US3315741A

US3315741A - Method and apparatus for drilling offishore wells

Info

Publication number: US3315741A
Application number: US557347A
Authority: US
Inventors: William C Triplett
Original assignee: Chevron Research and Technology Co
Current assignee: Chevron USA Inc
Priority date: 1957-04-15
Filing date: 1966-06-14
Publication date: 1967-04-25
Anticipated expiration: 1984-04-25

Description

April 25, y1967 Aw. c. TRIPLETT METHOD AND APPARATUS FOR DRILLING OFFSHORE WELLS 6 Sheets-Sheet l ll lllllll Original Filed April l5, 1957 llll FlG.5

INVENTOR W/LL/M C. TR/PTT jam@ ATTOR EYS FIG.6

April 25, 1967 w. c. TlPLr-:TT 3,315,741

METHOD AND APPARATUS FOR DRILLING OFFSHORE WELLS Original Filed April l5, 1957 @sheets-sheet z /M/J 44m ATTOR EVYS April 25', 1967 Original Filed April l5, 1957 W. C. TRIPLETT METHOD AND APPARATUS FOR- DRILLING OFFSHORE WELLS 6 Sheets-Sheet FIG/4 INVENTOR W/LL/AM C. 'TR/m57 7' QTSMM ATTORN YS April 25, 1967 w. c. TRIPLET'T 3,315,741

METHOD AND APPARATUS FOR DRILLING OFFSHORE WELLS Original Filed April l5. 1957 6 Sheets-Sheet 4 afa o o 208 `3.12 Erwin ll 2,2 'd' ,322 l Tr INVENTOR W/LL/AM CA TR/PLETT Flan MM@ if. ,gm

` ATTORN YS FIGS METHOD AND APPARATUSl FOR DRILLING OFFSHORE WELLS original Filed April 15, 1957 April 25, 1967 w. c. TRIPLE-r1' 6 Sheets-Sheet 5 April 25, 1967 w. c. TRIPLETT 3,315,741

METHOD AND APPARATUS FOR DRILLING OFFSHORE WELLS Original Filed April 15, 1957 6 Sheets-Sheet 6 FIG.1O

INVENTOR W/LL/AM c. TR/PLETT BY fwm M@ j 44M ATTORN Ys United States Patent O 2 Claims. (ci. 16e-.5)

This application is a division of application Ser. No. 652,756, filed Apr. 15, 1957.

This invention relates to a method and apparatus for drilling wells in earth formations located under a body of water and more particularly for drilling offshore wells from a floating drilling platform.

As the search for offshore petroleum deposits moves progressively into deeper water, the limitations of fixed offshore drilling platforms become more apparent. Fixed platforms not only yare very costly to build, but the engineering difficulties inherent in these structures increase exponentially as the water depth increases. A practical limitation is reached in waters well above the depth of those covering some potentially available petroleum deposits. Then, too, the susceptibilityto storm damage of fixed drilling platforms located in open Waters has been amply demonstrated by the destruction of such rigs by storms in the Gulf of Mexico and elsewhere.

It is desirable that some means be provided for drilling offshore wells which will not be limited in its application by the depth of the water; that relatively very maneuverable drilling apparatus be provided that can be moved from one well site to another with a minimum of delay and expense; that equipment be provided to control the opening of the well bore where it emerges from the submarine earth formations so that control of the well will not be subject to the hazard of damage through natural or other forces occurring in the Water at the well site; that the well control equipment be operated by remote control from the surface of the water to obviate the necessity of using divers to manipulate the equipment; that provision be made for detaching the drilling apparatus from the well control equipment to permit it to proceed to a new location while leaving the Well controlled by the submerged equipment; that provision be made for relocating a submerged drilled well from which the drilling apparatus previously has been disconnected and for reconnecting the drilling apparatusto the well by manipulation from the surface of the water; that provision be made to enable the drilling apparatus to avoid damage from heavy seas and storms; and that provision be made for controlling at the surface of the water the production from a completed well by remote operation of the submerged wellhead equipment.

It is among the objects of this invention to provide a novel method and means for satisfying the abovementioned desirable conditions. Other objects will become apparent as the description of the invention proceeds in conjunction with the accompanying drawings which form part of this specification.

In pursuance of this invention a floating drilling vessel is anchored over a submerged well site, and wellhead control equipment separate from the vessel is submerged in and at the bottom of the water and affixed to the bottom at the well site. The fixed wellhead equipment is connected to the oating drilling vessel by a string of flexible conductor casing which serves as a communicating conduit between the drilling vessel and the well. The flexible conductor casing string is arranged to permit the drilling vessel to move with the surface forces on the ICC water without placing undue strain .on or causing damage to the fixed wellhead control equipment. The wellhead control is operated from the floating drilling vessel remotely and independently of the vessels connection through the flexible conductor .casing string, and -is not exposed to the hazard of malfunctioning which could follow from damage to the flexible conductor casing. Means are provided for remotely detaching and reattaching the flexible conductor casing string to the submerged wellhead, so that the vessel may leave the drilling site or return to it and be reconnected with the well through the operation of the `apparatus aboard the vessel.

In the drawings:

FIGURE l illustrates diagrammatically in elevation and partly in section an example of apparatus employed in the method of this invention. p

FIGURE 2 illustrates in sectional elevation details of parts of the apparatus illustrated in FIGURE l.

FIGURE 3 is a plan view of a portion of the apparatus taken along the line 3 3 of FIGURE 2.

FIGURE 4 is an elevation-al view of a portion of the apparatus taken along the line 4 4 of FIGURE 3.

FIGURE 5 illustrates diagrammatically the arrangement of portions of the apparatus when the drilling vessel is being reconnected to a well.

FIGURE 6 illustrates in sectional elevationdetails of the apparatus shown in FIGURE 5.

FIGURE 7 is a plan view of a detail of the apparatus taken along the line 7-7 of FIGURE 6.

FIGURE 8 illustrates diagrammatically in elevation and partly in section a modification of apparatus employed inthe method of this invention.

