US3256936A

US3256936A - Drilling underwater wells

Info

Publication number: US3256936A
Application number: US118849A
Authority: US
Inventors: Glenn D Johnson; Bruce J Watkins
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1961-06-22
Filing date: 1961-06-22
Publication date: 1966-06-21
Anticipated expiration: 1983-06-21
Also published as: GB1008399A; GB1008398A

Description

J1me 1966 e. D. JOHNSON ETAL 3,256,936

DRILLING UNDERWATER WELLS Filed June 22, 1961 9 Sheets-Sheet 1 F I G l 24 INVENTORS:

BRUCE J. WATKINS GLENN D. JOHNS N BY: .Hfm TH RAGENT June 21, 1966 e. D. JOHNSON ETAL 3,256,936

DRILLING UNDERWATER WELLS Fue l June 22, 1961 24 9 Sheets-Sheet 2 FIG. 2A

,, I 3? FIG. 2B

FIG. 2

INVENTORS:

BRUCE J. WATKINS GLENN D. JOHNSON T IR AGENT J1me 1966 e. D. JOHNSON ETAL 3,

DRILLING UNDERWATER WELLS Filed June 22, 1961 9 Sheets-Sheet 5 lb Ill I 64 FIG. 3 3

BRUCE J. WATKINS GLENN D. JOHNSON TH IR AGENT June 21, 1966 G. D. JOHNSON ETAL 3,256,936

DRILLING UNDERWATER WELLS Filed June 22, 1961 9 Sheets-Sheet 4 FIG. 4

INVENTORSI BRUCE J. WATKINS GLENN D. JOHNSON ,HM QMZZ T EIR AGENT June 1966 e. D. JOHNSON ETAL 3,256,936

DRILLING UNDERWATER WELLS 7 Filed June 22, 1961 9 Sheets-Sheet 5 65 1 IIII II I ese w I I /l I --j.'

FIG. 5

I I INVENTORS: 3 BRUCE J. WATKINS GLENN D. JOHNSON TH IR AGENT June 21, 1966 e. D. JOHNSON ETAL 3,

DRILLING UNDERWATER WELLS Fizeo dune 22, 1961 9 Sheets-Sheet e INVENTORS:

BRUCE J. WATKINS GLENN D. JOHNSON TH IR AGENT June 1966 5. D. JOHNSON ETAL 3, 3

DRILLING UNDERWATER WELLS Filed June 22, 1961 9 Sheets-Sheet 7 BRUCE J. WATKINS GLENN D. JOHNSON R AGENT June 21, 1966 e. n. JOHNSON ETAL 3, 5 3

DRILLING UNDERWATER WELLS Filed June 22, 1961 9 Sheets-Sheet 8 IIOOOI FIG. 8

INVENTORS:

BRUCE J. WATKINS GLENN o. JOHNSON THEIR AGENT June 1966 e. D. JOHNSON ETAL 3,

DRILLING UNDERWATER WELLS Filec June 22, 1961 9 Sheets-Sheet 9 INVENTORS:

BRUCE J. WATKINS GLENN D. JOHNSON qlam aag THEIR AGENT United States Patent This invention relates to the drilling of oil and gas wells, and pertains more particularly to a method and apparatus for the drilling of offshore wells wherein the wellhead assembly is positioned on the ocean floor or a considerable distance under the surface of a body of used 'on land Wells, with the conventional wellhead assembly being attached to the top of the casing. Due to the steeply dipping nature of the short line on the Pacific coast of the United States, there is a relatively narrow strip of ocean floor under less than 300 feet of water which might be developed economically from platforms employing legs which extend down to the ocean floor. The remainder of the offshore land, in water greater than 300 feet in depth, particularly the area off the southern- California coast that includes deep basins potentially as productive as those on shore, can be developed economically only by drilling wells from floating vessels and by utilizing underwater well completion methods and apparatus wherein the wellhead assembly is located on or close to the ocean floor.

It is therefore a primary object of the present invention to provide a method and apparatus for drilling oil and gas wells from a floating, though preferably anchored, drilling barge in a manner such that the Wellhead assembly is positioned on the ocean floor.

A further object of the present invention is to provide a method for drilling and completing an offshore well in a manner such wellhead is located below the surface of a body of water, and for example, near the ocean floor, so that deep draft vessels can pass safely overhead, thus eliminating the blow-out hazard present by the possibility of ships hitting the wellhead or a supporting platform therefore.

Another object of the present invention is to provide a method for drilling and completing an offshore well from a remote location without the aid of divers or without employing a rigid structure extending from the well to a point above the surface of the water.

Still another object of the present invention is to provide a method for maintaining control of an offshore well at all times during drilling completion and production operations.

A still further object of this invention is to provide a method of running and cementing multiple strings of pipe within a well drilled at an offshore location where the wellhead assembly is positioned near the ocean floor.

