US3369599A

US3369599A - Subsea deep drilling apparatus and method

Info

Publication number: US3369599A
Application number: US507851A
Authority: US
Inventors: Edward M Evans
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1965-11-15
Filing date: 1965-11-15
Publication date: 1968-02-20
Anticipated expiration: 1985-02-20

Description

E. M. EVANS Feb. 2%, 1955 8 LLING APPARATUS AND METHOD SUBSEA DEEP DR 9 Sheets-Sheet 1 Filed Nov. 15, 1965 lNVENTOR EDWARD M. EVANS ATTORNEY E. M. EVANS Feb. 20, 1968 SUBSEA DEEP DRILLING APPARATUS AND METHOD 9 Sheets-Sheet 2 Filed Nov. 15, 1965 ATTORNEY Felb. 29, 1968 E. M. EVANS SUBSEA DEEP DRILLING APPARATUS AND METHOD 9 Sheets-Sheet 5 Filed Nov. 15, 1965 INVENTOR EDWARD M. EVANS BY ClaM/pamj ATTORNEY Feb. 20, 1968 E. M. EVANS 3,359,599

SUBSEA DEEP DRILLING APPARATUS AND METHOD Filed Nov. 15, 1965 9 Sheets-Sheet 4 FWE' If INVENTOR EDWARD M. EVANS 5y ATTORNEY Feb. 20, 1968 Filed Nov. 15, 1965 E. M. EVANS SUBSEA DEEP DRILLING APPARATUS AND METHOD 9 Sheets-Sheet 5 EDWARD M.EVANS BY O a-A ATTORNEY Feb. 20, 1968 E. M. EVANS 3,369,599

SUBSEA DEEP DRILLING APPARATUS AND METHOD Filed Nov. 15, 1965 9 Sheets-Sheet 6 FIG m" INVENTOR EDWARD M. EVANS ATTORNEY v Feb. 20, 1968 SUBSEA DEEP DRILLING APPARATUS AND METHOD Filed Nov. 15, 1965 9 Sheets-Sheet '7 INVENTOR EDWARD M. EVANS ATTORNEY Feb, 20, 3968 E. M. EVANS SUBSEA DEEP DRILLING APPARATUS AND METHOD 9 Sheets-Sheet 8 Filed Nov. 15, 1965 lNVENTOR EDWARD M. EVANS 5y Mom/5.

ATTORNEY Feb. 1968 EVANS SUBSEA DEEP DRILLING APPARATUS AND METHOD 9 Sheets-Sheet 9 Filed Nov. 15, 1965 INVENTOR EDWARD M. EVANS FIG 5y Ol a ATTORNEY Patented Feb. 20, 1968 3,369,599 SUBSSEA DEEP DRILLING APPARATUS AND METHOD Edward M. Evans, White Plains, N.Y., assignor to Mobil.

Oil fiorporation, a corporation of New York Filed Nov. 15, 1965, Ser. No. 507,851 11 Claims. (Cl. 166-.5)

ABSCT OF THE DISCLOSURE This specification dicloses a method and apparatus for drilling a subaqueous well in deep water from a floating vessel while having the wellhead equipped therefor located Within easy diver depth just below the turbulent surface zone. A buoyant platform from which a conductor pipe is suspended is tethered by cables anchored to a base platform fixed on the marine bottom. A method for locating the buoyant platform below the surface and for guiding a conductor pipe through the buoyant and base platform is described.

be extended to areas where bottom-supported surface 5 structures are neither as economically nor technologically feasible, as in the Gulf of Mexico, where such facilities are rather commonplace. In depths of three hundred feet or more, the statically or dynamically positioned floating drilling structure has become necessary.

