Nozzles of tungsten carbide alloy for drill bits used in hydraulic jet drilling of wells are mounted in openings extending downwardly from a central chamber in a drill bit body through the bottom of the bit by screwing the nozzle into the opening from the bottom of the bit. A helical groove is cut in the outer surface of the nozzle and in the wall of the opening. A helical coil placed in the groove on the nozzle acts as threads engaging the groove in the wall of the opening as the nozzle is screwed into place. A backsplash plate on the lower surface of the bit has holes of larger diameter than the openings in the bottom of the bit in alignment with those openings. A shoulder on the lower end of the nozzles fills the holes in the backsplash plate to restrain upward movement of the nozzles and protect the helical coil from erosion.

Current U.S. Class:	175/393 ; 285/390; 411/411
Current International Class:	E21B 7/18 (20060101); E21B 10/46 (20060101); E21B 10/60 (20060101); E21B 10/56 (20060101); E21B 10/62 (20060101); E21B 10/00 (20060101); E21c 015/00 ()
Field of Search:	175/422,393,340 285/390 85/32CS,46

Meyer Neishloss Deane E. Keith Paul L. Tillson

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Claims

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We claim:

1. A drill bit for the hydraulic jet drilling of wells comprising a drill bit body having a central opening therein, a bottom member closing the lower end of the central opening, a backsplash plate of abrasion-resistant material secured to the lower surface of the bottom member, a plurality of cylindrical openings extending through the bottom member at different distances from the center of rotation of the drill bit, a hole through the backsplash plate in alignment with each of the cylindrical openings, an elongated cylindrical nozzle of abrasion-resistant material in each of the openings, a helical groove in the outer surface of the nozzles, a matching helical groove in the inner surface of the openings extending to the lower end thereof, and a helical coil of wire in the groove on the nozzles extending into the groove in the wall of the openings to hold the nozzles in place.

2. A drill bit as set forth in claim 1 in which the holes through the backsplash plate have a diameter larger than the openings to allow passage of the helical coil through the holes, a shoulder at the lower end of the nozzles is adapted to engage the lower end of the opening to limit upward movement of the nozzle, and the outer diameter of the nozzle below the shoulder is enlarged to move into and close the holes when the nozzles are in the mounted position.

3. A drill bit as set forth in claim 2 in which the groove in the nozzles has a maximum depth of approximately one-half the diameter of the wire in the helical coil.

4. Apparatus as set forth in claim 3 in which the groove in the nozzles has a round bottom and the nozzles are constructed of tungsten carbide alloy.

5. A drill bit as set forth in claim 1 in which the pitch of the groove is less than 20.degree. but high enough that the lands between the groove are at least as wide as the diameter of the wire.

6. Apparatus as set forth in claim 5 in which nozzles extending through the bottom member of the bit are oriented in a plurality of different angles to the vertical.

7. In a drill bit for hydraulic jet drilling in which a plurality of tungsten carbide alloy nozzles extend downwardly through cylindrical openings in the bottom of the drill bit body and at least some of the nozzles are inclined from the vertical, an improved mounting for the nozzles comprising a helical groove in the wall of the openings extending to the lower end thereof whereby the nozzles are insertable into the openings from the bottom, a round-bottomed helical groove in the outer surface of the nozzles matching the groove in the wall of the openings, and a helical coil of wire in the groove in the nozzles and the groove in the wall of the openings.

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Description

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This invention relates to drill bits and more particularly to a novel method of mounting nozzles and drill bits used for drilling wells.

In the rotary method of drilling wells, a drill bit mounted on the lower end of drill pipe is rotated on the bottom of the borehole to break rock into particles that can be removed from the hole. A drilling mud is circulated down the drill pipe, discharged from the drill bit, and returned to the surface through the annulus surrounding the drill pipe. An important function of the drilling mud is removing from the borehole cuttings broken from the bottom of the borehole by the drill bit. In the conventional rotary drilling method using rock bits with mechanical cutting elements that break the rock, the drilling mud is discharged from the drill bit through nozzles of relatively large diameter designed to produce large volume streams of drilling mud capable of washing rock particles from the bottom of the hole to reduce grinding of cuttings by the drill bit. Nozzles are frequently secured in the drill bit of the conventional rock bit by means of snap rings which engage grooves in the drill bit body.

