US3657895A

US3657895A - Offshore platform

Info

Publication number: US3657895A
Application number: US114809A
Authority: US
Inventors: Rex V Phelps
Original assignee: Warren Petroleum Corp
Current assignee: Chevron USA Inc; Warren Petroleum Corp
Priority date: 1971-02-12
Filing date: 1971-02-12
Publication date: 1972-04-25
Anticipated expiration: 1989-04-25

Abstract

A platform for offshore oil wells having a curbing around the periphery of the deck of the platform. The deck slopes downwardly from the curbing into a central opening to drain all oil spilled on the deck into the opening. A cylindrical sleeve open at its lower end to admission of water extends downwardly, preferably to the marine floor, from the opening. The diameter of the sleeve is at least as large, and preferably in the range of 20 to 50 feet, as the opening whereby all oil or other liquids draining into the opening is confined within the sleeve. The platform can be entirely of steel, steel framework mounted on a concrete substructure, or of concrete modules assembled at the well site.

Description

United States Patent Phelps [151 3,657,895 [451 Apr. 25, 1972 [54] OFFSHORE PLATFORM Rex V. Phelps, Tulsa, Okla.

Warren Petroleum Corporation, Tulsa, Okla.

[22] Filed: Feb. 12, 1971 [I1] Appl.No.: 114,809

[72] Inventor:

[73] Assignee:

Primary Examiner-Jacob Shapiro Attorney-Meyer Neishloss, Deane E. Keith and Paul L. Tillson ABSTRACT A platform for offshore oil wells having a curbing around the periphery of the deck of the platform. The deck slopes downwardly from the curbing into a central opening to drain all oil spilled on the deck into the opening, A cylindrical sleeve open at its lower end to admission of water extends downwardly, preferably to the marine: floor, from the opening. The diameter ofthe sleeve is at least as large, and preferably in the range of 20 to 50 feet, as the opening whereby all oil or other liquids draining into the opening is confined within the sleeve. The platform can be entirely of steel, steel framework mounted on a concrete substructure, or of concrete modules assembled at the well site.

8 Claims, 4 Drawing Figures PATENTEDAPR 25 m2 SHEET 2 BF v GD INVENTOI? REX M PHELPS OFFSHORE PLATFORM This invention relates to offshore oil wells and more particularly to a platform structure for reducing pollution of water by such wells.

An important part of the world's production of oil and gas is derived from offshore wells. It can be expected that the importance of production from such wells will increase in the future because exploration of the most promising areas for oil and gas has been much more extensive on land sites than offshore. With the increase in offshore production that has already been experienced, there has been a serious increase of pollution of the ocean by oil spills at offshore wells.

The contamination of ocean water with oil from wells in some instances has resulted from leaks around the casing when there are very shallow productive formations penetrated by the well. Another source of oil spills has been leakage from production equipment on platforms after a well has been placed on production. Still another source of oil contamination of water is blowouts that may occur during the drilling of wells.

Several methods have been used in attempts to reduce contamination of the ocean resulting from oil spills at offshore wells. One method has been to provide floating barriers to confine the oil to a limited area and to skim the oil from the surface of water within the confined area. Another method has been to spray the oil with surfactants to disperse the oil. In some instances, the damage to marine life caused by the surfactants has been more severe than the damage caused by the oil spill.

This invention resides in a platform for offshore wells in which a curbing around the periphery of the platform contains oil spilled onto the deck of the platform and the deck of the platform slopes downwardly from the curbing to an opening in the platform surrounding the well. A sleeve of large diameter extends downwardly from the opening to confine within the sleeve all oil draining from the deck into the opening. The sleeve preferably extends downwardly to the ocean floor but is provided with openings allowing flow of seawater into the lower end of the sleeve whereby there is only a small pressure differential across the sleeve even though the platform is in water 200 to 600 or more feet deep.

In the drawings:

FIG. 1 is a diagrammatic view partially in vertical section of a permanent type steel platform constructed in accordance with this invention with a drilling rig mounted on its deck.

FIG. 2 is a plan view of the platform illustrated in FIG. 1 with the drilling rig and associated equipment removed from the deck to show a suitable arrangement of wells.

FIG. 3 is a diagrammatic view partially in vertical section of a steel platform mounted on a concrete base.

FIG. 4 is a diagrammatic vertical sectional view of a concrete platform utilizing this invention.

Referring to FIG. 1, a platform indicated generally by reference numeral is shown with steel legs 12 secured to the ocean floor 14. The platform 10 illustrated in FIG. 1 is a permanent type platform, but this invention is not restricted to such a platform. A jack-up type platform which can be moved from the well site after completion of drilling can be used in place of the permanent type platform illustrated in FIG. 1. Legs 12 can be washed or driven into the ocean floor 14 at a distance adequate to provide firm support for the platform. Suitable means for anchoring the legs are provided, for example, by drilling downwardly through the legs 12 into the ocean floor, running casing through the legs and cementing the casing in place.

