Underwater Liquid Storage Facility

Abstract

The invention relates to a deep water storage facility formed primarily of concrete, for holding a liquid such as crude oil having a lesser density than that of the surrounding water. The facility includes a floatable base which is supportably fastened to a storage tank. The latter includes a support foundation having an upstanding continuous side wall defining an enclosure. A canopy fastened to the upper rim of said foundation wall thereby defines a substantially closed storage compartment. Said canopy is formed of reinforced concrete and assumes an inwardly contoured or concave shape whereby to withstand compressive stresses induced by the buoying action of stored crude oil.

Description

BACKGROUND OF THE INVENTION

The underwater storage of crude and/or refined oil, as well as other liquid products, has been found to be both practical and economical. A subsea storage facility is not only protected from adverse weather conditions, but presents the possibility of virtually unlimited storage space. Such underwater facilities have achieved great favor at land based installations such as refineries, oil terminals and the like. They are particularly desirable at offshore installations and fields serving in lieu of pipelines and other similar oil transport means. This is particularly true when the storage facility is adaptable to be floated at the water's surface and transported for use or reuse at different underwater sites.

Further, with the rapid development of underwater activities including producing and storage of oil, the aspect of performing much, or at least part of the refining operation under water has become more feasible. For example, underwater separators communicated with offshore well heads, are in use whereby the produced flow of crude oil can be separated into water and usable products prior to the latter being either stored or shipped to a refining point.

One of the problems prevalent in considering any submerged facility particularly in offshore tidewater areas, is that of corrosion. This problem persists regardless of the metal used in the construction thereof, or of coatings applied to the metal surface to avoid or deter a corrosive situation. Concrete, however, is one material which by and large withstands to an infinite degree, any deleterious corrosive action. Concrete structures are not only less expensive than comparable steel structures, but they are more economical to fabricate and maintain.

One pointed drawback common in the use of concrete structures, is the limited ability of this material to withstand tensional stresses. On the other hand, cast concrete is traditionally accepted as an ideal material from the respective points of corrosive resistance, compressive strength, and cost in any architectural structure.

One of the objects of the invention therefore is to provide a relatively inexpensive, concrete underwater storage facility for holding fluids having a lesser density than the water in which the said facility is submerged. This primary objective is achieved by providing a liquid storage facility formed of prestressed and reinforced concrete, so shaped to provide the unit with maximum strength particularly in deep waters where the unit will be subjected to external pressures by stored crude or refined oil. The unit includes a submergible base incorporating buoyancy means that permits both the base as well as the storage portion to be raised to the water's surface. The roof or closure member for the storage compartment is inwardly concave to withstand the upward buoying force exerted by the lighter than water oil.

DESCRIPTION OF THE DRAWINGS

In the figures,

FIG. 1 illustrates a side elevational view showing the present storage facility positioned on the floor of a body of water.

FIG. 2 is a view similar to FIG. 1 illustrating the unit when supported at the water's surface by the buoyant base member.

FIG. 3 is a segmentary view on an enlarged scale and in cross-section of a portion of the unit shown in FIG. 1.

FIG. 4 is a segmentary view in cross-section taken along line 4--4 in FIG. 3.

Referring to the figures, the storage facility as shown in FIG. 1, positioned at the floor of a body of water, includes the lower positioned base 10 comprising a plurality of individual controllably buoyant floats 11. A foundation plate 12 carried on the upper side of base 10, is adapted to support the uppermost positioned tank 13 which embodies one or more internal storage compartments for crude oil. The entire unit rests on a template 14 which is at least partially imbedded in the substratum and there positioned by elongated piles 16 and 17 which connect with template 14 and are driven into the substratum a sufficient length to stabilize the unit at an underwater site.

As shown in FIG. 2, buoying of the facility at the surface of the water is achieved by controlled evacuation of the respective buoyant floats 11. The latter are of sufficient size as to floatably support the tank in an empty condition at the water's surface whereby to facilitate towing the same to a desired offshore location.

