US3435906A - Method and apparatus for offshore deep drilling from a floating platform - Google Patents

Description

April 1, 1969 y l K MNICOLSON v 3,435,905 i .METHOD AND AFPABATUS FOR v@FFSHORE DEEP DRILLING FRM` Av FLO'IINGv PLATFORM Filed A ug. 24.1967 sheet' 4/ of 5 mvENToR KINGSLEV M. N/COLSON BYQMLL* 435,906 Tus FOR OFFSHORE DEEP DRILLING FROM A FLOATING PLATFORM l K. M. NICOLSON April l, 1969 METHOD AND APPARA Sheet Filed Aug. 24, 1967 FIGB INVENTOR K/NGSLEV M. NICOLSON ATT '1 RNEYS 196:9 K.l M. NlcoLs'oN 3,435,906

METHOD AND APPARATUS FOR OFFSHORE DEEP DRILLING FROM A FLOATNG PLATFORM Filed Aug. 24. 1967 April 1, 1969 i K. M.N|coLsoN 3,435,906

METHOD AND APPARATUS FOR OFFSHORE DEEP DRILLING FROM A FLOATING PLATFORM Filed-Aug. 24, 1967 Sheeil 4 of 5 IN V ENTOR K/NGSLEV M. N/coLso/v April 1, 1969 K. M. NlcoLsoN 3,435,905 METHOD A-ND APPARATUS FOR OFFSHORE DEEP DHILLING FROMA FLOATING PLATFORM Filed Aug. 24, 1967 4 l -sheet f of 5 als sla

a 382 mvErlsToR i 382 FIG 10 /r//vGsLsr u. /v/co/.soN

FIG 9 Missa' BY t United States Patent O Int. Cl. E211) /02, 3/08 U.S. Cl. 175--7 9 Claims ABSTRACT 0F THE DISCLOSURE A continuous length of drill pipe wound on a reel is used for drilling and working in an offshore well from a oating vessel through a submerged wellhead axed in a vertical position on the underwater bottom. The drill pipe passes from the reel through a pipe straightener and thence through a gripper hung from the hook on the traveling block in a derrick. The gripper is ope-rated independently of the drawworks operated hook to lower and raise drill pipe in a continuous manner from the vessel into and out of the well bore. The position of the traveling block and hook in the derrick, and hence the corresponding position of the gripper, is governed by a constant weight control in the drawworks to compensate for vertical relative motion of the vessel. The drill pipe has concentric pipe passages throughout its length, one to conduct drilling fluid to a downhole fluid motor which drives the drill bit and the other to return exhausted drilling uid and cuttings from a pump at the bottom of the well to the surface.

This application is a continuation-in-part of my prior application Ser. No. 631,715, led Dec. 31, 1956 The present invention relates to a method and apparatus for drilling a submerged well from a fully floating platform. More particularly, the invention relates to a method and apparatus for drilling a vertical well bore into the underwater bottom whether or not the bottom is steeply dipping and for completing the well by procedures which permit expeditious handling of the drilling and well working tools to accomplish the operation in less time than would be required to drilling methods and apparatus used heretofore.

It is a particular object of this invention to provide a method of drilling a vertical well bore into an uderwater bottom from a fully floating vessel without requiring a template or other guiding means for spudding in the well bore by suspending a drill string from the deck of a fully floating vessel with a substantial portion thereof held in tension when the lower end thereof including a drill bit and a weighted portion of said drill string touches bottom. Then, with only the weighted portion of the drill string exerting thrust on the drill bit the drill string is rotated from the working deck of the vessel. The borehole is spudded in vertically by drilling ahead with the drill bit until a consolidated rock bed or other competent formation is drilled into. Then, at least one conductor pipe is cemented in the borehole before the drill string is disconnected from the borehole.

Another object of the present invention is to provide a method for drilling into an underwater bottom from a fully floating platform without danger of contaminating the body of water with oil or gas encountered in the well bore by establishing pressure control over the borehole with a wellhead on bottom before the borehole penetrates potential `reservoir formations. ln carrying out the method, such well head is set on bottom with all work performed on the working deck of the oating vessel by maintaining continuous engagement between the underwater bottom and the floating vessel after the drill string has been first spudded without templates or other means for guiding the bit into the bottom. In said preferred method of carrying out the invention, an assembled conductor pipe is lowered into the vertical borehole formed in the underwater bottom by the drill bit, but penetration thereinto is limited by assembling a landing ange .to the upper end of said pipe before it is lowered. The conductor pipe is then cemented in position through a drill string extending from the deck of the floating vessel into the borehole; said cementing being performed after a guide assembly is lowered on at least a pair of guide cables so that it slides down along the drilling string extending downward from the working deck into the borehole. The guide assembly is latched to the conductor pipe above said landing ange. Following cementing of the conductor pipe and securing of the guide cable assembly to said conductor pipe, the -interconnection between the drill string and the floating vessel is broken and the guide cables slacked to permit cement around said conductor pipe to set without vertical force -being applied to it through the vessel moving under wind and tide action. Pressure control equipment, including at least one blowout preventer assembly is then lowered along the guide cables after they are again drawn taut between the wellhead and the floating vessel. Said pressure control equipment is desirably coupled to the top of the conductor pipe by a safety joint or other quick-connect joint that requires less than one full rotation of the pressure control means, guide lines or said conductor pipe.

In this connection an individually significant object of the invention entails the detachable connecting of a wellhead assembly to cemented-in conduit .means in response to axial convergence of, and relative rotation between, the wellhead assembly and the conduit means vis--vis a safety joint. This detachable connection enables the wellhead .assembly to be selectively detached from the conduit means and raised in slidable engagement with exible guide means toward support means such as a floating vessel. This connection of the wellhead assembly with the conduit means prevents upward movement of the wellhead assembly and relative rotary movement between the wellhead assembly and the conduit means and also provides a drill pipe passageway in sealed communication with the interior of the conduit means. This drill pipe passageway is controlled, by means of the blowout preventer, `from the support means so that the passageway, from the support means, may be selectively closed off or opened.

In the drilling of `well bores to explore for oil, gas and the like through deep waters, it is necessary either to build a platform extending from the ocean bottom to a level well above the water surface or to drill from a floating platform. It is of course uneconomical to build large fixed platforms unless there is a high probability of nding oil. Accordingly, it is desirable to be able to drill a well 'bore from a mobile platform such as a floating platform. The greater mobility of a fully floating platform makes this type of drilling more attractive than platforms that have a floating foundation partly submerged by vertical anchors. While such restrained floating platforms provide easier drilling conditions, the cost of' vertical anchors makes their use economically unattractive.

While in general it has been proposed to anchor a vessel over a drilling site and then drill into t-he underwater bottom with conventional rotary equipment, such underwater bottoms are seldom level and hard so that adequate pressure control equipment can be set directly on bottom. The function of such pressure control equipment is to maintain hydrostatic pressure in the well bore that will always be greater than that of any -gas or oil encountered therein. Loss of such pressure control is known as a blowout The problem of blowouts is of course a serious one from the standpoint of explosion and lire hazards in land operations. It is even more serious in offshore operations, such as those along the California coast, where any release of oil or lgas could contaminate the ocean so that marine life is destroyed and the adjacent resort beaches ruined. Accordingly, it is considered imperative that adequate and complete wellhead control equipment be established before drilling is permitted in an underwater bottom where contamination of the water is possible.

It has been suggested heretofore that wellhead controls be located on the Working deck of the drilling vessel to give easy access for maintenance and to assure its recovery when drilling is completed. In this system, a conductor pipe runs from the well bore up to the control equipment located on the deck of the surface vessel. This of course requires that the conductor pipe be flexible enough to permit lateral and vertical movement of the surface vessel while drilling. One serious problem in using pressure controls at the deck is that the wind and tide forces on the vessel can put an undue strain on the con- `ductor pipe. Such strain, of course, makes the conductor pipe more susceptible to damage that can result in complete loss of wellhead control. For these reasons, it is desirable to position the wellhead control equipment on the bottom. However, the pressure control equipment is quite expensive and therefore it is desirable that it be possible to retrieve it after the well is drilled.

While it has been suggested heretfore that wellhead control equipment be placed on bottom, the method of initiating or spudding in the borehole, landing of conductor pipe and control equipment, as well as retrieving this equipment as practiced heretofore frequently required the aid of a human diver, or outher auxiliary equipment not forming part of the normal drilling equipment. The cost of diver service, in addition to rig time (.e., rental charges on drilling equipment, drill crew wages, etc.), makes these operations unusually expensive. In general, the cost of a diver service alone may run as high as $800 to $1,000 per day. Additionally, the time that a diver can operate, even in shallow water, is greatly limited by human, physical endurance. In deep waters, it is not feasible to use a diver even if one is required. Additionally, in water bottoms having a thick bed of unconsolidated sediments, diver service cannot be used with diiculty.

For the foregoing reasons, it is necessary and desirable that there be provided a system for drilling a vertical borehole into an underwater bottom irrespective of its slope or hardness and to a depth so that a conductor pipe can be set and cemented in a competent formation with at least an upper portion thereof extending above bottom to receive wellhead or pressure control equipment. (In this sense, competent -means an earth formation, such as a consolidated shale bed, having suflicient compaction to give it strength and being impermeable so that the pipe can be bonded to it with cement.)

