US3430695A

US3430695A - Method and apparatus for installing underwater wellhead support

Info

Publication number: US3430695A
Application number: US681600A
Authority: US
Inventors: Jack L Hubbard
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1967-11-08
Filing date: 1967-11-08
Publication date: 1969-03-04
Anticipated expiration: 1986-03-04

Description

Match 4, 1969 J. L. HUBBARD METHOD AND APPARATUS FOR INSTALLING UNDERWATER WELLHEAD SUPPORT Original Filed Jan. 14, 1966 Sheet FIG .H'

INVENTOR JACK L.HUBBARD ATTORNEY March 4, 19 69 J. L. HUBBARD 1 3,430,695

METHOD AND APPARATUS FOR INSTALLING UNDERWATER WELLHEAD SUPPORT Original Filed Jan. 14, 1966 Sheet 2 of 2 I ll W U U INVENTOR FM; J?

JACK L. HUBBARD BY CZ QM fi i ATTORNEY Patented Mar. 4, 1969 3,430,695 METHOD AND APEARATUS FOR INSTALLING UNDERWATER WELLHEAD SUPPORT Jack L. Hubbard, Springdale, Conn., assignor to Mobil Oil Corporation, a corporation of New York Continuation of application Ser. No. 520,591, Jan. 14, 1966. This application Nov. 8, 1967, Ser. No. 681,600 US. Cl. 166-5 14 Claims Int. Cl. E21 33/035, 43/ 01; E21c 19/00 This application is a continuation of application Ser. No. 520,591 filed I an. 14, 1966, now abandoned.

The invention relates to a method and apparatus for developing a subaqueous production well in deep water, at diving depth, from an exploratory well without the necessity of an initial investment in a permanent submerged wellhead support structure until commercial production is proven, and more particularly, the invention relates to means for guiding a submerged wellhead support structure into position over a well drilled in a subaqueous bottom, installing a permanent submerged wellhead thereon, within diving depth, beneath the surface, and connecting the well to production and/or storage facilities by fiowlines laid on the subaqueous bottom and connected to the subsea wellhead through the upper end of a flowline riser fixed to the wellhead support structure when the wellhead support structure is lowered to the marine bottom.

Present developments in the offshore oil and gas industry indicate that drilling efforts will be extended to underwater areas where bottom-supported surface structures are neither as economically nor technologically feasible as in the already developed leases in the Gulf of Mexico, where such surface production platforms are rather commonplace. In drilling exploratory holes at depths of three hundred feet or more the statically and dynamically positioned floating drilling vessels have dominated the scene. With wells that are now being drilled at these depths from floating vessels, and are to be put into production, it is generally believed that bottom or mudline completions are the most satisfactory solution, regardless of the fact that the marine bottom may be far below the depths at which a diver can work. While robotic and TFL (through flowline) tools have been developed and are available for routine servicing and workover operations, these devices are complicated and expensive and are at this time only used for a few limited tasks.

For production purposes it is desirable to complete a well so that certain servicing and repair operations, not as easily accomplished by remote controlled equipment, can be handled by a diver. One method for accomplishing this is to mount a completely submerged wellhead support structure over the well site, the support structure extending from the subaqueous bottom to a point beneath the surface that a diver can easily reach. Such a wellhead support structure would not need to be as large as one which would extend completely to the surface and furthermore would not need to be as massive, since the most violent wave forces occur at the surface or just beneath; furthermore, a submerged wellhead would not be a hazard to navigation.

One of the drawbacks of utilizing a submerged support structure is the large capital outlay necessary when it must be anchored on the subaqueous bottom prior to the drilling of a well, or wells, therethrough. The economics of locating an expensive structure permanently on the subaqueous bottom, before a subaqueous well is proven, has resulted in the general unacceptability of such a procedure to date. Moreover, it has not been usually considered practical to submerge a prefabricated platform over a bottom completed subaqueous well in deep water, after drilling, since it is very difficult to locate properly such a structure with respect to the upstanding wellhead without a diver being on the scene. It is also difiicult, in connecting the necessary fiowlines from the submerged wellhead to production and storage facilities, to bring the unsupported lines from the subaqueous bottom, upon which they are laid, to the submerged wellhead, perhaps several hundred feet above, without exceeding the design limitations of the presently available flowlines.