A further object of the present invention is to provide a method of drilling and completing a well wherein wellhead equipment is lowered through the water into place on the wellhead assembly without the use of a series of guide lines.

Another object of the present invention is to provide a method of drilling an offshore well which minimizes the number of trips necessary to lower into place various strings of pipe or equipment mounted on the wellhead.

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 diagrammatic view illustrating a floating drilling barge positioned over a drilling location and supporting concentric strings of pipe therefrom;

FIGURE 2 is a diagrammatic View of the foundation assembly used in accordance with the present invention with concentric pipe strings extending upwardly therefrom which are identical with the pipe strings that extend downwardly at the bottom of FIGURE 1;

FIGURE 2A is a view taken in partial longitudinal cross-section of the upper end of the foundation assembly of FIGURE 2;

FIGURE 23 is a view taken in partial longitudinal cross-section of the lower end of the foundation assembly of FIGURE 2 showing the connection between the conductor shoe and the lower end of the surface casing;

FIGURE 3 is a diagrammatic view illustrating the foundation assembly of FIGURE 2 positioned and cemented in a well borehole drilled in the ocean floor with a drilling barge positioned thereabove;

FIGURE 4 is a diagrammatic view illustrating the operation of lowering a drilling wellhead from a drilling barge onto the top of the foundation assembly on the ocean floor;

FIGURE 5 is a diagrammatic view showing the arrangement of equipment during the drilling of a well in accordance with the method of the present invention;

FIGURE 6 is a longitudinaldiagrarnmatic view illustrating a manipulator device positioned on a drilling wellhead near the ocean floor for carrying out operations thereon;

FIGURE 7 is a longitudinal diagrammatic view illustrating the operation of lowering a production head and flow lines down to an underwater casinghead extending upwardly from the ocean floor;

FIGURE 8 is a longitudinal diagrammatic view of a completed wellhead assembly positioned on the ocean floor in accordance with the present invention; and,

FIGURE 9 is a view taken in partial longitudinal crosssection of the casinghead employed in the apparatus of the present invention.

Referring to FIGURES 1 and 2 of the drawing, a drilling barge 11, of any suitable floating or floatable type is illustrated as floating on the surface of the water 12 and fixed positioned over a preselected drilling location by being anchored to the ocean floor 13 by anchor-

lines

14 and 15 running to anchors (not shown). Equipment of this type may be used when carrying on well drilling operations in water varying from about feet to 1500 feet or more. The drilling barge is equipped with a suitable derrick 16 containing a fall-line system, including a traveling block 17, a hoist 18, and an elevator 19. The barge 11 is also provided with other auxiliary equipment needed during the drilling of a well, such, for example as a rotary table 20 positioned on the operating deck 21, a hinged slip and spider assembly 22 positioned on a lower deck 23, etc. The elevator 19 is normally provided for suspending therefrom during drilling operations a drill string 24 or the kelly section at the top of the drill string, while the slip and spider assembly 22 is adapted to secure fixedly a string of pipe, for example, a string of surface casing 25, against vertical movement relative to the barge 11.

During some of the operations in accordance with the present invention, the surface casing 25 serves as a marine conductor pipe by which drilling mud may be circulated upwardly in the annulus formed between the surface casing 25 and the drill pipe 24. The derrick 16 is positioned over a drilling slot, or well 26, which extends Vertically through the barge in a conventional manner. When using the equipment of the present invention, the

slot 26 in the barge 11 may be either centrally located or extend in from one edge, however, drilling operations may be carried out over the side of the barge without use of a slot. It is also to be understood that in some areas the apparatus and the method of the present invention may be utilized when operating from either a permanently fixed platform, or a temporarily fixed and normally fioatable platform. However, for purposes of illustration, the present invention will be described with regard to its use when drilling and completing a well from a floating barge. which is preferably anchored, but not necessarily so. In many drilling operations, the floating barge may be maintained in a relatively fixed position on the surface of the ocean by means of two or more outboard motors or other marine propulsion units arranged to act in opposition.

In FIGURE 2, a foundation assembly 30 is illustrated as comprising a section of large diameter pipe or conductor pipe 31, say 36 inches in diameter, which is fixedly secured as by welding, to intermediate and small sections of

conductor pipe

32 and 33, respectively, with a conductor shoe 34 secured, as by screw threads, to the lower end of the conductor pipe 33. Although the foundation assembly has been described with regard to being made up of conductor pipe of varying diameters, it is to be understood that conductor pipe of a single diameter may be employed. Preferably, the portion of the conductor pipe, in this case, section 32 (FIGURE 3) in contact with the ground at the surface thereof is preferably a heavy-walled type in order to withstand the bending stresses during drilling. The upper portion of conductor pipe 31 is preferably of large diameter in order to serve as a base around which a manipulator device can rotate, as will be described herein below. A drill pipe 24 extends down through the conductor pipe of the foundation assembly, and drill collars 35 are normally secured to the lower end of the drill string above a drill bit 36 and a hole opener 37.

