US3221816A

US3221816A - Underwater oil gathering installation

Info

Publication number: US3221816A
Application number: US157654A
Authority: US
Inventors: Jr Howard L Shatto; Bruce J Watkins; Dozier James Ronald; Bill L Faulk; Benjamin L Goepfert
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1961-12-07
Filing date: 1961-12-07
Publication date: 1965-12-07
Anticipated expiration: 1982-12-07

Description

Dec. 7, 1965 H. L. SHATTO, JR., ETAL 3,221,816

UNDERWATER OIL GATHERING INSTALLATION Filed Dec. 7. 1961 4 Sheets-Sheet 1 FIG. I

INVENTORS:

H. L. SHATTO,JR. B. J. WATKINS B. L. FAULK J. R. DOZIER B. L. GOEPFERT BY: d. Hl- Q THEIR AGENT FIG. 2

Dec. 7, 1965 H. L. SHATTO, JR.. ETAL 3,221,816

UNDERWATER OIL GATHERING INSTALLATION 4 Sheets-Sheet 2 Filed Dec. 7. 1961 INVENTORS'.

H. L. SHATTQJR. B. J. WATKINS B. L. FAULK J. R. DOZIER FIG.

B. L. GOEPFERT d. H m THEIR AGENT Dec. 7, 1965 H. 1.. SHATTO, JR.. ETAL. 3,221,815

UNDERWATER OIL GATHERING INSTALLATION Filed Dec. 7, 1961 4 Sheets-Sheet 5 & INVENTORS:

H. SHATTO,JR. B. J. WATKINS B. FAULK i J. R. DOZIER B. L. GOEPFERT FIG. 7 45 1965 H. L. SHATTO, JR. ETAL 3,221,816

UNDERWATER OIL GATHERING INSTALLATION Filed Dec. '7, 1961 4 Sheets-Sheet 4 GAS COMPRESS/CEQ 4 CONDENSER f 1 e3 as T JSI T 73 6% T T I 74 BLOW 75 BLOW CASE CASE 7s a 0 82 W SEPARATOR 85 T 7 C? A A s m Z 1 f M 41 8e 85 J H.P. GAS

I J L J 11X 41% cflig" T T F 1 I 1 O TEST 0 TEST 0 BLOW 51.0w CASE CASE 5s A T T 'r 9 TEST i SEPARATOR II OTHER FIG. 8 WELLS {D 40 INVENTORSI T H. SHATTO,JR.

L B. J. WATKINS 56 B. FAULK 55 a. R. DOZIER B. GOEPFERT THEIR AGENT United States Patent 3,221,816 UNDERWATER 01L GATHERING INSTALLATION Howard L. Shatto, Jr., Palos Verdes, Bruce J. Watkins, West Covina, James Ronald Dozier, Whittier, Bili L. Faulir, Compton, and Benjamin L. Goepfert, West Covina, Calif., assignors to Shell Oil Company, New York, N.Y., a corporation of Eelaware Filed Dec. '7, 1951, Ser. No. 157,654 Claims. (Cl. 166-665) This invention relates to mobile underwater oil gathering installations of the type that can be anchored in any desired oflshore location, and pertains more particularly to a buoyant oil manifold-and-pump station positioned underwater for gathering oil from a plurality of offshore wells and conveying the oil to suitable production facilities located either offshore or on land.

To date, oil and gas wells have been drilled at oflishore locations from fixed platforms or from floating or submersible barges. At the conclusion of the well drilling operations, the well equipment and the Christmas tree attached to the top thereof extended above the surface of the water where it was surrounded by a platform which was fixedly supported from the ocean floor. In remote locations, the production facilities, such as an oil-and-gas separator and metering and storage tanks, were mounted on the platform at the well and the production fluid from the well was run into these tanks. In highly developed fields centralized production facilities for handling a number of wells would be constructed on piles sunk in the ocean floor at a centrally-located position among the wells. Individual production flow lines would then be run from the individual well to extend to the centralized production facilities where the production fluid would be gathered, separated and metered prior to transporting it to shore by means of tankers or through a pipe line.

