US3491842A - Apparatus for underwater drilling and coring loose sediments - Google Patents

Description

Jan. 27, 1970 J DELACQUR EI'AL 3,491,842

APPARATUS FOR UNDERWATER DRILLING AND CURING LOOSE SEDIMENTS Flled May 6, 1968 4 Sheets-Sheet 1 1970 J. DELACOUR ETAL 3,491,842

APPARATUS FOR UNDERWATER DRILLING AND CORING LOOSE SEDIMENTS Filed May 6, 1968 4 Sheets-Sheet 2 42 v 1 [11/ 4a 46 46\ I50 35- I I I 6 ,l' I Zo 25 m 7 I Fi Z a INVENTORJ ATTORNEY;

Jan. 27, 1970 J DELACOUR ET Al; 3,491,842

APPARATUS FOR UNDERWATER DRILLING AND 4 CORING LOOSE SEDIMENTS Filed May 6, 1968 .4 Sheets-Sheet 5 dllllllllllllllll 4Illllllllllllllllllllll Fig. 5 b

INVENTOR- Inna/ts ail-dram: 44/2/16 (AJTEL/I- Fave/e: 1704a ATTORNEY! Jan. 27, 1970 J. DELACOUR ET AL APPARATUS FOR UNDERWATER DRILLING AND CURING LOOSE SEDIMENTS Filed May 6, 1968 Fig. 4

4 Sheets-Sheet 4 ATTORNEYS United States Patent M 3,491,842 APPARATUS FOR UNDERWATER DRILLING AND CORING LOOSE SEDIMENTS Jacques Delacour, Paris, Andr Castela, Mesnil le Roi,

and Pierre Moulin, St.-Germain-en-Laye, France, assignors to Institut Francais du Petrole des Carburants et Lubrifiants, Rueil-Malmaison, Hauts-de-Seine, France Filed May 6, 1968, Ser. No. 726,721 Claims priority, application France, May 8, 1967, 105,625 Int. Cl. E21b 7/12 US. Cl. 1756 4 Claims ABSTRACT OF THE DISCLOSURE Apparatus for drilling cores at an underwater bottom with the core drill being inside a casing which prevents crumbling of the walls of the bore hole. Sections of the casing are connected or disconnected by rotary driven gripping means at the under bottom. The rotary driven gripping means can be driven up or down by an underwater drive means to insert or retract the casing. The core drill in the casing can be connected to the casing or disconnected therefrom.

.studies or for studying the mechanical properties of the underwater ground layers.

The apparatus according to the invention also permits to core the first metres of the underlying rocky sub-strata and to perform in situ measuring operations using such measuring instruments as cohesimeters, penetrometers, pressure measuring devices etc. at any depth within the sediments, whereby these measurements may follow the above-indicated coring operations or be performed in turns with them.

One of the most difficult problems arising during such coring or measuring operations performed in underwater loose sediments is to prevent the bottom of the hole or well drilled in these sediments of being filled with earth crumbling from the walls of this well, such crumbling making very difficult the interpretation of the performed measuring operations.

This crumbling occurs, in particular, when the measuring or coring operations are performed after drilling runs, the coring or measuring apparatus being then lowered into the drilled Well after having removed the drill bit.

Another possible application of the apparatus according to the invention is to drive into the underwater loose sediments tubings or casings having lengths of several tens meters with simultaneous removing of the sediments located within this casing so as to allow the subsequent introduction into this casing of reinforcements and of various cement slurries so as to constitute underwater anchoring means the anchoring strength of which is very high, for instance up to several hundred tons.

An important object of the invention is to permit the driving of an elongated member into the underwater grounds from a floating surface installation, without requiring any permanent connection between this rigid elongated member so as to not subject this member to 3,491,842 Patented Jan. 27, 1970 high stresses resulting from the movements of the floating installation, the complete suppression of these movements being impossible, even with means for precise anchoring or positioning of the floating installation, the cost of such means for precise anchoring being moreover very high.