The most universally accepted method of drilling a well from a floating structure is to set first a base platform on guide template on the bottom and have a number of flexible guidelines secured thereto and extended up to the floating vessel whereby equipment may be guided to and through the base platform for drilling purposes. The base platform is grouted or otherwise connected to the upper end of a conductor pipe inserted in the upper end of a partially drilled wellbore and serves the dual purpose of assisting in the support of the conductor pipe, in which the well casings are hung, and providing a means for spacing the guidelines around the conductor pipe. A similar technique is to drill first or wash a conductor pipe, with guidelines connected thereto, into the subaqueous bottom and then lower the base platform down over the conductor pipe with the aid of the guidelines connected to the conductor pipe. The adaptation of the above-described technique of utilizing guidelines to locate a subsea base platform on a conductor pipe set in the formations underlying the subaqueous bottom to installing submerged production structure over the subaqueous well would appear to be a solution to the problems enumerated above, the greatest economic advantages being realized when the production structure is installed over an already proven subaqueous well. However, the guidelines utilized for guiding equipment into the conductor pipe of the subaqueous well are mounted either on the well conductor pipe itself, or on adjacent guide columns on the base platform, and are grouped too close to the center of the well, and usually are not strong enough to be used in locating the legs of such a massive structure.

Accordingly, it is an object of the present invention to provide a means for locating a submerged wellhead support structure on the subaqueous bottom in relation to a proven well.

It is another object of this invention to provide a base platform assembly with primary and secondary guide means for guiding the well drilling and servicing equipment, and the subsurface wellhead support, respectively, from the surface.

It is a further object of the invention to provide a means for positively locating a submerged wellhead support structure over a submerged upstanding well conductor pipe.

It is still a further object of the invention to provide a method for laying the necessary flowlines on a subaqueous bottom and operatively connect these flowlines with an elevated wellhead mounted on a Wellhead support structure.

Other objects and advantages of this invention will be readily apparent from the following description, when taken in conjunction with the accompanying drawings that illustrate useful embodiments in accordance with this invention.

FIGURE 1 is a schematic view of a conductor pipe, driven into a subaqueous bottom, with primary guidelines extending therefrom to a surface vessel.

FIGURE 2 is a view of a base platform or guide template being lowered to the bottom and centered over the conductor pipe by primary guidelines.

FIGURE 3 is a view of the submerged conductor pipe with the guide template or base platform fixed to the subaqueous bottom over the conductor pipe, with the primary guidelines extending to the surface and having secondary guidelines with the outer ends thereof being weighted to the bottom, out of the way.

FIGURE 4 shows the wellhead support structure, with a flowline riser connected thereto along its length, being lowered to the subaqueous bottom over the secondary guidelines extending up from the base platform to the surface.

FIGURE 5 shows the support structure in place, anchored into the base platform, with a conductor extension pipe being lowered through the wellhead support structure to the submerged conductor pipe.

FIGURE 6 shows the completed subaqueous well with a subsea wellhead mounted on a wellhead support structure in place over the submerged conductor pipe of the subaqueous well and connected thereto.

