US3373806A

US3373806A - Apparatus and method for drilling wells

Info

Publication number: US3373806A
Application number: US361447A
Authority: US
Inventors: Virgil D Stone
Original assignee: Gulf Oil Corp
Current assignee: Gulf Oil Corp
Priority date: 1964-04-21
Filing date: 1964-04-21
Publication date: 1968-03-19
Anticipated expiration: 1985-03-19
Also published as: DE1261458B; GB1108482A; NL6505057A

Description

March 19, 1968 v. D. s'ToNE APPARATUS AND METHOD FOR DRILLING WELLS 5 Sheets-Sheet 1 Filed April 21, 1964 INVENTOR. V/QG/L 0. STONE ATTORNEY.

March 19, 1968 v. D. STONE APPARATUS AND METHOD FOR DRILLING WELLS 3 Sheets-Sheet 3 Filed April 21, 1964 I N VENTOR WQG/L 0. STONE k v Arra /VEK A March 19, 1968 v. D. STONE APPARATUS AND METHOD FOR DRILLING WELLS 3 Sheets-Sheet 5 Filed April 21,1964

INVENTOR. V/RG/L 0. 570M? ATTORNEK United States Patent 3,373,806 APPARATUS AND METHOD FOR DRILLING WELLS Virgil D. Stone, Morgan City, La., assiguor to Gulf Oil Corporation, Pittsburgh, Pa. Filed Apr. 21, 1964, Ser. No. 361,447 18 Claims. (Cl. 166.5)

This invention relates to oil and gas wells drilled in underwater locations, and more particularly to a method and apparatus for drilling and completing such wells.

Oil wells have been drilled and completed in offshore locations in water as deep as about 200 feet. If the offshore well is a wildcat well, a mobile rig is often preferred because such a rig can readily be moved to another location if the well should be a dry hole. If an offshore well in water deeper than about 50 feet should prove to be productive, it is necessary to keep the mobile rig on location to brace the well until a suitable platform for support of the wellhead assembly can be constructed. The cost of platforms for hanging casing and supporting the wellhead assembly increases rapidly with increases in depth of the water. For example, a platform for use in water 350 feet deep is estimated to cost approximately $2,000,000. It is apparent that platforms for wells in water of that depth will be built only after it has been established that the well has penetrated a reservoir containing a substantial amount of oil. However, rental for a rig capable of drilling in water of that depth i approximately $8,500 a day; hence any delay in installing a platform to support the well will cause large rental charges while the rig merely braces the casing.

One method that has been suggested for eliminating the cost of platforms to support the wellhead structure is to install the wellhead at or slightly above the botom of the body of water. In shallow locations, conventional wellhead structures can be installed on the well underwater by divers. Such installations are limited to wells in shallow water in which the pressure allows the divers to work safely.. Ordinarily, the cost of platforms supporting wells in shallow water is not excessive. Special wellhead connections and apparatus allowing the wellhead assembly to be installed by remote control have been suggested for use on wells completed at depths below those at which divers can safely work, but the many problems inherent in installing a wellhead assembly by remote control have greatly increased the cost and hazards of such well completions.

Moreover, it is desirable that the well and the flow lines from the well be readily accessible for servicing. For example, deposition of paraffin from the flow lines of a well to the separator can quickly plug a well and seriously reduce production from the well. In some areas in which the productive sands are unconsolidated, the flow lines of the well may become quickly plugged with sand. Both sanding and paraffin deposition frequently occur in wells drilled in the Gulf of Mexico off the Louisiana coast, an area in which drilling in deep water is most prevalent. The installations of wellhead assemblies at or near the bottom of the ocean floor by the techniques heretofore suggested have left the wells in a condition such that servicing was difficult.

This invention resides in a method and apparatus for completion of wells drilled in formations under Water more than fifty feet deep and which may be as much as 600 feet deep. The method and apparatus are particularly advantageous for the completion of wells in deep water ranging from 100 to 600 feet deep. In this invention, a heavy-walled tube having a diameter large enough to permit a man to be lowered through it and install a wellhead assembly is forced, either before or after the well is drilled,

into the ground at the bottom of the body of water, hereinafter referred to as the ocean floor, surrounding the well to a depth adequate to exclude flow of water into the tube. Preferably the tube is driven to refusal into the ocean floor. The tube, herein referred to as a snorkel tube, extends upwardly above the surface of the water. After the well is drilled, casing set, and the tube is in place, water is pumped from the snorkel tube to permit access to the well at any desired level above the ocean floor for the installation of conventional wellhead apparatus and flow lines by workmen who work at atmospheric pressure. The snorkel tube provides a support for the flow lines from the well and the necessary equipment for production of oil from the well. In one embodiment of the process of this invention particularly suitable for use in wildcat wells, a well is drilled and tested by any desired means, and thereafter the snorkel tube is driven into the ocean floor only when a producing well is assured.

