Flexible Storage Container For Offshore Facility

Abstract

A submergible flexible storage container for storing crude product anchored to columns beneath an offshore drilling and production platform or similar support structure. The container includes inlet and outlet means for receiving crude product and for disposing of crude product to a floating vessel. A manhole opening is also provided for ingress and egress of personnel in removing extraneous matter collected in the base of the flexible storage container.

Description

BACKGROUND OF THE INVENTION

Much of the world's supply of oil or crude product and present oil exploratory activity is being carried out in offshore locations. A great deal is known today of the relatively new technology for removing the crude product from strata in the tidelands or in the immediate offshore areas. However, as future sources of oil are sought farther offshore, the waters in which the drilling and producing operations will be conducted are much deeper, in the order of magnitude of 1,000 feet and greater.

Efficient working in such an underwater environment posed many problems which have been heretofore unrealized in the normal production of crude product from lesser water depths. Among the primary problems constituting a deterrent to further progress in offshore technology is the extraction and storage of crude product drawn from the earth along the continental shelf and adjacent areas. The necessity exists for provision of suitable means to bring the crude product to a refinery or land storage point from the well head. The most practical, albeit expensive, mode normally employed is a pipeline extending directly from the drilling site or well head to the refinery. This expediency is utilized, however, only where the output of an offshore field promises to be of sufficient volume to warrant the high cost of a pipeline.

Another means for conveying the crude product is by tankers, barges and the like, which are adapted to handle large quantities during each passage between the oil field and the refinery. The latter carrying means, however, by virtue of their requirement to move a load of crude product between the drilling site and the shore, require storage when the carrying means are not available to accept the crude product flowing from below the sea.

Also, tankers are a relatively expensive type of transportation and as such must be used as efficiently as possible. To extend the period for loading crude product onto the tanker because the flow from a well is not optimum, uses the tanker and its crew uneconomically. Needless to say, the ever present danger of the tanker being carried against the metal offshore facility with subsequent damage thereto, requires rapid loading and departure to reduce the chances of such impact.

Thus the storage of crude product in relatively deep waters, at or near the well head, has become a virtual necessity if deep water operations are to remain within the confines of economic practicality. It has been found that the use of completely submerged production and storage facilities embodies the primary advantage of being protected from adverse weather conditions at the water surface, while being subjected to a minimum degree of structural stress from the waves at the surface of the sea.

Metal tanks have been developed for storage of crude product below the water surface. These storage facilities, however, when depleted of crude product, are extremely buoyant and require sea water or other form of liquid as ballast. This of course causes a crude product-sea water interface during periods when crude product is being filled into or taken from the storage facilities, with a consequent intermixing of fluids. Thus, not only is some amount of crude product released with the sea water, but some amount of sea water from the storage facility is carried to the tanker with the crude product.

Storage of crude product below the sea has required expensive pumping facilities to transport the crude product from the storage facility to a waiting tanker. In offshore sites, not only must the equipment for pumping be initially transported to the offshore site, but also the supportive fuel requirements must be continually replenished. Additionally, the storage of pumping equipment and fuel reduces useful space on the offshore site.

The present invention in its basic form contemplates a means for overcoming the aforementioned problems by the provision of a convenient underwater storage facility. It further constitutes a storage facility that is entirely submerged in a body of water for protection against the elements normally present at the water surface and below high forces generated by storm waves and is not dependent on pumping requirements to deliver the crude product to the tanker. Also, as an added feature, extraneous matter such as sand is removed from the crude product by gravity separation prior to delivery of the usable constituents to a tanker.

SUMMARY OF THE INVENTION

Briefly, the present invention embodies a submerged offshore facility for storing crude product and other liquids. The facility includes a supported, flexible storage container having a base with a liquid inlet connection. A covered manhole opening is formed in the tank wall together with a liquid outlet connection in the upper portion of the latter. Anchoring means supportably connect the flexible storage container to an offshore drilling and production platform or a similar submerged framework. At least one of the tank support points is maintained by the anchoring means at a higher lever than the tank base. Additionally, the extraneous matter from the crude product settled out on the base can be removed through the manhole opening. Further, the crude liquid product is transferred from the flexible storage container to a floating transporting means by only the pressure of the surrounding water.

It is therefore one of the objects of the present invention to provide a submerged crude product storage facility of the type described, adapted for anchorage to a support structure anchored at the floor of the sea.

