WO2010120701A2

WO2010120701A2 - Ocean floor deep-sea submerged deck

Info

Publication number: WO2010120701A2
Application number: PCT/US2010/030782
Authority: WO
Inventors: James H. Shnell
Original assignee: Shnell James H
Priority date: 2009-04-14
Filing date: 2010-04-12
Publication date: 2010-10-21
Also published as: WO2010120701A3; US20100258320A1

Abstract

A system (20) for drilling a deep-sea borehole (20) in a seabed (30) is provided. The system includes a drill string (40) having a plurality of strands adapted to be reversibly connected together to assemble the drill string and reversibly disconnected from one another to disassemble the drill string. The system further includes a submerged drilling deck (50) anchored on the seabed, the deck adapted to reversibly connect the strands (40a, 40b) together and to reversibly disconnect the strands from one another. Methods of disassembling and assembling the drill string are also rovided.

Description

OCEAN FLOOR DEEP-SEA SUBMERGED DECK

CLAIM OF PRIORITY

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 61/169,203, filed April 14, 2009, which is incorporated in its entirety by reference herein.

BACKGROUND Field of the Invention

[0002] The present invention relates generally to a new method for disassembling and reassembling drill strings for drilling in the seabed of the deep ocean. Description of the Related Art

[0003] The current state of the art in deep sea well drilling utilizes long drill strings made up of segments of pipe that are 30 to 40 meters long. To replace a drill bit, to put well casing into the borehole, and for other purposes, the deck on the drilling ship or platform on the ocean surface (the "surface vessel") must pull up the string by disassembling it, make the necessary change, and then put the drill string back into the well by reassembling it. With a long string, as is the case in deep sea drilling, this takes time, which increases cost. Some deep-sea wells cost as much as $100 million to drill.

[0004] In current practice, the surface vessel is outfitted with a derrick. The derrick lifts 30 to 40 meters of the upper end of the drill string out of the water, and the part above the surface vessel's deck is then disconnected from the lower part of the drill string and set aside. In current practice, human "roughnecks" are assisted in this procedure by partially mechanized and partially automated machines commonly referred to as "iron roughnecks." This process is repeated, section-by-section, until the whole drill string is removed from the water. The drill string can only be raised 30 to 40 meters before the raising must be halted, and wait for that section of drill string to be disconnected, a process that takes time. When the drill string is thousands of meters long, there can be a hundred or more of such stops and pauses. When the drill string is inserted back into the well, the process is reversed, and there can be a hundred or more such stops and pauses while pieces of the drill string, each 30 to 40 meters long, are reconnected. Each raising and lowering of the drill string can take a day or longer and, since leasing and operating the drilling rig and hiring the drilling crew are expensive, the delays create significant costs. Also, repeated disassembling and reassembling the segments causes additional wear and tear on the drill string. In addition, lifting all the sections of the drill string out of the water requires a significant amount of energy, and handling each of the sections presents a certain amount of hazard to the crew.

SUMMARY

[0005] In certain embodiments, a system for drilling a deep-sea borehole in a seabed is provided. The system comprises a drill string comprising a plurality of strands adapted to be reversibly connected together to assemble the drill string and reversibly disconnected from one another to disassemble the drill string. The system further comprises a submerged drilling deck anchored on the seabed, the deck adapted to reversibly connect the strands together and to reversibly disconnect the strands from one another.

[0006] In certain embodiments, a method of disassembling a drill string is provided. The drill string comprises a plurality of strands and extends into a deep-sea borehole in a seabed. The method comprises providing a submerged drilling deck anchored on the seabed. The method further comprises positioning the drill string such that a first strand of the plurality of strands extends above the deck and a second strand of the plurality of strands extends below the deck into the borehole. The first strand comprises a first end portion and a second end portion and the second strand comprises a first end portion and a second end portion. The first end portion of the first strand is connected to the second end portion of the second strand. The method further comprises using the deck to reversibly disconnect the first end portion of the first strand from the second end portion of the second strand.

[0007] In certain embodiments, a method of assembling a drill string for drilling a deep-sea borehole in a seabed is provided. The method comprises providing a submerged drilling deck anchored on the seabed. The method further comprises providing a plurality of drill string strands comprising a first strand comprising a first end portion and a second end portion and a second strand comprising a first end portion and a second end portion. The method further comprises using the deck to reversibly connect the first end portion of the first strand to the second end portion of the second strand. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a cross-section schematic view of an example system in accordance with certain embodiments described herein for use with wells drilled without risers, with the drill string fully extended in the well.

[0009] Figure 2 is a cross-section schematic view of an example system in accordance with certain embodiments described herein for use with wells drilled without risers, with the drill string withdrawn from the well.

[0010] Figure 3 is a cross-section schematic view of an example system in accordance with certain embodiments described herein for use with wells drilled with risers, with the drill string fully extended in the well.

[0011] Figure 4 is a cross-section schematic view of an example system in accordance with certain embodiments described herein for use with wells drilled with risers, with the drill string withdrawn from the well.

[0012] Figure 5 is a cross-section schematic view of an example cabinet in accordance with certain embodiments described herein used for disconnecting the riser for use with wells drilled with risers, with doors open.

[0013] Figure 6 is a flow diagram of an example method of disassembling a drill string comprising a plurality of strands in accordance with certain embodiments described herein.

[0014] Figure 7 is a flow diagram of an example of using the deck to reversibly disconnect the first end portion of the first strand from the second end portion of the second strand in accordance with certain embodiments described herein.