While installations of the above-described types were satisfactory for oil fields located in shallow water, the same types of installations are impossible to construct or may be constructed only at excessive costs for deep-water fields. This is especially true where the oil and gas production fluid is coming from underwater wells, that is, wells wherein the wellhead facilities are positioned underwater or close to the ocean floor.

It is therefore an object of the present invention to provide an oil gathering production installation and pump station which may be economically constructed and positioned at an offshore location for handling the production fluid from a number of offshore wells.

Another object of the present invention is to provide a buoyant underwater oil manifolding-and-pump station for receiving production fluid from a plurality of underwater wells and for supplying the underwater wells with gas under pressure to produce the wells in the event that the wells are not of the free-flowing type.

While the production of offshore wells into a floating barge has been considered by some, installations of this type have undesirable features in that the equipment is subjected to corrosive conditions and to the wind and wave forces present on the surface of a large body of water.

It is a further object of the present invention to provide an oil-gathering installation for a plurality of offshore wells wherein the entire system is positioned underwater to overcome the problem of corrosion control normally associated with the splash zone of equipment extending above the surface, while getting the equipment away from the wind and wave forces at the surface. For example, a large measure of insulation or cushioning from violent action at the surface of the sea is realized by locating an underwater oil-gathering installation in accordance with the present invention at a depth of from about 60 to 100 3,221,816 Patented Dec. 7, 1965 feet or more below the ocean surface. The orbital motion of the wave particles is considerably reduced and the violent impact of a wave front at the surface is eliminated.

Another object of the present invention is to provide an underwater oil-gathering installation which is positioned at a depth suflicient to eliminate the possibility of collision with surface vessels and to eliminate the necessity of using costly navigational aids.

A still further object of the present invention is to provide an underwater oil gathering installation positioned near the surface of the water, say around feet in depth, so as to eliminate the high costs of equipment if the equipment were designed to withstand high hydrostatic pressures.

Another object of the present invention is to provide an underwater oil-gathering installation submerged at shallow depths so as to minimize the problem of tangled flow lines extending downwardly from the installation, as well as to control more readily the lateral movement of the underwater installation and reduce the time that it would take to float the installation to the surface as compared with a location near the bottom of the ocean. It is also desirable to have the underwater oil-gathering installation positioned at a depth so that divers can be readily used in the event of malfunctions of the buoyancy control system of the installation.

It is also an object of the present invention to provide an underwater oil-gathering installation with automatic control of liquid level therein to prevent uncontrolled ascent and descent of the installation.

Another object of the present invention is to provide an underwater oil-gathering installation with designed capacities of sealed buoyancy, variable buoyancy and weight of the anchoring system so that it is impossible to sink the installation to the bottom of the ocean even if the variable buoyancy tanks of the installation were completely flooded.

These and other objects of this invention will be understood from the following description taken with reference to the drawing, wherein:

FIGURE 1 is a schematic view illustrating an oilgathering installation in accordance with the present invention anchored at an underwater location with flow lines running to one or more oil and/or gas wells, while other lines run to shore or to an offshore production facility;

FIGURE 2 is a diagrammatic view taken in partial longitudinal section of one form of an anchoring device for anchoring the present oil-gathering installation;

FIGURE 3 is an enlarged detail view illustrating means by which auxiliary anchoring devices are mounted on the anchor lines of the present installation;

FIGURE 4 is a diagrammatic view taken in partial longitudinal section of one form of a hull of the present oil-and-gas handling vessel;

FIGURE 5 is a cross-sectional view taken along the line 55 of FIGURE 4;

FIGURE 6 is a plan view of the vessel of FIGURE 4 illustrating one form of a pipe-manifolding system for connecting a plurality of wells to the production-handling equipment positioned in the center of the vessel;

FIGURE 7 is a schematic view taken in partial longitudinal section of one form of a variable-buoyancy control system for the vessel of the present invention; and,

FIGURE 8 is a flow diagram of one form of typical production handling equipment to be positioned on the vessel of the present invention.

