WO2011028854A1

WO2011028854A1 - Tender assisted production structures

Info

Publication number: WO2011028854A1
Application number: PCT/US2010/047601
Authority: WO
Inventors: Stephen Craig Bultema; Keith Marvin Craik; You Sun Li; Joao Paulo Juliao Mastsuura; Arno Laurentius Michael Van Den Haak
Original assignee: Shell Oil Company; Shell Internationale Research Maatschappij B.V.
Priority date: 2009-09-04
Filing date: 2010-09-02
Publication date: 2011-03-10
Also published as: GB201201834D0; AU2010289487A1; NO20120146A1; GB2484052A

Abstract

A floating offshore system in a body of water, comprising a floating production structure; at least one anchor connected to a bottom of the body of water; a line connected to the anchor and the floating production structure; a floating drilling tender vessel adjacent to the floating structure, the drilling tender vessel comprising a dynamic positioning system.

Description

TENDER ASSISTED PRODUCTION STRUCTURES

Background of Invention

Field of the Invention

[0001] The present invention is directed to floating offshore production

structures.

[0002] Background Art

[0003] U.S. Patent Number 4,156,577 discloses a self-propelled drilling tender having mounted therewith a drilling rig and a jack-up platform adapted to be mounted on the drilling tender or ship for transportation from one drilling site to another site. Thereafter drilling operations occur with the drilling on the ship thus enabling the ship to operate as a drilling ship or the platform legs can be lowered to jack the platform off the ship to thereby enable the platform to operate independently as a drilling platform. Further, if desired, the rig can be disassembled or lifted from the drilling platform and moved to land operations adjacent or in the vicinity of the drilling platform and ship to thereby enable land drilling operations to occur. U.S. Patent Number 4,156,577 is herein incorporated by reference in its entirety.

[0004] U.S. Patent Number 5,423,632 discloses an improved method for conducting offshore well operations in which a compliant platform is installed adjacent a selected well site and an auxiliary vessel is temporarily docked to the compliant platform to provide for support for the well operations which will be produced through the compliant platform. In the practice of the improved method, the compliant platform is isolated from vertical loads upon the auxiliary vessel docked thereto during the performance of well operations conducted for the compliant platform by the offshore auxiliary vessel. Another aspect disclosed is an improved system for restraining an offshore drilling vessel temporarily to a compliant platform which uses a slide-connection for isolating the compliant platform from vertical loads upon the offshore drilling vessel during the well operations. U.S. Patent Number 5,423,632 is herein incorporated by reference in its entirety.

[0005] U.S. Patent Number 5,558,037 discloses a drilling tender having a pair of laterally spaced buoyant hulls with ballast chambers to permit the hulls to be moved between a submerged condition and a surface floating condition. Each hull supports a row of columns. The columns support a working platform including a main deck and a pipe rack deck above the main deck. A bow deck above a forward portion of the pipe rack deck has mounted on a corner portion thereof a main heavy duty crane. The support structure for the crane extends downwardly through the decks and down into one of the columns. Between the main and pipe rack decks, the support structure is formed by a plurality of bulkheads. These bulkheads have portions extending down into the column to transmit forces created by operation of the crane to the column. A personnel bridge is pivotably mounted on the bow deck to allow its free end to be pivoted onto a fixed- position work platform being serviced by the tender. An auxiliary crane is mounted on the pipe rack deck rearwardly of and laterally opposite the main crane. U.S. Patent Number 5,558,037 is herein incorporated by reference in its entirety.

[0006] U.S. Patent Number 6,092,483 discloses a method for reducing VIV for a spar platform having a deck, a cylindrical hull having a buoyant tank assembly, a counterweight and an counterweight spacing structure. The overall aspect ratio of the hull is reduced by providing one or more abrupt changes in hull diameter below the waterline. U.S. Patent Number 6,092,483 is herein incorporated by reference in its entirety.

[0007] U.S. Patent Number 6,463,870 discloses a mooring system for a semisubmersible tender which comprises a deck, a shape that results in a combined environmental load of less than 1000 kips in a 100-year extreme weather condition, a plurality of supports connected to the deck, a plurality of pontoons connecting to the supports, at least two hawsers for connecting the tender to a production platform, each having adequate elasticity to accommodate the wave frequency between the production platform and the tender, and adequate stiffness to synchronize the average and low frequency movement between the production platform and the tender under an environmental load produced during a storm having a designation of up to a 10-year storm in the tendering position, connectors securing each hawser, a hawser guidance system; and an at least 8-point mooring system with each mooring lines consisting of: a first length of steel wire rope; a length of polymer rope secured to the first length of steel wire rope; a second length of steel wire rope secured to the polymer rope; and creating global equilibrium between the production platform's mooring system and the at least 8 point mooring system of the tender. U.S. Patent Number 6,463,870 is herein incorporated by reference in its entirety.