[0015] Figure 8 is a flow diagram of an example of reversibly disconnecting the first end portion of the first strand from the second end portion of the second strand in accordance with certain embodiments described herein.

[0016] Figure 9 is a flow diagram of another example of reversibly disconnecting the first end portion of the first strand from the second end portion of the second strand in accordance with certain embodiments described herein. [0017] Figure 10 is a flow diagram of an example method of assembling a drill string for drilling a deep-sea borehole in a seabed in accordance with certain embodiments described herein.

DETAILED DESCRIPTION

[0018] Certain embodiments described herein involve drilling operations on the deep seabed and can increase the speed and decrease the cost of drilling wells in the deep seabed.

[0019] Certain embodiments described herein can use a submerged drilling deck anchored on the seabed at the site of the borehole of a deep-sea well. The submerged deck can be equipped to disconnect, at the level of the submerged deck, a long strand, comprising multiple segments, of the drill string above the submerged deck from the strand of the drill string below the deck (e.g., using tongs and other commonly practiced methods). In certain embodiments, fully automated iron roughnecks are built into the submerged deck and can be automated and managed by remote control (e.g., with the assistance of lights and cameras mounted on the submerged deck) from the surface vessel, which may be, for example, a drilling platform, a drilling ship, or a barge. The upper strand of the drill string of certain embodiments may be rotated by a motor on the surface vessel, a motor on the submerged deck, or both, as necessary. In certain embodiments, the submerged deck can be connected to the surface vessel by a remote control cable. In certain embodiments, the submerged deck can be connected to the surface vessel by a pulley, a cable, or other device for conveying parts and tools, as needed, between the surface vessel and the submerged deck.

[0020] If the well is drilled using a "riser," the riser may also be disconnected from the submerged deck in certain embodiments. The strand of the drill string above the submerged deck can be tethered at the top to the surface vessel and tethered at the bottom to the submerged deck. In certain embodiments, the surface vessel can, after the two strands of the drill string are disconnected from one another, pull the top of the strand of the drill string that remains in the borehole up to the ocean surface, and the submerged deck can disconnect, at the level of the submerged deck (e.g, by such automated methods and remote control), another strand of the drill string. Thus, the drill string of certain embodiments can be disassembled into strands that each have a length (e.g., substantially equal to the depth of the ocean at the location of the well) that is longer than that of conventional drill string segments (e.g., 30-40 meters). Since the water depth may be 2000 meters or more, the number of pauses to disassemble (and later to reassemble) the drill string may be only one or two, instead of 50 to 100 or more as for conventional systems. Also, there will be many fewer disconnections and reconnections and so there will be less wear and tear on the drill string, and the strands can remain in the water after being disconnected from the other strands, so the wasted energy and the hazards of removing the segments from the water can be reduced or avoided.

[0021] In certain embodiments, when the bottom portion of the drill string is raised to the submerged deck, a desired action can be performed on the bottom portion of the drill string at the submerged deck. For example, tools and spare parts on the submerged deck can be used to replace a worn out drill bit at the bottom portion of the drill string once the bottom portion of the drill string is raised to the submerged deck. In certain other embodiments, once the bottom portion of the drill string is raised to the submerged deck, the drill string can be moved aside away from the borehole to permit a new well casing to be inserted from the surface vessel into the lower parts of the borehole, and the drill string can then be moved back and lowered back down into the borehole. In certain embodiments, many of these functions, such as replacing a worn-out drill bit with a new drill bit, can be handled or performed by mechanisms at the submerged deck (e.g., mechanisms built into the deck and which are controlled by automation and/or remote control) because the extra drill bits and other tools that are utilized for such operations can be stored on the submerged deck. In certain embodiments, some of the more complicated or unusual operations may use a remotely operable vehicle to assist in the functions that the submerged deck is used to perform.

[0022] In certain embodiments, the well is drilled without use of a riser. In certain other embodiments in which the well is drilled with a riser, the riser can be moved, together with the uppermost strand of the drill string, away from the borehole, or the riser can be designed to accommodate more than one strand of the drill string. In either approach, the riser can retain the drilling fluid (e.g., drilling mud) without releasing it into the water. [0023] In certain embodiments described herein, in addition to the assembling and disassembling functions described above, the submerged deck located on the seabed can perform the drilling of the well, instead of the surface vessel. Certain such embodiments can be used to advantage at even greater water depths by avoiding creating the amount of drill string used to reach from the ocean surface to the seabed, and by avoiding creating the riser (except for the short distance from the submerged deck to the borehole) if drilling mud is used. Certain such embodiments also permit the application and control of the drilling force at the borehole by the submerged deck. In certain embodiments, if drilling mud is used, new or additional mud can be supplied by the surface vessel to the top of the drill string (e.g., via a flexible tube or hose) which is near the submerged deck, and mud returning up the borehole can be processed at the submerged deck and sent back down the drill string or to the surface vessel (e.g., via a flexible tube or hose). In certain embodiments, the ability of the submerged deck to perform the drilling of the well can be used to advantage by using several decks, operated from the same surface vessel, to drill several wells at the same time in the same general location.

[0024] Figures 1 and 2 are cross-sectional schematic views of an example system 10 for drilling a deep-sea borehole 20 in a seabed 30 in accordance with certain embodiments described herein. The system 10 comprises a drill string 40 comprising a plurality of strands (e.g., first strand 40a and second strand 40b) adapted to be reversibly connected together to assemble the drill string 40 and reversibly disconnected from one another to disassemble the drill string 40. The system 10 further comprises a submerged drilling deck 50 anchored on the seabed 30. The deck 50 is adapted to reversibly connect the strands 40a, 40b together and to reversibly disconnect the strands 40a, 40b from one another. As used herein, the term "strand" has its broadest reasonable meaning, including but not limited to, a portion of the drill string 40 longer than a conventional segment (e.g., longer than 30-40 meters).