In accordance with a preferred method of carrying out the present invention, a drill bit is assembled on the lower end of a conductor pipe having a predetermined weight. The drill bit and conductor pipe are then connected to a drill string through a vertically-reciprocable connection; said drill string in turn is rotated by a gimbaled rotary table positioned below a supporting drill derrick mounted on the working deck of the fully loating platform. The verticaly movable connection permits the entire string to hang freely as a pendulum below the vessel so that even in deep waters only the predetermined weight of the conductor pipe is imposed on the drill bit when the bit l'irst touches bottom. Then wit-hout further guiding thereof, the drill bit is rotated with only said predetermined weight thereon and with a substantial portion of the drill string in tension during spudding-in. By such rotation and holding said drill string in tension above the weighted section the bit and drill string is maintained vertical even on very steeply dipping bottoms. Drilling then continues until the borehole is deep enough to receive the full length of the conductor pipe. A landing ange otherwise serving as a feeler for bottom indicates when the conductor pipe has been drilled deep enough into the bottom. Desirably, this depth is preselected so the conductor pipe will be suiciently long to assure its penetration into a competent formation. After the landing flange has engaged bottom with the conductor pipe attached thereto and extending into the borehole, cement is supplied to the annular space between the conductor pipe and the borehole while connection between the drill string and borehole is maintained. Desirably, this is done without removal of the drill string from the well bore. Alternatively, the conductor or surface pipe may be cemented in the borehole using a cement string guided into the landed conductor pipe through a guide assembly lowered on at least a pair of cables along the drill string while said drill string is still in the well bore. In either method of cementing, said guide assembly is lowered to slide down along the drill string while said string is still in the borehole and to establish a continuity of connection between the deck of the drilling vessel and the conductor pipe in the borehole before cement is injected. This continuity of interconnection between vessel and -borehole just prior to the cementing operation is particularly essential to eliminate human diver service.

When the guide assembly, which desirably includes an enlarged funnel used to guide wellhead pressure control equipment into engagement with the conductor pipe, has been landed and interconnected, the drill string is disconnected from the borehole immediately above the landing ange. Then, the guide cables are released so that cement between the conductor pipe and the borehole may set without danger of the conductor pipe being pulled up by the cables due to action of wave and tide forces on the drilling vessel. Said conductor pipe not only serves to prevent slufling of the underwater sediments into the well bore, but also provides a firm vertical -anchor for blowout prevention equipment connected thereto as drilling proceeds below the cemented section of the conductor pipe down into potential oil and gas-bearing formations.

After said conductor pipe has been cemented in the borehole in accordance with the invention, drilling proceeds to a greater depth through blowout prevention equipment, and other wellhead control equipment, coupled directly to the conductor pipe. Such wellhead equipment is assembled to the conductor pipe by again tightening the guide cables and lowering it along them. Final assembly of said wellhead equipment to the conductor pipe is desirably made through a quick-connect joint, otherwise known as a safety joint, which permits a fluid-tight connection without requiring significant rotation of the guide cables, blowout preventer, drilling head or other equipment that guidably slides down along the cables. In particular, this equipment is not rotated through as much as a full revolution so that the control hydraulic lines and the drilling lluid return lines Will not become twisted during assembly. Thus, the hydraulic control means for remotely operating the wellhead equipment from the vessels deck can be connected prior to lowering of said equipment along the guide cables. At the same time, said guide cables are held nearly staright and vertical between the borehole and the drilling vessel. After assembly of said wellhead equipment and the drilling head, drilling proceeds by guiding a drill bit and the drill string along the guide cables and into the drilling head assembly and the borehole.

The drilling equipment used for the purpose of deepening the borehole may be similar to that used for on land drilling operations wherein a string of drill pipe is made up of sections which are added to the string as the latter is lengthened. A drill bit is connected to the lower end of the -drill string, and the upper end of it passes through a rotary table and is supported by a hook on the .5 traveling block of a derrick. The traveling block is operated by the drawworks to lower the drill string as the borehole deepens and to raise the string to the vessel when it becomes necessary to change the drill bit or for other purposes. When the drill string is being lowered or raised, it becomes necessary to respectively add or take off sections of drill pipe to lengthen or shorten the string. This operation accounts for an appreciable portion of the time spent drilling a well, particularly as the borehole becomes deep and a drill string of many sections of drill pipe is required.

In offshore drilling operations the time factor required for getting a drill string out of a submerged well bore and returning it to the drilling vessel can be of special signilicance if it becomes necessary to disconnect the drilling vessel from the submerged well in time to escape the hazards of an approaching storm or other sudden rough water conditions. It has been suggested that this hazard can be reduced by placing a device in the submerged wellhead apparatus to sever the drill string at that location should an emergency requiring this drastic procedure arise, The severed lower portion of the drill string then drops into the well bore, of course, and must be fished out, if possible, if subsequently the drilling vessel returns to continue operations in the well. Such a severing device is shown in my patent, 2,919,111, issued Dec. 29, 1959, entitled Shearing Device and Method for Use in Well Drilling. The device of this patent is further described hereinafter.

It is an object of the present modification of this invention to provide a novel method and means for accomplishing a drilling operation most expeditiously and for reducing very significantly the time required to lower a complete length of drill string from the floating drilling vessel into the bell bore or to return the drill string to the vessel. In furtherance of this object and to accomplish other purposes which will become apparent hereinafter a string of drill pipe of sufficient length to meet the full depth requirements of a projected well bore is wound on a reel which s mounted on the drilling vessel. The drill pipe is fed off the reel as required and passes through a pipe straightening device and thence through a gripping and pipe feeding apparatus, which latter is mounted on the hook of the traveling block of a derrick aboard the drilling vessel. The pipe rcel and the gripper are each operated by their own indvidual motors, and the rate at which the drill pipe is let off the reel can be coordin-ated with the rate at which it is fed through the gripper to enable the drill string to be lowered or raised smoothly and quickly without producing undue stresses or kinks in the drill pipe. Apparatus for handling a reel of pipe in the above manner and feeding it into a well will in some respects be similar to that shown in the patent to R. V. Cross, No. 3,313,346 issued Apr. ll, 1967, entitled Continuous Tubing Well Working System.

In addition to the pipe handling procedure referred to, which system will be described in more detail as the description of the invention proceeds hereinafter, the drawworks of the derrick aboard the drilling vessel may vbe controlled automatically to hold a substantially constant weight on the drill bit as the latter operates in the well bore. Such controls have been used heretofore for on-land operations to lower the drill bit automatically and continuously as it drills away at the bottom of the well bore. In offshore operations from a floating vessel such a control has added significance in that it can be used to compensate in Whole or in part for the vertical displacement of the drilling vessel in relation to the submerged earth as the drilling vessel moves with the everchanging water surface. By seeking to hold constant weight on the bit the drawworks will operate to lengthen or take up the lines reeved on the traveling block as the drilling Vessel respectively rises or falls with the surface of the water. Thus, the drawworks will operate to hold the hook of the traveling block relatively fixed in position with respect to the bottom of the borehole. A drawworkssuitable for this purpose is shown in the patent to William Fischer, No. 2,945,675 issued July 19, 1960, entitled Drawworks The present modification of the invention contemplates further the use of a string of drill pipe which contains at least two separate fluid passages, one to conduct drilling fluid to a downhole fluid-driven motor which operates the drill bit and the second passage to return the drilling fluid from the bottom of the borehole to aboard the drilling vessel. Thus the drilling fluid is entrained within the drill string throughout substantially its entire travel from aboard the drilling vessel down into the borehole and back to the drilling vessel. Both passages are continuous throughout the length of the drill string, and hence Iboth passages follow the drill bit as it deepens the well bore. A pump may be placed on the lower end of the drill string to assist the return circulation of the exhausted drilling fluid and the cuttings entrained with it. This pump also will serve to control the pressure of the drilling fluid on the earth formations exposed along the borehole and thereby reduce the tendency of the drilling iiuid to fracture the less cohesive earth structures.

In accordance with the concept of this invention, the drilling operation proceeds under full pressure control of the well bore. As disclosed herein, when a string of drill pipe having a single fluid passage through it is used together with guide lines and a submerged wellhead, the drilling fluid is forced downwardly from the drilling vessel through the drill pipe in a manner well known to the art and returns to the working deck through the well bore and thence through a mud return line connected to the wellhead at a point intermediate the blowout prevention equipment and the drilling head. When a continuous reeled drill string of the type heretofore: described is used, the drilling fluid is circulated both into and out of the borehole substantially entirely through the drill string which thus also forms the return conduit from the well bore to the working deck of the vessel.

Upon completion of drilling, if it is desirable to abandon said 'borehole but prevent any possible seepage or other escape of oil or gas therefrom, a cement plug is set in the Well ybore of sufficient length to bond both the uncased portion of the borehole and at least part of the cased section of the borehole. Such abandonment will of course occur where it is decided that production cannot be established, or for other reasons, it is not desired to complete a producing well through this particular borehole. After cement has been spotted in the hole, the well head control equipment is disconnected through said safety joint, or other quick-connect joint, and then lifted by a drill string to the Work deck of the drilling vessel. The guide cable assembly, then in turn, is retrieved either by increasing tension on said guide cables to sever a breakable link between the cemented conductor pipe or landing flange and the guide assembly, or by interconnecting said guide assembly with a portion of a drill `string to lift the guide assembly and sever the breakable link to the cemented conductor pipe.

In accordance with another method of carrying out the present invention, the conductor pipe is drilled into the underwater bottom by a concentric drill string including a plurality of drill collars directly above the bit but below the section of drill string held in. tension from the work deck so that the desired load is applied to the bit when it touches bottom. In accordance with the invention, no other guiding means is used to start said Well bore in the bottom. The conductor pipe then is lowered directly behind said drill string, which opens a pilot hole and then underreams it to expand the hole to a diameter large enough to let the conductor pipe pass into the borehole. The landing iiange assembled to said pipe limits its depth of penetration; in this method the landing liange and guide assembly are assembled to the conductor pipe and 7 the complete unit is lowered from the deck on the guide cables while said drill string is still in the well bore maintaining continuity of connection between the borehole and the deck.