FIGURE 9 illustrates in elevation and partly in section details of a portion of the Iapparatus illustrated in FIGURE 8.

FIGURE l0 is a plan View partly in section of the apparatus taken along the line lll-10 of FIGURE 9.

FIGURE 1l is a diagrammatic illustration in elevation and partly in section of details of a modification of a portion of the apparatus. Y l

FIGURE 12 is a schematic illustration of an alternate method for reconnecting the drilling vessel to the submerged wellhead.

Referring to the embodiment of the invention illustrated in FIGURE 1, there is shown a drilling vessel 10 which has been anchored on the surface of the water over the Well site. This vessel m-ay be a fioating platform such as a barge which is towed to theA well site, but preferably as illustrated it is a self-propelled ship which has been constructed or altered for-well drilling purposes. .The vessel is anchored by four anchors, two at the bow and two at the stern, and each pair of anchors is displaced at an angle of 45 to the longitudinal axis of the ship and hence at to each other to increase the stability of the vessel in its anchored position. The Winches 12` of the bow anchors are manually controlled in the usual manner. However, the stern anchor cables are wound on a winch 14 to be effective as a continuous line so that as the Winch rotates one cable will be taken up as the other is payed out. The operation of the winch is governed automatically by a gyroscopically controlled selsyn arrangement which is designed to hold the vessel Within 1A; of arc of rotation in a horizontal plane to the position where it originally has been anchored.

The vessel has a bulkhead 16 built transversely across the forward portion of its hull and extending upwardly from the keel a distance appreciably above the Water line. The bottom portion of the hull vforwardly of the bulkhead has an opening 18 formed in it to provide access to the subjacent body of Water from the interior 'of the vessel. A platform 20 is erected abovethe opening and above the surface of the water within the hull, and on this platform is positioned a rotary table 22. The platform 20 together with the rotary table and any other equipment which may be on the platform is removable so that access may be had to the opening in the bottom of the hull and equipment and apparatus may be passed through this opening and into the water for a purpose to be described hereinafter.

There is ere-cted on the deck of the vessel for operation in vertical al-ignment with the opening in the hull a derrick 24 by which equipment can be raised and lowered through the opening and through the water. The derrickv is tted with gear and tackle connected to suitable power-driven

drums

26 and 28 through which the hoisting operations can be accomplished. The vessel also is equipped with the power sources, pumps, tanks and other equipment normally used in a well drilling operation, as well as special equipment used in this invention, and to be described hereinafter.

When the vessel is anchored in position, wellhead control apparatus, designated generally by the number 30, is assembled and supported in the Water by

cylindrical pontoons

32 and 34. This apparatus comprises a base 36 which may be, by Way Iof example, made of concrete. The base is illustrated as circular in shape, although it will be apparent that this particular shape is not necessary for its function. One end of a length of rigid conductor casing 38 is secured integrally in the base so that the casing extends axially from the bottom of it. The conductor casing extends also above the base a distance suflicient to permit the secure connection of equipment to it.

Attached to the top of the conductor casing is an element 40 which has a portion 42 of its exterior surface formed with a conical conliguration. An axial conduit 44 is formed through the central portion of the element, in alignment and communicating fwithiithe interior of the conductor casing. Included in the conduit is a conically shaped chamber 46, the smallest diameter of which is comparable to the internal diameter of the conductor casing. Coarse screw threads y48 are formed in the upper cylindrical surface of the conduit 44 to receive complementary screw threads 50 lformed on an exterior surface `of a nipple 52. The upper end of element 40 terminates in la ilange 454, and the nipple 52 has a cornplementary ange 56 which mates with it. A gasket S8 may be placed between the flanges to form a huid-tight connection. The nipple has an axial opening 60 through it of the same internal dimension as and in alignment with the interior of the conductor casing. Aixed to the top of and in axial alignment with the nipple is a hydraulically actuated blowout preventer 62 to which flexible

hydraulic lines

64 and 66 are attached. The hydraulic lines are Wound on a drum 68 mounted on the vessel, and suitable valves are placed in .the lines so that the blowout preventer my be remotely operated from aboard the vessel. A second nipple 70 is aiiixed to the top portion of the blowout preventer and projects in axial alignment upwardly therefrom. This nipple is designed to receive an end of a string of ilexible conductor casing 72 which has an internal diameter comparable to that of the rigid conductor casing 38. The flexible conductor casing is preferably made of a rubber-like material reenforced with steel wires so that it |will have high tensile strength, and it may be fastened to the nipple 70 in any manner which will make a secure connection. As illustrated in FIG- URE 2, a split clamp 74 is used for this purpose. The iiexi-ble conductor casing may be made in sections for convenience in handling and the sections joined together by flanges 76 as illustrated in FIGURE l.

As illustrated in FIGURES 2, 3 and 4, the

cylindrical pontoons

32 and 34 are connected to the base '36 by means offour chains, two from each pontoon. The chains have a Ifixed attachment to the pontoons but are detachably connected to the base by a remotely controlled connection, so that the pontoons may be recovered at the surface'of the water when the base is landed on the well site. As shown in FIGURE 3, the free end of each chain terminates in an eye which is received within a clevis which is rigidly attached to the base; the clevis 78 receives the eye S0 of the respective chain 82, and the clevis 84 receives the eye y86 of the chain 88. A pin is inserted through the clevis and eye combination 78-80, and a pin 92 through the clevis and eye combination 84486. Each pin is attached to a frame 94 in a unitary manner so that when the frame is displaced longitudinally each pin also will be displaced the same distance simultaneously. A line 96 is attached to each frame and runs through a corresponding sheave 98 mounted on the base 36. The lines from each of the two frames are run through their respective sheaves and thence are joined together and connected to a single line 100. The sheaves are mounted at an angle on the base to accommodate the angle made by the line 96 and are positioned so that the stress in the line will be in axial alignment with the frame 94.

Line 100 is run through a set of sheaves 102 affixed to the side of pontoon 32 so that the line will clear the pontoon and not become entangled in the wellhead apparatus. The line continues upwardly through the water to aboard the drilling vessel from which it can be manipulated to draw the pins 90 and `92 from the eye and clevis attachments on the base to thereby release the pontoons so that they may be buoyed to the surface and recovered.

