US3631932A

US3631932A - Offshore drilling apparatus and method

Info

Publication number: US3631932A
Application number: US756897A
Authority: US
Inventors: Leonard A Lindelof
Original assignee: EJ Longyear Co
Current assignee: EJ Longyear Co
Priority date: 1968-09-03
Filing date: 1968-09-03
Publication date: 1972-01-04
Anticipated expiration: 1989-01-04

Abstract

Method and apparatus for taking core from a submerged earth formation that including drilling a casing into an earth formation a number of feet. A flotation tank is provided on the upper end of the casing while a cushion drum assembly is mounted on the lower end of the casing to control the rate of descent of the rotating casing into the formation; and such an assembly or weight on the lower end of the casing is provided to maintain the major portion of the casing in tension. After the casing is extended into the earth formation, a drill unit is supportedly mounted on the casing, a drill stem extended down through the casing and the drill stem drilled into the formation for continuing the core-taking operation.

Description

United States Patent Primary Examiner-Marvin A. Champion Assistant Examiner-Richard E. Favreau Attorney-Bugger, Peterson, Johnson & Westman ABSTRACT: Method and apparatus for taking core from a submerged earth fonnation that including drilling a casing into an earth fonnation a number of feet. A flotation tank is provided on the upper end of the casing while a cushion drum am sembly is mounted on the lower end of the casing to control the rate of descent of the rotating casing into the formation; and such an assembly or weight on the lower end of the casing is provided to maintain the major portion of the casing in tension. After the casing is extended into the earth formation, a drill unit is supportedly mounted on the casing, a drill stem extended down through the casing and the drill stem drilled into the formation for continuing the core-taking operation.

4? HI T /5'c PATENIED JMI 4:972 3,631. 932

SHEET 3 [IF 4 FIG! 4 OFFSHORE DRILLING APPARATUS AND METHOD BACKGROUND OF THE INVENTION The invention relates to offshore drilling operations, particularly to core drilling and the taking of samples of an earth formation.

Travers et al. U.S. Pat. No. 3,196,958, discloses using negative buoyance in a float that is attached to the upper end of a drill pipe while drilling a hole in an underwater earth formation; and after the hole is drilled, a casing extended into the hole and a foundation provided at the bottom to cement the casing in place, the float is evacuated to place the casing under tension. However, in using prior art apparatus there is the problem of retaining the casing substantially vertical while it is being lowered prior to any underwater drilling; and after the casing is lowered, to control the initial rate of penetration of the underwater earth formation, especially where the bottom is mucky. Also, in core-drilling operations, many times the recovery of the first few inches or feet of core of an underwater earth formation are considered to be of prime importance. One example is for ascertaining if valuable minerals have been deposited on the ocean floor. However, with prior an apparatus and methods, frequently the first few inches of core are lost, or only partially recovered, or are not recovered in a manner that accurately reflects the layers of the earth formation. This is especially true where the bottom is soft or mucky. In order to overcome problems of the above-mentioned nature, this invention has been made.

SUMMARY OF THE INVENTION Underwater drilling apparatus and method of using, including a casing having float means attached to the upper end portion and a weight mounted adjacent but spaced from the casing lower terminal end that-is used during the initial coring operation and thereafter has a drill stem extended therethrough for further core drilling. In mucky bottoms, a cushion drum assembly that includes said weight is provided to control the rate of descent of the casing.

One of the objects of the invention is to provide new and novel casing structure that is maintained in tension for taking an initial footage of core from an underwater earth formation and thereafter serve as the structure for supporting a drill unit for further coring. Another object of this invention is to provide new and novel apparatus for controlling the rate of initial penetration of an underwater earth fonnation during a drilling operation. A

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view illustrating a vessel, and a casing having a flotation tank and drum cushion assembly thereon after the casing has been lowered so that said assembly rests on a submerged earth formation, portions of casing being broken away;

FIG. 2 is a vertical cross-sectional view of the lower end portion of the structure illustrated in FIG. 1 prior to the initiation of the core-taking step, a vertically inten'nediate part being broken away;