Referring to FIGURE 1 of the drawing, the vessel 11 of the present underwater oil-gathering installation is shown as being anchored to the ocean floor 12 by means of

anchor lines

13, 14 and 15 which extend to any suitable type of anchor 16, which may be in the form of a post 3 or pile 16. The anchor lines 13, 14 and 15 are of sufficient length so that the vessel 11 may be floated to the surface 17 of the body of water 18.

In FIGURE 2 the anchor post 16 is in the form of a pile or tubular member 20 which has been drilled in the ocean floor 12 after which cement 21 has been pumped down the pile and around the bottom thereof until it formed a pad on the surface of the ocean floor, as illustrated. Slidably mounted on the top of the pile 20 is a tubular concentric sleeve 22 to which any suitable type of cable connector 23 may be fixedly secured for connecting the cable 13 thereto. While the sleeve 22 could be fixedly secured to the pile 20 permanently, it is preferably removably secured thereto by pins or bolts 24 which would be operatively engaged by means of a diver or by means of a remotely controlled underwater manipulator which could be mounted for movement around a circular track 25 which in turn was welded to the outside of the sleeve 22. If desired, the top of the sleeve 22 may be provided with a cap 26 at the top thereof which would be fastened on in any suitable manner as by bolts 27.

In addition to the usual function of maintaining a vessel 11 at a predetermined offshore location, the anchoring system of the present invention provides a vertical stabilizing characteristic for maintaining the vessel 11 at the designed operating depth, in this case 100 feet, below the surface of the water 17. For purposes of description the vessel of the present invention will be described as one designed to operate at water depths of from 60 to 100 feet although it is to be understood that the same vessel could be designed to operate in any depth of water. The vertical stabilizer characteristic of the anchoring system permits a fail-safe design in the sense that, should the anchoring system fail, the sealed buoyancy tanks of the vessel provide sufficient buoyancy to surface the unit. The vertical stabilizing characteristic of the anchoring system is provided by pendant weights attached to the anchor lines in a manner such as to offer rapidly increasing resistance to upward movement of the vessel and rapidly decreasing resistance to downward movement of the vessel from the normal operating depth of 100 feet. The flexible and automatically variable pendant weights are secured to and depend from the anchor lines intermediate the ends thereof at a point where at least a portion of the weight is in contact with the ocean floor. The

pendant anchor weights

30, 31 and 32 on

anchor lines

13, 14 and 15 may be in the form of multiple strands of anchor chain giving the desired weight per foot that it is desired to add to the buoyant vessel as the Vessel moves upwardly from its designed 100 foot operating depth. The

pendant anchor weights

30, 31 and 32 provide the vessel with resilient compliance to orbital wave motion by means of their spring characteristic as they are alternately picked up and laid down on the ocean floor. Variable pendant weights in the form of chains are particularly desirable in that they are less apt to crush a flow line than large solid steel anchors would be if they were to rest on a flexible flow line. It is understood that while the use of chains is preferred, other pendant weight systems having similar characteristics may be employed.

As is shown in FIGURES 1 and 3, each pendant weight (say, weight 32) is secured in a suitable manner to a slidable carrier 33 which is a tubular member having a slight curve therein which is adapted to slide over the anchor line 15. Fixedly secured to the anchor line 15 is a stop member 34 for limiting the downward travel of the slidable carrier 33. Depending from the slidable carrier 33 is any suitable type of harness or connector for connecting the pendant weight 32 thereto. Also connected to the harness 35 is a retrieving line 36 which extends downwardly to the vessel 11 so that the carrier 33 and its pendant weight 32 may be drawn upwardly to the vessel, after the vessel has been surfaced, in order to alter or change the weight design of the pendant weight 32. This is necessary in that a portion of a cable type of pendant weight may be lost after years of useage.