The frame 94 and its attached pins are held in place in the eye and clevis connections by a shear pin 104 which is passed transversely through the pin 90 as shown in FIGURE 3. The shear pins are proportioned to shear under a predetermined stress placed on the lines 96 and prevent the

pins

90 and 92 from being accidentally withdrawn from the eye and clevis connections prior to the time it is desired to release the pontoons from the base.

The line 100 is connected to the lines 96 by a shear pin connection 106 incorporating la shear pin 108. This latter shear pin is, of course, proportioned to shear under a greater stress than is required to shear the pins 104 together. Hence, after the pontoons are released from the base additional stress may be placed on the line 100 to release the connection 106, permitting the line .to be cleared from the wellhead assembly and recovered aboard the drilling vessel.

The cylindrical pontoons are connected together by rigid members 110 placed between the corresponding axial ends thereof. These yrigid members hold the pontoons in spaced relationship so that they 'will not impinge upon and damage the ilexible conductor casing 72 or other apparatus associated with the wellhead. The members may be and preferably are manifold conduits by which the pontoons are joined to receive simultaneously air or water introduced into them through the exible hoses `112 and 114 which are connected to appropriate sources of air and water aboard the drilling vessel. Obviously the buoyancy of the pontoons may be controlled from aboard the drilling vessel by manipulating appropriate valves to inject the proper amount -of air or water into the pontoon structures.

The well head equipment extending above the base 36 is braced by diagonal bracing members 116. These members are attached to the blowout preventer by a relatively rigid connection and extend thence diagonally outwardly to contact the base near its periphery. The ends of the diagonal members adjacent the base terminate in a foot 118 which is bent into a plane parallel with the top surface of the base. The foot has a circular opening 120 in it which is slotted 122 at one side so that the opening may receive the shank 124 of a headed pin 126 in :a sliding connection. The head of the pin engages the topmost surface of the foot to prevent an axial displacement of the foot from the pin connection. However, the

being lowered into the water.

foot may be slid out of connection with the pin when the blowout preventer is rotated about its longitudinal axis, carrying the diagonal braces 116 with it.

A valve controlled side take off conduit is provided in the wellhead equipment so that the flow of fluids from a completed well may be controlled and taken from the well directly at the wellhead where it emerges from the submarine earth formations. As illustrated, a conduit 12S is inserted through a side wall of the rigid conductor casing 38 in a fluid-tight fitting and extends radially therefrom. A remotely operable valve 130 is connected to the conduit in line with a second conduit 132 to which a pipe line 134 is connected. The conduits 12S and 132 may be cast into the concrete base 36 and the valve inserted in a recess formed in the base and covered with a water-tight cover 136.

Control lines

138 and 140 for the valve are passed through the cover through water-tight connections so that the valve and conduits will be protected from damage and from corrosion.

The pipe line 134 preferably is a flexible line such as a steel-reinforced rubber hose which can ybe brought to the surface so that its upper end may be secured to a buoy 142 until such time as the well is to be placed in production. At this time the pipe line will be connected to suitable separators and tanks on a floating vessel or will be extended by flexible or rigid line to reach along the bottom of the water to shore installations.

As stated previously, after the well site has been selected and the drilling vesesl anchored in place the wellhead control apparatus is assembled on-its base and supported by pontoons at the surface of the water. The ends of the control lines are attached to their respective apparatus in the wellhead assembly, and the end of the flexible conductor casing 72 is secured to the top of the blowout preventer. The control lines are reeled on appropriate drums aboard the vessel so that they can be payed out as the wellhead assembly is su'bmerged. For example, the air and water lines from the pontoons are reeled around the drum 144 which has incorporated with it rotary connections which permit the lines to be continuously connected to appropriate sources of pressurized air and water aboard the vessel.

The surface end of the flexible conductor casing is passed upwardly through the opening 18 in the bottom of the hull of the vessel and through an opening in the platform 20 so that it may be supported by the derrick.

The wellhead assembly is now ready to be lowered to the bottom of the water and xed there at the drilling site. This is accomplished by injecting water into the pontoons until their buoyancy decreases sufficiently to permit the wellhead assembly to sink slowly through the water. As the submerged depth of the wellhead assembly increases, sections of flexible conductor casing are added to the conductor casing string so that the upper end of it remains above the water. The upper end of the flexible conductor casing string may be held on the platform 20 by slips while a section is being added to it.

Buoyant elements 146 are affixed to the flexible conductor casing string at spaced-apart intervals as it is These buoyant elements are proportioned to give the flexible conductor casing string substantially neutral buoyancy in the water. Preferably, the buoyant elements are made of a water-impervious, relatively rigid cellular material such as a plastic foam. The presently available commercial material called Styrofoam is suitable for this purpose. The buoyant elements may be attached to the flexible conductor casing string within the hull of the vessel as the sections are made up, and of course if they are attached to the string above the platform 20 the platform will subsequently be removed to permit the flexible conductor casing string together with the attached buoyant element to pass downwardly through the opening 18 in the bottom of the hull.

The hydraulic control lines for the blowout preventer 62 are payed outfrom reel 68 and secured along the side of the flexible conductor casing string as it is made up and lowered into the water. The release line for the pontoons is also brought aboard the vessel and reeled on an appropriate drum, not shown.

