Spar-type Floating Production Facility

Abstract

A production facility for underwater oil and gas wells including an onbottom platform to which flow and trunk lines are connected, a marine riser supporting the weight of the vertical portions of the flow and trunk lines, a spar section, and a superstructure which contains all of the fluid handling and processing equipment, controls, personnel requirements etc. When the production system according to the present invention is in assembled condition, the marine riser is vertically disposed on the platform and extends upwardly with the body of water in a substantially self-supporting manner. The spar section and superstructure, after having been separately floated into position over the marine riser, are connected thereto so that a portion of the spar section and all of the super structure component are disposed abode the surface of the water.

Description

In an attempt to locate new oil fields, an increasing amount of well drilling has been conducted at offshore locations, such for example, as off the coasts of Louisiana, Texas and California. Such offshore wells may be drilled from fixed platforms or from floating or submersible barges. At the conclusion of the well-drilling operation, deep water oil and gas wells have been completed by positioning in operative association therewith underwater production wellhead assemblies which are disposed underwater or close to the ocean floor. For an example of one such suitable assembly design, reference may be had to U.S. Pat. No. 3,064,735, issued Nov. 20, 1962, to R. J. Bauer et al.

In remote offshore locations, the storage and treatment of production fluid from underwater wells becomes a problem. In the case of offshore wells positioned close to the shoreline, the production fluid therefrom may be conveyed by pipeline directly to the shore whereupon it will be pumped to suitable storage and production facilities positioned on the land. In shallow water locations distant from the shoreline, it has been the practice to mount the production facility, including an oil and gas separator and/or metering or storage tanks on a platform positioned above the water as upon piles sunk in the ocean floor. In highly developed fields, rather large centralized production facilities for handling a number of wells have been established in this manner at a centrally located position among the wells. Individual production flowlines would then be run from the individual wells to extend to the centralized production facility where the production fluid would be gathered, separated and/or metered prior to transporting it to shore by means of tankers or through a pipeline.

In deep-water offshore locations however, it becomes impractical or impossible to establish fixed platform means to support a production facility above the water in the above-described manner. For this reason, a number of approaches have been proposed in the past for storing and treating production fluid from underwater wells in deep water and remote locations. For example, floating production platforms have been positioned over the desired well sites for the reception and/or treatment of production fluids. However, production platforms floating on the surface of a body of water, in addition to being very expensive have the disadvantage that they normally require the use of flexible pipelines and a means of making underwater pipeline connections. In addition, floating production platforms of this nature are required to be maintained in a relatively stable position to fulfill their function and the maintenance of such stability becomes increasingly difficult during storms or other periods of great wave excitation or atmospheric disturbances influencing the dynamic behavior of the floating vessel. Alternatively, production facilities have been devised for positioning directly on the ocean floor. Many of the facility designs in this category, however, are complex and difficult to construct and maintain on the ocean floor.

SUMMARY OF THE INVENTION

It is therefore a primary object of the present invention to provide a production facility which may be economically constructed and readily positioned at an offshore location for handling the production fluid from underwater wells.

It is a further object of the present invention to provide a production facility which consists of a number of components which may be readily assembled and disassembled with respect to one another.

It is a still further object of the invention to provide a deep-water production facility of a semisubmersible type and having excellent hydrodynamic characteristics whereby desired positioning thereof with respect to the well site may be readily maintained.

These objects have been attained in the present invention by providing a production facility incorporating a number of readily separable components. These components include an onbottom platform which is lowerable into position on the ocean floor and serves to support an upstanding marine riser as well as serving for a junction and connection point for flow, gas lift, control and trunk lines associated with the facility. The marine riser portion of the facility extends from the platform in an upwardly direction. Means such as buoyancy tanks are provided in the marine riser construction so that the riser will be substantially free-standing and to prevent buckling of the riser structure. Various flow and control lines extend along the length of the riser and are connected at their respective lowermost ends to the lines incorporated on the onbottom platform. A semisubmersible spar section is operatively positioned over the upper end of the marine riser. The spar section incorporates elements of the facility mooring mechanism and is so constructed as to have variable buoyancy characteristics to support a still additional component of the present facility--the superstructure. These latter two components are of a construction permitting them to be transported separately and joined together on location. The superstructure contains all of the necessary fluid handling and processing equipment, controls, personnel requirements, etc. Since it is of a watertight construction, the reserve buoyancy thereof will prevent it from sinking in the event the buoyant portion of the spar section is damaged. When in operative position, the superstructure extends above the surface of the water with a portion of the spar section. The remainder of the spar section is disposed below the surface of the water and the portions of the spar section at the water line are of a design providing maximum strength while at the same time providing a minimal surface contacted by the waves.

