US2541785A - Coring device - Google Patents

Description

Feb 13, 1951 D. M. SMITH 2,541,785

CORING DEVICE Filed Aug. 22, 1946 3 Sheets-Sheet 1 29A @Nigel IN VEN TOR. DONALD M. SMITH BY JMJ/@ ATTORNEY Feb. 13, 1951 D, M, SMITH 2,541,785

CORING DEVICE Filed Aug. 22, 1946 3 Sheets-Sheet 2 F/G. 4 /l F/6.5 l/

INVENTOR. DONALD M. SMITH BY UWM/ v Arme/ver Feb. E3, 195i D. M. SMH-H 2,54L785 CORING DEVICE Filed Aug. 22, 1946 5 Sheets-Sheet 3 Ff@ Ff@ N Patented Feb. 13, 1951 CORING DEVICE Donald M. Smith, Long Beach, Calif., assignor to The Texas Company, New York, N. Y., a corporation of Delaware Application August 22, 1946, Serial N o. 692,165

(Cl. Z55-1.4)

9 Claims.

This invention is concerned with coring in bore holes and provides novel apparatus to the end that cores may be taken in rotary drilling operations and the like without contamination of the core and without loss of fluid therefrom.

In recent years, increasing attention has been paidv to core analysis in oil well drilling and the like. Data obtained from cores taken in such drilling are used in evaluation of oil reserves, in estimating the productivity and ultimate production of oil sands, in planning oil field development programs and for several other purposes. Heretofore, the data obtainedin many coring operations has been misleading due toerratic contamination of the cores by drilling fluids and t loss, prior to analysis, of fluids originally contained in the cores.

There is a distinct need for a coring device which will permit the taking of a core on the bottom of a hole without contamination of the cor (either in the coring operation per se or in bringing the core to the surface and thence to thelaboratory) 'and without the loss of formation pressure with consequent expulsion of the major portion of liquid and gas from the core. y -As a result of my investigations, I have developed a core barrel apparatus of the pressure type (i. e. one in which the coring tube or barrel is; pressed downwardly into the formation to be sampled) so constructed that contamination of the sample during the coring operation is prevented'in large measure, the sample being sealed immediately after it is taken from the bottom of the hole, so that any fluid in the core may be brought to the surface within the barrel at formation pressure and thus retained.

rIhe apparatus of my invention results in more accurate core information, with the result that yinterpretation of the data taken from the cores is likewise more accurate and permits more'nearly correct evaluation of oil field properties, better estimates of reserves and more accurate location of oil-water interfaces within an oil producing formation to the end that there may be improved recovery therefrom by gas or water injection. To be more specific, the 4pressure core barrel of my invention gives superior results in the determination of reservoir content, in the location of gas caps and oil producing formations, and in the determination of the content of the gas cap.

1 n With pressure-type core barrels heretofore available, the cores have been taken while surrounded by drilling fluid. When these cores are removed from the hole, the volume of the cores represents in many cases only 25% of the volume under pressure within the core barrel, the remaining 75%f' being drilling fluid. As a result, the measurement of oil contained in the core is reasonably ace' curate, but the amount of water is distorted due to the invasion of drilling fluid. This problem is c. TheV prevention of most of the contamination"` of and loss from cores which has heretofore" occurred, since nearly all cf the volume within the sealed core barrel is occupiedby the sample" itself; the drilling uid is excluded from the cor-l ing zone during the coring operation; andthe sample is sealed at formation pressure in the bot-' tom of the hole. f

In essence, my invention contemplates the come` bination in apparatus for taking a core from thef bottom of a drill hole, which comprises a core barrel fastened to the bottom of a drill stemv in alignment therewith and open at the lower end with a cutting edge that is driven into the formation by the weight of the stem, together with eans for closing the bottom or cutting end of the barrel while it contains the core and is in the bottom of the hole, so that a sample may be sealed in the barrel at the formation pressure and withdrawn in its original condition. ,v In its preferred form, the apparatus comprises', a mandrel mountable on the bottom of the drill stem in alignment therewith, a shell or sleeve slid-' ably mounted upon the mandrel, a core barrel mounted on the bottom of the mandrel, with an open lower cutting end, and a closure member adapted to close the lower end of the core barrel when the mandrel is slid upward with respect to the sleeve. -f

If desired, the mandrel and sleeve may be held in fixed position initially by a shear pin or other rupturable means which permits disengagement of mandrel and sleeve when weight of the drill stem is rested on the mandrel in the bottom of the well.