Further objects and advantages of the present inven- .tion residing in the method of its application to drill a vertical hole into bottom without templates or other guiding means while drilling from a floating vessel, in the method of remotely establishing said wellhead control on bottom from the working deck of a drilling vessel and in the method of using reeled drill pipe in a drill string which can be inserted continuously into a wellbore and continuously withdrawn therefrom while working from the deck of a floating vessel will become apparent from the following detailed description of the method and its mode of operation as illustrated by the various forms of apparatus shown in the accompanying drawings which form an integral part of the present specification.

FIGURE 1 is a schematic elevation view of one form of apparatus for drilling into an underwater bottom from a fully floating vessel in accordance with the method of the present invention;

FIGURE 2 is a vertical section of the lower end of the drill string illustrated in FIGURE 1 after the landing flange has been seated on bottom and cementing of the conductor pipe has begun;

FIGURE 3 illustrates the lower end of a conductor pipe including a drill bit attached thereto, at the completion of cementing between the well .bore and the conductor Plpe;

FIGURE 4 is a vertical view, partly in section, illustrating the positioning of the guide assembly after it slides down the drill string and engages the conductor pipe in the borehole with the drill string still connected to the well bore;

FIGURE 5 is a vertical view of the underwater wellhead or pressure control equipment being lowered along the guide cables to engage the safety joint that couples the conductor pipe to said wellhead equipment;

FIGURE 6 illustrates an alternative method for opening a borehole into the underwater bottom with an independent drill string wherein the conductor pipe and guide assembly are preassembled concentric with said drill string for lowering therealong into the borehole as a unit and said unit is held suspended below the drilling vessel on guide cables that lower it to the bottom;

FIGURE 7 illustrates setting of another surface pipe to be cemented within the conductor pipe in the method illustrated in FIGURE 6;

FIGURE 8 illustrates a preferred method of severing the upper end of surface pipe as seen in FIGURES 6 and 7 to permit recovery of the complete safety joint with the wellhead control equipment when the well bore is to be abandoned;

FIGURE 9 is a schematic elevation view of another form of apparatus for drilling into an underwater bottom from a fully floating vessel in accordance with the modification of the present invention in which a continuous length of reeled drill pipe is used;

FIGURE 10 is a schematic elevation view of a combination of apparatus which maybe used at the lower end of the drill string when the drilling apparatus illustrated in FIGURE 9 is employed;l

FIGURE l1 is a schematic illustration of a transverse section through the drill pipe of FIGURE 9 and illustrates the disposition of the concentric tubular conduits;

FIGURE 12 is a schematic illustration of a longitudinal section of a portion of the drill pipe taken along the line 12--12 of FIGURE l1; and

FIGURE 13 is a schematic illustration of the manner in which the lower end of the drill pipe is connected to the assemblage of apparatus illustrated in FIGURE l0.

Referring now to the drawings and in particular FIG- URE 1, there is illustrated a method of drilling a vertical well bore into an underwater bottom that may be steeply dipping from a fully floating vessel 10. As a rst step, vessel 10 is suitably positioned and anchored over the drill site as indicated schematically -by anchor lines 11. After the vessel has been positioned on the drill site, there is suspended through a central well 12 formed in vessel 10 a drill string 14 that includes an assembled section of conductor pipe 13. In the arrangement of FIGURE 1, conductor pipe 13 is to be cemented in hole 15, but is an integral part of drill string 14 that also includes drill bit 17, safety joint 19 and an upwardly extending, reduced diameter section 21 formed of a string of drill pipe. Conductor pipe 13 is assembled to a predetermined length depending on the depth of the unconsolidated sediments, identied generally as 23, and the depth needed to be drilled before a competent formation is found in the solid rock 25. `Conductor pipe 13 is likewise selected to have a predetermined weight that will act as the only weight on bit 17 when the bit rst touches bottom and irrespective of the depth of water between the vessel and bottom. In open Water, vessel 10 will be subjected to periodic rise and fall, as well as pitching and rolling, due to wave and tide action. For this reason, the string of drill pipe 21 includes as an integral part thereof, a splined or sliding sleeve connection 43 that assures that the bit will rest on bottom with only the desired load thereon. In the arrangemnet of FIGURE 1, drill string 14, including conductor pipe 13, is then supported `by vessel 10 through a conventional derrick 27 that includes hook 29, traveling block 31, cable 33 and drawworks 35. In drilling, it is to be noted that templates, pipes or other guide means are not required in accordance with this invention to start and drill borehole 1S vertically into a dipping bottom where the upper end 21 of drill string 14 is held in tension so that the entire string hangs as a compound pendulum below rotary table 39. Drill bit 17 is rotated on bottom by rotary table 39 driven by any suitable power source such as motor 41. Preferably, motor 41 is a rotary hydraulic motor so that the motor can be driven through flexible hydraulic lines with the motor supported on the gimbaled `bearings of rotary table 39. Rotary table 39 is so mounted to permit it to remain level when the vessel pitches and rolls.

For the purpose of indicating the condition when conductor pipe 13 has been drilled to the desired depth, and to limit its penetration a landing flange 45, formed as either a four-armed spider, or as a relatively flat plate of somewhat enlarged diameter, is clamped to the top end of conductor pipe 13. Thus, when conductor pipe 13 has been drilled to the desired depth, the driller will immediately be notified by an increase in torque at the rotary table and/or by a decrease in the weight supported by derrick 27 due to part of the weight of upper section 21 of drill string 14 being supported on flange 45. The drilling of the conductor pipe is desirably accomplished by using sea water as a drilling fluid. In the present arrangement this is illustrated by intake pipe 47 being interconnected to a pump 49 and to drill string 14 through hose 51 and swivel 53. During drilling-in with sea water, there is of course no return of the cuttings to vessel 10.

In the arrangement shown in FIGURES 1 to 3, drill bit 17 has an enlarged diameter and includes a core wiper arm 54 in the center of the bit that keeps the hole open through the center of conductor pipe 13.

When the conductor pipe has been drilled to suicient depth to enter a competent formation, landing ange 45 touches bottom as seen in FIGURE 2. The hole is then conditioned by continued circulation of sea water so that the hole is ushed of debris. After conditioning of the hole, cement is supplied by switching connections of valve 57 to pump cement from the mixing tank 59 through mud pump 49 and into drill pipe 14 through swivel 53 (FIG- URE 1). As best seen in FIGURE 2, cement is cleared from conductor pipe 13 by dropping a ball 61 through a side-opening port or kelly cock 63 connected directly below swivel 53. When ball 61 seats on the top of cement chaser 65, pump pressure, as indicated by meter 50, will be increased to release chaser 65 from its seat in coupling 67 in the drill string lying directly above safety joint 19. Cement chaser 65 then cleans cement Afrom the lower end of the conductor pipe as shown in FIGURE 3. Core wiper 54 stops the downward travel of cement chaser 65 and prevents back flow of cement 69 from well bore 15 into conductor pipe 13. Desirably, enough cement is used so that substantially the entire length of conductor pipe 13 is cemented in the hole, but not enough is used so that cement balls up over the top of landing flange 45.

After the cement is placed around the conductor pipe, a guide assembly, identified generally as 71, is lowered on a pair of `guide cables identified as 73. As seen in FIGURE 1, guide assembly 71 initially hangs in the well 12 of vessel 10 below the rotary table. Guide assembly 71 includes a tubular member or bucket element 75 that gives the assembly substantial weight. The assembly is free to slide down along drill pipe 21 and over the outer portion of safety joint 19 when the guide lines are slacked from cable drums 76 on the vessel. When landed adjacent to, or on top of, landing flange 45, as in FIGURES 4 and 5, bucket member 75 is latched to the lower or stationary portion 77 of safety joint 19 by a pair of latch `members 78 that engage groove 72 in lower member 77. Alternatively, bucket or weight member 75 may latch directly to conductor pipe 13 or to landing ange 45 if so desired. The function of latches 78 is to connect guide assembly 71 to the upper end of conductor pipe 13 by shearable links, such as pins 80. Pins 80 are breakable by an upward pull on bucket 75 of a predetermined magnitude that rotates latches 78 about pivot pins 82. The respective pins 82 pass through corresponding elongated openings formed through the pivoted end portions of the latch members 78. These openings are disposed to permit the latches to slide on the pins toward and away from the latching position as well as to pivot around the pins. A respective spring biases each latch to its latching position. Thus when the bucket member 75 is lowered over the portion 77 of the safety joint the radially disposed projections on the latter displaces the latch members outwardly to permit the bucket assembly to clear such projections until the latch members are in alignment with the groove 72. When the -bucket assembly reaches this position the biasing springs force the ends of the latch members into engagement with the groove. The groove-engaging end portion of the latch members are notched to form a surface complementary to that of the upper radially disposed surface of the groove. This provides a secure engagement between the ygroove and the latches and prevents the latch members from being displaced radially by normal working stresses, as indicated in FIGURE 5. As shown in FIGURES 4 and 5, guide assembly 71 has a pair of arms 79 that extend radially outward from the center line of the borehole to anchor the lower ends of guide cables 73.

