US3384192A

US3384192A - Hydraulic jet bit

Info

Publication number: US3384192A
Application number: US516493A
Authority: US
Inventors: Robert J Goodwin; Joseph L Pekarek
Original assignee: Gulf Research and Development Co
Current assignee: Gulf Research and Development Co
Priority date: 1965-12-27
Filing date: 1965-12-27
Publication date: 1968-05-21
Anticipated expiration: 1985-05-21
Also published as: NL6618207A; DE1301783B; GB1136739A; BE691783A; FR1506022A

Description

May 21, 1968 R. J. GOODWIN ET AL HYDRAULIC JET BIT 2 Sheets-Sheet 1 Filed Dec. 27, 1965 INVENTORS.

Fig. 2

P085271]. 6000M JQSEPH L. PA K/EEK May 21, 1968 R. J. eooowm ET AL. 3,384,192

HYDRAULIC JET BIT 2 Sheets-Sheet 2 Filed Dec. 2'7, 1965 INVENTORS. ROBERT J. 6000140 JOSE H L. PE/(AAEK United States Patent 3,384,192 HYDRAULIC JET BIT Robert J. Goodwin, Oakmont, and Joseph L. Pekarek, Penn Hills Township, Allegheny County, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Filed Dec. 27, 1965, Ser. No. 516,493 8 Claims. (Cl. 17 -422) ABSTRACT OF THE DISCLOSURE A drill bit for hydraulic jet drilling comprising an elongated drill bit body having a central opening therein closed at its lower end by a bottom member, the lower surface of which is covered by an abrasion-resistant backsplash plate at least one inch thick. Abrasion-resistant nozzles extend downwardly through the bottom member and the backsplash plate with their outlets substantially flush with the lower surface of the backsplash plate. The upper ends of the nozzles extend at least about /2 inch above the bottom member to reduce plugging of the nozzles and improve uniformity of fiow through the nozzles. Standoff bars unitary with the backsplash plate maintain the required spacing between the outlets of the nOZZles and the bottom of the borehole.

This invention relates to the drilling of wells, and more particularly to a bit for use in driiling wells by means of high-velocity jets of abrasive-laden liquids.

For many years, most oil and gas wells have been drilled by the rotary drilling method in which a bit mounted on the lower end of drill pipe is rotated against the bottom of the borehole while a liquid, usually referred to as drilling mud, is circulated down the drill pipe and upwardly through the annulus between the drill pipe and the borehole wall to carry cuttings from the borehole. In the usual rotary drilling operation, the penetration of the rock at the bottom of the borehole is by means of mechanical elements of the bit. For example, in a fishtail bit, blades extend from the bottom of the bit downward to cut into the bottom of the borehole. In rock bits, rollers having cutting teeth extending from their outer surface are mounted on the bottom of the bit to break rock from the bottom of the borehole as the drill pipe is rotated. With both the fishtail and roller bits, a substantial weight of the order of 3,000 pounds or more per inch of bit diameter is applied to the bit to increase the force of the cutting elements against the bottom of the borehole.

Nozzles in conventional rotary drilling bits direct the drilling mud against the cutters to remove cuttings from the cutters. One type of bit that has been used more Widely in recent years is the so-called jet bit. Nozzles of the jet bits are located to direct the drilling mud against the bottom of the borehole, rather than against the cutters, to sweep cuttings from the bottom and prevent their regrinding by the cutters. The stream of drilling mud actually penetrates softer formation to increase the drilling rate more than would result from mere cleaning of the bottom of the hole.

Rotary drilling with either conventional or jet bits has not been successful in increasing drilling rates in hard, abrasive formations such as those that occur in west Texas. The slow drilling rate that is experienced in those formations results in substantial wear of the bits and makes necessary frequent replacement of the bits during the drilling of the well. The time required for the round trips during which the bit is pulled from the hole and replaced contributes to the very high cost of drilling in hard formations.

