US3322191A

US3322191A - Underwater well drilling method

Info

Publication number: US3322191A
Application number: US283427A
Authority: US
Inventors: Bullard Billy Jack
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1963-05-27
Filing date: 1963-05-27
Publication date: 1967-05-30
Anticipated expiration: 1984-05-30
Also published as: NL6405803A; DK106426C

Description

May 30, 1967 B. J. BULLARD UNDERWATER WELL DRILLING METHOD 5 Sheets-Sheet l Filed May 27 FIG. 2

FIG.

INVENTORI B. J. BULLARD BY. 5

HIS AGENT y 30, 1967 B. J. BULLARD 3,322,191

UNDERWATER WELL DRILLING METHOD Filed May 27, 1965 5 Sheets-Sheet 2 INVENTORI B. J. BULLARD g' 4 jaQc HIS AGENT y 30, 1967 B. J. BULLARD 3,322,191

UNDERWATER WELL DRILLING METHOD Filed May 27, 1963 5 Sheets-$heet 5 INVENTORI B. J. BULLARD mag:

May 30, 1967 B. J. BULLARD UNDERWATER WELL DRILLING METHOD 5 Sheets-Sheet 4 Filed May 27 FIG. 8

FIG. 7

INVENTOR.

B. J. BULLARD BY? Q" 11.1w

HIS AGENT 1967 B. J. BULLARD 3,322,191

UNDERWATER WELL DRILLING METHOD Filed May 27, 1963 5 Sheets-Sheet 5 B. J. BULLA R D United States Patent Ofilice 3 322 191 UNDERWATER WELL DRILLlN G METHOD Billy Jack Bullard, Oklahoma City, Okla, assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed May 27, 1963, Ser. No. 283,427

6 Claims. (Cl. 166-.5)

This invention relates to methods and apparatus for use in drilling, completing and working-over underwater Wells wherein the wellhead assembly is positioned below the surface of a body of water.

In an attempt to locate the oil fields an increasing amount of well drilling has been conducted at offshore locations, such for example, as off the coast of Louisiana, Texas, or California. As a general rule, the strings of casiing in the well together with the tubing string or strings extend to a point above the surface of the water where they are closed in a conventional manner that is used on land wells, with a conventional wellhead assembly being attached to the top of the casing. Recently, methods and apparatus have been provided for drilling and completing a well wherein both the well casinghead and subsequently the wellhead assembly and casing closure device are located underwater at a depth sufficient to allow ships to pass over them. Preferably, the casinghead and wellhead closure assemblies are located close to the ocean floor. In order to install equipment of this type underwater at depths greater than the shallow depth at which a diver can easily operate, it has been necessary to design entirely new equipment for this purpose. Thus, when drilling and completing or working-over an oil or gas well at an olfshore location, the production or drilling wellhead equipment may have been assembled at its underwater location by one of two methods presently known to the art.

In one method of drilling underwater wells, a relatively shallow hole is originally drilled in the ocean floor and a foundation casing is cemented in the hole. Secured to the upper end of the foundation casing is a laterally-extending guide base from which one or more guide lines extend upwardly to a drilling vessel on the surface of the water where they are secured preferably by constant tension hoist means; Thus, with guide lines or cables extending between the vessel and the wellhead on the ocean floor, the various component parts of a drilling or production wellhead assembly may be guided from the vessel into position at the wellhead by lowering them down along the guide lines. When in position at the wellhead, the various pieces of equipment or the wellhead components may be secured together as by hydraulically-actuated latching devices which may be remotely operated from the vessel. One of the drawbacks of this method of drilling underwater wells is that the guide lines between the vessel and the wellhead must be kept taut in order to accurately align pieces of equipment at the wellhead and to prevent the guide lines from becoming entangled with hydraulic fluid control lines running from the vessel to the Wellhead. It may also be seen that after moving the vessel of? of location at the completion of a well, some dilficulties may be encountered in returning to the well and inserting new guide lines in the well base to extend to the vessel at the surface.