It is preferable to provide at least two core barrels with equivalent closure means so that duplicate samples may be taken from the formalf tion being tested.

In the preferred form of the apparatus, the top of the core barrel is open, and a sealing plugis provided within the barrel which is slidable flipJ 3 ward therein under the force of the sample being cut. For example, the plug'may slide upward to an apertured seat so as to drive drilling fluid or the like upwardly out of the core barrel and keep it out of contact with the sample.

The apparatus should be provided with means, preferably actuated through the rotation of the mandrel, ifor vcomp'resz'sing the closure means against the bottom of the core barrel after the sample is taken, thus assuring a tight seal. One preferred form of clamping means comprises a sealing nut of non-circular section mounted a corresponding longitudinal borerin the mandrel. The sealing nut is threaded on a boltwhich'be'ar's against the closure means. By rotating the mandrel, the sealing nut draws the bolt upward with respect to the core barrel and presses the 'closure means (say a cap) tight against the bottom. Lf desired, the sealing nut -may be mounted within a wrench sleeve which is'of circular outside cross section, 'this sleeve 'in 'turn being mounted in a circular bore in "the mandrel and held in positin bye. shear pin lor the like. When adequate clamping pressure has been 'eXeited by the bolt, the'shear ypin ruptures and prevents damage to the core barrel andthe 'rest 'ofthe assembly.

It is desirable to provide shoulders on the mandrel 'andial's'o "onthe sleeve to limit `the 'relatv longitudinal sliding movement of these two m'enbe'r's and to prevent 'the sleeve from sliding onf the bottom of the mandrel. Y

'The closure Ymeans for sealing thebottom of the core barrel preferably is 'a "cap or cup mountd'nth'e sleeve and rotatable 'onan axis parallel (aild Ypreferably coaxial) to that v'of sleeve 'and mandrel. Preferably the cap or cup is mounted on" a 'yoke 'which is spring actuated. In the initial position assumed by the apparatus inthe hle, the closure means prevented from swinging over Vvthe end of the core barrel by the core barrel. itself. When the core barrel and `man drel are pulled upward 'with vrespfec'zt to the sleeve after 'the sample is taken, 'the spring forces "the c'prt swing underneath the core barrel, after which' rotation of the 'drill stem, with consequent rotation 'of the mandrel, causes the 'sealing nut toturn o ii the center bolt and pull thec'up tight 'gans't 'the bottom of the" core barrel. nt the Sametime, 'the 'sealing plug is "pushed upwardly inV 'the "core barrel tight 'against its lseat. `This preserves formation pressure in the "core barrel.

'Preferably 'the bolt works through an 'upper yoke attached 'tb 'the "core bai-rel and a lower yoke `attached to the 4'sea'l'ir'ig cup. As the 'nut Ltightened on the bolt, the ykes are Yforced twrd each other, squeezing the "ends of `the barrel between the'n 'and sealing both ends; the upper end by pushing core and plug against its seat, the lower end with'the cup, This assembly Vis'le'tacha'ble from the apparatus and may be removed in toto for transport to the laboratory,

' thus assuring that the core is delivered .ior analy'sis vat formation pressure. d

Y'I'flie invention willebe understood more thoroughly in the light of the following detailed description of a presently preferred form of the apparatus, taken in conjunction with the accompanying drawings in which eFig. -1 .is a sectional elevation of the coring device in position in the bottom of a borehole just before the core cutting operation.; y

Fig. v2 is la sectional elevation of the vapparatus of Fig. 1 .just after the cores Vhave been out; Y y

Fig. 3 is a cross-sectional plan through the Fig. Y'lis 4across section taken along the line p 'lf--l of Fig. 4 showing the shear pins attaching mandrel to wrench sleeve;

Fi'g-.`-8 a crosssection taken along the line 8-8 of Fig. l showing the shear pins which 'initially hold the mandrel in fixed relation to Fig. 9 'is "an `enlarged' fragmentary cross-"sectional `elevation vof the top of one or the boring tubes or barreIs showing 'the manner in which it is sealed;