One method of drilling a well from a floating structure is to use an open drill pipe and to set the casinghead and BOPs on the bottom so that if the floating structure must be moved to avoid a storm or is accidentally moved due to a malfunction of the positioning system, the well may be easily closed off. Flexible guidelines are used to facilitate re-entry during the drilling operations as well as to re-establish contact after a move. However, problems have been encountered with such an arrangement where a diver cannot work at the mudline depth and the bottomsupported submerged apparatus must be retrieved peri odically. The retrieval entails the use of complicated sealing arrangements and guidelines on the submerged apparatus which are expensive and not always as reliable as desired. Also, the unsupported length of the drill pipe and mud return lines can cause failures of these components during the drilling operations.

Another method, solving some of the problems stated above, is that of using a conductor pipe, extending from the subaqueous borehole to the drilling ship, and having the BOP and the other related apparatus mounted on the deck of the ship beneath the drilling rig as in land-based operations. However, with such an arrangement, there are no provisions for leaving the conductor pipe in place if the borehole must be temporarily abandoned. Also, if the conductor pipe is removed, means must be employed to seal off the partially-drilled well until operations are resumed. Furthermore, such a conductor pipe must also have a certain built-in flexibility to allow for the lateral shifting of the ship as well as sliding couplings to compensate for heave.

As the depth of the water in which drilling is performed becomes greater, particularly in areas off the coast of California where the subaqueous land drops off quite quickly and the subaqueous bottom may be as much as six hundred feet beneath the surface, not far from shore, it is desirable to utilize a rigid conductor pipe to support the drill pipe along its length and to support also the apparatus such as the BOP at a point at which a diver can reach it if this becomes necessary, although below the surface where the apparatus may be left in place if rough Weather makes it necessary for the drilling ship to seek shelter. An intermediate platform submerged beneath the surface of the sea, within easy diver depth, is a compromise for solving these major problems. It could also be used for production when the BOP is removed and a wellhead is installed thereon. In subsea production gathering systems, as envisioned today, a production satellite containing product separation and pumping equipment and a wellhead control system would be centrally situated within a number of subaqueous wells and would be connected to the individual wellheads located beneath the surface. The satellite could be remotely disconnected from the wellheads and brought to the surface for repair. The wellheads could advantageously be mounted on the abovesuggested submerged platforms where the wellheads themselves could be reached by a diver in case of trouble while still sheltered from the turbulent surface conditions.

Accordingly, it is an object of the present invention to provide a buoyant intermediate platform beneath the surface of the sea.

It is another object of this invention to provide a floating drilling platform carrying the BOP and other related apparatus beneath the surface of the sea at a depth at which a diver can reach easily.

It is a further object of this invention to provide a means for guiding a conductor pipe into a subaqueous borehole from a floating surface structure when utilizing an intermediate buoyant platform.

It is a still further object of the invention to provide a substantially rigid drill pipe support and mud return conduit from the subaqueous borehole to the surface Without requiring support from the floating drilling 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.

In the drawings:

FIGURE 1 is an illustrative view of a catamaran drilling vessel incorporating the features of the present invention;

FIGURE 2 is a fragmentary plan view of the deck of the catamaran, with the deck house removed to illustrate the positioning of the rig, and the moon pool between the hulls;

FIGURE 3 is a cross-sectional view through line 33 of FIGURE 2 showing the moon pool with the base platform and a buoyant platform suspended therein;

FIGURE 4 is a perspective view of a cross wire ring assembly designed to guide a conductor pipe from the buoyant platform suspended below the surface of the water through the base platform lying on the subaqueous bottom;

FIGURE 5 is an elevational view, partially in cross section, showing the mounting of the buoyant platform and the cross wire ring assembly on the guide cables in conjunction with the conductor pipe subsequent to lowering the base platform to a point one hundred feet from the subaqueous bottom;

FIGURE 6 is an elevational view, partially in cross section, illustrating the interconnections between the upper end of the conductor pipe, above the buoyant platform, and the drilling ship; and

FIGURES 7 through 16 illustrate, in diagrammatic form, the method of the invention for installing a conductor pipe in a subaqueous borehole and drilling the well therethrongh.