As the wellhead assembly approaches the bottom of vthe water, the length of rigid conductor casing 38 projecting from the bottom of it comes in contact with the submerged earth formations. In muddy andsilty hottoms the weight of the apparatus can be used to cause the rigid conductor casing to penetrate some distance into the bottom. However, in order to insure a firm connection with the earth formations it is preferable to make the rigid conductor casing string of such length that it will penetrate through the silt and into contact with the firmer subterranean formations. When downward progress of the wellhead assembly is stopped by the contact of the lower end of the rigid conductor casing string with the firmer earth formations, a string of tubing to the lower end of which jetting nozzles are attached is inserted into the upper end of the flexible conductor casing string and projected downwardly through the wellhead control equipment and the rigid conductor casing string until the nozzles are proximate the earth formations. A jetting fluid under pressure is forced down the tubing to jet the rigid conductor casing string into the earth formations. letting will continue until the base 36 is seated on the earth formations at the bottom of the water. Where the bottom is relatively firm, the engagement of the base with the bottom will stop the further downward travel of the wellhead assembly. However, if the bottom is mushy, the wellhead assembly is held in this desired position by the action of the pontoons with the assistance of the derrick supporting the upper end of the flexible conductor casing string. It is desired to keep the wellhead assembly directly on the bottom and positioned so that the upper end of the rigid conductor casing string will not extend above the earth formations and be exposed in the water, nor will the wellhead assembly be sunk into and be covered by silt or mud.

When the base has been landed, the jetting tubing is removed from the casing string and cement tubing and packers inserted therein. Cement is forced down the cement tubing in a manner .analogous to the usual practice to cement the rigid conductor casing string'to the submerged earth formations. This will assist in holding the wellhead assembly in position, as well as prevent the topmost layers of earth from caving into the hole.

When the rigid conductor casing string has been cemented and the cement tubing withdrawn from the casing, a self-contained drilling mechanism 148, such as a mud-driven turbo drill or an electric drill, is inserted into the flexible conductor casing string, through the wellhead equipment and the rigid conductor casing string and into contact with the subterranean formations. The upper open end of the flexible conductor casing is closed by a head member 150, which is securely attached to the casing, through which the operating lines to the drilling mechanism will pass slidably in a fluid-tight connection. The drilling mechanism is supported in the derrick by a wire line 152 which is connected to the drum 26. This drum is automatically controlled to take up or let off line to hold constant weight on the bit while compensating for vertical motion of the drilling vessel and for the increasing depth of the bit as it drills into the subterranean formations.

When a mud-driven turbo drill is used, mud under pressure is fed to the drilling mechanism through va flexible hose 154 which also passes through the head member in a slidable fluid-tight connection. In the modification of the invention shown in FIGURE l the hose 154 is run over a pulley 156 attached to the derrick structure in a position albove the end of the flexible conductor casing string. The free end of the hose is connected to a mud pump 158 which will draw drilling mud from the 7 mud tank 160 and force it down the hose to drive the drill turbine.

The mud hose may be made in sections which are added to the string as the drill progresses deeper into the earth. As illustrated, the sections 162 may be stored aboard in a hold of the vessel from which they are lifted out by a crane 164 to be added to the mud hose string as needed. A power-driven winch 166 mounted on the deck is detachably secured by cables 168 to the mud hose before it passes over the pulley 156 so that the free end of the mud hose may be drawn up slack and disconnected from the mud pump when a section is to be added to the string. The winch 166 may also be used to place enough tension on the mud hose string to prevent an excess amount of it from following the drilling mechanism into the hole.

The head member 150 has a connection for a mud Lline 170 through which the mud circulated upwardly fro-m the drilling mechanism will pass from the flexible conductor casing to a shale shaker and screen 172 an-d `thence into the lmud tank. The return mud may, of course, -be treated, inspected and analyzed in conformance with the usual field practice. It will be appreciated that if an electric drill is used the ydrilling mechanism will be supported in the derrick by a constant feed apparatus in a manner analagous to that explained above, and the electrical conductors will be passed through the head members 150 through slidable fluid-tight connections. Mud will be circulated down to the drill and back through the flexible conductor casing and thence to the mud treating apparatus.

The upper end of the flexible conductor casing string may be supported on the platform 20. The flexibility .and buoyancy of the string will permit some motion of the vessel relative to the fixed wellhead equip-ment without placing undue strain on the parts. Alternatively the casing may be supported in the derrick by lines attached to the drum 28 which is automatically controlled to let off and take up line in accordance with the vertical motion of the vessel to prevent it from being placed under stress due to the latter cause.

With the drilling apparatus thus in place and connected to the sources of power aboard the vessel, a hole is drilled into the subterranean formations below the end of the rigid conductor casing string 3S of a diameter large enough to receive a string of surface casing 174. The length of the surface casing string will depend on the nature of the earth formations to which it is to be secure-d, on the depth of the well it is desired to drill, and on the pressures like to be encountered as drilling progresses. This string will, for example, extend 500 feet into the earth. When the hole has reached the desired depth, the drilling mechanism is withdrawn and a string of surface casing is made up aboard the drilling vessel and lowered through the flexible conductor casing string which will guide it through the wellhead control equipment and thence into the rigid conductor casing string 38. It will be appreciated that the surface casing string will be made up from sections in the usual manner and will be progressively lowered through the conductor casing. The upper end of the s-urface casing string is hung yby casing hangers in the rigid conductor casing string so that the upper end of it is adjacent the bottom portion of the wellhead control assembly. Cementing tubing is then run to the bottom of the surface casing string, which is cemented to the earth formations in a manner well known to the art. The cement slurry is placed under enough pressure so that it will be forced into the annular space between the surface casing string and the rigid conductor casing string to a point adjacent the bottom of the base 36. The wellhead assembly will thus be rigidly l secured to the surface casing string and thus held in place in its position at the bottom of the water.

The

pontoons

32 and 34 may now be detached from the base 36 and recovered. This is accomplished by decreasing the buoyancy of the pontoons to place slack in the chains 82 and 8S. The pins 911 and 92 are then withdrawn from the clevis and eye combinations so that the pontoons will be released from their attachment. Water may now be -displaced from the pontoons by compressed air and the pontoons floated to the surface where they may be recovered and cleared from the apparatus. It will be appreciated that under some conditions the pontoons may be released from the base prior to the time the surface casing is set and cemented in place.