A further object of the present invention is to provide an oil storage facility of the type described which does not require a crude product-sea water interface.

A still further object of the invention is to provide such a facility or storage system wherein crude product can be transferred periodically from the facility to a tanker or other transporting means without the use of auxiliary pumping means.

Still another object of the present invention is to provide a system of the type described which permits the separation out of the crude product of attendant extraneous matter before transfer of the crude product to a tanker.

These and other objects of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, wherein the invention will be further understood by reference thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings represent preferred forms of the invention, wherein:

FIG. 1 is an environmental representation of the presently described flexible storage container shown anchored to columns supporting an offshore drilling platform;

FIG. 2 is an elevation view of the side of the flexible storage container shown anchored to columns supporting an offshore drilling platform;

FIG. 3 is a segmentary view of a portion of the base of the flexible storage container shown in FIGS. 1 and 2, and taken along line 3--3 in FIG. 1; and FIG. 4 is a pictorial view of another embodiment of the present invention wherein a plurality of flexible storage containers are shown anchored to columns supporting an offshore drilling platform.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring more particularly to the drawings wherein like numerals of reference indicate corresponding parts throughout the several FIGURES, an offshore drilling platform 1 is shown supported from below the sea on three columns 2, together forming the outline of a truncated pyramid. At the mudline (unnumbered but indicated), support plates 3 are conventionally fastened to the bottom of each column, and anchor piles 4 are conventionally sunk deep through the mud into hard ground for support.

A producing well, generally shown at 5, is provided with well head pressure reading apparatus 5'. Well 5 is connected to and forces a controlled pressure stream of crude product through a lower conduit 6 and into a gas-liquid separator 7 connected thereto, the latter conventionally separates the gas and liquid in the crude product and passes the gas and liquid separately to a gas outlet (unnumbered) and a liquid outlet (unnumbered), respectively.

Gas separated from the crude product in separator 7 can either be passed directly from the gas outlet into the water as shown by the schematic representation of the bubbles (unnumbered) leaving the gas-liquid separator, or flared by known means.

The crude liquid product is passed through an upper conduit 8 which is connected to a flexible storage container 9 via a container inlet 10 in the flexible storage container to which the upper conduit is connected at the opposite end. It should be understood at this point that the gas-liquid separator 7 removes the gaseous part of the crude product so that the flexible storage container 9 will receive only liquid crude product.

A valve 11 is conventionally connected in the upper conduit 8 and is remotely controlled, pneumatically or otherwise, from the platform 12. Valve 11 can be, for example, a normally closed type which allows flow through the upper conduit to the flexible storage container 9 only when the valve is opened.

One embodiment of a flexible storage container 9 comprises a pair of adjacently disposed triangular shaped deformable sidewalls of panels (unnumbered). Corresponding edges of the respective sidewalls are joined to form a continuous, fluidtight peripheral seal. Introduction of a fluid to the space between the sidewalls causes the latter to deform outwardly thereby to define a collapsible storage compartment for a crude product.

One means for forming the peripheral seal consists of a flexible binding strip having lateral borders which overlap adjacent edges of the respective sidewalls and fasten to each. The binding strip can be any shape. In one embodiment, the binding strip narrows at either end of each side of the sidewalls to allow the respective points of the triangular forms to be joined to one another either directly or across a very narrow binding strip, all in a fluidtight manner. It should be understood that when empty, the flexible storage container lays flat on itself and thus is not excessively buoyant as would be an empty rigid walled metal container.

A portion of the binding strip connected to the lower side of the sidewalls forms a base 13. The flexible storage container is provided at its two base corners and apex (all unnumbered) with connecting openings 14 defined by heavy grommets. Support means engaging the frame work and flexible storage container for positioning the latter includes cables 15. A separate cable is resiliently connected to each column 2, for example, to lugs (not shown) provided thereon. Two cables connect opposite corners of base 13 to their respective columns and the remaining cable connects to the apex, the cables are so arranged that base 13 is disposed at the flexible storage container's lowest level.

The extraneous matter (such as sand, clay particles and other solid particles, carried along with the crude product from the well) in the crude product, being heavier than the crude product, settles to the base where it can accumulate and be periodically collected. The flexible storage container support means include a biasing member 16, such as a resilient cable (unnumbered) or a helically wound compression spring, connected in series with cable 15. The biasing member 16 introduces a continuous tension into cable 15 to prevent or reduce the incidence of tearing at the flexible storage container openings, due to displacement of the flexible storage container in response to loading and unloading of the flexible storage container.