A recently developed method for drilling hard rock formations is the hydraulic jet drilling method. In that method, penetration of the rock at the bottom of the borehole is obtained as a result of erosion of the rock by very high-velocity streams of abrasive-laden drilling liquid directed against the bottom of the hole. It is advantageous in hydraulic jet drilling to cut a plurality of concentric grooves in the bottom of the borehole with the high-velocity jet streams. Engagement of the drill bit with the bottom of the hole breaks the ridges separating the grooves. A jet stream velocity of at least about 650 feet per second is essential to obtain acceptable penetration rates in hard rock. That velocity is obtained by a pressure drop of at least about 4,000 psi through the nozzles from which the jet streams are discharged, and the high pressure drop makes it necessary for the drill bit body to have heavy walls. Nozzles in bits for hydraulic jet drilling are constructed of tungsten carbide alloys to reduce erosion by the abrasive particles suspended in the drilling liquid.

The nozzles through which the drilling mud is discharged in hydraulic jet drilling have a small diameter to permit the high velocities to be obtained without requiring an excessive total volume of liquid to be pumped through the drill pipe and the drill bit. A plurality of nozzles located at different radial distances from the center of rotation of the drill bit and oriented at different angles are used to obtain the desired cutting over the full diameter of the borehole. Because of the large number of nozzles, the heavy wall of the bit body, and the different angles at which the nozzles are oriented, mounting the nozzles in the bit is difficult and is facilitated by inserting the nozzles into openings in the drill bit body from outside of the drill bit. It has been found that the life of nozzles used under the extremely erosive conditions encountered in hydraulic jet drilling is increased if the nozzles are of substantially greater length than nozzles used in bits using mechanical cutting elements. The long nozzles further complicate mounting nozzles in the bits.

Abrasive particles discharged from the nozzles and rebounding from the bottom of the hole expose the lower end of the bit to severe erosion. Excessive erosion of the bottom of the drill bit by the rebounding abrasive particles is prevented by covering the bottom of the drill bit with backsplash plates of abrasion-resistant metals such as tungsten carbide alloys. If the snap rings used in the conventional rock bits to hold nozzles in place are used in hydraulic jet bits, the snap rings are rapidly eroded by rebounding particles. If the snap rings are positioned at an upper position on the nozzle to avoid erosion, a serious weakening of the nozzle is caused by the slot into which the snap ring extends. Snap rings would also require a nozzle of larger outside diameter to have sufficient metal to withstand the force tending to push the nozzle out of the bit. An increase in nozzle diameter aggravates the problem of mounting a large number of nozzles in the drill bit.

This invention relates to a drill bit for hydraulic jet drilling having a plurality of nozzles extending downwardly through the bottom of the bit for discharging high-velocity streams of abrasive-laden drilling liquid against the bottom of the borehole. The drill bit is constructed of steel and has its lower end covered with a backsplash plate of abrasion-resistant material such as tungsten carbide. Openings extending downwardly through the bottom member of the drill bit and the backsplash plate receive nozzles inserted into the openings from the bottom of the drill bit. The nozzles which are constructed of a hard abrasive-resistant alloy have grooves in their outer surface which match grooves in the wall of the opening through the bottom member. A helical wire coil in the grooves in the outer surface of the nozzle travels in the groove in the opening in the bottom member of the drill bit to permit the nozzle to be screwed into place. The groove in the outer surface of the nozzle is shallow; its depth is no more than one-half the diameter of the wire.

In the drawings:

FIG. 1 is a perspective view of a preferred drill bit for use in hydraulic jet drilling of wells.

FIG. 2 is a plan view of the bottom of the drill bit illustrated in FIG. 1.

FIG. 3 is a vertical sectional view taken along section line III--III in FIG. 2 of the drill bit.

FIG. 4 is a vertical sectional view along section line IV--IV in FIG. 2 with one of the nozzles removed to show the opening in which the nozzle is mounted in the bit.

FIG. 5 is a view partially in longitudinal section of the nozzle with the helical coil in the groove on the outer surface of the nozzle.

Referring to FIG. 1 of the drawings, a drill bit indicated generally by reference numeral 10 is shown having a drill bit body 12 with a shank 14 extending upwardly for connection to the lower end of drill pipe. As shown in FIG. 3, the upper end of shank 14 has a threaded pin 16 for engagement with threads on the lower end of the drill string, not shown. Drill bit body 12 has a central chamber 18 which communicates with the central opening 20 in the shank 14 for delivery of drilling liquid into the drill bit.