Referring to FIG. 3, base member 10 is of a sufficient breadth to support the upper tank 13 which is normally circular in configuration. Said base 10 includes the lower positioned pad-like template 14, formed of concrete embodying reinforcing members such as steel channels or beams running transversely of the respective concrete floats 11. Template -4 can be further provided with normal reinforcing means such as prestressed steel rods. Template 14 is of sufficient strength to withstand the great downward weight applied thereto when the unit is towed at the ocean's surface.

Template 14 is further provided with a funnel-like pile accommodating guide 18 which permits an anchoring pile to be prepositioned above the ocean floor and thereafter urged into the substratum by pile driving or similar means. The essential function of anchoring piles 16 and 17 of course, is to position base 10 at a desired location whereby to avoid lateral displacement thereof.

Elongated, buoyant floats 11 are fastened to the upper face of template 14, each of which floats comprises an elongated member preferably of cylindrical form, and having closed hemispherical ends. The cylindrical tank-like member may assume the cross-sectional configuration of a circle, square, or similar geometric shape whereby the interior of each of said members functions as a controllable buoyancy tank. The buoyancy of the respective tank-like members is regulated to determine the disposition of the storage facility whether in, or on the body of water.

The present embodiment illustrates tanks 11 arranged in parallel disposition, and spaced laterally one from the other. Each of said tanks is adapted to withstand the extreme pressures characteristic of a deep sea underwater environment. For example, the tanks are ideally formed of cylindrical concrete members embodying longitudinally spaced reinforcing rings of prestressed steel bands or cables. They are further provided with end covers preferably of hemispherical configuration to best withstand relatively high pressures experienced at underwater depths.

Referring to FIG. 4, buoyant tanks 11 are positioned at the upper face of template 14 by fastening means 19 or the like extending through the wall of the float and imbedded into the template 14. Such fastening is achieved by any of several different ways including the use of elongated bolts 21 which transverse the wall of the tank and are attached directly to the steel reinforcing beam 22 in base 14. The respective concrete cylindrical tanks are formed with a relatively heavy wall varying in thickness from 4 to 10 inches depending on the water depth wherein the facility will be immersed. While great wall thicknesses are not necessary when the unit is positioned at the sea bottom, when the unit is to be floated to the water's surface the tanks will be at least partially evacuated thereby creating a relatively great pressure on the tank walls thus necessitating the extraordinary thickness.

The cylindrical tanks 11 are intercommunicated with a buoyancy control system including the necessary pipes, manifolds, valves and other control features. Said members are represented in FIG. 3 by the transverse pipes 23 as well as the control valves 24 and 26. The system can be communicated with the water's surface by a removable conduit 27 and pump means at the water's surface, to either flood the respective storage tanks, fill them with a removable ballast material, or evacuate said tanks for buoying purposes. The manifold system can utilize two fluids such as sea water and a barite suspension. In such an instance, one fluid can be pressure fed into the tanks to replace the other fluid as needed.

Foundation plate 12 is carried at the upper side of the respective float tanks 11, fastened thereto to laterally brace the tanks with respect to each other. Said base plate 12 can include sufficient reinforcing as described with respect to template 14, as to qualify for supporting the upper storage tank 13. As shown in FIG. 4, the respective tanks 11 are connected to base plate in a manner similar to that illustrated by the template 14, that is by elongated bolts extending through the float wall and attached to the plate.

Storage tank 13 carried on plate 12, is formed of an upstanding, continuous, circular wall 31 whereby to define the periphery of the storage tank. Said circular wall likewise embodies steel ring reinforced concrete, whereby to best withstand tensional and compressive forces within the tank. Although the wall can be fabricated in virtually any desired configuration, the arrangement in which said continuous wall assumes the disposition of an upstanding cylinder is preferred. In such an instance, the configuration of the wall will be most effective toward withstanding varying pressures exerted by the environment when the tank is in the process of sinking at an underwater location. Further, outward pressures exerted by buoyant oil are more effectively resisted by internal hoops or rings within the circular reinforced wall.

