AU2012217700B2 - Surface close proximity wells - Google Patents

Abstract

An offshore oil production system, comprising a structure in a body of water, having a portion extending above a surface of the body of water; a first surface wellhead located at a top of the body of water; a second surface wellhead located at a top of the body of water; a first wellhead located at a bottom of the body of water; a second wellhead located at a bottom of the body of water; a first riser extending from the first wellhead to the first surface wellhead; and a second riser extending from the second wellhead to the second surface wellhead; wherein the first surface wellhead is a distance of less than about 12 feet from the second surface wellhead.

Description

1 SURFACE CLOSE PROXIMITY WELLS Field [0001] The present invention is directed to multiple risers located in close proximity for deepwater applications. Background Art [0002] U.S. Patent Applications 61/407,084, refiled as US 13/881,630 and published as US 2013 0240215, discloses an offshore oil production system, comprising a structure in a body of water, having a portion extending above a surface of the body of water; a wellhead located at a bottom of the body of water; a riser extending from the wellhead to the portion extending above the surface; a primary wellbore extending into a subsea formation beneath the body of water; and at least two secondary wellbores extending further into the subsea formation beneath the body of water and beneath the primary wellbore. This U.S. Patent Application is herein incorporated by reference in its entirety. [0003] U.S. Patent Application 61/407,086, refiled as US 13/881,604 and published as US 2013 0213663 discloses an offshore oil production system, comprising a structure in a body of water, having a portion extending above a surface of the body of water; a surface wellhead located at a top of the body of water; a first wellhead located at a bottom of the body of water; a second wellhead located at a bottom of the body of water; a first riser extending from the first wellhead to the surface wellhead; and a second riser extending from the second wellhead to the surface wellhead. This U.S. Patent Application is herein incorporated by reference in its entirety. [0004] U.S. Patent Application Publication 2010/0126729 discloses systems and methods usable to operate on a plurality of wells through a single main bore. One or more chamber junctions are provided in fluid communication with one or more conduits within the single main bore. Each chamber junction includes a first orifice communicating with the surface through the main bore, and one or more additional WO 2012/112668 PCT/US2012/025216 orifices in fluid communication with individual wells of the plurality of wells. Through the chamber junctions, each of the wells can be individually or simultaneously accessed. A bore selection tool having an upper opening and at least one lower opening can be inserted into the chamber junction such that the one or more lower openings align with 5 orifices in the chamber junction, enabling selected individual or multiple wells to be accessed through the bore selection tool while other wells are isolated from the chamber junction. U.S. Patent Application Publication 2010/0126729 is herein incorporated by reference in its entirety. [0005] U.S. Patent 5,775,420 discloses a dual completion for gas wells including a dual 10 base with a primary hanger incorporated in the base. Primary and secondary coiled tubing strings extend through the base at a downwardly converging angle of 2 DEG or less. The dual base is mounted on an annular blowout preventer. At the top of the annular blowout preventer is a tubing centralizer that aligns the two tubing strings parallel to one another. The blowout preventer has two side ports below the bladder 15 allowing the operator to produce gas from the annulus, to flare gas to atmosphere or to pump in kill fluid in the event of an emergency. The alignment of the tubing strings allows production recorders to be run in either string. U.S. Patent 5,775,420 is herein incorporated by reference in its entirety. [0006] U.S. Patent 3,601,196 discloses a method for perforating in a dual, parallel pipe 20 string tubingless well. A crossover passage or port connects these pipe strings. Each pipe string is provided with a landing nipple at about the same depth below the crossover port. A radioactive source tool, which includes a radioactive pill for transmitting radiation in angular directions and a seating member for seating the radioactive source tool in the landing nipple arranged in one of the pipe strings, is 25 pumped through the one pipe string until the seating member is landed in the landing nipple. The