As shown in FIGURE 2A, the intermediate section of conductor pipe 32 extends up through the larger diameter conductor pipe 31 with the annular space 40 between the two pipes being closed by any suitable closure means 41. The closure means 41 is provided with a lip or shoulder 42 around the inner wall thereof for seating annular stripper rubber 43. A retaining ring 44 is positioned above the stripper rubber 43 for holding it on the shoulder 42. The retaining ring is secured in any suitable manner, as by screws 45, to the closure means 41. The internal diameter of the stripper rubber 43 is slightly less than the normal outside diameter of the surface casing so as to provide a fluid tight seal therearound while allowing axial movement of the surface casing 25 relative to conductor pipe 31.

During the time when the well is being spudded and prior to the time when the foundation assembly is cemented in the well, the conductor shoe at the bottom of the foundation asesmbly 30 is releasably secured to the lower' end of the surface casing 25, as illustrated in FIG- URE 2B. A rigiddrillable closure member 46 is positioned between the conductor shoe 34 and a surface casing shoe 47. The closure member 46 is made of a drillable material, preferably cement, plastic or a soft or readily drillable metal, and may be provided with O-ring seals 50, if desired. The inner surface of the conductor shoe is preferably provided with a series of grooves 51 so that the closure member can be cast inside the shoe and will not move axially when a force is applied to it. Suitable connection means are provided between the closure member 46 and the surface casing shoe 47, such for example, as a J-slot connection or releasable left-hand thread 52. Although the present invention has been described as having the surface casing 25 and conductor pipe 33 being connected together at their lower ends, as by

shoes

34 and 47 with closure member 46, it is to be understood that it is easier to connect the lower ends of casing 5. 25 and conductor 33 together but that they could be connected at any joint above the end.

Prior to running any of the foundation assembly into the water and down to the ocean floor, the lowermost section of the surface casing would be inserted in the lowermost section of conductor pipe and the surface casing shoe 47 connected to the closure member 46. Thereafter, successive sections of pipe would be added to both the surface casing and the conductor pipe or foundation assembly 30 until the foundation assembly 30 had reached desired length, The foundation pipe would hang, by means of the closure member 46, from the lower end of the surface casing 25 as additional sections of surface casing were added to the top thereof to lower it to the ocean floor by means of the derrick hoist system. Prior to lowering the foundation assembly underwater a mud line 53 having 'a pull-off connection 54 would be attached to the conductor pipe 31 and would be in fluid communication with the conductor pipe 32 so as to serve as a mud return hose during future drilling operations.

With the equipment assembled in a manner illustrated in FIGURES 1 and 2, the lower section of the surface casing 25 is used in lowering and suspending the foundation assembly until the conductor shoe 34 thereof is positioned slightly above the ocean floor. The upper end the surface casing would be supported by the slip and spider assembly 22 from the lower deck of the drilling vessel 11. Well spudding operations are now carried out by installing the drill bit 36, hole opener 37, drill collar 35 and drill pipe 24 in the surface casing 25 and lowering it through the surface casing to the position shown in FIG- URE 2. If desired, the

conductor pipes

32 and 33 may be provided with centralizers 55. The drill bit and drill string is lowered to the ocean floor and drilling operations are commenced to drill the well. After a few feet of the hole 56 have been drilled, as illustrated in FIGURE 2, drilling is stopped and the foundation assembly and surface casing is lowered slightly so that the lower end of the foundation assembly is in the well bore, thus stabilizing the foundation assembly while the balance of the hole is being drilled for the conductor pipe. The hole for the conductor is preferably drilled using sea water as a circulating fluid which is pumped down through the drill string 24 and comes up outside the

conductor pipe

32 and 33.

After the hole for the conductor pipe has been drilled, the drill pipe 24 and bit 36 are removed. The foundation assembly is then lowered by adding sections of surface casings 25 at the top thereof until the foundation assembly 30 is supported either by the conductor shoe 34 at the bottom of the well, or from the large conductor section 31 at the top of the wellbore.

As shown in FIGURE 3, cementing operations can be carried out either through the drill pipe 24 prior to its removal, or through the surface casing 25, depending on the conditions and the operators preference, using an excessive amount of cement in order that conductor pipe be securely cemented to the ocean floor. The conductor pipe and foundation assembly then become the main structural member that supports the wellhead against any static or dynamic forces applied during such an operation.