In a second common method of drilling underwater wells a string of pipe, normally the drill string, extends from a drilling vessel on the surface of a body of water into a well drilled in the ocean floor so as to provide guide means for lowering elongated strings of well easing into the well with or without various wellhead equipment to be used. In order to use the pipe string between the well and the vessel as a guide when lowering strings of easing into the well, it is necessary that the larger diameter string 3,322,191 Patented May 30, 1967 of easing be stripped or lowered down over the guide pipe arranged in the bore of the casing. The

true in the event that the inner guide pipe has to be held in tension throughout the stripping operation.

It is therefore a primary object of the present invention to provide a method and apparatus of drilling underwater wells wherein strings of casing may be run into the well and wellhead equipment may be positioned at the top of the well without the necessity of stripping one pipe string over a smaller-diameter pipe string.

A further object of the present invention is to provide a method and apparatus for guiding the strings of well casing and wellhead equipment into place at an underwater well without the use of a plurality of flexible guide lines between a floating vessel and an underwater well.

Another object of the present invention is to provide a method and apparatus whereby an underwater well may be drilled in the ocean floor and a wellhead positoned beneath the surface of a body of water while contact is maintained at all times between a vessel on the surface of the water and the interior of the well or subsurface wellhead equipment.

A still further object of the vide a method and apparatus for drilling underwater wells wherein contact is maintained between the well and the drilling vessel at the surface of a body of water by an elongated guide element which is telescopically arranged within other equipment used during the drilling, completing or working-over of wells.

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

FIGURES 1-8 are diagrammatic views taken in longitudinal projection and partially in cross section illustrating a floating vessel positioned over a drilling location during the sequential steps of starting a well and arranging a tubular guide between the well and the vessel, attaching a well foundation casing and Well base to the top of the guide, lowering the equipment into a well until the foundation casing is at least partially inserted into the well, retrieving a guide from the assembled equipment, positioning the well foundation casing in the 'well and the well base on the ocean floor, removing components from a drilling wellhead assembly on the ocean floor to the vessel, running a string of easing from the vessel into the well, and reconnecting components of the drilling wellhead assembly to the well base of the ocean floor.

FIGURE 9 is a diagrammatic view taken in longitudinal cross section of hanging equipment for hanging the upper end of a drill string within the lower end of a larger diameter pipe or casing string;

FIGURE 10 is a longitudinal present invention is to proview taken along the bottom of a running pipe string and adapted to engage the upper end of a second pipe string.

In accordance with the method of the present invention, in drilling underwater wells, contact is maintained between a vessel on the surface of the water and a wellhead drilled in the ocean floor through an elongated tubular member or an assemblage of well and/ or well drilling components having a common bore or bores therethrough. By means of this tubular element or assemblage of tubular components and/ or elements the drilling vessel is in fluid flow communication with the interior of the well throughout any well drilling, completion or workover operation. During the operation of lowering a well member or wellhead component to its underwater location, contact is maintained between the vessel and the well by hanging [from the well member or wellhead component an elongated guide element which may be in the form of a length of drill pipe or a length of well casing. The upper end of the guide element used for this purpose is hung in any suitable manner within the bore of the wellhead component or well element in a manner such that the guide element may telescope or be drawn upwardly through the bore of the well element or wellhead component.

Referring to FIGURES l8 of the drawing, a drilling vessel, barge or platform 11, of any suitable floating or floatable type, is illustrated as floating on the surface of a body of water 12, while being substantially fixedly positioned over a pre-selected well location by suitable vessel-positioning means well known to the art, or 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 out well drilling operations or well workover operations in water varying from about 150 feet to 1500 feet or more in depth. The drilling vessel 11 is equipped with a suit-able derrick 16 containing the fall line system of a conventional derrick which includes a suitable hoist 18 and other related derrick equipment such as a traveling block and suitable hook and swivel or connect means adapted to be connected to a top of a drill pipe 21 during well drilling operations and being adapted to circulate a drilling fluid therethrough in a manner well known to the art.