radioactive pill is suspended from the seating member a predetermined distance which is approximately the level at which it is desired to perforate. A perforating assembly, which includes a directional perforating gun, a directional radiation detector, a radioactivity-sensitive gun-firing mechanism including a source of 30 electrical power for causing actuation of the perforating gun, a rotation device for causing the perforating gun to rotate, a seating member for seating the perforating assembly in the landing nipple arranged in the other pipe string, and a locomotive 2 3 device for moving the perforating assembly through the other pipe string, is then pumped through the other pipe string until the seating member lands in the landing nipple. The detector of the perforating assembly is suspended a predetermined distance from the seating member so that it is positioned at the same level as the radioactive pill in the adjacent pipe string. The firing mechanism utilizes a switch which is actuated when the radioactive count detected by the radiation detector reaches a predetermined level. The directional gun is aimed so as to fire in a predetermined angular direction when the directional detector is facing the radioactive pill. The perforating assembly is rotated by circulating fluid in the pipe strings. After the perforating gun has fired, the perforating assembly is removed from the other pipe string. The radioactive source tool is then removed from the one pipe string. The perforating gun may be reloaded and the perforating procedure repeated at a different level in the well bore after repositioning the radioactive source tool and perforating assembly. U.S. Patent 3,601,196 is herein incorporated by reference in its entirety. [0007] U.S. Patent 7,066,267 discloses a splitter assembly is positioned downhole within a conductor for separating two or more tubular strings placed within the conductor. A splitter housing may include a first bore and a second bore for separating a first well from a second well, and a plug positioned in one of the bores including a top face sloping downwardly toward the other bore. One or more guide plates secured to the splitter housing and positioned above the plug guide a bit or other tool toward one of the first bore and the second bore. The splitter housing may be positioned along the conductor after the conductor is jetted in place. According to the method, the plug in one of the bores is retrieved after a casing is run in one well, so that the second bit and the second casing will pass through the bore which previously included the plug. U.S. Patent 7,066,267 is herein incorporated by reference in its entirety. OBJECT [0007a] It is an object of the invention to improve upon the prior art at least to an extent or to provide an alternative thereto. SUMMARY OF INVENTION One aspect of the present disclosure provides an offshore oil production system, comprising a structure in a body of water, having a portion extending above a surface of the body of water 4 and having a wellbay slot; a first surface wellhead located at a top of the body of water; a second surface wellhead located at a top of the body of water; a first wellhead located at a bottom of the body of water; a second wellhead located at a bottom of the body of water; a first riser extending from the first wellhead to the first surface wellhead; and a second riser extending from the second wellhead to the second surface wellhead; wherein the first surface wellhead is a distance of less than about 12 feet from the second surface wellhead, wherein the offshore oil production system further comprises a tensioner connected to the structure in the body of water, and connected to both the first riser and the second riser, and wherein the first riser and the second riser are located in the same wellbay slot on the structure. [0008] Advantages of preferred embodiments of the disclosure include one or more of the following: [0010] Reduced size tree deck on an offshore structure; [0011] Reduced size offshore structure; and/or [0012] Increased number of risers connected to an offshore structure. BRIEF DESCRIPTION OF DRAWINGS [0012a] A preferred embodiment of the present invention will now be described, by way of an example only, with reference to the accompanying drawings wherein: [0013] FIG. 1A is a schematic diagram of a close proximity wellhead system configured with a tension leg platform in accordance with embodiments disclosed herein. [0014] FIG. 1B is a cross-sectional view of a close proximity wellhead system m accordance with embodiments disclosed herein. [0015] FIG. 2A is a schematic diagram of a close proximity wellhead system configured with a spar platform in accordance with embodiments disclosed herein.