[0025] In general, the deeper the boreholes, the more of an advantage certain embodiments described herein provide over the conventional systems and methods. For example, the advantages in time, ease, and efficiency are greater the deeper the borehole into the earth, the deeper the water above the borehole, or both. Also, as noted above, if the ocean floor in the location of the borehole consists of a number of layers of different kinds of rock, certain embodiments described herein will make it quicker and easier to switch drill bits to those that are designed for the type of rock being drilled. Since certain embodiments make it quicker and easier to switch drill bits, the drilling process can be faster as well, by utilizing drill bits that are specialized for the layers of rock being drilled. In certain embodiments, the deck 50 can be left in place once the well is completed, while in certain other embodiments, the deck 50, or only portions of the deck 50 (e.g., particular parts and equipment) can be retrieved once the well is completed (e.g., to be used on another well).

[0026] In certain embodiments, the drill string 40 comprises a plurality of strands. For example, the drill string 40 can comprise at least the first strand 40a, the second strand 40b, and further strands not shown in Figures 1 and 2. In certain embodiments, the plurality of strands comprises the first strand 40a extending above the deck 50 and the second strand 40b below the first strand 40a and extending below the deck 50. In certain such embodiments (e.g., where the two strands 40a, 40b are joined together by a threaded structure), the deck 50 is adapted to substantially rotate one of the first strand 40a and the second strand 40b about its axis while the other of the first strand 40a and the second strand 40b is not substantially rotated about its axis, thereby engaging or disengaging the threaded portions of the two strands 40a, 40b.

[0027] The two or more strands of certain embodiments comprises a drill bit at a lower portion of the drill string 40. In certain embodiments, one or more of the strands has a length greater than 100 meters, greater than 250 meters, greater than 500 meters, greater than 750 meters, greater than 1000 meters, or greater than 2000 meters. In certain embodiments, each of the first strand 40a and the second strand 40b has a length greater than 100 meters, greater than 250 meters, greater than 500 meters, greater than 750 meters, greater than 1000 meters or greater than 2000 meters. In certain embodiments, the drill string will also use sensors or other tools, and/or will be used for core sampling, and the ability to quickly place, monitor and retrieve such sensors, tools and/or core samplers at the deck will also be advantageous.

[0028] In certain embodiments, one or more of the strands comprises a plurality of segments. These segments of certain such embodiments are not adapted to be reversibly connected together to form the strand and reversibly disconnected from one another to disassemble the strand. In certain other embodiments, the segments are adapted to be reversibly connected together to form the strand and reversibly disconnected from one another to disassemble the strand. In certain such embodiments, the segments can be assembled together or disassembled from one another at the surface vessel 60, while in certain other embodiments, the segments can be assembled together and disassembled from one another at the deck 50. In certain embodiments, the strand(s) may not be disassembled into their respective segments once the well is completed, but instead kept intact and moved intact to the location of the next well to be drilled, if the two locations are proximate and the new location is at a depth similar to the depth of the first location, in order to save additional time in disassembling and assembling the drill string.

[0029] In certain embodiments, the deck 50 is self-contained, submerged, and located on the seabed 30 at the site of the deep-sea borehole 20. In certain embodiments, the deck may be mounted on pylons that are set into the ocean floor, in order that the deck will stay horizontal and steady, and so that there will be space under the deck for blowout preventers and other equipment that remain in place. In certain embodiments, the drill string may pass through a hole in the deck, and in other embodiments the drill string may pass down one side of the deck. In certain such embodiments, the deck 50 is adapted to be controlled remotely to perform the desired mechanical tasks. For example, in the example system 10 of Figures 1 and 2, the deck 50 is controlled remotely by a vessel 60 (e.g., platform, ship, or barge) at the ocean surface 70. In certain such embodiments, the system 10 comprises monitoring equipment (e.g., lights, cameras) mounted on the deck 50 (e.g., on a mechanical tower 52 which may be movable on at least one side of the deck 50) or on a portion of the system 10 separated from the deck 50 and utilizes automated equipment and sub-routines, as is commonly practiced in the industry, to perform the desired actions. For example, iron roughnecks and remotely operated underwater vehicles (ROVs) are commonly used in the industry, and may be used with certain embodiments described herein. In certain such embodiments, the tower 52 comprises an iron roughneck which is sufficiently mechanized and automated such that it can be operated entirely by remote control from the surface vessel 60. [0030] Figures 1 and 2 schematically illustrate an example system 10 for which the drilling fluid comprises seawater which is pumped through the drill string 40, and a riser is not used to contain the drilling fluid in accordance with certain embodiments described herein. However, in certain other embodiments, the drilling fluid comprises drilling mud which is pumped through the drill string 40 and a riser 80 is used to contain the drilling mud as it travels from the borehole 20 back up to the surface vessel 60. Figures 3 and 4 schematically illustrate an example system 10 comprising a riser 80 in accordance with certain embodiments described herein. The riser 80 is adapted to allow a drilling fluid to flow through the riser 80, and the drill string 40 (e.g., the first strand 40a) is adapted to pass through the riser 80. A first end portion 82 of the riser 80 is operatively coupled to the deck 50 and a second end portion 84 of the riser 80 is operatively coupled to the surface vessel 60.