Wall 31 is provided with means to evacuate sediment and solid materials which normally separate by gravity, from the crude product when the latter is at rest. Said wall is therefore provided at the lower edge adjacent the foundation plate 12, with one or more lateral passages 32 extending through the wall to communicate the tank interior with the surrounding water. Thus, as crude product is accumulated within tank 13, rather than settling sediment building up, there will be a tendency for the oil to rise to the surface of the tank whereas heavier solids will fall to the floor of the tank and flow outwardly through openings 32.

The upper rim 33 of the foundation wall 31 is provided with means to engage a top canopy 41 for positioning the latter in place. Canopy 41 according to the invention is formed in a generally concave shape, being supported at the circular rim 33 of foundation wall 31. Said canopy 41 thus forms a closure means at the wall upper edge to define a storage compartment within the tank's interior. At an underwater location, tank 13 will be buoyed upward by a force contingent on the volume of oil stored, and the area of said canopy 41 at a particular elevation. In one embodiment, the upper rim 33 of wall 31, and the periphery of canopy 41 are integrally cast incorporating steel reinforcing members to withstand tensional stress applied to the joint.

For normal subsea operation, crude oil is introduced to storage compartment 34 by one or more inlet conduits 36. The latter extend along the ocean floor and communicate with a source of oil at a subsea well head or the like. While not presently shown, it is understood that crude flow from the well head will ordinarily be at an elevated pressure due to accompanying gases. However the flow will be choked and processed in the usual manner to reduce the pressure commensurate with the water's depth at the point of storage.

This initial well effluent can be further treated by separating gases therefrom. However, the product eventually passed to storage compartment 34 will in general be characterized by a specific gravity less than the surrounding sea water, and substantially degasified.

The crude product that enters storage compartment 34 will be lighter than water on the order of approximately 0.8 of the specific gravity of water. Prior to introduction of crude, compartment 34 will normally be filled, or sufficiently filled with water as a consequence of the submerging operation as the storage unit is lowered to the ocean floor.

As the crude flow enters the lower end of compartment 34 by way of inlet conduit 36, it will be directed upwardly and displace water in tank 13 by flowing to the upper end thereof. Thereafter, a pool of the crude product will be held such that separable solids such as sand and the like will fall to the tank floor. At least a portion of the separated solid material will pass from the tank 13 by way of lateral openings 32.

Introduction of the crude product will be continued until the oil-water interface within compartment 34 approaches the upper edge of openings 32. Further oil entering the compartment will result in an overflow. As a consequence, tank 13 will at this point of loading be considered as filled to capacity. To regulate such flow, the tank can be provided with any one of a number of flow control means that sense the position of the oil-water interface, and automatically correct the flow.

The crude product is removed from compartment 34 by way of a piping system comprising one or more outlet conduits 37. The latter are carried in either the support foundation 31 or in canopy 41. As presently shown, conduit 37 is supported at the upper end of side wall 31, the conduit inlet being disposed adjacent the upper rim 33. A flow control system to regulate passage of oil from compartment 34 is represented by a remotely actuated valve 38 in conduit 37. Conductor means 39 extending from valve 38 to the water's surface may be fixed in place, or removably connected to the valve by diver, or with the aid of a submarine, depending on the water's depth.

With compartment 34 in a substantially filled condition, the upwardly acting or buoying force of stored crude against the underface of canopy 41, will be countered by the downwardly acting weight of the structure. Since compartment 34 is communicated by outlet 32 with its surrounding environment, the internal pressure within tank 13 will conform to the level of water-oil interface.

The upward force acting against canopy 41 is determined by the area and level of the canopy and the density of the stored crude. For example, for a canopy having a diameter of approximately 200 feet, and an average height of oil column of about 50 feet, the buoying force acting against canopy 41 underside will be (64.51)lb./ft..sup. 3 .times. 1,500,000 ft..sup.3 = 19.5 .times. 10.sup.6 lb. = 10,000 tons approximately. Therefore, the buoyant weight of the tank unit with ballast will be greater than 10,000 tons.

