BACKGROUND OF THE INVENTION 1. Field of the Invention
Embodiments of the present invention generally relate to a mobile offshore drilling unit.
2. Description of the Related Art
FIG. 1A illustrates a drilling rig 6. A drilling rig 6 is a portable factory for forming deep wellbores 40 in the ground. When a drill bit 10 is pressed against the ground and rotated, the teeth on the bit 10 grind and gouge the rock into small pieces. These pieces of rock or cuttings must be moved out of the way so the bit teeth can be constantly exposed to fresh, uncut rock. Drilling fluid, such as mud, is used to move the cuttings away from the bit 10. A mud pump 20 takes mud from mud tanks 22 and pumps it under high pressure up a standpipe 24, through the swivel 26, down the kelly 54, down the drill pipe 30, through the drill collars 32 and out jets in the bit 10. Mud, exiting under pressure from jets in the bit 10, clears the cuttings and moves then up the annulus 42 of the wellbore 40. The mud and cuttings are then passed over a shale shaker 44 which separates the cuttings from the mud and allows the mud to return to the mud tank 22 for recirculation. The cuttings are sampled periodically for geologic purposes, but most are discarded.
Since the drill bit 10 is usually rotated to form the wellbore, drilling rig 6 usually includes a rotary system. The rotary system includes drilling floor 50 and rotary table 52. Located near the center of the rotary table 52 is a kelly bushing and kelly 54. In many modern drilling units, a top drive motor (not shown) positioned in the derrick on rails replaces the rotary table, kelly bushing, and kelly for imparting rotation to the drill string. Rotational force is transferred from the rotary system to the drill string including drill pipe 30 and drill collars 32. The drill collars 32 are heavy and stiff and assist in maintaining the bit in a vertical position. The weight of the drill collars 32 applied directly above the bit assists in increasing the cutting ability of the bit 10.
FIG. 1B illustrates the draw works 68 of the drilling rig 6. Wells are now being drilled to depths in excess of 30,000 feet. The tremendous weight of the drill string must be supported by a substantial derrick 60. A drilling line 64 is attached to traveling block 66, sheaved over crown block 62 and attached to draw works 68. The draw works 68 includes a winch which is used to hoist the drill string, including the drill pipe 30, drill collars 32 and bit 10, out of the hole. Any drilling unit needs power to the turn the bit, power to drive the mud pump and power to run all the ancillary machinery. The power system on most offshore rigs is usually diesel/electric. The prime movers, being diesel, are used to drive generators to generate electric power which is used to power the other equipment.
Mobile offshore drilling units (MODUs) move from one drill site on the water to another. There are two basic types of MODUs used to drill most offshore wells: (1) bottom supported units including submersibles and jack-ups; and (2) floating units including lake barge rigs, drill ships, and semi-submersibles.
FIG. 1C illustrates a semi-submersible MODU 70. Floating units are typically used in water depths greater than where a bottom supported unit is capable. A semi-submersible 70 has a drilling rig 71 mounted in the middle and includes an opening, referred to in the industry as a moon pool (not shown), through which drilling operations are conducted. Semi-submersibles 70 include a lower barge hull 74 which floats below the surface of the sea 72 and is, therefore, not subject to surface wave action. Large stability columns 73 mounted on the lower barge hull 74 support the upper hull 78, which includes a main deck and machinery deck above the surface of the water 72.
SUMMARY OF THE INVENTION Embodiments of the present invention generally relate to a mobile offshore drilling unit. In one embodiment, a semisubmersible mobile offshore drilling unit (MODU) includes a submersible lower hull comprising a ring pontoon having a trapezoidal shape; an upper hull having the trapezoidal shape; three stability columns supporting the upper hull from the lower hull; and a drilling rig.
BRIEF DESCRIPTION OF THE DRAWINGS So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIG. 1A illustrates a drilling rig. FIG. 1B illustrates the draw works of the drilling rig. FIG. 1C illustrates a semi-submersible mobile offshore drilling unit (MODU).
FIG. 2A is a perspective view of a semi-submersible MODU in a drilling mode, according to one embodiment of the present invention. FIG. 2B is a plan view of the semi-submersible MODU in drilling mode. FIG. 2C is a profile view of the semi-submersible MODU in drilling mode.
FIGS. 3A-G illustrate a drilling rig, a.k.a. derrick equipment set (DES), of the MODU. FIG. 3A is a profile view of the DES. FIG. 3B is another profile view of the DES. FIG. 3C is a profile view of the drill pipe handling system. FIG. 3D is a plan view of the drill floor. FIG. 3E is a plan view of the process level. FIG. 3F is a plan view of the lower level. FIG. 3G is a plan view of the base.
FIG. 4A is a plan view of a mezzanine deck of the MODU. FIG. 4B is a plan view of a machinery deck of the MODU. FIG. 4C is a plan view of a tank deck of the MODU. FIG. 4D is a plan view of a lower level of the cabin. FIG. 4E is a plan view of an upper level of the cabin. FIG. 4F is a plan view of the helipad.