The particular apparatus necessary for drilling a subsea well, in conjunction withthe improved method disclosed herein, comprises a buoyant intermediate platform with a casinghead fixed to the upper face thereof, a weighted base platform, a cross wire ring assembly, and a specially designed conductor pipe. The drilling ship, which may be a barge, a catamaran, or any noncantilevered rig type floating vessel, has a drilling rig extending up from a drilling floor thereon. Located beneath the drilling rig floor, in the moon pool (a vertical well opening through the ship), is the buoyant intermediate platform and the weighted base platform. Equally spaced around the moon pool are a number of power drum reels, mounted on the deck of the ship, each with a cable slidably entrained through the buoyant intermediate platform and connected to the base platform. The buoyant platform is releasably supported in position in the moon pool so that the base platform can be separately lowered into the sea by the cables.

The first step in drilling the well, after positioning the drilling ship, is the lowering of the base platform to within about a hundred feet of the bottom of the sea by means of the cables. At this point the cross wire ring assembly is slidably mounted on the cables, beneath the buoyant intermediate platform which is still supported in the moon pool, where it floats due to its own buoyancy. (Although the cross wire ring assembly has been described as installed after the lowering of the base assembly, there is no reason why it cannot be originally installed in the moon pool between the buoyant intermediate platform and the weighted base platform, if the moon pool is deep enough.) A pair of stops are clamped to each cable just above and below the buoyant platform to restrain its movement with respect to the cables. A lower portion of the conductor pipe, having a toothed, drillable wash shoe on its depending end, is lowered from the drilling deck above, through the casinghead and a central threaded passage in the buoyant platform therebeneath. A shear ring is fixed to the conductor pipe beneath the buoyant platform and the pipe is lowered through a central ring in the cross wire ring assembly until the shear ring on the conductor pipe, above the wash shoe and bumper sub, abuts the central ring and a threaded section of the conductor pipe, above the shear ring, is threaded into the central passage through the buoyant platform; The cables are then simultaneously played out until the base platform rests.

solidly on the bottom and the buoyant intermediate platform floats about one hundred feet beneath the surface.

With the buoyant platform anchored in place. or tethered, by the cables, the lower portion of the conductor pipe is rotated until the short threaded section on the pipe is below the buoyant platform so that the upper portion of the pipe can freely slide therethrough. As new sections are added at the upper end, the lower end of the lower portion of the conductor pipe is guideddown by the cross wire ring assembly and through a central guide passage in the base platformand into the subaqueous bottom. The weight of the pipe breaks the shear ring, and by means of the wash shoe on the lower end thereof, the pipe isforced a few feet into the unconsolidated bottom beneath the base platform. The cross wire ring assembly floats up out of the way to a position just under the buoyant platform after the shear ring breaks. In order to permit the aforementioned operation, the diameters of the various pieces of equipment relative to one another are in the following descending order of size; the shear ring, the central ring of the cross wire ring assembly, the aperture in the base platform, the threaded section of the conductor pipe, and the conductor pipe itself.

A kelly sub and kelly are connected to the upper end of the lower portion of the conductor pipe above the retary on the drilling deck. The lower portion of the conductor pipe is washed down into the bottom until the kelly is seated in the rotary after which the combined rotary drilling and washing drives the lower portion of the conductor pipe down still further. Each time the kelly is drilled and washed down its full length, the lower portion of the conductor pipe is raised up and a new section is added beneath the kelly sub, the bumper sub at the bottom extending to keep the lower of the conductor pipe located in the subaqueous borehole during the first make up (addition of a conductor pipe joint). This process is continued until the TD. (total depth) is reached. The lower portion of the conductor pipe is then pulled up a distance equal to the depth of the buoyant platformand casing hangers and BOPs are fixed thereto at the upper end so that when the conductor pipe is lowered back it is supported in the casinghead on the buoyant platform with thewash shoe just above T.D.