Fig. 11 is a cross-'sectional elevation 'or the sealing cup of Fig. 10 'taken along 'the line l'l-'l'i' of this'gure. I` In essence, 'the apparatus "illustrated by 'the figures comprises a mandrel l0 'adapted t'ofbe fastened by a conventional 'tool j'oi'n't on the v'bute-y tom of a rotary drill Astem 1|. The Amandre1- slides man outer sleeve l2, "after a 'rst set 'of Shear 'pins 'l IA, HB 'haveub'tured (s'ee Fig. '1); The outer sleeve or shell ha'sa removable bottoni disc threaded v'or 'otherwise fastened therein'. The mandrely is cylin'dric'alin cross sectionand carries anru'pper'beveled shoulder 13, 'which sli es' downto mate "with a lower shoulder II4 `on "the sleeve. The mandrel has an inner 'shoulder l5 which 'prevents the "outer sleeve fromslidin'g ol the lower end ofthe mandrel.

Within'the mandrel iS a concentric 'infi' ye linuricai bore Lin which "a 'wrench' sleeve' lie/*is slidablyidisposed. This v'wrench 'sleeve is "of foute' side cylindrical VVcro'ss Jsection.' but has an inside tube of hexagonal cross section 'within'which slides 'a right hand 'sealing 'nutl that is 'threaded on 'ajcenter bolt i8. "sealing mit ispre; vented-from 'coming on the upper end of the center 'bolt by mea'nsoi 'a 'left hand lock' ymit le; Until the final sealing operation, the'wrench SI''V 'iS 'rigidly fst'ld -inside the vnlall'rfl fby a pair of shear .pins v^2'0, 20A "(se'e Fig.' 'l A'and Fig."7).

An upper `yoke 2l 'is mounted rigidly on .the bottomy of the mandrel and car-ries a pair of c'oretubes o r barrels 722, 2"2. The function of the upper'yoke, which connects the upper par-ts of the Vcoring assembly, is to transmit the Vsealin g Y.pressure Vvfrom the vsealing nut to the -core tubes. It is rigidly but detachably mounted on the mandrel.

AThe core barrels are disposed `opposite eaother with their axes :parallel to that of ythe center bolt. The bottom edges of the two barrels are ibeveled to afsharp `edge -to .permit penetrae tion of the lformation to be sampled, land the bore of each barrel is somewhat larger in lSits, upper-section so that it tends to retain and extract the core from the 4formation. The coring tubes vare attached vrigidly tothe drill Jstem through the upper yoke and the mandrel so that the entire weight of drill collars and pipes may be put on the coring tubes to push them into the formation to be sampled, as shown in Fig. 2.

The bottom of the sleeve is provided with a pair of cylindrical holes 23, 23A to permit the passage of the coring tubes to the bottom of the shell into the formation. (See Fig. 4.)

The apparatus is provided with a lower yoke 24 effectively mounted on the axis of the sleeve and rotatable around the lower portion of the center bolt. The lower yoke carries a pair of sealing cups 25, 25A which are rotated to seal thebottom of the coring tubes as described hereinafter. The center bolt passes through both yokes.

The respective coring tubes are provided with sealing plugs 26, 26A. Atthe beginning of the coring operation, as shown in Fig. 1, these plugs are located in the bottoms of the tubes. As the cores are cut, the plugs are pushed to the top of theirfcoring tubes by the cores.

Referring to Fig. 9, the plugs are equipped with packing rings 21, 28 which bear against the inside of the coring tubes and provide a lateral seal. The top end of each coring tube has an open bore 29 connecting with side outlets 29A in the upper yoke 2I through which mud or other material may be expelled. Each coring tube is provided with an annular soft metal seal 30 just below the outlet bore, and the sealing plug is provided with an annular knife edge 3| which bears against the soft seat and seals the top of the coring tube in one of the later phases of theoperation as described hereinafter.r Each sealing plug is provided with a valve 32 which is closed by the core itself when it pushes the sealing plug to the top of the coring tube. This valve permits accidentally entrapped fluid to be ejected. The valves in the sealing plugs are simple affairs comprising a seat 32A and a frusto-conical closure member 32B, which is mounted on the lower end of a stem 32C that slides in a vertical bore in the top of the plug.

AThe'sealing plug is in two parts, an upper portion 33 and a lower portion 34. The lower portion may be tightened against the upper portion bylmeans of anut 35 in order to squeeze the packing rings outwardly.

