Erosion Drilling

Abstract

An erosion bit for earth-drilling operations having a first nozzle system open for conducting drilling fluid and a second nozzle system closed by a pressure-sensitive closure means. Means are provided for plugging the first nozzle system and for actuating the pressure-sensitive closure means to open the second nozzle system. Drilling fluid can initially be flowed through the first nozzle system until the nozzles become eroded and then through the second nozzle system.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to erosion drilling. In one aspect it relates to an improved erosion-drilling method, and in another, to an improved erosion drill bit.

2. Description of the Prior Art

Erosion drilling is a technique for drilling boreholes using high velocity hydraulic jets as the principal mechanism for inducing stresses in the formation rock. The basic components of the erosion-drilling system comprise high-pressure pumps, high-pressure drill string, and an erosion bit provided with a plurality of nozzles. The erosion bit can also include auxiliary cutting devices such as cone cutters, drag bit blades or a diamond head. The principal source of energy, however, is derived from the high velocity jets discharging from the nozzles.

The nozzles are sized in relation to the available pump pressure to create high velocity jets (in excess of 500 feet per second) and are positioned on the bit to direct the jets impingingly against the formation rock. The high kinetic energy of the jets is thus spent on the rock causing it to shatter into fragments small enough to be carried away from the bit by the fluid stream returning to the surface through the annulus. The number and pattern geometry of the nozzles depend to a large extent upon the available mounting space on the bit body. An erosion bit equipped with drag bit blades or a diamond head provides space for mounting several nozzles in a variety of patterns. The nozzle pattern generally is such to provide a sweeping jet action as the bit is rotated. Cone cutters mounted on the erosion bit, on the other hand, greatly restrict the number and location of the nozzles. Moreover, the nozzles must be arranged so that the high velocity jets do not impinge against the cones.

Erosion drilling has a power output potential many times greater than that attainable with conventional rotary drilling equipment. Notwithstanding the potential of the erosion-drilling concept, it has not received broad application in commercial drilling operations, partly because of the short life span of the bits. At the extreme velocities and pressures required in erosion drilling, the nozzles wash out in a relatively short period of time which heretofore has necessitated withdrawal of the bit to replace the nozzles. For deep wells, this is a time-consuming and expensive operation.

It has long been recognized that if the erosion-drilling concept is to have practical application, even on a limited basis, equipment and techniques must be developed to increase bit life. Advances in metallurgy have produced nozzles having improved wear-resistant properties; however, nozzle erosion remains a major problem, particularly where the drilling fluid has sand particles or other abrasives entrained therein.

Retractible bits designed to permit replacement of eroded nozzles without tripping the drill string have been proposed but to date have not been entirely successful because of the difficulties experienced in dislodging the retractible portion of the bit from the bit body.

SUMMARY OF THE INVENTION

The purpose of the present invention is to prolong the operable lifespan of an erosion bit. The erosion bit constructed according to the present invention contains at least two sets of nozzle systems, one system being open for conducting drilling fluid and the other set being closed by a pressure-actuable closure means. In practice, the oil or gas well can be drilled using conventional rotary techniques until such a depth or such a formation is reached that erosion drilling is more economical. In this regard it should be pointed out that erosion drilling because of its high power output is particularly suited to drilling in hard to medium-hard formations. In order to convert from conventional to erosion drilling, the drill string is withdrawn from the borehole, the conventional bit replaced with an erosion bit, and returned to the bottom of the borehole. Initially, erosion drilling is through the open set of nozzles. When the nozzles become worn as evidenced by marked reductions in pump pressure or drilling rate, the first nozzle system can be closed by pumping a plug or plugs down the drill string. The plug or plugs seat in the bit closing all the nozzles. The pressure in the drill string is increased to the actuation pressure of the closure means, which is substantially above the normal drilling pressure. Actuation of the closure means opens the second nozzle system permitting the drilling to be resumed. A preferred form of the closure means is a rupture disc mounted in the main flow course of the second nozzle system or in the individual nozzles thereof. The rupture disc or discs provide a positive seal, contain no moving parts, and are easily adapted to the erosion bit.