DESCRIPTION OF THE DRAWING

Other objects, purposes and characteristic features of the present invention will be obvious from the accompanying drawing and from the following description of the invention. In describing the invention in detail, reference will be made to the accompanying drawing in which like reference characters designate corresponding parts throughout several views and in which:

FIG. 1 is a schematic elevational view illustrating the production facility according to the present invention positioned in a body of water with the various components of the facility in operative engagement;

FIG. 2 is a schematic, partial cross-sectional view illustrating the onbottom platform component of the present invention positioned on a pile or anchor means in the floor of the body of water;

FIG. 3 is a diagrammatic plan view of the onbottom platform illustrating trunk line conduits incorporated therein;

FIG. 4 is a schematic elevational view illustrating the installation of the onbottom platform on the bottom of the body of water by means of suitable equipment positioned on the surface of the water;

FIG. 5 is an enlarged, schematic elevational view in partial cross section illustrating a portion of the onbottom platform component of the present invention being lowered into engagement with the floor pile, and additionally schematically illustrating a running tool and flooding arrangement utilized for this purpose;

FIG. 6 is an enlarged diagrammatic side view illustrating the operation of aligning means provided on said onbottom platform and the anchor or pile means;

FIG. 7 is a diagrammatic longitudinal elevational view in partial cross section illustrating the marine riser component of the present invention in operative association with the onbottom platform component;

FIG. 8 is a diagrammatic longitudinal view in partial cross section illustrating a representative portion of the marine riser of FIG. 7;

FIG. 9 is a cross-sectional view of the marine riser taken along the line 9-9 of FIG. 8;

FIG. 10 is a schematic elevational view of the spar section component of the present invention;

FIG. 11 is a cross-sectional view of the spar section taken along the line 11-11 of FIG. 10;

FIG. 12 is a cross-sectional view taken along the line 12-12 of FIG. 10;

FIG. 13 is a diagrammatic longitudinal elevation illustrating the spar section component of the present invention floating on the surface of a body of water and prior to being placed in operative engagement with the remainder of the subject production facility;

FIG. 14 is a schematic elevation illustrating the superstructure and spar section components of the present invention preparatory to final flooding operation with respect thereto to place them into operative engagement;

FIG. 14A is a plan view of the components in the positions assumed when carrying out the operation shown in FIG. 14;

FIG. 15 is a schematic elevation illustrating the relative positions assumed by the superstructure and spar section immediately following the final flooding operation;

FIG. 16 is a schematic illustration showing the superstructure and spar section components being brought into operative engagement; and

FIG. 17 is a schematic elevation of the joined spar section and superstructure components after the deballasting has been carried out with respect thereto.

Referring now to FIG. 1, the production facility according to the present invention is illustrated as being operably positioned at an offshore location. The production facility includes the following components: an onbottom platform, indicated generally by means of reference numeral 11; a marine riser, indicated generally by means of reference numeral 12; a spar section, indicated generally by means of reference numeral 13; and finally, a superstructure component, indicated generally by means of reference numeral 14. As may clearly be seen, the production facility in its fully assembled operative condition extends upwardly from sea bed or ocean floor 15 a distance exceeding the depth of the body of water 10 so that the superstructure 14 of the production facility is positioned above the surface 16 of the water. A number of anchor lines such as lines 17, 18, 19 and 20, extend from the spar section 13 and are connected at their respective lowermost ends to suitable anchor means (not shown) embedded in ocean floor 15. It is to be assumed, of course, that the production facility according to the present invention has been positioned at an offshore location that is centrally disposed or otherwise conveniently positioned with respect to a plurality of producing underwater wells (not shown) which will be placed in operative engagement therewith by means of underwater flow lines.

Referring now to FIG. 2, it may be seen that the onbottom platform 11 when in operative position is disposed upon an upstanding pile or anchor member 21 which has been previously fixedly positioned with respect to ocean floor 15 by any suitable known expedient. For example, in the form illustrated, pile member 21 extends through and is fixedly secured to a base member 22 positioned on the ocean floor 15. The pile member 21, after passing through base member 22, extends downwardly into a surface casing 23, which has been secured as by means of cement within a borehole formed in ocean floor 15 by any conventional offshore drilling technique. The pile member 21 may be either fixedly secured to base member 22 and surface casing 23 as by means of welding or may be releasably positioned therein by means of its own weight. It is, however, necessary in the event that a fixed connection is not provided that some means, such as keyway means (not shown), be provided to maintain the pile member 21 against rotational movement with respect to the base member 22 and surface casing 23. The purpose for such limitation will be more fully brought out below.

Pile member 21 includes an enlarged portion 24 having a tapered upper shoulder portion 25 which provides a seating surface for onbottom platform 11 in a manner to be described more fully below. Pile member 21 has passing through the upper portion thereof two conduits spaced with respect to one another and extending from the top surface 26 of the pile member 21 in parallel fashion downwardly into the area of the pile member defined by enlarged portion 24. These conduits are designated by reference numerals 27 and 28 in FIG. 2 and are illustrated by means of dotted lines. As may clearly be seen with reference to that FIG., conduit 27 has a somewhat larger diameter than conduit 28. At their respective lower ends, conduits 27 and 28 communicate with curved passageways 29 and 30 which are formed in enlarged portion 24 of the pile member 21 to provide separated fluid flow paths. At their respective outermost ends, curved passageways 29 and 30 communicate with the interiors of trunk lines 31 and 32 which are fixedly associated in any known manner to pile member 21 and have connector elements 31a and 32a respectively positioned at their outer extremities. Trunk lines 31 and 32 are adapted to be placed into operative connection with gas and oil discharge lines (not shown), respectively, leading either to the coast or to an offshore tanker loading terminal.