The legs 12 support the body 16 of the platform high enough above the water surface 18 to be above the level reached by waves during storms. Platform 10 is shown in FIG. 1 with a drilling rig 20, helicopter landing pad 22, mud handling equipment 24 and workmens quarters 26. It will be appreciated that such equipment mounted on the deck 30 of the platform is merely illustrative. Other equipment such as production equipment could be mounted on deck 30.

Extending around the entire periphery of deck 30 is a curb ing 32. It is only necessary that curbing 32 be high enough to prevent outward flow of oil spilled on deck 30 over the outer edge of the platform. A height of 1 foot is ordinarily sufficient, but the curbing may be high enough to serve as a fence around the deck. Deck 30 slopes downwardly from the curbing 32 in the direction indicated by the arrows in FIG. 2 to an opening 36 below drilling rig 20. A sleeve 38 is attached to deck 30 around the periphery of opening 36 and extends downwardly from the deck to the ocean floor 14. The purpose of sleeve 38 is to confine all oil draining from deck 30 into opening 36. While sleeve 38 has been shown to be of the same diameter as opening 36 in FIG. 1, it could be of substantially larger diameter than the opening in the deck, as is illustrated in FIG. 4. The diameter of sleeve 38 will be such that the sleeve can store a large volume of oil if leakage should occur around the casing of the well or at the wellhead above the deck 30 of platform 10. The diameter of the casing will depend in part, therefore, on the depth of water at the location of the platform which determines the maximum length of the column of oil that can be stored in the sleeve. It is contemplated that sleeve 38 will have a diameter in the range of 15 to 50* feet and preferably in the range of 20 to 40 feet.

In the embodiment illustrated in FIG. 1, sleeve 38 extends downwardly to the ocean 14 and is partially supported by the ocean floor. Framework 40 of platform 10 provides additional support for the sleeve. Openings 42 in the lower end of the sleeve a short distance above the ocean floor 14 allow flow of water into or from the lower end of the sleeve. The low pressure differential across the wall of sleeve 38 and the support of the sleeve by the framework 40 of the platform allow the sleeve to be constructed of thin metal sheet.

The platform 10 is shown in FIG. 1 with casing of a single well 44 extending downwardly through the sleeve from the drilling rig 20. It is contemplated that the opening 36 and sleeve 38 will have a diameter large enough to permit drilling of multiple wells 46 through a single sleeve as shown in FIG. 2 of the drawings. The wells 46 can be deflected outwardly in the conventional manner to tap the underground oil reservoir at the desired location spaced laterally from platform 10. Some offshore platforms are equipped to move the drilling rig from one location on the platform to another to allow drilling of additional wells from the platform and to aid in obtaining the desired spacing of wells. A sleeve similar to sleeve 38 should extend downwardly from each of the locations from which drilling is conducted if the full benefit of this invention is desired for all of the wells.

In the operation of this invention, a well 44 is drilled downwardly through the sleeve 38 by conventional drilling methods and completed in the usual manner. If the conductor I pipe or surface casing ordinarily used in ofishore wells should penetrate a productive formation before cementing of such pipe or casing had been completed or if high pressure zones should be encountered during subsequent drilling to cause leakage around the casing of the well, oil leaking around the casing will be confined within sleeve 38. As the amount of oil confined within the sleeve increases, water is displaced through openings 42. Oil within the sleeve 38 can be removed by a pump 47 extending downwardly within the sleeve to approximately the water level 18. The oil is pumped to suitable storage such as a storage barge or into storage tanks on the platform 10. Similarly, if there should be a failure of equipment mounted on the deck 30 resulting in an oil leak either during drilling or production, oil spilled on the deck is drained through opening 36 into sleeve 38 where it is confined. Oil spewing upwardly through well 44 during a blowout and landing on the deck 30 drains into sleeve 38. The increased hydrostatic pressure resulting from oil entering the upper end of sleeve 38 is relieved by displacement of water through openings 42. Because offshore platforms, particularly those for use in locations where the water is 200 or more feet deep are large and, for example, may have dimensions of approximately 275 X feet, a substantial amount of oil will fall on the platform during a blowout.

A platform indicated generally by reference numeral 50 similar to platform but mounted on a concrete substructure is illustrated in FIG. 3 of the drawings. Platform 50 is constructed of open steel framework to reduce the forces exerted on he structure by waves. The concrete substructure comprises a base module 52 having a bottom member 54 of enlarged diameter. Base module 52 is of annular shape with a central opening 56 extending downwardly through it. The central opening 56 is surrounded by a buoyancy chamber 58. Mounted on the upper surface of base module 52 is an intermediate module 60 which is also of annular shape with a central opening extending vertically through it providing a continuation of the central opening 56. The central opening of intermediate module 60 is surrounded by a buoyancy chamber 62. The upper surface of the intermediate module 60 is provided with sockets 64 to receive the legs of platform 50 and suitable anchoring means 66 to hold the legs in place. The platform illustrated in FIG. 3 has a single intermediate module 60. The number of intermediate modules used will depend on the depth of the water and will be such as to locate the upper surface of the top intermediate module at a depth of 50 to 100 feet readily accessible to divers and below wave action.