Referring to FIG. 4, the flexible storage container 9 sidewalls can be fabricated for greater strength from a multilayered material with a metallic reinforcing element 17. For example, such reinforcing can consist of a steel cable disposed along and inside of the joined flexible storage container edges.

In an alternate embodiment, the material from which the flexible sidewalls and binding strips are fabricated consists of neoprene. In the latter instance, the neoprene sides can be molded with the steel cable reinforcing element 17 incorporated therein along the edges. The steel cable reinforcing element can also be integral with the openings 14 at the two base corners, and at the apex to prevent tearing at these points. The steel cable reinforcing element can be in addition to, or in place of, the heavy grommets in the base corner and apex openings.

The steel cable reinforcing about the openings 14 reinforces the container corner openings without relying for strength on the fabric of the flexible storage container. The steel cable can be of any size that would conventionally be used for the expected tension load. The cable reinforcing can further be manufactured of aluminum or fiber glass or provided with a corrosion resistant material.

At least one manhole 18 is provided in the base 13. Manhole 18 affords access to the storage compartment for a diver to work within to remove the collected extraneous matter. Metal straps 19 forming a T from the end and sides of the flexible storage container base are attached to the metal cable reinforcing 17 and to the fabric of the flexible storage container walls. The metal straps 19 support a flange 20 to which they are attached by welding or other conventional support attaching means. The flange 20 and the flexible wall of the base 13 form a conventional fluidtight seal. The size of the flange which forms the opening for the manhole 18 is adequate to permit a man to enter therethrough. A blind flange 21 is removably connected to the flange by bolts 22.

In the upper portion of the flexible storage container wall adjacent to the apex, a container outlet 23 is provided which is connected at a fluidtight joint to the input of a loading conduit 24. Loading conduit 24 extends upwardly to the top of the platform 12 where it connects in a fluidtight manner to an outlet connection 25. The outlet connection 25 can be removably connected to the storage area input connection (not shown) of a tanker or other transporting means. The upper portion of loading conduit 24 is flexible to permit connection thereof to the storage compartment input connection and also to move in conjunction with the tanker or other transporting means as it bobs and floats in the sea.

A flow control valve 26 is provided in the loading conduit. The flow control valve 26 can be a normally closed valve which prevents the passage of liquid therethrough unless actuated by manual or other conventional means.

When loading a tanker (unnumbered) or other transporting means, the loading valve 26 is opened. The pressure of the sea water at the depth of the flexible storage container provides a driving force against the container deformable walls, which urges the crude product out of the flexible storage container through the container outlet 23, loading conduit 24, outlet connection 25, and into the storage area input connection of the tanker or other transporting means. When the loading of crude product is completed, the loading valve 26 is closed to prevent further discharge of crude product from the flexible storage container.

The potential driving force for transferring the crude product from the flexible storage container to the tanker or other transporting means, depends on the depth of the flexible storage container in the sea water. Mathematically, the depth that the bottom of the flexible storage container should be to have a sufficient driving force depends on the height above sea water the storage area input connection initially stands. As the storage area is continually filled, this height above sea water diminishes because the tanker, barge, or other transporting means, will become heavier and sink lower in the sea water.

Mathematically, the depth at which the bottom of the flexible storage container must be maintained to provide a sufficient latent hydrostatic lifting pressure to deliver crude product to the necessary height above sea water is described by equations relating to two columns of liquid balancing each other. Assume that both columns have a similar cross section, for example 1 square foot. Also assume that one column is filled with sea water to the height of the surface of the sea and supports crude product in the other column. Therefore:

p.sub.s h= p.sub.c (h+h')

where:

p.sub.s is the specific gravity of sea water relative to pure water, both taken at 60.degree. F.,

h is the depth at which the bottom of the flexible storage container is maintained below the surface of the sea,

p.sub.c is the specific gravity of crude product relative to pure water, both taken at 60.degree. F.,

h' is the height above the surface of the sea water to which the crude product is pumped, both h and h' in the same linear units.

or:

Giving to h a value of 100 feet, to p.sub.s a value of 1.0262 and to p.sub.c a value of 0.8499, and substituting these in the equation for h', gives a value for h' of:

From the above equation it can be seen that for every 100 feet of depth that the bottom of the flexible storage container is maintained the crude product in the flexible storage container will be raised 20.74 feet above sea water by the latent hydrostatic lifting pressure.