If space permits, three separate nozzle systems can be used, in which case the second and third sets are provided with closure means actuable at substantially different pressures. The drilling operation then will proceed in sequential order using the first system, the second system, and finally the third system.

Experience has shown that in deep wells, the nozzles tend to fail before any of the other parts, particularly where the auxiliary cutting device is in the form of a diamond head or drag bit blades. Thus by providing the bit with two or more nozzle systems, the operable lifespan of the bit can be substantially increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an end view of an erosion bit constructed according to the present invention.

FIG. 2 is a simplified, longitudinal sectional view of the bit shown in FIG. 1, the cutting plane taken generally along the line 2--2 thereof. abrasive.

FIG. 3 is an end view of another embodiment of the present invention.

FIG. 4 is a longitudinal sectional view of the bit shown in FIG. 3, the cutting plane taken generally along the line 4--4 thereof.

FIG. 5 is an enlarged, sectional view of the burst plate assembly adapted to be mounted in the bit shown in FIGS. 1 and 2.

FIG. 6 is an enlarged, sectional view of an insert nozzle adapted to be connected to the bit shown in FIGS. 3 and 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in connection with an erosion bit provided with drag bit blades (FIGS. 1, 2, and 5) and with an erosion bit provided with cone cutters (FIGS. 3, 4, and 6). In either embodiment the bit contains at least two sets of nozzle systems, closure means for maintaining one system closed, and plugging means for closing the other system. Separate closure means and separate plugging means are disclosed in the two embodiments but it should be understood that either bit can be constructed to accommodate any combination of the closure means and plugging means disclosed.

With reference to FIGS. 1 and 2, an erosion bit 10 is seen to include a body 11 and a shank 12 threaded for connection to the lower end of a drill string (not shown). The body 11 has formed therein four radial wings 13, 14, 15, and 16 arranged in circumferentially spaced relation. Mounted on the bottom surface of each wing is a drag bit blade --blades 17, 18, 19, and 20 being secured, respectively, to wings 13, 14, 15, and 16. The leading edges of each of the blades 17-20 extend in a radial direction from the axis of the body 11 and are disposed to effect a cutting action attendant to counterclockwise rotation of the bit 10 as viewed in FIG. 1. The blades 17-20 can be welded to the body 11 by conventional techniques and provided with hard facing material such as tungsten carbide. Alternatively, the cutting blades 17-20 can be integrally formed in the bit body 11 and surfaced with the hard facing material. The outer peripheries of the blades 17-20 and wings 13-16 can be surfaced with diamonds to maintain bit gauge.

A central chamber 21 extends through the shank 12 and into the bit body 11 terminating at end wall 22 near the bottom of the bit body 11. The upper end of the shank 12 is internally beveled to provide a tapered inlet into the chamber 21. An upper longitudinal portion 23 of the chamber 21 is full opening having about the same diameter as the inside diameter of the drill string whereas a lower portion 24 is of reduced cross section. Beveled shoulder 25 interconnects the chamber walls defining upper and lower portions 23 and 24.

Each of the wings 13-16 are provided with a nozzle system which includes a set of nozzles and a flow course interconnecting the central chamber 21 and the nozzles. In accordance with this invention the nozzle systems are arranged in paired relation with one system being open for conducting fluid and the other system being provided with closure means to prevent the flow of fluid therethrough. In this embodiment, the nozzle system in wing 14 is arranged to cooperate with the nozzle system in wing 16. For the purpose of this disclosure, it can be assumed that the paired nozzle systems in wings 14 and 16 are identical to the paired nozzle systems in wings 13 and 15.

