Patent EA-001520-B1 (EA)
Title: Installation for producing oil from an off-shore deposit and process for installing a riser
Inventor: THOMAS PIERRE-ARMAND
IPC: E21B17/01
Filed: 1999-08-10
Abstract: 1. Installation for producing oil from an off-shore deposit, of the type comprising a semi-submersible platform (10), at least one riser (24) connecting the platform (10) to the sea bed, and means (28, 30) of tensioning the said riser (24), characterized in that the tensioning means comprise, for the or each riser (24), at least one submerged float (28) connected to a point on the main run of the riser (24) for hauling it towards the surface, and a mechanism (30) for hauling the riser (24), which mechanism (30) is installed on the platform (10) and applied to the top end of the riser (24), and in that it comprises means (60) for bringing the float (28) into abutment against the platform (10) in the upwards direction. 2. Installation according to claim 1, characterized in that the or each float (28) is dimensioned to apply to the riser (24) a hauling force which exceeds the hauling force applied by the top-end hauling mechanism (30). 3. Installation according to claim 1 or 2, characterized in that the float (28) is dimensioned to apply to the riser (24) a hauling force which is between 1 and 3 times the weight of the riser (24). 4. Installation according to any one of the preceding claims, characterized in that the platform (10) comprises a submerged base (16) and a hull (12) which is out of the water and connected by legs (14), the or each float (28) being arranged at the depth of the said base (16), which base comprises means (40) for the vertical guidance of the or each float (28). 5. Installation according to claim 4, characterized in that the base (16) comprises, for each float (28), a vertical passage (22) through which the float (28) can move axially. 6. Installation according to any one of the preceding claims, characterized in that the or each float (28) has a through conduit (32) through which the associated riser (24) runs. 7. Installation according to any one of the preceding claims, characterized in that the means providing the link between the or each float (28) and the associated riser (24) comprise a ball joint (46). 8. Installation according to claims 6 and 7 taken together, characterized in that the ball joint comprises a concave annular seat (48) secured to the said float (28) in the axial conduit (32) and a flange (50) with a convex surface (56) borne by the riser (24), the flange (50) being pressed against the concave seat (48) in order to apply tension to the riser (24). 9. Installation according to claim 6, characterized in that the through conduit (32) has a diameter greater than three times the diameter of the riser (24). 10. Installation according to any one of the preceding claims, characterized in that the top-end hauling mechanism (30) comprises at least one hydropneumatic ram (70) which, at each end, has a series of block-and-tackle pulleys (72, 74) over which at least one hauling line (76) applied to the said riser (24) is engaged. 11. Process for installing a riser (24) of an installation according to claim 1, characterized in that it comprises the successive steps consisting in: a - bringing the float (28) vertically into abutment against the platform (10); b - immersing the riser (24) with its lower end held some distance from the sea bed; c - weighing the platform (10) down with ballast; d - lowering the riser (24) and connecting it to the sea bed; e - releasing the float (28) from abutment with the platform (10); and f - removing the ballast from the platform (10). 12. Process for installing a riser (24) of an installation according to claim 1, characterized in that it comprises the steps consisting in: a - bringing the float (28) into abutment against the platform (10) ; b - immersing the riser (24) with its lower end held some distance from the sea bed F;' c - sinking the float (28) by placing ballast (92) on the float (28) ; d - lowering the riser (24) and connecting it to the sea bed (F) ; e - releasing the float (28) from abutment with the platform (10); and f - removing the ballast (92) weighing down on the float (28).