, A retaining nut 36 is screwed on the bottom of the center bolt which passes through a rotationvbearing 31 mounted concentrically on the` bottom of the sleeve.

shown particularly in Figs. 3 and 4, the lower yoke tends to be rotated by means of a spiral spring 38 placed around the collar 4I in a recess in the lower yoke. The Spring, however, cannot move the sealing cups into the sealing position until the coring tubes have been Withdrawn upwardly, as shown in Fig. 4.

The sleeve or'shell serves four functions. It prevents the clogging of the coring assembly. Its shoulders prevent vertical motion when the end of desired movement is reached. After the core has been cut and the drill string is lifted, the weight of the sleeve causes the lower part of the coring assembly t0 remain stationary until the sealing cups have slipped into position under the coring tube, as shown in Fig. 4. When the drill string is rotated to tighten the sealing nut on the upper yoke, the outer shell prevents rotation of the center bolt, being assisted in this action by two short sh tail blades 4D, 40A on its bottom. It may be noted that the center bolt is free to s lide relative to the upper coring assembly, but is rigidly connected to the outer shell I2. Its func- 6 tion is to force the coring tubes into the sealing cups and hold the assembly under pressure when it is brought out of the hole.

As already indicated, the sealing cups are actuated by the spiral spring located in a recess in the lower yoke. The spring is fastened to a collar,

4I on the center bolt, which in turn is attached to the bolt by a shear pin (not shown). The spring reacts yagainst the lower yoke and aligns the sealing cups with the coring tubes after the samples have been cut.

The sealing cups have extended lips on one side of their upper edge in order to hold the cups in alignment with the coring tubes against the tension of the spiral spring. Soft metal,` discs 43A, 43B in the bottom of'the cups bear against the cutting edge of the coring tubes when the assembly is sealed. (See Figs. 4, 5 and 11.)

The operation of the apparatus is as -fo1lows:.

The initial position of theapparatus justbegfore the cores are cut is shown in Fig. 1. As shown in this ligure, the center bolt has been rotated counterclockwise until the sealing nut has impinged against the locknut at the top of the bolt. This prevents further rotation of the center bolt and provides the spiral springwitha stop against which to workl in moving the sealing cups at a later stage in the operation. The spring is attached to the center bolt by the collar and shear pins, as described hereinbefore.

In assembling the apparatus for use, the sealing cups are rotated against the spring force until they are clear of the coring tubes, and the center bolt is pushed up in the wrench sleeve until its lower end is flush with the lower end of the outer shell or sleeve, which in turn is flush with the lower end of the coring tubes. The relathe bottom of the coring tubes. The sealing plugs are held in place by friction against the inside walls of the tubes. A

When the coring device has been assembled as described, it is threaded on the bottom of the drill string and lowered in the bore until it rests on the bottom of the hole. When the bottom of the shell encounters the hole bottom, the weight of the drill pipe is transferred to the shear pins I IA and IIB which lock the mandrel to the shell. These pins shear, and the weight of the drill string drives the coring tubes into the bottom of the formation.

During the core-taking operation, the sealing plugs keep mud and mud cake out of the lower parts of the coring tubes. As the coring tubes move downward, the shell is pushed up relative to the mandrel, and at the same time the cores move the sealing plugs upward in the coring tubes and force the mud above them out of the tubes through the bores 29 and outlets 29A. y In the next operation, the drill string is lifted so that the coring tubes are brought up -in the shell, as shown in Fig. 4. The weight of the shell itself causes it to remain on the bottom of the .hole until the inner shoulder I5 of the mandrel catches against the top of the shell. Before this point has been reached, the coring tubes have slipped up past the sealing cups sulllciently far to permit the spiral spring to rotate the lower ammasyolelso that'` the cupsareswung-'underthe coring tubes. In other words; the sealing oups snap intoV position underneath the coring tubesand-are heldl in-:thatposition byf spring tension.

' In;v the next stage ofV the; operation, the drill pine is. lowered until itis; certain that the tool is'. again on the bottom of the hole. ThisV lowering'operation anchors-the shell againstv the bot?n tomandmoves. the tubes dow-n-` intothe oupsl so that4 they seat therein (see Fig; 59g. Next, the drill pipe is rotated. The shell? and center bolt arefvhe'ld stationaryby contact with the bottom, so that the rotation of the drill pipe imparted to the sealing nutxthrough` the wrench sleeve causes the sealing nut'- to; thread downwardly on the center vboltfandbear against'the upper yoke. This'forces the lower edges: of.` the coring tubesA intothe soft metal gaskets in the-bottom of thesealihg oups as the? upper and lower yokes are brought closer together. off the tubes are squeezed into their'seats and seal the tops ofthe tubes.