Platform 11 is adapted to be lowered from the surface of the water 16, in a manner which will be subsequently described, and placed upon pile or anchor member 21 in the manner illustrated in FIG. 2. The platform 11 includes a central cylindrical portion 35 having a framework 36 affixed thereto and radiating outwardly therefrom in the manner shown in FIGS. 2 and 3. Framework 36 serves to support a skirt portion 37 which projects outwardly and downwardly with respect to cylindrical portion 35. The central cylindrical portion 35 of onbottom platform 11 is of a box-type construction including a plurality of centrally disposed inner chambers such as chambers 38a--38l as shown in FIGS. 2 and 5. The chambers are formed by the outer cylindrical wall 59 of cylindrical portion 35, a substantially cylindrically shaped inner wall 60 and a plurality of horizontal cross plates 61, all of which are secured together in fluid-type fashion as by means of welding. Cylindrical portion 35 is provided at its lower end with a tapered landing surface 42 which matingly engages with tapered upper shoulder portion 25 of pile member 21 when the onbottom platform 11 is in its landed or operating position as shown in FIG. 2. With the onbottom platform 11 in such position, the upper portion of the pile or anchor member 21 is in engagement with substantially cylindrically shaped inner wall 60 of the platform. When the platform 11 is in its illustrated operative position upon pile or anchor member 21, the platform 11 is located above the mud line of the ocean floor so that desired operations can be carried out above the mud and there will be no interference with the mating engagement between the platform 11 and the pile member 21.

Referring now to FIG. 4, the procedure whereby the onbottom platform 11 is installed upon pile or anchor member 21 will be described. With reference to that FIG., it is to be assumed that a guide line 45 has previously been attached to the pile member 21 by any known expedient. For example, the guide line 45 may have been attached to the pile member 21 during its actual installation in the ocean floor 15 with a float or buoy device (not shown) maintaining the other end of the guide line 45 at the surface of water 16. In any event, the installation of the platform 11 is effected by first warping the guide line 45 through a trunk line guiding conduit 46 (see FIG. 5), which projects upwardly and outwardly from cylindrical portion 35 and extends into the interior thereof in the manner shown. Trunk line guiding conduit 46 is welded or otherwise secured to cylindrical portion 35. Returning once again to FIG. 4, after guide line 45 is warped through trunk line guiding conduit 46 of the platform 11, it is hooked to an auxiliary hoist line 47 which is operatively associated with a constant tension device (not shown) on board derrick barge 48. Platform 11 (which has been positioned on the barge) is then picked up by the main hoist line 49 of the barge 48 and swung overboard. To prevent the platform 11 from twisting around the guide line 45, a warpline 50 attached to the platform 11 is held out at its other end by a tug or barge 51. The tug or barge 51 is maintained at a distance from derrick barge 48 substantially equal to the length of the warpline 50, which may be of the order, for example, of 100 feet.

The platform 11 is so designed that it has a slight negative buoyancy. Framework 36 of the platform 11 will be constructed of hollow tubular members, and the chambers or compartments of cylindrical portion 35 will be maintained in an air-filled, watertight condition. The hollow tubular members of the framework 36 are preferably in fluid communication with the chambers or compartments 38 of cylindrical portion 35. The warpline 50 is attached to a weight 52 on board tug or barge 51. As the main hoist line 49 is gradually payed out from derrick barge 48, weight 52 will be lowered from tug 51, at the same speed as platform 11, by means of a cable or line 53 operatively associated with a hoist member 54 on board tug 51.

Returning once again to FIG. 3, it may be seen that in addition to trunk line guiding conduit 46, platform 11 is provided with a second such trunk line guiding conduit 55. To ensure the alignment of trunk line guiding conduits 46 and 55 with conduits 28 and 27, some means must be provided to orient the platform 11 with respect to the pile member 21. One suitable arrangement for accomplishing this is illustrated in FIG. 6 in schematic fashion. It may be seen that pile member 21 incorporates a cam surface or wall 56 in communication with a guide slot 57. A pin member 58 affixed to platform inner wall 60 (FIG. 2) contacts cam surface 56 of pile member 21 as platform 11 is lowered thereupon. Upon continued downward movement of the platform, the pin 58 moves in the direction of arrow A along cam surface 56 into guide slot 57. The cooperation between pin 58, cam surface 56 and guide slot 57 results in the proper orientation of the platform 11 with respect to the pile member 21.

Referring once again to FIG. 5, it may be seen that chambers 38a--38l are defined by outer wall 59 and inner wall 60 of cylindrical portion 35. Also defining the limits of the chambers are a series of cross plates 61 which are welded or otherwise secured in a known manner between outer wall 59 and inner wall 60. Adjoining chambers are in fluid communication with one another through a series of vertical throughbores 62 which are formed in cross plates 61. In addition to the horizontal cross plates 61, a plurality of vertical cross plates 63 are disposed between outer wall 59 and inner wall 60. Vertical cross plates 63 are welded or otherwise secured to not only the inner and outer wall but also to the two horizontal cross plates 61 which define the upper and lower limits of the chamber with which the particular cross plate 63 is associated. Thus, it may be seen that the horizontal cross plates 61 and vertical cross plates 63 along with outer wall 59 and inner wall 60, serve to define the chambers 38a--38l, and, in addition, provide a cylindrical portion 35 of great strength.