3,384,192 Patented May 21, 1968 'One method that has been developed in an effort to obtain higher drilling rates in hard formations is hydraulic jet drilling. In that method of drilling, an abrasive laden liquid is directed in narrow streams at extremely high velocities against the bot-tom of the hole from nozzles in rotating bits to penetrate the formation by the abrasive action of the particles suspended in the drilling liquid rather than mechanical cutting or grinding elements. Hydraulic jet drilling allows substantially higher penetration rates to be obtained in hard formation-s than are obtained with conventional or jet-type rotary bits; however, the highly erosive conditions inherent in the hydraulic jet drilling process severely limit the life of both the body of the drill bit and the nozzles. It is desirable to provide drill bits having increased life to reduce the number of round trips necessary for replacement of the drill bit during the drilling of a well and also to provide high drilling rates.

The extremely high velocity of at least 500 feet per second, and preferably 600-900 feet per second, for high drilling rates, required for hydraulic jet drilling in hard formations makes necessary very high inputs of power. In a typical hydraulic jet drilling operation for drilling a borehole 7 inches in diameter, 2,000 to 2,500 horsepower is required for pumping the drilling liquid at the required rate. It is an important object of this invention to provide a bit for hydraulic jet drilling which will allow a high rate of penetration at a minimum power consumption.

This invention resides in a novel bit for drilling wells by hydraulic jets of abrasive-laden liquid in which an elongated hollow bit body closed at its lower end has a plurality of nozzles extending through the lower end and opening downwardly in position to cut a plurality of concentric groove-s in the bottom of the borehole as the bit is rotated. At least one of the nozzles is positioned near the periphery of the bit and angled outwardly to cut an annular groove of larger outer diameter than the bit body. The nozzle inlets extend upwardly above the upper surface of the bottom of the drill bit body, and the nozzle outlets are at substantially the lower surface of an abrasion-resistant backspl'ash plate covering the entire lower surface of the drill bit and having a substantial thickness to extend upwardly beyond the backsplash of abrasive particles discharged from the outer nozzles. Stand-oil bars of abrasion-resistant material protrude downwardly from the lower surface of the backsplash plate to fix the distance from the outlets of the nozzles to the bottom of the hole. The stand-off bars extend along the lower surface of the backsplash plate from the groove cut by the central nozzle to the groove cut by the outer nozzle.

In the drawings:

FIGURE 1 is a diagrammatic view, partially in cross section, of apparatus for drilling wells with the drill bit of this invention;

FIGURE 2 is a vertical sectional view of the drill bit attached to an adapter for connection to the lower end of drill pipe;

FIGURE 3 is a bottom view of the embodiment of the drill bit illustrated in FIGURE 2;

FIGURE 4 is a horizontal sectional view taken along section line 44 in FIGURE 2; and

FIGURE 5 is a fragmentary vertical sectional view taken along section line 5-5 in FIGURE 3.

Referring "to FIGURE 1, a derrick 10 is shown in place above a well, indicated generally by 12, having casing 14 set therein. Drill pipe 16 is shown extending downwardly in the well below the level of the casing. The drill bit 18 of this invention is connected to the lower end of drill piple1 16 and rests on the bottom of the borehole of the we The upper end of casing 14 is closed by a casing head 20. A discharge line 22 opens from the casing immediately below the casing head 20 for delivery of the drilling liquid with entrained cuttings to apparatus indicated by the legend, Drilling Liquid Treatment. Drilling Liquid Treatment will ordinarily consist of passing drilling liquid discharged from the well to a shale shaker for removal of cuttings, then to separators for the removal of excessive amounts of fine particles, and to cooling apparatus for adjusting the temperature of the drilling liquid and then adding abrasive to adjust the concentration of the abrasive in the drilling liquid before it is delivered to high pressure pumps capable of increasing the pressure on the drilling liquid to about 4,000 psi. or more for recirculation in the well. The drilling liquid discharged from the high pressure pumps is delivered through line 26 into the upper end of drill pipe 16 which passes through rotary table 24 for rotation of the drill pipe during the drilling operation. In the hydraulic jet drilling operation, in contrast to the ordinary rotary drilling operations, the weight applied to the drill bit is not substantial. A bit weight of 1,000 pounds per inch of bit diameter, or less, approximately one-fifth the weight applied in conventional rotary drilling operation, is adequate.