As best seen in FIGURE 1, guide cables 73 are normally maintained taut between bottom and floating vessel by a weight 81 hung on sheave assembly 83 below cable drum 76. After bucket 75 of guide assembly 71 has been latched to conductor pipe 13 preferably, the upper portion or barrel section 85 of safety joint 19 is disconnected by retracting the locking sleeve 86 (shown in FIGURE 2) from locking grooves in the stationary portion 77 (shown in FIGURE 5) so that the string of drill pipe 21 forming the upper section of drill string 14 can be raised and racked on the drill deck, ready for further drilling through the lower end of the cemented casing 13. The operation of this safety joint is described more fully in my Patent No. 2,950,929.

From the prior discussion and from the drawings, and especially FIGURE 5, it is obvious that this safety joint enables the wellhead assembly including the blowout preventer 99 to be detachably connected with conduit means 88 and 13 in response to axial convergence and limited 10 relative rotation between the wellhead assembly, which includes safety joint barrel 85, and the aforesaid conduit means which terminates in the safety joint mandrel 77.

As will be appreciated, the flexible guide cables 73 enable this limited relative rotation to take place.

This mode of connection is the obvious mode of operation involved in the coupling of the safety joint mandrel 77 to the safety joint barrel 85, in view of the prior description of the invention and the structure shown on FIGURE 5, which structure is well known in the art.

Those conversant with the art will also recognize from the safety joint structure shown on FIGURE 5 that the connection of the mandrel 77 with the barrel 85 will prevent upward movement of the wellhead assembly, including the barrel and blowout preventer 99, and will also prevent rotary movement between this wellhead assembly and the cemented-in conduit means 88 and 13.

With the operation of the safety joint having been reviewed, the previously interrupted description of the submerged wellhead preparation may now be resumed.

At this time, in accordance with the preferred embodiment of the present invention, guide cables 73 are slacked off so that conductor pipe 13 is left standing free in the well bore and supported on ange 45 while the cement sets. Thus, cement 69 is not worked by the conductor pipe or pulled up by the guide cables while it sets. Alternatively the drill string may remain connected to the conductor pipe after the cement is placed around the latter, the sliding connection 43 functioning to isolate the vertical motion of the vessel 10 from the conductor casing while the cement sets.

After cement 69 has set, conductor pipe 13 is securely anchored in a competent formation along the well bore. Drilling then proceeds through the conductor pipe, in a manner to be explained hereinafter, by drilling up ball 61 and the part of the cement at the bottom of the borehole. In accordance with the method illustrated by apparatus shown in FIGURES 1 to 5 inclusive, the wellhead or pressure control equipment is coupled directly to conductor pipe 13 through safety joint 19 heretofore forming part of the drilling string. In said method, as illustrated in FIGURE 5, the barrel 85, including locking sleeve 86 illustrated in FIGURE 2, of safety joint 19 are assembled below a wellhead assembly, identified generally as 87. While the wellhead or pressure control assembly will vary in accordance with the pressure conditions that are expected to be met in drilling ahead, in the present arrangement it comprises a pair of gate-type blowout preventers (hereinafter called BOPs) 89 and 91 assembled in series to the upper end of safety joint barrel 85. In a preferred form of apparatus for carrying out the invention, lower BOP 89 includes a pair of shearing rams constructed in accordance with my Patent No. 2,919,111, led Dec. 30, 1955. As disclosed in said patent, the opposite sides of the pipe-engaging rams that normally encircle a section of drill pipe, similar to those in BOP 91, as seen in FIGURE 5, are provided with shearing bars that override one another. The purpose of these shearing rams is to provide a system, such that if storm or other hazardous operating conditions require, the drill pipe in the borehole can be cut off at the wellhead without requiring each section of the entire string to be raised, uncoupled and racked before the hole can be abandoned. Such action is of course drastic in that the entire length of drill pipe would need to be recovered if the hole is to be used aagin; such apparatus provides a method for leaving the hole, but at the same time maintains full control of well pressures while abandoning the borehole under emergency conditions.

Upper blowout preventer 91 is of conventional design and may either completely close off the well bore, or grasp the sides of the drill pipe when the opposite rams and 92 are actuated through hydraulic lines 93. Similar hydraulic lines 94 permit control of BOP 89 from the deck of vessel 10.

Immediately below blowout preventer 89, there is provided a mud lill-up line connection identified generally as 95. A valve 97, hydraulically operable through line 96 permits drilling liuid to be added under pressure to the well bore when drill pipe is out of the borehole. For additional safety in the operation of wellhead assembly 87, there is included another pressure controlled full hole blowout preventer 99 connected directly to and above BOP 91. BOP 99 is operable through line 100. By this arrangement of BOPs 99, 89 and 91, it is possible to hold control of the well erven if control of one of the BOPs is lost by accident.

Above BOP 99, there is positioned a drilling head 101 whose function is to maintain a hydraulic seal around the rotating drill pipe; said drill pipe not only rotates but also reciprocates therein due to rise and fall of vessel due to waves. Drilling head 101 likewise places a back pressure on drilling fluid returning from the borehole around the outside of drill pipe 21 and forces said drilling uid to flow back to the deck of vessel 10 by way of mud return line 103. Control of the back pressure on drilling fluid returns is by a packing locked by hydraulic pressure applied through line 104. The returned drilling uid of course contains the cuttings from the formation being drilled. These can be tested by conventional gas and chip analysis methods. As indicated, return mud line 103 is connected through a side-opening lange member 105 positioned directly below drilling head 101.

As indicated above, various combinations of blowout prevention equipment, either of the full hole, or drill pipe engaging types may be assembled between the top of the cemented conductor pipe and the drilling head. However, desirably this entire assembly is made on the deck of vessel 10 or in the well 12 through the vessel and then lowered on a section of drill pipe 21A, as shown in FIGURE 5. In positioning this equipment through center well 12 of the drilling vessel an upper and lower pair of guide arms, indicated as 107 and 109 respectively, slidably engage the pair of guide cables 73. A spearing section of drill pipe 21A, preferably having a bull nose portion 111, extends downwardly through the entire wellhead assembly 87 and below safety joint barrel 85. In lowering assembly 87, rams 90 and 92 of upper BOP 91 are closed around a recessed collar portion 102 positioned a xed distance above bull nose 111.

As indicated schematically in FIGURE 5, bull nose 111 is guided along cables 73 by guide arms 107, 109 so that even with ship 10 rising and falling in the water, the wellhead assembly and in particular barrel 85 of safety joint 19 is guided over mandrel 77 of safety joint 19 by funnel 113 above bucket member 75. For this purpose, a funnel arrangement 113 has a suitably enlarged diameter that is formed as an integral part of guide assembly 71. Thus, with guide cables 33 again drawn taut, wellhead assembly 87 slides down said guide cables while lowered by derriek 27. Through the latching of barrel 85 to mandrel 77 of safety joint, or quick connect unit, 19 a positive connection is made between the wellhead assembly `and the conductor pipe.

As suggested by FIGURE 5, each of the control hoses 93, 94, 95, 96, 100, 103 and 104 is connected to the wellhead assembly before it is lowered to engage the conductor pipe. Preferably, this is also accomplished on deck, although it can be performed directly below the surface of the water as in well 12 in vessel 10. These control lines preferably pass over the side of the vessel 10 and are wound on a reel assembly. In their assembly, the entire bundle is passed over the side and the lower end shed up through center well 12 of vessel 10. Thus, the outer ends of each of the hoses may be attached while the assembly is in the well or on the working deck and above water; then, the entire assembly is lowered along guide cable 73. After the wellhead assembly is connected to the conductor pipe in the manner explained hereinbefore, the rams 90 and 92 of BOP 91 are opened to release 12 the drill pipe 21A, and the latter, together with the attached bull nose portion 111, is raised from the assembly and returned aboard the drilling vessel.

Drilling may now proceed to any desired depth with full pressure control over the well bore and with the wellhead located on the ocean bottom so that if required, for safety of vessel or personnel, the well can be abandoned temporarily without loss of pressure control in the well. In such abandonment procedure, the hoses can be severed and the guide line 73 dropped with only buoys to mark their location at the ocean surface, and if need be, the drill pipe can be severed in the hole without danger of contaminating the ocean waters or the adjacent beaches.

As best indicated in FIGURE 5, after the wellhead is assembled, the drill bit is assisted in entering and leaving the wellhead assembly by another funnel member 117 that is directly connected to upper guide arm 107. Funnel 117 and guide arm 107 are secured directly to drilling head 101. Additionally, the bit is guided by a collar arrangement, otherwise called a bit guide, that surrounds the drill pipe directly above the bit; said bit guide includes a pair of arms that engage and slide down along the guide cables to assist the bit in entering the drilling head.

There is illustrated in FIGURE 6 another method of establishing well pressure control after drilling into the underwater bottom by the method of the present invention. In this embodiment, a hole opener bit arrangement, identified generally as 121, including a pilot bit 123 first touches and penetrates the bottom to open a relatively small hole. Pilot bit 123 is then followed by an underreamer bit 125. In this system of drilling in, a desired length of conductor pipe or easing 127 is supported below the ships center well 12 and is assembled to a landing ange assembly 129 and guide assembly 131, so that `the entire assembly can be hung on guide cables 73 by arms 133. As shown in FIGURE 6, the guide assembly 131 is secured by links 135 directly to landing flange assembly 129, rather than to the conductor pipe, but in the present case flange assembly 129 is welded to conductor pipe 127. The conductor pipe 127, landing flange assembly 129, and guide assembly 131 are all assembled below the rotary table prior to spudding in of the well, and as shown drill string 122 is lowered through conductor pipe 127.