The vessel 11 in FIGURE 1 is illustrated as being provided with at least one flexible flow line 37 extending from the vessel downwardly to the ocean floor and thence along the floor to shore or to a production platform for conveying the production fluid from the vessel 11. At the same time a second flexible line 39 is provided and extends to the same location where it is connected to a source of gas under pressure whereby, if needed, a supply of gas pressure may be provided at the vessel 11 for running the production equipment thereon, gas lifting the wells, and providing gas to the vessel for buoyancy control. In the event that the underwater oil-gathering installation of the present invention was employed at an oil field where the wells were freely flowing, a production flow line 46 interconnecting the vessel 11 with the well (not shown) would be used along with a second line 41 which would be used to control the flow from the Well. However, in the event that the wells are to be produced by gas lift, the second flow line 41 would be provided between the vessel and the well for supplying gas under pressure thereto as well as for control of flow from the well. Thus, in most instances it will be necessary to have two flow lines, one for production fluid and one for gas or control, between the vessel 11 and each wellhead on the ocean floor. Although the

flow lines

37, 38, 40 and 41 have been described as being flexible, it is to be realized that most of the flow lines may be of a rigid material as long as there is a sufliciently long section of flexible fiow line between the vessel 11 and the ocean floor so as to permit the vessel 11 to be raised to the surface for maintenance operations.

One form of a vessel 11 may be similar to that illustrated in FIGURES 4 and 5. The vessel 11 comprises a hull 42 having buoyancy compartments 43 and 44 therein which are open to the ocean at all times through screened openings 45 in the bottom thereof. Thus, the

compartments

43 and 44 form variable-buoyancy chambers wherein the water level can be selectively adjusted so as to regulate the buoyancy of the vessel and hence its depth below the surface of the water. The hull 42 of the vessel is also provided with a designed amount of fixed buoyancy in the form of sealed tanks. For safety purposes, suflicient fixed buoyancy is provided by tanks 46 so that the vessel will not sink below a predetermined depth, say 150 feet, in the event that all of the variable buoyancy compartments 43 and 44 are flooded, or even if one or two of the sealed tanks 46 have been ruptured.

A compressor 47 is centrally positioned in the hull of the vessel 11 together with other production equipment such as a pair of

blow cases

50 and 51 which are alternately filled with production fluid and emptied by means of compressed gas in transporting the production fluid away from the vessel 11. The manifold piping system interconnecting various units of the production system on the vessel, as well as connecting them with the individual wells, is all located at the top of the vessel for ease of maintenance and this piping assembly may be covered by means of a flexible cover 96.

In addition to a compressor 47 and blow

cases

50, 50a, 51 and 51a, as illustrated in FIGURE 6, the vessel is also provided with a suitable separator 52 adapted to be connected to the wells for receiving the production fluid therefrom and separating the oil, gas and water phases thereof in a manner well known to the art. Preferably a second oil and gas separator 53 is provided which together with

blow cases

51 and 51a can be connected to the production flow line from one well at a time in order to test the production fluid thereof.

A typical flow diagram is shown in FIGURE 8 wherein the production fluid from a well assembly 55 passes out the production line 40 and through a remotely operated shut-off valve 56 which would normally be controlled either electrically, hydraulically or pneumatically from a land installation, or from a production platform at a distaut location. In the event that the well was not under test, the production fluid would pass through conduit 40 and out through open remotely-controlled valve 57 while valve 58 in bypassed test line 59 would be closed. From production line 40 the production fluid would enter the separator 52 where it would be separated with gas being discharged therefrom through line 61. The gas from line 61 would either be compressed by the compressor 47 through line 62 or .a portion of the gas not compressed would flow through line 63 and through remotely-operated shut-elf valve 64 and condenser 65 to flow through a separate line to the central production facility on shore, or at a distance platform.

A portion of the gas from the compressor 47 would flow through

lines

66, 67 and valve 68, and thence either through line 70 and valve 71 into blow case 50a, or through line 72 and valve 73 into blow case 50. The blow cases 50 and 50:: are provided with remotely-indicating liquid-

level indicators

74 and 75 which are connected to a suitable controller (not shown) well known to the art and located at the distant production facilities whereby the blow cases are alternately emptied by supplying gas under pressure to the top of first one blow case 50 and the second blow case 50a. At the same time liquid from the bottom of the separator 52 is flowing through discharge valve 76, preferably float operated, and through line 77 and check valve 78 into the bottom of blow case 50. When blow case 50 is being discharged, liquid from the separator flows through check valve 80 into the blow case 50a. Fluid from blow case 50 is discharged through check valve 81 into line 37 alternately with a flow of liquid from blow case 50a. The high pressure gas line 41 is preferably provided with remotely-reading

pressure transducers

83 and 84 on opposite sides of a remotelyoperated throttling valve 85 upstream of a remotely reading flowmeter 86.