U.S. Patent Number 6,601 ,649 discloses a semisubmersible multipurpose unit (MPU) having a deck, a multipurpose tower secured to the deck, supports, pontoons connected to the supports with each pontoon adapted for ballast transfer, at least two hawsers connected to the MPU for connecting the MPU to an object at sea having a mooring system, a hawser guidance system to direct each hawser to the object at sea, a crane secured to the deck of a semisubmersible MPU, and at least an 6- point mooring system, wherein the combination of the semisubmersible MPU, hawsers and 6-point mooring system create a global equilibrium between the mooring system of an object at sea and the at least 6-point mooring system and the hawsers have both an elasticity sufficient to accommodate the wave frequency between the object at sea and the MPU and a stiffness adequate to synchronize the average and low frequency movements during a 10-year storm. U.S. Patent Number 6,601 ,649 is herein incorporated by reference in its entirety.

U.S. Patent Number 7,383,784 discloses a system for lashing a tender assist drilling unit (TADU) to a floating production platform including a plurality of winches on the forward end of the TADU, a plurality of sheaves on the upper portion of the hull of the platform, a plurality of connection devices on the lower portion of the hull of the platform, and a set of lashing lines, each of which extends from one of the winches, through a corresponding one of the sheaves, and vertically down alongside the platform hull to a corresponding one of the connection devices to which it is attached. The winches are operable to reel in and to pay out the lashing lines to control the separation distance so as to maintain an optimal operational separation distance during normal environmental conditions, while allowing the separation distance to be increased in severe conditions. U.S. Patent Number 7,383,784 herein incorporated by reference in its entirety.

The prior art describes large floating drilling and production systems such as spars, tension leg platforms, and FPSO's. Usually such systems have weights in excess of 20-30 thousand metric tons. These systems have been used to drill and produce large reservoirs in the 500 million to 1 billion or more BOE (barrels of oil equivalent) recoverable volumes. With such large reservoirs the large expenditures to manufacture, install, and operate these systems has been justified. Unfortunately, more than 90% of the newly discovered deepwater discoveries have less than 250 million BOE recoverable volumes. As such, smaller and more economical drilling and production systems are needed to drill and produce these smaller deepwater fields.

The prior art also describes floating production systems that are moored to the sea floor that are connected by one or more hawsers to a drilling tender vessel such as a semi-submersible that is also moored to the sea floor. These floating production systems connected to a drilling tender vessel also have a large cost and weight. In addition, in the event of a hurricane or other large storm, there is the danger to crew and equipment of the two floating structures crashing into or otherwise interfering with each other.

There is a need in the art for one or more of the following:

An improved system and method of operating two floating structures in a body of water; [0014] An improved system and method of operating two floating structures that provides for drilling and producing deepwater oil and gas reservoirs;

[0015] An improved system and method of providing a connection of a drilling tender and a spar; and [0016] An improved system and method to provide for engagement of two floating structures.

SUMMARY OF INVENTION

[0017] In one aspect of the invention, there is disclosed a floating offshore system in a body of water, comprising a floating production structure; at least one anchor connected to a bottom of the body of water; a line connected to the anchor and the floating production structure; a floating drilling tender vessel adjacent to the floating structure, the drilling tender vessel comprising a dynamic positioning system.

[0018] Advantages of the invention may include one or more of the following:

[0019] An improved system and method of operating two floating structures in a body of water;

[0020] An improved system and method of operating two floating structures that provides for drilling and producing deepwater oil and gas reservoirs; [0021] An improved system and method of providing a connection of a drilling tender and a spar; and

[0022] An improved system and method to provide for engagement of two floating structures.

BRIEF DESCRIPTION OF DRAWINGS [0023] Figure 1 shows a prior art drilling and production structure.