Referring to the drawings:

FIGURE 1 is a diagrammatic view partly in vertical section of a well drilled by a mobile rig after testing and prior to cutoff of the upper portion of the well;

FIGURE 2 is an elevational view, partially in vertical section, showing the well illustrated in FIGURE 1 at an intermediate stage of completion with the snorkel tube and supporting structure in place;

FIGURE 3 is a diagrammatic view, partially in vertical section, of a Well completed and ready for production of oil;

FIGURE 4 is a horizontal sectional view taken along the section line 44 in FIGURE 2; and

FIGURE 5 is a diagrammatic view showing in elevation an embodiment of the invention in which the snorkel tube is installed prior to drilling the well.

Referring to FIGURE 1 of the drawings, a well indicated generally by reference numeral 10 is illustrated extending downwardly below a body of water with a mobile drilling rig 12 supported above the well by the ocean floor. Mobile drilling rig 12 is shown in FIGURE 1 only for purposes of illustration. One of the advantages of this invention is that it is suitable for use with either mobile drilling rigs supported by the bottom of the body of water or floating drilling rigs. The method of completing a well in accordance with this invention described with reference to FIGURE 1 is particularly valuable in drilling a wildcat well in that it permits drilling and testing the well before the expense of the snorkel 'tube or other supporting structure is incurred. Well 10 has the usual thin-walled conductor pipe 14, which may be from about 16 to 36 inches in diameter, washed or driven into the ocean floor. Extending downwardly through conductor pipe 14 to a depth depending on conditions encountered in the Well is a string of surface casing 16. Surface casing 16 is cemented in place within the conductor pipe 14 in any suitable manner with the cement displaced to a level 18 slightly above the ocean floor 20. The annular space 22 between casing 16 and conductor pipe 14 above level 18 is filled with sand. In the particular well 10 illustrated in FIGURE 1, a second string of casing 24 is run through casing 16 and is cemented in place by a suitable procedure which is not affected by this invention. In the well illustrated in FIGURE 1 a multiple-stage cementer 26 closes the annulus between the casing 24 and casing 16 and the annulus above cementer 26 is filled with cement 'to the height required by conditions encountered in the well and determined by the usual considerations.

After tests have indicated that the well has penetrated a productive zone which justifies completion of the well, the well 10 is plugged by 'the installation of a drillable cement retainer 28 inside casing 24 and a cement plug approximately feet long above the retainer. A second 3 drillable cement retainer 39 may be installed above the cement plug. Thereafter, the strings of

casing

24 and 16 and the conductor pipe 14 are cut above the ocean floor 20 and removed from the upper end of the well. Cutting of the casing can be accomplished, for example, by means of a high velocity abrasive slurry.

Referring to FIGURE 2 a snorkel tube support, indicated generally by reference numeral 32, is lowered into position over the stub of well 10 and secured to the ocean floor by piles 34. Support 32 has a guide sleeve 36 at its upper end and an annular storage tank 38 at its lower end. An oil line 40 extends from the upper end of storage tank 38 upwardly to the water surface for the delivery of oil into and withdrawal of oil from the storage tank 38. A vent line 42 at the lower end of storage tank 38 allows the sea water to flow out of or into the storage tank as oil is delivered into or withdrawn from the tank. Support 32 may be lowered into place from the drilling rig 12. One of the advantages of this invention, however, is that drilling rig 12 can be moved from its location immediately after the testing of the well to avoid rental charges for the drilling rig while awaiting production facilities. The support 32 and a snorkel tube 44 are constructed only after it is decided to complete the well.