According to the invention, these different problems can be simultaneously solved with an apparatus operable from a surface installation for driving into the underwater floor an elongated member constituted of a plurality of elements adapted to be connected end to end, particularly for offshore drilling and coring operations, including a base member which can be seated on the underwater floor and is provided with a central well for the passage of said elongated member and with rigid guide columns extending in a direction parallel to the axis of said central well, substantially parallel guide cables connecting said surface installation to the respective tops of said guide columns, a drill head slidable along said gmide columns and provided with a bore for the passage of said elements of the elongated member and with means inside said bore for gripping said elements, said drill head incorporating at least a submersible motor for driving said elongated member into the underwater floor, at least a power line and a line for remote control connecting said submersible motor and said gripping means to said surface installation, said apparatus including a connecting element provided with guide means arranged to ride down said guide cable and to be seated onto the top of said guide elements, said connecting element being adapted for detachable connection with the top of the upper element of said elongated member and being suspended by a flexible line from said floating installation for successively lowering the elements constituting said elongated member, in combination with remotely controlled means supported by said base plate for upwardly driving said drill head along said guide column.

Ainon-limitative embodiment of the invention, applied to coring the underwater ground layers, will be described hereinafter, with reference to the attached drawings wherein:

FIGURE 1 diagrammatically illustrates a coring apparatus according to the invention operated from a ship,

FIGURES 2a and 2b are sectional views, on a larger scale, of the drill head of the apparatus, FIGURE 2a corresponding to the section a--a indicated in FIGURE 2b and this last figure to a section of FIGURE 2a,

FIGURES 3a and 3b illustrate devices for gripping the casing,

FIGURE 4 is a sectional view of the upper part of the coring tool.

In the embodiment of the invention, illustrated by way of example by FIGURE 1, the coring apparatus is operated from the ship 1 which is maintained in a substantially fixed position by any suitable means-(not shown), such as by conventional anchoring or dynamic positioning, over the selected location of the water bottom 3 where the coring operation is to be performed.

Through the hull of the ship is provided a well 2 for the passage of the apparatus according to the invention (the proportions between the ship and the coring apparatus have not been respected in the drawing, so as to more clearly show the apparatus).

The coring apparatus includes abroad base plate 4 adapted to rest on the water floor 2 and provided with a central aperture or well 5. Twoguide columns 6 and 7 parallel to the axis of thewell 5 are integral with this base plate.

The tops of these columns are connected with the ship 1 by means ofguide cables 8 and 9 passing overreturn sheaves 10, 11 carried by the ship and are wound onWinches 12 and 13 of conventional type adapted to keep thecables 8 and 9 under tension.

Theguide cables 8 and 9 are used for handling thebase plate 4 from the ship, i.e. for lowering and rais ng this base plate, as well as for guiding the successive casing elements which are lowered from the ship in the manner to be indicated in the following.

The casing used for lining the drilled Well during the coring operation, i.e. for holding up the walls of this well, is formed of tubular elements such as 14a, 14b, 140 which can be connected end to end such as by screwing or by any other suitable means and the unit-length of which is at least equal to the greatest height of the successive coring runs.

.Thelower element 14a of this casing is provided at its bottom with adrill crown 15 which is provided with teeth or cutting elements.

The apparatus according to the invention includes adriving drill head 16 constituted of a frame displaceable along the guide columns over a length thereof at least equal to that of a casing element and which is traversed by abore 17 providing a passage for this casing.

A guide funnel-shaped element facilitates the introduction of the casing elements into thebore 17.

The upright displacements in either direction of thedrill head 16 along theguide columns 6 and 7 are produced, in the considered embodiment, by means of twoendless chains 19 and 20 passing overtoothed wheels 21 to 24, located at both ends of each guide column. Thedrill head 16 is secured to one line of each chain at locations such as 25 and 26.

In the illustrated embodiment thechains 19 and 20 are driven by a reversible hydraulic motor, through thechain belt 27.

This hydraulic motor is actuated by a hydraulic unit secured to thebase plate 4.

The electric motor driving the pump of this hydraulic unit is supplied with electric current from theelectricgenerator 29 located on the ship, through theline 30.

This line is constituted of a cable in which are embeddedelectric power conductors 31 as well as electric conductors for remote control, the latter permitting to control the different operations performed on the water bottom from a telecontrol station 33, in particular the actuation, in either of its directions of rotation, of the hydraulic motor driving thechains 19 and 20.

These conductors for remote control are connected with electrically operated valves of a conventional type adapted to the hydraulic circuit of theunit 28.

The construction of this circuit will be obvious to those skilled in the art and is therefore not described here.

The drill head includes devices for clamping, holding and driving in rotation the casing, the whole of these devices being designated by thegeneral reference 39 in FIG. 1.