After the borehole has been opened and underreamed to a Sufficient depth and diameter to receive the preassembled length of conductor pipe 127, said conductor pipe and guide assembly 131 are lowered along the drill string in the same manner as guide assembly 71 is lowered along drill string 21 in the arrangement of FIGURES 1, 4 and 5. With the conductor pipe set in the well bore and guide assembly 131 connected to the vessel through cables 73, drill string 122 can be withdrawn to substitute a cement shoe for `bit 121. However, if desired said drill string can include a cement shoe so that the drill need not be removed from the borehole to cement conductor pipe 127 in the borehole. The conductor pipe is cemented in the well bore in much the same manner as illustrated in FIGURE 2. Where a cement tool is used, it is guided into the conductor pipe by a bit guide sliding down the guide cables 73 and into the borehole by funnel 137. Suiiicient cement is of course added to ll the annular space between the side of the well bore and the conductor pipe. Desirably, only enough cement is added at this stage so that the cement does not rise to the top of the conductor pipe as shown in FIGURE 7. As will be explained later in connection with FIGURE 7, this permits ports 141 in landing ange assembly 129 to act as cement openings when another pipe or liner 143 is cemented within conductor pipe 127.

In accordance with the method disclosed in the arrangement of FIGURES 6, 7 and 8, the well bore is drilled to a greater depth before setting of blowout preventers or other wellhead control means. Such an operation is usually undertaken when a knowledge of the geology of the underwater bottom indicates that gas and oil under pressure will not be encountered during the first few hundred feet of drilling. Accordingly, drilling can proceed through the bottom of cemented conductor pipe 127, after that pipe is set to prevent debris or unconsolidated sediments from sloughing into the borehole. In practice, the conductor pipe will be set to a depth of about 50 to 75 feet, the depth of surface casing 143 may be of the order of 300 feet, and usually is deep enough so that a competent formation, such as a thick bed of impervious shale or other non-porous rock is encountered by the borehole. By going deeper into the earth before cementing surface casing 143, a much greater depth and higher pressures can be withstood by the pressure control equipment without danger of high pressure oil and gas accumulations blowing out.

There is illustrated in FIGURE 7 a preferred method of assembling the blowout prevention equipment, as well as the preferred method of cementing the surface casing into the deepened Well bore. As there shown, surface casing 143 extends downwardly to about 300 feet and is run into the well through conductor pipe 127. The upper end of surface pipe 143 preferably includes a cement sleeve 145 that extends axially along the upper end of surface casing 143, Sleeve 145 is tapered at its lower end 147 so that it can be sealed by welding to the outer surface of the surface casing. The upper end of sleeve 145 frictionally engages coupling 149 on the mandrel 277 of a safety joint 219. The purpose of cement sleeve 145, as best seen in FIGURE 7, is to permit ythe upper end of surface casing 143 to be cemented into conductor pipe 127, but to leave an annular space 159 that will not be lled with cement.

As further distinguished from the arrangement of FIGURES 4 and 5, a conically tapered portion of mandrel 277 of safety joint 219 seats within a conical section 157 of landing flange assembly 129 that serves as a tubing hanger for surface casing 143. In this way, casing 143 is supported throughout its length until it is cemented into the well bore as illustrated in FIGURE 7. In the present embodiment, surface pipe 143 is hung in the well bore on safety joint 219 so that the drill string thereabove can be disconnected after cement has been set through cement shoe 151 at the lower end of pipe 143. Pipe 143 is guided into the hole by bit guide 221 that will pass the barrel of safety joint 219 to let it rest above guide arms 133 of guide assembly 131. The upper end of mandrel 277 is sealed against cement by O-rings 161.

Deep drilling is then possible under full pressure control by landing wellhead equipment, identical to that of FIGURE 5, on safety joint 219. This couples the blowout preventers and the drilling head to axially cemented section of surface casing 143. After the desired depth is drilled, it may be desirable to abondon the well bore. When it is desired to leave the well, the surface casing will normally be left in the well bore with cement spotted therein to prevent any possible blowout from the borehole. Then, the entire assembly of wellhead equipment is recovered by severing the upper portion of surface casing 143 opposite annular section 159 between cement sleeve 145 and the casing. FIGURE 8 represents a preferred manner of severing casing 143 with a shaped explosive charge. The tubing can also be cut by a milling cutter run into the casing. Upon severance of the upper end of casing 143, the complete safety joint 219 and the wellhead equipment secured thereto can be withdrawn from within landing ilange assembly 129. After release of the wellhead equipment, the guide assembly 131 can also be recovered in much the same manner as that illustrated in FIGURES 4 and 5. That is, the lines or cables 73 can be tightened to sever pins 163 that hold links 135 to landing flange assembly 129. Desirably, guide assembly 131 is pulled free 'from landing flange assembly 129 by a special tool run into guide assembly 131 on a drill string.

As indicated in FIGURE 8, weight or bucket element 165 of the guide assembly has a pair of diametrically opposed I-slots 167 formed in its upper, inner surface. Slots 167 can be engaged by the lifting tool so that the drill derrick hoist can apply the necessary force to shear pins 163. In this way, only the cemented casing and landing flange assembly 129 are left on bottom.

Where only a single pipe is cemented in the well bore, as in the apparatus shown in FIGURES 1 to 5, the conductor pipe also desirably has a cement sleeve surrounding its upper end. This is best seen in FIGURE 5, where the details of the connection between safety joint 19 and conductor pipe 13 are shown in vertical section. In this arrangement sleeve 88 is welded to conductor 13 at its lower end and slips over the lower coupling end of mandrel 77 of safety joint 19. In this embodiment, severance of conductor 13 within the cement sleeve allows recovery of landing plate 45 as well as safety joint 19.

An embodiment of the invention in which a reel of a continuous length of drill pipe is used in conjunction with complementary apparatus in a novel arrangement aboard the drilling vessel and in the borehole will now be described. In the following description parts of the equipment and apparatus directly similar to like parts illustrated in FIGURES 1 to 8 of the drawings and as described heretofore in this specification will be designated by like numerals.

Thus, FIGURE 9 illustrates the fully floating vessel 10 having a central well 12 and positioned above a borehole 15 formed in the earth formations 23 and 25. As shown in FIGURES 7 and 9, a conductor casing 127 extending be- 10W the landing flange assembly 129 is cemented in the well bore. A string of surface casing 143 extends from the elevation of the landing flange assembly down into the well bore below the bottom of the conductor casing and is cemented both to the well bore and to the conductor casing.

Guide assembly 131 is secured to the landing flange assembly and the guide lines 73 extend upwardly from guide arms 133 to the lloating vessel where they are connected to apparatus which can function to maintain constant tension in the guide lines as illustrated in FIGURE 1. Alternatively, the guide lines may be operably connected to a tensioning system of the type shown in the patent to William Fischer, Patent No. 2,984,455 issued May 16, 1961, entitled, Multiple-Cable Tensioning De- Vice, wherein the guide lines are Wound on respective drums which are connected to a motor, the torque of which can be set to hold the lines at a predetermined tension.

As shown in FIGURES 5, 7 and 9, wellhead components comprising pressure control equipment are secured to the casing cemented in the borehole. Briefly, this equipment includes blowout preventers 89, 91, and 99 and a drilling head 101, all as described heretofore. The arrangement of FIGURE 9 differs from that of FIGURE 5 in that the mud return line 103 shown in the latter is not required for the drilling system illustrated in FIGURE 9 since in this system the mud return takes place through the string of drill pipe. The remainder of the hydraulic control and mud lines connected to the submerged Wellhead indicated in FIGURE 9 are similar to those shown in more detail in FIGURE 5, including the mud lill-up or kill line 95.

In the modification illustrated in FIGURE 9, preferably these lines are gathered into a bundle 300 at a location adjacent the submerged wellhead, and the bundle is Wound on a reel assembly 302 aboard the vessel 10 as described heretofore. At the reel the individual lines of the bundle are spearated and connected to complementary rotary couplings mounted at the axis of the reel. The rotary couplings are, of course, connected in communication with corresponding parts of the apparatus aboard the vessel. For example, the lill-up line communicates through the rotary coupling 304 and the conduit 306 with the pump 308. The inlet ofthe pump is connected through the conduit 310 with a reservoir 312 of heavy drilling mud. This weighted drilling -uid can thus be pumped down into the annulus between the drill pipe and the wall of the borehole to control high-pressure formations after the blowout preventers have been closed to contain the well pressure, all of which is known to the art.

As stated heretofore, the drill pipe used in this modication of the invention preferably is made up of concentric tubular conduits to provide two separate fluid passages through the drill pipe. As illustrated in FIGURE 1l, the drill pipe comprises the inner tubular member 314 surrounded `by the outer tubular member 316. Preferably the inner member has centralizer ns or spacers 318 formed on or made unitary with it and projecting radially outwardly from its outer surface to contact the inner surface 320 of the outer tubular member. The centralizer fins are proportioned to enable the inner tubular member to move longitudinally relative to the outer tubular member as may be required during assembly of the string of drill pipe and to accommodate relative longitudinal displacement of the tubular members as they are wound onto and unwound from the pipe reel or during other manipulation of the drill string. Preferably, each of the separate centralizer fins is of relatively short length, as indicated in FIGURE 12, and sets of fins are spaced in axial alignment along the exterior surface of the inner tubular member 314. Thus, there will be a single annular passage 322 between the inner and outer tubular members.