At apredetermined wrench force on the Sealing nut, the pins 2o and 26A between the wrench sleeve and the mandrel are sheared, sov that no further tightening action is permit-ted. rlhis set off shear pins thus prevents excessive pressure from. being exerted upon the sample tubes and the restv of the assembly.

When the drill pipe is rotated, the corin'g' assembly rotates againstV the tension of the spiral spring,Y and'. as thisv rotation continues, the spring shears the collar away'fromr the centerbolt, this operation taking' place af-ter the coring tubes have entered thecups. It will be noted that the lower yokeis set onv a bearing and is free to rotate aboutthe center bolt after the spring is: released.

As soon as the shear pins which connect the wrench sleeve to the mandrel havexbeen released; the coring assembly assumes the position shown in Fig. 5-andis ready tocome out of the' hole.

After the coring device hasl been withdrawn to the surface, it is detached from the drill string. Thereafter the lower endof the outer shell is removed; the upper yoke is detached from the mandrel; andthe tubes with thesealing'assembly proper are withdrawn from theY apparatus and taken to the laboratory or elsewhere for" tests. Thusv withdrawn, the assembly; in. addition to the tubes containing the cores, includes.thc upper and lower yokes, the sealing plugs; the sealing cups and the center bolt.V This assembly is light enough to be easily handled.

In the' laboratory, the usual'testsiupon the. cores are run' with thev assurance that the results will not be vitiated by contamination of' the core samples or leakage therefrom'.

To summarize the movements in the sampling operation just described. the stern with theV corihg eqm'pment attached is lowered until the latter rests onthe bottom of theY hole. Some rotation during the lowering operation is permissible. if desired, andA circulation to the bottom ofthe hole is possibleat anytime.

' In' the second phase of' the operation, all or part of thel weight of the drill string is set on the bottom of the hole in order to. causeI the core tubes topenetratev the formation.

In the third stage of the operation, the drill string'is raised until the cori'ng'device is offbot.- tom. This permits the sealing cups to rotate into sealing position.

In the fourth operation, the-tool is again set on the bottom, and: the drill pipe is rotated or40 turns to-cause the'yo'kesv to move closer together At-th'ezsame time the plugs in the top Lil) and`sealupperand? lower' endsiof' thefcoring tubes lI-he fifth stagev of thev operation is merely the withdrawal off the drill-l string and! theremoval of the samples in the oori'ng'tubes.

1. In apparatus for attachmentto the bottom of a drillstern for taking a forma-tionsani-plein the bottom of a drill hole, the combination which com-prises a mandrel mountable onv the bottom or the stem in alignment therewith, a shell sliolalcrly4A mounted upon theV mandrel, ruptura-ble means initially connecting mandrel and shell toprevent' such sliding; a core barrel? mounted onY the'bottom of the mandrel and having an'4 open lower cutting end, and a closure member mounted on theshell and?v adapted to close thee lower end of' thecore barrel' when the mandrel is slidupwardfwitr respect" tothe shell.

2. In apparatus for attachment to the bottom. of a drill stem for takingy a formation sample-in the bottom of a drill hole, the combination which comprises a. mandrel mountable on theA bottom or' the stem in alignment therewith; a shell sllid-l ably mounted upon the mandrel, a core barrel mounted: on the bottom of the mandrel and have ingy an open lower cuttingend and also-an open. upper end, a closure member mounted onthe shell and adapted to close the lowerend of the core barrel when the mandrelfis slid upward' with! respect to the shell, and a sealing plugI slida'ble in the borey of the core barrel.

3. In apparatus for attachment' toV thelbottomi of a rotaryv drill stem fortak-ing a formation sample in the bottom or adrill' hole, the conrbination which comprisesY a mandrel' mountable? on the bottomof the stem in alignment' there wth, av shell slidably-mounted' upon themand'rel a core barrel mounted on-thebottomof' the man--l drel and having an open lower cutting endl and also an open upper end, av closureu member mounted on the shell and adapted to closethe' lower end of the corev barrel when-` the mandrel is slid upward with respectv tothe shell; av seal"- ing plugslidable-in thebore of the barrel, a' seat for the plug adjacent the topV 0I" the barrer, and clamping means' actuated by" rotating the drill'l stem'Y for pressing thev closure. member against said lower end.

4-, Apparatus according to cl'aim- 3 provided with a- Valve in the plug which is seated when a core is' pushed upwardly in the barrel.

5. In apparatus for attachment tothe lmttonrk of a rotary drill stem for taking a formation sample in the bottomY ofl a dril'li hole, the come bi'nationI which comprisesa mandrel; mountable? on the bottom of the stern in alignment therewith, a shell slidably mounted upon the mandrel; a core barrelmounted onthe'bottom of' the man.- drel and having an open lower cutting' end). a closure member mounted on the shell and, adapted to closev the lower. end' of" the core barrel when the" mandrel is slid upward' with respect'. to the shell, a threaded bolt attachedY to the clos'- ure member and extending up into.- a. wrench. bore of non-circular cross section on the. axis. of. the mandrel, a nut slidable along the. bore butf rotatable thereby and., threaded; on the boli-l, an upper yoke attached to the barrel. and a. lower:v yoke attached to the. closure member with. the bolt arranged to press the two yokes. togetherv when the nut is rotated, thereby pressing, the closure member against the lower endf of. the barrel.

6. Apparatus according to. claim.. 5. provided.: With a wrench sleeve of' cylindrical section mounted in a bore in the mandrel and containing the wrench bore, and shearable means connecting the wrench sleeve to the mandrel.

7. In apparatus for attachment to the bottom of a rotary drill stem for punching out and recovering a sample from the bottom of a drill hole, the'combinaton which comprises a mandrel mountable on the bottom of the stem in alignment therewith, a sleeve mounted around the mandrel and slidable and rotatable with respect to the mandrel, rupturable means initially axing the sleeve to the mandrel, at least one core barrel mounted on and below the mandrel in alignment therewith, and having yan open lower cutting end and an open seat at its upper end, a sealing plug slidable upward in the core barrel to abut the seat, a closure member mounted on the sleeve to swing on an axis extending in the direction of the drill string to seal the lower end of the core barrel when it and the mandrel have slid upward sufficiently with respect to the sleeve, a spring for so moving the closure member and clamping means actuated through rotation of the mandrel and adapted to press the closure member upwardly against the bottom of the core barrel.

8. In apparatus for attachment to the bottom of a rotary drill stem for punching out and recovering a sample from the bottom of a drill hole, the combination which comprises a mandrel mountable on the bottom of the stem in alignment therewith, a sleeve mounted around the mandrel and slidable and rotatable with respect to the mandrel, rupturable means initially axing the sleeve to the mandrel, an upper yoke attached to the mandrel, at least one core barrel mounted on and below the mandrel in alignment therewith, and having an open lower cutting end and an open seat at its upper end, a sealing plug slidable upward in the core barrel to abut the seat, a closure member mounted on a lower yoke attached to the sleeve to swing on an axis extending in the direction of the drill string to seal the lower end of the core barrel when it and the mandrel have slid upward sumciently with respect to the sleeve, a spring for so moving the closure member, a threaded bolt passing through both yokes and extending up into a wrench bore of non-circular cross section on the axis of the mandrel, and a nut slidable along the bore, but rotatable thereby and threaded on the bolt above the upper yoke, the bolt and yokes being so arranged that rotation of the mandrel causes the nut to press the yokes toward each other.

9. In apparatus for attachment to the bottom of a rotary drill stem for taking a formation sample in the bottom of a drill hole, the combination which comprises a mandrel mountable on the bottom or the stern in alignment therewith, a shell slidably mounted upon the mandrel, a core barrel mounted on the bpttom of the mandrel and having an open lower cutting end, a closure member adapted to close the lower end of the core barrel when the mandrel is slid upward with respect to the shell, and clamping means actuated by rotating the drill stem for pressing the closure member against said lower end, said clamping means comprising a threaded bolt attached to the closure member and extending up into a bore of non-circular cross section in the mandrel on the axis thereof, a nut of corresponding cross section slidable in the bore and threaded on the bolt, an upper yoke attached to the barrel below the bolt, and a lower yoke attached to the closure member, the two yokes being so arranged that they are pressed toward each other by rotation of the nut on the bolt.

DONALD M. SMITH.

REFERENCES CITED The following references are' of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,617,659 Whinnen Feb. l5, 1927 2,216,962 Sewell Oct. 8, 1940 2,238,609 Sewell Apr. 15, 1941 2,373,323 Macready Apr. 10, 1945

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