These devices will be described in the following more in detail with reference to FIGURES 2a and 2b showing sectional views on a larger scale ofthedrill head 16.

This drill head includes arotor 34 for driving the casing in rotation, constituted for a peripherally toothed crown in mesh with driving pinions.

Two of these pinions are rotated by the reversiblehydraulic motors 37 and 38 which are supplied with bydraulic fluid by thehydraulic unit 28 through a flexible hydraulic hose 40 (FIG. 1). This flexible hose can follow the displacements of thedrill head 16 along the guide columns and includes at least a pipe supplying fluid under pressure and a pipe for conveying the low pressure fluid back to thehydraulic unit 28.

Therotor crown 34 has aninternal bore 41 of a diameter suflicient to provide for a very easy passage to the different elements of the casing.

On this rotor are locateddevices 42, 43 for automatically clamping or gripping the casing, providing for 4 the rotation thereof (the number of these clamping elements is not limited to two).

In the illustrated embodiment, these elements have an internal wall including acylindrical part 44, 45 having a shape adapted to fit the outer wall of the casing with a high friction factor.

In these clamping elements are provided along a direction substantially parallel to the axis of therotor 34studholes 46 and 47 respectively, each of which having a cross-section which is elongated along a direction deviating from the axis of therotor 34 in the direction opposed to the direction of rotation of the latter.

In the stud-holes of the self-clamping elements are insertedstuds 48 and 49 integral with therotor 34 and the cross section of which has a shape complementary to that of the stud-holes 46 and 47, permitting to bring the selfclamping elements more or less near the axis of therotor 34, and which is adatped to prevent the rotation of these clamping elements about the studs towards the axis of therotor 34. This rotation might otherwise happen when no casing element is inserted in thedrill head 15, which would then make diflicult, if not impossible, and subsequent passage of a casing element through this drill head.

The location of thestuds 48 and 49 on therotor 34 permits an easy passage of the casing elements when the self-clamping elements 42 and 43 have been moved aside from the axis of therotor 34 and a clamping action on these casing elements which is suflicient to make them fast in rotation with therotor 34, when these clamping elements are simultaneously brought nearer the rotor axis.

The shape of theelements 42 and 43 as well as their respective locations on therotor 34 are so selected that all the clamping elements are in abutment and automatically grip or clamp the casing, when the rotor is rotated in its normal direction of rotation (indicated by the arrow on FIG. 2a) which corresponds to the coring operation, whereby this clamping action is automatically suppressed by simply reversing the directon of rotation of therotor 34 which allows to clear thedrill head 16 from the casing element traversing this drill head.

Inside thedrill head 16 is also located arotary crown 50 coaxial with thebore 17 and provided withdevices 51, 52 for axially holding the casing, these devices being hingedly secured to thecrown 50 in the illustrated embodiment.

These devices which are illustrated on a larger scale on FIGURES 3a: and 3b are devices for self-clamping the casing, adapted to withstand longitudinal forces exerted on the casing either downwardly (device of FIG. 3b) or upwardly.

They may be in any number, being regularly distributed at the periphery of the crown 50'. In the illustrated embodiment, each of these elements lncludes a gripping shoe (53, 54) integral with a horizontal stud which is guided by a groove or stud-hole (55, 56) integral with therotary crown 50. These gripping shoes are secured to the end of a lever arm (57, 58) hingedly mounted on the crown 50'.

Thegrooves 55 and 56 having the shape of arcs of circles are so located as to bring the gripping shoe towards the rotation axis of thecrown 50, either when the gripping shoe is lowered (device of FIG. 3a) or when the gripping shoe is raised (device of FIG. 3b). There is thus provided by self-gripping action the axial blocking in both directions of the casing traversing thedrill head 16.

The springs 57a and 58a when expanding push thelever arms 57 and 58 back to their clamping position in which the casing is gripped by theshoes 53 and 54.

The releasing of the casing by moving apart the clamping shoes is performed in the illustrated embodiment by means of anannular pisto 59 which is slidably mounted in the annular cylinder 60 (FIG. 2b) and which, by pressing thelever arms 57 and 58, causes the gripping shoes to move away from each other. a

The control of the displacements of thepiston 59 is performed from the station 33 at the water surface, by remotely controlling the inlet of hydraulic fluid under pressure into any of the two compartments of thecylinder 60 through the flexiblehydraulic coupling 40 and one or the other of thepipes 61 and 62;

This apparatus according to the invention also includes a coring tool 63 (FIG. 1 and 4) the lower part of which is constituted of acore barrel 64 provided with an internal bore for housing thecore 66.