A subsea base platform assembly, for supporting a submerged conductor pipe in the marine bottom beneath a body of water and for supporting a submerged wellhead support structure, consists of a large weighted block or base platform having a plurality of spaced guide apertures for slidably constraining flexible primary guidelines or cables extending from the submerged conductor pipe to the surface. Directly secured to the base platform, at the outer periphery thereof, are a number of platform leg guides, each having a secondary guideline or cable connected thereto. After the conductor pipe has been set in the subaqueous formations beneath the subaqueous bottom, with the primary guide cables extending to the surface, the base platform assembly is lowered by means of at least a pair of the secondary cables to the bottom, guided by the primary cables connected to the conductor pipe, so that the base platform assembly settles into the overburden on the subaqueous bottom surrounding the conductor pipe and can be cemented thereto if it is so desired. Alternatively, the base platform assembly is first lowered to the subaqueous bottom and then the conductor pipe is lowered down through the body of Water into the base platform assembly with the aid of the primary guidelines which are secured to the base platform assembly. In this instance, the conductor pipe is hung in a central aperture in the base platform assembly supporting the conductor pipe until it is cemented in place. The secondary guide cables are weighted at their outer, free ends and submerged to the bottom, to avoid entanglement during the subsequent drilling operation, with marker buoys connected to the outer ends for later location. After this operation the well is drilled in the usual manner, utilizing the primary guide cables, until the well has been proven.

When it is decided that a subaqueous well should be completed, the outer ends of the secondary guide cables are brought back to the surface. At this point the primary guide cables may be completely disconnected. A wellhead support structure, having a plurality of vertical supporting legs, is lowered from the surface until the legs are guided into the leg "uides on the base platform by the secondary guide cables. Subsequently, piles can be driven through the hollow legs of the wellhead support structure and the leg guides to anchor the structure in the formations underlying the subaqueous bottom. One method of driving the piles through the submerged legs is shown by the patent application, Ser. No. 266,734, by William F.

Manning, for Apparatus and Method for Installation of a Pile-Jacket Assembly in a Marine Bottom. A conductor extension pipe is lowered through the anchored wellhead support structure and is connected at its lower end to the upper end of the buried conductor pipe near the mudline by some manner of automatic connection device, such devices being old in the art. The conductor extension pipe can be guided into contact with the upper end of the submerged conductor pipe by concentric guide means in the wellhead support structure. The upper end of the conductor extension pipe is cut off at the upper end of the wellhead support structure. Production well tubing can be hung in the well proper, with the upper end thereof at the subaqueous bottom, and with a section of tubing extension releasably connected to the upper end of the production Well tubing to extend a production fluid path into the submerged wellhead on the upper end of the conductor extension pipe or the production tubing can be hung directly within the wellhead on the upper end of the conductor extension pipe.

Prior to submerging the wellhead support structure, a flowline riser is connected along one of the legs to form a portion of a flowline to be connected to the submerged wellhead and laid along the bottom of the body of Water, a flexible flowline portion being connected to the lower end of the flowline riser so that when the wellhead support structure is installed in the base platform, and a wellhead is mounted on the upper end of the wellhead support structure, the flowline already operatively extends, supported from a point within diving depth, on the upper end of the wellhead support structure, to the bottom and back to the surface of the body of water and may be simply laid from a vessel on the surface supporting the free end of the flowline, along the bottom from the wellhead support structure to production and/ or storage facilities. In the usual case, the flowline riser would be rigid while the flowline portion connected thereto would be flexible. After the wellhead support structure is set in place and the lower end of the extension conductor pipe extension is secured to the conductor pipe by remote mechanical means, or by grouting, a diver connects the upper end of the conduction extension pipe to a production wellhead lowered from the surface. The upper end of the fiowline riser at the upper end of the wellhead support structure is connected to the now mounted submerged wellhead and the well can be thereafter put on flow.

The submerged wellhead is now situated only a short distance beneath the surface, perhaps a hundred feet, where it can be easily reached by a diver. The only elements of the assembly above the subaqueous bottom that cannot be reached by a diver are the lower end of the wellhead support structure itself, the connection between the conductor pipe and the conductor extension pipe, and the connection of the flowline riser to the flexible flowline portion. The chances of the wellhead support structure or the connections needing repair are very slim and would justify a permanent method of connecting this apparatus. However, if it is felt that there was an advantage to being able to bring the wellhead support structure back to the surface at some later date, releasable slips could be mounted in the lower ends of the legs to lock in the leg guides and the piles would be grouted directly to the leg guides on the base platform rather than to the legs themselves. A remotely releasable device could also be used to connect the conductor extension pipe to the submerged conductor pipe.