Platform 50 has a curbing 68 extending around its periphery and a deck 70 sloping downwardly from curbing 68 to an opening 71 in the deck. Extending downwardly from opening 71 in the sloping deck 70 of platform 50 is a sleeve 72. The sleeve extends downwardly into the central opening 56 through the concrete base structure. Suitable sealing means 74 are provided to prevent leakage between the outer surface of sleeve 72 and the wall of the central opening of the concrete substructure. A water inlet line 76 extends downwardly through sleeve 72 and the central opening 56 from below the water surface 78 tojust above the marine floor 80. Water inlet line 76 is turned upwardly at its lower end to prevent entry of any oil that might leak around the casing 82 of a well extending downwardly through sleeve 72.

The concrete substructure on which platform 50 is mounted will be floated into position at the desired site and then sunk into place. The bottom member 54 is of cellular construction and is provided with suitable valved openings 84 which can be opened to flood the cells and sink the bottom member. Similar water inlets 86 are provided to allow entry of water into the

buoyancy chambers

58 and 62. Vent lines 88 are connected to a compressed air source on a work barge to control the volume of water in the buoyancy chambers to control the rate of sinking of the base module and intermediate modules.

The platform indicated generally by reference numeral 90 in FIG. 4 is constructed of a plurality of concrete modules fabricated on shore, floated to the well site, and assembled at the well site by controlled sinking of the modules. Platform 90 includes a base module 92 having a bottom member 94 from the upper surface of which concentric cylindrical inner wall 96 and outer wall 98 extend. A top 100 across the upper ends of inner wall 96 and outer wall 98 closes the upper end of a buoyancy chamber 102 between those walls. The central opening 104 within the cylindrical inner wall 96 continues downwardly through the bottom member 94 to the marine floor 106. Bottom member 94 is of cellular construction and includes means indicated diagrammatically by opening 108 and compressed air supply line 110 for controlling the volume of water in the cells to control the buoyancy of the bottom member 94. An opening 112 in outer wall 98 and a compressed air line 114 similarly provide control of the volume of water in the buoyancy chamber 102. An opening 115 in inner wall 96 allows water to enter central opening 104 when the base module 92 is resting on marine floor 106.

Outer wall 98 of base module 92 extends upwardly beyond top 100 to form a socket at the upper end of the base module to receive an intermediate module 116. Intermediate module 116 also is an annular cylindrical structure which provides an upward continuation of central opening 104 when at rest on base module 92. A buoyancy chamber 118 between the inner and outer walls of the intermediate module 116 provides buoyancy for module 116. Intermediate module 116 has a water inlet 120 near its lower end and a compressed air supply line 122 near its upper end for control of the volume of water in the buoyancy chamber and, hence, the buoyancy, either positive or negative, of the intermediate module 116. The lower end of intermediate module 116 is suitably shaped to nest in the upper end of base module 92. Latching means 124 provide positive attachment of intermediate module 116 to base module 92.

A plurality of intermediate modules 116 are assembled to extend the platform to a level below the water surface 126 allowing a top module 128 to be floated above the upper surface of the uppermost intermediate module 116 and sunk onto that module. Top module is of annular shape to provide a continuation of central opening 104 up to an opening 130 in a deck 132 on the upper end of the top module 128, and is of a length such that deck 130 is located above the level reached by waves during storms. Deck 132 slopes downwardly from a curbing 134 around the periphery of the deck to the opening 130. In the structure illustrated in FIG. 4, the diameter of central opening 104 is substantially larger than the diameter of opening 130 to increase the volume of spilled oil that can be retained in the central opening. A pump 136 is installed in central opening 104, preferably substantially at the level of water surface 126, for removal of oil from the central opening 104.

Drilling or production equipment has been omitted from FIG. 4 because that equipment is only incidental to this invention and would merely complicate the drawings. Similarly,

air supply lines

118 and 122 have not been continued upwardly to the deck because to do so would only add detail not a part of this invention to the drawings. Casing 137 of a well is shown extending upwardly through opening 104.