Thelower portion of the conductor pipe is permanentlycemented in the subaqueous borehole and a flexible riser portion of the conductor pipe, having at least one longitudinally slidable joint therein, in extended from the upper end of the conductor pipe, just above the surface of the water, to the drilling deck beneath the rotary table. A mud return line connects the flexible riser portion of the conductor pipe with the mud system on the floating drilling vessel. In accordance with recent practice the flexible riser portion of the conductor pipe can be, if desired,,completely dispensed with and the flexible mud return line can be connected directly to a specially designed casinghead beneath the surface on the buoyant platform. Of course, when using the latter method, the drill pipe to be inserted into the subaqueous borehole would be in open water and unsupported from the moon pool to the casinghead. The well is then drilled through the conductor pipe wash shoe and into the subaqueous earth in the usual manner until the desired depth is reached.

The buoyant platform, as may be seen, not only pro-.

vides a deck upon which drilling apparatus may be mounted, but also supports the upper end of the lower portion of the conductor pipe. When the well is completed, the wellhead may be mounted on the buoyant intermediate platform, which is left in place, or the conductor pipe can be cut off at the base platform and the wellhead mounted there. The buoyant platform is not'prone to being torn free since it is below the usual turbulent zone affected by surface wave action and storms. Due to its depth, the

platform is not a navigational hazard and yet it is easy 1 to reach for repairs, if such are necessary. Surface buoys may be connected by mooring lines to the buoyant'platform to help relocate the well.

FIGURE 1 shows a catamaran drilling vessel, generally designated 10, consisting of a pair of hulls 12 and a connecting deck 14. A heliport 16 covers and overhangsa pilot house and bridge 18 atthe front end of the vessel while a drilling derrick 20 .rises from a deck house 22 at the rear. The roof 24 of the deck house 22 serves as the drilling floor in which the rotary table ismounted and a shed 26 on the roof of the deck house contains the drawworks (not shown) for the derrick 20. An open area between the deck house 22 and the heliport 16 is used for the storage and racking of pipe and on this expanse are two cranes 28, one on each hull 12. On the outer side,

located beneath the derrick 20 and centrally between the hulls 12. Drum reels 36, driven by electric motors 38, are shown located around the moon pool 34. As shown in FIGURE 3, the drum reels 36, within the deck house 22, v

are connected by cables 40, entrained over pairs of rollers 42 which are journalled in cantilevered pedestals 44, to the corners of a base platform 46. The base platform is fixed against movement relative to the vessel by hydraulically controlled locking pins 48 extending through the walls of the moon pool 34 and into a circumferential groove 50 in the side of the platform 46. The base platform is a concrete-filled steel structure having a central passage 52 that is coaxial with a rotary table 54 journalled in the roof 24 of the deck house 22 above. A rather short cylindrical shield 56, surrounding the central passage 52, depends perpendicularly from the lower face.

A buoyant intermediate platform 58 is hung in the moon pool 34 over the base platform 46 by four releasable chains 60 .(two shown) depending from a pair of bridging supports 62 .(one shown), the cables 40 passing slidably through vertical passages 64, near the periphery of the platform 58. The buoyant platform is also rigidly fixed in place by locking pins 66 extending through the walls of the moon pool and into cooperating apertures 68 in the sides of the platform. The buoyant platform consists of a hollow steel shell with a threaded central passage 70 coaxial with the passage in the base platform 46 and the rotary table 54. A conventional drilling casinghead 72 is welded, or otherwise fixed, to the upper face of the buoyant platform 58 over the threaded central passage 70 and a dual purpose air/ water connection 71 is also fixed to the upper face to permit a hose (not shown) to be connected for controlling the buoyancy.

FIGURE 4 is a perspective View of the cross wire ring assembly 73 consisting of four floats 74, each slidably mounted on one of the four guide cables 40, extending between the moon pool 34 and the base platform 46, and a conductor pipe guide ring 76 centrally located between the four slidable floats 74. The slidable floats 74 are connected by peripheral wires 82 while the guide ring 76 is strung between the floats 74 by means of cross wires 78 connecting the guide ring directly to each of the sliding floats 74, and cross wires 80, connected between the guide ring 76 and one of the opposing pairs of peripheral wires 82. Each of the floats 74 is split so that the cross wire ring assembly can be mounted on the cables after the base platform is lowered toward the bottom, without removing the guide cables 40 from the drum reels 36. The split halves of the floats 74 may 'be rigidly connected in any manner well known in the art such as with bolts extending therethrough or by a quick setting epoxy resin.