FIG. 3 is a crosssectional view generally taken along the line and in the direction of the arrows 33 of FIG. 2;

FIG. 4 is a vertical cross-sectional view of the lower end of the casing and a retractable wire line core or sample barrel latched therein;

FIG. 5' is a perspective view, part in cross section, to show the flotation tank mounted on the casing;

FIG. 6 is a perspective view showing the drill unit platform mounted on the casing and the drill unit mounted on the platform for operating the drill stem extending through the casing;

FIG. 7 is a view similar to that of FIG. 2 other than the weights in the drum and casing have been operated to the lowermost position of said weights relative the drum; and

FIG. 8 is a horizontal cross-sectional view of the lower end portion of the casing of FIG. 6 to indicate that a core barrel inner tube assembly is located within the drill stem.

Referring now to the drawings, in FIG. 1 there is illustrated a drilling vessel, barge or platform 10 of a suitable floating type that is floating on the surface of a body of water 11. The vessel is substantially fixed over a preselected floating location by suitable vessel-positioning means (not shown) or by being anchored to the ocean floor 12. The vessel includes a derrick and drill unit 13 for initially lowering the sections of the casing 15 and cushion drum, generally designated 16, supporting the various sections of the casing as the casing is being assembled, and initially rotating the casing to drill the lower end of the casing into the ocean floor as will become more apparent hereinafter.

The casing, when in an assembled condition, has an enlarged diameter lower end portion 15:; that may extend, for example, 200 feet. The lower end of the casing portion is provided with a diamond drill bit 150 that is mounted thereon to rotate therewith. Advantageously, the upper end portion of the casing 15b may be of a smaller outside diameter than portion 150, portion 15b extending above. the level of the water ll. Mounted on the casing portion 15a in a selected axial position, for example 22 feet above the lower edge of the drill bit 15c is a bearing support member 18 (see FIG. 2). An annular weight 19 has a casing portion rotatably extended therethrough and is mounted on the bearing member 18. The upper end portion of weight 19 is of reduced diameter to provide a shoulder 19a to support the flange portion 210 of the drum 21 of the cushion drum assembly 16. The enlarged diametric portion of the weight 19 is located within the annular main body 21b of the drum 21 and forms a sliding fit with the inner peripheral wall thereof. A seal 22 is provided in a groove on the lower end portion of the weight to provide a sealing fit with the inner peripheral wall of the drum. The drum wall 21b is provided with one or more vent apertures 23 at an elevation that is slightly below the lower surface of the weight 19.

Secured to the lower edge of the drum wall 2lbis an annular shield 25, theshield having a central aperture 26 that is defined by the lower edge 25a of the shield. The shield has an outer terminal edge 25b, the radius of curvature of edge 25b being substantially greater than that of the drum wall 21b while the radius of curvature of aperture 26 being substantially less than that of the inner peripheral radius of the drum wall. When the drum is in a vertical upright condition such as illustrated in FIG. 2, the shield in vertical cross section curves relatively sharply upwardly and slightly outwardly, thence curves predominantly outwardly and slightly upwardly; and adjacent to terminal edge 25b, curves slightly downwardly and outwardly. As a result, the edge 25b is located at a lower elevation than the edge 25a while the drum wall 21!: is secured to the shield at a higher elevau'on than edge 25b. A plurality of reinforcing web plates 27 are welded to the shield surface opposite the drum wall 21b, the web plates extending from adjacent the aperture 26 to adjacent the terminal edge 25b. Advantageously, one or more weights 28 are located in surrounding relationship to the drum wall 21b and supported by the shield. Also one or more weights 24 are in surrounding relationship to the casing and are vertically stacked on the weight 19; the outer diameter of the additional weights 24 being less than the inner diameter of the flange 21a of the drum. The casing is rotatably relative to weights 24.