The drilling mechanism is now again lowered through the flexible conductor casing string and guided through the wellhead control equipment and the string of surface casing and into contact with the subterranean formations. It is then placed into operation to drill the well. The blowout preventer 62 will assist in maintaining control of the well should conditions require it. As noted previously, the blowout preventer is connected by

lines

64 and 66 to appropriate valves aboard the vessel by which its action may be controlled. The blowout preventer is preferably of the Well-known type which will close around the drill tubing and seal the opening of the well. When a flexible steel-reenforced rubber hose is used for drill tubing, it may be desirable to embed spacedapart sections of a rigid conduit in the inner wall of the flexible tubing so that the blowout preventer may close on the tubing without crushing it. Additionally, a complete shutoff blowout preventer may be connected in axial alignment with the blowout preventer 62 to completely close the opening of the well when the drill tubing is withdrawn from the apparatus.

The well is drilled to the desired depth and completed in accordance with the usual practice. The opening of the well may now be closed by lowering a mass of cement slurry 176 on a wire line 17S to rest in the conical charnbcr 46 of element 40. The cement slurry maybe contained in a plastic sack 180', FIGURE 6, inside of a flexible metal petal basket 182 formed of interleaved spring metal segments, -a device known to the art. The basket will be collapsed about the sack of cement slurry as it is lowered through the flexible conductor casing string and the blowout preventer, and the petals will be expanded when the basket is located in the conical chamber 46 to confine the mass of slurry in this position. The cement slurry will be placed under sufficient pressure to cause it to conform to the shape of the chamber so that when it is set a fluid-tight seal is made.

With the well thus sealed the flexible conductor casing string and the attached blowout preventer may be disconnected from the wellhead control assembly. This is accomplished by placing the upper end of the flexible conductor casing string in the rotary table 22 and rotating it to unscrew the connection 48-50 at the top of the element 40. All of the principal equipment except the element 40 and the base 36 and the connections between them may now be recovered. The control lines 13S and remain attached to the side take off valve 130 so that this valve can be actuated to control the flow of well fluids through the pipe line 134. Hence the well is completely sealed at the bottom of the water and, except for the control lines, and in some instances the pipe line, no apparatus extends substantially above the bottom to be damaged by water forces or solid objects impinging against them.

When the cement plug was set in the element 40 the wire line 178 on which it was lowered had attached to it at spaced intervals along its length guide members 184,. These guide members are proportioned with a circumferential portion of slightly less diameter than the internal diameter of the flexible conductor casing and are secured to the wire line so that they will extend radially from it. When the flexible conductor casing string is detached from the wellhead assembly, the wire line 178 with the attached guides remains secured to the cement plug 176, and the casing is slipped upwardly over the guides. With the casing removed, the upper end of the Wire line is buoyed at the surface of the water so that it may be recovered.

Should it become necessary to gain entrance to the well for cleaning or other purposes, the wire line 178 and the attached guide members 184 serves as a means for guiding the flexible conduc-tor casing string back to the wellhead. For reconnecting purposes a special guide tting 186 is clamped to the lower end of the ilexible conductor casing string. This guide tting has a circum-ferential skirt portion 188 extending downwardly from it and proportioned to slip over the ange 54 and seat upon the conic-ally shaped outer surface 42 of the element 40. The tting has an inner cylindrical extension 190 upon the outer surface of which screw threads are formed to mate with and be received by the screw threads 48 of the element 40. The wire line and guide members will thus guide the lower end of the flexible conductor casing string to the submerged xed wellhead and with the assistance of the depending skirt portion 188 it will be brought into axial alignment with the element 40. The upper end of the flexible conductor casing string is then rotated to engage the screw threads to connect the lowerend of it to the wellhead assembly. When the connection has been made the wire line 178 is severed where itenters the cement plug and the plug is drilled out to open the well so that the appropriate reworking equipment can be guided down through the reattached flexible conductor casing string and into the well. When the reworking of the well has been completed, the cement plug 176 again is'established in the chamber 46 and the exible conductor casing string is removed in the manner explained hereinbefore.

FIGURE 8 illustrates another embodiment of this I1uvention. In this modication, the drilling vessel has an opening 200 placed through the bottom portion of the hull, and axed to its` periphery in a water-tight manner is the end of a vertical open cylinder 202. The cylinder is open to the water at the bottom and extends upwardly into the hull above the water line. A removable platform 204 is placed across the top of the cylinder and above the surface of the Water in it. An opening 206 is formed through lthe deck of the ship in alignment with the cylinder 202, and this opening also is covered with a removable platform 208.

A crane or lderrick 210 is mounted on the deck of the vessel in a position to hoist equipment into and out of the water through the aligned openings in the deck and hull of the vessel and is connected to an automatically controlled hoisting apparatus 212 constructed to let off -or take up the lifting cables to compensate for the vertical movement of the ship and the increasing depth of the drill bit when a drilling operation is in progress. This vessel contains the usual apparatus normally used in a rotary drilling operation.

The wellhead equipment in this modification of the invention is more clearly depicted in FIGURES 9 and 10. A base 214 is fabricated of metal members and is per manently secured upon

cylindrical pontoons

216 and 218. The pontoons are connected together `by conduits 220 and .are attached to sources of pressurized air and water aboard the drilling vessel by

flexible hoses

222 and 224 so that their buoyancy may be controlled from the vessel. A string of rigid conductor casing 226 is secured to the center of the base in `a unitary manner so that its lower end extends below it.

Wellhead control equipment is secured to the top surface of the base and to the upper end of the string of rigid conductor casing. This equipment comprises an element 228 which has a portion 230 of its lower outer surface of conical conguration with the smaller diameter disposed upwardly. A projection 232 extends upwardly from the lower portion, and this also has a generally conical outer coniguration with the smaller di-ameter disposed upwardly. There is an axially disposed opening 234 through the element, in alignment with and having an internal diameter comparable to the conductor casing. A portion of the opening is expanded into a conical chamber 236 -which also has its smaller diameter disposed upwardly. Axially spaced

circumferential grooves

238 and 240 are formed in the exterior surface of the projection. These grooves are proportioned to engage parts of a clamping device 242 which is used t-o detachably secure other portions of the apparatus to the wellhead.