The support 32 provides lateral bracing of the snorkel tube at a location between the ocean floor and the surface of the water. The upper end of the support 32 will preferably engage the outer surface of the snorkel tube approximately 50 to 100 feet below the surface of the water. Because at that level the support 32 is not exposed to strong forces created by winds or waves and because the support 32 does not carry the weight of the wellhead assembly and production equipment, the support 32 may be a relatively inexpensive lightweight structure. The exact location of the upper end of the support will be determined largely by the depth of the body of water in which the well is drilled. In some instances, it may be desirable to provide lateral bracing of the snorkel tube at or even above the surface of the water, but such an arrangement loses some of the advantage over platforms of reduction of the area of equipment exposed to wind and wave action. In shallow water, for example 50 feet, the snorkel tube may be used without a support giving it lateral bracing. In deeper water a comparison between the added cost of a snorkel tube of adequate rigidity and the cost of a support 32 may determined whether or not a support is used, particularly if storage at the well site is not needed.

The snorkel tube 44 is a heavy-walled tube having a diameter large enough to permit workers to be lowered through the tube and to install a conventional Christmas tree on the upper end of the casing. Snorkel tube 44 should have a diameter of about 36 to 72 inches, preferably 40 to 48 inches and a well thickness of approximately to 2 inches. The thickness of the wall of the snorkel tube is dependent on the depth of water in which the tube is used, the tube diameter, and the length of the unbraced upper section of the snorkel tube. For example, a wall thickness of /3 inch is adequate for a 48-inch diameter snorkel tube in water 100 feet deep while a wall thicknes of more than one inch is required for water 350 feet deep. In contrast with platforms which have been suggested for supporting wells above the surface of the water, the snorkel tube exposes only a small area to forces exerted by waves and Wind. Thus the heavy-walled snorkel tube, being firmly anchored in the ocean floor, and not being subjected to the weight of the casing and wellhead asem'bly, provides a firm support for lightweight production equipment above the surface of the water.

The snorkel tube 44 is lowered through sleeve 36 around the stub of well ltl and driven, preferably to refusal, into the ocean floor. The snorkel tube is driven or jetted into the ocean floor a distance adequate to support the full weight of the snorkel tube and to prevent flow of water around the lower end of the snorkel tube and upwardly through the tube to the level of the mud line even though 4,. the body of water is 200, or more, feet deep. Thereafter, water is pumped from the snorkel tube and workmen are lowered through the snorkel tube to install conventional surface-type wellhead equipment at or slightly above the ocean floor 20. Blowout preventers are connected to the upper end of well 10 and the

cement plug retainers

30 and 28 and the cement plug are drilled from the well. Thereafter the well is completed, for example, as illustrated in FIGURE 3 with a conventional Christmas tree and wellhead assembly indicated generally by reference numeral 46.

In atypical wellhead assembly illustrated in FIGURE 3, workmen lowered into the snorkel tube cut off the conductor pipe above the level 18 of the cement in the annulus 22 and below the upper ends of surface casing 16 and casing 24. The surface casing 16 is then cut off below the upper end of casing 24. A short externally threaded joint 47 of surface casing is welded at 48 to the upper end of the surface casing 16 and easing head 50 is screwed to the upper end of joint 47.

Casing head 50 has an upwardly opening bowl surface 52 adapted to receive a casing hanger 54 which slides over the upper end of the second string of casing 24 and seats in bowl surface 52. Casing hanger 54 has internal slips, not shown in the drawings, which engage the outer surface of the casing 24, as that string of casing is pulled up, and hold casing 2-4 in tension. The casing 24 is then cut off a short distance above the upper surface of easing hanger 54 and may, if desired, be welded to the casing hanger. A casing spool 56 is secured to the upper end of the easing head 50 by suitable means. Casing spool 56 has a downwardly facing surface adapted to engage the upper surface of casing hanger 54. Seal rings 58 and 60 prevent leakage between the casing hanger and the casing spool and casing head. If desired, tubing can be run downwardly through casing 24, in which event conventional tubing hangers will be mounted in the usual manner in suitable fittings supported by the upper end of casing spool 56. Positive chokes are usually installed in the wellhead assembly to reduce the pressure in flow lines exposed to damage by collision or storms. It will be apparent that the particular wellhead assembly illustrated in FIGURE 3 is shown merely for purposes of illustration, and this invention is not restricted to any particular type of equipment used to make up the wellhead assembly.