Mounted within the interior of the drum at a slightly higher elevation than the shield is an annular support member 30, said support member in turn mounting an annular member 3I that mounts a seal member 32 to retain the casing in concentric relationship relative the drum wall and at the same time permit the casing to freely rotate and move vertically relative the drum wall 21b. Additionally members 30-32 prevent water thereabove that is in the drum from exhausting through aperture 26. The interior of the drum vertically between the support member 30 and the lower surface of the weight 19 in its elevated condition relative the drum wali such as illustrated in FIG. 2 is free of structure other than for the portion of the casing that extends vertically therebetween At an elevation just above the support member 30 or to open through the support member, a relief valve 33 is mounted on the drum wall exterior of the casing to open into the interior of the drum. The relief valve has an outlet that opens to the flow control valve 34 to control the rate of exhaust of water from the drum as will be more fully set forth hereinafter.

The upper part of the casing portion 15b extends through a compartmentalized annular tank 40 (see FIG. Hearing support members 41 retain the tank in a fixed position relative the casing but at the same time permit the casing to rotate relative the tank. The tank is located at a substantial elevation beneath the surface of the water, for example 20-40 feet. A plurality of lines 49 open into the tank, one set of said lines extending back to the vessel for permitting the pumping of compressed air into the various compartments tank while the other set of lines is provided with a suitable control valve for controlling the inlet and exhaust of water from the compartments of the tanks. Although not shown, the water lines extend adjacent the bottom ofthe respective compartment.

Once the lower end of the casing has been drilled into the earth formation as will be described hereinafter, a platform 42 is mounted onto the upper end of the casing 15, the platform in part being supported by an annular member 43 that is secured to the casing adjacent the upper edge thereof and the remainder by an annular member 44 that is secured to the easing intermediate the level of the water and member 43. A plurality of braces 45 at their one ends are attached to member 44 and the opposite ends of the platform. Mounted on the platform 42 to be supported thereby is a conventional drilling unit, generally designated at 46. Appropriate lines (not shown) for conducting fluid to the drill unit and for controlling the drill unit extend to the vessel. Further, a catwalk 47 and guy lines 48 may be extending between the platform and the vessel although weight of the drill unit and platform 42 are solely supported by the casing 15.

Using the apparatus of this invention, the vessel is moved to a location where the core is to be taken advantageously underwater television camera being utilized to aid in the selection of an appropriate spot for drilling. If from the viewing of the television camera it appears that the ocean floor is of a mucky consistency, or it is uncertain as to whether or not it is of a mucky consistency, then the lower end of the casing portion a is extended through the weights and into the drum, and a bit 15c mounted on the lower end of the casing so that the parts are located in a relative position such as illustrated in FIG. 2 and the bearing 18 supports the weights and drum assembly when the casing portion is upright. Further, based upon the depth of the ocean floor at the point of drilling, the desired rate of penetration of the formation 12 by the drill bit 150, the weights and the flotation tank being used, the vale 33 is preset to open at a predetennined pressure and the flow control valve 34 is set to limit the rate of exhaust of liquid therethrough. Now, the lower end of the casing with the cushion drum assembly mounted thereon is lowered into the water. During the lowering process, air vents through aper tures 23 and the interior of the drum fills with water. Additional sections of the casing are connected to one another until the time that the shield 27 bears against the ocean floor.

A flotation tank 40 is mounted on a section of the casing to be located at a selected distance below the level of the body of water, for example -40 feet and air is pumped in or water is allowed to enter the tank to exert the desired degree of upward force on the casing such that the neutral point between the load condition of the casing and the tension force that is exerted by tank 40 is located, for example, within range of approximately 50 to 150 feet above the surface of the ocean floor, i.e. within the length of section 15a.

Assuming that the ocean floor is a mucky bottom, the edge, a penetrates the ocean floor and the shield continues to sink until part or substantially all of the surface thereof abuts against the bottom. To be noted is that during the initial period of sinking, the part of the bottom circumscribed by edge 25a protrudes through the aperture 26 upwardly to be at a location beneath the core bit 150. However, to be noted is that the apparatus functions properly even only if a part of the shield abuts against the bottom, for example, a sloping bottom.