The vessel 11 is provided with a drilling slot or well 22 which extends vertically through the barge in a conventional manner below the derrick 16. When using equipment of the present invention, a slot in a vessel 11 may be either centrally located or extend in from one edge. Alternatively, drilling operations may be carried out over the side of the vessel without use of a slot. For example, the drilling vessel may be provided with a deck portion which overhangs the hull of the vessel.

The vessel 11 is also provided with other auxiliary equipment needed during well drilling operations, such for example as a rotary table 23 positioned on the operating deck 25 of the vessel. Positioned on a lower or auxiliary deck 26, a portion of which is preferably removable, is a removable spider assembly 27 having removable sli-ps 28 insertable in the bore through said spider assembly 27 for engaging and suspending therefrom tubular elements such as a drill string 21. In FIGURE 1, the base or foundation plate 29 of an underwater wellhead assembly is shown as being suspended from the auxiliary deck 26 by means of

tie rods

30 and 31.

Although for ease of illustration the drill string 21 is shown as a unitary length of pipe, it is well known that a pipe string or drill string used in well drilling operations is made up by threadedly connecting together several short (say 30 feet) sections of pipe to make up a pipe string of the desired length. One or more drill collars 32 may be connected together to form the lower end of the drill string 21 with a drill bit 33 being connected to the lowermost drill collar. The drill string 21 preferably includes a telescoping joint 34 in its length to compensate for the rise and fall of the vessel 11 relative to the drill string 21. The length of the telescoping joint 34 is selected to be preferably slightly greater than the expected rise and fall of the vessel so that the drill bit 33 remains in contact with the bottom of the well 35 regardless of weather conditions at the surface. The telescoping joint 34 may be near the upper end of the drill string at the start of the drilling operations or it may be located just above or between drill collars 32 in the form of a bumper sub in a manner well known to the art. The bumper sub may have a telescoping length of say five feet, and more than one bumper sub may be employed, if desired.

FIGURE 1 illustrates a period during well drilling operations after which the well or pilot hole has been drilled in the ocean floor 13 to a depth slightly greater (say 50 or feet) than the water depth in which drilling operations are being carried on. As the depth of the well 35 increases during drilling, additional sections of drill pipe are added to the upper end of the drill string 21 to continually increase its length. After drilling the well 35 to a depth suflicient to receive the foundation pile or casing 36 (FIGURE 2), the upper end of the drill string 21 (FIGURE 1) is disconnected from the kelly section (not shown) and rotary table 23 and hung by means of slips 28 in the slip and spider assembly 27 at the lower level 26.

With the upper end of the drill pipe 21 hung from slips 26 in slip and spider assembly 27 as shown in FIG- ure 9, a special shoe or short section of large diameter pipe 37 is lowered concentrically over the drill pipe 21. A special hanger element 38 is then threadedly connected into the top of the drill pipe 21. The outer surface of the hanger 38 may be provided with a series of vertical grooves 39 dividing the hanging surface or landing surface 38a into a series of segmental portions. These segmental hanger portions may be tapered upwardly to a point as at 40 if desired. The upper end of the special shoe 37 is threaded, as at 41, for connection to the threaded lower end 42 of the foundation casing 36. The diameter of the hanger 38 is slightly less than the internal diameter of the foundation pile or casing 36 so that it may pass upwardly or be withdrawn through the casing 36. At the same time, the diameter of the hanger 38 is greater than the diameter of the shoulder or landing surface 43 formed on the inner wall of the special shoe 37 so as to be able to be hung therefrom.

Thus, in the operation shown in FIGURE 9, the lower end of the foundation casing 36 (FIGURE 1), which is supported either by slips in the rotary table 23 or by the hoist system of the derrick 16, is disengaged so that it can be lowered downwardly over the top of the hanger 33 (FIGURE 9) and into the upper end of the shoe 37 which is then threaded to the lower end of the foundation casing 36. The foundation casing 36 is then raised by means of the hoist system of the derrick until the landing shoulder 43 of the shoe engages the hanging surfaces 38a of the hanger 38 and the combined assembly is then raised slightly so that the slip 26 can be disengaged from the spider assembly 27 which would then be moved out of the way, if desired.

