DE2227505A1 - LOW VOLTAGE SPARK DRILLS - Google Patents

Description

Patent attorneys

Dr.-Ing, HANS RUSCHKt
D = pl.-Ing. HEINZ AGULAR

Our reference * T 1141

TRW Inc., Redondo Beach / California (V.St.A.)

Low voltage spark drill

The invention relates to and relates to drilling equipment Point discharge drills used to generate pressure waves serve in a drilling fluid, which break down underground structures.

Point discharge drills and other types of drills are common in the book entitled "Novel Drilling Techniques" by William C. Maurer, published by Pergamon Press 1968, explained. The current state of the art of spark drilling technology is also in U.S. Patent 3,500,942 to Smith Jr., published on 3/17/1970.

209881/0442

In general, drilling tools work through the rock one of four basic mechanisms, namely mechanically generated loads, dissolution, evaporation and chemical reactions. The arc or spark drill is one of the various drills that are used in the Class of drills fall which work with mechanically generated forces. The spark drill requires one Working fluid that fills the area between the electrodes and the work surface. Between the electrodes Discharged sparks generate pressure waves which hit the work surfaces and thereby into the underground structure transmit an energy that causes the breakup.

The broken rock is then flushed out by the liquid, which is essentially in the drill pipe pumped down into the work area and returned on its face along the outside of the drill pipe will. In spark drilling technology, it is typical that a flushing fluid is used as the working fluid serves, in which the pressure or shock waves are generated.

Spark drills are particularly advantageous because

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they supplied energy with high efficiency on the Transfer underground structure. A primary disadvantage of such drills has heretofore been the need for high Drilling voltages, which were usually 50 kV. Stresses of this magnitude are difficult to handle and control in the oil production field. Furthermore Significant losses occurred in the transmission of such energy quantities as direct current from the Establishment on the surface of the earth to a spark drill which is many hundreds of meters (several thousand feet) below the surface can lie.

The technology of spark plugs includes the use of semiconductor material between the spark plug electrodes a, to prevent contamination of the spark plugs and finds particular application in the field of Aviation, where reliability is an important factor. One arrangement of this type is shown in U.S. Patent No. 2,963 by Knudson, etc., published December 6, 1959.

The invention is based on the finding that the use of a semiconductor shunt path between the Electrodes of a spark drill not only enable the generation of sparks, but also certain pollution

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has preventive properties when the drill is operated in a liquid and moreover allows the operation of the spark drill with lower voltages, namely in the range of 5 KV and underneath. This is a significant advantage in underground drilling technology. E.g. are such tensions already exist at many drilling sites. Furthermore, current technology enables an effective transfer of such low-voltage alternating currents to the drill. If this is the case, can the associated circuit for spark generation, which arrangements for rectification, for energy storage and contains for discharge, in the bit section or in other sections of the drill string in the vicinity of the bit be arranged. The flashover voltage previously required to operate a spark drill in liquids required such a large capacitor that the limited space required the placement of such a circuit Made drill impossible.

Even though it was known that spark drills had a higher drilling speed than conventional drills made possible, they were nevertheless due to the high voltage required for the comparable operation with regard to the required

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nisse of the insulation and the energy loss unused, -, bar. The higher drilling speed, which in connection with the practical applications of the spark drill according to of the disclosure is achieved creates significant economic benefits, e.g., decrease high drilling speeds Time, costs, which can be in the range of US $ 30,000 per day.

It is accordingly an object of the invention to provide a spark drill for underground drilling, which does not have the above-mentioned problems and shortcomings of the known drill.

Another object of the invention is to provide a spark drill which has a relatively low voltage required for operation.

Yet another object of the invention is to provide a spark drill head which provides the circuit for contains the spark generation.

According to the invention there is provided a spark drill for underground drilling which has at least one pair of electrodes has, between which a lining made

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a semiconductor material. The drill contains
furthermore means for supplying a drilling fluid into the region between the electrodes and the
Work surface. Even if different designs can be carried out, the basic scheme allows the use of relatively low working voltages. In addition, the circuit can be placed close to the drill to convert a low voltage alternating current into a relatively high voltage direct current arc.

The invention is explained in more detail below with reference to the drawings of exemplary embodiments.