Looking at FIGURE 1, a conductor pipe 10 has been set, or buried, in the subaqueous bottom 12 with a plurality of flexible primary guidelines 14 extending back to a surface drilling platform, a floating vessel 16 on the surface 18 of a body of water. FIGURE 2 shows a base platform assembly 20 being lowered to the subaqueous bottom 12 from a point adjacent the surface 18 by means of a plurality of secondary guidelines 22 secured thereto.

The base platform assembly 20 is guided into position around the buried conductor pipe by means of the primary guidelines 14 connected between the conductor pipe 10 and the floating vessel 16 on the surface (not shown in this view). The base platform assembly 20 has a number of guide passages 24, for slidably guiding the base platform assembly with respect to the primary guidelines 14, and outwardly mounted upstanding leg guides 26 within which the secondary guidelines 22 are secured.

FIGURE 3 shows the base platform assembly 20 positioned on the marine bottom 12 surrounding the upper end of the conductor pipe 10 extending a short distance above the bottom. The outer, free ends of the secondary guidelines 22 have been submerged to the bottom by means of anchors 28 and are marked with buoys 30 connected thereto by anchor lines 32. The primary guidelines 14, now spaced by the guide passages 24, extend between the base platform assembly 20 and the surface 18 of the body of water to provide the flexible interconnection for guiding drilling apparatus to the subaqueous well through the conductor pipe 10 from the floating vessel 16.

FIGURE 4 shows a wellhead support structure 34 being lowered from the surface to the base platform assembly 20 after a subaqueous well has been drilled and proven. The wellhead support structure 34, consisting in this illustrative example of three parallel spaced legs 36 and interconnecting braces 38, is guided down to the base platform assembly 20 by means of the secondary guide cables 22 which have been brought back to the surface. One end of a flexible flowline portion 40 is connected to the lower end of a rigid flowline riser 41 supported along the axial length of a leg 36 of the wellhead support platform 34.

FIGURE 5 shows the wellhead support structure 34 located on the base platform assembly 20 with the lower ends of the legs 36 thereof positioned within the leg guides 26. The wellhead support structure 34 is firmly anchored in the marine bottom by means of piles 42 driven down through the legs 36, which are hollow, and through the respective leg guides 26 of the base platform 20 into the bottom 12. One end of the flexible flowline portion 40 is now rigidly anchored to a point adjacent the lower end of the wellhead support structure near the bottom, by means of the fixed flowline riser 41, so that the flowline portion 40 can be laid across the bottom 12 to storage and production facilities (not shown). A conductor extension pipe 44 is shown being lowered down through the support structure 34 to the upper end of the conductor pipe 10 to which it will be permanently connected.

FIGURE 6 shows the completed well with a submerged wellhead 46 mounted on top of the submerged wellhead support structure 34 on the upper end of the conductor extension pipe 44 that is now permanently connected to the upstanding conductor pipe 10. The flowline riser 41 is operatively connected to the wellhead 46 to complete a closed fluid path from the wellhead 46 to the subaqueous bottom 12 and along the bottom to distant production or storage facilities. While the bottom is hundreds of feet beneath the surface, the subsea wellhead 46, arranged a hundred feet below the surface as shown in FIGURE 6, would be at a depth which a diver could easily reach while still being sheltered from the more violent surface area of the body of water, and further, all the interconnections between the elevated wellhead and the marine bottom 12 are supported.

Although the present invention has been described in connection with details of the specific embodiments thereof, it is to be understood that such details are not intended to limit the scope of the invention. The terms and expressions employed are used in a descriptive and not a limiting sense and there is no intention of excluding such equivalents, in the invention described, as follow in the scope of the claims. Now having described the apparatus and methods herein disclosed, reference should be had to the claims which follow.