Structurally, canopy 41 is formed of reinforced concrete in a disc-like conformation, having a central hub 42 that radiates outwardly to a peripheral engaging edge 43. The latter is connected to upper seating rim 33 of support wall 31. The internal reinforcing element within canopy 41 and across the peripheral juncture with rim 33, can, in the usual manner be provided by a series of interconnected structural bars 44 prearranged to conform to the contour of the roof. Subsequent to the positioning of the reinforcing bars, concrete is introduced to a form disposed about the reinforcement network whereby to completely encase the latter and form a non-corrosive covering thereto.

The steel reinforcing bars 44 can be prestressed or pretensioned whereby to introduce an additional strength factor into the roof structure.

As shown, the actual contour of canopy 41 can assume several dispositions including an arcuate configuration defining a concave surface that extends downwardly into storage compartment 34. Similarly, a conically shaped canopy will function in the desired manner.

At such time as the submerged storage facility outlives its usefulness in a particular field it can be readily removed or replaced. Further, when the accumulation of separated sediment within the lower end of compartment 34 becomes excessive the entire unit can be readily raised to the water's surface to facilitate sediment removal.

The method for elevating the unit to a floating position at the water's surface consists of forcing out ballest material from ballast respective buoyant floats 11 by way of the previously mentioned buoyancy system. Thus, whether the ballast material be barite suspension in water, or other flowable material, the latter is forced from the respective floats to a degree that the unit will be self-elevating from the ocean floor.

At the water's surface the unit can be stabilized at a desired buoyancy to assume a safe floating disposition which will permit the unit to be towed to a desired location. Thereafter the sediment may be removed or the unit can be relocated at a desired spot by controlled flooding of the respective floats 11.

Other modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

Claims

We claim:

1. A submergible storage facility for use in offshore water holding fluids having a lesser density than the density of said offshore water in which said facility is submerged, which comprises;

a floatable base having controllable buoyancy means, and being operable to regulate the disposition of said storage facility in said body of water,

a support wall positioned on said base, having a seating rim at the upper end thereof and defining a continuous peripheral enclosure,

a rigid, contoured canopy having an outer edge carried on said seating rim in fluid tight relation thereto to form a closure atop said support wall, and to define a fluid storage compartment therein, the center of said canopy extending downwardly into said storage compartment.

2. A submergible storage facility as defined in claim 1 wherein; said rigid, contoured canopy includes a generally concave configuration, the center thereof being spaced equidistant from said outer edge, and depending downwardly into said compartment.

3. A submergible storage facility as defined in claim 1 wherein; said floatable base includes at least two horizontal plates spaced vertically apart and defining an interspace therebetween, and

said buoyancy means includes controllably buoyant floats positioned within said interspace, and

a buoyancy system communicated with each of said buoyant floats, said system being actuatable from the water's surface when said facility is in submerged position, to remotely regulate the disposition thereof and anchoring means carried on the lower of said vertically spaced horizontal plates adapted to position said storage facility at the floor of said body of water.

4. In a submergible storage facility as defined in claim 3 wherein; said controllably buoyant floats include; a plurality of longitudinally arranged elongated cylindrical members having closure means at opposed ends thereof defining a fluid tight chamber with each of said members, and

said buoyancy system includes conduit means communicated with each of said fluid tight chambers for regulating the fluid content thereof.

5. In a submergible storage facility as defined in claim 1, wherein said support wall includes; drainage means formed at the lower end thereof adjacent to said base, communicating the interior of said storage compartment with the surrounding water.

6. In a submergible storage facility as defined in claim 5, wherein said drainage means includes; a plurality of peripherally spaced openings formed in said wall whereby to permit passage of solid materials accumulated in said compartment to the exterior thereof.