US3705623A

US3705623A - Offshore well equipment with pedestal conductor

Info

Publication number: US3705623A
Application number: US151748A
Authority: US
Inventors: Wouter H Van Eek; Bob E Busking; Adrianus W Van Gils
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1970-06-17
Filing date: 1971-06-10
Publication date: 1972-12-12
Anticipated expiration: 1989-12-12
Also published as: GB1245740A; FR2095313A1; ES392303A1; CA937161A; FR2095313B1; JPS549122B1

Abstract

Apparatus and method for drilling and completing subsea wells using a wellhead mounted on a pedestal conductor supported above a conductor pipe string by a buoyant member. The conductor string supports a plurality of casings which are cemented over their entire lengths. A single small-diameter casing is suspended from the wellhead and extends over the length of the pedestal conductor.

Description

United States Patent van Eek et al.

[451 Dec. 12, 1972 OFFSHORE WELL EQUIPMENT WITH PEDESTAL CONDUCTOR Inventors: Wouter H. van Eek; Bob E. Busking; Adrianus W. van Gils, all of The Hague, Netherlands Assignee: Shell Oil Company, New York, N.Y.

Filed: June 10, 1971 Appl. No.: 151,748

Foreign Application Priority Data June 17', 1970 Great Britain ..29,424/70 US. Cl ..l66/.6, 166/49 Int. Cl. ..E2lb 7/12, E2lb 43/01 Field of Search ..l66/3l5, .6; 175/6, 7, 8, 9, 175/10, 171

References Cited UNITED STATES PATENTS 3,196,958 7/1965 Travers et al.. 3,340,928 9/1967 Brown ..175/7 X Primary Examiner-Richard E. Moore Attorney-Harold L. Denkler and Rand N. Shulman ABSTRACT Apparatus and method for drilling and completing subsea wells using a wellhead mounted on a pedestal conductor supported above a conductor pipe string by a buoyant member. The conductor string supports a plurality of casings which'are cemented over their en- -tire lengths. A single small-diameter casing is suspended from the wellhead and extends over the length of the pedestal conductor.

10 Claims, 10 Drawing Figures PATENTEDUEC 12 I972 3.705.623

SHEET 1 OF 6 IN VE N TORS PATENTED DEC 12 m2 SHEET 3 OF 6 W H Van Eek B. E Busk/ng A. W Van G/Is INVENTORS IN VE N TORS B. E. Busking A. W Van Gils W H. Van Eek PATENTED DEC 12 I972 sum a nr 6,

PATENTED DEC 12 m2 SHEET 6 OF 6 W. H. Van Eek B. E. Busking A. W Van Gils IN VE N TORS OFFSHORE WELL EQUIPMENT WITH PEDESTAL CONDUCTOR BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to equipment for a well penetrating a formation located below a body of water, and more particularly to well equipment comprising a wellhead mounted on a pedestal conductor.

2. Description of the Prior Art Several types of equipment for drilling underwater wells are already known. Use can be made for instance of a marine structure supported on the bottom of a body of water and extending with the upper part thereof above the water level. The drilling installation is located on this upper part of the marine structure, and a well is drilled via'a conductor string extending from the drilling installation into the formation to be drilled. Wellhead equipment typical for land operations is applied above the level of the water. 1

In another manner, wells are drilled below a body of water by special equipment comprising wellheads suitable to be placed on the bottom of the body of water. The necessary operational techniques to be carried out at the wellhead may be performed by divers or by remotely controlled manipulators. This technique is suitable for application in water which is either too deep for placement of permanent marine structures of wherein structures above sea level are not allowed for navigational reasons.

However, in still deeper water, the placement of wellhead equipment at or near the sea bottom will create problems if repairs toor substitution of such equipment cannot be carried out or can only be effected by divers. To solve these problems, it has been proposed to place the wellhead on a pedestal conductor, which extends from a level at or below the sea bottom to a level at which divers can easily operate.

Such a pedestal conductor is kept in an upright position by guy-lines and/or by a buoyancy member connected to the top of the conductor and/or by buoyancy members distributed along the length of the conductor.

SUMMARY OF THE INVENTION The present invention relates to equipment for underwater wells which are drilled and completed in subsea formations lying below very deep water, i.e., waters in which divers cannot actually or economically operate at or near the bottom thereof. In the new equipment, the drilling operations take place via the pedestal conductor, which is kept in an upright position by at least one buoyancy member connected to the upper part thereof. The coupling and uncoupling of the various parts of the wellhead during the drilling operation, as well as the installation of the various tubular members in the well, may take place either by remote control or by robot-like equipment. It is also possible, since the wellhead can be located at diving depth, to carry out such operations by means of divers.

One object of the present invention is to provide equipment for a well penetrating a formation located below a body of water, said equipment comprising a pedestal conductor carrying a wellhead and suspended by at least one buoyancy member, by means of which equipment the well can be operated in a very safe manner.