The upper end of the foundation casing 36 may be of larger diameter, as at 360. The entire foundation casing is then lowered into the water until its upper end is suspended from the spider assembly 27, as shown in FIG- URE 2. The foundation casing may also include a curved wall section 44 adapted to seat in a mating portion 44a of the base platform 29 in a manner similar to a ball-andsocket joint so that the platform 29 may tilt relative to the axis of the foundation casing 36 to conform to the slope of the ocean floor 13. The drilling wellhead assembly, generally represented by numeral 4-5, is then lowered by the hoist system of the derrick 16 until it engages and may be connected to the upper end of the foundation casing 36. It is to be understood that the drilling wellhead assembly rnay be made up from various combina tions of components such as a wellhead connector 46,

v blowout preventer 47, connector 48, flexible joint 49,

well known to the art, as by hydraulic pressure fluid or electrical power. Alternatively, a connector, such for example as connector 416, may have a series of horizontally directed connecting screws 51 adapted to engage the upper end 36b of the foundation casing. When drilling operations are carried out in shallow depths, these screws 51 may be actuated by a diver. When operating in deep water, the screws may be operated by an underwater manipulator provided with a remotely act-uatable power wrench of a type well known to the art. If desired, the upper end of the foundation casing 36b may be provided with a circumferential track 52 on which an underwater manipulator may be hung or seated when moving around an apparatus to connect the screws 51. After securing the connector 46 to the top of the foundation casing 36b, the entire structure is lifted slightly by the hoist system of the derrick 16 so that the spider assembly 2'7 and beams 53 and 54 can be removed. The entire assembly is then lowered until the curved wall section 44 of the foundation casing 36b seats in its socket 440 in the center of the base platform 29. After the foundation casing has been connected to the foundation plate 29, the tie rods 30 and the entire structure is lowered the water as shown in FIGURE 3.

Lowering of the combined apparatus from the position shown in FIGURE 2 to that shOWn in FIGURE 3 is accomplished in a manner well known to the art, as by adding successive sections of large diameter pipe to the upper end of the marine conductor pipe 50 as it is hung in the slip and spider assembly 27. After each section of pipe has been added to the top of the marine conductor pipe 50, the hoist system of the derrick is connected to the upper end of the and 31 are removed downwardly through length of the pipe added, Which pipe would then be secured in the slip and spider assembly 27 as still another section of pipe was added to the upper end of the marine conductor pipe. This series of operations is repeated to lengthen the marine conductor pipe 50 until the foundation plate 29 of the wellhead structure is positioned on the ocean floor 13, ,or alternatively, until at least the lower end of the foundation casing within the well 35. As the combined apparatus is lowered FIGURE 9. In the been drilled, when the bottom of the at the top of the 21 will be forced upwardly off the landing shoulder 43 in the special shoe 37 and thence upwardly through the foundation pile or casing 36.

FIGURES 3 and 4 illustrate the operation of retrieving the section of drill pipe 21 which depended from the shoe 37 at the bottom of the foundation casing 36. With the marine conductor 50 supported by the spider and slip assembly 27, a suitable fishing tool on a pipe or wire line is run down through the marine conductor pipe 50 to engage the top of the hanger 38 (FIGURE 9) so that the hanger 38 and drill string 21 secured thereto can be pulled upwardly through the foundation casing 36 of the marine conductor 50 to the vessel '11. One way of carrying out this operation is illustrated in FIGURE 3 wherein a small diameter pipe string 55 having a retrieving tool 56 secured to the lower end thereof is run down through the marine conductor pipe d. During this operation, the upper end of the running or fishing pipe string 55 may be supported by conventional elevators 57 which are supevent that only a shallow well 35 has the drill bit 33 comes in contact with well 35, the hanger 38 (FIGURE 9) drill string ported by the hoist system of the derrick.