The drilling liquid circulated in the hole contains an abrasive material such as sand, ferrous grit, or ferrous shot which is discharged at an extremely high velocity from nozzles in the drill bit against the bottom of the hole. The particle size of abrasive material will depend upon the size of the orifices in the nozzles in the drill bit. It is desirable to use the largest abrasive particles that will pass through the nozzles and can be handled in the high pressure pumps because the drilling rate is faster with larger particles. Nozzles having an orifice diameter of inch have been found to be especially effective. If the orifice diameter of the nozzles in the drill bit is inch, abrasive particles of 7 to 80 mesh in the U.S. Sieve Series, and preferably 16 to 50 mesh particles, can be used. The size of abrasive particles used will vary with the type of abrasive. For example, ferrous abrasive particles of 50 80 mesh give drilling rates as high as 20-40 mesh sand particles. The concentration of the abrasive particles in the drilling liquid also will depend upon the particular abrasive material used. For example, if sand is the abrasive, a concentration of 6 percent by volume sand in the drilling liquid has been found to be effective. If ferrous abrasive is used, an abrasive concentration of about /2 to 4 percent, by volume, and preferably 1 /2 to 2 /2 percent, is used.

Referring to FIGURE 2 of the drawings, drill bit 18 is illustrated having an elongated, substantially cylindrical hollow body having a lower cylindrical section 28 joined to the lower end of a central adapter section 30 which in turn is joined to the lower end of an upper cylindrical section 32. The lower end of the drill bit 18 is closed by a bottom member 34 and the upper end by a top 36 having a threaded centrally positioned upwardly opening box 38 for the reception of the threaded lower end of the drill pipe 16.

If the drill bit is of circular cross section, the internal diameter of the drill bit body should be at least the internal diameter immediately above the bottom for a distance above the bottom at least 1 /2 times the outside diameter of the bottom to provide an elongated internal chamber 40 of relatively large diameter. With a drill bit body of irregular cross section, such as drill bit 18 illustrated in FIGURE 2, the c=ross-section area of the drill bit body should be at least 55 percent of the cross-sectional area at the top surface of the bottom member 34 for a distance above the bottom member at least 1 /2 times the maximum outside diameter of bottom member 34. Drilling liquid discharged from the drill pipe tends to channel directly toward nozzles located in the center of the drill bit. The elongated chamber 40 of large diameter breaks up the flow pattern of drilling liquid discharged from the drill pipe 16 and causes more uniform distribution of abrasive particles to all of the nozzles. It also reduces the velocity of the drilling liquid approaching the nozzle inlets and reduces erosion of the nozzles. In the drill bit illustrated in FIGURE 2 of the drawings, an internal web 42 extends across the adapter section of the drill bit to reinforce the drill bit and thereby improve its ability to withstand hi h internal pressures.

It is preferred that the body of the drill bit have sections of reduced outer diameter to provide space for flow of drilling liquid and cuttings upwardly around the drill bit. In the drill bit illustrated in FIGURES 2 through 5, such space is provided by diametrically opposed flutes 44 best illustrated in FIGURE 4 of the drawings. The flutes pro vide a continuous passage from the bottom member 34 opening upwardly into the annular space surrounding the drill ipe 16. As is best shown in FIGURE 4, the reinforcing web 42 extends across the adapter 30 in alignment with the flutes 44.