4a [0016] FIG. 2B is a cross-sectional view of a close proximity wellhead system m accordance with embodiments disclosed herein. [0017] FIG. 3 is a top view of a conventional tree deck of a spar platform having single wellheads disposed thereon. [0018] FIG. 4 is a top view of a tree deck on a spar platform having close proximity wellhead systems in accordance with embodiments disclosed herein. [0019] FIG. 5 is a top view of a tree deck on a spar platform having close proximity wellhead systems in accordance with embodiments disclosed herein. DETAILED DESCRIPTION [0020] In one aspect, embodiments disclosed herein relate to a close proximity wellhead system. More specifically, embodiments disclosed herein relate to a close proximity wellhead system that may be used in deepwater applications with, for example, a WO 2012/112668 PCT/US2012/025216 tension leg platform (TLP) or a spar platform, or other fixed or floating structures as are known in the art. [0021] Figures la & lb: [0022] Referring to Figure la, a schematic diagram of a TLP close proximity wellhead 5 system in accordance with embodiments disclosed herein is shown. In this embodiment, a close proximity wellhead system 110 may be connected to a TLP 100 to allow fluid to flow from multiple subsea wellheads (e.g., subsea wellheads 140 and 150) to TLP 100. Close proximity wellhead system 110 includes a first wellhead 1 10a and a second wellhead 1 Ob mounted on a platform 1 Oc. 10 [0023] In one embodiment, TLP 100 may be an offshore floating platform above sea level 181. Further, TLP 100 may be used for production of fluids in deepwater applications and may be vertically tethered to seafloor 180 by tethers or tendons (not shown) to mitigate vertical and/or horizontal movement of TLP 100. The tethers or tendons may have a high axial stiffness and a low elasticity to mitigate any vertical 15 movement of TLP 100. However, those having ordinary skill in the art will appreciate that the tethers or tendons may be any type of structure disposed between the TLP and the sea floor that may mitigate vertical and/or horizontal movement of the TLP. [0024] TLP 100 may include multiple decks and levels (e.g., a main deck 102, a weather deck 104, a rig skid base 105, and a drill floor 109) from which to secure and suspend 20 drilling and production risers (e.g., a drilling riser 108 and production risers 124 and 134). In this embodiment, drilling riser 108 is suspended by a drilling riser tensioner 107 at rig skid base 105, below drill floor 109. However, those having ordinary skill in the art will appreciate that a riser may be suspended by a tensioner at other various positions on a TLP. Drilling riser tensioner 107 may be used to prevent outer drilling 25 riser 108 from experiencing extreme forces that may result from vertical movement of TLP 100 due to currents, storms, etc. For example, drilling riser tensioner 107 may prevent drilling riser 108 from buckling if TLP 100 were to move downward. Similarly, drilling riser tensioner 107 may prevent outer drilling riser 108 from experiencing extreme tension forces if TLP 100 were to move upward. Although, in 30 this embodiment, TLP 100 is shown having a drilling riser and a drilling riser tensioner (e.g., drilling riser 108 and drilling riser tensioner 107) separate from a production riser and a production riser tensioner (e.g., production risers 124 and 134 and production 5 WO 2012/112668 PCT/US2012/025216 riser tensioner 117), those having ordinary skill in the art will appreciate that separate drilling risers and tensioners and production risers and tensioners may not be necessary. For example, once drilling has been completed, a drilling riser may be removed from a riser tensioner and removed from a TLP and one or more production risers may be 5 configured to engage with the tensioner and may replace the drilling riser in the TLP. [0025] As shown in Figure la, a blowout preventer (BOP) stack 106 is connected to outer drilling riser 108. In this embodiment, BOP stack 106 may be configured to seal, control, and monitor an oil or gas well (not shown). BOP stack 106 may also be configured to control pressure changes within outer drilling riser 108, which may 10 prevent a outer drilling riser 108 or drilling or production fluid from being blown out of an oil or gas well. One having ordinary skill in the art will appreciate that BOP stack 106 may include one or more ram-type BOPs, annular BOPs, or combinations thereof. Although BOP stack 106 is shown connected to outer drilling riser 108, those having ordinary skill in the art will appreciate that a BOP stack may be connected to several 15 different tubular members. For example, a BOP stack may be connected to drill pipe, production pipe, or well casing. [0026] As shown in Figures la and 1b, close proximity wellhead system 110 is suspended by a production riser tensioner 117 at main deck 102, below weather deck 104. However, those having ordinary skill in the art will appreciate that a close 20 proximity wellhead system may be positioned at various other positions on a TLP. For example, production riser tensioner 117 may be used to prevent production risers 124 and 134 from experiencing extreme forces that may result from vertical movement of TLP 100. Further, production riser tensioner 117 may prevent production risers 124 and 134 from