Although not shown, it is to be understood that cylindrical portion 35 incorporates chambers similar to chambers 38a--38l throughout the entire circumference thereof with the various chambers being partitioned or separated from one another by means of plates similar to horizontal cross plates 61 and vertical cross plates 63. It should be noted that vertical cross plates 63 have formed therein horizontal throughbores 64. In this manner, fluid communication is provided between all of the chambers lying along the same level of the cylindrical portion 35. For example, chamber 38d is in fluid communication with chamber 38j through horizontal throughbores 64 which are associated not only with these chambers but with the intermediate chambers (not shown) lying between them as well. In other words, horizontal throughbores are not only formed in vertical cross plates 63 but also in all intermediate cross plates (not shown) forming the other chambers. It thus may be seen that all chambers of cylindrical portion 35 are in fluid communication with one another through vertical throughbores 62 and horizontal throughbores 64.

Referring now to FIGS. 4 and 5, and returning once again to the operations involved with respect to the installation of onbottom platform 11, as the platform nears the top of the pile or anchor member 21 warpline 50 is disconnected from platform 11 by any known expedient, such, for example, as by dropping a weighted pipe (not shown) down cable or line 53 to effectuate actuation of any desired disconnect coupling. By disconnecting weight 52 from platform 11, the platform will be free to orient itself with respect to pile or anchor member 21 through the pin and cam surface arrangement previously described. With reference to FIG. 5, the main hoist line 49 is connected to platform 11 by means of a latch mechanism 68 which is releasably secured to trunk line guiding conduit 46. Trunk line guiding conduit 46, on the other hand, is fixedly secured to the remainder of the onbottom platform 11 such as by being welded thereto. Latch mechanism 68 is connected to main hoist line 49 in any known manner such as by means of a bracket member 69, comprising part of latch mechanism 68, which is secured as by means of a pin 70 to the end of the hoist line 49. Bracket member 69 is secured to a downwardly facing cup portion 71 which during the lowering operation is positioned over the end of trunk line guiding conduit 46 in the manner illustrated. An aperture 72 is formed in cup portion 71 and is of a size to receive guide line 45 and allow free passage of the guide line 45 therethrough. In this manner, the cup portion 71 is freely slidable along the guide line 45 as the platform 11 is lowered into position.

Slidably positioned about downwardly facing cup portion 71 is a sleeve member 73 which is formed at its lower end in such a manner as to provide an inwardly facing channel 74. During the lowering operation, sleeve member 73 is biased either by a spring means (not shown) or by means of its own weight to the position illustrated in FIG. 5. It should be noted that in this lowermost position, sleeve member 73 serves to bias in an inwardly direction lock elements such as latching dogs 75a and 75b so that they pass through cooperating apertures formed in cup portion 71 and engage a cooperating outwardly facing channel 76 formed in trunk line guiding conduit 46 about the periphery thereof. This arrangement serves to lock cup portion 71 and hence hoist line 49 into engagement with the trunk line guiding conduit 46.

Secured to sleeve member 73 is a downwardly extending actuating rod 77 which is freely slidable within a throughbore 78 formed in the upper portion of onbottom platform 11 in the manner shown. As the platform is lowered into position on pile or anchor member 21, the lower end of actuating rod 77 contacts the pile or anchor member 21 and is thus moved upwardly in the direction of arrow B as the platform 11 is lowered. Actuating rod 77 then forces sleeve member 73 in an upwardly direction whereby inwardly facing channel 74 of the sleeve member is moved into registry with latching dogs 75a and 75b. The latching dogs 75a and 75b will then be free to enter the channel 74 and be disengaged from trunk line conduit 46. The hoist line 49 may be then pulled upwardly from derrick barge 48 to disengage cup portion 71 from the trunk line guiding conduit 46. As hoist line 49 continues to be pulled upwardly by derrick barge 48 it serves to tighten a wire loop 79 which has one end thereof secured to the cup portion 71. The other end of wire loop 79 is secured to a plug member 80 which is normally secured in a fluidtight manner within a sleeve 81 defining an aperture or fluid flow entryway into the interior of cylindrical portion 35, and more particularly, to chamber 38g of platform 11. When the wire loop 79 has been sufficiently tightened by pulling hoist line 49 in an upwardly direction, plug 80 will be removed from sleeve 81 thus permitting water to flow into the sleeve 81 and into the interior of chamber 38g. As previously noted, throughbores such as vertical throughbores 62 and horizontal throughbores 64 provide fluid intercommunication between the various chambers 38 of the platform 11. Therefore, water is free to flow into all of the chambers 38, and, if a fluid communication is present, into the hollow tubular members forming the frame 36. The onbottom platform 11, having been disconnected from weight 52 and hoist line 49 and having been flooded, will then rest with its full weight on the pile or anchor member 21. As previously noted, when onbottom platform 11 has been lowered completely into position on pile or anchor member 21, tapered landing surface 42 of cylindrical portion 35 will rest in engagement with tapered upper shoulder portion 25 of the pile or anchor member 21.