A further object of the present invention is to provide equipment for a subsea well comprising a pedestal conductor which is of such a construction that it can be very easily and quickly installed, thus reducing the possibility of failureduring installation thereof.

A still further object of the invention is to provide equipment for an underwater well comprising a buoyancy member from which tubular means are suspended, the tubular means being of minimum weight without endangering the safety of the operations carried out in the well.

Another object of the present invention is to provide equipment for an underwater well comprising a buoyancy member mounted on a pedestal conductor, wherein the volume of the buoyancy member is as small as possible.

According to the invention, equipment for a well penetrating a formation located below a body of water comprises a conductor string arranged for at least the greater part thereof in the well and cemented to the formation, said conductor string being provided with coupling means at its upper end; at least one string of tubular means arranged in part in the conductor string and suspended in the conductor string by means arranged near the upper end of the conductor string; a pedestal conductor provided at the lower end thereof with coupling means sealingly coupled to the coupling means of the conductor string; at least one buoyancy member connected to the pedestal conductor near the upper end thereof; a wellhead mounted on the upper end of the pedestal conductor and provided with means from which at least one string of tubing is suspended, which string of tubing at the lower end thereof communicates with the upper end of the string of tubular means arranged in the conductor string.

Coupling means may be provided between the lower end of the string of tubing and the upper end of the string of tubular means.

The coupling means arranged between the lower end of the pedestal conductor and the upper end of the conductor string may include blowout preventer equipment.

The lower end of the string of tubing may be connected to the lower end of the pedestal conductor.

The coupling means arranged between the conductor string and the pedestal conductor may be of the automatic type which performs the coupling action upon relatively longitudinal movement of the coupling elements.

The pedestal conductor may have a single string of tubing suspended therein, whereas the conductor string may have suspended therein several strings of tubular means. The string of tubing suspended in the pedestal conductor communicates with the string of tubular means having the smallest diameter and is capable of withstanding the same pressures as this string of tubular means.

The annular spaces around substantially the entire lengths of the strings of tubular means suspended from the conductor string are preferably filled with solid material, such as hardened cement.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a side view partially in cross-section of a well installation according to the invention.

FIG. 2 shows a longitudinal section of part of the well installation according to FIG. 1 on a scale larger than that of FIG. 1.

FIG. 3 shows a longitudinal section over the conductor string during placement thereof in the formation.

FIG. 4 shows a longitudinal section over the conductor string when cemented in position in the well.

FIG. 5 shows a side view of the well installation during placement of the pedestal conductor.

FIG. 6 shows the well installation in longitudinal section during further deepening of the borehole after th pedestal conductor has been placed.

FIG. 7 shows in longitudinal section the well equipment arrangement after a first casing has been placed in the borehole. v

FIG. 8 shows in longitudinal section the well equipment arrangement after a second casing has been placed in the borehole.

FIG. 9 shows in longitudinal section part of the well installation accordingto the invention in an embodiment wherein the coupling between the pedestal conductor 'and the conductor string includes blowout preventer equipment.

FIG. 10 shows another embodiment of the well installation according to the invention in longitudinal section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, we see a drilling ship 1 (partly shown) provided with a derrick 2 and all other equipment (not shown) necessary for carrying out drilling operations in wells below the sea level 3. The ship 1 is kept in the position above a location where a well 21 is to be drilled by means known per se, such as dynamic positioning I means (not shown) which make use of propulsion units controlled by position locators. A conductor string 5 is cemented in the well 21 which is being drilled into a formation 4. This string 5 is suspended from the sea bottom 6 by a base plate 7 provided with guide line posts 8. A casing 9 is suspended from the conductor string 5, and a casing 10 is suspended directly from the casing 9 (and indirectly from the conductor string 5) in a manner as will be described hereinafter. The lower part 11 of the well 21 can be drilled by a bit 12, which is temporarily retracted from the well 21 as shown in FIG. 1. The connection between the drilling ship 1 and the well 21 is formed by a marine conductor 13 (which may include a telescopic section) which conductor is guided by means of guide bars 15 via guide lines 14 to a wellhead 16 mounted on the upper end of a pedestal conductor 17. The pedestal conductor 17 is coupled at its lower end to the conductor string 5 by means of coupling 18 and is kept in an upright position by a buoyancy member 19 connected to the upper end of the pedestal conductor 17. The buoyancy member 19 carries guide line posts 20 to which the guide lines 14 are connected. The guide line posts 20 are, just as the guide line posts 8, known per se and will not be described in detail. The guide lines 14 are kept taut in the usual manner, e.g., by constant-tension devices (not shown), such as counter weights or winches arranged on the ship 1.

Reference is now made to FIG. 2, which shows the characteristic parts of the well equipment according to FIG. 1 in longitudinal section, and in greater detail than FIG. 1. Identical parts in FIGS. 1 and 2, as well as in the other figures, are indicated by the same reference numerals.