[0024] Figures 2A, and 2B show a floating vessel located adjacent a floating production structure. [0025] Figure 3 shows a floating vessel located adjacent to multiple floating production structures in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

[0026] In one aspect, embodiments of the present disclosure generally relate to a platform for offshore drilling operations, for example a spar platform. In particular, embodiments of the present disclosure relate to a spar platform including a tender assisted drilling platform. Typically, a selection of platforms are available for offshore drilling operations {e.g., fixed platform, tension leg platforms, etc.). Spar platforms are one type of platform that may be used, particularly, in ultra-deepwater environments. The spar platform includes a large cylinder that floats in the water and is tethered to the seafloor by a series of lines comprizing chains, cables, synthetic ropes or combinations thereof. Because the spar platform is a floating platform that is not attached to the seafloor, it is able to move in the water when affected by winds, waves and currents in the sea or even to absorb a hurricane. The drilling spar of the present disclosure may be intended to be deployed across a range of water depths, extending at least from 1 ,000 to 10,000 feet (300 to 3000 m).

[0027] Embodiments of the present disclosure include a drilling tender vessel that is used with a production spar. A drilling tender vessel is typically a support vessel that serves in support of a drilling rig. The drilling tender vessel acts as storage for supplies and is stationed alongside the drilling rig from which the rig will work off of to reduce the loads on the actual rig. Drilling tender vessels can be jack-up style (like a lift boat), semisubmersible, barge or ship-shaped . By using a drilling tender vessel, a majority of drilling equipment, consumables and services may be carried onboard the drilling tender vessel during drilling operations, which allows the spar to be optimized according to its "permanent" functional requirements {e.g., operating as a wellhead platform, with or without production equipment, quarters etc.). Figure 1 :

[0028] Referring to Figure 1 , prior art system 100 is shown. System 100 includes a floating structure 102 connected to the sea floor by multiple mooring or anchor lines 1 12. Floating structure 102 includes drilling rig 1 10 to drill wells in the sea floor 108. Floating structure 102 is connected to a wellhead 106 by riser 104. After well 120 has been drilled and completed, drilling rig 1 10 may be used to drill other wells. Produced fluids from well 120 may be transported to floating structure 102 for production processes as are known in the art prior to being shipped, pipelined, or otherwise transported to shore.

[0029] In general, floating structure 102 is permanently moored on location and is not moved until the field has been exhausted. Floating structure 102 has a weight of at least 20,000 metric tons.

Figures 2a & 2b:

[0030] Referring to Figure 2A, a drilling and production system 200 is shown in accordance with embodiments of the present disclosure. The tender assisted drilling and production system 200 includes production structure

202, such as a TLP, FPSO, or spar. System 200 also includes a drilling tender vessel 203. The drilling tender vessel 203 floats in the water and may be characterized as a semisubmersible, barge or ship-shaped unit or rig. The drilling tender vessel 203 includes a dynamic positioning (DP) system with thrusters or other propulsion mechanisms 212 to keep vessel 203 on station at a desired location. U.S. Patents 6,840,322, 6,799,528, 6,378,450, 6,257,165, and 6,247,421 disclose suitable dynamic positioning (DP) systems which can be used with drilling tender vessel

203. U.S. Patents 6,840,322, 6,799,528, 6,378,450, 6,257,165, and 6,247,421 are herein incorporated by reference in their entirety.

[0031] In some embodiments, the drilling tender vessel 203 may be kept on station at a location from about 10 meters to about 25 meters from production structure 202, for example about 15 meters. [0032] In some embodiments, the drilling tender vessel 203 may have a length from about 50 to about 200 meters, for example from about 100 to about 150 meters.

[0033] In some embodiments, the drilling tender vessel 203 may have a weight from about 5,000 to about 20,000 metric tons, for example from about 10,000 to about 15,000 metric tons.

[0034] In some embodiments, the drilling tender vessel 203 may have cruising speed of at least 8 knots, for example from about 10 to about 20 knots. [0035] In some embodiments, the production structure 202 may have a weight from about 3,000 to about 15,000 metric tons, for example from about 5,000 to about 10,000 metric tons.

[0036] Further, drilling tender vessel 203 may include drilling rig 210, accommodation 214 for all required personnel, a pipe storage and handling system 216, mud storage 218, and one or more cranes 222.

Other storage 220 may also be provided.

[0037] Production structure 202 may be connected to the sea floor 208 by multiple mooring or anchor lines (not shown). Floating structure 202 is connected to a subsea structure 206 by riser 204. [0038] Referring to Figure 2A, drilling tender vessel 203 is moved adjacent to production structure 202.