One form of .a retrieving tool 56 is illustrated in FIG t3 URE 14 as comprising a body member 58 having a lower portion 58a of a diameter small enough to tilt within a bore of a pipe or of an element to be retrieved by the tool. A

her in any suitable operative manner, as by spring arms 60 depending from a follower plate 61 which is normally urged downwardly by the compression spring 62. The teeth of the slip element 59 are preferably formed as threads so as to engage the threaded opening within the bore of the hanger element 38.

Another form of a hanger element 63 is shown in FIGURE 10 as having an internally threaded recess 64 extending axially within the bore thereof. To engage the retrieving tool 56 with the threaded recess 64 of a

hanger

38 or 63, the retrieving tool 56 (FIGURE 14) is either stabbed or rotated down into the threaded opening in the top of the hanger. After the connection has been made between the fishing tool and the hanger 38, the hoist system of the derrick pulls the fishing pipe string 55, retrieving tool 56, hanger 38, drill string 21 and drill bit 33 upwardly through the bore of the assembled equipment. In order to accomplish this, it is evident that the bore 37a (FIGURE 9) of the shoe 37 must be slightly larger than the diameter of the drill bit 33 being recovered. Since the diameter of the shoe 37 and the foundation casing 36 is greater than that of the drill bit 33 being retrieved, it is quite evident that it is previously necessary to enlarge the hole 35 in the ocean floor in a manner well known to the art by means of a hole opener or a reaming bit of slightly larger diameter than the largest tubular member to be run into the well.

With the drill pipe having been removed from the wellhead drilling assembly, the entire assembly is lowered until the foundation plate 29 is positioned on the ocean floor. Continual lowering of the foundation plate to the ocean floor is accomplished in a manner described hereinabove, that is, by adding successive sections of marine conductor pipe 50 until the marine conductor pipe extends between the drilling wellhead assembly and the ocean floor and the vessel 11 as shown in FIGURE 5.

Support cables

65 and 66 running from constant tension hoists 67 and 68 are secured to the upper end of the marine conductor pipe 50 below any telescoping joints 69 therein. The small diameter or upper section 69a of the telescoping joint 69 is secured to the vessel 11, as by

tie rods

70 and 71. The foundation casing 36 is cemented in the well by conventional cementing methods such for example as running a small-diameter pipe string down through the marine conductor pipe Si) and positioning the cementing head, carried at the lower end, near the lower end of the foundation casing 36. Cement is then pumped down through the cementing string and up the annulus between the foundation casing 36 and the well wall to fill the space with cement 72. The cementing pipe string is then withdrawn from the marine conductor.

After the cement has hardened, drilling operations are continued in a conventional manner by lowering a drill string down through the marine conductor pipe 59, the drilling wellhead assembly and through the foundation casing 36. While the power transmission lines have not been illustrated to the various wellhead components, it is to be understood that such components as the blowout preventer 47 and the connector 48 may have hydraulic or electrical control lines extending thereto from the vessel 11. However, the connector 48 may be of the type that is actuated and operated by an underwater manipulator or a diver.

After the well 35 has been drilled deep enough to receive a predetermined length of easing, such for example as 10% inch surface casing, a length of surface casing 73 (FIGURE 5) of a length equal to or greater than the water depth, say 50 feet longer than the water depth, is run down through the marine conductor pipe 50. A hanger 63 is secured to the top of the surface casing string 73 in order to be able to hang the surface casing from the drilling wellhead assembly. Preferably, as shown in FIG- URE 10, a short section of drill pipe or small-diameter pipe 74 is interposed between the hanger as and a surface casing 73 so that when the hanger 63 is hung from a landing surface within the wellhead assembly of the blowout preventer 47 (FIGURE the short section of smalldiameter pipe 74 will be within the blowout preventer 47 so that a fluid tight seal may be obtained more readily around the smaller-diameter pipe in an emergency.