Referring now to FIGURE 9, a continuous length of drill pipe 324 is found on a reel 326 aboard the vessel 10. When the well bore is being drilled or the well otherwise worked in, an end portion of the drill pipe is unwound from the reel and passed through the pipe bender and level winder 327. Here the pipe is bent into an arc which extends in a smooth curve to the pipe gripper and feeder unit 328. The latter is hung by bails 336 from the hook 29 of the derrick 332.

The traveling block 31 to which the hook 29 is connected is guided in its vertical travel along the tracks 334 by means of guide arm assemblies 3361. Thus the traveling `block and hook are prevented from swaying and hammering against the derrick structure as the vessel rolls and pitches. However, the lgripper mechanism 328 is permitted sufcient universal movement by the hook 29 and bail supports 330 to follow some relative angular displacements between the suspended string of drill pipe and the vessel 10 without causing the drill pipe to bind in its passage through the gripping mechanism or to be kinked or otherwise damaged because of the aforesaid relative displacement.

The pipe gripping and feeding mechanism also includes a pipe bender 338 which receives the arc of pipe extending from the reel assembly and removes the curvature from it so that it will extend in a substantially straight line through the pipe gripper and feeding mechanism and downwardly into the submerged well bore. The unrestrained arc of pipe extending between the reel assembly and the pipe gripping mechanism affords a flexibility in this system which permits the traveling block to move vertically with respect to the vessel 1() and the reel 326 without damaging the pipe or other components of the assembly.

The pipe reel 326 is driven by a motor 341i through an appropriate linkage 342 to let ofic or take up pipe as controlled from the drillers console 344. The pipe bending mechanism 32,7 is driven by its own self-contained motor through the line 346 connecting it with the drillers console, and the pipe gripper and feeder assembly 328 also has self-contained motors connected by the lines 348 with the drillers console. Hence, the rate of feeding of the pipe off the reel 326 can be controlled independently of the rate of feed of the pipe through the pipe gripping mechanism 32S, and the relative rates of feed of these units can be coordinated to maintain a preselected form of unsupported arc of drill pipe between them while accommodating changing differences in elevation between the pipe reel and the gripper mechanism. Preferably the various motors described in relation to FIGURE 9 are hydraulically operated, although it is apparent that other types of fluid-operated motors or electric motors also could be used.

Reference is made to the patent to R. V. Cross, Patent 3,313,346 issued Apr. ll, 1967, entitled Continuous Tubing Well Working System. This patent is directed to a system for handling reeled tubing used for working in a well and illustrates additional details of some of the apparatus useful in the present invention. Reference also is made to the patent to D. T. Slator, Patent 3,285,485 issued Nov. 15, 1966, entitled Apparatus for Handling Tubing or Other Elongated Objects. The apparatus shown in this latter patent is similar to that of the tubing injector of the Cross patent noted above and illustrates a suitable device for use as the gripper and feeder mechanism 328 in the present invention.

Referring still to FIGURE 9, the central and annular concentric passages of the drill pipe 324 are separately connected in communication with respective rotary couplings mounted at 350 on the axis of reel 326. The central conduit 314 communicates through its rotary coupling and the conduit 352 with pump 356, the inlet of which is connected by conduit 358 with a reservoir 360 of drilling fluid.

The outer concentric conduit 316 communicates through its respective coupling at 350 with the conduit 362, which directs the return drilling fluid to the mud treating apparatus 364 from which it flows to the reservoir 360. A choke valve 366, which is controlled from the drillers console 344 through the line 363, is connected in the conduit 3,62. This choke valve permits control of the pressure in the drilling fluid return conduit and can be used to assist in controlling the pressure in the well bore. It will be understood that a check valve or float 314 to prevent suddenly increased well pressure from blowing the drilling fluid out of this conduit.

As noted heretofore, the bundle of control lines from the submerged wellhead illustrated in FIGURE 9 is wound on a reel 302 aboard the vessel 10. The individual control lines of the bundle are separated at the reel and connected in communication with respective rotary couplings mounted at 304 at the axis of the reel. Except for the fill-up line 95, the disposition of which has been described heretofore, the separate control lines are connected through their Vrespective rotary couplings with the control station 370. As will be appreciated in the art, control station 370 includes the pressure fluid pumps and accumulators and the remotely operated valves by which the apparatus of the submerged wellhead, such as the blowout preventers and the drilling head, are operated. The control station 370 is connected by control lines 372 with the drillers console 344 so that the operation of all the apparatus can be controlled remotely from the drillers station.

Referring now to FIGURE 10, there is illustrated schematically a combination of apparatus which comprises a set of well working tools connected to the lower end of the string of drill pipe. The various elements illustrated in this combination are known to the art and hence will be described only insofar as it is necessary to indicate their interrelationship and function in the present invention.

A drill bit 380 at the lowest end of the drill string is operatively connected to and driven by a fluid motor 382` preferably located directly above it. Connected in the string above the motor are drill collars 384 and 386, and above the drill collars is connected a telescoping joint or bumper sub 388. The inclusion of the bumper sub in the assembly permits the drill bit and the components connected directly above it to be isolated from the vertical motion of the upper portion of the drill string within the range of stroke for which the bumper sub is designed. This range may be increased, of course, by placing several bumper subs in series in the string. The bumper subs are of known design which permits relative longitudinal motion while preventing relative rotary motion between the telescoping portions of the device. Thus, when the drill bit is operated against the earth formations at the bottom of the borehole to drill the well deeper, the reaction torque of the motor-driven bit will be transmitted to and resisted by the string of drill pipe.

In one embodiment of the present invention, sufficient capacity for relative longitudinal motion is placed in the bumper subsection of the drill string to isolate the drill bit from the effects of vertical displacement of the upper portion of the drill string when the vessel heaves on the surface of the Water under predetermined normal sea conditions. When this capacity of the telescoping section of the drill string is exceeded, as by suddenly arising abnormal sea conditions, means described hereinafter are provided for operating the drawworks automatically to keep the drill bit at the bottom of the well bore. Also under `some circumstances it may be desirable to omit the telescoping section of the drill string and use the automatic operation of the drawworks alone to keep the bit on bottom.

When the telescoping section 388 is placed in the drill string, a sufiicient weight of drill collars as represented by the drill collars 384 and 386 are connected above the motor 382 and below section 388 to place a predetermined weight on the bit 380. As will be understood in the art, the upper portion of the drill string is lowered to place the telescoping sub at its mid-stroke position when the vessel 10 is at its mid position of cyclical vertical movement so that as the vessel rises and falls it neither lifts the bit off bottom nor increases the weight imposed on it. Thus, the weight placed on the bit is that due to the motor and drill collars connected above it, and this weight remains uniform so long as the stroke of the telescoping joint section of the drill string is not exceeded.

Still referring to FIGURE 10, there is connected above the section 388 a second series of drill collars as represented by the numerals 390 and 392. A sufficient weight of drill collars is added to this portion of the drill string to pull the drill pipe taught enough below the gripping device 328 so that it will not easily be displaced or bowed by subsurface water currents and so that it will feed through the wellhead assembly without binding or hanging up as the drill string is lowered into the well bore.

It will be understood, of course, that the drill collars and telescoping section referred to above have a central interconnected passage through them which permits the drilling fluid to be forced under pressure downwardly from the drilling vessel through the central passage of the drill pipe and the central passage of the aforesaid assembly to the motor 382. After passing through and energizing the motor, the drilling fluid is exhausted through the drill bit and passes into the annulus between the drill string and the wall of the borehole entraining and carrying along with it the drill cuttings. The pressure of the drilling fluid issuing from the bit forces the exhausted drilling fluid upwardly along the annulus surrounding the drill string and to the elevation of the section of the drill string containing the member 394.

The member394 has openings 396 through its outer wall and communicating with an interior passage 398 which peripherally surrounds a central passage l400 as shown in FIGURE 13. The member 394 is constructed to be connected to the end of the string of drill pipe described heretofore with the peripheral passage 398 of the member in communication with the peripheral passage 322 of the string of drill pipe and with the inner concentric passage 400 of the member in communication with the passage 410 of the central conduit 314 of the drill pipe. As illustrated in this figure, the member 394 is attached by a screw threaded connection 402 to the tubular member 316 while the central tubular member 314 of the drill pipe is telescopically connected to the central tubular portion 404 of member 394. An O`ring 406 or other appropriate packing is used to make a fluid-tight connection between the inner conduits.

Referring still to FIGURE 13, it will be noted that the centralizing fins 318 at the lowest end of the string of drill pipe are welded or otherwise firmly secured to the inner wall 320 of conduit 316 as indicated by the weldment 408. Thus the inner and outer conduits of the drill pipe are secured rigidly together at this location and relative motion between them is prevented in the area where the drill pipe is attached to the remainder of the drill string.

As noted heretofore, when the apparatus of this invention is assembled, a length of drill pipe is wound on the reel 326 suflicient to reach the full depth of the well scheduled to be drilled. During operation of the equipment drilling fluid is pumped from the reservoir 360 through the entire length of the wound and unwound drill pipe to the bit in the well bore. Likewise, the returning drilling fluid flows from the bottom of the well bore through the entire length of drill pipe, wound and unwound, and into the reservoir 360. Thus, if a borehole several thousand feet deep is scheduled and that much drill pipe is wound on the reel, the drilling fluid will be circulated through these several thousand feet of drill pipe from the time the drill bit is placed in operation, even though the borehole may at that time be only several hundred feet deep or to the depth of the lower end of the surface casing 143.

