellhead housing;
• then
• lowering the inner wellhead housing from a drilling vessel on a string of conduit into the outer wellhead housing until the pins contact the guide surfaces, the guide surfaces causing the inner wellhead housing to rotate a limited amount if necessary until each of the pins registers with one of the slots, then lowering the inner wellhead housing further until each of the pins locates in one of the slots to prevent rotation of the inner wellhead housing in the outer wellhead housing due the swinging movement of the drilling vessel.