The clamp is marde with two

stages

244 and 246, one superimposed axially on the other. The clamp body has an axial opening 248 through it of suicient internal diameter to receive within it the projection 262. Each stage has four similar power cylinders 250 disposed in a plane and operatively mounted within the body of the clamp to each slidably move a corresponding connecting rod 252 in a direction radial to the longitudinal axis of the opening 248. Each connecting rod is attached to a ram 254, and hence the rams will be moved radially inwardly and outwardly toward and away from the projection 232. The rams are formed as quadrants of a disc in which the radially inwardly portion has been removed to form a circular edge 256 of approximately the same diameter as the base of the

grooves

238 and 240. When the rams are brought together their complementary edges will approach each other closely, and their radially inwardly portion-s will seat Within the grooves and closely approach the base. A ring of packing material 258 of a resilient substance such as rubber is placed on the bottom of the grooves so that the rams will seat in the groove with a Huid-tight connection. Resilient packing material 260 is placed also -on the radial edges of the rams and within the body of the rams as at 262, so that when the rams are forced together the packing material will form a uidtight seal both between the ram quadrants and between the rams and the adjacent interior surfaces 264 of the body of the clamp. Thus, when the rams are forced inwardly to engage the grooves a fluid-tight seal is formed which will prevent fluids from escaping between the projection 232 and the clamp mechanism. The power cylinders of the clamp are manifolded together and connected by

lines

266 and 268 to the drilling vessel so that they may be operated simultaneously to attach or detach the clamp and the element 228.

Extending from the bottom of the clamp housing is a depending skirt portion 270 which terminates in a flared portion 272 in the form of an inverted funnel. The skirt has a lower interior circumferential surface 274 of a conical coniiguration complementary to the conical surface 230 of the element 228. The skirt is constructed to engage with and seat on the conical surface 230 to assist in bracing the clamp structure on the wellhead and in centralizing the clamp in axial alignment with the projection 232. It also positions the clamp so that the appropriate rams 254 are in alignment with the

corresponding grooves

238 and 240 to enable the clamp to be engaged with and disengaged from the element 228.

A blowout preventer 276 is secured to the top portion of the clamp body and in axial alignment with it, and to the top of the blowout prev-enter is secured the end of a flexible conductor casing string 278. The blowout preventer is connected by

lines

280 and 282 to the drilling vessel for operation therefrom.

A valve-controlled side take off conduit 284 is provided in the wellhead control equipment in communication with the upper portion of the rigid conductor casing string 226. It is connected to a remotely controllable valve 286 which in turn is connected to a conduit 288 to which the pipe line 29) is attached. The

flexible control lines

292 and 294 for operating the valve are reeled around an appropriate drum aboard the drilling vessel, and the end of the flexible pipe line is buoyed to the surface so that subsequently it may be retrieved land l l connected to separating equipment and tanks aboard a vessel or to a land installation.

The wellhead control equipment is assembled at the surface of the water and floated on its two pontoons to a position above the well site. The various -control lines are fastened to the appropriate units of the wellhead equipment, and they are arranged aboard the vessel so that they may -be payed out as the wellhead assembly is lowered through the water. Prior to lowering, the iblowout preventer together with the lower end of the flexible conductor casing string is attached to the element 228 through the action of clamp 242. The upper end of the flexible conductor casing string is passed upwardly through the opening 200 in the hull of the vessel and extends upwardly through an opening in the platform 204.

The wellhead control assembly is now lowered through the water by controlling the buoyancy of the pontoons from aboard the vessel through the

lines

222 and 224. As the wellhead assembly sinks, additional sections are added to the flexible conductor casing string 278 so that the upper end of it remains within the hull of the vessel. Buoyant elements 296 are positioned along the length of the flexible conductor casing string as it is made up` These buoyant elements may, as mentioned heretofore, be made of a relatively rigid cellular material, such as plastic foam. The buoyant elements may be substantially toroidal in form and be made in sections to be put together circumferentially around the flexible conductor casing string. They are then secured together and to the casing so that they will remain in place as they become submerged in the water and distribute their buoyant effect along the length of the casing string. In the instant modification of the invention it is preferable that the conductor casing string be given a positive buoyance for a purpose to be described hereinafter.

The control lines to the clamping device 242, and the lines to the blowout preventer, may be secured to the side of the flexible conductor casing string as it is made up, and are wound on

appropriate drums

298 and 300 respectively aboard the vessel. Appropriate valves are placed in the control lines so that the submerged apparatus :can be operated from aboard the vessel.

The Iwellhead control assembly is lowered until the bottom of the rigid conductor casing string contacts firm submarine earth formations, after which the rigid conductor casing string is jetted in until the

pontoons

216 and 218 rest on the earth formations at the bottom of the water. In silty or muddy bottoms the pontoons may be permitted to sink into the bototm until the base 214 is substantially even with the surface of the earth formations at the bottom of the water. The penetration of the pontoons into the bottom may, of course, be controlled by regulating their buoyancy.

As the wellhead control assembly is landed, a length of rigid casing 302 is added to the topmost portion of the flexible conductor casing string in a position to extend through the opening in the platform 204 and for some distance above and below the platform as illustrated in FIGURE 8. A gimbal mounting 304 is positioned on the platform and circumferentially surrounding the section of rigid conductor casing. This section of casing fits slidably within the gimbal mounting so that it may move longitudinally relative thereto as the ship is displaced vertically by the action of the water. Roller bearings 306 may be placed in the radially inwardly face of the gimbal mount so that the casing section may slide through it with minimum friction. The positive buoyancy `of the flexible conductor casing will assist in retaining the rigid section 302 within the gimbal mounting, and the top of the flexible conductor casing string may be additionally supported from the derrick by an automatically operated device to compensate for vertical movement of the vessel, analagous to that discussed with reference to FIGURE l. A flange 30S is placed on the topmost portion of the rigid section to assist in preventing it from disengaging with the `gimbal mount. This arrangement permits the drilling vessel to move with the water with the minimum displacement of the upper end of the flexible conductor casing string. With the apparatus thus assembled, the rigid conductor casing string is cemented to the earth formations it penetrates.