Ordinarily, to accomplish the proper circulation of the drilling fluid, it must have sufficient pressure when it is exhausted from the drill bit to force the exhausted drilling fluid and the cuttings entrained by it back to the drilling fluid reservoir through the several thousand feet of drill pipe. In some geologic environments the subterranean formations at these relatively shallow depths will not have enough cohesion to withstand the pressure placed on them by the drilling fluid, and the formation will fracture and the drilling fluid will be lost into it. Also in other locations the subterranean formation may have suicient permeability to permit the drilling fluid to escape into it under elevated pressures. In any circumstance Where it is not prudent to expose the earth formations in the well bore to such high pressures means are provided by this invention to reduce the pressure at the fact of the borehole while providing sufficient pressure to force the returning drilling fluid back to the drilling vessel.

To this end the element 394 is replaced by a downhole pump and the openings 396 become the pump inlet. The pump is operably connected to a motor 412 which is operated by the pressurized drilling fluid in a manner similar to that of the motor 382. As with the motor 382, the drilling fluid energizes and passes through the motor 412 and continues downwardly through the central passage of the drill string, subsequently energizing the motor 382 as described heretofore. Thus the pump is driven in synchronism with the quantity of drilling fluid passing downwardly through the drill string and operates to draw the returning drilling fluid in through the inlet ports 396 to force it back up the drill string to the drilling vessel. The pump and motor combination is proportioned to return the exhausted drilling fluid at a suflcient rate to hold the pressure of the drilling fluid at the bottom of the well bore at substantially what the pressure would be under the hydrostatic head of the well bore lled with drilling fluid. Thus the higher pressure differential which occurs when the drilling fluid is circulated back through the continuous length of reeled drill pipe without the aid of a pump is eliminated.

The circulation of drilling fluid down through the drill bit and back to the drilling vessel takes place substantially entirely within the string of drill pipe. However, the annulus surrounding the drill string in the well -bore normally will be filled with fluid up to the drilling head 101. As described heretofore, this drilling head is constructed to withstand some fluid pressure while permitting the string of drill pipe to slip longitudinally through it. The quantity of drilling or other well fluids contained in the well above the element 394, or the pump which replaces it, will be in a substantially static condition since the return fluids from the bit are diverted into the drill string below this point. The return circulation pump, when it is used, may be proportioned to place the static column of fluids under a slightly greater pressure than hydrostatic to prevent the sea water from seeping through the drilling head and diluting the drilling fluid.

During drilling operations, as it becomes necessary to change the drill bit or adjust or repair other parts of the downhole apparatus, the drill string is guided between the submerged wellhead and the floating vessel through the cooperation of the guide lines '73 with the guide arm structure 412, which latter is similar in construction and operation to the bit guide 221 of FIGURE 7. Briefly, guide 412 is proportioned to slip over the string of drill pipe and the assembly of drilling tools and rest on the shoulder 414 of the drill bit 380 as the drill string is being lowered and guided to the submerged wellhead. When the bit guide reaches the submerged apparatus it engages and rests on the funnel 117 While the drill string is continuously lowered into the well bore. When the drill string is retracted, the bit re-engages the guide structure 412, and the latter is raised along with the drill string to aboard the drilling vessel.

The apparatus described heretofore is designed to use metal drill pipe and is capable of lowering steel pipe into and retracting it from a well bore at the rate of several hundred feet a minute. While the drill string is being lowered the gripper 328 will act primarily as a controlled brake to prevent the drill string from running away under the pull of its own weight including the drill collars and other tools connected to the end of it. The weight of the drill string vand the load on the gripper device, pipe benders and reels can be reduced by making the drill pipe of aluminum.

On retracting the drill string the gripper 328 will be operated in the reverse direction to raise the string smoothly and continuously from the well bore and back to the vessel while it is being wound on the reel 326. Since it is not necessary to assemble or disassemble sections of drill pipe in the familiar manner as the drilling mechanism is being lowered into or retracted from the well bore, `a significant saving of time is accomplished. As noted previously, this time factor not only is economically advantageous but may be of primary importance when it becomes necessary to disconnect the drilling vessel from the well site. Drilling vessels have been swamped and sunk because of their inability to free themselves from the well site in time to seek shelter from, or be maneuvered to ride out sudden storms.

As mentioned heretofore, the drawworks of this invention may be operated automatically to compensate for the periodic changes of elevation of the drilling vessel in relation to the underwater bottom. Briey and schematically, the drawworks may provide a winch drum 416 connected through an adjustable torquelimiting clutch 418 with an energizing motor 420. The clutch is set to hold a predetermined constant tension in the derrick line 422. If the tension in this line falls below the predetermined value, the winch drum automatically is operated by the motor 420 through the clutch 418 to drive the drum and wind up line until the preselected tension is again achieved. If the tension in the line increases above the preselected value, the clutch slips to let line off the drum until the preselected tension again is achieved. Reference is made in this regard to patent to W. Fischer, Patent 2,945,675 issued July 19, 1960, entitled Drawworks.

The derrick line 422 is reeved through the traveling block 31 to raise and lower the hook 29. In operation of this invention if the hook load is increased above that which will place the preselected tenSQn in line 422, line 20 automatically is let olf the drum 416. If the hook load decreases below that necessary to hold the preselected tension in line 422, winch drum 416 is driven to take up line until the preselected tension again is achieved.

It will be observed from FIGURE 9 that the drill string projecting downwardly from the vessel into the well bore and the weight of the drilling tools attached to the end of the string of drill pipe, except for such weight as is supported by the drill bit in contact with the bottom of the borehole, is supported from the hook of the traveling block. The tension in derrick line 422 may 'be set to support the weight o-f the upper portion of the drill string when the telescoping connection 388 is at its midpoint of travel so that the weight of the drill bit 38() and the motor and drill collars connected directly above it is not imposed on the upper portion of the drill string. If under these conditions the vessel heaves with the surface of the water an amount exceeding the stroke of the telescoping connection 388, the weight of the lowest portion of the drilling tools will be added to that of the remainer of the drill string, increasing the hook -load proportionately. Therefore, line automatically will be reeled off the drum 416 until the drill `bit is again lowered into contact with the bottom of the borehole and the tension in line 422 returns to its preselected value. Conversely, if the vessel 10 falls with the surface of the water an amount exceeding the stroke of the telescoping connection 388 to impose some of the weight of the upper portion of the drill string on the drill bit, the load on the hook 29 will be decreased and the drawworks will operate automatically to take up line on drum 416 until the tension in line 422 and therefore the load on the hook 29 return to the preselected value.

Under conditions of fairly quiet water is possible to drill a well bore successfully relying on the automatic operation of the drawworks to keep the drill bit in proper engagement with the bottom of the borehole. However, under rough water conditions and particularly in environments exposed to sudden storms it is advisable to include telescoping sections in the drill string.

As noted heretofore, in accordance with the present invention a vertical well bore is drilled into the underwater bottom, a casing set in it and a wellhead attached to the casing in accordance with the procedures illustrated in FIGURES l to 5, inclusive or in FIGURES 6 and 7, which procedures are fully described in the present lspecification. In pursuance of these procedures a rotary table as illustrated by the table 39 of FIGURE 1 is used to rotate the drill string to drill the borehole in a manner familiar to the art. In accordance with the present modification of the invention, the rotary table is placed on a removable platform, indicated by the dashed lines and the numeral 424, FIGURE 9, which bridges the deck opening 426 of the central well 12 of the drilling vessel 10. The rotary table and platform supporting it are removed from the top of the well 12 after the wellhead has been secured to the submerged Well opening. At this time, of course, the drill string 21 will have been retracted to aboard the vessel and the swivel 53, FIGURE 1, will have been removed from the hook 29. Thus, with the well 12 cleared as shown in FIGURE 9, the gripper and feeding device 328 is hung from the hook 29 by the bails 330 to receive the drill pipe 324 as described heretofore.

The hydraulic lines 348 are connected to the gripper device 328 by quick-connect couplings 428. Preferably this connection is not made until after the gripper device 328 is mounted on the hook 29 thus preventing the hydraulic lines from becoming entangled or otherwise damaged as a `crane is maneuvering the gripper device into position. Slabsequently, the hydraulic lines are attached to connect the gripper mechanism to the control station 344.

The foregoing description presents a method and apparatus for drilling vertical well bores into a sloping or otherwise underwater bottom from a floating vessel and for expeditiously completing the well to a scheduled depth using a continuous length of reeled drill pipe in conjunction with downhole motor-driven drilling tools. It will be apparent that various modifications and changes can be made in both the described method and apparatus without departing from the` present invention. Accordingly, all such inodications and changes falling within the scope of the appended claims are intended to be included Ithere- 1n.

I claim:

1. The method of drilling a well in an lunderwater location from a floating vessel, comprising the steps of: lowering a landing base from the vessel by means of a shouldered conductor pipe to rest the landing base on bottom, the conductor pipe having a bit at its lower end, drilling a portion of the conductor pipe into the bottom formation by means of a tubular member connected to said conductor pipe and extending from the vessel, lowering an apertured guide frame by means of a pair of cables extending from the vessel over the tubular member and over the upper end of the conductor pipe to rest on the landing base, disconnecting lsaid tubular member from said conductor pipe, guiding the lower end of a continuous string of drill pipe having drill tools including a drill bit operatively attached to the lower end thereof into the upper end of said conductor pipe by means of said cables extending between the vessel and the said frame while controllably unwinding said continuous string of drill pipe from a reel aboard said vessel, lowering said drill pipe and drill tools through said conductor pipe while continuously controllably unwinding said drill pipe from said reel until said drill bit is in contact with the earth formation below said conductor pipe, providing means on said vessel operatively engaging said drill pipe to adjust automatically the vertical relationship between .said vessel and the portion of said drill pipe extending below said vessel to compensate for relative vertical motion between said vessel and said earth formation to thereby maintain said drill bit in contact with said earth formation as said vessel moves vertically with the surface of the water, and operating said drill tools from said vessel while controllably unwinding said drill pipe from said reel and lowering said drill pipe from said vessel to thereby form a b'orehole extending below the lower end of said conductor pipe.