[0031] Figure 5 schematically illustrates an example deck 50 used with a riser 80 in accordance with certain embodiments described herein. The riser 80 can convey the drilling fluid (e.g., drilling mud) from the borehole 20 to the surface vessel 60. The first end portion 82 of the riser 80 is operatively coupled to the deck 50, and the second end portion 84 of the riser 80 is operatively coupled to the surface vessel 60. In certain embodiments, the riser 80 comprises at least one valve 86 adapted to form at least one seal to substantially contain drilling fluid within the riser 80 (e.g., one or more annular valves which form at least one seal around the first strand 40a extending within the riser 80).

[0032] In certain such embodiments, the deck 50 comprises a cabinet 90 having a top portion 92 and a bottom portion 94. The top portion 92 is operatively coupled to the first end portion 82 of the riser 80 and the bottom portion 94 is operatively coupled to the borehole 20, and the drill string 40 is adapted to pass through the riser 80, the cabinet 90, and into the borehole 20. Furthermore, in certain embodiments, to facilitate assembly and disassembly of the drill string 40, the top portion 92 of the cabinet 90 can be reversibly separated from and reversibly reattached to the bottom portion 94 of the cabinet 90. As described more fully below, certain such embodiments allow the riser 80 and the top portion 92 of the cabinet 90 to be spaced from and moved relative to the bottom portion 94 of the cabinet 90 while the first strand 40a extends within the riser 80 above the top portion 92 of the cabinet 90 and the second strand 40b extends within the borehole 20 below the bottom portion 94 of the cabinet 90.

[0033] In certain embodiments, the deck 50 further comprises a conduit 54 (e.g., a pipe) adapted to allow drilling fluid to flow through the conduit 54 and to operatively couple the bottom portion 94 to the borehole 20, and the drill string 40 is adapted to pass through the conduit 54 into the borehole 20. In certain embodiments, the conduit 54 is not substantially movable, and further comprises blow-out preventers and other pieces of equipment between the deck 50 and the borehole 20 that remain in place in relation to the borehole 20. In certain embodiments, the conduit 54 further comprises at least one valve 56 adapted to form at least one seal to substantially contain drilling fluid within the borehole 20 (e.g., one or more annular valves which form at least one seal around the second strand 40b extending within the conduit 54).

[0034] In certain embodiments, the cabinet 90 comprises at least one door 96 (e.g., two doors on a side of the cabinet 90) that can be selectively opened or closed. The at least one door 96 is ordinarily closed during drilling, but can be opened to provide access to the portion of the drill string 40 within the cabinet 90 (e.g., when accessing the joint 46 between the first strand 40a and the second strand 40b for assembly/disassembly of the drill string 40). For example, the at least one door 96 can generally face selected components of the deck 50 (e.g., the tower 52) and can be opened on a hinge 98 to allow the components to access the joint 46 for automated assembly/disassembly of the drill string 40.

[0035] Figure 6 is a flow diagram of an example method 200 of disassembling a drill string 40 comprising a plurality of strands (e.g., a first strand 40a and a second strand 40b), the drill string 40 extending into a deep-sea borehole 20 in a seabed 30 in accordance with certain embodiments described herein. While the method 200 is described herein by referring to the example system 10 of Figures 1-5, other configurations of the system 10 are also compatible with certain embodiments described herein. In certain embodiments, the method 200 uses the deck 50 to disassemble the drill string 40 when the drilling fluid comprises seawater, and a riser 80 is not used to contain the drilling fluid. In certain other embodiments, the method 200 uses the deck 50 to disassemble the drill string 40 when the drilling fluid comprises drilling mud, and a riser 80 is used to contain the drilling fluid. [0036] In an operational block 210, the method 200 comprises providing a submerged drilling deck 50 anchored on the seabed 30. In an operational block 220, the method 200 further comprises positioning the drill string 40 such that the first section 40a extends above the deck 50 and the second strand 40b extends below the deck 50 into the borehole 20. The first strand 40a comprises a first end portion 42a and a second end portion 44a, and the second strand 40b comprises a first end portion 42b and a second end portion 44b. The first end portion 42a of the first strand 40a is connected to the second end portion 44b of the second strand 40b (e.g., at a joint 46). In an operational block 230, the method 200 further comprises using the deck 50 to reversibly disconnect the first end portion 42a of the first strand 40a from the second end portion 44b of the second strand 40b.

[0037] In certain embodiments, the method 200 further comprises suspending the second end portion 44a of the first strand 40a from the surface vessel 60 while using the deck 50 to reversibly disconnect the first end portion 42a of the first strand 40a from the second end portion 44b of the second strand 40b. For example, as shown schematically in Figure 1, the second end portion 44a of the first strand 40a is suspended from the surface vessel 60 by a cable 100. In certain embodiments, after the deck 50 is used to reversibly disconnect the first end portion 42a of the first strand 40a from the second end portion 44b of the second strand 40b, the second end portion 44a of the first strand 40a remains suspended from the surface vessel 60 (e.g., by the cable 100), as schematically illustrated by Figure 2.

[0038] In addition, in certain embodiments, the second end portion 44b of the second strand 40b is attached to a cable 102, as commonly used in the industry, extending from the surface vessel 60. One or more balloons, buoys or other flotation devices may also be attached to the second end portion 44a of the first strand 40a, to the second end portion 44b of the second strand 40b, or both to enable the surface vessel 60 to impart neutral buoyancy (e.g., neither positive or negative buoyancy) to the first strand 40a, the second strand 40b, or both at the appropriate times. In certain embodiments, the deck 50 comprises one or more arms 1 10 adapted to be attached to the first end portion 42a of the first strand 40a, the first end portion 42b of the second strand 40b, or both. The one or more arms 1 10 in certain embodiments are extendable and retractable by the deck 50. Therefore, once the first strand 40a is detached from the second strand 40b, the first strand 40a (which can be almost as long as the distance from the surface vessel 60 to the deck 50) can remain suspended from the surface vessel 60 by the cable 100 (and by the flotation device, if used), and can remain connected to the deck 50 but separated from the second strand 40b by ϊhe extended arm 110 of the deck 50.