FIGURE 5 shows the cross wire ring assembly 73 slidably mounted on the cables 40 directly beneath the buoyant platform 58, which is now fixed to the cables 40 by means of restraining clamps 84 on each of the cables 40 above and below the cable passages 64 extending therethrough. An upstanding lower portion of the conductor pipe 86 depends through the rotary table 54, with a pair of table blocks or bushings 88 (shown in FIGURES 3 and 6) removed, through the casinghead 72 in the buoyant platform 58, and into the cross wire ring assembly 73. The threaded section 88 of the conductor pipe portion 86 is threaded into the central passage 70 in the buoyant platform while a shear ring 90, on the conductor pipe portion 86 beneath the threaded portion, abuts the guide ring 76 in the cross wire ring assembly 73. The conductor pipe portion 86 has a bumper sub 92 connected to the lower end thereof with a wash shoe 94 beneath. The wash shoe 94 has a drillable jet orifice 96 therewithin and peripheral teeth 98 depending from the lowermost portion.

When the catamaran vessel 10 is dynamically positioned, with the drilling rig located over the well site in the subaqueous bottom, the base and

buoyant platforms

46 and 58, respectively, are fixed within the moon pool as shown in FIGURE 3. The subsequent sequence of operations is shown in FIGURES 7-15. The weight of the base platform is taken up by the cables 40 and the locking pins are retracted therefrom. The base platform 46 is lowered by the cables 40 to a point above the sea bottom 99 equal 6 to the intended depth of the buoyant platform 58 beneath the surface, in this instance one hundred feet, as shown in FIGURE 7.

In FIGURE 8, the restraining clamps 84 have been fixed to the cables 40 above and below the buoyant platform 58 and the cross wire ring assembly 73 is assembled on the cables 40 beneath the buoyant platform. A first joint of the conductor pipe portion 86, with the bumper sub and wash shoe attached, is lowered through the rotary table 54, with the table bushings removed, and into the threaded passage in the buoyant platform 58. The shear ring is installed on the conductor pipe portion 86 from below the buoyant platform 46 and the conductor pipe portion 86 is rotated to connect its threaded portion with the threaded central passage in the buoyant platform to connect the two securely together. While making this connection, the shear ring 90 on the conductor pipe abuts the guide ring 76 of the cross wire ring assembly 73.

In FIGURE 9 just enough cable has been played out from the drum reels to bring the base platform 46 to rest on the bottom while the conductor pipe portion 86 is made up in the usual manner of being supported by the derrick blocks (not shown) and run through the rotary table 54. The buoyant platform 58 is now moored or tethered at one hundred feet below the surface of the water. As shown in FIGURE 10, the conductor pipe portion 86 is rotated further to lower the threaded portion thereof beneath the threaded central passage 70 of the buoyant platform 58, allowing the conductor pipe portion 86 to slide down freely through the threaded passage with its lower end guided by the cross wire ring assembly 73 driven down by the abutting guide ring 76. Conductor pipe joints are added as the pipe portion 86 is fed downward toward the bottom. The conductor pipe portion 86 is guided into the central passage in the base platform, as show-n in FIGURE 1'1, and weight is placed on the pipe, breaking the shear ring 90. In FIGURE 12 the cross wire ring assembly 73, unencumbered now by the shear ring 90 has floated up out of the way beneath the buoyant platform 58. A kelly sub 112 and kelly 114 are added above the rotary table 54 and the pipe portion 86 is washed in.

The conductor pipe portion 86 (FIGURES 13 and 6) is washed in far enough to bring the kelly 114 into the rotary table 54. The table bushings 88 are replaced, a kelly bushing 116 dropped into the table bushings, and power thereafter applied to the rotary table 54. The conductor pipe portion 86 is driven in by washing and drilling. When adding the first joint after the primary washing operation, the extended bumper sub 92 (FIGURE 5) keeps the lower end of the conductor pipe portion 86 in the borehole (FIG- URE 14). The conductor pipe portion 86 is made up as the borehole progresses downward until T.D. is reached.