2. The method of working in a submerged well bore from a floating vessel, which well bore has casing affixed therein and wellhead apparatus aflixed to the top of said casing comprising positioning a floating vessel over a submerged well site, providing on said vessel a reel of a continuous length of drill pipe, providing means'for controllably progressively unwinding and winding lsaid length of drill pipe off of and onto said reel, providing hoist means aboard said vessel together with a traveling block and hook mounted therein and with associated drawworks for raising and lowering said traveling block and hook, supporting from said hook adjustable .gripping apparatus for gripping a portion of said drill pipe .unwound from said reel with said gripping apparatus being operable to lower and raise the unwound end portion of said length of drill pipe from and toward said vessel independently ofthe operation of said drawworks and said traveling block, operatively attaching well working tools to the unwound end of said length of drill pipe, lowering and guiding the said end portion of said drill pipe and the attached said well working tools from said vessel to said wellhead apparatus while operating said gripping apparatus and while continually unwinding said drill pipe from said reel, further lowering said end portion of said drill pipe and the said attached well working tool through said wellhead apparatus and said casing and into said well bore by operation of said gripping apparatus and operating said well working tools from said vessel.

3. The method in accordance with claim 2 including automatically operable means connected in said drawworks for adjusting the position of said traveling block in said hoist means in accordance with the changing load on said well working tools caused by the changing vertical relationship between said vessel and the submerged said well bore as said vessel moves with the surface of the water, and in which the operation of said adjustable gripping apparatus is controlled independently of the operation of said automatically operable means.

4. Apparatus for working a submerged well bore from a oating vessel, which well bore has casing affixed therein and wellhead apparatus affixed to the top of said casing comprising a floating Vessel positioned over a submerged well site, a reel of a continuous length of drill pipe mounted on said vessel, means for unwinding and winding said length of drill pipe respectively off of and onto said reel, pipe bending tineans mounted adjacent said reel and operative to bend and straighten said drill pipe as it is wound onto and unwound off of said reel, hoist means aboard said vessel, said hoist means including a traveling Iblock and hook mounted therein, drawworks operatively connected to said traveling block andl operable to raise and lower said traveling block and hook in said hoist means, adjustable gripping apparatus supported from said hook `for gripping the portion of said drill pipe unwound from said reel, means for operating said gripping apparatus to lower and raise the end of the unwound portion of said length of drill pipe from and toward said vessel independently of the operation` of said traveling block, well working tools operatively attached to the end of said unwound portion of drill pipe, means for guiding the said end and the attached said well working tools from said vessel to said wellhead apparatus as said unwound end portion of said length of drill pipe is lowered from said vessel by operation of said gripping apparatus, means for lowering said end portion of said length of drill pipe and the said attached well working tools through said wellhead apparatus and said casing and into said well bore by operation of said gripping apparatus, and means for operating said well working tools from said vessel.

5. The method of drilling and working in a borehole from a tloating vessel which comprises positioning said vessel over an underwater drilling site, suspending below said vessel an dabove the underwater bottom a conductor pipe by means of a string of drill pipe detachably connected in concentric relationship to the upper end of said conductor pipe, said conductor pipe having a drill -bit of larger diameter than said conductor pipe aixed to the bottom end thereof and a flange of larger diameter than said drill bit affixed adjacent the upper end thereof, lowering said conductor pipe vertically from said vessel to place said drill bit in contact with the submerged land, rotating said string of drill pipe by means aboard said vessel while continually lowering said string of drill pipe to thereby drill a borehole into said submerged land until said flange is in contact with said submerged land, subsequently securing a guide assembly to the submerged upper end of said conductor pipe and `adjacent said flange, said guide assembly including at least a pair of guide cable members yieldably connecting said vessel with said guide assembly and disposed in sym-metrical relationship around the axis of said conductor pipe, owing cement from said vessel through said string of drill pipe and said conductor pipe downwardly to the bottom of said conductor pipe and upwardly -between the outer wall of said conductor pipe and the wall of said borehole, disconnecting said string of drill pipe lfrom the upper end of said conductor pipe and reducing the tension in said guide members while the cement sets, subsequently increasing the tension in said guide cable members and then lowering a drilling head assembly having a guide member attached thereto and cooperating with said guide cable members along said guide cable members to the submerged said upper end of said conductor pipe, guiding said drilling head assembly into concentric relationship with the said upper end of said conductor pipe by means of said guide assembly and securing said drilling head assembly to said upper end of said conductor pipe by an automatically operating connector, said guide assembly being adapted to receive a drill string in concentric slidable relationship, guiding the lower end of a continuous string of drill pipe, having drill tools including a drill bit operatively attached to the lower end thereof and having a guide lmember connected thereto and cooperating with said guide cable members, downwardly from said vessel along said guide cable members and into concentric relationship with said drilling head assembly while controllably unwinding said continuous string of drill pipe from a reel aboard said vessel, continually lowering said string of drill pipe while unwinding said string of drill pipe from said reel to project the lower end of said string of drill pipe and the said drill tools through said drilling head assembly and through said conductor pipe to place said drill bit in contact with subterranean formations at the bottom of said borehole, providing means on said vessel operatively engaging said string of drill pipe for adjusting automatically the length of said string of drill pipe extending -below said vessel in a direction to compensate for the relative vertical motion between said vessel and the said subterranean formations yas said vessel moves vertically with the surface of the water to assist thereby in maintaining said drill lbit in contact with said subterranean formations, and operating said drill tools from said vessel while continually unwinding from said reel and lowering from said vessel said string of drill pipe to drill said borehole to a desired depth.

6. Apparatus for working in a well bore comprising a reel of a continuous length of drill pipe, means for rotating said reel for progressively unwinding and winding a portion of said length, pipe bending means mounted adjacent said reel and operative to bend and straighten the said pipe as it is wound onto and unwound off of said reel, hoist means including a traveling block and hook mounted in said hoist rneans and including drawworks operatively connected to said traveling block to raise and lower said traveling block and said hook, adjustable `gripping apparatus supported from said hook for gripping the portion of said drill pipe unwound from said reel, means for operating said gripping apparatus to lower and raise the end of said portion respectively from land toward said vessel and into and out of a Well bore independently of the operation of said drawworks, well working tools operatively attached to the said end, said well working tools including a tiuid actuated motor, a drill bit operatively connected to said motor, a first conduit extending throughout said length of drill pipe and communicating with said motor for conducting pressurized drilling liuid to said motor to actuate said motor, means for exhausting said uid subsequently into said well bore, a second conduit extending throughout said length of drill pipe, and means placing said second conduit in communication with said well bore adjacent the said end of said drill pipe.

7. Apparatus in accordance with claim 6 wherein said continuous length of drill pipe comprises concentric separate pipe means coextensive with each other and with both said pipe means extending throughout said continuous length of drill pipe, spacer means rigidly connected to the outer surface of the inner one of said concentric pipe means and extending radially therefrom, said spacer means engaging the inner surface of the outer one of said concentric pipe means in slidable relationship, and means securing the said separate pipe means rigidly together at the end of said length of drill pipe connected to said well working tools.

8. Apparatus in accordance with claim 6 comprising a second uid actuated motor included in said well working tools attached to said end of said drill pipe, means placing said first conduit in communication with said second motor for conducting pressurized drilling fluid to said second motor to actuate said second motor, a pump operably connected to said second motor, an intake passage for said pump, said intake located adjacent the said end of said drill pipe, said second conduit communicating with said pump as the discharge passage therefor.

9. Apparatus in accordance with claim 6 including means for spacing said reel for said drill pipe apart from said gripping apparatus supported from said hook, and means for projecting said drill pipe Ifrom said reel to said gripping apparatus in the form of a smoothly curved unsupported arc.

References Cited UNITED STATES PATENTS 2,512,783 6/1950 Tucker 175-6 2,984,455 5/1961 Fischer 175-7 X 3,116,781 l/l964 Rugeley et al. -103 3,259,198 7/1966 Montgomery et al. 175-7 3,276,746 10/1966 Berne 175-5 X 3,306,357 2/1967 C-ullen et al. 175-103 X 3,313,346 4/1967 Cross 166-77 X y CHARLES E. OCONNELL, Primary Examiner.

R. E. FAVREAU, Assistant Examiner.

fgggo UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,l35,906 Dated April l. 1%9

Inventor(s) KINGSLEY M. NICOLSON It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r-Col. 3, line 47, nwith" should read without Col. 7, line 6l, nmaybeu should read may be Col. lO, line 66, "aagin" should read "again-- co1. 11, line 51+, "83" should read- 73" Col. 16, line 37, after "float" and before "311+" the following line is missing:

--valve (not shown) may if desired be placed in the central conduit-- Col. 20, line 31+, "water is possibleu should read --water it is possible-- co1. 21, claim 2, line 67, "tool" should read "tools-- Col. 22, Claim 1I, line 7, "working a" should read --working in a Col. 22, Claim 5, line LIB, "an daboveH should read --and above-- SIGNED AND SEALED SEP 3 0 1969 (SEAL) L Arrest:

Edward M. Fletcher, Ir.

WILLIAM E. SGHUYLER, JR. Attesng Officer Gomissioner of Patents

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