Again referring to FIG. 1, drill bit 10 has a plurality of flutes 22 spaced at intervals around the periphery of the drill bit and extending longitudinally along the outer surface of the drill bit to provide space between the drill bit and the borehole wall through which drilling liquid and cuttings can flow. Flutes 22 are separated by lobes 24. As is best shown in FIG. 3, a socket 26 is drilled downwardly from chamber 18 into each of the lobes for delivery of drilling liquid into the lower part of the drill bit and into the nozzle inlets, as is hereinafter described. Sockets 26 terminate above the lower end of the lobes 24 to leave a bottom member closing the lower end of the drill bit. Abrasion-resistant buttons 27 may be mounted in the drill bit body to reduce wear caused by the body rubbing against the borehole wall.

In the drill bit illustrated in the drawings, lobes 24 continue downwardly to form plateaus 28 separated by a recess 30 on the bottom surface of the drill bit providing space between the plateaus for the flow of cuttings. The lower end of each of the plateaus 28 is covered by a backsplash plate 32 of a hard abrasion-resistant material such as a tungsten carbide alloy. Stand-off elements 34 extend downwardly from the lower surface of the backsplash plates 32 to fix the distance between the lower surface of the backsplash plates and the bottom of the borehole. That portion of stand-off elements 34 below the lower surface of the backsplash plates 32 is of generally hemispherical shape with flattened surfaces 36 adapted to ride in grooves cut in the bottom of the borehole, as is hereinafter described. A plurality of nozzles 38 extend from sockets 26 within the bit downwardly through plateaus 28 and backsplash plates 32. The outlet ends of the nozzles are substantially flush with the lower surface of the backsplash plates.

Although a preferred type of drill bit has been illustrated in the drawings, this invention is not limited to those details of drill bit structure. For example, the drill bit could be of substantially cylindrical shape in horizontal cross section with a substantially flat bottom from which stand-off elements extend. While the recesses 30 are advantageous in facilitating flow of cuttings from below the drill bit, they are not essential to this invention. Similarly, the button-type, generally hemispherical stand-off elements are not necessary. While button-type stand-off elements are advantageous because they ride partially within grooves cut in the bottom of the hole, any stand-off elements of suitable height to fix the distance between the bottom of the borehole and the outlets of the nozzles can be used.

Because it is desirable to optimize the amount of cutting achieved per horsepower used or to achieve the highest possible drilling rate per horsepower spent, bits for hydraulic jet drilling of wells have a large number of nozzles of small diameter to allow discharging jet streams at high velocities against the bottom of the borehole at intervals over the full diameter of the borehole. A suitable arrangement of nozzles is illustrated in FIG. 2 in which inwardly sloping nozzles 38a are adapted to cut a central hole in the bottom of the borehole, vertical nozzles 38b, 38c and 38d are positioned to cut a plurality of concentric grooves in the bottom of the borehole spaced from each other and from the central hole by intervening ridges, and outwardly sloping nozzles 38e and 38f are positioned cut additional concentric grooves at larger radial distances from the center of the hole. The high-velocity streams discharged from nozzles 38f cut a groove having an outer diameter equal to the desired borehole diameter. Nozzles 38 identified in FIG. 2 by the same suffix are at the same distance from the center of rotation of the bit. Stand-off elements 34 are positioned to extend into the grooves cut by the nozzles and ride on the ridges separating the grooves to break the ridges and thereby speed rock removal from the bottom of the borehole. Drill bits for use in hydraulic jet drilling and having the standoff element and nozzle locations disclosed in the drawings of this application are described and claimed in U. S. Pat. No. 3,542,142 of Horst H. Hasiba entitled "Method of Drilling and Drill Bit Thereof." Stand-off elements 34 having the same letter suffix in FIG. 2 are the same distance from the center of rotation of the bit.

Nozzles 38 have outlets substantially flush with the lower surface of the backsplash plates on the lower ends of the plateaus 28 and open at their upper end into the socket 26 extending downwardly into those plateaus. Machining an opening 40 for nozzles 38 and inserting the nozzles downwardly from within the drill bit body 12 is virtually impossible because of interference of the wall of the drill bit body. In FIG. 4, an opening 40f is shown with a nozzle 38f in place and an opening 40a is shown before insertion of nozzle 38a. Openings 40 are drilled from the lower end of the plateaus 28 at the desired angle through the bottom member to open into the sockets 26. In this invention, backsplash plates 32 formed with openings 42 for the nozzles at the desired location and orientation are secured in place on the plateaus before the openings 40 are drilled. Each of openings 40 has a spiral groove 44 cut in its wall from the lower end of the openings 40 upwardly a distance to receive the full length of the coil, hereinafter described, mounted in the groove on the nozzle. Openings 42 through the backsplash plates 32 are not grooved but are of slightly larger diameter than the diameter of openings 40 to allow insertion of the nozzles with the helical coils in place on their outer surface.