If desired, all of the operations on the vessel which are run by high pressure gas may be run without the use of the compressor 47 on the vessel, with high-pressure gas from a remote location being used to control all operations. Thus, the high pressure gas coming to the vessel through conduit 41 may be piped through

line

87 and 88 to the pumps or blow

cases

50 and 50a. In a like manner the high pressure gas could be utilized to run the

test blow cases

51 and 51a. In the event that well 55 was put on test for say an 8 or 24-hour period, valve 57 in the production line would be closed while valve 58 in the bypassed test line 59 would be open, thus allowing the production fluid to run into the test separators 53. The operations carried out in the test separator and test

blow cases

51 and 51a are identical with those carried out in the main separator and blow

cases

50 and 50a with the fluid being discharged through flow line 37a which would be interconnected with the main flow line 37, preferably, before leaving the vessel. Thus, it will be seen that the blow cases form means, i.e., pump means, for pumping liquids from the vessel to a remote location. The oil flows by its own pressure from the separators into the bottom of the blow case. When the blow case is full, the liquid inlet closes, the liquid outlet opens and the high pressure inletopens. The high pressure gas on the liquid pushes it into the discharge line. When the case empties, the gas is vented to the separator outlet and the valve reposition for another charging cycle. The high pressure gas can be supplied from either the gas lift manifold or high pressure gas line from shore or from the discharge of the gas compressor. A gas compressor would be usually installed in order to prevent loss of production due to high well back pressures, or to eliminate the high cost of extended gas lines. The compressor is supplied with gas by the separators and compresses the gas to whatever pressure is required to overcome discharge line friction.

All of the normal operating functions of the vessel are monitored and controlled from a central production facility at a remote location. Operating parameters which are monitored include pressures, valve positions, blow case cycles, fluid levels in the process equipment and the vessel flotation tanks, compressor bearing temperatures, and gas temperatures. Normal producing operations, such as flowing to group or test facilities, scraping the flow lines, opening up or shutting down wells, circulating fluid, killing wells, or raising or lowering the vessel can 'be controlled from the central production facility.

For repairs or unusual operations, the vessel of the present invention can be floated to the surface. The change in buoyancy necessary to raise or lower the vessel is obtained by varying the gas volume in the open bottom tanks 43 and 44 (FIGURE 4). The gas volume is accurately controlled by any suitable type of closed-loop liquid level control system which is remotely operated. One form of a liquid level control system is illustrated in FIGURE 7 as comprising the liquid-level sensing element which may be in the form of a displacement element 90 connected to a transmitter 91 which is remotely connected to a liquid-level controller 92 at a distant location which opens or closes valve 93 and sets valve 94 either to admit high pressure gas from conduit 41b through valves 93 and 94 into the open bottom tank 44, or resets valve 94 to discharge gas out discharge line 95. The liquid-level sensing device may be of any suitable type well known to the art such for example as a differential pressure measuring device employed with a bubble column, a conductance type liquid-level control unit manufactured by Instruments, Incorporated, Tulsa, Oklahoma, bulletin LT-559, or a capacitance-sensitive level control device as manufactured by Instruments, Incorporated, Tulsa, Oklahoma, bulletin 159.

The automatic control of liquid level in

tanks

43 and 44 is required to prevent uncontrolled ascent and descent of the vessel. For example, without the liquid-level control the vessel would rapidly accelerate to the surface once the critical raising buoyancy was reached. The acceleration would be caused by the expanding gas volume at decreasing hydrostatic pressures resulting in rapidly increasing amounts of buoyancy. The liquid-level control operates to vent gas automatically on ascent or to inject gas on descent to maintain a constant liquid level and buoyancy. In the event that the

tanks

43 and 44 are interconnected a single liquid-level controller may be employed. In order to maintain smooth raising and lowering operations it is necessary that the buoyancy of the present vessel be controlled by liquid-level controllers rather than by pressure controllers.