Thebore 65 is at its upper part provided with a gaugedvalve 67 to allow water to escape from above thecore 66.

Thehead 68 of the coring tool is in the following referred to by the expression handling head since this head is used as a seat or abutment for the successive casing elements during the lowering and the raising thereof as hereinafter described.

This handling head is traversed by one orseveral channels 69 for delivering flushing fluid to theannular space 70 between the coring tool and the casing which constitutes a lining of the walls of the well 71 drilled through the sediments. i

The supply with flushing fluid is performed through aflexible pipe 72 at the lower end of which the coring tool is suspended.

This pipe passing over theguide pulley 73 supported by the ship is reeled on awinch 74.

The upper end of thepipe 72 secured to the rim of thewinch 74 is supplied in a known manner with water under pressure which constitutes the flushing fluid, by means of thepump 75 drawing up water from the sea through thepipe 76 and delivering this Water into thepipe 72 through thepipe 77 and through a rotary coupling or swivel 78 of a conventional type.

Guilding elements permit to lover and raise the successive casing elements by sliding along theguide cables 8 and 9.

These guiding elements include (FIG. 1 and 4)radial arms 79, 80 integral with slidingsleeves 81 and 82 through which the guide cablen pass and which are adapted to fit the upper part of theguide columns 6 and 7 (these sleeves being however stopped above theupper pinions 21, 23 of these columns).

A tubular coupling orconnectig element 83 which is externally threaded at its lower part and is integral with theradial arms 79 and 80 allow to hang on to the guiding element (79 to 82) each casing element such as 14c( FIG. 1) during the lowering and the raising of this element.

Theflexible pipe 72 permits to perform these operations of lowering and raising a casing element screwed to the connectingelement 83 integral with thearms 79 and 80 which then come in abutment against the top of the handling head 58 (FIG. 4).

This handling head includes (FIG. 4) retracting anchoring fingers or pawls such as thefinger 84 integral with apiston 85 which can silde in thecylinder 86 against the action of a return spring, Thecylinder 86 communicates with thechannel 69 delivering flushing fluid upflow from a throttling (nozzle 87 of this channel.

With such a arrangement, the fluid under pressure supplied by theflexible pipe 72 causes automatically the movement of thefingers 84 away from one another, since the pressure of the flushing fluid in thechannel 69 upflow from the throttling 87 is higher than its pressure downflow from this throttling.

By interrupting the supply of thepipe 72 with fluid under pressure thefinger 84 is automatically retracted by the action of the return spring.

Thelower element 14a of the casing is internally provided with an annular shoulder 88 (FIG. 1) under which the anchoringfingers 84 come into abutment when they are spaced away from one another under the action of the flushing fluid, this annular shoulder preventing thecore barrel 63 to be displaced upwardly in thecasing element 14a, when the latter is driven into the sediments.

In the illustrated embodiment (FIG. 1) thecore barrel 64 is downwardly extended by a cutting tubular element 93 (of small wall thickness) the length of which is so selected that this tubular element is downwardly protruding from thecoring crown 15 over a few centimeters when the core barrel occupies its position within thelower element 14a of the casing.

The handlinghead 68 is further provided with an annular sealing packing 89 constituted of an annular recess which is outwardly limited by a flexible Wall, this recess communicating with thechannel 69 delivering flushing fluid under pressure, upflow from the throttling 87.

The water under pressure supplied from theflexible pipe 72 causes the inflation of the sealing packing which is pressed against the internal wall of the casing which surrounds the coring tool, so that the flushing fluid can only flow towards the bottom of the drilled well 71.

In the embodiment illustrated by FIG. 3, thecylinder 86 and the annular sealing packing 89 are adapted to anannular element 90 rotatably mounted with a small clearance around the body of the handlinghead 68 by means of bearings.

In that way the coring tool which includes thecore barrel 64 is not driven in rotation together with the casing when thefingers 84 and the annular sealing packing are pressed against the internal wall of this casing. The rotation of thecore barrel 64 is prevented by the resistance of theflexible pipe 72 to torsional stresses.