In the assembly of platform 90, base module 92 is located over the well site and cables 138 from winches on work barges, not shown, are secured to the bottom member. Base module 92 is sunk, by controlled admission of water into the cells of the bottom member 94 and buoyancy chamber 102 to a depth allowing intermediate module 116 to be floated into position directly over the bottom module. The intermediate module 116 is sunk onto the base module, secured thereto, and the assembly of the base module 92 and intermediate module sunk to a level for receiving another intermediate module. Buoyancy of the assembled modules is controlled by the introduction of compressed air through line 114 into buoyancy chamber 102 and lines 122 into buoyancy chambers 118. The procedure is repeated until the base module 92 is resting on the ocean floor 106 and the structure is of proper length for installation of the top module 128. The structure illustrated in FIG. 4 and the method of constructing it are the subject of my application entitled Deep-Water Drilling, Production and Storage System filed concurrently with this application. The operation of the embodiment illustrated in FIG. 4 is the same as the operation of the other embodiments with the central opening 104 functioning in the same manner as sleeve 38 or sleeve 72. Oil collecting in the upper end of central opening 104 either as a result of a leak around casing 137 or a spill on deck 132 displaces water from the central opening 104 through opening 115, buoyancy chamber 102 and opening 112.

The platform herein described provides an ideal method and structure for preventing contamination of ocean water by oil spills during drilling of or production from wells in that the oil leaked is confined within the sleeve and has no chance to spread on open water. The oil in the sleeve is completely protected from wave action which greatly reduces the effectiveness of barriers in the open sea. Because the oil is confined within the sleeve in a deep column, there is no problem of skimming a thin layer of oil from the water. Moreover, there is no reason to use surfactants to disperse oil in the water.

The large diameter of the sleeve and of the central opening in the concrete substructure provides substantial space around the casing of wells extending downwardly through the sleeve. If there should be a leak around the casing below the level of the marine floor, oil moving upwardly around the casing from the leak flows readily into the sleeve, and is not directed outwardly beyond the substructure.

lclaim:

1. A platform for an offshore oil well in a body of water comprising support means engaging the marine floor for supporting a deck at a height over the water surface of the body of water above the level reached by waves, a curbing around the periphery of the deck, an opening extending downwardly through the deck for well casing, said opening having a size providing space around the well casing for the flow of liquids, a sleeve extending downwardly from the opening in the deck at least substantially to the marine floor, the opening in the sleeve being at least as large as the opening in the deck whereby oil draining through the opening in the deck is confined within the sleeve, and conduit means for allowing flow of water into and out of the lower end of the sleeve, said deck sloping downwardly from the curbing to the opening in the deck 2. A platform for offshore wells as set forth in claim 1 in which the sleeve has a diameter of to 50 feet.

3. Apparatus as set forth in claim 2 in which the sleeve extends downwardly all of the way to the marine floor.

4. Apparatus as set forth in claim 2 including pumping means for withdrawal of liquid from the sleeve at substantially the water level of the body of water.

5. A platform for offshore wells as set forth in claim 4 in which the support means is steel framework.

6. Apparatus as set forth in claim 4 in which the support means comprises a concrete substructure resting on the marine floor and having a central opening extending downwardly therethrough to the marine floor, steel framework mounted on the concrete substructure and extending upwardly to the deck, said sleeve extending downwardly into the central opening in the concrete substructure, and sealing means preventing leakage between the sleeve and the central opening in the concrete substructure.

7. Apparatus as set forth in claim 6 in which the conduit means comprise a pipe opening at its lower end into the central opening in the concrete substructure and extending up wardly through the opening to the sleeve and outwardly through the sleeve above the level of the concrete substructure.

8. An offshore platform as set forth in claim 4 in which the support means comprises a plurality of stacked annular concrete modules latched together to :form a column with a central opening extending therethrough from the deck to the marine floor, the central opening in the column constituting the sleeve extending downwardly from the opening in the deck.

Claims

1. A platform for an offshore oil well in a body of water comprising support means engaging the marine floor for supporting a deck at a height over the water surface of the body of water above the level reached by waves, a curbing around the periphery of the deck, an opening extending downwardly through the deck for well casing, said opening having a size providing space around the well casing for the flow of liquids, a sleeve extending downwardly from the opening in the deck at least substantially to the marine floor, the opening in the sleeve being at least as large as the opening in the deck whereby oil draining through the opening in the deck is confined within the sleeve, and conduit means for allowing flow of water into and out of the lower end of the sleeve, said deck sloping downwardly from the curbing to the opening in the deck.

2. A platform for offshore wells as set forth in claim 1 in which the sleeve has a diameter of 15 to 50 feet.

7. Apparatus as set forth in claim 6 in which the conduit means comprise a pipe opening at its lower end into the central opening in the concrete substructure and extending upwardly through the opening to the sleeve and outwardly through the sleeve above the level of the concrete substructure.

8. An offshore platform as set forth in claim 4 in which the support means comprises a plurality of stacked annular concrete modules latched together to form a column with a central opening extending therethrough from the deck to the marine floor, the central opening in the column constituting the sleeve extending downwardly from the opening in the deck.