US3472032A - Production and storage system for offshore oil wells - Google Patents

Description

Oct. 14, 1969 e. c. HOWARD 3,472,032

PRODUCTION AND STORAGE SYSTEM FoR OFFSHORE OIL WELLS Filed Dec. 1. 1967 34 I INVENTOR.

ll! gggEoReE c. HOWARD I BY M 5 ATTORNEY United States Patent 3,472,032 PRODUCTION AND STORAGE SYSTEM FOR OFFSHORE OIL WELLS George C. Howard, Tulsa, Okla., assignor to Pan American Petroleum Corporation, Tulsa, Okla., a corporation of Delaware Filed Dec. 1, 1967, Ser. No. 687,244 Int. Cl. E02d 21/00; E21c 19/00; E21]: 43/01 US. Cl. 61-46 13 Claims ABSTRACT OF THE DISCLOSURE A completion and producing system is described for a well drilled in an area covered by deep water. It includes a large buoyant storage tank positioned in the water below wave action. The tank has a slight upward buoyancy. It 18 held in position by a long, preferably flexible, conduit connected to the well head in the floor of the body of water. A smaller production conduit is positioned inside the large outer flexible conduit and is connected to the string of producing tubing in the well. A narrow cylindrical neck extends from a large tank to above the surface of the water where it supports a work deck and helicopter deck. A gas-oil separator and other treating equipment is carried within the large buoyant tank. Means are rovided to transport oil from the storage tank to a transport vessel.

SPECIFICATION This invention relates to the production of petroleum from a well drilled in a marine location.

BACKGROUND In recent years the search for oil and gas has extended into water-covered areas. At first this search was in relatively shallow water, tag, 50 to 100 feet. In water of this depth, either an island or a platform was built over the proposed well site and the well was drilled from the island using dry land techniques. The islands were formed by, for example, dredging up large amounts of gravel until the islands extended above the surface of the water. Platforms were ordinarily formed by driving piling or long columns of steel into the ocean floor and attaching the deck to the ends of the piling which extend above the surface of the body of water. If a commercial well was obtained, the well head was on the platform or the top of the island similarly as on dry land wells.

More recently, the search for oil and gas has extended into deeper waters, for example, up to depths of 400600 feet or more, and in a few instances even in excess of 1,000 feet. At these depths it is seldom feasible to build up an island or platform. Consequently, wells from this depth are drilled from large floating vessels. This drilling technique has advanced quite rapidly, and although there are still many problems associated therewith, the practice has been fairly successful. If production of oil is found in paying quantities, there must be some satisfactory way of completing the well. This area of exploitation is in its infant stage and is not nearly so well developed as that of drilling from floating vessels. It is with this completion stage that this invention is concerned.

BRIEF DESCRIPTION OF THE INVENTION Broadly speaking, this invention concerns a completion assembly for a well drilled to the bottom of a body of water. A production tubing string in the well extends upwardly toward the surface of the body of water. A conduit means larger than the production tubing string surrounds such production tubing. The conduit means is secured to the floor of the body of water. Buoyant means are attached near the upper end of the conduit means but be- 3,472,032 Patented Oct. 14, 1969 low the main action of waves. The buoyant means preferably includes treating means for the oil and chambers for storing the oil after treatment. A neck extends upwardly from the buoyant means to above the surface of the water. A deck is supported by such neck.

THE DRAWING DETAILED DESCRIPTION In FIGURE 1 of the drawing there is illustrated a well head oranchor base 10 in thebottom 12 of the body ofwater 14. Supported in body ofwater 14 is a buoyant storage means 16. Above the body of water is awork deck 18 and a helicopter port deck means 20.

I shall first consider means of positioningbuoyant storage tank 16 in position. This is provided by aconduit 22 which is connected tosurface casing 24.Surface casing 24 is held in position by being cemented into the previously drilled well and attached to the wellhead base plate 10 in any well-known manner. Riserconduit 22 flexibly connectstank 16 to suchsurface conduit casing 24. This flexibility can be built intoriser 22 by making it of a flexible material such as rubber containing reinforcing steel wires therethrough to give it strength. Alternatively, riser conduit means 22 can be made of high strength steel, which is that commonly used in riser pipes in offshore drilling operations, and the lower end thereof can contain aflexible joint 26 which can conveniently be a ball joint type connector.

Conduit 22 is connected at its lower end throughautoconnect 28 tosurface casing 24. The upper end of riser conduit means 22 is connected to buoyant storage means 16. It is thus seen that storage tank means 16 is anchored to the ocean floor by thesurface casing 24. This anchorage is not rigid but rather is flexible so thatriser 22 and storage means 16 can give with the effects of currents and tides. Thestorage tank 16 is spaced a suflicient distance below the surface of the water to minimize the effects of Wave action thereon. Thus, by controlling the buoyancy of the floating tank, the strength required in riser conduit means 22 can also be minimized.

