US3467206A - Plasma drilling - Google Patents

Description

Sept. 16, 1969 w. P. ACHESON ETAL 3,467,206

PLASMA DRILLING Filed July 7, 1967 2 SheetsSheet l AFMSQGV 56 4191770 34 r 4/1 0 [QM/WIN ,rwarm/4.: i 600/?6235 IN VENTORS. W/LLARD P. ACf/ESOA/ MICHAEL .4. 72786450 Sept. 16, 1969 w. P. ACHESON ETA!- 3,467,205

PLASMA DRILLING Filed July 7, 1967 2 Sheets-Sheet 2 Fig. 2

IN v ENTORS. M11490 RAG/550V M/fil/AEL 4. 7026450 United States Patent 3,467,206 PLASMA DRILLING Willard P. Acheson, Pittsburgh, and Michael A. Torcaso, Arnold, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Filed July 7, 1967, Ser. No. 651,830 Int. Cl. E21!) 7/18 US. Cl. 175-13 10 Claims ABSTRACT OF THE DISCLOSURE Method and apparatus for drilling wells in the earth utilizing a stream of disassociated gas (plasma) a reelable tubing to achieve wire line-like operation, and adding fiuxing agents to melt at the bottom of the hole to automatically case the well as it is drilled. The plasma generator is mounted on the drill so that the stream of plasma crosses the axis to cover the entire bottom of the hole as the drill rotates.

This invention relates generally to the art of drilling wells in the earth, especially for the recovery of hydrocarbon deposits, and more particularly is directed to methods and apparatus for drilling such wells utilizing plasma.

As used herein, the term plasma shall mean a stream of gas whose molecules have been disassociated and ionized. A plasma generator therefore is a device that produces such plasma. As is well known, when plasma is directed at a target, the gas will reassociate, and will produce tremendous quantities of heat at very high temperatures, temperatures on the order of 60,000 F. can be achieved. The present invention uses a plasma generator to drill wells.

The plasma drilling method of the present invention is not to be confused with and is materially different from the so-called electric arc types of drilling. In said electric arc drilling means are provided to create an electric are at the bottom of the borehole, and the heat of the arc itself is utilized to crack and spall the formation. The heat is therefore very close to the electrodes and consumes them rapidly. The electric arc method also avoids melting of the formation because the melted rock would foul the equipment. In the present invention, the heat is transmitted by the plasma which releases its heat upon re-association, and the object is to melt the rock. The melted formation in the present invention will not foul the equipment because of the provision of both the stream of plasma which itself keeps the melted rock away from the plasma torch, and secondly, the stream of scourging gas which serves the same purpose, in addition to serving the purposes of cooling the plasma generator and as a carrier to bring the melted and aerated rock to the surface. Since the heat is released at points spaced from the generator, the electrodes are not so rapidly consumed.

Another feature of the present invention is that the drill head rotates while drilling the hole. Rotation of the drill head achieves advantages over both electric arc and plasma type drills wherein the torch or generator is oscillated. In such oscillating head drills, the method is inherently discontinuous and therefore less eflicient. If the arc of oscillation is less than 360 then an arcuate area will exist that will not be positively drilled. If the arc of oscillation is more than 360 then the overla region will be drilled twice which is a waste of time and which causes lost motion of the drill head. Thus, by rotating instead of oscillating the drill head, the net effect is that the drill cuts faster and smoother without any dead spots, which results in smaller and more easily transported cuttings.

The method of the present invention is also materially different from and has advantages over those types of drill bits wherein a flame is used to remove the formation. In the present invention, under normal operating conditions, that is, in the absence of combustible fluids in the formation, there will be no flame, In such prior flame drills, there is a problem of keeping the flame away from the torch to prevent it from destroying the torch, there IS a problem both technologically and economically in supplying fuel to the torch, and there is a problem of corrosion since the products of combustion are corrosive to the drill. The present invention avoids all of these problems since there is no fuel supply, since the gas re-associates at zones spaced from the generator, and since there is no combustion and therefore no products of combustion.

One problem common to virtually all kinds of drilling methods presently in use is that a drill string, comprising long lengths of heavy walled pipe, is utilized to both transmit energy to the drill bit at the bottom of the hole, and to transmit cooling and chip carrier fluids, known as drilling mud, to the bottom of the hole. Such drill strings are in themselves expensive, require large amounts of energy to tum, and require considerable time to periodically remove from the hole for purposes of changing the bit, and for other purposes.