A flow line 62 extends upwardly from the well head assembly through the snorkel tube above the water line 64 for connection to a lubricator 66 mounted in the upper end of the snorkel tube 44. Flow line 62 continues upwardly to a separator unit 68 provided with suitable flow controls for control of flow of oil from the separator. An oil line 70 from the separator is connected to oil line 40, which extends upwardly from the oil storage tank 38, for delivery of oil from the separator 68 to the storage tank. Mounted in the upper end of the snorkel tube above the separator 68 is a turbine 72 driven by gas from the separator to operate a generator unit 74 which supplies electricity for a foghorn and light unit 76 mounted on the top of the snorkel tube. If desired, the generator unit can be driven by LPG, compressed air, or other suitable means, or can be replaced by a suitable battery to supply electricity for the foghorn and light unit.

Manholes

78, 80, and 82 are provided along the upper end of the snorkel tube above the water line 64 to allow access to the equipment supported in the snorkel tube.

In the operation of the well, oil produced from the well flows upwardly through line 62 into the separator 68 and downwardly from the separator through oil line 70 into oil line 40 and then into the oil storage tank 38. Oil flowing into oil storage tank 38 displaces water from the lower end of the tank through vent line 42. Because storage tank 38 is open through line 42, it is at substantially the same pressure inside and out; hence, may be constructed of thin gauge metal. Oil is periodically delivered from the storage tank 38 to a barge through line 40 and valve 84 by hydraulic pressure of water entering the storage tank. Service work on the well can readily be accomplished through the lubricator 66 when necessary. If repair to connections in the Christmas tree assembly 60 is necessary, a workman can be lowered through the snorkel tube to make the necessary repairs at atmospheric pressure.

This invention has been described for use on a wildcat well where it is not known whether or not the well would penetrate productive formations. In such operations, the cost of the snorkel tube is delayed until production from the formation is proven. Moreover, by plugging the well in the manner described, the heavy mobile rig can be moved from location and the high cost of rent of the rig while the snorkel tube is constructed can be avoided. The snorkel tube can later be lowered into position and the cement plugs drilled from a less expensive rig.

When drilling into a proven reservoir, it is advantageous to install the snorkel tube before the well is drilled, as is illustrated in FIGURE 5. Referring to FIGURE 5, the snorkel tube support 32 is lowered into position and secured in place by piles 34 driven into the ocean floor 20. Snorkel tube 44 is then lowered from a drilling rig 86, illustrated as a floating rig, and either washed or driven for the desired depth into the ocean floor. Thereafter a drill bit 88 is lowered through the snorkel tube and the well drilled by conventional procedures. After the well has been drilled, the casing within the snorkel tube 44 is cut off. As in the embodiment described with reference to FIGURES 1 through 4, the casing can be cut by means of a milling tool or a rotating abrasive jet operated from the rig 86. The height at which the well is cut off can range from approximately the level of the ocean floor 20 up to the maximum height above ocean floor 20 at which the well casing will safely'support the wellhead assembly. The wellhead assembly is installed and the flow lines and production apparatus connected in the manner described with respect to FIGURES 1 through 4. An alternative procedure would'be to install the initial part of the wellhead assembly near the ocean floor with blowout preventers bolted to the head, also near the ocean floor level. After drilling, the blowout preventers would be removed and the well completed at the ocean floor in conventional manner, except for sub-sea locations.

The installation of the wellhead assembly below the surface of the water and preferably slightly above the ocean floor avoids the necessity of a platform to support an otherwise long, slender well column. Because the support for the snorkel tube only supplies lateral bracing, it can be of relatively lightweight construction. Only the relatively small surface of the snorkel tube is exposed to waves, wind, and collision; the wellhead assembly and the Christmas tree are located out of danger at the ocean floor. Flow lines extending to the surface of the'water where they may be damaged by collision or wave action do not contain well fluids under high pressure, since there is a positive choke in the wellhead.

The snorkel tube, being of heavy-walled construction, provides protection and support for production apparatus located at or above the surface of the water, and being permanently installed, provides a continuously open passage to the wellhead assembly. The flow lines both above and below'the wellhead assembly being vertical are readily serviced by wire line equipment on an ordinary small reworkingrig. Service of a well can be performed immediately without special equipment for gaining access to the wellhead connections by workmen working at atmospheric pressure. Because the snorkel tube is driven deep into the ocean floor, for example as much as 100 or more feet, the seeping of water upwardly through the snorkel tube to the level of the ocean floor is very slow, even though the body of water is 500 feet deep. Unlike the usual caisson, it is not necessary to maintain a high pressure in the snorkel tube to exclude water.