As shown in FIG. 2, the flow passages for the nozzle system in wing 14 includes a common header 26 which extends outwardly from lower portion 24 of the central passageway 21, and individual flow courses 27, 28, and 29 which extend downwardly from the common header 26 through the bottom of the bit body 11. In the area of the flow course exits, the body can be counterbored and the flow course exits threaded to permit attachment of insert nozzles 30, 31, and 32 to the body 11.

The nozzle system provided in wing 16 and adapted to cooperate with the nozzle system in wing 14 includes a common header 33 which extends radially outwardly from the upper portion 23 of central chamber 21 through wing 16 exiting at threaded opening 33a. Individual flow courses 34, 35, and 36 extend downwardly from the common header 33 and exit through the bit body 11. The bit body 11 can be counterbored in the area of the discharge ends and the lower extremities of the flow courses 34-36 can be threaded to permit attachment of nozzles 37, 38, and 39 to the bit body 11.

An inner portion 40 of the common header 33 adjacent the central chamber 21 is threaded to receive pressure-sensitive closure means for maintaining the flow passages of the second set of nozzles closed. Preferably, the closure means includes a frangible member which is rupturable at a predetermined upstream pressure. In this embodiment the closure means is in the form of a rupture disc assembly 41. As shown in FIG. 5, the rupture disc assembly 41 includes a steel tube 42, a disc 43, and a bushing 44. The outer periphery of the tube 42 is threaded for connection to the threaded portion 40 of the header 33. One end 45 of the tube 42 is counterbored and provided with internal threads for receiving the bushing 44. In assembling the parts, the disc 43 is inserted into the counterbored end 45 of the tube 42 positioned to bridge the internal opening thereof. Bushing 44 is screwed into the tube 42 clampingly engaging the flanges of the disc 43. The assembly 41 is then inserted through the opening 33a and screwed into the body 11. Finally, a pipe plug 46 is screwed to threaded opening 33a closing the outer end of header 33. O-ring seals, provided on the disc assembly 41 and the plug 46, maintain fluidtight seals for the threaded connections.

As mentioned previously, the nozzle system in wing 13 can be similar to that in wing 14 including internal flow passages (not shown) leading to nozzles 47, 48, and 49 (see FIG. 1). Likewise, the nozzle system in wing 15 can be similar to that in wing 16 including internal flow passages (not shown), a rupture disc assembly (not shown) and nozzles 50, 51, and 52 (see FIG. 1).

The nozzles 30-32, 37-39, and 47-52 can be constructed by the method disclosed in U.S. Pat. No. 3,131,779 to D. S. Rowley et al. Each nozzle includes a metal carbide insert mounted in a steel sleeve. The steel sleeve can be threaded for screwing into the threaded flow course exits. A sealing element extending around the outer periphery of the nozzle assembly insures a fluidtight seal at the threaded connection.

As shown in FIG. 1, the nozzles of the paired systems are arranged in diametric alignment. However, the pairings and nozzle patterns can be according to any geometry permissible within the space limitations of the bit 10. Moreover, the nozzle dimensions and nozzle pattern of one system can be different from those of its paired system permitting the bit 10 to adapt to different drilling conditions by merely closing one nozzle system and opening the other.

Thus, the bit 10 as run on the drilling string includes two open nozzle systems (wings 13 and 14) and two closed systems (wings 15 and 16). The open systems communicate with the central chamber 21 below the beveled shoulder 25, whereas the closed systems are adapted to communicate with the central chamber above the shoulder 25.

