# US 7,073,593 B2 · Method of drilling and operating a subsea well > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,073,593 B2 - Document ID: US7073593B2 - Status: Granted - Kind: B2 - Application number: 10/466,131 - Filed: 2002-01-09 - Published: 2004-04-22 - Granted: 2006-07-11 - Earliest claimed: 2001-01-10 - Assignees: 2H Offshore Engineering Limited - Inventors: Stephen A. Hatton; Frank Lim; Hugh Howells - Web page: https://patentgrep.com/patent/US7073593B2 ## CPC - E21B 33/035: specially adapted for underwater installations (E21B33/043, E21B33/064, E21B33/076 take precedence) - E21B 7/128: from floating support with independent underwater anchored guide base - E21B 17/01: Risers - E21B 17/012: {with buoyancy elements (E21B17/015 takes precedence)} - E21B 43/01: specially adapted for obtaining from underwater installations - E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS ## Abstract A method of preparing and operating a subsea well (23), comprising the steps of: locating a drill-through subsea tree (24) on a subsea wellhead; sealingly connecting a high pressure drilling riser (22) between the tree and a drilling platform at the sea surface; mounting a blow out preventer (16) at the top of the riser (22); drilling the well through the drilling riser and the subsea tree; and establishing a production connection between the tree (24) and a production collection facility at the sea surface through a production riser (52) which is separate from the drilling riser (22). ## Claims ### Claim 1 A method of preparing and operating a subsea well, the method comprising the steps of: locating a plurality of drill-through subsea trees on a respective plurality of subsea wellheads, each of the plurality of drill-through subsea trees being connected by a manifold; sealingly connecting a high pressure drilling riser between one of the plurality of trees and a drilling platform at the sea surface; mounting a blow out preventer at the top of the riser; drilling the well through the drilling riser and the subsea tree; and establishing a production connection between the tree and the manifold through a production riser which is separated from the drilling riser; wherein the high pressure drilling riser comprises two concentric riser pipes, the inner of the pipes being a high pressure riser and the outer of the pipes being a low pressure riser; and wherein the low pressure riser is first connected between the tree and the drilling platform with a low pressure blow out preventer mounted at the top of the riser, the well is drilled to a first depth, the low pressure blow out preventer is removed, the high pressure riser is run into the low pressure riser, a high pressure blow out preventer is mounted at the top of the high pressure riser, and the well is drilled to a second, greater depth. ### Claim 2 A method of preparing and operating a subsea well, the method comprising the steps of: locating a plurality of drill-through subsea trees on a respective plurality of subsea wellheads, each of the plurality of drill-through subsea trees being connected by a manifold; sealingly connecting a high pressure drilling riser between one of the plurality of trees and a drilling platform at the sea surface; mounting a blow out preventer at the top of the riser; drilling the well through the drilling riser and the subsea tree; and establishing a production connection between the tree and the manifold through a production riser which is separated from the drilling riser; wherein the drilling platform and a production collection facility are provided on separate platforms at the sea surface. ### Claim 3 (depends on 2) A method as claimed in claim 2, wherein the one or more production risers are initially connected to the drilling platform for early production and are subsequently disconnected and reconnected to the production collection platform. ### Claim 4 A method of preparing and operating a subsea well, the method comprising the steps of: locating a plurality of drill-through subsea trees on a respective plurality of subsea wellheads, each of the plurality of drill-through subsea trees being connected by a manifold; sealingly connecting a high pressure drilling riser between one of the plurality of trees and a drilling platform at the sea surface; mounting a blow out preventer at the top of the riser; drilling the well through the drilling riser and the subsea tree; establishing a production connection between the tree and the manifold through a production riser which is separated from the drilling riser; and providing one or more manifolds to connect the plurality of drill-through subsea trees; and wherein a single production riser is associated with each manifold; wherein the or each manifolds are installed through a moonpool of a moored, floating vessel and are initially run in a vertical orientation in order to pass the moonpool and are subsequently rotated horizontally after landing on the seabed or in midwater. ### Claim 5 A floating drilling and production system for deep water comprising a floating vessel, a plurality of drill-through subsea trees located below the floating vessel, the plurality of trees being connected to a subsea manifold, a high pressure drilling workover riser extending between one of the plurality of trees and the vessel, a blow-out preventer located on the vessel at the top of the riser, and a production riser extending from the manifold to near the water surface, the production riser being separated from the drilling riser; wherein the drilling riser comprises means by which it can be selectively coupled to one of the trees and can be moved from one tree to another. ### Claim 6 A floating drilling and production system for deep water comprising a floating vessel, a plurality of drill-through subsea trees located below the floating vessel, the plurality of trees being connected to a subsea manifold, a high pressure drilling workover riser extending between one of the plurality of trees and the vessel, a blow-out preventer located on the vessel at the top of the riser, and a production riser extending from the manifold to near the water surface, the production riser being separated from the drilling riser; wherein there are a plurality of manifolds, and each manifold has a production riser. ### Claim 7 A floating drilling and production system for deep water comprising a floating vessel, a plurality of drill-through subsea trees located below the floating vessel, the plurality of trees being connected to a subsea manifold, a high pressure drilling workover riser extending between one of the plurality of trees and the vessel, a blow-out preventer located on the vessel at the top of the riser, and a production riser extending from the manifold