After the onbottom platform 11 has been positioned on pile or anchor member 21 in the manner previously described, the marine riser section of the production facility according to the present invention will be positioned in place. As may be seen with reference to FIGS. 1 and 7, the marine riser, indicated generally by reference numeral 12, is positioned vertically upon onbottom platform 11 and secured thereto by any known expedient. In accordance with the present invention, the marine riser design is governed by the fact that it be free-standing after it has been connected to the onbottom platform 11 and be capable of supporting the various conduits and trunk lines associated therewith. For accomplishing this, it is necessary to provide buoyancy providing means whereby a major portion of the marine riser 12 is under tension after installation upon the onbottom platform 11. To accomplish this, the center of buoyancy of the marine riser 12 should be located as high as possible above the center of gravity thereof. Although it would be possible to make the marine riser 12 neutrally buoyant, i.e., to keep the total weight of the riser 12 under tension, this preferably should not be done. A certain contact pressure between platform 11 and riser 12 should be maintained to avoid a lifting force on the platform 11. Only a small portion of the marine riser 12 is thus subjected to compression from its own weight. In addition, the riser 12 must be so constructed as to resist considerable hydrostatic pressure and must be designed to prevent collapse of the buoyancy providing members.

With particular reference to FIG. 7, marine riser 12 comprises an upstanding tubular or cylindrical member 82 which is positioned with one end thereof maintained in engagement with platform 11. The cylindrical member 82 may be of unitary construction or, alternatively, may be comprised of individual marine riser sections assembled in an end-to-end manner as is well known in the art. In the event the marine riser 12 is of unitary construction, it may be floated in its entirety in an air-filled condition over the assembly location whereupon controlled flooding of the riser 12 is initiated so that the entire riser 12 will tip into a vertical position in an obvious manner. In the case of a marine riser 12 to be assembled from individual sections positioned end-to-end, such installation may be carried out by lowering the marine riser 12 into position from a floating vessel by adding thereto the individual sections thereby increasing the length of the riser 12 to its operative length in the well-known manner. Regardless of the form of riser 12 to be used, however, it is necessary that the upper portion thereof be constructed in such a manner as to provide a certain degree of buoyancy. With the particular form of riser 12 illustrated, this is accomplished by providing near the upper portion thereof a plurality of buoyancy vessels or tanks such as vessels 83, 84, and 85 which are disposed internally of the marine riser 12 and may be placed in an end-to-end manner as shown. As previously stated, the center of buoyancy of the marine riser 12 should be located as high as possible above the center of gravity. Therefore, the exact placement of the buoyancy tanks would be determined by this factor. It is preferred that the buoyancy vessels or tanks 83, 84 and 85 be filled with air which is partly pressurized. This will provide additional strength to the marine riser 12 itself to resist the pressures exerted by the water and the internal pressures of the buoyancy vessels may vary in accordance with the hydrostatic pressure to which they would be exposed. To provide additional strength in this regard, stiffener rings, such as ring 86, may be employed either within the vessels or externally of the vessels about the inner periphery of cylindrical member 82.

Extending internally of tubular or cylindrical member 82 throughout the full length of marine riser 12 are conduits 90 and 91 as may most readily be seen with reference to FIGS. 8 and 9. FIGS. 8 and 9 illustrate a nonbuoyant, i.e., normally flooded section of the marine riser 12, but it should be understood that conduits 90 and 91 extend not only through the floodable section of the marine riser 12 but through the buoyant section as well. Conduits 90 and 91 are maintained in a fixed relative position within cylindrical member 82 of the marine riser 12 by means of a plurality of crossties 92, which extend inwardly from the inner surface of the cylindrical member 82 (as may be best seen in FIG. 9) and are welded or otherwise secured to the cylindrical member 82 and the conduits 90 and 91. As is the remainder of the riser 12, the crossties and conduits are preferably formed of steel. It should be noted that stiffener rings 86 similar to those found in the buoyant section of the marine riser 12 are also provided about the inner periphery of the cylindrical member 82 within the buoyant section thereof. Conduits 90 and 91 are adapted to receive therein trunk lines 93 and 94 which extend the full length of the riser 12 and are adapted to pass with their respective lower ends through trunk line guiding conduits 55 and 46, said ends being adapted by suitable coupling devices to be connected to conduits 27 and 38 of pile member 21. It should be noted that a support member 96 constructed of rubber or similar material is secured to the lower end of the marine riser 12. This member 96 serves the function of resiliently supporting the marine riser 12 on the onbottom platform 11. It should also be understood, of course, that rather than providing separate trunk lines 93 and 94 within conduits 90 and 91 an interconnection could be made with the platform conduits 55 and 46 directly with the conduits 90 and 91 themselves so that production fluid could flow directly within these conduits and from these through suitable coupling devices into conduits 27 and 28. However, by inserting separate trunk lines within the conduits greater flexibility may be obtained with respect to repair or maintenance thereof.

Marine riser 12, in addition to accommodating within the interior thereof the above-described trunk line and conduit means, has affixed to the outer periphery thereof in any known manner flow line means which after running the full length of the riser drape over skirt portion 37 of the onbottom platform 11 in the manner shown in FIG. 2 and which are connected at their outer ends to the various underwater wells associated with the subject production facility. In FIGS. 2, 7 and 9, two such flow lines 97 and 98 are illustrated as being associated with marine riser 12 and passing over the skirt member 37 from whence they proceed to the underwater wells (not shown). For ease of illustration, only two such flow lines have been shown, but it is to be understood that the number of flow lines to be used will depend upon the number of underwater wells associated with the production facility and upon the number of operations to be carried out with respect to these wells. For example, lines extending along the marine riser in this manner may be used as gas lift lines, hydraulic control lines, and means whereby through-the-flowline operations may be carried out with respect to the individual wells. The external flow lines may be either rigidly affixed to the riser or releasably attached thereto as by means of cooperating guide means of the type shown, for example, in application Ser. No. 585,645, filed Oct. 10, 1966, now U.S. Pat. No. 3,426,843 issued Feb. 11, 1969, to R. C. Visser. It should be noted that platform 11 is located at a fixed distance, say 8 feet, above the mud line of the ocean floor. The portion of the flow lines 97 and 98 between platform 11 and the sea bottom 15 is unsupported and will take the shape of a catenary as indicated in FIG. 2. To avoid kinking of these line segments, the shape of the upper plane of the platform 11, i.e., skirt portion 37, has been adapted to this catenary. The radius of all bends in the lines is preferably limited to a minimum of 5 feet to permit passage of through-the-flowline tools. It is of course to be understood that the various underwater line connections may be made by any of the known techniques such as pull-through techniques. The use of human divers may be made when possible and, in addition, the various connecting operations may be carried out by means of an underwater manipulator device of the type shown, for example, in U.S. Pat. No. 3,099,316 issued Jul. 30, 1963 to G. D. Johnson.