buckling if TLP 100 were to move downward. Similarly, production riser 25 tensioner 117 may prevent production risers 124 and 134 from experiencing extreme tension forces if TLP 100 were to move upward. Those having ordinary skill in the art will appreciate that a tensioner may be any apparatus or mechanism that may control the vertical position of a tubular member. For example, a tensioner may be a system of hydraulically controlled cylinders that may be operated and adapted to control the 30 vertical position of a tubular member. [0027] As shown in Figure 1b, close proximity wellhead system 110 includes first wellhead 1 Oa connected to production riser 134, and second wellhead 1 Ob connected 6 WO 2012/112668 PCT/US2012/025216 to production riser 124. First wellhead 1 10a and second wellhead 1 10b are mounted on platform 1 10c, which in turn is located on deck 102. Production riser 124 and production riser 134 share the same slot and are connected to tensioner 117. Close proximity wellhead system 110 includes two or more wellheads 1 10a and 1 Ob, located 5 on a single platform 1 Oc, and connected to a single tensioner 117. [0028] Close proximity wellhead system 110 allows two or more risers to connect to a two or more close proximity wellheads installed on a single platform and connected to a single tensioner. The risers extend downward through a single slot and toward multiple subsea wellheads (e.g., subsea wellheads 140 and 150). Although close proximity 10 wellhead system 110 is shown connected to two risers, production risers 124 and 134, those having ordinary skill in the art will appreciate that a close proximity wellhead system may be connected to two or more risers sharing the same slot. For example, a close proximity wellhead system may be connected to three or four risers, which may be used to produce fluid from multiple subsea wellheads. 15 [0029] As shown in Figure 1, subsea wellheads 140 and 150 are located on seafloor 180 and may provide a suspension point and pressure seals for tubular members, such as casing strings, pipes, or risers (e.g., production risers 124 and 134). As fluids are produced from the formation through subsea wellheads 140 and 150, production risers 124 and 134 allow the production fluids to travel from the subsea wellheads 140 and 20 150 to the wellheads 1 Oa and 1 Obb TLP 100. [0030] Figures 2a & 2b: [0031] Referring to Figures 2a and 2b, a schematic diagram of a close proximity wellhead system configured with a spar platform in accordance with embodiments disclosed herein is shown. In this embodiment, a close proximity wellhead system 310 25 may be connected to a spar platform 300 to allow fluid to flow from multiple subsea wellheads (e.g., subsea wellheads 340 and 350) to a spar platform 300. In this embodiment, spar platform 300 may be an offshore floating platform at sea level 381. Further, spar platform 300 may include a counterweight 311 disposed within a main body 301 of spar platform 300, which may help stabilize spar platform 300. 30 Counterweight 311 of spar platform 300 may be filled with water or any other material known in the art and may assist in stabilizing spar platform 300 in offshore conditions. Further, mooring lines (not shown) may be connected to spar platform 300 and may 7 WO 2012/112668 PCT/US2012/025216 assist in anchoring spar platform 300 to the seafloor 380. Mooring lines may be flexible members that may connect spar platform 300 to the seafloor 380. Heave plates and buoyancy modules (not shown) may also be provided on body 301, as are known in the art. 5 [0032] Spar platform 300 may include multiple decks and levels (e.g., a drill floor 309 and a cellar deck 302) from which to secure and suspend drilling and production risers. In this embodiment, production risers 324 and 334 are suspended by a production riser tensioner 317 at cellar deck 302, below drill floor 309. However, those having ordinary skill in the art will appreciate that a riser may be suspended by a tensioner at other 10 various positions on a spar platform. Production riser tensioner 317 may be used to prevent production risers 324 and 334 from experiencing extreme forces that may result from vertical movement of spar platform 300. For example, production riser tensioner 317 may prevent production risers 324 and 334 from buckling if spar platform 300 were to move downward. Similarly, production riser tensioner 317 may prevent production 15 risers 324 and 334 from experiencing extreme tension forces if spar platform 300 were to move upward. [0033] Further, as shown in Figures 2a and 2b, production risers 324 and 334 exit main body 301 of spar platform 300 at a keel point 319 and connect to subsea wellheads 340 and 350, respectively. Subsea wellheads 340 and 350 are situated on seafloor 380 and 20 may provide a suspension point and pressure seals for tubular members, such as casing strings, pipes, or risers (e.g., production risers 324 and 334). As fluids are produced from the formation through tubings (not drawn) to the subsea wellheads 340 and 350, production risers 324 and 334 may allow the production fluids to travel through the tubings from the subsea wellheads 340 and 350 to the surface (e.g., close proximity 25 wellhead system 310 on spar platform 300). [0034] As shown in Figure 2b, close proximity wellhead system 310 includes first wellhead 310a connected to production riser 334, and second wellhead 310b connected to production riser 324. First wellhead 310a and second wellhead 310b are mounted on the same wellbay slot on platform 310c, which in turn is located on deck 302. 