While it is realized that a landing surface may be provided at any point in the drilling wellhead assembly to receive hangers such as 38 and 63 (FIGURES 9 and 10), it is preferred that a landing surface be provided in the drilling wellhead assembly above the connector unit 48 at the lower end of the marine conductor 58 or in the upper portion of the connector 48 (FIGURE 11) so that when the connector is disconnected from the blowout preventer 47, the landing shoulder 7 5 and then the hanger positioned thereon will be pulled back to the vessel with the upper portion of the connector 48. As shown in FIGURE 11, thedrilling wellhead assembly is provided with a mandrel 76 extending upwardly from the blowout preventer 47 in alignment with the bore 77 through the blowout preventer 47. The connector 48 is provided with a remotely actuatable clamping member such as, for example, a split ring 78 adapted to be tightened to secure the connector 48 to the mandrel 76. It is to be understood that the shoulder 75 formed on the inner wall of the connector 78 may also be alternatively positioned in the lower end of the flexible joint 49 or in the lower end of the marine conductor pipe 56. The diameter of the landing surface 75 is preferably greater than that of the hanger 38 (FIGURE 9) so that the hanger 38 may pass readily through it as it is withdrawn to the vessel. However, in the event that a relatively small-diameter (say 16 inch) marine conductor pipe 50 is to be employed, the landing surface 75 (FIGURE 11) may be substan tially equal to the diameter of the landing surface 43 (FIGURE 9) and smaller than the overall diameter of the hanger 38. If the outer surface of the hanger 38 is grooved in a manner described hereinabove, the hanging surface 75 within the connector 48 is grooved in a cooperating manner so that the raised portion on the outer surface of the hanger 38 may pass through the grooves 7 9 formed in the inner surface of landing shoulder 75 in a manner illustrated in FIGURE 12. Since the other hanger 63 (FIGURE 10) does not have to pass the landing shoulder 75 of the connector 48 (FIGURE 11), the outer surface of the hanger may not be grooved. In the event that a grooved hanger was to be seated on a grooved landing surface 75, it may be necessary to rotate the hanger slightly so that the grooves are substantially in alignment.

The surface casing 73 in its hanger 63 are lowered by means of a running pipe string 88 having a retrieving tool 56 at the lower end thereof which may be disengaged by the hanger 63 when the latter is seated on the landing shoulder 75 (FIGURE 11) of the connector 48. The running string 80 (FIGURE 5) and its retrieving tool 56 are then disconnected and withdrawn to the vessel.

The surface casing 73 (FIGURE 5) of a length greater than the water depth is hung within the connector 48 of the drilling wellhead assembly so as to serve as a guide element when the drilling wellhead assembly is pulled back to the vessel 11 and subsequently run back down to the foundation casing 36!). Since the well is still relatively shallow, a drilling wellhead assembly 45 including the blowout preventer 47 can be disconnected at connector 51 and pulled back to the vessel by means of the hoist system of the derrick pulling the marine conductor pipe back to the vessel where it would be disconnected in sections and put aside for future use. As the drilling wellhead assembly is pulled upwardly, the depending surface casing string 73 would also be pulled up to the vessel where it would be secured in the slip and

spider assembly

27 and 28. The lower threaded end 74a of the short pipe section 74 secured to the hanger 63 (FIGURE 10) would be disconnected from the top of the surface casing string as shown in FIGURE 6. The hanger 63 in pipe section 74 would then be removed from the drilling wellhead assembly 45. The desired length of surface casing 73 would then be added in sections to the upper end of the casing string which would be lowered into the well to the desired depth. Thus, the lower end of the surface casing 73 would be positioned in the well a distance above its final landed position which is equal substantially to the water depth or to the distance between the wellhead and the slip and spider assembly on the drilling vessel 11.