Secured to the bottom member 34 of the bit is a backsplash plate 45 of a hard abrasive material such as tungsten carbide. The backsplash plate 46 should have a Rockwell A hardness of at least and preferably at least 90. It must have resistance to impact as well as abrasion and must be capable of withstanding corrosive effects of the drilling liquid used in the drilling operation. A suitable abrasive-resistant material is a tungsten carbide alloy containing tungsten and cobalt in a ratio of approximately 94.5 25.5. Such alloys are available commercially. The backsplash plate 46 should have a substantial thickness, for example, at least 1 and preferably 1 /2 to 2 inches to prevent erosion of the side of the drill bit by abrasive particles discharged from the outer nozzles, hereinafter described, rebounding from the bore hole walls. Abrasives and cuttings merely carried upwardly around the drill bit by the ascending drilling liquid do not cause serious erosion; hence, a backsplash plate thicker than 2 inches does not result in advantages justifying the additional cost. Backsplash plate 46 can be secured to the lower surface of the bottom member 34 by a suitable silver solder resistant to the drilling liquid or by other suitable means such as bolts.

Formed as an integral part of the backsplash plate 46 are stand-off bars 48 protruding downwardly from the otherwise substantially fiat lower surface of the backsplash plate a distance adapted to fix the outlet of the nozzles a desired distance from the bottom of the borehole in the manner hereinafter described. Stand-off bars 48 should project from the remainder of the lower surface of the backsplash plate 46 a distance of A1, inch to 1% inches, and preferably will extend for a distance in the range of about inch to 1 inch from the bottom of the backsplash plate. At the lower range of thickness of the stand-off bars, erosion of the drill bit is severe because of the backsplash of the abrasive-laden liquid from the bot-tom of the hole. If the thickness of the stand-off bars is greater than about 1% inches, the rate of cutting by the high velocity stream of liquid is seriously reduced.

It is preferred that the stand-off bars 48 be positioned directly below the flutes 44 to make most effective use of the space available in the bit since that space cannot readily be occupied by nozzles. Wedge-shaped stand-off bars, as best shown in FIGURE 3 of the drawings, give a maximum mass of abrasive-resistant material. The inner end of the stand-off bars is spaced from the center of rotation of the drill bit to provide clearance for the highvelocity stream of drilling liquid discharged from the inner nozzle, hereinafter described. Stand-off bars 43 are of a hard material such as tungsten carbide alloys to withstand abrasion by the hard formations drilled, as well as the highly erosive conditions resulting from backsplash of the abrasive particles. To avoid erosion at welds or soldered joints, stand-of]? bars 48 and backsplash plate 46 should be composed of a single piece of hard abrasive material such as Kennametal K-6, Kennametal 3055, or

Kennarnetal 3411, for example, tungsten carbide alloys.

Bottom member 34 and backsplash plate 46 are drilled to receive a plurality of nozzles 50. As illustrated in FIG- URE 5 of the drawings, the lower end of the receptacles drilled for the nozzles 50 is tapered to prevent downward movement of the nozzle during the drilling operation. Leakage into the receptacle along the outer wall of the nozzles is prevented by a suitable sealing material such as an epoxy cement or silver solder. The taper at the lower end of the receptacles positions the nozzles with the center line of their outlets substantially in the plane of the lower surface of the backsplash plate 46. Thus, the stand-off bars 48 fix the distance of the nozzle outlets from the bottom of the borehole. Nozzles 50 are at least about 2 /2 inches long, and preferably about 3 inches long, such that the inlet end extends upwardly above the upper surface of bottom member 34 for a distance of at least /2 inch. It has been found that plugging of the nozzles with abrasive is reduced by extending the nozzles above the bottom member 34. Moreover, because the long nozzles have their inlets closer to the center of the drill bit body and require less change in direction of the drilling liquid, they are not eroded as severely as shorter nozzles.

Nozzles 50 are constructed of a highly abrasi0nresistant metal, such as tungsten carbide. The nozzles are substantially entirely within the bit body. Any part of the nozzles that might be below the lower surface of the backsplash plate 46 is small and, further, is protected from impact with the bottom of the borehole by the standoff bars 48; hence, the abrasion resistance of the metal from which the nozzles are made is of controlling importance, and the ability to withstand impact is of less importance than for backsplash plate 46 and stand-off bars 48. Nozzles 50 are constructed of a material having a Rockwell A hardness of at least 85.