30 Production riser 324 and production riser 334 share the same wellbay slot and are connected to tensioner 317. Close proximity wellhead system 310 includes two or more 8 WO 2012/112668 PCT/US2012/025216 wellheads 310a and 3 1Ob, located on a single platform 310c, sharing the same wellbay slot, and connected to a single tensioner 317. [0035] Close proximity wellhead system 310 allows two or more risers to connect to a two or more close proximity wellheads installed on a single platform sharing the same 5 wellbay slot and connected to a single tensioner. The risers extend downward toward multiple subsea wellheads (e.g., subsea wellheads 340 and 350). Although close proximity wellhead system 310 is shown connected to two risers, production risers 324 and 334, those having ordinary skill in the art will appreciate that a close proximity wellhead system may be connected to two or more risers. For example, a close 10 proximity wellhead system may be connected to three or four risers, which may be used to produce fluid from multiple subsea wellheads. [0036] As shown in Figure 2a, subsea wellheads 340 and 350 are located on seafloor 380 and may provide a suspension point and pressure seals for tubular members, such as casing strings, pipes, or risers (e.g., production risers 324 and 334). As fluids are 15 produced from the formation through subsea wellheads 340 and 350, production risers 324 and 334 allow the production fluids to travel from the subsea wellheads 340 and 350 to the wellheads 310a and 3 1Ob. [0037] Figure 3: [0038] Referring to Figure 3, a top view of a conventional tree deck of a spar platform 20 having single wellheads disposed thereon is shown. Specifically, Figure 3 shows a conventional tree deck 474 of a spar platform 402 having thirty-two single wellheads 412 disposed thereon, each configured to engage with a single riser (not shown). Each riser may be configured to connect with a single subsea wellhead (not shown). As such, the tree deck 474 of spar platform 402 may be configured to connect with thirty-two 25 subsea wellheads. A tree deck (e.g. tree deck 474) may be any deck on an offshore platform (e.g., spar platform 402) in which wellheads and/or BOP trees (e.g. single wellheads 412) are located. [0039] Figure 4: [0040] Referring now to Figure 4, a top view of a tree deck on a spar platform having 30 close proximity wellheads in accordance with embodiments disclosed herein is shown. Specifically, Figure 4 shows a top view of a tree deck 572 on a spar platform 500 9 WO 2012/112668 PCT/US2012/025216 having sixteen close proximity wellhead systems 510, each including two wellheads right next to each other, where each of the wellheads is configured to engage with a riser. As discussed above, each riser may be configured to connect with a single subsea wellhead. As such, the tree deck 572 of spar platform 500 may be configured to 5 connect with thirty-two subsea wellheads. As discussed above, each two wellheads may be mounted on a single platform and connected to a single tensioner and share a single wellbay slot. [0041] Referring generally to Figures 3 and 4, although the number of close proximity wellhead systems 510 (sixteen) may be half of the number of wellheads 412 (thirty 10 two), both tree decks 572 and 474 may connect to the same number risers (thirty-two) and, thus, connect to the same number of subsea wellheads (thirty-two). Because the number of close proximity wellhead systems 510 is less than the number of wellheads 412, as shown in Figures 4 and 3, respectively, the surface area of tree deck 572 may be less than the surface area of tree deck 474. As such, the overall size of spar platform 15 500 may be smaller than the overall size of spar platform 402. Although Figures 3 and 4 are shown having thirty-two wellheads and sixteen wellhead systems, respectively, those having ordinary skill in the art will appreciate that the number of wellheads on an offshore platform is not limited to these quantities. For example, an offshore platform may include more or less than the number of wellheads described above. 20 [0042] Although the number of subsea wellheads that may be accessed by risers may be the same (e.g. thirty-two) in Figures 3 and 4, the surface area required for tree deck 572 having close proximity wellhead systems 510 may be less than the surface area required for tree deck 474 having wellheads 412. Accordingly, the surface area required for a tree deck on a spar platform may be reduced by decreasing the riser spacing between 25 each pair of wellheads on the tree deck. Although Figures 3 and 4 refer to configurations of a tree deck on a spar platform, those having ordinary skill in the art will appreciate that increasing the riser density that may be configured with each wellhead may reduce the surface area required for a tree deck on any deepwater platform. For example, increasing the number of risers that may be configured with 30 each wellhead may reduce the surface area required for a tree deck on a TLP. 10 WO 2012/112668 PCT/US2012/025216 [0043] Figure 5: [0044] Referring now to Figure 5, a top view of a tree deck 672 on a spar platform 600 having close proximity wellheads in accordance with embodiments disclosed herein is shown. Specifically, Figure 4 shows a top view of a tree deck 672 on a spar platform 5 600 having eight tree platforms 610a - 610h, each of the tree platforms aligned with a wellbay slot on the spar platform 600. Each tree platform includes two wellheads right next to each other, such as platform 610a including a first wellhead 612 and second wellhead 614, where each of the wellheads is configured to engage with a riser. As discussed above, each riser may be configured to connect with a single subsea wellhead. 