Either prior to, or after the casing has been lowered so that the cushion drum assembly bears against the submerged earth formation, a retractable wire line core barrel inner'tube assembly or wire line sampling barrel assembly, generally designated 60, is lowered in the casing until the latches 61 seat in the latch seat a in the lower part (core barrel outer tube) 70 of the casing, the suspension ring 62 seats on the landing ring 70b mounted in the casing, and the inner tube 68 extends to a lower elevation than the casing bit. A bearing housing assembly 63 connects the inner tube to the spindle 64 which in turn is connected to the latch body 65. A spring 66 on the spindle resiliently urges the bearing housing to move the inner tube away from the latch body, but permits the inner tube retracting into the casing in the event the inner tube engages a relatively hard earth formation. The core barrel outer tube 70 includes the drill bit 15c.

Preferably, the inner tube extends a few inches downwardly below bit 15c, and at a time prior to lowering the casing relative the drum to initially penetrate the earth formation with the bit 15c, the lower terminal edge of the inner tube 68 is located at a higher elevation than aperture 26. As a result, the drilling fluid flowing between the casing and the inner tube can flow radially outwardly across the drill bit fact whereby such fluid flow does not tend to wash away any of the soft bottom directly beneath the inner tube.

Now upon proper adjustment of the downward force exerted on the casing (controlling the degree of buoyancy exerted by tank 40 by, for example, exhausting water from the tank 40) the gravitational force exerted by the casing and the

weights

19, 24, 28 in a downward direction against the water within the drum increases to a pressure to open valve 33 and water starts to flow out of the drum through

valves

33 and 34. Valve 33 had been previously preset to open at a higher pressure than the pressure of the water at the elevation of the surface of formation 12. At the same time a drill unit which is supported from the vessel and which has been connected to the upper end of the casing is operated to rotate the casing. As the casing rotates and the casing-weight combination moves downwardly within the drum wall the core-taking cycle is begun. The drilling fluid passing through the casing can come up along the outside of the casing, flow through aperture 26 and thence through channel 83 that opens through member 30 and the adjacent part of the drum to permit water below members 30-32 to exhaust to outside of the drum.

After the casing is moved downwardly a sufficient distance that the weight 19 rests against the support member 30, the drill unit presently mounted on the upper end of the casing is stopped and the core barrel inner tube assembly 60 is retracted with conventional wire line overshot equipment. At this time, the casing extends a sufficient distance into the earth formation to anchor" the lower end of the casing.

After the core barrel inner tube assembly 60 has been retracted, and the drill unit connected to the casing disattached, the platform, including members 43-45, and the drill unit 46 are mounted on the upper end of the casing such as illustrated in FIG. 6. Now a drill stem 59 having a core barrel outer tube 59a on the lower end thereof is lowered through the casing to extend from the drill unit 46 to bit 15c. A conventional wire line inner tube assembly 5% is lowered in the drill stem 59 until it latches in place in the core barrel outer tube 59a and thence the coring operation is continued. The assembly 59b may be of the same construction as that of assembly 60, except of a smaller diameter and therefore is not fully illustrated. It is to be noted that at this time the physical weight of the drill unit 46 is supported by the casing and therefore movement of the vessel 10 does not affect the drilling operation. Now the drill stem is rotated to drill further into the earth formation and core recovered through the use of assembly 59b.

The tanks and weights retain the casing in tension to prevent buckling and also retain the casing in a vertical direction when the casing is being lowered..The weight of the weights in part depends upon the type of bottom (mucky or rocky bottom) and the depth between the surface and the bottom. If the depth is, for example, 600 feet of water, then usually the weights would total 2,000-4,000 pounds. Under such conditions, the flotation tanks would advantageously be of a size to provide 2,000 pounds flotation.

As a further example of the invention but not as a limitation thereof, if the drilling is to be carried out in a mucky bottom, then the diameter of the drum wall is advantageously 6 feet while the outer diameter of the lower portion a of the casing is 5%; inches; while if the drilling is to be carried out on a firmer bottom, then using the same diameter casing, the drum wall may be of a diameter of 18 inches.