The function of the nozzles is to discharge the abrasive-laden drilling liquid at a high velocity against selected areas at the bottom of the borehole to cut grooves in the formation being drilled. Nozzles having outlet orifices in the range of about to i inch are preferred for this purpose. Larger orifices demand excessive hydraulic horsepower because the volume of fluid discharged from the nozzles is proportional to the square of the diameter of the nozzle orifice. Smaller orifices require extremely finely divided particles which are less efiective than larger particles in cutting grooves in the bottom of the borehole.

The nozzles 50 are positioned in the drill bit and oriented to accomplish several purposes. The number of nozzles and their location and orientation in the drill bit will be dependent on the size of borehole to be drilled. Nozzles should be positioned to cut a hole in the formation with a diameter preferably about A to /2 inch larger than the largest diameter of the body of the drill bit. For this purpose, outwardly slanting nozzles 50a are positioned near the outer edge of the backsplash plate and slant outwardly to direct streams against the bottom of the borehole to cut a groove having an outer diameter larger than the diameter of the drill bit. Other nozzles are positioned to cut grooves in the bottom of the borehole spaced apart a small enough distance to allow the stand-off bars to break intervening ridges from the bottom of the borehole. Generally, such ridges should have a width not greater than /2 inch.

In the drill bit illustrated in FIGURE 3, a plurality of outwardly slanting nozzles 50b are positioned at a smaller distance from the center of rotation of the drill bit than nozzles 50a. Stil-l closer to the center of rotation of the drill bit are outwardly slanting nozzles 50c adapted to cut a groove spaced inwardly from the groove cut by nozzles 50b. Nearer the center of rotation of the bit is a nozzle 50d slanting inwardly to cut a hole in the center of the borehole extending outwardly beyond the inner ends '52 of the stand-off bars 48.

Nozzles

50a, 50b, and 500 slope outwardly, and nozzle 50d slopes inwardly. Nozzle 50d should be positioned to direct the drilling liquid between the inner ends of the stand-off bars to reduce erosion of them. Positioned at a radial distance from the center of rotation to discharge a stream against the bottom of the borehole between the groove cut by nozzles 50c and the hole cut by nozzle 50d is a vertical nozzle 50s, shown in FIGURES 3 and 5. Nozzles 50c reduces the width of the base of the ridge between grooves cut by inwardly slanting nozzle 50d and outwardly slanting nozzles 50c. The slanting nozzles cut wider grooves and cause less erosion from backsplash than vertical nozzles, and also locate the inlet end of the nozzles near the center of the bit to obtain more uniform flow rates and more direct flow into the nozzles. In general, the number of nozzles at any particular radial distance from the center of rotation of the bit increases, not necessarily directly, as the radial distance increases because of the larger amount of rock that must be removed in the outer grooves.

In the operation of the drill bit, drilling liquid having abrasive suspended therein is delivered under a pressure of the order of 4,000 pounds or more through the drill pipe 16 to the inlets of the nozzles 50. The drilling liquid is discharged at a high velocity of at least 500, and preferably more than 600, feet per second from the nozzles to cut grooves in the bottom of the borehole. During the drilling operation, the drill pipe 16, and consequently drill bit 18, is rotated whereby the nozzles cut annular grooves in the bottom of the borehole.