10 As such, the tree deck 572 of spar platform 500 may be configured to connect with sixteen subsea wellheads. As discussed above, each two wellheads may be mounted on a single platform 610a - 610h and connected to a single tensioner and share a single wellbay slot. Platform 610i is a larger platform, and is being used as a drilling platform and houses blowout preventer 616. At the conclusion of drilling operations, platform 15 610i may also be used to house one or more wellheads like the other platforms. [0045] Spacing 618 between a center of the production pipe in wellheads 612 and 614 may be from about 1 to about 10 feet, for example from about 2 to about 8 feet, or from about 3 to about 7 feet. [0046] Illustrative Embodiments: 20 In one embodiment, there is disclosed an offshore oil production system, comprising a structure in a body of water, having a portion extending above a surface of the body of water; a first surface wellhead located at a top of the body of water; a second surface wellhead located at a top of the body of water; a first wellhead located at a bottom of the body of water; a second wellhead located at a 25 bottom of the body of water; a first riser extending from the first wellhead to the first surface wellhead; and a second riser extending from the second wellhead to the second surface wellhead; wherein the first surface wellhead is a distance of less than about 12 feet from the second surface wellhead. [0047] In some embodiments, the system also includes a first wellbore extending further 30 into a subsea formation beneath the body of water and beneath the first wellhead, and further comprising a second wellbore extending further into the subsea formation beneath 11 WO 2012/112668 PCT/US2012/025216 the body of water and beneath the second wellhead. In some embodiments, the system also includes a production tubing within each of the first wellbore and the second wellbore. In some embodiments, each production tubing extends from the first wellbore to the first surface wellhead and from the second wellbore to the second surface 5 wellhead. In some embodiments, the system also includes a tensioner connected to the structure in the body of water, and connected to both the first riser and the second riser. In some embodiments, the first riser and the second riser are located in a single wellbay slot on the structure. In some embodiments, the first wellbore further comprises a casing string. In some embodiments, the first surface wellhead comprises a first surface tree, 10 and wherein the second surface wellhead comprises a second surface tree. In some embodiments, the structure comprises a tension leg platform. In some embodiments, the structure comprises a spar platform. In some embodiments, a center of the first surface wellhead is a distance of from about 2 to about 10 feet from a center of the second surface wellhead. 15 [0048] Embodiments described herein may provide for one or more of the following advantages. In accordance with the present disclosure, production fluids may be produced from multiple subsea wellheads to a close proximity wellhead system disposed on a floating platform, such as a TLP or spar platform. However, those having ordinary skill in the art will appreciate that the close proximity wellhead system, 20 described above, may be adapted to be used on floating platforms other than a TLP or spar platform. Space for close proximity wellheads may be limited on an offshore platform for deepwater fluid production applications, as construction and maintenance costs may increase as the size of the offshore platform increases. Further, constructing and maintaining the offshore platforms may also become more costly as the size of the 25 offshore platform increases. The close proximity wellhead system described above may reduce the number of floating offshore platforms needed for producing fluids in deepwater conditions, because the close proximity wellhead system may allow fluids to be produced from multiple subsea wellheads to a single close proximity wellhead on an offshore platform. Alternatively, any extra space that may be available on existing 30 offshore platforms as a result of the close proximity wellhead system, described above, may be used for other equipment and processes. 12 WO 2012/112668 PCT/US2012/025216 [0049] While the present invention has been described in terms of various embodiments, modifications in the apparatus and techniques described herein may be made without departing from the concept of the present invention. It should be understood that embodiments and techniques described in the foregoing are illustrative and are not 5 intended to limit the scope of the invention. 13