[0039] Referring to Figure 2B,once drilling tender vessel 203 is on station, drilling rig 210 is moved from drilling tender vessel 203 to production structure 202 with crane 222. Likewise, pipe 216 can be moved to production structure 202 or back to drilling tender vessel 203 with crane

222.

[0040] Rig 210 may be used to drill multiple wells from production structure 202. Mud tank and pump system 218 may be connected to production structure 202 with hose or line 224 to assist with drilling operations. Mud return line 226 is used to return mud from production structure 202 to mud tank and pump system 218. Other drilling operations and functions may be divided between production structure 202 and drilling tender vessel 203 as desired.

[0041] In some embodiments, pipe handling system 216 allows drillpipe to be transferred from the production structure 202 to the drilling tender vessel 203, or vice versa, as needed. Similarly, the power, cement, and mud lines 224, 226 provide electrical communication, cement for setting casing, and drilling mud, respectively to the production structure 202 or drilling tender vessel 203.

[0042] Additionally, the production structure 202 includes gang plank 228 that allows personnel to walk between drilling tender vessel 203 and production structure 202.

Figure 3:

[0043] Referring to Figure 3, system 300 is illustrated including production structure 302 and drilling tender vessel 303 which may be substantially the same as production structure 202 and drilling tender vessel 203 described above with reference to Figure 2b.

[0044] System 300 also includes production structures 332 and 342.

Production structure 332 is connected to subsea equipment 336 such as a wellhead, separator, manifold on the sea floor 308 by riser 334. Production structure 342 is connected to subsea equipment 346 such as a wellhead, separator, manifold on the sea floor 308 by riser 344.

[0045] Production structure 332 is a distance d2 352 from production structure 302. Production structure 342 is a distance d1 350 from production structure 302. Distance d1 350 and d2 352 may be from about 2 to about 200 kilometers, for example from about 3 to about 100, from about 4 to about 50, or from about 5 to about 10 kilometers. Operation

[0046] In operation, production structure 302 is installed in a body of water.

Drilling tender vessel 303 is located alongside production structure 302, and drilling rig 310 and possibly other equipment is installed from drilling tender vessel 303 to production structure 302. The two vessels are used together to drill multiple wells which are connected back to production structure 302. At the completion of the drilling campaign, drilling rig 310 and possibly other equipment is removed from production structure 302 and placed back on drilling tender vessel 303. Produced fluids from the wells are then piped to production structure 302.

[0047] Sometime prior to completion of the production structure 302 drilling campaign, production structure 332 is installed in a body of water. Drilling tender vessel 303 is located alongside production structure 332, and drilling rig 310 and possibly other equipment is installed from drilling tender vessel 303 to production structure 332. The two vessels are used together to drill multiple wells which are connected back to production structure 332. At the completion of the drilling campaign, drilling rig 310 and possibly other equipment is removed from production structure 332 and placed back on drilling tender vessel 303. Produced fluids from the wells are then piped to production structure 332.

[0048] Sometime prior to completion of the production structure 332 drilling campaign, production structure 342 is installed in a body of water. Drilling tender vessel 303 is located alongside production structure 342, and drilling rig 310 and possibly other equipment is installed from drilling tender vessel 303 to production structure 342. The two vessels are used together to drill multiple wells which are connected back to production structure 342. At the completion of the drilling campaign, drilling rig 310 and possibly other equipment is removed from production structure 342 and placed back on drilling tender vessel 303. Produced fluids from the wells are then piped to production structure 342.

[0049] At the completion of the production structure 342 drilling campaign, drilling tender vessel 303 may be used to support workovers of production structures 302, 332, and/or 342, and/or drilling tender vessel 303 may be used to support drilling campaigns for other production structures (not shown).

[0050] Advantageously, embodiments of the present disclosure provide a drilling tender vessel that carries the majority of drilling equipment, consumables and services needed during drilling operations, allowing the production structure to be optimized according to more permanent functional requirements, such as production. This reduces development costs in comparison to a production structure designed to provide an integral drilling capability. Additionally, embodiments disclosed herein may reduce costs of newly built drilling tender vessels while also allowing existing shallow water drilling tender units to be economically modified to operate in deep water (e.g., by eliminating the need to upgrade the mooring system of the drilling tender). Finally, embodiments disclosed herein may provide a drilling tender vessel capable of being redeployed multiple times and being used across multiple well locations, which reduces day rates and lowers overall well costs.