What is claimed is:

1. A base platform assembly to be located on a subaqueous bottom, beneath a body of water comprising: a base platform, means associated with said base platform for spacing the lower ends of a plurality of primary guidelines with respect to each other and with respect to an upstanding conductor pipe to be set in the formations underlying a subaqueous bottom, said plurality of primary guidelines being adapted to extend to the surface of a body of water in which said base platform assembly is to be located to position said base platform assembly and the upstanding conductor pipe with respect to each other and a wellbore extending into the formations underlying the subaqueous bottom; a plurality of upstanding leg guides of said base platform assembly fixedly spaced outward of said means for spacing the lower ends of a plurality of primary guidelines, each of said leg guides being adapted to coact wtih one of a plurality of spaced legs of a wellhead support structure to locate a wellhead support structure with respect to a conductor pipe to be set in the wellbore extending into the formations underlying a subaqueous bottom with the upper end of the conductor pipe located beneath the surface of the body of water; and a plurality of secondary guidelines, one end of each of said secondary guidelines being secured to said base platform at spaced intervals outward of said plurality of primary guidelines and adapted for extending to the surface of a body of water In which said base platform assembly is to be located to guide a wellhead support structure through the body of water to contact the legs of the wellhead support structure with said upstanding leg guides.

2. The base platform assembly of claim 1 wherein a central aperture extends through said base platform to encircle the upper end of an upstanding conductor pipe to be set in the formations underlying a subaqueous bottom.

3. The base platform assembly as recited in claim 1 wherein said plurality of primary guidelines are adapted to be secured to the conductor pipe, said means for spacing said primary guidelines being a plurality of spaced guide apertures extending through said base platform whereby said base platform assembly is guided to the bottom after a conductor pipe is set in the formations underlying the subaqueous bottom by the sliding engagement of said primary guidelines in said spaced guide apertures while said base platform assembly is lowered from the surface.

4. The base platform assembly as recited in claim 1 wherein said means for spacing the lower end of said primary guidelines are means for directly securing said plurality of primary guidelines to said base platform, whereby said conductor pipe, in sliding engagement with said primary guidelines, is guided down to and through the previously anchored base platform assembly.

5. Apparatus for completing a subaqueous well beneath the surface of a body of water and above a subaqueous bottom, comprising an upstanding conductor pipe set in the formatons underlying said subaqueous bottom and extending a short distance above said subaqueous bottom; a submerged base platform assembly located on said subaqueous bottom, means for locating said base platform assembly with respect to said conductor pipe, said base platform assembly comprising a base platform, means associated with said base platform for spacing the lower ends of a plurality of primary guidelines with respect to each other, said plurality of primary guidelines each being of a length sufficient to extend to the surface of the body of water in which said base platform assembly is located, a plurality of upstanding leg guides of said base platform assembly spaced outward of said means for spacing the lower ends of a plurality of primary guidelines, each of said leg guides being adapted to coact with one of a plurality of spaced legs of a wellhead support structure to locate the wellhead support structure with respect to said conductor pipe set in said formations underlying said subaqueous bottom, and a plurality of secondary guidelines, one end of each of said secondary guidelines being secured to said base platform at spaced intervals outward of said plurality of primary guidelines, each of said plurality of secondary guidelines being of suflicient length to extend to the surface of the body of water in which said base platform assembly is located and adapted to guide a wellhead support structure through the body of water to contact the legs of the wellhead support structure with said upstanding leg guides.

6. Apparatus as recited in claim wherein there is a wellhead support structure installed on said base platform assembly, a plurality of legs of said wellhead support structure being located one in each of said plurality of leg guides, means for securing said plurality of legs of said wellhead support structure in said leg guides of said base platform assembly, a submerged wellhead mounted on the upper end of said wellhead support structure, and a conductor extension pipe connected between said conductor pipe and said subsea wellhead to form a fluid path therebetween.