In FIGURE 3, the foundation pipe as illustrated is cemented in pl-ace with a pad of cement 57 being formed around the top of the borehole. Prior to commencing further drilling operations, the surface. casing 25, and its shoe 47 are released from the conductor shoe 34 by rotating the surface casing 25 until the left-hand threads become disengaged. The surface casing string 25 is then raised slightly to a position where the stripper rubber 43 (FIGURE 2A) is positioned between two collars 58 on the surface casing 25, thus permitting sliding axial movement of the surface casing string 25 within the stripper rubber 43, a distance equal to the length of a section of surface casing, normally 30 feet. The use of a stripper rubber in this manner eliminates the need of a buoyancy chamber ora slip joint attached to the surface casing. In the position shown in FIGURE 3, the surface casing 25 is suspended from the slip and spider assembly 22. A flow nipple 61 and a mud return line 62 are connected to the top of the surface casing 25.. Drilling operations may now be resumed using a drilling fluid in a conventional manner, pumping the fluid down the drill string 24, through the small size bit 63. Flow of mud would then proceed up the annulus between the surface casing 25 and the drill string 24 tothe flow nipple and

mud line

61 and 62 respectively, from whence, the mud could be discharged into a settling pit (not shown) on the barge, or could be discarded, as desired. A drill string 24 with the small size bit 63 and a hole opener 64 would be lowered through the surface pipe 25 as drilling progressed. Suflicient hole is then drilled and the well is otherwise conditioned to receive a surface casing 25.

At any time during the drilling operation, the depth of the well is known. After drilling the borehole for the suflicient length of surface casing 25 desired, a length of surface casing is run into the well by adding additional sections to the top of the surface casing string until the surface casing shoe 47 is positioned at a distance above its final cemented position which is equal to the distance between the lower deck 23, of the barge 11 and the upper end of the large diameter conductor pipe 31. As is shown'in FIGURE 4, a drilling wellhead assembly 65, having a manipulator track 66 and blow-out

preventers

67 and 68 secured thereto, is attached to the upper end of the surface casing, as by a threaded connection. The blow-out preventer is provided with a series of electrical or hydraulic conduits 70, as well as a choke and kill line 71. A riser mandrel 72 (FIGURE 4) is provided at the top of the blow-out preventer 68' to which a string of drill pipe 24 may be connected for purposes of lowering the assembled apparatus down into position on top of the large diameter conductor pipe 31. A guide skirt 73 on the bottom of the assembly helps to guide the drilling wellhead assembly 65 and its manipulator track 66 into position over the upper end of the conductor pipe 31, as shown in FIGURE 5. The surface casing is then cemented in place by pumping cement down the drill pipe 24 used for lowering (FIGURE 4) and surface casing, up the outside of the surface casing 25 until a cement plug 74 (FIG- URE 4) has been discharged from the bottom thereof i in a conventional manner. The fluid in the well druing the cementing operation is forced up the outside of the surface casing 25 and up through the return mud line 53. At the termination of the cementing operation, the mud line 53 is pulled loose at its pullout connection 54..

Prior to or subsequent to the cementing of the surface casing 25 a large diameter pipe string known as a drilling riser or marine conductor 75 is lowered or stripped down over the drill pipe 24 in a manner described in copending patent application Serial No. 118,989, filed June 22, 1961. The lower end of the drilling riser 75 is provided with a Regan Forge and Engineering Company type K preventer 76 which is of the contractable bagtype and may be provided with a guide skirt 77 at the lower end. Additionally, the drilling riser 75 may be provided with a telescopic joint 80 immediately below the drilling vessel and, if desired, a buoyancy tank '81. A nipple 61 and return line 62 are also connected to the top of the drilling riser 75 for handling mud returns therefrom. The Regan preventer 76, which serves as a flexible joint for the riser 75, is provided with control hoses 82 prior to lowering it into position. When in engagement with the riser mandrel 72 (FIGURE 4) at the top of the blow-out preventer 68, the preventer is secured in a fluidtight manner by applying pressure fluid through a control hose 82. Alternatively, instead of employing a preventer 76 at the lower end of the drilling riser 75 and using a drill pipe'24 to land the drilling head 65 and

blowout preventers

67 and 68 in the top of conductor pipe 31, the

preventer 76 may be omitted and the top of the blowout preventer 68 may be connected to the bottom of-the drilling riser 75 which would be used to run the

blowout preventers

67 and 68 into place with the drilling head assembly 65.

