Patent EA-000594-B1 (EA)
Title: Underwater installation a method for building same
IPC: E21B43/01
Filed: 1997-03-07
Abstract: 1. An underwater installation for use in offshore drilling of and production from, respectively, oil and/or gas wells in deep and moderate deep water, comprising an intermediate station in the form of a buoyancy based hollow body (16) tension strut/leg anchored at the seabed (10) and situated at a depth substantially closer to the surface of the sea than the seabed (10), at least one hydrocabon conveying pipeline extending between the hollow buoyancy body (16) and seabed depth for the transfer of hydrocarbons from the reservoir to the hollow buoyancy body (16), characterized in that at a casing extension pipe string (18a - 18h) from one or more wells constitutes the tension strut/leg anchoring of the hollow buoyancy body (16). 2. A method for the building of an underwater installation comprising a submerged, buoyancy based, tension strut/leg anchored intermediate station in the form of a hollow buoyancy body (16) which is assigned a hydrocarbon conveying, downwardly extending pipeline for the transfer of hydrocarbons from the reservoir to the hollow buoyancy body (16), which is equipped with a production hose (20) or a similar hydrocarbon conveying hose/pipeline extending upwardly in a position of use, and wherein, in a first phase, from a seabed frame (12), a template or similar frame, one or more wells are predrilled and thereafter, temporarily, plugged, and wherein said hollow buoyancy body (16) is submerged and positioned, possibly equipped with further, readily temporary buoyancy units or is ballasted, respectively, the submersion and positioning in relation to the well or a seabed frame comprising several wells, respectively, being effected by means of guys (14) attached to the seabed frame (12) or another anchor on the seabed (10), characterized in a) that care is taken that last set casing's upper end portion at the seabed (10) carries fasteners in the form of internal/external threads or the like, in order to enable the interconnection thereof with a corresponding upward extension pipe (l8a - 18h); b) that a pipeline connection is established in the form of one casing extension pipe string for each underlying well, between the hollow buoyancy body (16) and said last set casing's fastener provided upper end at the seabed (10), said casing extension pipe string (l8a - 18h) being equipped with a connecting device for the interconnecting cooperation with the fasteners of last set casing, e.g. in the form of mutually meshing internal and external threads; c) whereafter the drilling is concluded, and further casings are set in successively descreasing dimensions from the floating rig while each well is assigned a blowout preventer on the hollow buoyancy body (16); d) whereafter the uppermost end portion of the casing extension pipe string(s) (l8a - 18h) is mounted by the attachment of the upper end of the casing extension string (s) (l8a - 18h) within the hollow buoyancy body (16), whereafter the casing extension pipe string(s) (l8a - 18h) act(s) as tension legs/struts for the hollow buoyancy body (16). 3. A method as set forth in Claim 2, characterized in that said guys (14) are tensioned during the attachment of the casing extension pipe string(s) (l8a - l8h) in the hollow buoyancy body (16), whereafter the guys (14) are slackened or, possibly, removed, in order to subject the casing extension pipe string(s) (l8a - l8h) to tensile stress.