After the marine riser 12 has been positioned on the onbottom platform 11 and the desired connections have been made between these two components as well as between the various conduits and lines, a still further component of the present invention, i.e., the spar section, will be placed in operative position. As may be seen with reference to FIGS. 10 and 11, the upper portion of the spar section 13 consists of six large-diameter, hollow vertical columns 101--106 which are interconnected by a large-diameter, hollow lower grid 107 and a small-diameter, hollow upper grid 108. The walls of the large-diameter vertical columns 101--106 form the bulkheads for the lower grid, subdividing it into six separate watertight compartments. This construction is most clearly shown in FIG. 11. Those compartments which will not be used for storage or ballast tanks can be filled with polystyrene foam for increased safety, i.e., to insure against the sinking of the spar section. Located in the upper portion of the vertical columns 101--106 are mooring system anchor winches (not shown) of conventional design. The upper grid, in addition to its function as a structural member may serve as a connecting tunnel between winch compartments. Grids 107 and 108 are secured to columns 101--106 by any known expedient, as by welding.

Connected to the lower ends of large-diameter vertical columns 101--106 are hollow structural members 111--116, respectively. Hollow structural members 111--116 extend downwardly in a substantially parallel vertical manner and are maintained in such fixed relative position by means of hollow bracing members such as bracing members 117 and 118 which are interconnected with one another and with the hollow structural members 111--116 throughout the length of such structural members. As are the above-described vertical columns and grids, the hollow structural members 111--116 and hollow bracing members 117 and 118 are of watertight construction and may be selectively flooded by operating a system of valves or by operating a suitable pumping system. If emptying is desired, a suitable pumping system may be operated or gas under pressure may be admitted to displace the water therefrom. To facilitate the flooding thereof, the hollow structural members 111--116 and hollow bracing members 117 and 118 may be connected in fluid communication. Connected to the lowermost ends of hollow structural members 111--116 are watertight buoyancy compartments 121--126 respectively which are preferably in fluid communication with members 111 through 118. The buoyancy compartments 121--126 may be selectively flooded by operating a system of valves or by operating a suitable pumping system. Emptying, if desired, may be done by operating a suitable pumping system or by admitting a gas under pressure to displace the water. In addition, certain of the compartments may provide watertight space for mooring system anchor winches of any known type. In the interest of simplicity and since such winches are well known in the art, it has not been deemed necessary to illustrate them.

Having described the general construction of spar section 13, the installation of this component will now be described. As previously stated, the spar section is of unitary construction and it can be built on a slipway of a shipyard and launched in the ordinary way. After being launched the spar section 13 will float in the water in the manner illustrated in FIG. 13 since the interiors of most if not all of the compartments of the spar section are free of water. Since the spar section 13 is of watertight construction, the section will float on the surface 16 of the water until flooding of the constituent elements thereof is accomplished such as by opening flood valves. Since the portion of the spar section including large-diameter vertical columns 101--106 and grids 107 and 108 will provide greater buoyancy than that portion of the spar section including watertight buoyancy compartments 121--126, it may be necessary to partially flood the former portion to maintain the spar section in the substantially horizontal position illustrated in FIG. 13 as it floats on the surface of the water. For example, the large-diameter grid 107 may be wholly or partially flooded to accomplish this end.

In any event, after the spar section 13 has stabilized at the illustrated substantially horizontal position, the spar section 13 may be towed by means of a suitable towing vessel (not shown) to its installation site. After the spar section 13 has arrived at its destination, the spar section is tipped to the vertical position illustrated in FIG. 14. This is done by flooding that part of the spar section incorporating buoyancy compartments 121--126 and members 111--118. This can be accomplished by simply providing the watertight buoyancy compartments with flood valves which may be opened and closed as desired. When using such flood valves, precise control of the tipping operation may be had through the use of vent valves (not shown) incorporated on the other end, i.e., the topmost ends of members 111--116. When in a vertical position, the spar section 13 can be sunk to a certain depth by, in the first stage, closing the vent valves and keeping flood valves open, which will cause lowering of the spar section until the air pressure in the upper portion of the section is equal to the hydrostatic pressure outside. Then, in the second stage, the spar section is sunk to the desired depth by opening the vent valves, allowing accurate control of the flooding. Operation of the flood valves and the vent valves may be carried out from a suitable control vessel such as control vessel 130 viewed in FIGS. 14 and 14A. Operative connection between control vessel 130 and spar section 13 may be had through a suitable control line such as line 129. Control line 129 will preferably provide, in addition to hydraulic, pneumatic, or electrical conduits for controlling the valves, an air supply hose which is connected between a source of air pressure on board vessel 130 and the upper portion of the spar section as viewed in FIG. 14. It may be necessary to add more air to the upper portion of the spar section to adjust the amount of buoyancy.