The extension of nozzles 50 above the upper surface of the bottom member 34 of the drill bit has been found to reduce plugging of the nozzles with abrasive particles. Because plugging of any nozzles in a drill bit decreases the efficiency of the bit and can make it necessary to pull all the drill pipe 16 from the hole to clean the bit, important savings in time are made possible by positioning the upper ends of the nozzles above the bottom member 34. The elongated nozzles also position the inlet ends of the nozzles near the center of the body 28, and, in combination with the elongated body of large diameter, cause flow of drilling liquid at substantially uniform rates through the various nozzles. In this manner, the depth of the several grooves cut in the bottom of the hole can readily be made substantially the same, and optimum stand-off from the bottom of the hole for all of the nozzles can be obtained to give a high rate of penetration of the formation being drilled,

We have found that the serious erosion heretofore encountered on the body of the drill bit has been caused primarily by rebounding of abrasive particles discharged from the outer nozzles and that erosion of the body of the drill bit by the upwardly flowing stream of cuttings and drilling liquid is not severe. The thick unitary backsplash plate and stand-off bars raise all welds, solder joints, and steel parts above the area of severe erosion, and thereby eliminate serious erosion and weakening of the body of the bit.

We claim:

1. A drill bit for the hydraulic jet drilling of wells comprising an elongated tubular body adapted to be connected to the lower end of a drill string, said body having a central opening extending downwardly therethrough communicating with the drill string, a bottom member closing the lower end of the body, the cross-sectional area of the central opening being at least 55 percent of the cross-sectional area at the upper surface of the bottom member for a distance at least 1 /2 times the outside diameter of the bottom member, a backsplash plate of abrasion-resistant material at least one inch thick covering the entire lower surface of the bottom member, a plurality of abrasion-resistant nozzles extending through the bottom member and backsplash plate for the discharge of drilling liquid therethrough, the outlets of the nozzles being substantially flush with the lower surface of the backsplash plate, said nozzles being positioned to cut in the bottom of the borehole an outer groove having a diameter slightly larger than the outside diameter of the drill bit, a central hole, and intermediate grooves between the central hole and outer groove, and a stand-off bar of abrasion-resistant material unitary with the backsplash plate extending for a distance in the range of /1 inch to 1% inches downwardly from the lower surface of the backsplash plate.

2. A drill bit as set forth in claim 1 in which the nozzle inlets are at least /2 inch above the upper surface of the bottom member.

3. Apparatus as set forth in claim 1 in which the back splash plate has a thickness of at least 1- /2 inches, and the nozzles have a length in the range of 2 /2 to 3 inches.

4. In a drill bit for the hydraulic jet drilling of wells in which an elongated hollow drill 'bit body is mounted on the lower end of a drill string for rotation in the well, said drill bit body having a central opening therein communicating with the drill string and a bottom member closing the lower end of the central opening, the improvement comprising an abrasion-resistant backsplash plate at least 1 inch thick covering the entire lower surface of the bottom member, said backsplash plate being substantially fiat over the major portion of its lower surface, standoff bars unitary with the backsplash plate protruding downwardly from the lower surface for a distance of /1 inch to 1% inches, an inwardly sloping nozzle extending downwardly through the bottom member and the backsplash plate adapted to cut a central hole in the bottom of the borehole, an outwardly sloping nozzle extending downwardly through the bottom member and the backsplash plate in position to cut an outer groove having a diameter larger than the diameter of the drill bit, said standoff bars extending from the lower surface of the backsplash plate over an interval to overlap the central hole and the outer groove cut by the inner nozzle and the outer nozzle, said nozzles being constructed of abrasion-resistant material and having their outlets substantially flush with the bottom of the backsplash plate.

5. A drill bit for hydraulic jet drilling of wells comprising a hollow drill bit body adapted to be mounted on the lower end of drill pipe, said drill bit body having a central opening extending downwardly therethrough for communication with the drill pipe, a bottom member closing the lower end of the drill bit body, said central opening having a cross-sectional area at least 55 percent of the cross-sectional area of the upper surface of the bottom member for a distance above the bottom member of at least 1 /2 times the outside diameter of the drill bit, a backsplash plate of abrasion-resistant material at least 1 /2 inches thick secured to the lower surface of the bottom member, outwardly slanting outer nozzles extending downwardly through the bottom member and backsplash plate positioned to direct a stream against the bottom of the borehole and cut a groove therein having an outer diameter larger than the outer diameter of the drill bit, an inwardly slanting inner nozzle extending downwardly through the bottom member and backsplash plate positioned to cut a central hole in the bottom of the borehole, intermediate outwardly slanting nozzles extending downwardly through the bottom member and backsplash plate positioned to cut intermediate grooves in the bottom of the borehole with intervening ridges between the central hole and the outer groove, said nozzles being constructed of abrasion-resistant material and having their outlets substantially flush with the bottom surface of the backsplash plate, an abrasion-resistant stand-off bar unitary with the backsplash plate and protruding downwardly therefrom for a distance of inch to 1% inches, said stand-01f bar extending continuously from the outer edge of the drill bit to an inner end above the central hole cut in the bottom of the borehole.