If it is known the bottom is a solid type, for example, of rock formation, then the drum and shield need not be used, but rather the casing drilled into the rock formation until the weight 19 bears against the rock formation. Then the drill unit 46 is mounted on the casing and drill stem 59 extended into the casing.

What is claimed is:

1. In apparatus for drilling into an underwater earth formation, an elongated casing having an upper end portion, a lower end portion and a terminal lower end, weight means mounted on the lower end portion of the casing a preselected distance from said terminal lower end, said weight means including a weight member in relative rotatable surrounding relationship to the casing and bearing means mounted on the casing for mounting the weight means on the casing and permitting rotation of the casing relative the weight member, float means mounted on the casing upper end portion a substantial distance beneath the surface of the water for supporting at least part of the weight of the casing and cooperating with the weight means to retain a major portion of the length of the casing in tension, a platform mounted on said casing at an elevation above the float means and supported by the casing, and a drill unit mounted on said platform.

2. In apparatus for drilling into an underwater earth formation, an elongated casing having an upper end portion, a lower end portion and a terminal lower end, weight means mounted on the lower end portion of the casing a preselected distance from said terminal lower end, said weight means including a weight member in relative rotatable surrounding relationship to the casing and bearing means mounted on the casing for mounting the weight means on the casing and permitting rotation of the casing relative the weight member, float means mounted on the casing upper end portion for supporting at least part of the weight of the casing and cooperating with the weight means to retain a major portion of the length of the casing in tension, said casing lower end portion including a core barrel outer tube having a latch seat, and a retractable wire line core barrel inner tube mounted in said core barrel outer tube.

3. The apparatus of claim 2, further characterized in that said core barrel outer tube includes a drill bit.

4. The apparatus of claim 2, further characterized in that there is provided a drum having an upper end portion and a lower end portion, said drum upper and lower end portions respectively having a top opening and a bottom opening that are of larger diameters than the casing, said drum upper end portion and weight means having cooperating means for suspendingly supporting the drum from the weight means to extend to a substantially lower elevation than the weight means while permitting the weight means to move downwardly in the drum, said weight means having means for forming a sliding fluid seal with the drum.

5. The apparatus of claim 4 further characterized in that valve means is attached to the lower end portion of the drum to open to the interior thereof for providing a liquid discharge passageway to permit the escape of liquid from the interior of the drum only after the liquid pressure in the drum exceeds a preselected level.

6. The apparatus of claim 5 further characterized in that a flow control valve is connected to the valve means to control the rate of discharge of liquid through the valve means and that the drum includes means for venting air prior to any substantial downward movement of the weight means in the drum.

7. The apparatus of claim 6 further characterized in that said vent means comprises a drum wall portion having a vent aperture that is at a slightly lower elevation than the seal means when the drum is suspendingly supported from the weight means.

8. The apparatus of claim 6 further characterized in that there is provided a shield that is attached to the drum lower end portion, said shield having an opening of a size for the casing to pass therethrough.

9. The apparatus of claim 8 further characterized in that said shield has an outer peripheral edge bounding a substantially larger area than the cross-sectional area of the drum transverse to the direction of elongation of the casing, and that the shield is of a shape to slope downwardly and inwardly from its outer peripheral edge in a direction toward said shield opening.

10. The apparatus of claim 8 further characterized in that a platform is mounted on said casing at an elevation above the float means and is supported by the casing and that a drill unit is mounted on the platform.

11. The apparatus of claim 8 further characterized in that there is provided means in the drum for forming a rotary fluid seal between the drum and the casing at an elevation between the shield and the opening of the valve means to the drum.

12. Apparatus for taking core samples from an underwater earth formation, comprising an elongated casing having an upper end portion and a lower end portion, said lower end portion including a drill bit, at least one weight, bearing means mounted on the lower end portion a preselected distance from the drill bit for mountingly retaining said weight on the casing substantially spaced from the drill bit, an elongated drum of a greater length than said preselected distance extending in surrounding relationship to said weight, said drum and weight having cooperating means for suspendingly supporting the drum from the weight while permitting the weight to move downwardly in the drum, means on the weight for forming a slidable fluid seal with the drum, and means opening to the interior of the drum for controlling the rate of exhaust of water from the drum as the weight moves downwardly in the drum.