We claim as our invention:

1. A system for gathering production fluid from underwater wells and transferring at least the oil portion of said production fluid to remote oil handling facilities, said system comprising in combination with at least one well assembly aflixed to the ocean floor, an oil and gas handling vessel buoyantly positioned in a body of water, resilient anchoring means resiliently positioning said vessel at a selected depth in said body of water, fluid intake conduit means connecting each well assembly with said vessel for delivery well fluid into said vessel, fluid transfer means carried by said vessel for transferring at least the oil portion of said fluid from said vessel, fluid discharge conduit means interconnecting said vessel with a fluid handling facility at a remote location for conducting fluid from said fluid transfer means, and valved manifold means connecting said fluid transfer means in fluid communication between said intake conduit means, and said discharge conduit means.

2. The apparatus of claim 1 wherein each of said conduit means has at least a flexible portion of its length sufficient to reach from the ocean floor to the vessel when it is floating at the surface of the water.

3. A system for gathering production fluid from underwater wells and transferring at least the oil portion of said production fluid to remote oil handling facilities, said systern comprising in combination with at least one underwater well assembly aflixed to the ocean floor, an oil and gas handling vessel buoyantly positioned in a body of water, resilient anchoring means resiliently positioning said vessel at a selected depth in said body of water fluid intake conduit means connecting each well assembly with said vessel for delivering well fluid into said vessel, fluid separation means carried by said vessel for separating at least the oil portion from said production fluid, pump means carried by said vessel for transferring at least the oil portion of said fluid from said vessel, fluid discharge conduit means interconnecting said vessel with a fluid handling facility at a remote location for conducting fluid from said pump means, and valved manifold means connecting said fluid pump means in fluid communication between said intake conduit means, said discharge conduit means and said fluid separation means, each of said conduit means having at least a flexible portion thereof adjacent said vessel, said flexible portion being of a length sufl'icient to reach from the ocean floor to the vessel when said vessel is floating at the surface of the water.

4. The apparatus of claim 3 including power transmission means extending from a remote power source and being connected to said pump means.

5. A system for gathering production fluid from underwater wells and transferring at least the oil portion of said production fluid to oil handling facilities on shore, said system comprising in combination with at least one underwater well assembly positioned on the ocean floor, an oil and gas handling vessel 'buoyantly positioned in a body of water, resilient anchor means resiliently positioning said vessel at a depth suflicient to be substantially unaffected by wave forces, flexible fluid intake conduit means connecting each well assembly with said vessel for delivering Well fluid into said vessel, fluid separation means carried by said vessel for separating at least the oil portion from said production fluid, pump means carried by said vessel for transferring at least the oil portion of said fluid from said vessel, flexible fluid discharge conduit means interconnecting said vessel with a fluid handling facility at a remote location on shore for conducting fluid from said pump means, valved manifold means connecting said fluid pump means in fluid communication between said' intake conduit means, said discharge conduit means and said fluid separation means, power fluid transmission means extending from a power fluid source and being connected to said pump means for the operation thereof, and

gas conduit means extending from short to said vessel to each well assembly for conveying gas under pressure therebetween.

References Cited by the Examiner CHARLES E. OCONNELL, Primary Examiner.

Claims

1. A SYSTEM FOR GATHERING PRODUCTION FLUID FROM UNDERWATER WELLS AND TRANSFERRING AT LEAST THE OIL PORTION OF SAID PRODUCTION FLUID TO REMOTE OIL HANDLING FACILITIES, SAID SYSTEM COMPRISING IN COMBINATION WITH AT LEAST ONE WELL ASSEMBLY AFFIXED TO THE OCEAN FLOOR, AN OIL AND GAS HANDLING VESSEL BUOYANTLY POSITIONED IN A BODY OF WATER, RESILIENT ANCHORING MEANS RESILIENTLY POSITIONING SAID VESSEL AT A SELECTED DEPTH IN SAID BODY OF WATER, FLUID INTAKE CONDUIT MEANS CONNECTING EACH WELL ASSEMBLY WITH SAID VESSEL FOR DELIVERY WELL FLUID INTO SAID VESSEL, FLUID TRANSFER MEANS