Another problem present in conventional types of drilling is that the sides of the borehole are left unprotected as depth increases. This is often a problem when unconsolidated formations, such as loose sand or the like, are encountered. The problem is solved, conventionally, by casing the well, which comprises removing the drill string from the well, inserting relatively large diameter pipe into the well to the zone it is desired to case off, and then filling the space between the outside of the pipe and the side of the borehole with cement, to thereby seal off the troublesome zone. Casing is an expensive and time consuming procedure. The present invention eliminates or at least substantially reduces the amount of casing that must be done by means of the inclusion of fluxing agents into the scourging or ionizing gas. When such fluX- ing agents are exposed to the very high temperature which will be generated at the bottom of the borehole during drilling, they will melt, and in effect, a lining for the side of the borehole will be created as a by-product of the drilling operation and simultaneously therewith. The particular flux used will depend upon the nature of the formation being drilled.

In the accompanying drawing forming a part of this disclosure: FIG. 1 is a diagrammatic vertical cross-sectional view of the apparatus of the invention showing the plasma drill of the invention drilling a well; and FIG. 2 is a longitudinal cross-sectional view through the drill of the invention.

Referring to FIG. 1, there is shown a borehole 10 which is being drilled by plasma drill 12. The surface equipment includes a well head 14. It will be understood that well head 14 is diagrammatic only, and will include but does not show conventional safety equipment such as blow-out preventers, and other conventional equipment well known to those skilled in this art. Drill 12 is connected to the surface by a composite cable 16 which connects the drill to a reel 18 mounted on a reel support 20. Preferably, reel and reel support 18 and 20 are mounted close to and may be a part of a derrick assembly 22 which includes guide rollers 24 which guide cable 16 and drill 12 in vertical motion in the well 10.

As will appear more clearly in the detailed description of drill 12 below, the drilling method of the invention requires that ionizing gas, scourging air, electricity for the electrodes within the plasma generator, and electricity to turn the plasma generator be supplied through cable 16 from the surface to the drill 12. In some cases, it will also be desirable to supply fluxing agents through the cable to the drill.

Reference numeral 26 designates a black box labeled Energy and Materials Sources in FIG. 1. This black box indicates the various pieces of equipment that supply the above energies and materials to cable 16 for delivery to drill 12. It will be understood that any suitable means may be used for the supply functions. For example, the ionizing gas may be supplied by a pump. The two separate electrical currents may be supplied by generators on the drill site, or by connection to utility company service lines in the area if such are available. The scourging air may be supplied by tank trucks of compressed air, on-site compressors, or the like, and means such as a gravity feed hopper, aspirator, screw feeder, or the like, may be used to supply the fluxing agents in powdered form. Supply conduits, generally indicated by conduit 28, connect the energy and material sources to the hub 30 of reel 18, and various electrical brush and rotating valve assemblies, not shown, are provided within hub 30 to transmit the energy and materials to the various parts of cable 16, as will be described more clearly below.

Reference numeral 32 designates a black box labeled Separation Equipment in FIG. 1. This black box indicates equipment to separate the formation material removed by drill 12, equipment to detect any fluids such as hydrocarbon liquids or gases that may be included in such material, and equipment to vent the cleansed air after the above matter is removed from it. It will also include equipment to flare gas if gas is used as the scourging fluid. Separation equipment 32 serves the function of the mud tanks, pumps, shale shakers, and the like used in conventional rotary drilling. The formation removed by the drill 12 will be returned to the surface in the form of a crystallized froth or as solidified aerated globules, and these cuttings may be removed from the air by appropriate equipment such as screens, cyclones, settling chambers, or the like. A conduit 34 connects the separation equipment 32 to well head 14 and communicates the annulus between the borehole 10 and the cable 16 with the separation equipment. As in conventional drilling, the energy and materials are supplied through the cable, analogous to the drill string, and returned via the annulus.

Referring to FIG. 2, drill 12 is essentially a two-part structure comprising an upper member 36 and a lower member 38. Upper member 36 serves as a weight and stabilizing bar, and as an energy and material distribution point for the drill.