After the spar section has been tipped to the vertical position illustrated in FIG. 14, the final component of the production facility according to the present invention, i.e., the superstructure 14, will be brought into position. As previously stated, the superstructure contains all the fluid handling and processing equipment, controls, personnel accommodations, etc. associated with the production facility. Since the precise nature of the constituent elements of the superstructure 14 form no part of the present invention and may be adapted or modified as desired in accordance with the requirements of practice, they will not be described further. Since the superstructure 14 is to be towed into position by means of a floating vessel, it is necessary that the superstructure 14 be of watertight, buoyant construction so that it is reasonably sea worthy and stable during the towing operation. It should also be noted that the spar section 13 and the superstructure 14 could be fabricated as a single unit, however, the forces imposed on these joined components by hydrostatic head and wave action during the tow to location would necessitate a heavier superstructure 14. This added weight would have an adverse affect on the stability of the unit. Single unit construction, moreover, would require that the equipment located in the superstructure 14 be installed either after reaching location or while the unit lay on its side in a shipyard. The first of these alternatives is economically unattractive while the second may be technically impractical.

Upon arrival of the superstructure 14, fully equipped and provided with the necessary auxiliaries for installation, assembly of the superstructure 14 and the spar section 13 can proceed. From winches 131 and 132 (FIGS. 14 and 14A) mounted in the gangway of the superstructure 14, wires 133 and 134 as well as tackle blocks 135 and 136 associated therewith are played out and attached to pad eyes on top of two opposing columns, in this case columns 101 and 104, on the spar section. After this has been accomplished, lines 137 and 138 are run from a vessel 139 and attached to opposing sides of superstructure 14 in the manner illustrated. By maintaining a slight tension on lines 137 and 138 and wires 133 and 134 the superstructure 14 and spar section 13 will be situated in such a way that the wires 133 and 134 are substantially parallel as shown most clearly in FIG. 14A. When the components are in the illustrated relative positions, the spar section 13 is additionally flooded so that a negative buoyancy of predetermined magnitude will be obtained. As stated above, this flooding may be carried out by manipulating a vent valve incorporated in the upper portion of the spar section (assuming that a corresponding flood valve or valves are opened in the lower portion thereof). If desired, flooding can be effected instead by actuating suitable pump means associated with the spar section.

After the necessary flooding has been accomplished, spar section 13 will be totally submerged beneath the floating superstructure 14 as shown in FIG. 15. When the spar section 13 and superstructure 14 are in the illustrated equilibrium position, winches 131 and 132 (FIG. 14A) will be actuated. Despite the fact that this operation will probably be performed in a smooth sea, a constant tension device of any known type should be added on the winches to minimize any possibility of damage as the superstructure and spar section approach each other. Continued actuation of the winches will draw the two components together as shown in FIG. 16. When contact has been made, suitable cooperating couplings or locking devices (not shown) between the components will be actuated to lock the superstructure 14 and spar section 13 into operative engagement. This may be done by operating the locking devices from the superstructure gangway (as by use of reach rods) or directly by means of a diver. After this has been accomplished, air is blown into the spar section 13 through control hose 129 to deballast the spar section 13 thereby lifting the entire superstructure 14 out of the water 10 as shown in FIG. 17, until the desired freeboard has been obtained. The combined superstructure 14 and spar section 13 are then maneuvered over marine riser 12 as by means of a tug (not shown) or other suitable prime mover or manipulator means. The spar section 13 is then slowly flooded to drop the spar section so that it can be connected to the marine riser 12. The spar section 13 is connected to the marine riser 12 in such a way that vertical movements of the spar section 13 are not transferred to the marine riser 12, and horizontal (lateral) movements of the spar section 13 are transferred to the marine riser 12. Of course the main object is to connect the trunklines and the flowlines to the spar section 13, so that oil and/or gas can flow to, and away from, the spar section 13 and the superstructure 14.

Finally, the anchoring which is utilized to anchor the facility is installed. Since anchoring systems are well known in the prior art, no attempt has been made to describe a suitable system in detail. Suffice it to say that such an anchoring system would include anchor lines 17--20 which would be connected at their respective ends to suitable anchors positioned at the sea bed or ocean floor 15. In addition, pipelines of any suitable type would be connected between the superstructure 14, spar section 13 and the terminal portions of the various conduits and lines associated with the riser 12 and terminating at its upper end. Any suitable known coupling means may be used to provide this operative engagement.

The production facility according to the present invention provides a very stable and versatile structure. The facility is particularly resistant to wave forces. The areas of the facility subjected to the forces of the waves are kept at a minimum. At the surface of the body of water, only spaced upstanding columns of relatively small cross section are subjected to surface wave activity. In addition, drag forces created by wave action on the submerged portion of the facility are minimized due to the open construction of the lower portion of the spar section.