FIG. 2 shows the buoyancy member 19 consisting of metal (preferably steel) contains at least partially filled with air, and having a water displacement of at least sufficient magnitude to keep the pedestal conductor 17 under tensional stress. The design of the member 19 is such that the walls thereof can withstand any pressure differences which may exist between the fluids inside and outside the member.

The buoyancy member 19 carries the guide line posts 20 and the wellhead 16, which is of a design suitable for submarine operations. Since a great number of such designs are already known, no details of the wellhead 16 are given.

The upper end of the pedestal conductor 17 is connected to the wellhead 16 in a suitable manner. The lower end of the pedestal conductor 17 is provided with a coupling member 18 suitable to co-operate with the upper end of the conductor string 15 which is cemented in the bore hole 21 by a cement layer 22.

The upper end of the conductor string 5 is further provided with a base plate 7 for supporting the conductor string 5 during cementing thereof. The base plate 7 carries guide line posts 8 to which guide lines 23 are connected for guiding the pedestal conductor 17, which is provided with guide bars 24, downwards to bring the coupling 18 thereof into alignment with the upper end of the conductor string 5 when placing the pedestal conductor. Guide bars 24, guide lines 23 and guide line posts 8 may be of the usual type and in the usual number and are hence not described in detail.

The casing 9 is suspended from the conductor string 5 by a casing suspension means such as a hanger 25 which may include pack-off means and which is preferably provided with fluid by-pass means. Such hangers are known per se and for the sake of simplicity are indicated only schematically in the figures.

The casing 9 extends downwards through the conductor string 5 to a level in the bore hole 21 below the lower end of the conductor string 5. The casing 5 is surrounded along the entire length thereof by a cement layer 28, and thus no free annular space is left around this casing, in which space gas or liquid pressure might build up which would require the application of venting means to control the pressure in such space.

The casing 10 is suspended in the casing 9 by suspension means 26 (which can be of the same type as suspension means 25) and provided with a cement layer 29 arranged along substantially the entire length thereof, such that no free annular space is left around this casing. Casing 10 extends downwards through the casing 9 to a level of the well bore 21 below the lower end of easing 9.

Within the casing 10, the production tubing 30 is suspended from the casing 10 by the suspension means 27 (which suspension means can be of the same type as suspension means 25 The production tubing 30 is cemented by a layer 31 over substantially the entire length thereof and communicates at or near the lower end thereof with the oil production layer 32 of the formation 4.

The upper end of the production tubing 30 communicates with a string of tubular means 33 which is suspended from the wellhead 16 by means suitable for the purpose and known per se. The production tubing 30 and the string of tubular means 33 communicate via coupling means 34 which are known per se and therefore shown schematically only. a

The well equipment as shown in the situation according to FIG. 2 is suitable for the production of fluids from the layer 32.. These fluids are driven out of the layer 32 into the production string 30 and flow upwards through the string of tubular means 33, and via the wellhead 16 into a flow line (not shown) through which they are transported to a suitable storage means (not shown). I

Since the various casings used'in the well 21 extend upwards only to the sea bottom 6, and are suspended (indirectly) from the conductor string 5, the buoyancy member 19 has to be designed for carrying (besides its own weight) only the weight of the wellhead 16, the pedestal conductor 17 and a string of tubular means 33. The dimensions of the buoyancy member 19 are minimal since the weight of the

casings

9 and 10, as well as of the production tubing 30 is not carried thereby.

The wall thickness of the string of tubular means 33 suspended from the buoyancy member 19 is preferably chosen equal to the wall thickness of the production tubing 30 communicating therewith. Since this tubing 30 is designed to withstand the maximum pressure which may be expended at the depth to which it extends, the string3'3 will also be capable of withstanding this pressure and thus prevent damage of the pedestal conductor 17 by such pressure.

The way in which the well 21 is drilled and completed will now be described in more detail.

As shown in FIG. 3, a drill string 50 is let down from a drilling ship (not shown) at a location where the well should penetrate into the formation 4. The drill string 50 carries a coupling member 51 which is suitable for being coupled to the upper end of the conductor string 5. The coupling member 51 is of a known type and may comprise an annular piston 52 axially displaceable in an annular cylinder 53 and capable of actuating locking dogs 54 co-operating with a groove 55 in the upper parts of the outer wall of the conductor string 5. The piston 52 can be actuated by hydraulic fluid which is supplied to and drained from the cylinder parts above and below the piston via suitable conduits (not shown) leading to the drilling ship. Suitable sealing means (not shown) may be provided to seal the clearance between the coupling member 51 and the conductor string 5.

The coupling member 51 is provided with guide bars 56 co-operating with the guide lines 23 and the guide line posts 8 arranged on the base plate member 7.