In operation, erosion drilling is initially performed using the nozzle systems of wings 13 and 14 and proceeds until the nozzles 30-32 and 47-49 become eroded as evidenced by reduced drilling rates or pressure. At this time, a plug 50 configurated to seat on shoulder 25 is pumped down the drill string and into the chamber 21. As shown in FIG. 1, the plug 50 has a tapered leading end 51, a cylindrical portion 52 provided with an annular sealing member 53, and a beveled flange 54 shaped to mate with shoulder 25. The plug 50 can also be provided with a wire line fishing head 55 to permit running and retrieving by use of wire line equipment. Once the plug 50 seats on the beveled shoulder 25, the pressure in chamber 21 upstream of the plug 50 is increased by surface pumping until the rupture pressure of the disc 43 is reached rendering the assembly 41 inoperative as a closure means. The disc 43 is selected to have a rupture pressure substantially higher than the maximum drilling pressure. Thus if the maximum upstream nozzle pressure during drilling operations is to be 15,000 p.s.i., the rupture disc 43 of appropriate material and thickness is selected to break at about 18,000 p.s.i. Suitable disc materials include aluminum, copper, steel, nickel, Monel, stainless steel, and the like. Any disc debris that becomes lodged in the nozzles will be quickly eroded away by the high velocity jets.

Another embodiment of the present invention will be described with reference to FIGS. 3, 4, and 6. As shown in FIGS. 3 and 4, an erosion bit 60 includes a body 61 and a shank 62 threaded for connection to the bottom of a drill string (not shown). The bit 60 includes two cone cutters 63 and 64 journaled to the body 61 in the conventional manner. A central chamber 65 extends axially through shank 62 into the bit body 61 terminating at end wall 66.

Flow courses 67 and 68 formed in the body 61 extend radially outwardly from the central chamber 65, bend downwardly, and exit through the bottom surface of the bit body 61. Counterbores 69 and 70 surrounding the flow course exits receive extension tubes 71 and 72. The tubes 71 and 72 are welded to the body 61 and are internally machined to provide a smooth continuation of flow courses 67 and 68. The lower ends of tubes 71 and 72 are provided with end walls 73 and 74, respectively, which are located slightly above the lower extremity of the cone cutters 63 and 64. Each of the end walls 73 and 74 are provided with side-by-side boreholes threaded for receiving flow nozzles. As illustrated, the extension tubes have mounted in their end walls 73 and 74 normally open nozzles 75 and 76, respectively, and normally closed nozzles 77 and 78, respectively.

The normally open nozzles 75 and 76 can be constructed by the method described in U.S. Pat. No. 3,131,779 to D. S. Rowley et al., each having a mounting sleeve and a hollow cylindrical nozzle secured therein. The internal passages through the nozzles 75 and 76 are provided with tapered inlets 79 and 80, respectively.

The normally closed nozzles 77 and 78 are constructed to include closure means for maintaining the flow passages therethrough closed during a portion of the drilling operation. As shown in FIG. 6 the nozzles 77 and 78 each include a steel or other ferroalloy support sleeve 81 having a threaded section 82 milled in its outer periphery, an internal bore 83, and a hex head 84. O-ring 92 provides a fluidtight seal for threaded connection to the body 61. Secured to the interior surface of the sleeve 81 are an upper insert 85, a rupture disc 86, and a lower insert 87 arranged in stacked relation. The stacked parts 85, 86, and 87 can be inserted as a unit and silver brazed to the sleeve 81 by conventional welding techniques. The inserts 85 and 87 are hollow having aligned internal openings 88 and 89. Opening 88 can be provided with a tapered inlet 90. The inserts 85 and 87 can be composed of abrasive-resistant material such as one of the hard ceramics, the hard metal carbides, particularly tungsten carbide, being preferred. The disc 86 can be composed of aluminum, copper, steel, nickel, Monel, stainless steel, and the like. The discs 86 are precision made and have a bursting pressure within about 5 percent of a specified pressure.