I claim:

1. A method of completing a well below a body of water at least about 50 feet deep comprising forcing a heavy-walled snorkel tube permanently encircling and separate from casing of the well downwardly into the ground below the body of water whereby said snorkel tube is supported by the ground and extends upwardly above the surface of the water, said snorkel tube having a diameter of approximately 40 to 72 inches to permit a workman to descend in the tube to install wellhead connections, pumping water out of the tube, cutting olf casing of the well adjacent the bottom of the body of water, installing a wellhead assembly on the upper end of the casing, running a flow line from the wellhead assembly upwardly through the tube to above the surface of the Water, and supporting the flow line within the tube for delivery of well fluids above the surface of the water.

2. A method as set forth in claim 1 in which a positive choke is installed in the flow line at the wellhead assembly.

3. A method of completing a well below a body of water at least about 50 feet deep comprising forcing a heavy-walled snorkel tube into the ground below the body of water a distance adequate to support the tube, said tube permanently extending upwardly above the surface of the water and having a diameter of about 40' to 72 inches allowing lowering of workers therethrough and installation of a wellhead assembly therein, lowering a drill bit through the tube and drilling the well to the desired depth, setting casing in the well, cutting off the casing within the tube adjacent the bottom of the body of water, pumping water from the tube to expose the upper end of the casing to the atmosphere, installing a wellhead assembly on the upper end of the casing, running a flow line from the wellhead assembly upwardly through the tubeto above the surface of the water, and supporting the flow line within the tube for delivery of well fluids above the surface of the water.

4. A method as set forth in claim 3 in which the flow line is extended upwardly through the tube to a separator mounted in the upper end of the tube above the surface of the water.

5. A method of completing a Well extending into subterranean formations below a body of water at least about 50 feet deep comprising drilling a borehole to the desired depth through the subterranean formations, setting casing in the borehole, temporarily plugging the casing below the bottom of the body of water, cutting off the easing at a level between the bottom of the body of water and the maximum height at which the casing will safely support a wellhead assembly, forcing a unitary heavy- Walled snorkel tube having a diameter of approximately 40 to 72 inches permitting workers to descend therethrough into the ground below the body of water a distance adequate to support said tube and prevent substantial seepage into the tube, said tube encircling and separate from the casing and permanently extending upwardly above the surface of the water, removing water from the tube to expose the upper end of the tube to the atmosphere, drilling the temporary plugs from the casing, installing a wellhead assembly on the upper end of the casing, running a flow line from the wellhead assembly upwardly through the tube to a level above the surface of the water, and supporting the flow line within the tube for delivery of well fluids above the surface of the water.

6. A method of completing a well in water at least about feet deep comprising forcing a unitary heavynwalled snorkel tube having a diameter of approximately 40 to 72 inches adequate to permit lowering of workmen therethrough into the bottom of a body of water to a depth adequate to support the tube and prevent substantial seepage of water into the tube, said tube extending permanently upwardly above the surface of the water, cutting off adjacent the bottom of the body of water casing encircled by the snorkel tube and extending downward to a subterranean formation, pumping water from the snorkel tube to lower the level of water thereinto to below the upper end of the casing, lowering a workman through the snorkel tube to the upper end of the casing, installing a wellhead assembly on the upper end of the casing, running a flow line up through the snorkel tube and supporting the flow line by the snorkel tube for delivery of well fluids above the surface of the water, and bracing said snorkel tube against lateral movement at a location 50 to 100 feet below the surface of the water.

'7. A method of completing a well in a body of water at least about 100 feet deep, said well having casing extending downwardly into the ground for a desired distance into a subterranean formation, comprising driving a heavy-walled snorkel tube having a diameter of 40 to 72 inches adequate to permit a man to descend in the tube and install wellhead equipment downwardly into the bottom of a body of water to a depth adequate to support said snorkel tube and prevent substantial seepage of water upwardly through the snorkel tube, said snorkel tube encircling and separate from the casing and permanently extending upwardly above the surface of the body of water, laterally bracing the snorkel tube at a depth about 50 feet below the surface of the body of water, pumping the water out of the snorkel tube, lowering a workman in the snorkel tube, installing a wellhead assembly on the casing adjacent the bottom of the body of water, running fluid flow lines from the wellhead assembly upwardly through the snorkel tube to above the surface of the water, and supporting the flow lines by the snorkel tube for delivery of well fluids above the surface of the water.