A drill bit 83 of suitable size is run down through the apparatus assembled in FIGURE 5 on a drill string 24 and drilling operations are continued until the bore hole has been drilled deep enough to receive a production casing. Prior to running a string of production casing in the well, the drill pipe 24 and bit 83 are withdrawn therefrom and an under-water manipulator device 84 is landed on the track 66.v The underwater manipulator device 84 is of a type described on co-pending application Serial No. 24,558, filed April 25, 1960, and comprises a housing 85 adapted to be lowered by means of a cable 86, swum into position by means of propellers in housings 87 and hung by means of a pair of wheels 90 on the track 66-to move thereabout while a pair of idler wheels 91 contact the outer surface of the larger diameter conductor pipe 31. The manipulator device 84, is provided with at least one arm 92 preferably horizontally-positioned, as illustrated, and adapted to move in and out, up and down, or to rotate at the discretion of an operator at a remote location on the drilling barge 11. In this particular application the moveable arm 92 would be provided with the wrench 93 of the outwardly extending in thereof for cont-acting the bolts 94 on the drilling wallhead assembly 65.. Lights 95 and a television camera 96 are provided on the manipulator device and are movable in any direction, normally being used to observe the operation carried out by the wrench 93, or to aline it on one of the bolts 94.

In FIGURE 6, the production casing 97 is shown as having been lowered to its desired position in the well at which point it is cemented. The production casing 97, is lowered by means of a drill pipe (not shown) which would be attached to a left-hand thread release 98 formed on the inner Wall of the production casing hanger 100, as shown in FIGURE 9. After being landed, the production casing 97 is locked to the casinghead 101 by the lower control screws 102. These screws would be run into place by means of the Wrench 93 of the manipulator device 84 (FIGURE 6). The production casing 97 is cemented in place by use of a Baker Company J cementing collar (not shown) which would be installed on the lower end of the cementing pipe string or on the drill pipe, and inserted in the upper end of the production casing 97 in 'a manner well known to the art. The cement is circulated down through the drill pipe or cementing string with return of fluid passing through the cementing collar and up through the choke and kill line 71 of the iblo-w out preventer 67. Subsequent to cementing the production casing, the lower end of the drill pipe or cementing string would be released from the left-hand thread 98- in the casing hanger and the pipe would be withdrawn to barge 11. The well is now ready for additional drilling operations or for receiving production tubing. If further drilling is to be performed, a combination tool guide and seat \protector (not shown) may be installed, if desired, in the casing hanger 100 to serve as a guide for tools and to protect the tubing hanger seat 103.

As shown in FIGURE 9, the wellhead assembly used during drilling operations comprises the drilling wellhead portion 65 which seats on a landing surface 104 of an intermediate section or upper casinghead section 105, and is secured thereto by a series of upper lock screws 106, only one lock screw being shown. The upper casinghead section 105 in turn is seated on a landing sunface 107 formed at the top of the casinghead 101 on the outer surface thereof, with a series of lower iock screws securing

casinghead sections

101 and 105 together. The casinghead 101 is preferably provided with a support base 111 which is fixedly secured thereto, as by weld-ing. This support base 111 in turn may rest on top of the foundation pipe assembly section 31 (FIGURE 2). Whileit is preferred in the present invention to employ a wellhead having upper and lower casinghead sections, 105 and 101, respectively, on which a drillinghead 65 can be secured, it is quite apparent that the upper and lower sections of the casinghead, 105 and 101, respectively, could be formed as a single element, in which case the lower lock screws 108 could be eliminated. However, as a safety precaution in underwater wellhead structures, the housing employs upper and lower casing heads,

section

105 and 101, respectively, secured together by a means of the lower locking screws 108 which are preferably made of an alloy carbon steel or of a suitable material so that they can be drilled out in the event that the upper lock screws 106 become wedged or corroded in a manner so that they cannot be withdrawn from their seating position in order to remove the drilling head 65, or a production head, therefrom.

A tubing hanger 112 is illustrated as being seated on .the landing surface 103 formed in the top of the casing hanger 100. The tubing string 115, depending from the tubing hanger 11 2, is concentrically arranged within the surface casing string 25. The outer surface of the tubing hanger 112 at the lower end thereof is provided with a tapered seating surface 113, preferably provided with seal means 114, such for example as any suitable type of packing, or O-rings. The tubing hanger 112 is adapted to be secured at its lower end to the top of a string of tubing 115, for example, by screw threads. One or more fluid flow passageways 116 extend vertically through the tubing hanger 112 in communication between the annulus 117, formed between the outer wall of the tubing string 115 and the inter wall of the production casing 97, and the space above the tubing hanger 112.

The interior wall of the tubing hanger 112 is provided with suitable means, for example, a left-hand thread 120 by which the tubing hanger 112 can be attached to the lower end of a pipe string (not shown) for lowering the tubing hanger 112 and its depending tubing string into the well from the barge 11. After landing the tubing, the tubing hanger 112 is locked down by tightening the upper set of control screws 121 by means of the wrench 93 carried by the manipulator device 84. The tubing string 115 is run with any conventional downhole equipment that prevents communication between the formation and the tubing or casing string. Prior to running the tubing string, or subsequent thereto, the well casing could have been perforated in any suitable manner well known to the art.