[0039] In certain embodiments, the method 200 further comprises raising the second strand 40b out of the borehole 20 (e.g., by using the surface vessel 60 to retract the cable 102 attached to the second end portion 44b of the second strand 40b). In certain embodiments, the second end portion 44b of the second strand 40b can be raised to be in proximity to the surface vessel 60, as schematically illustrated in Figure 2. In certain other embodiments, the second strand 40b is raised such that the first end portion 42b of the second strand 40b is pulled from the borehole 20. In certain such embodiments, the second strand 40b is sufficiently short that upon the first end portion 42b of the second strand 40b clearing the entrance to the borehole 30, the second end portion 44b of the second strand 40b is not yet in proximity to the surface vessel 60. In certain embodiments, the method 200 further comprises suspending the second strand 40b from the surface vessel 60 after the second strand 40b has been raised out of the borehole 20.

[0040] In certain embodiments in which the drill string 40 comprises additional strands, merely disconnecting the first strand 40a from the second strand 40b may be insufficient to completely remove the drill string 40 from the borehole 20 or to position the portion of the drill string 40 to be operated upon at an accessible location. In certain such embodiments, the method 200 can be repeated by raising the second strand 40b such that a joint between the second strand 40b and an additional lower strand is in an appropriate position, and using the deck 50 to reversibly disconnect the first end portion 42b of the second strand 40b from a second end portion of the additional lower strand. In certain such embodiments, the system 10 comprises a sufficient number of cables 100, 102 and arms 1 10 to accommodate all the strands of the drill string 40 so that the method 200 can be repeated as many times as desired to completely remove the drill string 40 from the borehole 20 or to position the portion of the drill string 40 to be operated upon at an accessible location.

[0041] Figure 7 is a flow diagram of an example of using the deck 50 in the operational block 230 to reversibly disconnect the first end portion 42a of the first strand 40a from the second end portion 44b of the second strand 40b in accordance with certain embodiments in which the system 10 comprises a riser 80 to convey the drilling fluid (e.g., drilling mud) from the borehole 20 to the surface vessel 60. While the method 200 and the operational block 230 are described herein by referring to the example system 10 of Figures 3-5, other configurations of the system 10 are also compatible with certain embodiments described herein.

[0042] In an operational block 310, the first end portion 42a of the first strand 40a and the second end portion 44b of the second strand 40b are positioned within the cabinet 90. For example, as schematically illustrated in Figure 5, the joint 46 between the first strand 40a and the second strand 40b is positioned within the cabinet 90 (e.g., by using the surface vessel 60 to raise the drill string 40 until the joint 46 of the drill string 40 is raised into the cabinet 90).

[0043] In an operational block 320, at least one first seal is formed to substantially contain drilling fluid within the riser 80. For example, as schematically illustrated by Figure 5, at least one annular valve 86 can be closed to form at least one seal around the first strand 40a extending within the riser 80. In certain embodiments, the at least one annular valve 86 is attached to the riser 80 by bearings which are adapted to allow the at least one annular valve 86 to turn while closed with the first strand 40a extending within the riser 80. In certain other embodiments, the at least one annular valve 86 comprises bearings (e.g., at an inner surface) which are adapted to allow the first strand 40a to turn within the at least one annular valve 86 while the at least one annular valve 86 is closed.

[0044] In an operational block 330, at least one second seal is formed to substantially contain drilling fluid within the borehole 20. For example, as schematically illustrated by Figure 5, at least one annular valve 56 (e.g., similar to the annular valves commonly used in the industry for blowout protectors) can be closed to form at least one seal around the second strand 40b extending within the conduit 54. In certain embodiments, the at least one annular valve 56 is adapted to allow additional segments of the drill string 40, including the additional joints, to be drawn up through the at least one annular valve 56 while the at least one annular valve 56 is closed, thereby substantially containing drilling fluid within the borehole 20. [0045] In an operational block 340, drilling fluid is removed from the cabinet 90 between the at least one first seal and the at least one second seal. For example, once the at least one annular valve 86 and the at least one annular valve 56 are closed, the drilling fluid inside the cabinet 90 can be removed and replaced with seawater. In certain such embodiments, the drilling fluid removed from the cabinet 90 is stored in a tank 120 on the deck 50, as schematically illustrated by Figure 5. The at least one door 96 at the side of the cabinet 90 can then be opened without having the drilling fluid escape from the deck 50.

[0046] In an operational block 350, the first end portion 42a of the first strand 40a is reversibly disconnected from the second end portion 44b of the second strand 40b. In certain embodiments, the second end portion 44a of the first strand 40a can be suspended from the surface vessel 60 (e.g., by the cable 100 and/or balloons, buoys or other floatation devices) and the second end portion 44b of the second strand 40b can be attached to the surface vessel 60 (e.g., by the cable 102), as schematically illustrated by Figures 3 and 4. In certain embodiments, remote control and automated subroutines, as are known in the industry, are used by the deck 50 to disconnect the first strand 40a from the second strand 40b at the joint 46.