8. A method as set forth in claim 7 in which the snorkel tube is driven to refusal in the bottom of a body of water and piles are driven into the bottom of the body of water to anchor a support providing lateral bracing of the snorkel tube.

9. A method of completing an oil well in a body of water at least 100' feet deep and producing oil therefrom comprising driving a heavy-walled snorkel tube having a diameter in the range of 40 to 72 inches to refusal in the bottom of the body of water, said snorkel tube permanently extending upwardly above the surface of the water, lowering a drill through the snorkel tube and drilling a hole to a desired depth into a subterranean formation, setting casing in said hole, pumping water from the snorkel tube to expose casing at the level of the bottom of the body of water to atmospheric pressure, cutting off casing within the snorkel tube adjacent the bottom of the body of water, lowering workmen through the snorkel tube and installing a wellhead assembly on the casing adjacent the bottom of the body of water, running flow lines from the wellhead assembly upwardly through the snorkel tube to a separator supported by the snorkel tube above the surface of the body of water, separating oil from gases delivered through the fiow line in the separator, delivering oil from the separator to a storage tank at substantially the bottom of the body of water to displace oil from the lower end of said storage tank, and periodically delivering oil from the storage tank to a receiver at the surface of the body of water.

10. A well extending from an underground fluidbearing formation upwardly to a body of water at least about 50 feet deep at the surface comprising casing extending from the fluid-bearing formation upwardly to a level slightly above the bottom of the body of water, a unitary permanent heavy-walled snorkel tube having an internal diameter of approximately 40 to 72 inches permitting passage of workers therethrough extending continuously from above the surface of the water downwardly into the ground below the body of water a distance adequate to support the tube and prevent substantial seepage of water into the tube, said heavy-walled tube encircling and separate from the casing, a wellhead assembly connected to the upper end of the casing slightly above the 8 bottom of the body of water, and a flow line extending upwardly throughand supported by the tube for delivery of well fluids above the surface of the water.

11. A wall as set forth in claim 10 in which a positive choke in the wellhead assembly controls fiow through the flow line.

12. An underwater well extending downwardly into subterranean formation below a body of water at least about 50 feet deep comprising casing extending for the desired depth into the subterranean formations, a heavywalled snorkel tube encircling and separate from the casing and extending from above the surface of the water into the ground below the body of water to a depth adequate to support the tube and prevent substantial flow of water into the tube, said tube having a diameter permitting passage of men therethrough and installation of a wellhead assembly therein, a wellhead assembly connected to the upper end of the casing slightly above the bottom of the body of water, a flow line extending upwardly through the tube from the wellhead assembly, and a separator mounted in the upper end of the tube above the water level, said flow lines being connected to the separator for delivery of well fluids into the separator.

13. An underwater well as set forth in claim 12 in which the body of water is at least about feet deep and a well support engages the outer surface of the tube about 50 feet below the surface of the Water to provide lateral support for the tube.

14. An underwater well as set forth in claim 12 in which the body of water is 100 to 600 feet deep and a Well support engages the outer surface of the tube about 50 to 100 feet below the surface of the water to provide lateral support for the tube.

15. An underwater well extending into subterranean formations below a body of water at least about 100 feet deep comprising casing extending for the desired depth into said subterranean formations, a heavy-walled snorkel tube encircling the casing and extending from above the surface of the water into the ground below said body of water whereby the ground supports said snorkel tube, a wellhead assembly connected to the upper end of the casing at a level above the bottom of the body of water and below the surface of the water whereby the casing supports the wellhead assembly, a separator mounted in the upper end of the snorkel tube above the surface of the water, a flow line extending from the wellhead assembly upwardly through the snorkel tube to the separator, a supporting structure secured to and supported by the bottom of the body of water engaging the outer surface of the tube about 50 feet to 100 feet below the surface of the water, an oil storage tank secured to said supporting structure, and an oil line extending downwardly from the separator into the upper end of the oil storage tank, said oil storage tank having a vent in its lower end to permit flow of water into said storage tank.

16. A well in water at least about 100 feet deep comprising a heavy-Walled tube having a diameter of approximately 40 to 48 inches driven to refusal in the bottom of a body of water, said tube extending upwardly above the surface of the water and being open to the atmosphere at its upper end, means laterally bracing the tube at a level at least about 50 feet below the surface of water, casing within the snorkel tube and separate therefrom extending downwardly to the desired depth into a subterranean formation, a wellhead assembly mounted on the casing adjacent the bottom of the body of water, and a flow line extending upwardly through the snorkel tube to above the surface of the body of water.