The lower end of the drill pipe 50 is connected to a hydraulic turbine 57 of known design, which is actuated by a flow of fluid being passed through the drill string 50. The turbine shaft 58 carries a drill bit 59 and is provided with a splined section 60 co-operating with a splined section 61 of a casing shoe 62, which is rotatably arranged on the lower end of the conductor string 5. Locking means 64 lock the shoe 62 against longitudinal displacement with respect to the conductor string 5. This shoe is at the lower end thereof provided with an annular row of cutting means 63. A cutting element is thus formed by the bit 59 and the means 63 suitable to drill a hole having a diameter greater than the outer diameter of the conductor string 5. Thus, the conductor string 5 can be let down in the hole 21 when the drilling operation is being carried out at the bottom thereof by the bit 59 and the cutting means 63 arranged on the rotatable casing shoe 62.

The splined section 60 co-operating with the splined section 61 is arranged such that this section 60 and the bit 59 can, together with the turbine 57, be retracted from the shoe 62 in axial direction thereof by lifting the drill string 50 after the coupling 51 has been uncoupled from the conductor string 5. This operation is carried out whenthe hole 21 has a depth sufficient to receive the entire length of the conductor string 5. This string is then supported by the base member 7 resting on the sea bottom 6.

' When the drill string 50, the coupling member 51, the hydraulic turbine 57 and the bit 59 have been retracted from the conductor string 5, the string is cemented in the bore hole 21. To this end, a cementing tube 65 (FIG. 4) provided with a coupling member 66 and packer means 67 (known per se) is let down in the water. No details are shown in FIG. 4 of coupling member 66, since this member is of a construction similar to the construction of the coupling member 51 shown in FIG. 3. The tube 65 is guided from the ship (not shown) into the conductor string 5 by guide bars 68 (known per se) co-operating wi'ththe guide lines 23 and the guide line posts 8 arranged on the base plate 7. In the position shown in FIG. 4 the coupling member 66 is coupled to the upper end of the string 5, and the packer 67is set to seal off the annular space around the cementing tube 65 at the level indicated.

Via the cementing tube 65, cement is injected into the bore hole 21, thereby filling the annular space around the conductor string 5 with a cement layer 22. The cement overflowing at the upper end of the bore hole forms a cake 69. It will be appreciated that the casing shoe 62 is cemented in the well together with the conductor string 5.

To minimize the pressure and the velocity at which the cement will enter the hole 21, a restriction (not shown), such as a spring-loaded valve, may be arranged at or near the lower end of the cementing tube 65. Fracturing of the formation 4 can then be prevented as the high pressure prevailing at the lower end of the cement column within the tube 65 is decreased by the resistance which is met by the cement flowing through the restriction.

After the cement has hardened, the packer 67 is loosened and the coupling member 66 detached from the conductor string 5. Thereafter the cementing tube 65 is retracted from the string 5 together with the packer 67.

Subsequently the pedestal conductor 17 is mounted on the conductor string 5. To describe this operation, reference is first made to FIG. 5, which shows on a scale similar to FIG. 1 the pedestal conductor 17 after it has been built from the drilling ship 1.

To assemble the pedestal conductor, the buoyancy member 19, which is provided with a central opening, is first positioned such that the central opening is in alignment with the moonpool or well 70 arranged vertically through the ship 1 and having the central axis thereof coinciding with the axis of the derrick 2 arranged on deck of the ship 1. Thereafter the coupling 18 provided with guide bars 24 is arranged below the buoyancy member 19 and the pedestal conductor 17 is assembled by passing the various parts thereof through the moonpool or well 70 of the ship 1 and through the central opening of the buoyancy member 19, interconnecting these parts and connecting the lowest part to the coupling member 18 carrying the guide bars 24. When the pedestal conductor 17 has the desired length, the upper part thereof is connected to the buoyancy member 19, whereafter wellhead equipment 16 as is normally used for underwater drilling, is mounted on the upper part of the pedestal conductor 17. As the type and size of this equipment 16 vary during the various stages of the drilling of the well, this equipment is only schematically indicated. During the various stages of the drilling and completion of the well, this equipment may, for example, include blowout preventers and casing suspension means, both of various sizes.

After the pedestal conductor arrangement comprising the pedestal conductor 17, the buoyancy member 19 and the equipment 16 has been completed, the whole system is lowered to a level below the wave zone by means of a string of tubing 71 attached to the wellhead 16 mounted on the buoyancy member. This is the position shown in FIG. 5. In this position, the lower end of the pedestal conductor 17 is preferably at a sufficiently great distance from the upper end of the conductor string to prevent damage thereof by the pedestal conductor 17 if the ship 1 should be subject to very high waves.

During a period of low waves, the pedestal assembly is lowered, and guided by means of the guide bars 24 co-operating with the guide lines 23 onto the upper end of the conductor 5. Directly after the coupling member 18, which is of a construction similar to that of the coupling 51 shown in FIG. 3, is landed on the upper end of the conductor string 5, the coupling is made in a manner such as described with reference to coupling 51 and groove 55 shown in FIG. 3. Since high pressure differences may exist between the interior and the exterior of the pedestal conductor, the coupling 18 is preferably provided with sealing means.

As the above-mentioned coupling operation can be performed in a very short time, the chances that deteriorating weather conditions might influence the coupling operation can be neglected. Thus, the placement of the pedestal conductor on the well entrance is a very safe operation.