In the drawings show;

Pig. 1 shows an axial section through a spark drill
according to the invention,

Pig. 2 is a plan view of the lower end face of the spark drill according to FIG. 1,

3 schematically shows a block diagram of the electrical circuit as it can be used as a trigger circuit for the spark drill according to FIG. 1
is and

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Pig. 4 and 5. schematically a modification

des in Pig. 1 to 5 shown point drill.

In the drawings, in which like reference characters refer to like parts, particularly in Pig. 1 and 2, is a spot drill 10 is shown, which is particularly suitable for attaching to the lower end of a drill string, as in Oil hole is used ^ ~ ge ~ e ± gnet_. Is. The punk drill 10 has a cylindrically shaped housing 11 which serves as one of at least two electrodes. The case or the electrode 11 is threaded at its upper end for insertion into the lower end of the drill string to be screwed in.

The point drill further includes a second, central electrode 12, which is defined by a number of radially projecting Legs 13 is marked. The outer and middle electrodes are except for the lower one Part isolated by a dielectric material 14. The one radially from the middle electrode 12 to the outer electrode 11-directed paths are formed by a layer 15 of a semiconductor material. According to the invention is preferred the semiconductor layer is set back somewhat from the lower surface of the electrodes. Each of the radially forward

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The jumping sole handle 15 forms a spark gap in connection with the outer electrode 11. In operation occurs create a random pattern of sparks between the electrodes.

The spark drill further includes a supply tube 16 for a drilling fluid that has fastening threads has to be attached to a feed pipe that starts at the surface of the earth. The liquid supply pipe 16 ends in a number of drilling fluid distribution pipes 18th

In operation, the spark drill is inserted into the earth and a viscous drilling fluid, occasionally "cloudy" (mud) called, is through the supply pipe 16 and the distribution pipes 18 pumped down to fill the area between the underground structure and the electrodes. The liquid can then be entrained along the outside of the sink drill and the drill pipe the broken particles of the underground structure flow upwards. It is common practice to use the drilling fluid to 'collect and return.

In previously known spark drills such a large voltage is applied between the electrodes that one

209881/0442

Discharge occurs between the electrodes. This discharge, if it is generated with a high degree of repetition, causes shock waves, which immediately below transferred to the underground structure by the drill and impinge on it. Have drills of this type, like duroh trial demonstrated the possibilities of high working speeds. However, such drills require generally high voltages in the region of 50 KV µm initiate the discharge. Tensions In Oil Production are available, they usually do not exceed 10 KV.

According to the invention, the semiconductor layer 15 creates a shunt path between the electrodes 11 and 12. With a single minor orbit, tensions are applied of less than 10 KV is required to generate an electrical discharge. It can be assumed that such a large current flow through the Nebensohlußbahn goes that the molecules of the semiconductor surface are ionized. When this occurs it becomes an electrical path with very little Resistance created and a spark created. The invention explained heretofore makes it practically possible to use Liohtbogenentladungseinriohtungen to be used in underground drilling operations.

209881/0442

Drills built according to these principles operate at voltages of 1-3 KV ", which is in the voltage range Common oilfield submersible pumps and electric drills are available and can be used with common electric Cables and other readily available facilities.

In those applications in which electrical direct current energy over a very long drill string must be transmitted downwards, the associated high capacitance of the electrical cable can reduce the spark discharge Reduce. The spark drill can be operated by transmitting alternating current in the drill string below and arrangement of the circuit for generating the spark discharge in the spark drill head itself or as a sub-arrangement, which is part of the drill string and the drill combination forms, to be improved.

In Fig. 2 is a corresponding circuit for this Purpose shown. The energy in joules released during a spark discharge is E »1/2 C V, where C is the capacitance in microfarads and V is the charge potential in KV. Experimental work reports show that an energy of 45 - 375 joules is required to penetrate the rock. As a result, an electricity

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supply of 3 KV to a capacitor with 100 microfarads to generate sufficient energy.