With regard to the mass properties of the disclosed facility it is axiomatic that an increase in the mass of a vessel requires a corresponding increase in buoyancy to fulfill Archimedes' principle. Added weight, however, means higher cost and with the present design effective mass is provided that does not require offsetting buoyancy. This is due to the fact that when the spar section is in operative position with respect to the marine riser, the effective mass of the facility is increased due to the mass of water which floods and is entrapped within the lowermost portion of the spar section. Inherent with the structural design of a spar-type floater, a large mass moment of inertia about the roll and pitch axis exists due to the remote location of the masses. By employing large-diameter cylinders at the lowermost end of the spar section in accordance with the present invention, not only is a large mass moment of inertia obtained from the amount of steel incorporated in the construction thereof, but also from the water trapped within the cylinders or compartments. The mass moment of inertia about the vertical axis of the spar section is small and could thus be relatively ineffective against yaw motions. However, with the present design only small yawing moments result since the tangential forces from the mooring system have only a small moment arm from the center of rotation. In the event severe conditions are encountered, however, with respect to wave activity, it would be a relatively simple matter to disconnect the spar section from the marine riser. Automatic shutdown valves could be utilized as the flow lines and conduits associated with the spar section are broken away from the marine riser.

In addition, the disclosed arrangement provides great flexibility by permitting easy access to the superstructure so that suitable process and control equipment within the superstructure may be replaced and/or added. Similarly, the onbottom platform and the marine riser allow flow line flexibility with respect to the addition and/or substitution of underwater wells into cooperative relationship with the facility.

While this invention has been described with particular reference to a preferred embodiment thereof, it should be understood that the particular form disclosed has been selected to facilitate explanation of the invention rather than to limit the number of forms which it may assume. Attention is drawn to the fact that, instead of towing the superstructure 14 to the spar section 13, it is possible to suspend the superstructure 14 above the water surface 16 by means of a floating crane (not shown). In that case it is not necessary to sink the spar section 13 to such a depth that it is floating below the water surface 16, but the superstructure 14 can be simply lowered on the top of the spar section 13 by means of the crane. Further, it should be understood that various modifications, alterations and adaptations may be added to the specific form described to meet the requirements of practice without in any manner departing from the spirit of the invention or the scope of the subjoined claims.

Claims

I claim:

1. Production facility apparatus for receiving production fluid from a plurality of underwater wells, said apparatus comprising:

platform means positioned in the water a predetermined distance above the ocean floor and in the vicinity of said plurality of underwater wells upon an upstanding pile member which is fixedly secured to the ocean floor;

said platform means including a central cylindrical portion having a skirt portion affixed thereto and radiating outwardly and downwardly therefrom, said central cylindrical portion including a plurality of inner chambers and being adapted to matingly engage the pile member so that the platform means is supported thereby;

marine riser means end mounted with respect to said platform means and extending upwardly therefrom;

an open-framework spar section releasably engaged to the upper end of said marine riser means and extending upwardly therefrom so that at least the upper portion of the spar section is above the surface of the water; and

a superstructure component positioned on said spar section whereby said spar section maintains said superstructure component above said water surface.

2. The apparatus according to claim 1 wherein said platform includes trunkline conduit means extending therethrough and wherein fluid flow path means is formed in said pile member, said platform and said pile member including cooperating orienting means whereby said platform conduit means and said pile member fluid flow path means are in communication when said pile member and said platform are matingly engaged.

3. The apparatus according to claim 1 wherein said marine riser means includes buoyancy providing means positioned such that the center of buoyancy of the riser is located above the center of gravity of the riser whereby said riser is substantially free-standing as it extends upwardly from said platform.

4. The apparatus according to claim 3 wherein said marine riser means comprises a cylindrical member and wherein said buoyancy providing means comprises a plurality of buoyancy vessels mounted within said cylindrical member near one end thereof.

5. The apparatus according to claim 4 wherein fluid flow passage means is provided both internally and externally of said cylindrical member and running substantially the full length thereof.

6. The apparatus according to claim 1 wherein the open-framework spar section includes a plurality of large-diameter columns maintained in spaced parallel relationship by means of interconnecting grid means, structural members extending from said large-diameter columns, bracing members disposed between said structural members, and buoyancy compartments affixed to said structural members at the end thereof remote from said large-diameter columns, said open-framework spar sections being of watertight construction and selectively floodable so that it may assume a variety of attitudes in the water.

7. The apparatus according to claim 1 wherein said central cylindrical portion includes an inner cylindrical wall and an outer cylindrical wall, cross plates extending between said walls to define said inner chambers, said cross plates defining throughbore means whereby said inner chambers are in fluid-flow communication.

8. Production facility apparatus for receiving production fluid from a plurality of underwater wells said apparatus comprising:

an upstanding pile member;

means fixedly positioning said pile member relative to the ocean floor in the vicinity of said plurality of underwater wells;

pipe support platform means positioned upon said pile member above the ocean floor, said platform means being adapted to support a substantially laterally extending pipe adjacent a point on said pile member above the ocean floor and at least along a portion of the distance between said point on said pile member and the ocean floor;

marine riser means end mounted with respect to said platform means and extending upwardly therefrom;

a buoyant open framework spar section releasably engaging the upper end of said marine riser means and extending upwardly therefrom so that at least the upper portion of the spar section is above the surface of the water; and

a superstructure component positioned on said spar section whereby said buoyant spar section maintains said superstructure component above said water surface.