After the tubing string 115 has been positioned in the well, and the well is otherwise conditioned to receive the Christmas tree, the underwater manipulator device 84 is employed to unscrew the upper lock screw 106 which hold the drilling head 65 into the upper section 105 of the casinghead. The drilling riser 75 and the equipment associated therewith, that is, the connector device 76, the blow-out

preventers

67 and 68, and the drilling head 65 are raised or stripped out of the water over the pipe string employed to run the tubing hanger into place. This stripping operation is carried out in a manner described in co-pending patent application Serial No. 118,989, filed June 22, 1961.

In order to produce oil from the well, a production head 122 (FIGURE 7) is lowered or stripped down over the tubing running string 118 which extends from the top of the tubing within the casinghead to the barge 11. The production head is preferably of the type described in co-pending patent application Serial No. 72,168, filed November 28, 1960, which alters the two concentric pipe strings in a well to two parallel flow passageways in which control valves may be located. The production head is provided with

control valves

123 and 124 and

side outlet valves

125 and 126 which control fluid flow through

flow lines

127 and 128, respectively. Normally, only one flow line would be employed to produce fluid from the oil or gas zone. However, in certain areas dual flow lines may be employed. After the normal flow of a well has decreased to an extent it no longer will produce out of a flow line, the other fioW line can be employed to inject gas into the well to gas life production fluid therefrom.

The top of the Christmas tree, made up of valves 123 through 126, may be closed in any suitable manner, as by a wellhead closure member or a lubricator mandrel 130 which is releasably secured to the lower end of a running pipe string 131 used to lower the production and Christmas tree down over the tubing landing string 118. The tubing landing string 118 is a small-diameter pipe and may have a wire line or cable (not shown) running therethrough, the cable being made up in sections as long as each pipe and being secured at its lower end to the lowermost tool joint at the bottom of the tubing string of each section. Thus, in the event that the tubing landing string should break, the cable would be sufficient to support the weight of the equipment.

When the production head 122 has been seated on the upper portion of the casing head, the lock screws 132 carried by the production head 122 are run into place by the wrench 93 on the underwater rnunipulator 84. The tubing landing string 118 (FIGURE 7) is then disconnected from a tubing hanger by rotation and it is then pulled up to the barge through the running string 131. secured to the lubricator mandrel 130. A closure 133 is then run through the lubricator pipe string 131 and secured in a fluidtight manner in the top of the lubricator mandrel 130. The lubricator mandrel is preferably of the type having at least two concentric vertical flow passages therethrough with a cross-over chamber at the bottom of the outermost flow passage in communication, through one flow passageway in the Christmas tree, with the tubing-casing annulus of the well.

The manipulator device 84 (FIGURE 7) may then be lifted off the track 66 by means of cable 86 and raised to the surface. This leaves the wellhead assembly on the ocean floor with its two

flow lines

127 and 128 extending down from the Christmas tree and running along the ocean floor 13. The master valves 123 and 123A as well as valves 124 and 124A are of a normally-closed type, preferably, whereas the

side arm valve

125 and 126 are preferable of a normally-open type. All of the valves are operated by means of gas pressure supplied through one of the

flowlines

127 or 128 from a suitable source. Under operating conditions, master valves 123 and 123a are held open by the pressure in the high pressure gas line 128 while production fluid leaves the well through flow line 127.

If it becomes necessary to open the well and re-enter it with tools, the manipulator device 84 (FIGURE 7) is lowered on its cable together with a guide line (not shown) which is attached by the manipulator device to the top of the lubricator mandrel 130 or its closure plug 133. Using this guide line which would extend up to the barge 11 at the surface, drilling riser 75 (FIGURE 5) similar to the pipe string 131 of FIGURE 7, and carrying a Regan connector at its lower end similar to element 76 of FIGURE 5, would be lowered down onto and attached to the top of the lubricator mandrel 130. The drilling riser used in re-entry and work-over operation on the well may be much smaller in diameter than the riser used in drill operations. After the work-over riser is attached to the lubricator mandrel 130, the mandrel cap can be removed by means of a wire line tool or a retrieving tool positioned at the lower end of a pipe string. The upper end of the riser at the vessel would be provided with suitablemeans for connecting it to a source of hydraulic fluid-whereby a pressure fluid could be applied to the riser mandrel to open control valves 124 and 124A. The well would then be completely connected to the barge 11 and would be in er condition to be entered, with wire line tools, or could be filled with drilling mud for more extensive work-over operations. The well can also be filled by circulating mud through the

flexible flow lines

127 and 128. After the well is filled and otherwise plugged, the Christmas tree and production head can be removed by having the wrench 93 carried by the manipulator device 84 unscrew the upper lock screws 132 (FIG- URE 8). However, if difficulty is encountered in disconnecting the Christmas tree at this point, the upper control screw 121 and the lower lock screws 107 can be backed off by the manipulator device 84 and the tree, production head 122, and upper portion of casing head 105 can be removed. After the production tree has been removed the drilling riser and blow-out preventers can be reattached to the well by reversing the steps in the operation described herein above. It may be seen from the assembly method and equipment described that all parts of the wellhead equipment subject to possible damage can be removed, repaired and reinstalled at any time during the productive life of the well.