It will be appreciated that the buoyancy of the member 19 may be controlled such that the string of tubing 71 is under a small tensional load. Once the coupling 18 has been coupled to the upper end of the conductor string 5, the buoyancy of the member 19 is preferably increased, so as to bring the pedestal conductor 17 under tensional stress.

To control the buoyancy of the member 19 during its descent, the interior of the member 19 is preferably in open communication with the exterior near the lower part thereof. Thus, the buoyancy can be controlled by pumping air into the interior (or venting air therefrom). To this end, float chambers of the member 19 communicate with air compressors which are mounted on board of the ship 1 and connected to the float chambers of the member 19 by flexible conduits.

After the pedestal conductor 17 has been mounted on the conductor string 5, the marine conductor 13 (FIG. 6) is lowered through the moonpool of the ship 1, and guided by means of guide bars 15 along guide lines 14 onto the wellhead 16 and connected thereto in a manner known per se. Thereafter, the drilling operation is continued by means of a bit 72 connected to a drill string 73. The diameter of the bit 72 is smaller than the diameter at which the first part of the hole 21 has been drilled (see FIG. 3). When a sufficient depth has been reached, the bit 72 is retracted from the hole, and a casing 9 is lowered into the hole 21 by means known per se. The casing 9 is suspended (FIG. 7) in the conductor string 5 by means of a hanger 25 which is also known per se and hence not described in detail. Thereafter the annular space around substantially the entire length of the casing 9 is cemented in a manner similar to'that described with reference to FIG. 4, with the difference, however, that the cementing tube 65 (FIG. 4) is not provided with a coupling member 66. The cement layer 28 substantially fills the entire volume of the annular space around the casing 9, thus preventing any build-up of fluid pressure in this space and eliminating the need for means suitable to measure such pressure and to vent this space.

After the casing 9 has been set in the bore hole 21, a string of tubing 75 is suspended from the wellhead 16, the lower end of this string being sealingly connected by a coupling member 76 to the upper end of the casing 9. The tubing 75 has substantially the same diameter and substantially the same wall thickness as the casing 9. Since the casing 9 is designed to withstand the maximum formation pressure which may be met during the further drilling of the hole 21 to a depth at which the next casing is to be set, the tubing 75 is advantageously sufliciently strong to withstand such pressure and protect the pedestal conductor 17 against damage by such pressure.

Subsequently, the bore hole 21 is deepened further in a manner similar to that described with reference to FIG. 6. When a sufficient depth has been reached, a liquid with extremely high density is circulated into the well. Thereafter the string of tubing 75 is withdrawn from the pedestal conductor 17, and the casing 10 (FIG. 8) is introduced via the pedestal conductor 17 into the well 21 and suspended from the casing 9 by suspension means 26 which are of the same construction as the means 25. This casing 10 is then cemented in such a manner that the cement layer 29 fills substantially the entire volume of the annular space around the casing 10.

Either before or after the casing 10 has been cemented, a string of tubing 77 is suspended from the wellhead 16. The lower end of the string of tubing 77 is sealingly coupled to the upper end of the casing 10 by means of a coupling member 78. The diameter and wall thickness of the tubing 77 are advantageously substantially equal to the diameter and thickness respectively of the casing 10. Thus the tubing 77 can withstand the maximum pressure which might be met during a further deepening of the well, and thus will protect the pedestal conductor 17 against damage by such pressure.

The borehole 21 is further deepened in a manner similar to that described with reference to FIG. 6. When the desired depth has been reached (in this case the oil containing layer 32), the well is pumped dead by circulating a mud with very high density into the well. Thereafter the production tubing 30 (FIG. 2) is suspended from the casing 10 by suspension means 27 which are of a construction similar to that of the suspension means 25. Subsequently the tubing 30 is cemented bymeans of a layer 31 substantially filling the entire volume of the annular space around the tubing 30.

When the tubing 30has been set, the string of tubing 77 (FIG. 8) is retracted from the pedestal conductor 17 and replaced by a string of tubing 33 (FIG. 2) which is also suspended from the wellhead 16, but is sealingly connected by means of a coupling member 34 'to the upper end of the production tubing 30. As the coupling member 34 is known per se, no detailed description will be given thereof. 7

Tubing 33 is advantageously as strong as tubing 30, and thus will withstand all the pressures that the production tubing 30 can withstand.

Subsequently the well is completed, e.g., by perforating the lower end of the production tubing 30 where it penetrates the production zone 32, removing the marine conductor 13 and connecting the necessary flow lines to the wellhead 16. It will be appreciated that in case no oil or gas is found, the well 21 can be abandoned by plugging back of the well, retracting the tubing 33 and removing the pedestal conductor 17 and buoyancy member 19 after having uncoupled the coupling 18.