In this modification of the invention, dri-lling is accomplished by rotating a string of drill tubing 310 by a rotary table 312 mounted on the platform 208. The string is made up in the derrick `from the deck of the vessel in a manner analagous to that commonly used in oil field practice and inserted into the upper end of the flexible conductor casing string, which guides it down to the submerged wellhead control equipment. The drill string is extended downwardly until the bit 314 is in contact with the submerged earth formations. Drilling mud is pumped down the drill tubing from the mud tank 316 through a swivel 318 and returns through the flexible conductor casing string, from which it flows through a connection 320 in the drilling head assembly 322. The mud is reconditioned and returned to the mud tank for recirculation.

A bore hole is drilled below the end of the conductor casing string to accept a predetermined length of surface casing 324 which is inserted into the bore hole and cemented in place and to the conductor casing string, in a manner described heretofore, to anchor the wellhead control equipment to the well.

When the well has been drilled to the desired depth, a cement plug is set in the conical chamber 236 of the element 228. The cement plug is let down into the chamber on a wire line which has guide elements for the flexible conductor casing string attached to it in the manner described heretofore.

When the cement plug is set, the clamp 242 is released from its engagement with the element 228 by remote operation from the floating drilling vessel. The flexible conductor casing string, together with the blowout preventer and clamp attached to the end of it, is withdrawn from the water and onto the drill-ing vessel. The air and water lines to the pontoons may now be severed at the wellhead and reeled aboard the vessel.

As described heretofore the side take off valve 286 is operated through the

lines

292 and 294 to control the flow of fluids from the producing well. It will be appreciated that when the vessel leaves the drilling site these control lines will be disconnected from the vessel,

and supported at the surface of the water by a buoy 326 so that they may subsequently be retrieved and conneted to a suitable power source to again control the va ve.

When it is desired to reopen the well for reworking or other purposes, the clamp 242 is attached to the lower end of the flexible conductor casing string which is guided down to the wellhead on the wire line attached to the element 228 in the manner described heretofore with relation to FIGURES 5 and 6. As has been noted previously, projection 232 is of a generally conical configuration with the smaller diameter positioned uppermost. Thus as the depending skirt 270 of the clamp body approaches the fixed wellhead equipment it will be guided over the upper end of the projection, assisted by the flared portion 272, and thence proceed downwardly along its conical outer surface, guiding the clamp body 1nto a position surrounding and in axial alignment with the proJection. When the interior conical surface 274 of the depending skirt portion seats on the complementary conical surface 230 of Ithe element 228, the clamp will be positioned so that the rams 254 are in radial alignment with the

grooves

238 and 240. The clamp is then actuated to close the rams onto the projection 232 to -secure the lower end of the flexible conductor casing string to the fixed wellhead equipment.

An alternative means for reconnecting the flexible conductor casing to the submerged wellhead apparatus is illustrated in FIGURES l1 and 12. In this modification the massof cement slurry 176 which is used to occlude the opening of the well at the element 228 has embedded in it a socket 328 lof drillable tubular material such `as an appropriatesynthetic resin, or soft metal. A centralizer 330` of drillable material is attached to the upper portion of the socket in a position to extend above the mass of cement slurry. The socket and centralizer are incorporated in the assemblage prior to the time the basket of slurry is lowered to the wellhead apparatus. The centralizer element is made with an outside diameter which will permit it to slide through the flexible conductor casing string and associated equipment and t snugly within the opening 234 of the element 228. It is designed to hold the open end of the socket 328 centralized within and in axial alignment with the opening 234. The upper surfaces of the centralizer element and socket are formed with a conical configuration 331 to assist in guiding apparatus into the socket. When the cement is positioned in the conical chamber 236 and is set, the socket will be xed rigidly in its axially aligned position.

The wire line 332 by which the basket of cement slurry was lowered into the chamber 236 has guide members 334 secured along its length in a manner similar to that of the guide members 184 described heretofore. However, the guide members 334 have an external diameter which will permit a string of pipe or tubing 336 to be slid over them. The wire line and guides are employed to guide the lower end of the string to the submerged wellhead and into the socket 328. The inside diameter of the socket is large enough to receive freely the end of the string 336.

Flexible packing elements

338 and 340 are aflixed to and positioned circumferentially around the end of the string where it engages the inner wall of the socket to act as centralizers to hold the lower end of the string in axial -alignment with the opening 234 and thus with the element 228.

The string 336 now forms a means connecting the submerged wellhead equipment and the floating drilling platform and can be used as a guide while lowering the end of the flexible conductor casing and its `attached clamp to the submerged wellhead equipment for reattachment thereto. The string of pipe or tubing provides a more rigid guide means than the wire line 332 and hence will assist in guiding the lower end of the exible conductor casing and its attached equipment more positively into axial alignment with the submerged element 228, especially when rough water or strong ocean currents lare present at the drill site. Obviously guide elements similar to the elements 184 described heretofore may be attached to the string 336 at intervals along its length, in a manner similar to that described in relation to FIGURES 5 and 6, for guiding the exible conductor casing string to the submerged wellhead. However, if the apparatus of the present modication is employed, these guide means may be dispensed with by using a blowout preventer, such as the blowout preventer 276 described hereinbefore, as part of the assembly attached to the lower end of the exible conductor casing string when it is lowered for reattachment to the submerged wellhead.

In accordance with this latter procedure the blowout preventer 276 is closed lightly upon the string 336 when the flexible conductor casing is to be lowered for reattachment to the submerged wellhead, in a manner to permit the blowout preventer and the equipment connected to it to slide downwardly along the string without permitting appreciable lateral motion of the parts. Thus the string will guide the clamp 242 to the submerged element 228 and substantially in `axial alignment with the latter. The depending skirt portion 270 will perform the function as explained hereinbefore of `centering the clamp over the projection 232 and in radial alignment with the

circumferential grooves

238 and 240, so that the clamp rams can be closed to attach'the flexible conductor casing string to the submerged wellhead.