The structure above the water will next be discussed. A neck 30 extends from the center of buoyancy means 16 to well above the surface of the water, e.g., 20 to 30 feet. Neck 30 supportslower work deck 18 and thehelicopter port deck 20. Access means are provided at the upper end of neck 30 so that it can be closed for most of the time but opened when it is necessary to have access to the interior thereof. By way of example, it is anticipated that neck 30 can be in the order of 8-l0 feet in diameter and riser conduit means 22 may be in the order of 2 feet.

Attention is next directed toward the oil producing tubing. Atubing string 32 is suspended inproduction string 34 in the well bore. Asafety cutoff valve 36 is provided intubing 32 below the ocean floor to shut in the well in event the upper production string is broken. Tubing 32 is connected totubing extension 32A which extends upwardly in the inside of riser means 22.Tubing extension 32A extends on upwardly through neck 30 to aboveport deck 20 and it is provided with a well head assembly such as indicated by valve means 38. The outlet ofvalve 38 is connected to adown pipe 40 which goes down to a treating means such as a gas-oil separator 42 located in buoyant storage means 16. The outlet of gas-oil separator 42 is into one of the storage compartments of buoy ancy means 16. Buoyancy mean 16 has a plurality ofvertical baffle plates 86 which may or may not be provided with openings so that oil may freely flow one compartment to the other. It may be desirable to have a compartmental tank to minimize oil loss in event of damage. The gas from theseparator 42 goes throughoverflow pipe 48 where it can be flared or otherwise disposed of according to existing regulations.

Means for transferring oil from the storage tank will now be discussed. This includes adischarge pipe 50 which extends from the interior storage compartments of buoyancy means 16 up through the supporting neck 30 anddeck 18. Apump 52 can conveniently be provided in the lower end ofdischarge pipe 50. Anoutlet 54 is provided on the outer end ofdischarge conduit 50 so that a suitable hose can be connected thereto so that a ship can be loaded.

If desired, anchor lines 56 can be provided from the buoyancy means 16 to anchors in the ocean floor (at a spot not shown). These anchor lines 56 are in reality restraining lines instead of anchor lines and will ordinarily be slack as illustrated in the drawing.

Attention will now be directed toward means of placing thebuoyancy tank 16 and associatedriser pipe 22, neck 30 andwork deck 18 in the position shown in the drawing. Conveniently, this can be accomplished by making up buoyancy means 16, riser pipe means 22, neck 30, decks l8 and 20 and auto-connect 28 fabricated similarly as shown. These could be floated to location in a horizontal position. When over location,winch lines 60 are connected at 62 to guidearms 64. Winch lines 60 extend from theguide arms 64 on the auto-connect 28 which is connected toriser pipe 22. Winch lines 60 extend on downwardly throughpulleys 66 which are anchored to anchorblock 10. The ends of the winch lines have previously been attached to buoys so that the lines can be recovered when needed for pulling the riser down. From thepulleys 66, thewinch lines 60 go to the surface where they are connected to winch lines or a tugboat or the like (not shown). Bywinch lines 60, the apparatus or completion system is moved to the position shown in the drawing and auto-connect 28 is drawn into line with its counterpart onsurface casing 24. The upper ends ofwinch lines 60 are disconnected from the tugboat and can be supported by buoys, not shown, in event it is necessary to use them again.

Various other ways or methods of placing thebuoyancy tank 16 and associated equipment in the position shown in FIGURE 1 are possible. One alternate method is to float the apparatus including the buoyant storage means 16,work deck 18,helicopter deck 20 andriser assembly 22 into place above the well head or surface casing 24 in a vertical orientation. This is accomplished by emptyingbuoyant means 16, and having it of sufficient buoyancy so that it floats on the surface. When the device is over surface casing 24, buoyant means 16 is flooded. The tank is flooded and deflooded by well known means, not shown.

As the compartments of buoyant storage means 16 are flooded, the device is sinking into the water.Riser 22 and auto-connect 28 are guided into place using a sonic well head locator, for example. Lateral movement is effected by tugboat (not shown) moving the equipment to location.

Buoyant storage means 16 typically is about 15,000 bbl. capacity or days producing capacity of the well, whichever is larger. Transfer of the oil is preferably effected bypump 50 as explained above. Alternatively, it can be accomplished by allowing sea water to enter the compartments through inlets, not shown, and forcing the oil up throughoutlet pipe 50. If this system is used it is preferred to provide a minimum buoyancy by use of afloatation compartment 70 on the lower side of the storage means. This compartment can be filled with styrofoam, if desired. Another way of insuring a vertical buoyancy is to maintain a cushion of inert gas in the upper portion of buoyant storage means 16.