We claim as our invention:

1. A method of drilling an offshore well from an operational platform positioned above the surface of a body of water, said method comprising assembling a foundation assembly, having a vertical opening therethrough, inserting a stringof surface easing into the vertical opening of the foundation assembly, releasably connecting together the lower end of said surface casing and said foundation assembly, suspending said surface casing from said operational platform, inserting a drill string and bit through said surface casing, rotating said drill string and bit to drill a hole in the ocean floor of a diameter and length to receive at least the lower portion of said foundation assembly, lowering said foundation assembly supported by said surface casing and connected thereto along said drill string and into the hole in the ocean fioor, and cementing the foundation assembly in the hole in the ocean floor.

2. The method of claim 1 including the step of releasing the lower end of the surface casing from the lower end of the cemented foundation assembly by manipulating the upper end of the surface easing from the vessel.

3. The method of claim 2 including the steps of subsequently installing a drill string and bit through said surface casing and resuming drilling operations.

4. A method of drilling an offshore well from an operational platform positioned above the surface of a body of water, said method comprising assembling a foundation assembly having a vertical opening therethrough, inserting a string of surface casing into the vertical opening of the foundation assembly, sealing the space between said surface casing and said foundation assembly near the top thereof in axial sliding arrangement, releasably connecting together the lower end of said surface casing and said foundation assembly, suspending said surface casing from said operational platform, inserting a drill string and bit through said surface casing, rotating said drill string and bit to drill a hole in the ocean floor of a diameter and length to receive at least the lower portion of said foundation assembly, lowering said foundation assembly and said surface casing connected thereto along said drill string and into the hole in the ocean floor, and cementing the foundation assembly in the hole in the ocean floor.

5. A method of drilling an offshore well from an operational platform positioned above the surface of a body of water, said method comprising assembling a foundation assembly having a vertical opening therethrough including a conductor pipe with a mud return line intermediate the ends thereof and a conductor shoe at the lower end thereof, inserting a string of surface casing into the vertical opening of the foundation assembly, sealing the space between said surface casing and said foundation assembly near the top thereof in axial sliding arrangement, releasably connecting together the lower end of 'said surface casing and said foundation assembly, suspending said surface casing from said operational platform, inserting a drill string and bit and hole opener through said surface casing, rotating said drill string'and bit to drill a hole in the ocean floor of a diameter and length to receive the majorportion of said foundation assufiicient to place-the sealed zone at the top of said foundation assembly in a position intermediate the end of a section of surface casing, and resuming drilling operations.

6. A method of drilling an offshore well from an operational platform positioned above the surface of a body of water on a floating barge, said method comprising assembling a foundation assembly having a vertical opening therethrough including a conductor pipe with a mud return line intermediate the ends thereof and a conductor shoe at the lower end thereof, inserting a string of surface casing into the vertical opening of the foundation assembly, sealing the space between said surface casing and said foundation assembly near the top thereof in axial sliding arrangement, releasably connecting together the lower end of said surface casing and said foundation assembly, suspending said surface casing from said operational platform of said floating barge, inserting a drill string and bit and hole opener through said surface casing, rotating said drill string and bit to drill a hole in the ocean floor of a diameter and length to receive the major portion of said foundation assembly, lowering said foundation assembly and said surface casing connected thereto along said drill string and into the hole in the ocean floor, removing the drill string, cementing the foundation assembly in the hole in the ocean floor, releasing the lower end of the surface casing from the lower end of the foundation assembly by manipulating the upper end of the surface casing from the vessel, raising the surface casing suflicient to place the sealed zone at the top of said foundation assembly in a position intermediate the ends of a section of surface casing, installing a drill string and drill bit through said surface casing and resuming drilling operations.