The modification of apparatus exemplified in FIG- URES 11 and l2 lends itself to a further alternative means for reattaching the flexible conductor casing string to the submerged wellhead equipment. In this alternative, the `blowout preventer 276 is again included in the apparatus attached to the lower end of the liexible conductor casing string. The blowout preventer is closed tightly upon the string 336 and adjacent its lower end prior to the time the string i's lowered along the wire line guide. Enough of the lower end of the string 336 is left projecting below and beyond the clamp body so that the lower end of the string may be received within a socket 328 Without interference from the equipment attached above it. The lower end of the flexible conductor casing string together with its associated equipment, is lowered together with the string 336, and the wire line guide means will direct the end of the string into engagement with the socket. When this engagement has been accomplished, the blowout preventer 276 is opened by remote control from the oating drilling platform a suiiicient amount to permit the lower end of the exible conductor casing string and its associated equipment to slide down the remaining length of the string until the clamp device 248 is positioned to engage and be affixed to the submerged element 228.

As has been explained hereinbefore, after the lower end of the exible conductor casing string has been reattached to the submerged wellhead equipment the wire line, which was used to lower the basket assembly of cement slurry into place to occlude the opening of the well and which subsequently functioned as a guide means for reattaching the flexible conductor casing string to the submerged wellhead equipment, is severed and the cement plug is drilled out to reopen the well.

It is lapparent from the above description of the several exemplary embodiments of the apparatus employed in the method of this invention that it achieves the objects set forth at the beginning of the specification. It is obvious that other modifications than those illustrated may be made employing the inventive concept without departing from it; therefore it is desired that this invention not be limited by the specific exemplary embodiments illustrated herein, but that it include all equivlaents within the scope of the appended claims.

I claim:

1. An offshore structure for carrying out Well operations generally above submerged wellhead means, said structure adapted to be positioned at a selected offshore location in a manner sufficiently stationary to carry out operations wherein pipe means projecting generally upwardly from submerged wellhead means may be engaged generally above said submerged wellhead means at two vertically displaced levels, said structure comprising:

an operating deck having a vertical rst opening therethrough of a size suiiicient to pass well tools and equipment therethrough,

an auxiliary lower deck positioned below said operating deck, having a vertical second opening therethrough of a size suiiicient to pass well tools and equipment therethrough, and in general vertical alignment with at least a portion of said first opening,

first pipe-engaging means supported by said operating deck and arranged in general alignment with at least a portion of said first opening in said operating deck,

second pipe-engaging means, independent of submerged wellhead means over which said structure is adapted to be positioned, carried by said auxiliary deck, and adapted to be positioned in general alignment with at least a portion of said second opening in said :auxiliary deck,

said second pipe-engaging means being movably positioned relative to said auxiliary deck for movement into and out of general alignment with at least a portion of said second opening in said yauxiliary deck, and

platform means, interposed 'between said second pipeengaging means and said auxiliary deck for `supporting said second pipe-engaging means, said platform means being removable from placement extending at least partially across said opening.

2. The offshore structure of claim 1 wherein -said offshore structure comprises a vessel continuously floating while carrying out said Well operations, said vessel buoyantly supporting both said operating deck `and said auxiliary deck.

References Cited by the Examiner UNITED STATES PATENTS CHARLES E. oCoNNELL, Primary Examfnr.

R. E. FAVREAU, Assistant Examiner.

Claims

1. AN OFFSHORE STRUCTURE FOR CARRYING OUT WELL OPERATIONS GENERALLY ABOVE SUBMERGED WELLHEAD MEANS, SAID STRUCTURE ADAPTED TO BE POSITIONED AT A SELECTED OFFSHORE LOCATION IN A MANNER SUFFICIENTLY STATIONARY TO CARRY OUT OPERATIONS WHEREIN PIPE MEANS PROJECTING GENERALLY UPWARDLY FROM SUBMERGED WELLHEAD MEANS MAY BE ENGAGED GENERALLY ABOVE SAID SUBMERGED WELLHEAD MEANS AT TWO VERTICALLY DISPLACED LEVELS, SAID STRUCTURE COMPRISING: AN OPERATING DECK HAVING A VERTICAL FIRST OPENING THERETHROUGH OF A SIZE SUFFICIENT TO PASS WELL TOOLS AND EQUIPMENT THERETHROUGH, AN AUXILIARY LOWER DECK POSITIONED BELOW SAID OPENING DECK, HAVING A VERTICAL SECOND OPENING THERETHROUGH OF A SIZE SUFFICIENT TO PASS WELL TOOLS AND EQUIPMENT THERETHROUGH, AND IN GENERAL VERTICAL ALIGNMENT WITH AT LEAST A PORTION OF SAID FIRST OPENING, FIRST PIPE-ENGAGING MEANS SUPPORTED BY SAID OPERATING DECK AND ARRANGED IN GENERAL ALIGNMENT WITH AT LEAST A PORTION OF SAID FIRST OPENING IN SAID OPERATING DECK, SECOND PIPE-ENGAGING MEANS, INDEPENDENT OF SUBMERGED WELLHEAD MEANS OVER WHICH SAID STRUCTURE IS ADAPTED TO BE POSITIONED, CARRIED BY SAID AUXILIARY DECK, AND ADAPTED TO BE POSITIONED IN GENERAL ALIGNMENT WITH AT LEAST A PORTION OF SAID SECOND OPENING IN SAID AUXILIARY DECK, SAID SECOND PIPE-ENGAGING MEANS BEING MOVABLY POSITIONED RELATIVE TO SAID AUXILIARY DECK FOR MOVEMENT INTO AND OUT OF GENERAL ALIGNMENT WITH AT LEAST A PORTION OF SAID SECOND OPENING IN SAID AUXILIARY DECK, AND PLATFORM MEANS, INTERPOSED BETWEEN SAID SECOND PIPEENGAGING MEANS AND SAID AUXILIARY DECK FOR SUPPORTING SAID SECOND PIPE-ENGAGING MEANS, SAID PLATFORM MEANS BEING REMOVABLE FROM PLACEMENT EXTENDING AT LEAST PARTIALLY ACROSS SAID OPENING.