Illustrative Embodiments:

[0051] In one embodiment, there is disclosed a floating offshore system in a body of water, comprising a floating production structure; at least one anchor connected to a bottom of the body of water; a line connected to the anchor and the floating production structure; a floating drilling tender vessel adjacent to the floating structure, the drilling tender vessel comprising a dynamic positioning system. In some embodiments, the floating production structure comprises a cylindrical hull. In some embodiments, the floating production structure comprises a spar. In some embodiments, the floating drilling tender vessel comprises a drilling derrick movable to the floating production structure. In some embodiments, the floating production structure comprises a weight less than about 20,000 metric tons. In some embodiments, the floating production structure comprises a drill floor. In some embodiments, the floating production structure comprises a moonpool. In some embodiments, the floating production structure comprises a plurality of drillstrings extending from the floating structure to the bottom of the body of water. In some embodiments, the system comprises a plurality of floating production structures. In some embodiments, the system comprises at least two floating production structures within a distance of 10 kilometers of each other.

[0052] In one embodiment, there is disclosed a method of exploiting an offshore oil and gas reservoir, comprising installing a first floating production structure in a body of water; locating a drilling tender vessel adjacent the first floating production structure; moving a drilling rig from the drilling tender vessel to the first floating production structure; drilling a plurality of wells from the first floating production structure with the drilling rig; moving the drilling rig back to the drilling tender vessel; installing a second floating production structure in a body of water; locating a drilling tender vessel adjacent the second floating production structure; moving a drilling rig from the drilling tender vessel to the second floating production structure; and drilling a plurality of wells from the second floating production structure with the drilling rig. In some embodiments, the method comprises keeping the drilling tender vessel on station adjacent the first floating production structure with a dynamic positioning system.

[0053] In one embodiment, there is disclosed a method of exploiting an offshore oil and gas reservoir, comprising installing a first floating production structure in a body of water; locating a drilling tender vessel adjacent the first floating production structure; moving a drilling rig from the drilling tender vessel to the first floating production structure; drilling a plurality of wells from the first floating production structure with the drilling rig; sensing a hurricane or other severe storm near the first floating production structure; and moving the drilling tender vessel away from the first floating production structure during the storm.

[0054] While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims

C L A I M S

1 . A floating offshore system in a body of water, comprising:

a floating production structure;

at least one anchor connected to a bottom of the body of water;

a line connected to the anchor and the floating production structure;

a floating drilling tender vessel adjacent to the floating structure, the drilling tender vessel comprising a dynamic positioning system.

2. The floating offshore system of claim 1 , wherein the floating production structure comprises a cylindrical hull.

3. The floating offshore system of one or more of claims 1 -2, wherein the floating production structure comprises a spar.

4. The floating offshore system of one or more of claims 1 -3, wherein the floating drilling tender vessel comprises a drilling derrick movable to the floating production structure.

5. The floating offshore system of one or more of claims 1 -4, wherein the floating production structure comprises a weight less than about 20,000 metric tons.

6. The floating offshore system of one or more of claims 1 -5, wherein the floating production structure comprises a drill floor.

7. The floating offshore system of one or more of claims 1 -6, wherein the floating production structure comprises a moonpool.

8. The floating offshore system of one or more of claims 1 -7, wherein the floating production structure comprises a plurality of drillstrings extending from the floating structure to the bottom of the body of water.

9. The floating offshore system of one or more of claims 1 -8, further comprising a plurality of floating production structures.

10. The floating offshore system of one or more of claims 1 -8, further comprising at least two floating production structures within a distance of 10 kilometers of each other.

1 1 . A method of exploiting an offshore oil and gas reservoir, comprising:

installing a first floating production structure in a body of water;

locating a drilling tender vessel adjacent the first floating production structure; moving a drilling rig from the drilling tender vessel to the first floating production structure;

drilling a plurality of wells from the first floating production structure with the drilling rig;

moving the drilling rig back to the drilling tender vessel;

installing a second floating production structure in a body of water;

locating a drilling tender vessel adjacent the second floating production structure; moving a drilling rig from the drilling tender vessel to the second floating production structure; and

drilling a plurality of wells from the second floating production structure with the drilling rig.

12. The method of claim 1 1 , further comprising keeping the drilling tender vessel on station adjacent the first floating production structure with a dynamic positioning system.

13. A method of exploiting an offshore oil and gas reservoir, comprising:

installing a first floating production structure in a body of water;

sensing a hurricane or other severe storm near the first floating production structure; and

moving the drilling tender vessel away from the first floating production structure during the storm.