FIGS. 5A-E illustrate the DES being deployed in tender assist drilling mode. FIG. 5A is a plan view of the main deck. FIG. 5B is a plan view of the MODU connected to a platform. FIG. 5C is a profile view of the DES having been hoisted from the MODU and set on the platform. FIG. 5D is a profile view of the DES in place over the platform's moonpool. FIG. 5E is a perspective view of the MODU in tender assist drilling mode.
DETAILED DESCRIPTION FIG. 2A is a perspective view of a semi-submersible MODU 100 in a drilling mode, according to one embodiment of the present invention. FIG. 2B is a plan view of the semi-submersible MODU 100 in drilling mode. FIG. 2C is a profile view of the semi-submersible MODU 100 in drilling mode.
The MODU 100 may be semi-submersible and include a helipad 101, an upper hull 105, one or more stability columns 110, a submersible lower hull 115, one or more cranes 120a-c, one or more life-rafts 125, a cabin 130, a remotely operated vehicle (ROV) 135, a mooring system 140, a drilling rig, a.k.a. derrick equipment set (DES), 150, and a moonpool 155. The helipad 101 may be used for shuttling roughnecks to and from the MODU 100. The upper hull 105 may have an trapezoidal shape, such as isosceles trapezoidal, and may include one or more decks, such as a main deck 105p, a mezzanine deck 105z, a machinery deck 105m, and a tank deck 105t. As discussed above, the upper hull 105 and stability columns 110 may float on the lower hull 115 and three stability columns may support the upper hull from the lower hull. The lower hull 115 may include one or more pontoons and a ballast system. The pontoon may be a ring pontoon having a trapezoidal shape corresponding to the upper hull. The pontoons may float near or on the surface when empty for towing the MODU 100 between locations and may submerge when ballasted for drilling or tender assist drilling mode (discussed below). The ROV 135 may be deployed to perform subsea work. The mooring system 140 may be employed to maintain position of the MODU 100 during drilling or tender assisted drilling. Alternatively or additionally, the MODU 100 may include a dynamic positioning system to maintain position of the MODU 100.
FIGS. 3A-G illustrate the DES 150 in drilling mode. FIG. 3A is a profile view of the DES 150. The DES 150 may include a derrick 205, a top drive 210, a drill floor 215, a process level 220, a lower level 225, a base 230, drawworks 235, a crown block 240, a blow out preventer (BOP) 245 (see FIG. 3B), a drill pipe handling system 250, a mud treatment system 255, a driller's cabin 265 (see FIG. 3D), and a skidding system 275. The derrick 205, drill floor 215, process level 220, and lower level 225 may be mounted on the base 230, such as by fasteners. In the drilling mode, the derrick 205 may be located over the moonpool 155 to conduct drilling operations and the base 230 may rest on the main deck 105p and/or be fastened to the upper hull 105.
FIG. 3B is another profile view of the DES 150. The derrick 205 may include an upper mast portion 205m and lower housing portion 205h. In drilling mode, the mast 205m may extend from the housing 205h. The portions 205h,m may be connected, such as fastened, at an overlap 205c. To transport the derrick 205 for tender assist drilling mode or when towing the MODU 100 between locations, one of the cranes 120a-c may be fastened to the mast 205m, the connection 205c disassembled, and the mast 205m may then be lowered into the housing. The connection 205c may be reassembled, the derrick 205 may be disconnected from the base 230, and the derrick 205 may be laid down on the main deck 105p (see FIG. 5A).
FIG. 3C is a profile view of the drill pipe handling system 250. FIG. 3D is a plan view of the drill floor 215. The drill pipe handling system 250 may include a bridge crane, a racking arm, a racking board, an elevator, one or more power tongs (IR), an offline stand building (OSB), and one or more pipe bins. Single joints of drill pipe 260 may be stored in the pipe bins. During and before drilling, the joints 260 may be assembled into stands of two or more joints, such as quad stands. The joints 260 may be assembled by retrieving a joint from the bins using a catwalk machine, raising the joint to a vertical position using the elevator, setting the joint into a mouse hole, and engaging slips of the mouse hole spider. A second joint may then be hoisted over the first joint in a similar fashion. The power tongs may engage the joints and make-up a threaded connection between the two joints. This process may be repeated until a quad stand is assembled. The racking arm may then retrieve the assembled stand and the bridge crane may lift the racking arm to store the stand in the racking board.
Once the drill string has drilled to an end of a capable depth, the top drive may raise the drill string and set the drill string in a spider of a rotary table in the drill floor. The top drive may then be disconnected from the drill string and raised to a height proximate to the racking arm. The racking arm may retrieve the stand from the racking board and the bridge crane may lift the racking arm and the stand and hold the stand proximate to the top drive. The top drive may then engage the stand with a backup tong, and connect the stand to the quill. The top drive may then lower the stand to an end of the drill string. A second set of power tongs may engage the stand and make-up a threaded joint between the stand and the drill string. While the top drive is drilling with the extended drill string, the handling system 250 may be assembling and storing more stands as needed.
The drill floor 215 may further include other accessories, such as a hydraulic power unit, an air compressor, a mud logger building, a measurement while drilling (MWD) building, a choke manifold, and a standpipe manifold.