The flushing fluid reaches thecylinder 86 and the annular recess limited by the packing 89, by following thechannel 91 and entering the annular cavity limited by the twoannular grooves 92a and 92b facing each other respectively provided in theannular element 90 and in the non-rotatable part of the handlinghead 68.

The operation of the coring apparatus according to the invention is performed in the manner described hereinunder.

The ship 1 is positioned and maintained over the location selected for coring.

Thebase plate 4 provided with the drill head is then suspended to the twoguide cables 8 and 9 and lowered to the water bottom where it is laid. The guide cables are kept under tension.

A length of casing constituted for example of thelower element 14a and of the adjacent element 14b located just above is lowered, hanging at the lower end of theflexible pipe 72 in the manner which has been illustrated by FIG. 1 for the lowering of the element 150, i.e. the element 14b of the casing is screwed at its lower part to the connectingelement 83 integral with the element for guiding along theguide cables 5 and 6 and the whole is lowered by unwinding thepipe 72.

Thedrill head 16 is raised up to the top of theguide columns 6 and 7 by remotely controlling thehydraulic unit 28 and thegripping shoes 51, 52'are moved away from the axis of thebore 17 of the drill head, also by remote control causing the downward displacement of the annular piston 59 (FIG. 2b).

The casing may then be easily inserted into thebore 17 through the guiding funnel-shapedelement 18.

Thegripping shoes 51 and 52 are then pressed against the external wall of the casing by remotely controlling the raising of theannular piston 59 in thecylinder 60.

It is no longer necessary to support the upper element 1411 by theflexible pipe 72 and, by continuing to unwind this pipe, thecoring tool 63 can be lowered into thelower casing element 14a.

When the coring tool has reached its proper level in thiscasing element 14a, theflexible pipe 72 is supplied with water under pressure, thereby expanding thefingers 84 holding the coring tool under theannular shoulder 88 and simultaneously providing for sealing at the level of the packing 89.

By remotely controlling the actuation of the hydraulic motor driving thechains 19 and 20 and of the hydraulic motors such as 37 and 38 (FIG. 2b), the casing is rotated, which results in the unscrewing of the upper part of this casing from the connecting element 83 (FIG. 4), since the twosleeves 81 and 82 of the guide element 80 (FIG. 1) are then secured to the tops of theguide columns 6 and 7, which prevents the rotation of the connectingelement 83. The well 71 is then bored (FIG. 1) by the toothed crown orbit 15, a core being formed in thehousing 65 of thecore barrel 64, the drill head being moved downwardly by thechains 19 and 20 thereby drilling the well 71.

When thedrill head 16 reaches its lowermost position shown by FIG. 1, the first coring run is finished and it is then necessary to add a new casing element 140. Since the connectingelement 83 is no longer screwed at the top of the casing element 14b, the coring tool '63 surmounted by theguide element 79, 80 can be easily raised by winding up theflexible pipe 72 on thewinch 74.

The shoes gripping the casing element 14b are moved away from this casing by remote control from the water surface and then the drill head is raised up to the top of theguide column 6 and 7.

An additional casing element 140 is lowered in the manner illustratedby FIG. 1 and is introduced into thebore 17 of thedrill head 16 through the funnel shapedguide element 18, the lower part of this new casing element coming into abutment against the upper part of the preceding casing element 14b.

It will generally be necessary that additional guide elements, which have not been illustrated in FIG. 1 so as to not complicate the drawing, for example hydraulically actuated jaws supported by thebase plate 4, can grip the casing element 14b before the raising of thedrill head 16 so as to keep the axis of thebore 17 of the drill head.

In that Way the additional casing element 140 is located exactly in the extension of the preceding one 1412.

The operation of remotely controlling the gripping of thecasing element 14c by the grippingshoes 51 and S2 is then followed by telecontrolling the actuation of the motor driving thechains 19 and 20 and of the motors driving therotor 34.

This causes successively the screwing end to end of the casing element 14b and of thecasing element 14c, the unscrewing of the upper part of theelement 14c from the connecting element 83 (FIG. 3), then the rotation of the whole casing for a new coring run at the end of which a new length of easing will be added in the manner which has already been described.

During the coring runs it will be necessary, in this embodiment, to unwind a suflicient length of theflexible pipe 72 so as to prevent the device from being subjected to vertical movements which the ship is subjected to at the surface, since these movements would be transmitted to the device by a pipe which is too much stretched.