As it is well known that, for example, barges vary from water level to deck from between 8-30 feet and tankers vary from water level to deck from between 25-60 feet, maintaining the bottom of the flexible storage container below 300 feet will be sufficient to drive the crude product from the flexible storage container to the highest tanker having a deck level of 60 feet.

When loading a tanker or other transporting means from the flexible storage container, the valve 11 and the flow control valve 26 can be simultaneously opened. This permits simultaneous filling and depleting of the crude product in the flexible storage container for a quicker fill time.

When the tanker or other transporting means is filled to capacity, as desired, the standard operating procedure would be to first close the valve 11, if open, and then to close the flow control valve 26. This order of closing of valves 11 and 26 prevents the inadvertant filling of the flexible storage container with crude product beyond the capacity thereof, i.e., with the loading valve 26 closed (and no crude product leaving the flexible storage container) and the valve 11 open (and crude product from the well 5 flowing into the flexible storage container).

When more than one flexible storage container is at the storage facility, there can be either a multiplicity of loading conduits 24 connected to inlets in a joining section 27 or separate outlet connections 25 can be provided for each loading conduit 24 (not shown). Each loading conduit is provided with a separately controlled flow control valve 26 to control the flexible storage container separately, for example, when loading a multiplicity of tankers or other transporting means docked at the offshore drilling rig.

Operation and use of the desired flexible storage container has been illustrated with reference to the storage of crude product. It is understandable, however, that other liquids or combinations of liquids can be as readily stored and transferred. Also, with more than one flexible storage container provided, the liquids in each flexible storage container can be different or similar as desired.

While the foregoing description encompasses various embodiments of the invention, it is appreciated that all such embodiments have not been disclosed and with certain changes and modifications, an embodiment of the inventive concept can be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims

I claim:

1. A liquid storage facility for a submerged offshore well installation which comprises;

a. a marine platform positioned at said offshore location including a plurality of support legs extending to, and fixed at the lower end thereof to the floor of said body of water;

b. a flexible walled fluid container supportably engaging at least two of said support legs and having inlet and outlet ports, the latter being connected with fluid collecting means at the water's surface;

c. conduit means communicating said flexible walled container inlet port with a source of said fluid to be stored;

d. said connecting means including, a plurality of cables extending from support points on said fluid container to said support legs, and biasing means interposed in said connecting means to produce into the latter a continuous tension under varying loading conditions of said container.

2. In a liquid storage facility as defined in claim 1, wherein said biasing means includes a spring member interposed in said connecting means to maintain a continuous tension on the latter.

3. In a liquid storage facility as defined in claim 1, wherein said flexible walled fluid container includes; upper and lower ends, at least one of said connecting means engaging said container upper end and extending to a support leg, at least two of said plurality of connecting means engaging said container lower end and extending to adjacent supporting legs whereby to fixedly position said container with respect to said marine platform.

4. In a liquid storage facility as defined in claim 3, wherein said container discharge port is disposed at the container upper end, and said inlet port in the lower end thereof.

5. The combination with a submerged fluid producing well located at the floor of an offshore body of water of a marine structure having at least three elongated support legs extending from said floor, to a point above the water's surface, and a deck supportably positioned at the upper end of said at least three elongated support legs,

a liquid storage container depending from said marine structure and comprising,

oppositely positioned, resilient sidewalls being sealed along adjacent edges thereof,

a base member sealably engaged to one end of said respective sidewalls to define a closed compartment within said storage container,

an inlet port in said base member, communicated with said submerged fluid producing well, and a discharge means at the upper end of at least one of said sidewalls,

first connecting means supportably engaging said upper end of said storage container to one of said at least three support legs,

other connecting means supportably engaging said base member to other of said structure's elongated support legs, to maintain said base member at a lower elevation than the elevation of said container inlet port,

said respective connecting means including a biasing element therein for maintaining a tension on said container sidewalls during all phases of the container loading.

6. In a combination as defined in claim 5, wherein said other connecting means are disposed at the lower elevation on said other of said support legs and extend outwardly from said container.

7. In a combination as defined in claim 5, wherein said other of said connecting means are supportably connected to adjacently disposed support legs of said marine structure.