After reaching T.D. the conductor pipe portion 86 is pulled up and set back in the derrick for about one hundred twenty feet, which includes the depth of the buoyant platform 58 beneath the surface plus the length of the kelly sub 112 and the kelly 114. As shown in FIGURE 15, the necessary casing hangers (not shown), a conductor flange 115, and the required BOPs 117, with a quick release coupling (not shown) at the upper end, are attached to the upper end of the conductor pipe portion 86 and the pipe portion is then lowered back down with conductor pipe joints being added above the quick release coupling until the casing hanger (not shown) is seated in the casinghead 72. Hoses (not shown) for controlling the BOPs 117 are attached just before the BOPs 117 are lowered into the water. Preferably, remotely controlled means are used to hang permanently the conductor pipe portion 86 in the casinghead 72 attached to the upper face of the buoyant platform 58, but it can also be accomplished by diver assistance. The conductor pipe portion 86 is cemented in the subaqueous borehole, as illustrated in FIGURE 16, and a flexible riser pipe portion of the conductor pipe is extended from the upper end of the conductor pipe portion 86 to a point below the rotary table. A mud return line 108 connects the flexible riser pipe portion 100 with the mud tanks (not shown) on the boat 10. Drilling may now proceed through the conductor pipe.

FIGURE 6 shows the relationship of the elements directly beneath drilling floor 24 during the later drilling operation, after the installation of the conductor pipe portion 86. The flexible riser pipe portion 100 of the con ductor pipe consists of an upper section 102 and an interiorly telescoped lower section 103 forming a sliding coupling therewithin. The upper section 102 connects, by an upper circumferential flange 104, to a mating circumferential flange 106 depending from the drilling deck 24 coaxially with the rotary table 54. The lower end of lower section 103is coupled, or otherwise rigidly sealed, to the upper end of the conductor pipe portion 86. The mud return line 108 is connected to the upper section 102 of the flexible riser pipe portion 100 at a point above the maximum upper position of the lower section 103 within the upper section 102.

The table bushings 88 are reinserted after a first joint of drill pipe 110 is made up with the kelly sub 112 and a kelly 114 and lowered through the flexible riser pipe portion 100 and the rigid conductor pipe portion 86. The kelly bushing 116, on the kelly 114, is fitted into the table bushings 88 and the drilling may proceed in much the same manner as a land-based operation. Since the casinghead and the BOPs can be easily reached by a diver, being only one hundred feet beneath the surface, they can be serviced without too much difficulty.

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 method and apparatus herein disclosed, reference should be had to the claims which follow.

What is claimed is:

1. Apparatus for drilling a subaqueous well, comprismg:

(a) a floating drilling vesseltlocated in a body of water, said vessel having a drilling deck with a drilling rig mounted thereon, the space between said drilling deck and said body of water being open;

(b) a base platform on said subaqueous bottom, a substantially vertical passage extending through said base platform for guiding a conductor pipe into said subaqueous bottom;

(c) at least one flexible guide cable secured to said base platform on said subaqueous bottom; and

(d) an intermediate buoyant platform tethered on said flexible guide cable at a point below said drilling vessel, a guide passage extending vertically through said buoyant platform.

2. Apparatus, for drilling a subaqueous well as recited in claim 1 wherein there is:

(e) a conductor pipe extending from a subaqueous borehole to a point above said surface of said body of water, said conductor pipe extending through said passages in said base platform and said buoyant platform;

3. Apparatus for drilling a subaqueous well as recited in claim 2 wherein said buoyant platform has a casin head mounted thereon in alignment with said guide passage in said buoyant platform, said casinghead being adapted to support said conductor pipe in conjunction with casing hanger means.