to near the water surface, the production riser being separated from the drilling riser; wherein the drilling riser comprises a dual string concentric pipe arrangement with an outer riser extending from the floating vessel connected and sealed to a drill through subsea tree connected onto a subsea well, for drilling an initial low pressure interval, and a retrievable inner riser extending from the surface to the subsea tree inside the outer riser and connected and sealed on the bore of the subsea tree or wellhead. ### Claim 8 (depends on 7) A floating drilling and production system as claimed in claim 7, wherein the inner string is a casing. ### Claim 9 A floating drilling and production system for deep water comprising a floating vessel, a plurality of drill-through subsea trees located below the floating vessel, the plurality of trees being connected to a subsea manifold, a high pressure drilling workover riser extending between one of the plurality of trees and the vessel, a blow-out preventer located on the vessel at the top of the riser, and a production riser extending from the manifold to near the water surface, the production riser being separated from the drilling riser; wherein a control umbilical is run on the outside diameter of the drilling riser to provide control of the subsea tree. ### Claim 10 A floating drilling and production system for deep water comprising a floating vessel, a plurality of drill-through subsea trees located below the floating vessel, the plurality of trees being connected to a subsea manifold, a high pressure drilling workover riser extending between one of the plurality of trees and the vessel, a blow-out preventer located on the vessel at the top of the riser, and a production riser extending from the manifold to near the water surface, the production riser being separated from the drilling riser; wherein the manifold is connected to an adjacent offset production riser via spools that provide production, annulus access and control functions. ### Claim 11 (depends on 10) A floating drilling and production system as claimed in claim 10, wherein the or each offset riser consists of near vertical steel pipes connected by threaded couplings. ### Claim 12 A floating drilling and production system for deep water comprising a floating vessel, a plurality of drill-through subsea trees located below the floating vessel, the plurality of trees being connected to a subsea manifold, a high pressure drilling workover riser extending between one of the plurality of trees and the vessel, a blow-out preventer located on the vessel at the top of the riser, and a production riser extending from the manifold to near the water surface, the production riser being separated from the drilling riser; wherein the system further comprises a production vessel, the production riser being connected to the production vessel. ### Claim 13 A floating drilling and production system for deep water comprising a floating vessel, a plurality of drill-through subsea trees located below the floating vessel, the plurality of trees being connected to a subsea manifold, a high pressure drilling workover riser extending between one of the plurality of trees and the vessel, a blow-out preventer located on the vessel at the top of the riser, and a production riser extending from the manifold to near the water surface, the production riser being separated from the drilling riser; wherein the production riser is vertically supported by near surface aircans which maintain tension in the riser sufficient to withstand environmental and operational loads. ### Claim 14 (depends on 13) A floating drilling and production system as claimed in claim 13, wherein a flexible pipe jumper is used at the top of the production riser to connect between the riser and the production vessel. ### Claim 15 A floating drilling and production system for deep water comprising a floating vessel, a plurality of drill-through subsea trees located below the floating vessel, the plurality of trees being connected to a subsea manifold, a high pressure drilling workover riser extending between one of the plurality of trees and the vessel, a blow-out preventer located on the vessel at the top of the riser, and a production riser extending from the manifold to near the water surface, the production riser being separated from the drilling riser; wherein the or each production riser is concentric dual string for production and the outer annulus may be used for insulation of gas injection/lift. ### Claim 16 A floating drilling and production system for deep water comprising a floating vessel, a plurality of drill-through subsea trees located below the floating vessel, the plurality of trees being connected to a subsea manifold, a high pressure drilling workover riser extending between one of the plurality of trees and the vessel, a blow-out preventer located on the vessel at the top of the riser, and a production riser extending from the manifold to near the water surface, the production riser being separated from the drilling riser; wherein the or each manifold has near neutrally buoyant rigid flowline spools. ### Claim 17 A floating drilling and production system for deep water comprising a floating vessel, a plurality of drill-through subsea trees located below the floating vessel, the plurality of trees being connected to a subsea manifold, a high pressure drilling workover riser extending between one of the plurality of trees and the vessel, a blow-out preventer located on the vessel at the top of the riser, and a production riser extending from the manifold to near the water surface, the production riser being separated from the drilling riser; wherein a radial orientation key is provided in the bore of the high pressure drilling riser to locate and align a tubing hanger landed in the bore of a drill-through spool tree. ### Claim 18 A floating drilling and production system for deep water comprising a floating vessel, a plurality of drill-through subsea trees located below the floating vessel, the plurality of trees being connected to a subsea manifold, a high pressure drilling workover riser extending between one of the plurality of trees and the vessel, a blow-out preventer located on the vessel at the top of the riser, and a production riser extending from the manifold to near the water surface, the production riser being separated from the drilling riser wherein the drilling riser is a single string drilling riser, and a shear ram module is provided at the base of the riser to isolate the well in the event of a riser failure and wherein the shear ram module connects to the subsea tree mandrel via a remote connector and has at its top end a mandrel onto which the drilling riser is connected.