With the upper end of the surface casing at the vessel, it can be either secured to another drilling assembly for drilling to greater depths or it can be secured to the lower portion of a production wellhead assembly through which drilling operations can be continued. In FIGURE 7, the upper end of the surface casing 73 is secured to a landing head 81 adapted to be fixedly secured as by bolts or latches to the upper end 36b of the foundation casing. The landing head 81 is permanent well equipment and forms the mount for the lower portion of the production wellhead assembly 82 which is fixedly secured above it. Prior to completion of the well this portion 82 of a production wellhead assembly forms part of a second welldrilling assembly which includes remotely-operable ramtype blowout preventers 84 as well as a bag-type blowout preventer 47, connector 48, flexible joint 49 and marine conductor pipe section 56). Wellhead drilling assembly 83 is connected to the landing head 81 which in turn is secured to the top of the surface casing 73, as illustrated in FIGURE 7. The entire assembly may be lowered into the well by one of two methods. In one method additional sections of marine conductor pipe 50 are added to the top of the section of marine conductor pipe secured to the flexible joint 49. As successive sections of marine conductor pipe were added one at a time, the assembly would be lowered into place at the wellhead in a manner similar to the operation described with regard to FIGURE 5. A small-diameter cementing pipe string preferably with swab cups at the lower end thereof would be run down through the marine conductor pipe 50, the drilling wellhead assembly and down through the surface casing 73 to, say, about 100 feet from the lower end thereof. The bag-type blowout preventer 47 would then be closed around a cementing pipe string and cement followed by a displacing fluid would be pumped from the vessel down through the cementing pipe string, out the bottom of the surface casing and up the annular space between the outside of the surface casing and the wall of the well, in a manner well known to the art. Thereafter, the cementing pipe string would be withdrawn back to the vessel and a drill string would be run down through the same equipment in the event that it was desired to drill the well deeper.

In the second method, a string of drill pipe 85 would be made up as it was lowered down through the marine conductor pipe and into the well. A suitable connector or adaptor would be connected in the drill pipe string between two sections thereof. The connector or adaptor may take the form of a plug 86 threaded as at 87 so as to be threadedly secured with a left-hand thread to the top of a section of marine conductor pipe 50. If additional sections of drill pipe are being added to the top of the drill pipe string 85 as the drilling wellhead assembly 47 is lowered through the water to the underwater base, the drill pipe string 85 becomes a running pipe string for running the equipment into place. With the drilling wellhead assembly 83 fixedly secured to the top of the foundation casing 36b, the connector 48 above blowout preventer 47 would be disconnected allowing the pipe string 85 to be withdrawn to the vessel along with flexible joints 49 and connector 48. The one seetion of marine conductor pipe 50 at the top of the flexible joint 49 would be hung in the slip and spider assembly 27 while the adaptor 86 was disconnected from the top of pipe 56 and removed from the drill pipe string 85 also. The drill pipe string 85 would then be made up with additional sections and lowered to substantially the bottom of the surface casing to serve as a cementing pipe string which would be utilized to cement the surface casing in a manner described hereinabove.

After cementing the surface casing 73 in place, the drill pipe string 85 would then be pulled back to the vessel except for a length greater than the water depth which would be hung from the slip and spider assembly 27. At this time, with only the top of one section of drill pipe extending above the slip and spider assembly 27 a landing head 63 (FIGURE 10) would be secured to the top of the drill pipe string. This landing head 63 would be lowered onto the landing shoulder 75 of the connector 48, then positioned at the vessel, and additional sections of marine conductor pipe 50 will be connected successively to the top of the section 50' above the flexible joint 49 and connector 4% as these elements were lowered through the water with the drill pipe 85 depending therefrom in a manner described with regard to FIGURE 2.

After the connector 48 was seated on its cooperating mandrel '76 and secured thereto, the upper end of the marine conductor pipe would be secured to the vessel 11 in a manner described with regard to FIGURE of the drawing. A fishing too] similar to that shown in FIGURE 14 would then be run down through the marine conductor pipe 59 in a manner described with regard to FIG- URES 3 and 4 to engage the top of the hanger 63 (FIG- URE after which the fishing tool, hanger and well pipe depending therefrom would be withdrawn to the vessel. In the event that additional drilling is necessary in the well, a drill bit would be attached to the lower end of the drill string and run down through the assembled equipment into the well. It may be seen that by using the apparatus of the present invention and practicing the methods disclosed hereinabove that there is a guide element such as a string of pipe always hanging from any well need for stripping larger-diameter pipe over small-dian1- eter pipe as in other methods. While it is realized that a landing sur its depending guide elements may within the drilling wellhead assembly, it is preferred to provide the landing shoulder 75 in or above the wellhead connector 48 located above at least one blowout preventer 47 (FIGURE 5). Thus, in the event that a hole develops in the wall of the marine conductor 50 caused by the rotation of drill pipe therein, the blowout preventer 47 can be closed around a guide element when the latter is depending from a disconnected wellhead connector 48.

sirable since they may have a tendency to be come unlatched thus allowing the guide element to become disconnected and fall into the well which would cause a break in the connection between the vessel and the wellhead.