Upper member 36 comprises a main body member 40 formed with suitable connection means, such as a threaded nipple 42, to receive the lower end of the outside wall 44 of cable 16. A collar member 46 is threaded on nipple 42 and holds the lower end of the outside wall 44 of cable 16 onto the drill 12. The connection means 42, 46 is exemplary only, and it will be understood that various means are available to attach the cable wall to the upper end of the drill. The outside wall of cable 16 may be formed of any suitable material which will bear the weight of the drill, and which will allow itself to be reeled. Within outside wall 44 cable 16 includes a relatively small diameter conduit 48 which carries the ionizing gas, and a second small diameter conduit 50 which carries the electrical leads. The ID. of outside wall 44 is considerably larger than the sum of the diameters of conduits 48 and 50, and the relatively large annulus inside wall 44 is used to transmit the scourging fluid, preferably air, to the drill head, as will be explained below. If desired, the conduits 48 and 50 could be fabricated integrally with outside wall 44. Gas carrying conduit 48 could be a flexible metal tubing, and electrical lead carrying conduit 50 could be of insulated, multi-wire construction.

Since plasma generators are essentially high amperage/ low voltage devices, and since the required electrical lead diameter is a function of amperage, it may be desirable to include a downhole transformer in upper member 36, along with associated rectifying equipment to convert the energy to DC. This equipment is not shown in the drawing, but it may be easily provided in upper member 36, if it should be desired. It is desirable to work with relatively thin electrical leads as far as possible, from the economy viewpoint, and from the viewpoint of keeping the total size of the reelable cable 16 as small as possible.

Main body member 40 serves as a weighting member to maintain the drill stable in the hole and to aid it in its downward movement as it drills the hole. The upper member 36 is shown broken to indicate that any length of member 40 could be provided dependent upon the amount of weight desired, and, as will be explained below, the upper member 36 can be readily changed during the drilling of a hole. Additional means are provided to stabilize the drill in the hole. To this end, a pair of spring loaded arms 52 are hinged to the top of the body member as at 54 and are biased outwardly against the sides of the borehole 10 by springs 56. As will be understood by those skilled in this art, more than two arms 52 could be provided. The arms 52 serve to centralize the drill in the hole, and other types of centralizers such as how springs could be provided in their place.

Upper member 36 is provided with a longitudinal central opening 58 through which the conduits 48 and 50 pass, and which is in communication with the inside of cable 16. Thus, longitudinal opening 58 serves as a scourging gas conduit to deliver the scourging gas to the drill.

Means are provided to permit quick connection and disconnection of gas and electrical conduits 48 and 50 between upper member 36 and lower drill member 38. To this end, a cover plate 60 is provided at the lower end and at one side of upper member 38. Suitable means such as gasket 62 and bolts 64 are provided to permit ready removal of the cover plate. Under cover plate 60, body member 40 is formed with a radial opening 66 in which is mounted a terminal block 68 in which are removably mounted a quick disconnect coupling 70 for the electrical conduit 50 and a quick disconnect coupling 72 for the gas conduit 48. Lower member or drill 38 includes a protective sheath 74 which extends into a suitably formed opening in cover plate 60 and through which passes electrical leads 76 and gas lead 78 which lead to the quick disconnect couplings 70 and 72, respectively. At its extreme lower end, body member 40 is formed with a conventional drill pipe box or female pipe thread connection 80, which cooperates with a pin or male connection 82 on the upper end of drill 38. Suitable conventional sealing means, not shown, may be provided between pin and box connection 80, 82.

Thus, the upper weighting and stabilizing member 36 can be asembled or dissembled from the drill, or a heavier or lighter member can be provided, by removing cover plate 60, breaking quick disconnect couplings 70 and 72, and breaking thread connections 80, 82.

Drill 38 comprises an axial longitudinal chamber 84, which is in tandem with opening 58 to provide a continuous passageway from the inside of cable 16 to the drill head through the drill and the upper member. After its passage through sheath 74 gas lead 78 passes through a suitable radial opening 86 in the body of drill 38 to a rotary seal device 90 positioned in air chamber 84. Rotary seal 90 is held in place by any suitable means such as struts 92. A rotating gas delivery pipe 94 is connected to the lower end of rotary seal 90 and delivers the ionizing gas to the plasma generator 96 located in the rotary drill head 98, as will be described below.