It will be appreciated that during the replacement of the tubing 75 (FIG. 7) by the tubing 77 (FIG. 8), and of the tubing 77 (FIG. 8) by the tubing 33 (FIG. 2), the buoyancy of the buoyancy member 19 has to be controlled, as otherwise the pedestal conductor 17 would be overstressed. By replacing the tubing suspended from the wellhead 16 by a tubing with smaller diameter whenever a new casing (or the production tubing) is suspended in the bore hole 21, the weight to be carried by the buoyancy member 19 will be kept as small as possible. This results in a member 19 which will be easier to manipulate than a buoyancy member used in com bination with a well system in which each casing extends upwards to the wellhead 16.

It has been remarked already, that the coupling member 18 as indicated in FIG. 2 for coupling the pedestal conductor 17 to the conductor string 5, may be of a construction similar to that of the coupling member 51 shown in FIG. 3. However, any other design of coupling member may be used for this purpose, such as an automatic coupling member which can couple the pedestal conductor 17 to the conductor string by a longitudinal movement of these members relative to each other.

It will be appreciated that the coupling member 18 shown in FIG. 2 may be combined with blowout preventer equipment and/or with articulated couplings (for allowing an angular displacement of the pedestal conductor 17 with respect to the production tubing). A design of well equipment provided with a blowout preventer included in the coupling between the conductor string 5 and the pedestal conductor 17 is schematically shown in FIG. 9. In this design a blowout preventer 80 provided with shear rams 81 is connected to the lower end of the pedestal conductor 17 by a coupling member 82 which may be: hydraulically actuated in the manner described with reference to coupling 51 shown in FIG. 3. The housing 83 of the blowout preventer 80 is designed such that it is able to withstand the highest pressures which will be met in the well during the drilling and production of this well.

The shear rams 81 can be actuated by means of the pistons 84 slidably arranged in the cylinders 85 located in the housing 83. Suitable conduits (not shown) lead to the cylinder spaces to actuate the shear rams 81 by hydraulic fluid. When actuated, the rams close off the passage through the housing 83, thereby shearing any tubular equipment which is caught therebetween.

A coupling member 18, as described hereinbefore, is

' connected to the lower end of the housing 83 of the blowout preventer 80. During placement of the pedestal conductor 17, this conductor 17 is lowered in combination with the blowout preventer and the coupling member 18. Subsequent to this placement, the. well 21 is deepened in the same manner as described with reference to FIG. 6 hereinabove. After the desired depth has been reached, a casing 86 can be suspended from the blowout preventer 80 by means of a casing hanger 87 known per se and cemented therein by a cement layer 88. Drilling of the hole is continued through casing 86 after a casing 89 having the same thickness and diameter as the casing 86 has been suspended from the wellhead (not shown) carried on top of the pedestal conductor 17. The lower end of casing 89 is provided with a packer 90 for sealing the entrance to the annular space between the casing 89 and the pedestal conductor 17.

After the desired depth of the borehole 21 has been reached, the drill bit is retracted from the borehole and a casing 91 is run into the hole via the casing 89 and suspended in the housing 83 of the blowout pre'venter 80 by a casing suspension means 92 known per se. Thereafter the annular space around the casing 89 is filled with cement forming a solid layer Subsequently, the casing 89 suspended by the wellhead is replaced by a casing 94 provided with a packer 95. By choosing the diameter and thickness of casing 94 equal to the diameter and thickness of the casing 91, the pedestal conductor 17 is protected against the maximum pressures which can be met when the borehole is further deepened.

It will be appreciated that on further drilling of the hole, the number of casings suspended therein may be increased. Preferably, however, only a single casing is suspended from the wellhead, since this decreases the weight which has to be carried by the buoyancy member carrying this wellhead. The single string of casing is preferably of the same type as the casing of smallest diameter suspended from the blowout preventer 80.

The well may be completed by applying a production string which is partly suspended from the blowout preventer housing and partly suspended from the wellhead carried by the buoyancy member. In this case, the wellhead only supports the part of the production string located within the pedestal conductor.

However, the well may also be completed by loosening the packers and suspension means from all the easings ending in the housing 83 of the blowout preventer 80, removing the casing(s) suspended from the wellhead, and thereafter uncoupling coupling 18 and lifting the pedestal conductor 17 and the blowout preventer 80 from the upper part of the conductor string 5. Subsequently a wellhead (not shown) is lowered onto the upper end of the casing 91 and coupled thereto. Production tubing suitable for the purpose may be supported by this wellhead.

It will be appreciated that this latter type of well completion may also be used in combination with the equipment shown in FIG. 2 after the coupling 18, the pedestal conductor 17, the string of tubular means 33, and the buoyancy member 19 and the wellhead 16 have been removed. Y

It will be appreciated that the casing suspension means 87 and 92 shown in FIG. 9 may, if desired, be set in a thickened wall 96 of the upper portion of the conductor string instead of in the housing 83 of the blowout preventer 80. In the same manner, the

packers

90 and 95 may be set in a thickened wall 97 of the lower portion of the pedestal conductor 17.