FIG. 3E is a plan view of the process level 220. FIG. 3F is a plan view of the lower level 225. The mud treatment system 255 may include a process tank, one or more shale shakers, a degasser, a desander, a desilter, a centrifuge, one or more feed pumps, an agitator, one or more trip tanks, and a gas separator. The process tank may include a sand compartment, a degas compartment, a desand compartment, a desilt compartment, and a clean mud compartment.
FIG. 3G is a plan view of the base 230. The base 230 may include a frame operably coupled to the skidding system 275. The skidding system may include one or more linear actuators and one or more skid beams. Each linear actuator may be connected to the base and a respective skid beam. Each linear actuator may be hydraulic, such as a piston and cylinder assembly, or electric, such as a motor and ball-screw assembly. The skid beams may rest on the main deck 105p in drilling mode. The base 230 may be slidable on the skid beams by operation of the linear actuators.
Additionally, the MODU 100 may include riser pipe for assembly and deployment of a riser string (see FIG. 2C). Further, the MODU may include production tubing (not shown) for assembly and deployment of a production tubing string. Further, the MODU may include a subsea wellhead and a subsea production tree (a.k.a. Christmas tree), such as a vertical or horizontal tree for deployment to the wellhead. The MODU 100 may prepare, drill, and complete a subsea wellbore. Alternatively, the MODU 100 may be deployed for workover of an existing subsea wellbore.
FIG. 4A is a plan view of the mezzanine deck 105z. The mezzanine deck 105z may include crew quarters and crew facilities, such as a washroom, toilets, locker room, and utility room.
FIG. 4B is a plan view of the machinery deck 105m. The machinery deck 105m may include a diesel/electric power system including diesel drivers and electric generators and a plurality of electrical control panels. The machinery deck may further include one or more mud pumps and one or more mud tanks, one or more reserve mud tanks, pre-load/ballast tanks, dry mud containers, dry cement containers, one or more cement blenders, and one or more cement pumps. The machinery deck may further include additional crew quarters and facilities, such as a galley, mess hall, cinema, and gym.
FIG. 4C is a plan view of the tank deck 105t. The tank deck 105t may include mud pit cellar tanks, drilling water tanks and fuel oil tanks. The tank deck may further include additional pre-load/ballast tanks. Further, electrical cables and piping (not shown) may extend between the decks 105p,z,m,t and the DES 150 for transferring fluids and electricity.
FIG. 4D is a plan view of a lower level 130l of the cabin 130. FIG. 4E is a plan view of an upper level 130u of the cabin 130. FIG. 4F is a plan view of the helipad. The cabin 130 may include crew quarters, a hospital, offices, a lounge, an emergency generator, a utility room, a control house, a conference room, a waiting area for the helipad, and an HVAC system.
FIGS. 5A-D illustrate the DES 150 being deployed in tender assist drilling mode. FIG. 5A is a plan view of the main deck 105p. In tender assist drilling mode, the DES 150 may be located on an adjacent production platform 500. The MODU 100 may be connected to the platform 500 as if the DES were in drilling mode, supplying drilling fluid and electricity to the DES 150. The MODU 100 may be connected using one or more hawsers and one or more umbilicals. Tender assisted drilling may be useful for workover of existing wells having the existing production platform 500 in place and connected to a subsea production tree (not shown). Otherwise, the existing production platform 500 would have to be disconnected from the subsea production tree and moved so that the MODU 100 could be moved over the production tree and connected to the tree. To move the DES 150 from the MODU 100 to the platform 500, the DES 150 may be disassembled as discussed above. The DES 150 may be disassembled prior to towing the MODU 100 to the platform 500. The MODU 100 may further include a telescopic personnel bridge 505 rotatable about the main deck 105p for deployment to the platform 500.
FIG. 5B is a plan view of the MODU 100 connected to a platform 500. FIG. 5C is a profile view of the DES 150 having been hoisted from the MODU 100 and set on the platform 500. FIG. 5D is a profile view of the DES 150 in place over the platform's moonpool. FIG. 5E is a perspective view of the MODU 100 in tender assist drilling mode. The MODU 100 may be moored and/or dynamically positioned in place adjacent the platform 500. The telescopic bridge 505, hawsers, and umbilicals may be deployed to the platform 500. The base 230, drilling floor 215, process level 220, and lower level 225 may then be hoisted by the crane 120a onto the platform 500. The crane 120a may include an elevator and a tower so that the crane boom may be raised on the tower to accommodate height difference between the MODU 100 and the platform 500. The derrick 205 may then be hoisted by the crane 120a onto the platform 500. The DES 150 may then be assembled. The DES 150 may be assembled on an edge of the platform 500 and skidded to the platform's moonpool using the skidding system 275. The drill pipe 260 may be hoisted from the MODU to the platform and loaded into the rig's bins.
Alternatively, instead of the drilling rig, the MODU 100 may include a J-lay tower (not shown) pivotably mounted to the main deck over the moonpool. The J-lay tower may be transported in a horizontal position and then raised to a vertical or near-vertical position for deployment of a subsea pipeline. Alternatively, the MODU 100 with the J-lay tower may be used to lay tendons for a tension leg platform.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