6. A drill bit as set forth in claim 5 in which the inlet ends of the nozzles extend at least /2 inch above the bottom member.

7. In a drill bit for the hydraulic jet drilling of wells in which an elongated drill bit body is mounted on the lower end of a drill string for rotation in the well and delivery of an abrasive-laden liquid to the drill bit, said drill bit body having a central opening therein of substantially larger cross section than the opening through the drill string, and a bottom member closing the lower end of the drill bit body, the improvement comprising an abrasion-resistant backsplash plate at least one inch thick covering the entire lower surface of the bottom member of the drill bit, a plurality of outwardly slanting abrasion-resistant nozzles extending downwardly through the bottom member and the backsplash plate positioned to discharge a high-velocity stream against the bottom of the borehole to cut an outer groove therein having an outer diameter larger than the outer diameter of the drill hit, an inwardly slanting abrasion-resistant nozzle extending through the bottom member and backsplash plate positioned nearer than the outwardly slanting abrasionresistant nozzles to the center of the drill bit body to cut a central hole in the bottom of the borehole, intermediate abrasion-resistant nozzles extending through the bottom member and backsplash plate positioned to cut grooves in the bottom of the borehole between the central hole and outer groove, said nozzles having their upper ends at least about /2 inch above the upper surface of the bottom member and their outlets substantially flush with the lower surface of the backsplash plate, and an abrasion-resistant standoff bar unitary with the backsplash plate extending downwardly therefrom Mt inch to 1% inches.

8. A drill bit for hydraulic jet drilling of wells comprising an elongated hollow drill bit body adapted to be mounted on the lower end of drill pipe to receive abrasiveladen drilling liquid therefrom, said drill bit body having a central opening extending downwardly therethrough for communication with the drill pipe, a bottom member closing the lower end of the central opening, flutes extending longitudinally along the outer surface of the drill bit body above the bottom member, a backsplash plate of abrasion-resistant material at least one inch thick secured to the lower surface of the bottom member, substantially flat-bottomed, abrasion-resistant standoff bars extending inch to 1% inches downwardly from the lower surface of the backsplash plate directly below the flutes, outer nozzles extending downwardly through the bottom member and backsplash plate positioned to discharge drilling liquid against the bottom of the borehole to cut an outer groove having an outer diameter larger than the drill bit diameter, a central nozzle extending downwardly through the bottom member and backsplash plate positioned to cut a central hole in the bottom of the borehole, intermediate nozzles extending downwardly through the bottom member and backsplash plate to cut grooves in the bottom of the borehole between the central hole and the outer groove, said nozzles being of abrasionresistant material and having their outlets substantially flush with the lower surface of the backsplash plate, said standofi bar extending continuously from an inner end nearer than the inner nozzle to the center of the drill bit to an outer end farther than the outer nozzle from the center of the drill bit.

References Cited UNITED STATES PATENTS 1,661,672 3/1928 Morrison -422 2,315,496 4/1943 Boynton 175-67 2,758,653 8/1956 Desbrow l75422 X 2,785,875 3/1957 Hayes 175-422 X 3,020,965 2/1962 Keller 175-422 3,081,828 3/1963 Quick 175-67 3,112,800 12/1963 Bobo 17567 ERNEST R. PURSER, Primary Examiner.

NILE C. BYERS, JR., Examiner.