Although only a single buoyancy member has been shown in the example of the present invention described hereinabove with reference to the drawing, it will be understood that the present invention is not limited thereto. Also the pedestal conductor 17 may be provided with buoyancy means distributed along the length thereof. Such buoyancy means may be in the form of separate floats, or may be formed by using double-walled tubing for the pedestal conductor.

The application of the invention is not limited to the number of casings used in the example described above. Any desired number of easing strings may be applied. Moreover, any desired number of strings of tubular means may be applied within the pedestal conductor. It will, however, be appreciated that the use of only a single string of tubular means is to be preferred since this reduces the size of the buoyancy member considerably.

The tubing 30 (FIG. 2) may be used as a casing as shown in FIG. 10. In this embodiment a production tubing 30a may be extended from the top of the pedestal conductor 17 to a level below the lower end of the conductor string 5. The production tubing 30a may be suspended from the wellhead 16. The production tubing 30a may extend through the tubular means 30 and 33. The annular space between the casing 30 and the production tubing 30a is preferably packed off above the production layer 32 with a packer 100.

The buoyancy member may be of any desired type and be arranged below the ship or within the moonpool 70 (FIG. 5) thereof in any desired manner.

The replacement of a string of tubular means suspended from the wellhead equipment by a string of smaller diameter may either take place prior to or after cementing of the casing which will have to communicate with the string of smaller diameter.

It will further be appreciated that the supervising of the well drilled and completed in accordance with the present invention is simplified by the fact that all the casing and the production tubing is cemented along the entire length thereof, thus eliminating the need for control of fluid pressures which would otherwise develop in the spaces around the casings or the production tub- Where necessary, the tubular equipment or the couplings may be provided with a telescopic joint. Thus, by providing the coupling 34 (FIG. 2) with a telescopic joint, expansion and/or contraction of the string of tubular means 33 can be compensated in a simple manner.

It will be appreciated that the application of the invention is not restricted to systems making use of guide cables. If desired, other types of re-entry systems may be applied as well.

The application of the invention is further not restricted to the use of the turbine 57 in combination with the rotatable casing shoe 62. If desired, other means for actuating the drilling bit may be applied, which bit may be of a type permitting a decrease in the outer cutting diameter when the bit is to be moved through the conductor string 5.

We claim as our invention 1. Apparatus for completing a well which penetrates a formation located below a body of water comprising:

a conductor string arranged for at least the greater part thereof in the well and cemented to the formation;

a pedestal conductor for providing a wellhead location above the bottom of the body of water;

at least one buoyancy member connected to the pedestal conductor near the upper end thereof for supporting the pedestal conductor in the body of water above the conductor string;

means for sealingly coupling the lower end of the pedestal conductor to the upper end of conductor string;

a wellhead mounted on the upper end of the pedestal conductor;

pipe suspending means arranged in the conductor string near the upper end thereof;

at least one string of tubular pipe suspended from the pipe suspending means in the conductor string and extending into the well below the lower end of the conductor string; and

a string of tubing suspended from the wellhead and extending downwardly through the pedestal conductor and into the conductor string, the string of tubing being connected at its lower end in communication with the string of tubular pipe suspended in the conductor string.

2. The apparatus of claim 1 including means for coupling the lower end of the string of tubing to the upper end of the string of tubular pipe suspended in the conductor string.

3. The apparatus of claim 1 wherein the means for coupling the lower end of the pedestal conductor to the upper end of the conductor string includes a blowout preventor.

4. The apparatus of claim 1 wherein a plurality of strings of tubular pipe of different diameters are suspended from the conductor string, and wherein the string of tubing suspended from the wellhead is connected at its lower end in communication with the string of tubular pipe of smallest diameter.

5. The apparatus of claim 4 wherein the string of tubing suspended from the wellhead is of the same diameter as the string of tubular pipe of smallest diameter.

6. The apparatus of claim 4 wherein there is an annular space around each of the plurality of strings of tubular pipe and wherein the annular space around each of the strings of tubular pipe is filled with solid material part of the suspended string of casing; and suspending the production tubing string from the wellhead. 10. A method of drilling a well into a formation around substantially the entire length of the string of 5 located below a body of water comprising the steps of:

tubular pipe.

7. The apparatus of claim 4 including a production tubing suspended from the wellhead and extending downwardly into the well through the string of tubing suspended from the wellhead and through the string of tubular pipe of smallest diameter.

8. In a well drilled into a formation located below a body of water and provided with equipment of the type comprising a relatively large diameter conductor pipe string positioned in the upper part of the well, at least one string of casing extending to the bottom of the well, and a wellhead mounted above the conductor pipe string on a pedestal conductor coupled to the conductor pipe string and at least in part supported in the water by buoyant support means, an improved method of equipping the well comprising the steps of:

suspending the string of easing at a point below the upper end of the conductor pipe string from casing suspension means supported by the conductor pipe string;

cementing the suspended string of casing in the borehole throughout substantially the entire length of the suspended string of casing below the casing suspension means;

extending a string of tubing from the wellhead to the upper end of the suspended string of easing; coupling the string of tubing to the suspended string of casing; and

suspending the string of tubing from the wellhead,

thereby providing a continuous conduit from the wellhead to the bottom of the string of easing a substantial portion of which is not supported by the pedestal conductor on which the wellhead is mounted.