[0047] Figure 8 is a flow diagram of an example of reversibly disconnecting the first end portion 42a of the first strand 40a from the second end portion 44b of the second strand 40b in the operational block 350 in accordance with certain embodiments described herein. In an operational block 352, at least one seal is formed to substantially contain drilling fluid within the first strand 40a. The first strand 40a of certain such embodiments can comprise one or more valves or screw caps (e.g., at the first end portion 42a) which are closed by the deck 50 (e.g., using a mechanism on the mechanical tower 52) to substantially retain drilling fluid within the first strand 40a. In an operational block 354, at least one seal is formed to substantially contain drilling fluid within the second strand 40b. The second strand 40b of certain such embodiments can comprise one or more valves or screw caps (e.g., at the second end portion 44b) which are closed by the deck 50 (e.g., using a mechanism on the mechanical tower 52) to substantially retain drilling fluid within the second strand 40b.

[0048] In an operational block 356, the top portion 92 of the cabinet 90 is reversibly detached from the bottom portion 94 of the cabinet 90. For example, the top portion 92 and the bottom portion 94 can be adapted to be reversibly attached to one another and reversibly detached from one another. In an operational block 358, the first strand 40a, the riser 80, and the top portion 92 of the cabinet 90 are moved away from the second strand 40b, as schematically illustrated by Figure 4. Once moved so as to allow access to the second strand 40b, the top portion 92 of the cabinet 90 can be rested on one or more supports (e.g., to one side of the deck 50 or separated from the deck 50).

[0049] In certain such embodiments, the method 300 further comprises suspending the second end portion 44b of the second strand 40b from the surface vessel 60 and raising the second strand 40b out of the borehole 20 (e.g., by using the surface vessel 60 to retract the cable 102 attached to the second end portion 44b of the second strand 40b), as schematically illustrated by Figure 4. In certain embodiments, the second end portion 44b of the second strand 40b can be raised to be in proximity to the surface vessel 60, as schematically illustrated in Figure 4. In certain other embodiments, the second strand 40b is raised such that the first end portion 42b of the second strand 40b is pulled from the borehole 20. In certain such embodiments, the second strand 40b is sufficiently short that upon the first end portion 42b of the second strand 40b being extracted from the borehole 30, the second end portion 44b of the second strand 40b is not yet in proximity to the surface vessel 60.

[0050] In certain embodiments, raising the second strand 40b from the borehole 20 comprises filling the vacated volume in the borehole 20 (e.g., the volume previously occupied by the second strand 40b) with fluid (e.g., by injecting additional drilling fluid, or another fluid that can be recaptured, through a tube or hose 130 from the surface vessel 60 to an opening or hole 140 in the conduit 54 of the deck 50. In certain embodiments, another tube or hose from the surface vessel 60 to another hole in the conduit 54 can be used in conjunction with the hose 130 and hole 140 to maintain circulation of the drilling fluid in the borehole 20, if such circulation is desired.

[0051] Figure 9 is a flow diagram of another example of reversibly disconnecting the first end portion 42a of the first strand 40a from the second end portion 44b of the second strand 40b in the operational block 350 in accordance with certain embodiments described herein. In certain embodiments, the riser 80 is not disconnected from the deck 50 or moved to one side, as described above. Instead, the riser 80 remains in place, but is sufficiently large, in cross-section, to accommodate not only the first strand 40a within the riser 80, but also all the other strands (e.g., at least the second strand 40b) used to drill the borehole 20. In certain such embodiments, the operational block 350 comprises the operational block 352, the operational block 354, and an operational block 360 in which the second end portion 44b of the second strand 40b is raised out of the borehole 20 and into the riser 80. For example, the second strand 40b is suspended from the surface vessel 60 and mechanisms mounted on the inside wall of the riser 80 at appropriate locations and intervals can pull and hold the second strand 40b, as well as any other strands of the drill string 40, within the riser 80. In certain such embodiments, the tower 52 is within the cabinet 90, and the cabinet 90 does not have any door(s) to open or any valves 56. In certain such embodiments, the disassembly and assembly of the drill string 40 is accomplished in the same manner as described above for configurations which do not include a riser, by performing all the desired tasks or operations on the drill string 40 within the riser 80 and the cabinet 90.

[0052] In certain embodiments, once the desired operation (e.g., replacing the drill bit at the first end portion 42b of the second strand 40b, placing a new well casing in the borehole 20, or both) has been performed, the disconnected strands (e.g., first strand 40a and second strand 40b) can be reconnected together. Figure 10 is a flow diagram of a example method 400 of assembling a drill string 40 for drilling a deep-sea borehole 20 in a seabed 30 in accordance with certain embodiments described herein. While the method 400 is described herein by referring to the example system 10 of Figures 1 and 2, other configurations of the system 10 are also compatible with certain embodiments described herein.

[0053] In an operational block 410, the method 400 comprises providing a submerged drilling deck 50 anchored on the seabed 30. In an operational block 420, the method 400 further comprises providing a plurality of drill string strands comprising a first strand 40a and a second strand 40b. The first strand 40a comprises a first end portion 42a and a second end portion 44a, and the second strand 40b comprises a first end portion 42b and a second end portion 44b. In an operational block 430, the method 400 further comprises lowering the second strand 40b into the borehole 20, then using the deck 50 to reversibly connect the first end portion 42a of the first strand 40a to the second end portion 44b of the second strand 40b.