Nozzles 38 have an enlarged shoulder 46 at their lower end adapted to fit slidably but snugly within the openings 44 in the backsplash plate 32. Shoulder 46 prevents the wire coil being exposed to the fluid rebounding from the bottom of the grooves and limits upward movement of the nozzle. A helical groove 48, best illustrated in FIG. 5, is cut in the outer surface of the nozzle 38 over a portion of the nozzle above the shoulder 46. Because nozzles 38 are constructed of tungsten carbide, a very hard material of low tensile strength, groove 48 preferably has a round bottom to minimize tensile stresses in the nozzle. A helical coil 50 of a suitable metal such as high carbon steel is inserted in the groove 48. Groove 48 has a depth not exceeding one-half the diameter of the wire; hence, is no more than one-half the depth that would be required for conventional threads. It is preferred that the depth of grooves 44 and 48 be substantially the same and approximately equal to one-half the diameter of the wire in coil 50. Music wire has been used effectively for holding nozzles in drill bits in accordance with this invention, but softer metals can be used. The long length of the coil results in a shear loading much lower than would be applied against a snap ring. The pitch of the groove is relatively low, for example less than 20.degree., to prevent loosening of the nozzle during use, but should be high enough that the lands between the grooves are at least as large as the wire diameter.

In the assembly of the nozzles in the drill bit, backsplash plates are secured to the lower surface of the plateaus 28 by a suitable method such as silver soldering and then holes 40 are drilled in the drill bit body. The helical coil 50 is then placed in the groove 48 on the outer surface of the nozzle, and the nozzle screwed into the openings 40. Screwing the nozzle into place is facilitated by slots 54 in the lower end of the nozzles. To prevent flow through the openings 40 around the outer surface of the nozzle, a sealing material is preferably placed on the outer surface of the nozzle before it is inserted into the openings 40. If desired, a thin rubber ring can be placed on the nozzle at the upper end of the shoulder 46 and compressed against the wall of the openings 40 when the nozzle is screwed into position. Epoxy cement also can be used for sealing and aids in holding the nozzle in place; however, it is preferred to use a sealing material which will permit removal of the nozzle for replacement. The sealant should not soften at temperatures reached by the bit. If the bit is to be used at temperatures higher than the softening points of epoxy sealants, low-melting point metallic alloys can be used as a sealant and the nozzles inserted and removed while the bit is at a temperature higher than the softening point of the alloy.

After mounting all of the nozzles in the drill bit, the drill bit is connected to drill collars and lowered into the well on the lower end of the string of drill pipe. Drilling liquid laden with an abrasive, preferably steel shot, is pumped down the drill string while the drill string is rotated, and the drilling liquid is discharged through the nozzles of the drill bit at a velocity exceeding 650 feet per second. The abrasive-laden liquid cuts grooves in the bottom of the borehole. Ridges between the grooves are broken by the stand-off elements. The cuttings are circulated from the bottom of the hole to the surface by the drilling liquid, and the drilling liquid is treated to remove the cuttings and is recirculated down the hole for further drilling.

This invention permits the construction of a drill bit for hydraulic jet drilling operations without limitations on the position of the nozzles resulting from interference with inserting the nozzles in the drill bit. The groove in which the helical wire is inserted can be easily cut in the outer surface of the nozzle even though the nozzle is constructed of a hard material such as tungsten carbide. In contrast, threads can only be cut with great difficulty on such alloy. This invention also allows avoidance of the concentration of tensile stresses that occurs in the conventional thread and is particularly damaging to hard materials such as tungsten carbide. Moreover, the depth of the groove in the outer surface of the nozzle is at most one-half the diameter of the coil; hence, is substantially less than the depth of a thread. The pitch of the groove is such that strong broad lands separate the groove and thereby avoid high concentration of tensile stresses in the relatively weak-in-tension tungsten carbide alloy of which the nozzles are constructed.

An important advantage of this invention is that worn nozzles may be removed from the drill bit and replaced with new nozzles without damaging the bit. In contrast, if the nozzles are inserted into the openings therefor from within the bit by welding the upper part of the drill bit body to the bottom after insertion of the nozzles, the worn nozzles cannot be removed without cutting the bit apart. It has been our experience that the drill bits and backsplash plates have a life at least twice as long as that of the nozzles; therefore, nozzle replacement permits substantial savings in bit costs.

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