9. The method of claim 8 including the steps of extending a production tubing string into the well through the string of tubing and through at least drilling a borehole into the formation with equipment lowered from the water surface;

extending a relatively large diameter conductor pipe string into the bore hole;

cementing the conductor pipe string in the bore hole;

positioning in the water above the conductor pipe string a pedestal conductor supported by at least one buoyant support means;

coupling the pedestal conductor to the conductor pipe string;

extending drilling equipment from the water surface into the bore hole through the pedestal conductor and the conductor pipe string;

drilling the bore hole deeper into the formation with the drilling equipment to a point below the lower end of the conductor pipe string;

extending a casing into the deepened bore hole thereby defining an annular space around the exteriorpf this casing; suspending the casing in the conductor pipe string with a pipe suspension means;

filling the annular space around the suspended casing with cement along substantially the entire length of the suspended casing;

extending a string of tubing into the well to a point adjacent the top of the suspended casing;

coupling the lower end of the string of tubing to the upper end of the suspended casing;

suspending the string of tubing from a wellhead mounted on the top of the pedestal conductor;

extending drilling equipment from the water surface into the bore hole through the string of tubing and the suspended casing; and

drilling the bore hole deeper into the formation with the drilling equipment to a point below the lower end of the suspended casing.

Claims

1. Apparatus for completing a well which penetrates a formation located below a body of water comprising: a conductor string arranged for at least the greater part thereof in the well and cemented to the formation; a pedestal conductor for providing a wellhead location above the bottom of the body of water; at least one buoyancy member connected to the pedestal conductor near the upper end thereof for supporting the pedestal conductor in the body of water above the conductor string; means for sealingly coupling the lower end of the pedestal conductor to the upper end of conductor string; a wellhead mounted on the upper end of the pedestal conductor; pipe suspending means arranged in the conductor string near the upper end thereof; at least one string of tubular pipe suspended from the pipe suspending means in the conductor string and extending into the well below the lower end of the conductor string; and a string of tubing suspended from the wellhead and extending downwardly through the pedestal conductor and into the conductor string, the string of tubing being connected at its lower end in communication with the string of tubular pipe suspended in the conductor string.

6. The apparatus of claim 4 wherein there is an annular space around each of the plurality of strings of tubular pipe and wherein the annular space around each of the strings of tubular pipe is filLed with solid material around substantially the entire length of the string of tubular pipe.

8. In a well drilled into a formation located below a body of water and provided with equipment of the type comprising a relatively large diameter conductor pipe string positioned in the upper part of the well, at least one string of casing extending to the bottom of the well, and a wellhead mounted above the conductor pipe string on a pedestal conductor coupled to the conductor pipe string and at least in part supported in the water by buoyant support means, an improved method of equipping the well comprising the steps of: suspending the string of casing at a point below the upper end of the conductor pipe string from casing suspension means supported by the conductor pipe string; cementing the suspended string of casing in the borehole throughout substantially the entire length of the suspended string of casing below the casing suspension means; extending a string of tubing from the wellhead to the upper end of the suspended string of casing; coupling the string of tubing to the suspended string of casing; and suspending the string of tubing from the wellhead, thereby providing a continuous conduit from the wellhead to the bottom of the string of casing a substantial portion of which is not supported by the pedestal conductor on which the wellhead is mounted.

9. The method of claim 8 including the steps of extending a production tubing string into the well through the string of tubing and through at least part of the suspended string of casing; and suspending the production tubing string from the wellhead.

10. A method of drilling a well into a formation located below a body of water comprising the steps of: drilling a borehole into the formation with equipment lowered from the water surface; extending a relatively large diameter conductor pipe string into the bore hole; cementing the conductor pipe string in the bore hole; positioning in the water above the conductor pipe string a pedestal conductor supported by at least one buoyant support means; coupling the pedestal conductor to the conductor pipe string; extending drilling equipment from the water surface into the bore hole through the pedestal conductor and the conductor pipe string; drilling the bore hole deeper into the formation with the drilling equipment to a point below the lower end of the conductor pipe string; extending a casing into the deepened bore hole thereby defining an annular space around the exterior of this casing; suspending the casing in the conductor pipe string with a pipe suspension means; filling the annular space around the suspended casing with cement along substantially the entire length of the suspended casing; extending a string of tubing into the well to a point adjacent the top of the suspended casing; coupling the lower end of the string of tubing to the upper end of the suspended casing; suspending the string of tubing from a wellhead mounted on the top of the pedestal conductor; extending drilling equipment from the water surface into the bore hole through the string of tubing and the suspended casing; and drilling the bore hole deeper into the formation with the drilling equipment to a point below the lower end of the suspended casing.