7. Apparatus for completing a subaqueous well beneath the surface of a body of water and above a subaqueous bottom, and for laying a submerged flowline from the submerged wellhead of the completed well to a distant production and/or storage facility comprising: a submerged wellhead support structure fixedly positioned with respect to said subaqueous bottom; a submerged wellhead mounted on the upper end of said submerged wellhead support structure spaced above said subaqueous bottom; conductor pipe means for providing a fluid path between said submerged wellhead and a subaqueous well formed in the formations underlying said subaqueous bottom; a flowline riser fixedly attached along said wellhead support structure to provide a fluid path from said subaqueous bottom to said upper end of said wellhead support structure; means for connecting said submerged wellhead to said flowline riser; and a flexible flowline portion connected at one end to the lower end of said flowline riser, the other end of said flexible flowline portion extending to a floating vessel at the surface for laying a flowline along said subaqueous bottom.

8. A method of drilling and completing a subaqueous well beneath the surface of a body of water, in water deeper than diving depth, utilizing said base platform assembly of claim 1, set on said marine bottom and with a conductor pipe set in the wellbore of said well, extending through the subaqueous formations underlying said subaqueous bottom, and extending through said base platform, including the following steps:

(a) guiding well drilling apparatus from a floating vessel into said subaqueous well by said plurality of primary guidelines extending between said vessel and said base platform assembly to drill a subaqueous well through said conductor pipe;

(b) submerging a wellhead support structure and guiding it with said plurality of secondary guidelines toward said base platform assembly until said legs of said wellhead support structure are located in said leg guides of said base platform assembly to install said wellhead support structure on said base platform assembly;

(c) extending said subaqueous well drilled through said conductor pipe to the upper end of said submerged wellhead support structure installed on said base platform assembly in part by a conductor extension pipe connected at its lower end to said upper end of said conductor pipe; and

(d) mounting a submerged wellhead on the upper end of said conductor extension pipe on the upper end of said submerged wellhead support structure at a depth at which a diver can work.

9. A method of drilling and completing a subaqueous well under the surface of a body of water, as recited in claim 8, including the following additional steps:

(e) prior to guiding well drilling apparatus from said floating vessel into said subaqueous well by said plurality of primary guidelines, completely submerging said secondary guidelines by weighting the free end thereof; and

(f) subsequent to drilling and proving said subaqueous well and prior to submerging said wellhead support structure, retrieving said free end of said secondary guidelines and supporting said retrieved free ends from a floating vessel.

10. The method of claim 8 including the following additional steps:

(g) fixedly attaching a flowline riser, connected at its lower end to a first end of a flexible flowline portion, along the length of said wellhead support structure before submerging said wellhead support structure so that said flowline riser is supported from the upper end of said wellhead support structure to said subaqueous bottom after installing said wellhead support structure in said base platform assembly;

(h) connecting the upper end of said flowline user to said submerged wellhead mounted on the upper end of said wellhead support structure; and

(i) laying a flowline, connected to a second end of sa1d flexible flowline portion, along said subaqueous bottom from said wellhead support structure to distant production and/or storage facilities.

11. The method of claim 8 including the further steps (j) anchoring said wellhead support structure by setting a pile through each of said legs of said wellhead sup port structure and said associated leg guide into the formations underlying said subaqueous bottom; and

(k) connecting each of said piles to said respective leg.

12. A method of completing a subaqueous well under the surface of a body of water at an elevated level on a wellhead support structure and for laying a flowline from the elevated completion along a subaqueous bottom to a distant production and/ or storage facility, comprising the following steps:

(a) supporting a flowline riser on a wellhead support structure, said flowline riser extending from the upper to the lower end of said wellhead support structure;

(b) connecting a first end of a flexible flowline portion to the flowline riser at the lower end of said wellhead support structure;

(0) installing said wellhead support structure on a subaqueous bottom with said upper end thereof below the surface of the overlying body of water;

((1) supporting a second end of said flexible flowline portion of a flowline at the surface of the body of water while installing said wellhead support structure; and V (e) laying said flowline, comprising in part said flexible flowline portion, on said subaqueous bottom as the free end of said flowline, supported at the surface, is moved away from said wellhead support structure.