Means are provided to rotatably mount and to cause rotation of rotary drill head 98 with respect to drill body 88. To this end drill body 88 is of a generally elongated U-shaped configuration in cross section to receive a stem portion 100 of rotating drill head 98. Upper bearing 102 and lower bearing 104, of conventional anti-frictional roller or other type, is provided between the drill body 88 and drill head stem 100. Drill 38 includes a motor 106 which drives the drill head. The stator 108 of motor 106 is mounted by means of suitable electrical insulation 110 in drill body 88, and the rotor 112 with suitable insulation 114 is mounted in stem portion 100 in juxtaposition to the stator. Electrical energy is supplied to stator 108 by a pair of the electrical leads 76 after they pass through sheath 74. Four sets of electrical brushes and commutator assemblies 116 are provided between body 88 and stem portion 100. Two brush assemblies 116 are used to transmit electrical energy delivered by two of the leads 76 to rotor 112 of motor 106, The remaining two brush assemblies 116 pass through a conduit 118 in rotating head 98 and deliver electrical energy to the plasma generator 96.

As shown, motor 106 comprises only one rotor/stator stage. It will be understood that more than one such stage, with the appropriate brush assemblies 1'16, may be provided to provide a more powerful motor. The drill is shown broken between lower bearing 104 and motor 106 to indicate the inclusion of additional electrical motor stages, if required.

As explained above, the scourging gas passing through cable 16 and passageways 58 and 84 to the bottom of the borehole serves several important functions, i.e., cooling of the plasma generator 96, as a vehicle to carry the melted formation particles away, and to aid in directing the stream of plasma away from the generator. Therefore, the lower end of rotating drill head 98 is formed with several different passageways each of which receives some of the scourging gas and which serve these various purposes. Passageways 120 and 122 are directed upwardly from the generator and stream of plasma and serve primarily to push the cuttings up the annulus to the surface. Passageway 124 is directed downwardly and tangentially at a small angle to the direction of the plasma stream and serves primarily to direct the plasma stream away from the generator. Passageway 126 is connected to the internal cooling passageways within the generator, and serves primarily to cool the generator. A passageway 128 exhausts the air supplied through passageway 126 and also serves to direct formation particles out towards the sides of the borehole. It will be understood that the passageways 122 through 128, shown and described, are but representative of the various types of passageways and that several of each type of passageway may be provided.

The lower end of rotating head 98 is of triangular crosssection and includes the lowest part of the drill. At said lowest part an idler roller assembly 130 is provided which guides the rotational motion of the drill head. Roller assembly 130 comprises an axle 132 and an idler roller 133 which comprises a hemispherical end face 134, joined to the body of the roller by a sharp edge 136. Thus, the roller makes a sliding point contact with the side of the borehole on hemispherical portion 134, and a rolling contact with the bottom of the borehole on edge 136.

The plasma generator 96 is disposed at an angle and is directed downwardly with respect to the axis of the drill, and is positioned to one side of said axis with its exit orifice close to said axis, so that the stream of plasma will cross the axis and travel a distance greater than the transverse radious of the hole. The length of said stream is adjustable by adjusting certain parameters within the generator, such as throttling means for the ionizing gas and the physical configuration of exit orifices and the like, and is set so that the effective length of the stream will be such that a hole having the desired diameter will be produced. The bottom of the hole will therefore have a cone or hill-like configuration as shown.

By locating the plasma generator as described, the generator will drill across the axis of the hole, which results in accurate control of hole diameter. The generator may be adjusted and controlled, from the surface, by increases or decreases in one or both of the supply of ionizing gas or electrical power.

By so directing the plasma stream in combination with the inclusion of fluxing agents, which will melt and migrate towards the side of the borehole, the advantage of obtaining a self-casing borehole will be obtained, The finely powdered particles of fiuxing agent in either the ionizing gas or scouring gas will melt, and when directed outwardly by the stream of plasma, as primarily by the passageways 124 and 126, will coat the side of the borehole with a glass-like lining. The fluxing agents will be so finely powdered that they will not clog any of the passageways in the generator or the rotating drill head. Suitable materials for use as the fiuxing agent include borax, feldspar, silicon oxides, or other suitable minerals, dependent upon the nature of the formation being drilled. The ionizing gas is preferably a diatomic inert gas such as argon, nitrogen, or suitable other gases or combinations of gases. The scourging gas is usually air, but in those cases where it is anticipated the hydrocarbon deposits will be in the form of natural gas, air is not desirable because of the explosion danger. In such wells, gas, methane or natural gas readily available in many oil fields, may be used as the scouring gas, or even the exhaust gases from the various engines on the drill site, properly treated to remove solids and corrosive agents, could be used as the scouring gas.

The intense heat generated by the re-association of the gas will melt the rock. The relatively large amount of scourging gas, air or methane or whatever is being used, added into the molten rock will cause the rock to froth trapping bubbles of this gas as well as bubbles of the re-associated gas as the rock cools, resulting in a light material which may be easily driven up the annulus. The molten froth will, because of its light weight and rapid motion, quickly give up its heat primarily to the surrounding formation, and will then be carried up to the surface and delivered to separation equipment 32. The scourging gas will also help to cool the cuttings.