4. Apparatus for drilling a subaqueous well as recited in claim 1 wherein there is a guide assembly slidably fixed on said flexible guide cable between said buoyant platform and said base platform whereby a conductor 8 pipe can be guided from the guide passage in said buoyant platform into said passage in said base platform.

5. Apparatus for drilling a subaqueous well as recited in claim 4 wherein said guide assembly is buoyant.

6. Apparatus for drilling a subaqueous Well as recited in claim 1 wherein said guide passage extending through said buoyant platform is threaded to mate with a threaded section on the lower end of a conductor pipe to be lowered therethrough.

7. A conductor pipe for use with the apparatus for drilling a subaqueous well as recited in claim 5 wherein there is a shear, ring fixed to said conductor pipe near the lower end thereof so that said shear ring will bear on the upper face of said guide assembly as said conductor pipe is lowered into said base platform, said shear ring being constructed to break away when said conductor pipe enters said passage in said base platform and the weight of said conductor pipe is upon said shear ring, said guide assembly being slidable onsaid conductorpipe so i that it will float up said conductor pipe after said shear ring breaks away.

8. Aconductor pipe as recited in claim 7 having a threaded section just above said shear ring, said guide passage extending through said buoyant platform having complementary internal threads whereby said conductor pipe can be lowered into said buoyant platform and rotated until the complementary threaded portions coact t0 axially locate said buoyant platform on said conductor pipe to lower said buoyant and base platforms by lowering said conductor pipe and whereby said conductor pipe can be then rotated through said threaded passage until said threaded portion of said pipe is below said buoyant platform and said conductor pipe can be lowered further, down in the water with respect to said buoyant platform.

9. A method of drilling a subaqueous well in a body of water from a surface station with a base platform set on the bottom, an intermediate buoyant platform suspended at diver depth, and a conductor pipe extending upward from a subaqueous borehole through said base platform and said buoyant platform, including the following steps:

(a) entraining said buoyant platform over flexible guide cables, said cables being suspended from said surface station;

(b) securing said flexible guide cables to said base platform beneath said surface station near the surface of said body of water;

(c) lowering said base platform by playing out said flexible guide cables from said surface station until said base platform is a distance from said subaqueous bottom equal to the predetermined distance from said surface that said buoyant platform is to be submerged;

(d) securing said buoyant platform relative to said flexible guide cables; and

(e) lowering saidbase platform to said bottom by playing out said flexible cables from said surface station and thereby submerging said buoyant platformsaid predetermined distance below said surface.

10. A method of drilling a subaqueous well as recited in claim 9 including the following steps:

(f) lowering a well conductor pipe into the subaqueous bottom through said buoyant platform and said base platform;

(g) forming a borehole beneath said conductor pipe in said bottom;

(h) lowering said conductor pipe into said hole until the total depth is reached;

(i)- cementing said conductor pipe in said borehole;

and

(j) fixing said conductor pipe, near the upper end thereof, in said buoyant platform whereby said buoyantv platform will support and locate, saidupper end of said conductor pipe.

11. A method of drilling a subaqueuous well as recited in claim 9 including the following steps:

(k) slidably mounting a guide assembly on said flexible guide cables prior to submerging said buoyant platform;

(1) lowering a well conductor pipe through a passage in said buoyant platform and said guide assembly until a shear ring mounted on said conductor pipe, near the lower end thereof, abuts said guide assembly;

(m) lowering said conductor pipe and abutted guide assembly to guide said conductor pipe into said base platform; and

(n) weighting said conductor pipe until said shear ring breaks away and said conductor pipe drops unen- 15 cumbered into said subaqueous bottom.

References Cited UNITED STATES PATENTS Lang 175-8 Tucker 175-8 Stratton 175-7 X Rhodes et a1 175-7 Postlewaite 175-7 'Frick 175-7 Wepsala 61-465 Travers et a1. 166-05 Fisher 175-7 McClintock 166-05 X CHARLES E. OCONNELL, Primary Examiner.

RICHARD E. FAVREAU, Assistant Examiner.