13. The method of claim 12, including the following additional steps, to be performed prior to step (c):

(f) drilling a subaqueous well from a floating surface vessel; and

(g) proving the production of said subaqueous well.

14. The method of claim 13, including the following additional steps:

(h) prior to step (f), locating a base platform on said subaqueou bottom;

(i) connecting guidelines between said base platform and said floating surface vessel; and

(j) guiding equipment, including said wellhead support structure, between said floating surface vessel and said subaqueous bottom in conjunction with said guidelines.

References Cited UNITED STATES PATENTS Tucker 175-8 Kofahl 175-7 Travers et a1 166-.5 X

Matthews 166 5 JAMES A. LEPPINK, Primary Examiner.

R. E. FAVREAU, Assistant Examiner.

US. Cl. X.R. 1757

Claims

1. A BASE PLATFORM ASSEMBLY TO BE LOCATED ON A SUBAQUEOUS BOTTOM, BENEATH A BODY OF WATER COMPRISING: A BASE PLATFORM, MEANS ASSOCIATED WITH SAID BASE PLATFROM FOR SPACING THE LOWER ENDS OF A PLURALITY OF PRIMARY GUIDELINES WITH RESPECT TO EACH OTHER AND WITH RESPECT TO AN UPSTANDING CONDUCTOR PIPE TO BE SET IN THE FORMATIONS UNDERLYING A SUBAQUEOUS BOTTOM, SAID PLURALITY OF PRIMARY GUIDELINES BEING ADAPTED TO EXTEND TO THE SURFACE OF A BODY OF WATER IN WHICH SAID BASE PLATFORM ASSEMBLY IS TO BE LOCATED TO POSITION SAID BASE PLATFORM ASSEMBLY AND THE UPSTANDING CONDUCTOR PIPE WITH RESPECT TO EACH OTHER AND A WELLBORE EXTENDING INTO THE FORMATIONS UNDERLYING THE SUBAQUEOUS BOTTOM; A PLURALITY OF UPSTANDING LEG GUIDES OF SAID BASE PLATFORM ASSEMBLY FIXEDLY SPACED OUTWARD OF SAID MEANS FOR SPACING THE LOWER ENDS OF A PLURALITY OF PRIMARY GUIDELINES, EACH OF SAID LEG GUIDES BEING ADAPTED TO COACT WITH ONE OF A PLURALITY OF SPACED LEGS OF A WELLHEAD SUPPORT STRUCTURE TO LOCATE A WELLHEAD SUPPORT STRUCTURE WITH RESPECT TO A CONDUCTOR PIPE TO BE SET IN THE WELLBORE EXTENDING INTO THE FORMATIONS UNDERLYING A SUBAQUEOUS BOTTOM WITH THE UPPER END OF THE CONDUCTOR PIPE LOCATED BENEATH THE SURFACE OF THE BODY OF WATER; AND A PLURALITY OF SECONDARY GUIDELINES, ONE END OF EACH OF SAID SECONDARY GUIDELINES BEING SECURED TO SAID BASE PLATFORM AT SPACED INTERVALS OUTWARD OF SAID PLURALITY OF PRIMARY GUIDELINES AND ADAPTED FOR EXTENDING TO THE SURFACE OF A BODY OF WATER IN WHICH SAID BASE PLATFORM ASSEMBLY IS TO BE LOCATED TO GUIDE A WELLHEAD SUPPORT STRUCTURE THROUGH THE BODY OF WATER TO CONTACT THE LEGS OF THE WELLHEAD SUPPORT STRUCTURE WITH SAID UPSTANDING LEG GUIDES.