[0054] In certain embodiments, the drill string strands are reconnected to one another to reassemble the drill string 40 in the reverse order in which they were previously disconnected from one another (e.g., in accordance with the method 200 of Figure 6) and lowered back into the borehole 20. For example, the last strand of the drill string 40 that was removed from the borehole 20 (e.g., the second strand 40b) can be reinserted into the borehole 20 and lowered until the second end portion 44b is in proximity to the deck 50. The drill string strand that was removed immediately prior thereto (e.g., the first strand 40a) can be suspended from the surface vessel 60 (e.g., by cable 100) and placed in position at the deck 50 (e.g., by retraction of the arm 1 10) to be reconnected to the second strand 40b. The first end portion 42a of the first strand 40a can then be reconnected to the second end portion 44b of the second strand 40b, and the reconnected strands can then be further lowered into the borehole 20. Such reconnections of the plurality of drill string strands in certain embodiments can be performed by the mechanical tower 52 on the deck 50 by remote control and automated subroutines. The second end portion 44a of the first strand 40a can be suspended from the surface vessel 60 (e.g., by cable 100) while using the deck 50 to reconnect the first strand 40a to the second strand 40b. In certain embodiments, the steps of the method 400 can be repeated for additional strands of the drill string 40, until the entire drill string 40 is reassembled (e.g., in its original order).

[0055] In certain embodiments, using the deck 50 to reversibly connect the first end portion 42a of the first strand 40a to the second end portion 44b of the second strand 40b comprises positioning the first end portion 42a of the first strand 40a and the second end portion 44b of the second strand 40b within the cabinet 90. In certain such embodiments, using the deck 50 further comprises opening the valves or removing the screw caps on the first end portion 42a of the first strand 40a and on the second end portion 44b of the second strand 40b. In certain embodiments in which additional fluid (e.g., drilling fluid) was added to the borehole 20 while extracting the drill string 40 from the borehole 20, the additional fluid can be retrieved from the borehole 20 as it is displaced from the borehole 20 by the reassembled drill string 40, and put back into storage. In certain embodiments in which the riser 80, the top portion 92 of the cabinet 90, and the first strand 40a were displaced away (e.g., to the side of the deck 50), they can be moved back into position and reconnected to the bottom portion 94 of the cabinet 90 and to the second strand 40b, the one or more doors 96 can be closed, the cabinet 90 can be refilled with the drilling fluid (e.g., between the at least one valve 86 and the at least one valve 56), and the at least one valve 56 and the at least one valve 86 can be opened to allow drilling fluid to flow through the borehole 20, the cabinet 90, and the riser 80.

[0056] In certain embodiments, in addition to the functions described above of assembly and disassembly of the drill string 40, the submerged deck 50 can operate the drill string 40 to drill the borehole (e.g., using a drill motor on the submerged deck 50, instead of on the surface vessel 60) by automated routines and remote control at the submerged deck 50 (e.g., utilizing sensors and monitoring devices as described above). Certain such embodiments advantageously permit the application and control of the drilling force at the top of the borehole 20, and advantageously shorten the drill string 40 and remove the use of the riser 80 (except for the short distance from the submerged deck 50 to the borehole 20) in a well drilled with drilling fluid or mud. If drilling mud is used, new or additional mud can be supplied in certain such embodiments by the surface vessel 60 (e.g., to the top of the drill string 40, which is at the submerged deck 1, through a flexible tube or hose), and drilling mud returning up the borehole 20 can be processed at the submerged deck 50 and sent back down the drill string 40 or up a tube or hose to the surface vessel 60. In certain embodiments, multiple decks 50 can each have a drill motor, advantageously allowing the multiple decks 50 to be controlled by a single surface vessel 60 and allowing multiple wells to be drilled simultaneously.

[0057] Various embodiments have been described above. Although this invention has been described with reference to these specific embodiments, the descriptions are intended to be illustrative of the invention and are not intended to be limiting. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A system for drilling a deep-sea borehole in a seabed, the system comprising: a drill string comprising a plurality of strands adapted to be reversibly connected together to assemble the drill string and reversibly disconnected from one another to disassemble the drill string; and a submerged drilling deck anchored on the seabed, the deck adapted to reversibly connect the strands together and to reversibly disconnect the strands from one another.

2. The system of Claim 1, wherein the deck is adapted to be controlled remotely from a vessel at the ocean surface or from a remotely operable underwater vehicle.

3. The system of Claim 1, wherein the plurality of strands comprises a first strand extending above the deck and a second strand below the first strand and extending below the deck, wherein the deck is adapted to substantially rotate one of the first strand and the second strand about its axis while the other of the first strand and the second strand is not substantially rotated about its axis.

4. The system of Claim 1 , wherein one or more of the strands has a length greater than 1000 meters.

5. The system of Claim 1, wherein the plurality of strands comprises a drill bit.

6. The system of Claim 1 , further comprising a riser adapted to allow a drilling fluid to flow through the riser, wherein a first end portion of the riser is operatively coupled to the deck and a second end portion of the riser is operatively coupled to a vessel at the ocean surface, wherein the drill string is adapted to pass through the riser.

7. The system of Claim 6, wherein the deck comprises a cabinet having a top portion and a bottom portion, the top portion operatively coupled to the first end portion of the riser, the bottom portion operatively coupled to the borehole, wherein the drill string is adapted to pass through the riser, through the cabinet, and into the borehole.

8. The system of Claim 7, wherein the deck further comprises a conduit adapted to allow drilling fluid to flow through the conduit and to operatively couple the bottom portion of the cabinet to the borehole, wherein the drill string is adapted to pass through the conduit.

9. The system of Claim 7, wherein the riser and the top portion of the cabinet are adapted to be spaced from and moved relative to the bottom portion of the cabinet while a first strand of the plurality of strands extends within the riser above the top portion of the cabinet and a second strand of the plurality of strands extends within the borehole below the bottom portion of the cabinet.