I claim as my invention:

1. In a method of drilling an underwater well from a vessel at the surface of a body of water, the operation of running a casing string down into axial register with the well already containing a drill string movably positioned therein, said operation comprising the steps of:

forming hole in the ground beneath said body of water with a drill string and leaving said drill string in said hole;

raising the drill string partially out of the well so that its upper end is above water in the vicinity of the vessel and its lower end is off the bottom of the well a distance at least greater than the depth of water under the vessel;

hanging the upper end of said drill string at the vessel from the interior of a casing string supported at the vessel so that the pipe string is adapted to be moved upwardly within said casing string;

lowering the combined casing string and drill string hanging therefrom into the well until at least the lower end of the casing string has entered the top of the 'well,

guiding and lowering a retrieving tool from the vessel down through the casing string;

engaging the upper end of said drill string with said retrieving tool; and,

pulling the retrieving tool and drill string up through said casing string to the vessel.

2. The method of claim 1 including the subsequent step of lowering said casing string into the well to a predetermined point.

3. The method of claim 1 including the step of attaching to the upper end of the casing string a well base and drilling wellhead assembly.

4. The method of claim 3 including the step of lowering said casing string into the well until the well base is supported on the ocean floor.

5. The method of claim 3 including the subsequent step of cementing the casing string in the Well.

6. The method of claim 5 including the step of inserting a cementing pipe string through a conductor pipe forming part of the drilling wellhead assembly and extending to the vessel, running the cementing string to a predetermined depth in said casing string, and pumping cement through said cementing string and casing string and into the well to cement the casing string therein.

References Cited UNITED STATES PATENTS CHARLES E. OCONNELL, Primary Examiner. R. E. FAVREAU, Assistant Examiner.

Claims

1. IN A METHOD OF DRILLING AN UNDERWATER WELL FROM A VESSEL AT THE SURFACE OF A BODY OF WATER, THE OPERATION OF RUNNING A CASING STRING DOWN INTO AXIAL REGISTER WITH THE WELL ALREADY CONTAINING A DRILL STRING MOVABLY POSITIONED THEREIN, SAID OPERATION COMPRISING THE STEPS OF: FORMING HOLE IN THE GROUND BENEATH SAID BODY OF WATER WITH A DRILL STRING AND LEAVING SAID DRILL STRING IN SAID HOLE; RAISING THE DRILL STRING PARTIALLY OUT OF THE WELL SO THAT ITS UPPER END IS ABOVE WATER IN THE VICINITY OF THE VESSEL AND ITS LOWER END IS OFF THE BOTTOM OF THE WELL A DISTANCE AT LEAST GREATER THAN THE DEPTH OF WATER UNDER VESSEL; HANGING THE UPPER END OF SAID DRILL STRING AT THE VESSEL FROM THE INTERIOR OF A CASING STRING SUPPORTED AT THE VESSEL SO THAT THE PIPE STRING IS ADAPTED TO BE MOVED UPWARDLY WITHIN SAID CASING STRING; LOWERING THE COMBINED CASING STRING AND DRILL STRING HANGING THEREFROM INTO THE WELL UNTIL AT LEAST THE LOWER END OF THE CASING STRING HAS ENTERED THE TOP OF THE WELL, GUIDING AND LOWERING A RETRIEVING TOOL FROM THE VESSEL DOWN THROUGH THE CASTING STRING; ENGAGING THE UPPER END OF SAID DRILL STRING WITH SAID RETRIEVING TOOL; AND PULLING THE RETRIEVING TOOL AND DRILL STRING UP THROUGH SAID CASING STRING TO THE VESSEL.