13. The apparatus of claim 12 further characterized in that the last-mentioned means includes a valve set to open at a predetermined pressure of liquid in the drum, and that an annular shield is mounted on the lower end of the drum for engaging an earth formation, said shield having a central aperture for the casing to pass through, said aperture being at a lower elevation than the drill bit when the weight suspendingly supports the drum.

14. Apparatus for drilling into an underwater earth formation comprising a casing having an upper end portion, a lower end portion and a drill bit lower terminal end portion, float means attached to the casing upper end portion a substantial distance beneath the surface of the water for supporting a substantial part of the weight of the casing, means for rotating the casing and first means attached to the lower end portion of the casing for engaging the underwater earth formation and controlling the rate of descent of the casing as it is being rotated.

15. The apparatus of claim 14 further characterized in that said first means comprises an elongated drum having an upper end portion and a lower end portion, second means opening into the interior of the lower end portion of the drum for discharging liquid from the drum at a controlled rate, and a weight attached to the casing a preselected distance above the drill bit to move with the casing and being movable downwardly in the drum from a first position to a lower second position to force water out of the drum through the second means.

16. The apparatus of claim further characterized in that said weight has means to form a slidable fluid seal with the drum, that said drum has vent means for exhausting air from the drum, said vent means being at a higher elevation than the above-mentioned sealing means between the drum and the weight after the weight has moved a short distance downwardly from its first position toward its second position, that the second means includes valve means opening into the drum that opens at a higher pressure than the pressure of the liquid in the drum when the drum is closely adjacent the earth formation, and that the first means includes means at a lower elevation than the opening of the valve means to the drum for forming a fluid seal between the drum and the casing while permitting the casing to move relative the drum.

17. A method of drilling an earth fonnation underwater wherein an elongated casing having an upper end portion, a lower end portion and a lower terminal end is used, said method comprising the steps of attachably mounting a weight member on the lower end of the casing a preselected distance from the lower terminal end of the casing, lowering the casing in water until the lower end of the casing is adjacent the earth fonnation, attaching a flotation tank to the casing upper end portion to retain at least a major portion of the casing in tension, further lowering the casing until the lower end of the easing abuts against the earth formation, drilling the casing to a depth in the earth formation that the weight member is located substantially more closely adjacent the earth formation than when the casing lower end abutted against said formation, then mounting a drill unit platform on the casing for being supported thereby and then utilizing the drill unit to lower a drill stem through the casing and operate the drill stem to penetrate the earth formation to a greater depth than the casrng.

18. The method of claim 17 further characterized in that the drilling with a casing is continued until the weight member abuts against the earth formation.

19. The method of claim 18 further characterized in that the step of attaching a weight member also includes mounting a drum to at least in part surround said weight member and form a cylinder to effectively provide a piston cylinder combination and presetting a flow control valve to open to permit water to exhaust out of said combination at a controlled rate of flow after the water pressure in the casing has exceeded a preselected level to control the rate of penetration of the casing into the earth formation.

20. In a method of'drilling into an earth formation below the surface of a body of water wherein an elongated casing having a lower end and an upper end portion is used, the steps of attaching a cushion drum assembly to surround a substantial length of the lower end portion of the casing including mounting a weight on the casing a preselected distance above the lower end of the casing and suspendingly supporting a drum on the weight, setting a valve to exhaust water from the interior of the drum at a pressure higher than the pressure of water in the interior of the drum at the time the drum has been lowered to the earth formation, lowering the casing, applying a buoyant force to the upper end portion of the casing through a submerged float to retain a major portion of the length of the casing between the float and the weight in tension, and imparting a rotary motion to the casing when the drum device has engaged the earth formation.

21. The method of claim 20 further characterized in that the rate of exhaust of the water from the drum is controlled to thereby control the rate of descent of the casing as it drills into the earth formation.