At the end of the coring operations, the raising of the successive elements is performed after interrupting the supply of theflexible pipe 72 with fluid under pressure. The fingers 84 (FIG. 3) and the annular sealing packing 89 are then retracted and thecoring tool 63 can then be easily raised by winding up theflexible pipe 72 on thewinch 74.

The tubing can in turn be raised, for example by lowering at the lower end of thepipe 72, also by following theguide cables 8 and 9 a fishing tool of a type conventionally used during offshore drilling operations and adapted to be connected with the top of the casing, this tool remaining connected with the ship by a fishing cable suspended at the top of a mast or of a lifting derrick.

By suppling the interior of the casing with water under pressure through the flexible pipe to top of the casing being obturated by the fishing tool a swabbing effect is created which is favourable to the extraction of the tubing, this extraction being performed by means of the fishing tool.

When the casing has been raised into the well 3 of the ship it will be gripped at this level by conventional (not illustrated) means, then unscrewed element after element, so as to be stored on the ship deck.

If the casing cannot be extracted from the water floor, the loss will be limited to a few casing lengths, only thelower element 14a (FIG. 1) of which is of a special type.

The operation will be achieved by raising the base plate by means of theguide cables 8 and 9. Although the present invention has been described with reference to a particular embodiment thereof illustrated by the attached drawings, it must be understood that numerous changes may be made in this embodiment which was indicated by way of illustration, without departnig from the spirit and scope of the present invention. For example the driving of thedrill head 16 by means of chains may be replaced by constituting the guide columns '6 and 7 as endless worms rotated around their upright axes by means of at least one hydraulic motor actuating two pinions each of which is integral with one of these guide columns, each of the latter traversing a non rotatable threaded nut integral with thedrill head 16.

It is also possible to constitute each of the guide elements as an upright toothed rack in mesh with a toothed pinion having an horizontal axis and rotated by an hydraulic motor carried by thedrill head 16.

Thecore barrel 63 may be of any known type suitable for collecting cores of loose sediments with as little alteration as possible occurring within the sample, the present invention being by no way limited to the use of any particular core barrel.

This-core barrel may be simple, provided or not with obturating devices and with devices for withholding the core, and may protrude from the lower part of the casing by a tubular element having a thin cutting wall.

This core barrel may also be double (formed of two concentrical tubes) and optionally be provided with a flexible sleeve continuously covering the core as the latter is being formed.

What is claimed is:

1. Apparatus operable from a surface installation for driving into the underwater floor an elongated member constituted of a plurality of elements adapted to be connected end to end, particularly for offshore drilling and coring operations, including a base member which can be seated on the underwater floor and is provided with a central well for the passage of said elongated member and with rigid guide columns extending in a direction parallel to the axis of said central well, substantially parallel guide cables connecting said surface installation to the respective tops of said guide columns, a drill head slidable along said guide columns and provided with a bore for the passage of said elements of the elongated member and with means inside said bore for gripping said elements, said drill head incorporating at least a submersible motor for driving said elongated member into the underwater floor, at least a power line and a line for remote control connecting said submersible motor and said gripping means to said surface installation, said apparatus including a connecting element provided with guide means arranged to ride down said guide cable and to be seated onto the top of said guide elements, said connecting element being adapted for detachable connection with the top of the upper element of said elongated member and being suspended by a flexible line from said floating installation for successively lowering the elements constituting said elongated member, in combination with remotely controlled means supported by said base plate for upwardly driving said drill head along said guide column.

2. Apparatus according to claim 1, wherein the elements constituting said elongated member are rotatably connected with one another, said submersible motor being adapted for rotation of said elongated member and said connecting element being detachable from the upper element of said elongated member through said rotation, when said guide means are seated at the top of said guide columns.

3. Apparatus according to claim 1, wherein said elongated member is a tubular casing terminated at its lower end by a drill bit, and wherein said flexible line is a flexible pipe for supplying said drill bit with flushing fluid.

4. Apparatus according to claim 3, for underwater coring in loose sediments, wherein said flexible pipe is terminated at its lower end by a core barrel the top of which constitutes a seat for said connecting element during the lowering of the successive elements of said tubular casing, said apparatus including releasable means for anchoring said core barrel within the lower element of said tubular casing.

l 0 References Cited UNITED STATES PATENTS CHARLES E. OCONNELL, Primary Examiner RICHARD E. FAVREAU, Assistant Examiner US. Cl. X.R.

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