We claim:

1. A method of drilling earth boreholes with plasma comprising the steps of rotatably mounting a plasma generator on a drill, holding the body of the drill stationary with respect to rotation about the axis of the drill, rotating the plasma generator about the axis of the drill, directing the stream of plasma produced by the plasma generator from one side of the axis of the drill at an angle to said axis acros said axis and over the entire bottom of the borehole during each revolution of the generator, and lowering the drill as the drill creates the borehole.

2. A method of drilling earth boreholes with plasma comprising the steps of rotatably mounting a plasma generator on an axially rotatable drill to direct the stream of plasma produced by the plasma generator from one side of the axis of the drill at an angle to said axis across said axis and over the entire bottom of the borehole during each revolution of the generator, mounting said drill on a reelable cable, supplying electrical energy to said plasma generator through said cable, supplying electrical energy to a motor in said drill through said cable to cause said plasma generator to rotate with respect to said drill, supplying a disassociatable gas to said plasma generator, supplying a stream of scourging gas to said drill through said cable, and lowering said drill on said reelable cable as said drill creates the borehole.

3. The method of claim 2, and supplying finely powdered fluxing material to said scourging gas.

4. The method of claim 2, and supplying finely powdered fiuxing material to said disassociatable gas.

5. Apparatus for drilling earth boreholes comprising a drill, a plasma generator mounted on said drill, means to cause rotation of said generator about the axis of said drill, cable means connected to the upper end of said drill, means to reel and unreel said cable means from the surface to raise or lower said drill in the borehole, and said plasma generator being mounted on one side of said drill with respect to the axis thereof and disposed at an angle with respect to the axis thereof and with the plasma outlet end of said generator close to the axis thereof, whereby the stream of plasma issuing from said generator will flow across the axis of said drill.

6. The apparatus of claim 5, said means causing rotation of said generator about the axis of said drill comprising an electrical motor, said motor comprising a motor stator mounted on a body portion of said drill, means to hold said body portion stationary with respect to rotation about the axis of said drill, said drill comprising a stem portion rotatably mounted within said body portion of said drill, said drill comprising a drill head portion forming part of said drill stem portion, said motor comprising a motor rotor mounted on said drill stem portion in juxtaposition to said motor stator, said plasma generator being mounted on said drill head portion, and means to supply electrical energy to said motor rotor and said motor stator from the surface through said cable means.

7. The apparatus of claim 5, said drill comprising a body portion, means to hold said drill body portion stationary with respect to rotation about the axis of said drill, said drill comprising a rotating portion carrying said plasma generator, and motor means disposed on said stationary portion and said rotating portion to power said rotating portion with respect to said stationary portion.

8. The apparatus of claim 5, said drill comprising an upper member and a lower member, means to removably join said upper member to said lower member, said upper member and said lower member being formed with axial passageways in communication with each other and in communication with the central opening within said cable means, whereby a flow of scourging gas may be supplied from the surface through said cable means and the passageways in the portions of said drill to said generator and the bottom of the borehole; said upper member comprising a weighting and stabilizing member, and said lower member comprising a drilling member.

9. The apparatus of claim 5, and cable means including means to supply a flow of disasociatable gas from the surface to said plasma generator, said cable means including means to supply electrical energy from the surface to said plasma generator, and said cable means including means to supply a flow of scourging gas from the surface to the vicinity of and to said plasma generator.

10. The apparatus of claim 9, said drill comprising an upper weighting and stabilizing member and a lower drilling member, said upper and lower members being formed with communicating axial passageways which also communicate the space within said cable means with the bottom of said borehole and said plasma generator, said upper member comprising quick disconnect means adapted to quickly connect and disconnect said electrical energy supply means and said disassociatable gas supply means, said scourging gas supply :means comprising said communicating passageways within said upper and lower members, and means to connect or disconnect said upper and lower members, whereby said upper and lower members may be readily separated from each other for replacement of either of said upper and lower members.

References Cited UNITED STATES PATENTS 2,327,496 8/1943 Burch -13 2,816,735 12/1957 Dalinoa et a1. 175-15 3,045,766 7/1962 Fleming 175-14 ERNEST R. PURSER, Primary Examiner US. Cl. X.R. 175l4, l5

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