17. A method of drilling and completing an offshore Well in water at least 50 feet deep comprising locating a drilling rig at the Well site, drilling the well to the target formation, setting casing in the well, testing the well for production, setting a plug in the well to prevent upward flow of fluids through the well, cutting the casing slightly above the ocean floor, moving the drilling rig from the site, driving a heavy-walled tube having a diameter of 40 to 72 inches into the ocean floor, said heavy-walled tube encircling and separate from the casing and extending from above the surface of the water into the ocean floor a distance adequate to support the tube and prevent flow of water into the lower end thereof, pumping water from the heavy-walled tube to expose the ocean floor within the tube to atmospheric pressure, installing a blowout preventer on the casing slightly above the level of the ocean floor, removing the plug from the well, and installing a wellhead assembly on the casing at a level slightly above the ocean floor.

18. A method of drilling and completing an offshore well in water at least 50 feet deep comprising locating a drilling rig at the well site, setting conductor pipe extending from above the surface of the water downwardly into the ocean floor, lowering a drill through the conductor pipe and drilling to an intermediate depth, setting surface pipe in the well, locating cement in the annulus between the surface pipe and conductor pipe from the bottom of the surface pipe to approximately the level of the ocean floor, filling said annulus above the cement with sand, drilling the well to the target formation and setting casing in the well, testing the well for production, setting a plug in the well to prevent upward flow of fluids through the well, cutting the casing, surface casing, and conductor pipe at a level slightly above the ocean floor, moving the drilling rig from the site, driving a heavy-walled tube having a diameter of 40 to 72 inches into the ocean floor, said heavy-walled tube encircling and separate f om the casing and extending from above the surface of the water into the ocean floor a distance adequate to support the tube and prevent flow of water into the lower end thereof, pumping water from the heavy-walled tube to expose the ocean floor within the tube to atmospheric pressure, installing a blowout preventer on the casing slightly above the level of the ocean floor, removing the plug from the well, and installing a wellhead assembly on the casing at a level slightly above the ocean floor.

References Cited UNITED STATES PATENTS 2,631,558 3/1953 Harris 114-.5 2,684,575 7/1954 Pryor et a1 1758 X 2,699,321 1/1955 Nelson 1758 2,731,168 1/1956 Watts 114.5 2,854,215 9/1958 Cox et al 61-82 X 2,906,500 9/1959 Knapp et al 166.5 2,988,144 6/1961 Conrad 166-.5 3,020,956 2/1962 Suderow 1755 X 3,125,171 3/1964 Stewart 175-9 X 3,202,218 8/1965 Watts et a1. 166.5 3,221,816 12/1965 Shatto et al. 166.5

CHARLES E. OCONNELL, Primary Examiner.

ERNEST R. PURSER, Examiner.

RICHARD E. FAVREAU, Assistant Examiner.

Claims

1. A METHOD OF COMPLETING A WELL BELOW A BODY OF WATER AT LEAST ABOUT 50 FEET DEEP COMPRISING FORCING A HEAVY-WALLED SNORKEL TUBE PERMANENTLY ENCIRCLING AND SEPARATE FROM CASING OF THE WELL DOWNWARDLY INTO THE GROUND BELOW THE BODY OF WATER WHEREBY SAID SNORKEL TUBE IS SUPPORTED BY THE GROUND AND EXTENDS UPWARDLY ABOVE THE SURFACE OF THE WATER, SAID SNORKEL TUBE HAVING A DIAMETER OF APPROXIMATELY TO 72 INCHES TO PERMIT A WORKMAN TO DESCEND IN THE TUBE TO INSTALL WELLHEAD CONNECTIONS, PUMPING WATER OUT OF THE TUBE, CUTTING OFF CASING OF THE WELL ADJACENT THE BOTTOM OF THE BODY OF WATER, INSTALLING A WELLHEAD ASSEMBLY ON THE UPPER END OF THE CASING, RUNNING A FLOW LINE FROM THE WELLHEAD ASSEMBLY UPWARDLY THROUGH THE TUBE TO ABOVE THE SURFACE OF THE WATER, AND SUPPORTING THE FLOW LINE WITHIN THE TUBE FOR DELIVERY OF WELL FLUIDS ABOVE THE SURFACE OF THE WATER.