7. Apparatus for use at an offshore well drilled from an operational platform positioned above the surface of a body of water,.said apparatus comprising a large-diameter conductor pipe adapted to be lowered from an operational platform into a well drilled in the ocean floor, a string of surface casing pipe positioned concentrically within said conductor pipe, releasable weight-supporting connector means securing together said lower portion of said surface casing pipe and said conductor pipe intermediate the ends thereof, said connector means being of a material drillable by a well drill bit, there being an annular space formed above said connector means between said surface casing pipe and said conductor pipe and means for guiding the concentric pipes from the platform into the well. I

8. Apparatus for use at an offshore well drilled from an operational platform positioned above the surface of a body of water, said apparatus comprising a large-diameter conductor pipe adapted to be lowered from an operational platform into a well drilled in the ocean floor, a string of surface casing pipe positioned concentrically within said conductor pipe, releasable weight-supporting connector means securing together said lower portion of said surface casing pipe and said conductor pipe intermediate the ends thereof, said connector means being of a material drillable by a well drill bit, there being an annular space formed above said connect-or means between said surface casing pipe and said conductor pipe, resilient seal means carried by said conductor pipe near the top thereof for closing said annular space and means for guiding the concentric pipes from the platform into the well.

9. The apparatus of claim 8 including conduit means extending from said operational platform and through the wall of said conductor pipe below the seal means thereof for allowing fluid to flow from said conductor pipe to said operational platform.

10. Apparatus for use at an offshore well drilled from an operational platform positioned above the surface of a body of water, said apparatus comprising a large-diameter conductor pipe adapted to be lowered from an operational platform into a well drilled in the ocean floor, a string of surface casing pipe positioned concentrically within said conductor pipe, releasable weight-supporting connector means securing together the lower ends of said surface casing pipe and said conductor pipe, said connector means being of a material drillable by a well drill bit, there being an annular space formed above said connector means between said surface casing pipe and said conductor pipe, resilient seal means carried by said conductor pipe near the top thereof for closing said annular space, said seal means forming substantially fiuidtight seal arranged for sliding engagement with the outer surface of said surface casing pipe when the lower ends of said surface casing pipe and said conductor pipe are disconnected one from the other and means for guiding the concentric pipes from the platform into the well.

11. Apparatus for use at an offshore well drilled from an operational platform positioned above the surface of a body of water, said apparatus comprising a large-diameter conductor pipe adapted to be lowered from an operational platform on a floating drilling barge into a well drilled in the ocean floor, a shoe carried at the lower end of said conductor pipe, a string of surface casing pipe positioned concentrically within said conductor pipe, a shoe carried at the lower end of said surface casing pipe,

releasable weight-supporting connector means securing together the shoes at the lower ends of said surface casing pipe and said conductor pipe, said connector means being of a material drillable by a well drill bit, there being an annular space formed above said connector means between said surface casing pipe and said conductor pipe, resilient seal means carried by said conductor pipe near the top thereof for closing said annular space, said seal means forming a substantially fiuidtight seal arranged for sliding engagement with the outer surface of said surface casing pipe when the shoes at the lower ends of said surface casing pipe and said conductor pipe are disconnected one from the other and means for guiding the concentric pipes from the platform into the well.

References Cited by the Examiner UNITED STATES PATENTS 2,512,783 6/ 1950 Tucker -7 2,626,781 1/ 1953 Reynolds 175-294 2,689,139 9/1954 Jones et a1. 166-75 X 2,819,879 1/1958 Beck 175-300 2,891,770 6/1959 Bauer et a1 175-7 2,897,895 8/1959 Ortloif 166-75 X 2,917,281 12/1959 Kofahl 175-7 2,984,308 5/1961 Bauer et a1 175-7 3,012,610 12/1961 Bauer et al. 166-665 CHARLES E. OCONNELL, Primary Examiner.

R. E. FAVREAU, Assistant Examiner.

Claims

1. A METHOD OF DRILLING AN OFFSHORE WELL FROM AN OPERATIONAL PLATFORM POSITIONED ABOVE THE SURFACE OF A BODY OF WATER, SAID METHOD COMPRISING ASSEMBLIES A FOUNDATION ASSEMBLY, HAVING A VERTICAL OPENING THERETHROUGH, INSERTING A STRING OF SURFACE CASING INTO THE VERTICAL OPENING OF THE FOUNDATION ASSEMBLY, RELEASABLY CONNECTING TOGETHER THE LOWER END OF SAID SURFACE CASING AND SAID FOUNDATION ASSEMBLY, SUSPENDING SAID SURFACE CASING FROM SAID OPERATIONAL PLATFORM, INSERTING A DRILL STRING AND BIT THROUGH SAID SURFACE CASING, ROTATING SAID DRILL STRING AND BIT TO DRILL A HOLE IN THE OCEAN FLOOR OF A DIAMETER AND LENGTH TO RECEIVE AT LEAST THE LOWER PORTION OF SAID FOUNDATION ASSEMBLY, LOWERING SAID FOUNDATION ASSEMBLY SUPPORTED BY SAID SURFACE CASING AND CONNECTED THERETO ALONG SAID DRILL STRING AND INTO THE HOLE IN THE OCEAN FLOOR, AND CEMENTING THE FOUNDATION ASSEMBLY IN THE HOLE IN THE OCEAN FLOOR.