FIGURE 2 illustrates a modification of the system shown for moving the riser pipe down into proper engagement with thewell head casing 24. In this system a buoyant means is secured by latchingmeans 84, shown schematically, toriser pipe 22A.Arms 64A from auto-connect 28A are provided with cable winches 78. These winches are provided power from the surface byelectric cable 76.Lines 60 fromwinches 78 extend downwardly to anchors which are secured to anchor base 10A.Guide lines 60 are conveniently set and attached with base plate 10A when it is set. Thusline 60 could extend to the surface and be supported by buoys in a known manner. Then when it is desired to lower theriser pipe 22A and associated equipment,lines 60 are connected towinches 78. Upon actuation ofwinches 78, the riser pipe assembly is pulled into proper position.Buoyant tanks 80 maintain tension on theriser pipe 22A. The pipe is thus pulled down against this upward force ofbuoyant means 80.

While the above invention has been described with a great deal of detail, it is to be understood that various modifications thereof can be made without departing from the spirit or scope of the invention.

I claim:

1. A completion assembly for a well drilled into the bottom of a body of water and having:

(a) a production string inside said well and extending upwardly toward the surface of said body of water;

(b) buoyant means including an oil storage chamber connected to said production string;

(0) riser conduit means larger than said production string and surrounding said production string, said riser conduit means being secured at one end to the floor of said body of water and at the other end to said buoyant means whereby said buoyant means exerts the only upward force on said riser conduit means, said riser conduit means including means flexibly connecting said buoyant means to the floor of said body of water.

2. An assembly as defined in claim 1 in which said riser conduit means is made of a flexible material reinforced by a stronger flexible material.

3. An assembly as defined in claim 1 in which said buoyant means is positioned a sufficient distance below the surface of the body of water so as to be essentially free of effects of wave action.

4. An assembly as defined in claim 1 including means for connecting said production string to oil transport means.

5. An assembly as defined in claim 4 in which said buoyant means contains oil treating equipment.

6. An assembly as defined in claim 1 including winch means connected to said riser conduit means, cable means on said Winch means, and anchor means anchored to the ocean floor, said cable means connected to said anchor means.

7. An assembly as defined in claim 1 wherein said buoyant means includes a plurality of compartments and further including means to flood and deflood each compartment with sea water.

8. An assembly as defined in claim 3 including an extension neck of larger size than said riser conduit means extending from said buoyant means to above the surface of the body of water and a working deck supported above said surface of water by said extension neck.

9. An assembly for a well head drilled in the floor of a body of water and in which casing anchored to the floor has been set which comprises:

a riser conduit means extending from near the upper end of said casing toward surface of said body of water;

means for releasably latching the lower end of said riser conduit means to said casing in a sealing relationship therewith;

a buoyant storage means attached to said riser conduit means at its upper end below the surface of the body of water;

a string of tubing suspended within said well;

a production conduit extending from said tubing to said buoyant storage means, said production conduit means including means for controlling from the surface the flow of fluid through such production conduit means;

discharge means for removing oil from said buoyant storage means. 7

10. An assembly as defined in claim 9 including a flexible joint connecting said riser conduit means to said casinganchor to the floor.

11. An assembly as defined inclaim 10 including an extension rieck extending from said buoyant storage means to abojve' the surface of the water permitting ingress and egress to said buoyant storage means and including a work deck supported above the surface of the body of water by said extension neck.

12. An assembly as defined in claim 9 including pulleys anchored to the ocean floor adjacent said anchored cas- 111g;

guide arms connected to the lower end of said riser conduit means;

winch lines extending from said guide arms through said pulleys to the surface of said body of water.

13. completion assembly for a well drilled into the bottom of a body of water and having:

(a) a production string inside said well and extending upwardly toward the surface of said body of water;

(b) buoyant means;

(c) riser conduit means larger than said production string and surrounding said production string, said riser conduit means being secured at one end to the floor of said body of water and at the other end to said buoyant means whereby said buoyant means exerts an upward force on said riser conduit means, said riser conduit means including means flexibly connecting said buoyant means to the floor of said body of water; 1

(d) a well head assembly attached to the upper end of said production string.

References Cited UNITED STATES PATENTS OTHER REFERENCES The Oil & Gas Journal of Jan. 25, 1960, pp. 122-123.

JACOB SHAPIRO, Primary Examiner US. Cl. X.R.

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