Thus during initial erosion-drilling operations, the drilling fluid flows through two passages: one comprising course 67, tube 71 and nozzle 75 and the other comprising course 68, tube 72, and nozzle 76. Drilling continues through these passages until the drilling rate or pressure has reduced sufficiently to indicate erosion of the nozzles 75 and 76. Sealing balls 91 composed of tough, resilient material such as teflon or nylon or other plastic material can then be pumped down the drill string through the flow courses until the balls seat in nozzle inlets 79 and 80. The balls 91 will follow the stream of flow and be carried to the open nozzles 75 and 76 and nest in the nozzle inlet. The application of pressure causes the balls to deform to the contour of the inlets 79 and 80 much in the manner illustrated in FIG. 4. The resulting pressure-seal can withstand pressures as high as 20,000 p.s.i. In this embodiment two balls 91 can be dropped at sufficient time intervals to insure that both balls do not enter the same flow course. When the pressure seal has been effected by the balls 91 seating in nozzles 75 and 76, pressuring up of the drill string causes the discs 86 to rupture at predetermined levels, opening the second set of nozzles 77 and 78. Drilling then can be resumed through these nozzles. The high velocity jets rapidly erode away the disc fragments remaining in the nozzle openings.

In the typical erosion-drilling operation, the maximum nozzle pressure will be in the order of 15,000 p.s.i. Under these conditions, the rupture discs 86 should be sized to rupture at pressures in the order of 18,000 to 20,000 p.s.i. The pump pressure should be increased to at least a few hundred p.s.i. above the designated burst pressure to insure that both discs are broken.

The nozzles 77 and 78 containing the rupture discs 86 can be used in the bit 10 of FIG. 1 in lieu of the rupture disc assembly 41. Likewise the plastic balls 91 can be used to seal the open nozzles shown in FIG. 1 in lieu of the plug 50.

Laboratory experiments revealed that sintered tungsten carbide nozzles and boron carbide nozzles are susceptible to rapid erosion by drilling fluids containing abrasives. These data are particularly important in evaluating erosion drilling in areas where weighted drilling fluids are required. Drilling fluids generally become contaminated with abrasive particles and are therefore considered to be highly abrasive. The following table summarizes the laboratory data: ##SPC1##

From these data it is evident that the effectiveness of the erosion-drilling mechanism becomes drastically reduced within a relatively short period of time particularly when using abrasive drilling fluids. Moreover, it is unlikely that other bit parts, e.g., cone cutters, scraper blades, or a diamond head will show appreciable wear in this period of time. In accordance with an object of the present invention, the bit life can be substantially increased by providing the bit with separate nozzle systems described above.

Claims

We claim:

1. In an apparatus for drilling boreholes using high velocity jet streams, an improved bit comprising: a body adapted to be connected to the lower end of a tubular drill string; a first nozzle system including a first set of nozzles secured to the body and flow passage means formed in the body providing fluid communication between the drill string and each of said nozzles, said first set of nozzles being arranged on said body to provide a distributed jet pattern as said bit is rotated and fluid is flowed through said first nozzle system; a second nozzle system including a second set of nozzles secured to the body and flow passage means formed in the body providing fluid communication between the drill string and each of the nozzles of said second set, said second set of nozzles being arranged on said body to provide a distributed jet pattern as said bit is rotated and fluid is flowed through said second nozzle system; closure means disposed in said second nozzle system for preventing the flow of fluid therethrough, said closure means being rendered inoperative in response to the application of a predetermined pressure in the drill string; and means passable through the drill string and adapted to lodge in said bit body to close said first nozzle system.

2. The invention as recited in claim 1 wherein said flow passage of said second system includes a common header and said closure means includes a member disposed across said common header.

3. The invention as recited in claim 1 wherein said closure means includes a rupture disc mounted in each of the nozzles of said second set.

4. The invention as recited in claim 1 wherein said first and second flow passages include a common central chamber extending partially through said body, said central chamber being configurated to provide valve seating means therein, said second flow passage extending from said central chamber upstream of said valve seating means to said second set of nozzles, said first flow passage extending from said central chamber downstream of said valve seating means to said first set of nozzles and said means for closing said first nozzle system includes a valve member passable through said drill string into said central chamber and seatable on said valve seating means.