Claims (9)

1. An offshore oil production system, comprising: a structure in a body of water, having a portion extending above a surface of the body of water and having a wellbay slot; a first surface wellhead located at a top of the body of water; a second surface wellhead located at a top of the body of water; a first wellhead located at a bottom of the body of water; a second wellhead located at a bottom of the body of water; a first riser extending from the first wellhead to the first surface wellhead; and a second riser extending from the second wellhead to the second surface wellhead; wherein the first surface wellhead is a distance of less than about 12 feet from the second surface wellhead, wherein the offshore oil production system further comprises a tensioner connected to the structure in the body of water, and connected to both the first riser and the second riser, and wherein the first riser and the second riser are located in the same wellbay slot on the structure.

2. The system of claim 1, further comprising a first well bore extending further into a subsea formation beneath the body of water and beneath the first wellhead, and further comprising a second wellbore extending further into the subsea formation beneath the body of water and beneath the second wellhead.

3. The system of claim 2, further comprising a production tubing within each of the first wellbore and the second wellbore.

4. The system of claim 3, wherein each production tubing extends from the first wellbore to the first surface wellhead and from the second wellbore to the second surface wellhead.

5. The system of claim 2, wherein the first well bore further comprises a casing string.

6. The system of claim 1, wherein the first surface wellhead comprises a first surface tree, and wherein the second surface wellhead comprises a second surface tree.

7. The system of claim 1, wherein the structure comprises a tension leg platform. 15

8. The system of claim 1, wherein the structure comprises a spar platform.

9. The system of claim 1, wherein a center of the first surface wellhead is a distance of from about 2 to about 10 feet from a center of the second surface wellhead. Shell Internationale Research Maatschappij B.V. Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON