US3254508A - Resilient unit for drill strings - Google Patents

Description

June 7, 1966 w. R. GARRETT 3,254,508

RESILIENT UNIT FOR DRILL STRINGS Filed Sept. 18, 1963 5 Sheets-Sheet 1 VV/ am orfe z INVENTOR ATTORNEY June 7, 1966 w. R. GARRETT 3,254,508

RESILIENT UNIT FOR DRILL STRINGS Filed Sept. 18, 1963 5 Sheets-Sheet. 2

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. BY 'Y United States Patent C 3,254,508 RESILIENT UNIT FOR DRILL STRINGS William R. Garrett, Midland, Tex., assignor to Drilco Oil Tools Inc., Midland, Tex., a corporation of ',Iexas Filed Sept. 18, 1963, Ser. No. 309,630 18 Claims. (Cl. 64-1) This invention pertains to a resilient unit for drill strings and more particularly to such a unit adapted to be placed in a rotary drill string between the drill collars and rock bit used in earth boring, e.g. for oil wells. It is believed that the use of such a unit increases the life of the bit and of the connections between the drill collars by reducing the magnitude of the stresses thereon as the bit rises and falls in the bottom of the hole being drilled.

Requirements of resilient drill string units, in addition to the provision of a member having a low longitudinal stress-strain ratio compared to the rest of the drill string, are the transmission of torque, longitudinal stress (tension and compression), and fluid between the drill pipe and drill bit, as required for drilling. A variety of means have heretofore been used to achieve these ends, including metal members in the form of helical springs and long thin tubes, rubber members in the form of sleeves and blocks, and various fluids including elastic fluids in sealed piston and cylinder units and viscous fluids in dashpots. Diliiculties encountered with the prior art units include the need for special seals and splines in some units, short life with others, and excessive overall length in the case of still other forms. Y

Ac'cording to the present invention a long life unit of reasonably short length is provided using only metal for stress transmission. All pressure seals, splines, and other parts subject to early failure due to wear, deterioration from heat and oil, fatigue, and other causes are eliminated. Specifically, a low stress-strain ratio mernber is provided comprising a plurality of thick metal washers and tubular rings utilized, e.g. by brazing, by welding or' by integral formation from a single piece of material, to form a bellows shaped corrugated pipe. The resulting structure is of suiiicient strength to transmit both torque and longitudinal stress and the high pressure drilling fluid between the drill collars and drill bit. To take care of bending moments there is provided a stiff tube concentric with and, preferably, surrounding the corrugated pipe with one end of the tube rigidly connected to the portion of the unit above the corrugated pipe and the lower end of the tube telescopically engaging a cylindrical bearing on the part of the unit below the corrugated pipe. The bearing has suiiicient length to transmit bending moments between tube and bearing without excessive angularity of tube and bearing. The tube has sufficient stiffness to transmit the bending moment without undue deformation. The tube also serves as a housing to keep the corrugated pipe out of contact with the wall of the bore hole.

The corrugated pipe used in the subject resilient unit, though of bellows shape, is made of rigid material as distinct from the eXible cloth, paper, and leather and similar thin flexible materials out of which accordion bellows, fire bellows, and expansible iile jackets and the like are made. It is to be distinguished also from a straight pipe which can contract only with the same overall stressstrain ratio as the metal of which it is composed. It is also to be distinguished Vfrom an open coil spring which, because of the spaces between the turns thereof, does not provide a fluid conduit. It is also to be distinguished from various devices employing rubber and other elastomeric materials which are subject to deterioration at high temperature.

According to one embodiment of the invention a further tube or liner is provided concentric with and inside of the rice .corrugated pipe to shield it from drilling iiuid. This rnner tube is rigidly connected to the part of the unit above the corrugated pipe and telescopically engages the part of the unit below the corrugated pipe. In addition the space between the outer tube or housing and the corrugated pipe is vfilled with a lubricating material, e.g. a liquid, to prevent the corrugated pipe from fretting against the outer tube. A floating seal is provided between the housing and the lower part of the unit to retain the lubricant.

For a detailed description of preferred embodiments of the invention reference will now be made to the accompanying drawings wherein FIGURE 1 is an elevation, partly in section showing one preferred embodiment of the invention;

FIGURE 2 is a view to a larger scale showing the crosssection of the wall of the corrugated pipe of the structu-re shown in FIGURE l.

FIGURE 3 is an enlarged cross-section of the seal forming a part of the structure shown in FIGURE l;

FIGURE 4 is an elevation partly in section showing another preferred embodiment of the invention;

FIGURE 5 is a View to a larger scale showing the crosssection of the wall of the corrugated pipe of the structure shown in FIGURE 4;

FIGURE 6 is a View similar te FIGURE 5 Showing another form of corrugated pipe;

FIGURE 7 is a vertical section through an integral corrugated pipe suitable for use in a resilient unit ernbodying the invention; and

FIGURES 8 and 9 are fragmentary vertical sections showing corrugated pipe fabricated by welding that are suitable for use in resilient units embodying the invention.

Referring now to FIGURE 1 there is shown 'a resilient drill string unit comprising a nipple 10 of drill collar outer and inner diameters with a tool joint threaded pin 11 at the upper end thereof. The nipple has'a pipe 12 of reduced outer diameter extending down from the full thickness central portion thereof. The pipe 12 is interiorly threaded to receive at 13 the threaded upper end of a pipe 14.

Pipe 14 has a neck 15 of reduced diameter compared to the rest of the sleeve. To the neck 15 is brazedjthe inner periphery of the uppermost of a series of thick metal washers 16 forming corrugated pipe 17. As shown best in FIGURE 2, the upper and lower surfaces 20 and 21 and the inner and outer peripheries 22 and 23 of each washer 16 are conical as is the outer periphery of neck 15 to which the uppermost washer 16 is brazed. The resulting cross-section is rectangular.

The outer periphery 23 of each washer 16 is brazed to one of a plurality :of outer tubular rings 25. Likewise the inner periphery 22 of each washer 16 is brazed to one of a plurality of inner tubular rings 26. The washers 16 alternate with one washer having its conical surfaces 20, 21 converging upwardly and the adjacent washer having same converging downwardly. This places `adjacent upper and lower surfaces of the washers at an acute angle and adjacent peripheral inner surfaces 22 and adjacent peripheral outer surfaces 24 at obtuse tangles. The rings 25 and 26 have inner and :outer peripheries respectively provided with pairs of conical surfaces at obtuse angles correlative to adjacent cuter peripheral surrfaces 23 and adjacent inner peripheral surfaces 22 and brazed thereto. The inner peripheral surface 22 of the lowermost washer 16 of corrugated pipe 17 is brazed to a correlative conical outer peripheral surface on neck 30 at the upper end of pipe 31. The washersil are thick, that is their thickness is in excess of 50% of their radial extent (between inner and outer peripheries). It will be apparent that the large areas of the inner and outer peripheral surfaces of the I washers and the adjacent correlative surfaces of the inner and outer rings reduce the shear stress in the brazed connections, whereby, through the use of good brazing methods and materials, torques well in excess of the 25,000 ft.lbs. needed as a maximum can be transmitted by the corrugated pipe. Included in the term brazing as herein used are all metallic joinings of metals (usually with a joining metal different from the metals being, joined) in which the joining metal is brought to a liquid state but the metals being joined are not. For example copper, copper alloys, silver solders and nickel silver may be used as material joining steel parts. The washers 16 and rings 25, 26 are preferably made of steel having a quench temperature below the melting point of the brazing material.

Into the lower end of pipe 31 is screwed the reduced diameter upper end 32 of the pipe 33. The lower end of pipe 33 is belled out to provide a tool joint threaded box 34.

An .outer tube or housing 40 is screwed at its upper end to the exterior of pipe 12, abutting the full diameter portion of nipple 10, thereby providing a rigid connection. The housing 40 extends down along the outside of corrugated pipe 17, concentric therewith and normally spaced therefrom, even when the corrugated pipe is fully loaded in compression.

The lower part 41 of housing 40 serves as a guide and ts telescopically over the cylindrical bearing surface 42 on pipe 31.

To the lower end of housing 40 is screwed a safety joint 50 having an inwardly projecting radial flange 51 which' is captured between stop surface 52 provided by the lower end of pipe 31 and stop surface 53 provided by a shoulder between the upper end 32 and the middle portion of pipe 33. There is thus formed a lost motion connection means which allows the corrugated pipe 17 to contract and elongate but which prevents complete separation and provides for transmission of longitudinal tension and compression forces in case the corrugated pipe breaks.

Portions 60 and 61 of the safety joint above liange 51 provide additional guides telescopically fitting over additional cylindrical bearing surfaces 62, 63 on pipes 31 and 33. For adequate support the combined length of the several guides and bearings should be at least as great as the diameter of the bearings. It will be seen that this minimum is exceeded several times with the illustrated embodiment.4 i

Referring now also to FIGURE 3, the lower part 70 of safety joint 50 has an enlarged inner diameter forming with the exterior of pipe 33 an annular chamber 71. Within chamber 71 is disposed an annular oating rubber seal 72. The core of the seal 72 is a metal ring 83.

Inner and outer annular lips 74, 75, 76, 77 are formed in the rubber part of the seal at the upper and lower ends thereof.

Below seal 72 an annular plug 70a is screwed into the lower end of safety joint 50, to prevent the entrance of trash into chamber 71 beneath the seal. The plug also positively retains the floating seal although it will stay in place by itself.

Above seal 72 in chamber 71 and in the clearances between, on the one side, the portion of the safety joint thereabove and housing 40 and, on the other side, pipes 33k and 31 and corrugated pipe 17 and pipes 14 and 12, there is disposed a lubricant 77, e.g. a light inert mineral oil, to prevent fretting between the housing 40 and corrugated pipe 17. The floating seal 72 keeps the drilling fluid from commingling with the lubricant. The seal adjusts its own position to allow for contraction and expansion of the lubricant, the seal sliding up or down in chamber 71 as the pressure of the drilling fluid and the temperature of the lubricant change.

Assording to the size of the clearances referred to in the preceding paragraph, the lubricant may have varying degrees of damping effect on the spring action of corrugated pipe 17. Preferably the clearances are large enough to reduce the damping substantially to zero, the lubricant serving merely as a lubricant to protect the exterior of corrugated pipe 17 from fretting against the housing 40.

To protect the interior of the corrugated pipe 17 against the abrasive action of the drilling fluid, an inner tube 'or liner 80 is provided concentrically within -the corrugated pipe. The upper end of tube 80 is screwed into the lower end of neck 15. The lower end of tube 80 forms a guide 81 telescopically engaging within a cylindrical surfaceor bearing 82 in pipe 31. The inner tube provides means additional to outer tube 40 to transmit bending moments from the upper end of the resilient unit to the lower end thereof.

summarizing, corrugated pipe `17 is provided at its upper end with pipe connection means comprising nipple 10 and .pipe 14, at its lower end with pipe connection means comprising pipes 31 and 33, and is protected interiorly by tube 80 and exteriorly by housing 40 and the lubricant 77.

In operation, the box 34 is usually connected to a bit, either directly or by means of a sub, and pin 11 is connected to the lowermost drill collar of a drill string, either directly or by means of a sub or drill collar connector. The corrugated pipe 17 reduces the magnitude of the stresses set up in the drill string and bit during drilling by allowing the bit to rise quickly when it rolls over a high spot, despite the inertia of the heavy drill collars thereabove.

Referring now to FIGURE 4 there is shown another preferred embodiment of the invention which is the same as that of FIGURE l except as follows:

(1) The inner tube or liner 80 has been omitted.

(2) The inner rings 26 of the corrugated pipe are formed integrally with the washers 16, as best shown in FIGURE 5.

(3) The washers 16 are of tapered cross-section, being thinner nearer the center of the washers and thicker at their outer peripheries, as shown best in FIGURE 5.

(4) The seal chamber 71 and seal 72 and lubricant 79 are omitted, the previously discussed clearances being large to reduce the washing-wearing action of the drilling -uid which fills the space occupied by the lubricant 79 of the FIGURE 1 embodiment.

In the FIGUR-E 4 embodiment, the drilling uid itself yacts as a lubricant to prevent fretting of the corrugated pipe against the housing 40. The integral washers and inner sleeves form bifurcated toroidal rings, indicated'at on the drawings, which are less subject to the abrasive action of the drilling Huid than the brazed connections of the inner `rings and washers of the FIGURE 1 embodiment, reducing the need for a liner such as .tube 80 of the FIGURE 1 embodiment. Since ythe integral construction of FIGURE 4 has greater ultimate unit strength, the juncture of washers 16 and inner ring 26 need not be of as large an area to transmit the necessary torque, whereby the washers may be tapered in cross-section as previously mentioned. This makes the corrugated pipe have a lower stress-strain ratio and makes it possible to use a shorter corrugated pipe than in the FIGURE 1 embodiment. By shortening the corrugated pipe and eliminating the floating seal, the overall length of the resilient unit of the FIGURE 4 embodiment is reduced compared to that of FIGURE 1. The operation of the unit of FIGURE 4 is generally ythe same as that of the embodiment of FIGURE l.

summarizing as to the FIGURE 4 unit, the bellows shaped corrugated pipe 90 is connected between a rst metal tubular means including a portion providing one pipe connection means including threaded box 34 and a portion thereabove providing a bearingsurface, and a second metal tubular means including a portion providing another pipe connection means including threaded nipple 11 and a tube portion including housing 40 telescopically engaging said bearing surface.

FIGURE 6 shows a further modication of the corrugated pipe construction in which half of the brazed joints of the corrugated pipe of the FIGURE 5 construction are eliminated by making the lower ends of the rings 25' integral with the toroidal rings 90'. In addition, the washer 16 is formed integral with neck 15 on pipe 14', and the lowermost bifurcated ring 90" is formed integral with neck 30. Otherwise the FIGURE 6 corrugated pipe is the same as that of FIGURE 5.

Depending-on such factors as cost, strength, life, and reliability, it may be preferred that the entire corrugated pipe be made as an integral unit, as shown in FIGURE 7. Internal and external grooves may be tu-rned in a tubular member leaving a series of washers 1116, interconnected by inner and outer rings 125, 126. Flat washers, as shown, would be easier to machine. The bottoms 117 of the grooves would be rounded with a diameter equal to the washer spacing. Corners 118 at the groove mouths are rounded also. The pipes 14 and 31 of the FIGURE 1 and 4 embodiments would also be formed integral with the corrugated pipe, e.g. as shown at 114 at the top of the FIGURE 6 corrugated pipe and at 131 at vthe bottom thereof.

Instead of unitizing the washers and rings by brazing as shown in FIGURES l and 2 or by for-ming them integrally as shown in FIGURE 7 or combinations thereof as shown in FIGURES 4 through 6, the Washers and rings could be welded together in -whole or in part. FIGURE 8 shows a construction wherein the Washers and inner rings are formed integrally providing bifurcated rings 290 similar tothe rings 90 of FIGURE 5, and outer rings 225 are welded to the rings 290, each ring 225 having an inturned supporting and spacing ange 226 and the rings 225 having welding lips 2.91. The rings are nested, and .then welded at 300. FIGUR-E. 9 shows la construction like FIGURE 8 except that the lower ends of the outer rings 225 are integral with the tops of the bifurcated rings 290' and the tongues 226 are omitted. The various corrugated pipes described herein can all be used in resilient units of the types shown in FIGURES l and 4.

While preferred embodiments of the invention have been shown and described, many modifications thereof can be made by one skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. A tubular unit to be 'connected between the drill bit portion and the drill collar portion of a rotary drilling string, said tubular unit comprising :an upper rigid fluid tight pipe,

pipe connection means at the upper end of .said upper pipe adapted for making connection to the drill co1- lar portion of a drill string.

a lowe-r rigid iiuid tight pipe,

pipe connection means at the lower end of said lower pipe adapted for making connection to the drill bit portion of a drill string, an intermediate resilient corrugated fluid tight pipe connected at its upper end to the lower end of the upper pipe and connected .at its lower end to the upper end of the lower pipe, said corrugated pipe having a lower stress-strain ratio than said rigid pipes with respect to axial loading to reduce the magnitude of Aaxial forces 'transmitted to the upper pipe and the drill collar portion of a drill string connected thereto resulting from short duration forces applied to the lower pipe and the drill bit portion of a drill string 'connected thereto, -said corrugated pipe having a large Aenough stressstrain ratio to provide means for resilently supporting the weight of :at least one drill collar on a drill bit without the corrugations going solid,

said corrugated pipe -further providing a uid conduit for transmitting iiuid under pressure when the upper rigid pipe is connected to the drill collar portion of a drill string and the lower rigid pipe is connected to the drill bit portion of a drill string,

a tube concentrically disposed around said corrugated pipe and connected at one end to one of said rigid pipes and lat the other end telescopically slidingly engaging the other of said rigid pipes,

and means to vent uid from the annulus formed between the ins-ide of the tube and the outside of the corrugated pipe in an amount equal to the volume reduction of :said annulus when said rigid pipes move toward each other and said corrugated pipe contracts.

2. Combination according to claim 1 with a safety joint connected to said tube, and means including a radial llange captured between stops to limit axial movement of said joint on the pipe with which said tube telescopically engages.

3. Combination according to claim 2 in which the radial `tlange is an inturned radial il'ange carried by said joint and the stops are on said pipe connection means.

4. Combination of claim 1 wherein said annulus is iilled with a lubricant, and including lioating seal means closing the space between the tube and the portion of the .pipe telescopically engaged therewith, said floating seal means including an annular ring free to move axially relative to both said tube and the last said pipe.

5. A resilient unit adapted to 'be connected between the -bit and drill collars of a rotary drill string comprismg upper and lower metal pipes each ot drill collar diameter at its maximum outer diameter part, the

lower end of the lower pipe being screw threaded for connection to `a bit and the upper end of the upper pipe being screw threaded for connection to a drill collar, i

an intermediate metal, resilient, corrugated pipe fixedly connected 'at its uper end'to the lower end of said :upper pipe and at its lower end to the upper end of said lower pipe and providing means to transmit tension, compression, torque, and duid pressure from said upper pipe to said lower pipe,

the maximum outer diameter of said corrugated pipe being of less than drill collar diameter,

a metal tube or drill collar diameter 'at its exterior and of larger inner diameter than the outer diameter of said corrugated pipe, said tube being rigidly connected to one end to one of said pipes and telescopically engaging the exterior of the other of said pipes to transmit bending moments therebetween,

the minimum inner diameter of said corrugated pipe being as large as the inner diameter of said pipes,

the entire radial extent of the corrugated pipe lying Within the volume defined by the inner periphery of said tube and the axial projection of the inner surfaces of said pipes,

said corrugated pipe providing a Huid tight barrier means independent of other means for separating the iluid pressure inside the unit from the fluid pressure outside of the unit.

. 6. A resilient unit for a drill string, said unit comprislng a first tubular metal pipe connection means,

a second tubular metal pipe connection means coaxial with the tirst pipe connection means and 'axially separated therefrom,

means to transmit bending moments between said pipe connection means including a metal tube concentricrwith said pipe connection means rigidly con-` nected at one end to the first pipe connection means and at its other end telescopically engaging the exterior of the second pipe connection means and corrugated pipe means concentrically disposed inside said metal tube and connected at its ends to said pipe connection means for resilently transmitting said corrugated pipe means also transmitting uid pressure from the rst pipe connection means to the second pipe connection means independently of said metal tube.

7. A resilient unit for a drill string, said unit having a one end and an other end, said unit comprising a rst metal tubular means including a portion providing one pipe connection means and a portion providing a bearing surface, said portions being rigidrly connected,

a second metal tubular means coaxial with said rst tubular means and including a portion providing an other pipe connection means and a tube portion telescopically engaging said bearing surface,

said tube portion being rigidly connected to said portion providing said other pipe connection means, said one pipe connection means being located near said one end of said unit and said other pipe connection means being located near said other end of said unit,

said bearing surface portion and said tu'be portion telescopically engaging same forming means to transmit lbending moments between the said portions that provide pipe connection means, and

corrugated pipe means concentrically disposed inside said tube portion and connected at its ends to said portions providing pipe connection means for resilently transmitting tension, compression, and torque between said portions providing pipe connection means,

said corrugated pipe means also transmitting fluid pressure from said portion providing one pipe connection means to said portion providing said other pipe connection means independently of said tube portion.

8. Combination of claim 7 wherein the corrugated pipe includes a plurality of pairs of metal washers, the outer peripheries of each of said pair of washers being unitized with outer metal rings and the inner periphery of each washer being unitized with the adjacent washer in the adjacent pair of washers with inner metal rings.

9. Combination of claim 8 wherein the corrugated pipe includes a tube extending axially from the washers at each end of the corrugated pipe and integral therecated ring has an outwardly extending lip to which the outer ring is welded.

' 12. Combination according to claim 10 wherein the 55 bifurcated rings are each integral with one of the adjacent outer rings.

` 13. Combination of claim 8 wherein said washers are conical, the washers in each adjacent pair converging in opposite directions, the pairs converging toward each other being each unitized at their inner peripheries with an inner one of said rings, the pair converging away from each other being each unitized at their outer peripheries with an outer one of said rings.

14. Combination according to claim 13 in which the outer peripheries of said Washers are thick (thickness exceeds 50% of radial extent), said unitization of the outer peripheries of the washers with the outer rings being =brazed joints.

15. Combination according to claim 14 wherein the inner peripheries of said washers are also thick and said utilization of said inner peripheries with said inner rings :are brazed joints.

16. Combination according to claim 15 wherein the inner and outer peripheries of said washers are conical surfaces with the peripheral surfaces of adjacent pairs that are unitized with the rings forming obtuse angles measured exterior to the washers, the rings having surfaces correlative to said peripheral surfaces.

17. Combination according to claim 13 wherein the inner peripheries of said washers are thinner than the outer peripheries.

18. Combination according to claim 17 wherein the inner peripheries of said Washers fare unitized with said inner rings by being formed integrally therewith.

References Cited by the Examiner UNITED STATES PATENTS 1,471,143 10/1923 Cromwell 64-15 2,301,105 11/1942 Yost 175-321 2,565,296 8/1951 Chyle 138-121 2,870,617 1/ 1959 Peters 64-15 3,023,014 2/1962 Donner 227--173 3,106,414 10/ 1963 Peters 285-226 3,122,902 3/1964 Blair et a1. 64-23 FOREIGN PATENTS 471,118 2/ 1929 Germany.

812,135 8/1951 Germany.

272,052 2/ 1951 Switzerland.

References Cited by the Applicant UNITED STATES PATENTS 2,815,928 12/1957 Bodine.

FOREIGN PATENTS 631,398 6/1936 Germany.

BROUGHTON G. DURHAM, Primary Examiner. ROBERT C. RIORDON, Examiner.

Claims (1)

1. A TUBULAR UNIT TO BE CONNECTED BETWEEN THE DRILL BIT PORTION AND THE DRILL COLLAR PORTION OF A ROTARY DRILLING STRING, SAID TUBULAR UNIT COMPRISING AN UPPER RIGID FLUID TIGHT PIPE, PIPE CONNECTION MEANS AT THE UPPER END OF SAID UPPER PIPE ADAPTED FOR MAKING CONNECTION TO THE DRILL COLLAR PORTION OF A DRILL STRING. A LOWER RIGID FLUID TIGHT PIPE, PIPE CONNECTION MEANS AT THE LOWER END OF SAID LOWER PIPE ADAPTED FOR MAKING CONNECTION TO THE DRILL BIT PORTION OF A DRILL STRING, AN INTERMEDIATE RESILIENT CORRUGATED FLUID TIGHT PIPE CONNECTED AT ITS UPPER END TO THE LOWER END OF THE UPPER PIPE AND CONNECTED AT ITS LOWER END TO THE UPPER END OF THE LOWER PIPE, SAID CORRUGATED PIPE HAVING A LOWER STRESS-STRAIN RATIO THAN SAID RIGID PIPES WITH RESPECT TO AXIAL LOADING TO REDUCE THE MAGNITUDE OF AXIAL FORCES TRANSMITTED TO THE UPPER PIPE AND THE DRILL COLLAR PORTION OF A DRILL STRING CONNECTED THERETO RESULTING FROM SHORT DURATION FORCES APPLIED TO THE LOWER PIPE AND THE DRILL BIT PORTION OF A DRILL STRING CONNECTED THERETO, SAID CORRUGATED PIPE HAVING A LARGE ENOUGH STRESSSTRAIN RATIO TO PROVIDE MEANS FOR RESILIENTLY SUPPORTING THE WEIGHT OF AT LEAST ONE DRILL COLLAR ON A DRILL BIT WITHOUT THE CORRUGATIONS GOING SOLID, SAID CORRUGATED PIPE FURTHER PROVIDING A FLUID CONDUIT FOR TRANSMITTING FLUID UNDER PRESSURE WHEN THE UPPER RIGID PIPE IS CONNECTED TO THE DRILL COLLAR PORTION OF A DRILL STRING AND THE LOWER RIGID PIPE IS CONNECTED TO THE DRILL BIT PORTION OF THE DRILL STRING, A TUBE CONCENTRICALLY DISPOSED AROUND SAID CORRUGATED PIPE AND CONNECTED AT ONE END TO ONE OF SAID RIGID PIPES AND AT THE OTHER END TELESCOPICALLY SLIDINGLY ENGAGING THE OTHER OF SAID RIGID PIPES, AND MEANS TO VENT FLUID FROM THE ANNULUS FORMED BETWEEN THE INSIDE OF THE TUBE AND THE OUTSIDE OF THE CORRUGATED PIPE IN AN AMOUNT EQUAL TO THE VOLUME REDUCTION OF SAID ANNULUS WHEN SAID RIGID PIPES MOVE TOWARD EACH OTHER AND SAID CORRUGATED PIPE CONTRACTS.

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