Drilling vessel and drilling vessel mooring system and method

Claim 1

A system for mooring a drilling vessel to a seabed over a selected subsurface location, said vessel floating on the sea surface and having a hull, a longitudinal axis, a wind and water pressure center line and a work area on the vessel from which subsurface drilling and other well operations may be conducted, said work area being longitudinally spaced from said pressure center line and said system comprising: an anchor lowerable from the vessel to the seabed at said selected location; a riser pipe extending from the work area to said anchor; said anchor having a central bore through which well bore equipment connected to said riser pipe may extend, having a ballast chamber for receiving fluid to vary the buoyancy of said anchor, and having a swivel device rotatable around said central bore, said swivel device having connecting means for attachment to mooring lines; means extending from said ballast chamber to said vessel for controlling the flow of fluid into and out of said ballast chamber; the hull of said vessel having a recess for receiving said anchor, said recess being of a size sufficient to contain said anchor substantially wholly within it; and a mooring line connected at its lower end to said swivel on said anchor and at its upper end to said vessel at a point between the work area of the vessel and the wind and water pressure center line of the vessel so that when said mooring line is taut, said work area is in substantially vertical alignment with said selected subsurface location, whereby, as said vessel drifts in response to the net force of the wind and water, said vessel swings about a point on said sea surface about said selected subsurface location to keep said work area in substantially vertical alignment with said subsurface location and to maintain said longitudinal axis substantially aligned with said net force of wind and water so that said riser pipe is not subjected to excessive bending stresses and remains substantially vertical and drilling and other well operations may be conducted from said vessel on said work area.

Claim 2

A system for mooring a drilling vessel to a seabed over a selected subsurface location, said vessel floating on the sea surface and having a hull, a longitudinal axis, a wind and water pressure center line and a work area on the vessel from which subsurface drilling and other well operations may be conducted, said work area being longitudinally spaced from said pressure center line and said system comprising: an anchor lowerable from the vessel to the seabed at said selected location; a riser pipe extending from the work area to said anchor; said anchor having a central bore through which well bore equipment connected to said riser pipe may extend, having a ballast chamber for receiving fluid to vary the buoyancy of said anchor, and having a swivel device rotatable around said central bore, said swivel device having connecting means for attachment to mooring lines; means extending from said ballast chamber to said vessel for controlling the flow of fluid into and out of said ballast chamber; the hull of said vessel having a recess for receiving said anchor, said recess being of a size sufficient to contain said anchor substantially wholly within it; and a mooring line connected at its lower end to said swivel on said anchor and at its upper end to said vessel at a point between the work area of the vessel and the wind and water pressure center line of the vessel so that when said mooring line is taut, said work area is in substantially vertical alignment with said selected subsurface location, whereby, as said vessel drifts in response to the net force of the wind and water, said vessel swings about a point on said sea surface about said selected subsurface location to keep said work area in substantially vertical alignment with said subsurface location and to maintain said longitudinal axis substantially aligned with said net force of wind and water so that said riser pipe is not subjected to excessive bending stresses and remains substantially vertical and drilling and other well operations may be conducted from said vessel on said work area.

Claim 3

A system for mooring a floating drilling vessel to a seabed over a selected subsurface location, the vessel having a hull, a longitudinal axis, a wind and water pressure center line and a work area on the vessel from which subsurface drilling and other well operations may be conducted, the work area being longitudinally spaced from the pressure center line, the system comprising: an anchor lowerable from the vessel to the seabed at the selected location; a riser pipe extending downwardly from the work area to the anchor; the anchor having a central bore through which well bore equipment connected to the riser pipe may extend, having a ballast chamber for rEceiving fluid to vary the buoyancy of the anchor, and having a swivel device rotatable around the central bore, the swivel device having connecting means for attachment to mooring lines; the hull of the vessel having a recess for receiving the anchor, the recess being of a size sufficient to contain said anchor substantially wholly within it; and a mooring line connected at its lower end to the swivel on the anchor and at its upper end to the vessel at a point between the work area of the vessel and the wind and water pressure center line of the vessel so that when the mooring line is taut, the work area is in substantially vertical alignment with said selected subsurface location, whereby, as the vessel drifts in response to the net force of the wind and water, the vessel swings about a point on the sea subsurface location to keep the work area in substantially vertical alignment with the subsurface location and to maintain the longitudinal axis substantially aligned with the net force of wind and water so that the riser pipe is not subjected to excessive bending stresses and remains substantially vertical and drilling and other well operations may be conducted from the vessel on the work area.

Claim 4

A system for mooring a floating drilling vessel to a seabed over a selected subsurface location, the vessel having a hull, a longitudinal axis, a wind and water pressure center line and a work area on the vessel from which subsurface drilling and other well operations may be conducted, the work area being longitudinally spaced from the pressure center line, the system comprising: an anchor lowerable from the vessel to the seabed at the selected location; a riser pipe extending downwardly from the work area to the anchor; the anchor having a central bore through which well bore equipment connected to the riser pipe may extend, having a ballast chamber for rEceiving fluid to vary the buoyancy of the anchor, and having a swivel device rotatable around the central bore, the swivel device having connecting means for attachment to mooring lines; the hull of the vessel having a recess for receiving the anchor, the recess being of a size sufficient to contain said anchor substantially wholly within it; and a mooring line connected at its lower end to the swivel on the anchor and at its upper end to the vessel at a point between the work area of the vessel and the wind and water pressure center line of the vessel so that when the mooring line is taut, the work area is in substantially vertical alignment with said selected subsurface location, whereby, as the vessel drifts in response to the net force of the wind and water, the vessel swings about a point on the sea subsurface location to keep the work area in substantially vertical alignment with the subsurface location and to maintain the longitudinal axis substantially aligned with the net force of wind and water so that the riser pipe is not subjected to excessive bending stresses and remains substantially vertical and drilling and other well operations may be conducted from the vessel on the work area.