22. The method of claim 21 further characterized in mounting a drill unit on the upper end of the casing to be supported thereby after the casing has been drilled a selected depth into the earth formation, and operating a drill stem through said casing to drill a deeper hole in the earth formation, and collecting core samples through the use of the drill stem.

23. The apparatus of claim 22 further characterized in that there is provided a drill steam extendedthrough the casing and operated by the drill unit for penetrating the earth formation to a greater depth than the casing.

24. Apparatus for drilling into an underwater earth formation comprising a casing having an upper end portion, a lower end portion and a drill bit lower terminal end portion, float means attached to the casing upper end portion for supporting a substantial part of the weight of the casing, means for rotating the casing and first means attached to the lower end portion of the casing for engaging the underwater earth formation, said first means including weight means mounted on the lower end portion of the casing a preselected distance from said lower terminal end portion to cooperate with the float means to retain a major portion of the length of the casing in tension, and a drum having an upper end portion and a lower end portion engageable with the underwater earth formation, said drum upper and lower end portions respectively having a top opening and a bottom opening that are of larger diameters than the casing, said drum upper end portion and weight means having cooperating means for suspendingly supporting the drum from the weight means to extend to a substantially lower elevation than the weight means while permitting the weight means to move downwardly in the drum, said weight means having means for forming a close sliding fit with the drum.

25. Apparatus for drilling into an underwater earth formation comprising a casing having an upper end portion, a lower end portion and an earth-penetrating lower terminal end portion, first means attached to the casing upper end portion for supporting a substantial part of the weight of the casing, second means attached to the casing for moving the casing to penetrate the underwater earth formation and third means attached to the lower end portion of the casing for engaging the underwater earth formation to control the rate of penetration of the underwater earth formation by the casing as the casing is moved by the second means.

26. The apparatus of claim 25 further characterized in that the first means comprises float means attached to the casing, and that the second means is attached to the casing above the float means.

i i I t

Claims

16. The apparatus of claim 15 further characterized in that said weight has means to form a slidable fluid seal with the drum, that said drum has vent means for exhausting air from the drum, said vent means being at a higher elevation than the above-mentioned sealing means between the drum and the weight after the weight has moved a short distance downwardly from its first position toward its second position, that the second means includes valve means opening into the drum that opens at a higher pressure than the pressure of the liquid in the drum when the drum is closely adjacent the earth formation, and that the first means includes means at a lower elevation than the opening of the valve means to the drum for forming a fluid seal between the drum and the casing while permitting the casing to move relative the drum.

17. A method of drilling an earth formation underwater wherein an elongated casing having an upper end portion, a loWer end portion and a lower terminal end is used, said method comprising the steps of attachably mounting a weight member on the lower end of the casing a preselected distance from the lower terminal end of the casing, lowering the casing in water until the lower end of the casing is adjacent the earth formation, attaching a flotation tank to the casing upper end portion to retain at least a major portion of the casing in tension, further lowering the casing until the lower end of the casing abuts against the earth formation, drilling the casing to a depth in the earth formation that the weight member is located substantially more closely adjacent the earth formation than when the casing lower end abutted against said formation, then mounting a drill unit platform on the casing for being supported thereby and then utilizing the drill unit to lower a drill stem through the casing and operate the drill stem to penetrate the earth formation to a greater depth than the casing.

20. In a method of drilling into an earth formation below the surface of a body of water wherein an elongated casing having a lower end and an upper end portion is used, the steps of attaching a cushion drum assembly to surround a substantial length of the lower end portion of the casing including mounting a weight on the casing a preselected distance above the lower end of the casing and suspendingly supporting a drum on the weight, setting a valve to exhaust water from the interior of the drum at a pressure higher than the pressure of water in the interior of the drum at the time the drum has been lowered to the earth formation, lowering the casing, applying a buoyant force to the upper end portion of the casing through a submerged float to retain a major portion of the length of the casing between the float and the weight in tension, and imparting a rotary motion to the casing when the drum device has engaged the earth formation.

23. The apparatus of claim 22 further characterized in that there is provided a drill steam extended through the casing and operated by the drill unit for penetrating the earth formation to a greater depth than the casing.