10. The system of Claim 1, wherein the deck further comprises a drilling motor configured to be remotely controlled from a position away from the deck.

11. The system of Claim 1 , further comprising: a second drill string comprising a second plurality of strands adapted to be reversibly connected together to assemble the second drill string and reversibly disconnected from one another to disassemble the second drill string; and a second submerged drilling deck anchored on the seabed at a position spaced from the deck, the second deck adapted to reversibly connect the second plurality of strands together and to reversibly disconnect the second plurality of strands from one another, wherein the deck and the second deck are both adapted to be controlled remotely from a single vessel at the ocean surface.

12. A method of disassembling a drill string comprising a plurality of strands, the drill string extending into a deep-sea borehole in a seabed, the method comprising: providing a submerged drilling deck anchored on the seabed; positioning the drill string such that a first strand of the plurality of strands extends above the deck and a second strand of the plurality of strands extends below the deck into the borehole, the first strand comprising a first end portion and a second end portion and the second strand comprising a first end portion and a second end portion, the first end portion of the first strand connected to the second end portion of the second strand; and using the deck to reversibly disconnect the first end portion of the first strand from the second end portion of the second strand.

13. The method of Claim 12, further comprising suspending the second end portion of the first strand from a vessel at the ocean surface while using the deck to reversibly disconnect the first end portion of the first strand from the second end portion of the second strand.

14. The method of Claim 12, further comprising suspending the second end portion of the first strand from a vessel at the ocean surface after using the deck to reversibly disconnect the first end portion of the first strand from the second end portion of the second strand.

15. The method of Claim 12, wherein the first strand has a length greater than 1000 meters and the second strand has a length greater than 1000 meters.

16. The method of Claim 12, wherein the drill string passes through a riser adapted to allow a drilling fluid to flow through the riser, wherein a first end portion of the riser is operatively coupled to the deck and a second end portion of the riser is operatively coupled to a vessel at the ocean surface.

17. The method of Claim 16, wherein the deck comprises a cabinet having a top portion and a bottom portion, the top portion operatively coupled to the first end portion of the riser, the bottom portion operatively coupled to the borehole, wherein the drill string is adapted to pass through the riser, through the cabinet, and into the borehole.

18. The method of Claim 17, wherein using the deck to reversibly disconnect the first end portion of the first strand from the second end portion of the second strand comprises: positioning the first end portion of the first strand and the second end portion of the second strand within the cabinet; forming at least one first seal to substantially contain drilling fluid within the riser; forming at least one second seal to substantially contain drilling fluid within the borehole; removing drilling fluid from the cabinet between the at least one first seal and the at least one second seal; and reversibly disconnecting the first end portion of the first strand from the second end portion of the second strand.

19. The method of Claim 16, further comprising: forming at least one seal to substantially contain drilling fluid within the first strand; forming at least one seal to substantially contain drilling fluid within the second strand; reversibly detaching the top portion of the cabinet from the bottom portion of the cabinet; and moving the first strand, the riser, and the top portion of the cabinet away from the second strand.

20. The method of Claim 19, further comprising suspending the second end portion of the second strand from the vessel and raising the second strand out of the borehole.

21. The method of Claim 16, further comprising: forming at least one seal to substantially contain drilling fluid within the first strand; forming at least one seal to substantially contain drilling fluid within the second strand; suspending the second end portion of the second strand from the vessel and raising the second strand out of the borehole and into the riser.

22. A method of assembling a drill string for drilling a deep-sea borehole in a seabed, the method comprising: providing a submerged drilling deck anchored on the seabed; providing a plurality of drill string strands comprising a first strand comprising a first end portion and a second end portion and a second strand comprising a first end portion and a second end portion; and using the deck to reversibly connect the first end portion of the first strand to the second end portion of the second strand.

23. The method of Claim 22, further comprising suspending the second end portion of the first strand from a vessel at the ocean surface while using the deck to reversibly connect the first end portion of the first strand to the second end portion of the second strand.

24. The method of Claim 22, further comprising suspending the second end portion of the first strand from a vessel at the ocean surface before using the deck to reversibly connect the first end portion of the first strand to the second end portion of the second strand.

25. The method of Claim 22, wherein the first strand has a length greater than 1000 meters and the second strand has a length greater than 1000 meters.

26. The method of Claim 22, wherein the first strand passes through a riser adapted to allow a drilling fluid to flow through the riser, wherein a first end portion of the riser is operatively coupled to the deck and a second end portion of the riser is operatively coupled to a vessel at the ocean surface.

27. The method of Claim 26, wherein the deck comprises a cabinet having a top portion and a bottom portion, the top portion operatively coupled to the first end portion of the riser, the bottom portion operatively coupled to the borehole, wherein the drill string is adapted to pass through the riser, through the cabinet, and into the borehole.

28. The method of Claim 27, wherein using the deck to reversibly connect the first end portion of the first strand to the second end portion of the second strand comprises: positioning the first end portion of the first strand and the second end portion of the second strand within the cabinet, wherein at least one first seal around the first strand substantially contains drilling fluid within the riser and at least one second seal around the second strand substantially contains drilling fluid within the borehole; reversibly connecting the first end portion of the first strand to the second end portion of the second strand; closing the cabinet and filling the cabinet with drilling fluid between the at least one first seal and the at least one second seal; and opening the at least one first seal and opening the at least one second seal to allow drilling fluid to flow through the borehole, the cabinet, and the riser.