For this purpose, FIG. 3 shows an alternating current supply 20 which lies on the borehole surface and which is in connection with a direct current supply 21, which in turn is connected to the electrodes 11 and 12 and the lift-off path 15. The direct current supply 21 is through block 21 in Pig. 1 and includes a rectifier and a trigger circuit to generate the arc. Fig. 1 also shows a cylindrical container 22 which contains the electrical circuit encloses and an electrical connection 23 as an attachment point for an electrical cable from the AC power supply 20.

In FIG. 3, a 3 KV alternating current supply 20 is connected to the trigger circuit 21 by the cable 24. The trigger circuit consists of a rectifier circuit 25, a capacitor 26 and a T.rigger arrangement 27, which a spark gap with a known Breakdown voltage or a solid state control device which is designed so that a known amount of energy pulses are transmitted to the electrodes 11 and 12 will.

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As another embodiment, the spark drill according to FIGS. 1 and 2 in FIGS. 4 and 5 is advised with a number of or middle electrodes and an equal number of DC power supplies, not all shown are shown. As shown in FIG. 4, the direct current supply 21 is provided with a center electrode 12 connected, which is at a distance from an outer electrode 11, with a semiconductor layer between the two 15 lies. Other direct current supplies 21a, 21b are for supplying direct current pulses to the other electrodes 12a, 12b, as shown in Fig. 5, is provided. As shown in Fig. 5, the number of center electrodes may be the bottom surface of the spark drill may be spaced apart. The layer of semiconductor material must be of everyone Electrodes 12, 12a-12d run to the outer electrode 11. The semiconductor material doesn't need that cover middle area between the middle electrodes and as shown, lies the dielectric Isolation material free. Each direct current supply can be connected to two or more central electrodes or can be provided in a ratio of 1: 1.

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Claims (12)

Claims 1. Underground spark drill, characterized by a first electrode (11), a second electrode (12), a layer (15) of semiconductor material, which between is disposed on the electrodes and forms an electrical shunt path therebetween, and during at least one fluid passage (16,18) with an opening in the region of the electrodes (11,12) and arranged so that a drilling fluid in the Area between the electrodes and the underground structure can be distributed in such a way that energy from the Spark discharge between the electrodes through which the liquid is transferred to the underground structure. 2. Spark drill according to claim 1, characterized in that that the first electrode (11) essentially surrounds the second electrode (12). 209881/0442 3. spark drill according to claim 1, characterized in that the second electrode (12) a number of radially has outwardly extending legs (13), each of which is spaced from the first electrode (11) and each forms a spark gap in conjunction with the first electrode. 4. Spark drill according to claim 1, characterized in that that the first electrode (11) is essentially cylindrical and has an outer diameter approximately equal to but slightly less than the diameter of the borehole, the cylindrical electrode so long is that it is a housing for the associated Building elements " 5 »Spark drill according to claim 1, characterized by A DC power supply (21), which is connected to the electrodes (11,12) is connected « 6. spark drill according to claim 5, characterized in that the direct current supply has an output of below 10 KV. 7, spark drill according to claim 1, characterized by a circuit (21) whose output with the electrodes 2 U 9 8 8 1 / Q 4 4 2 (11,12) for the transmission of green current voltage pulses is coupled between, these and to apply the voltage across the Uefeenschlußweg, which is formed by the layer (15.) made of semiconductor material, the circuit (21) having an input (24-) which is connected to an electrical power source. 8. spark drill according to claim 7, characterized in that that the circuit contains * a capacitor (26) parallel to the electrodes (11,12), and a trigger (27) with a link generating arrangement, which is in series connected to the capacitor (26) and the electrodes (11, 12) in order to effect the transmission of voltage pulses to the electrodes. 9. Spark drill according to claim 8, characterized in that that the power supply (21) has an output of less than 5 KV and that the capacitor is selected so that it causes a discharge energy in the range of 45 joules. 10. point drill according to claim 1, characterized by a number of second electrodes (12, 12a-d), where- 2-U9 88 1/0442 in the case of the layer (15) made of semiconductor material between, the number of second electrodes (12, 12a - 12d) and the first electrode (11) is arranged to form shunt paths therebetween. 11. Spark drill according to claim 8, characterized in that that the circuit (21) is a rectifier circuit (25) includes the input of which is connected to an alternating current source (20), with a trigger circuit (27) has its input connected to the output of the rectifier circuit (25) and to its output is connected to this number of second electrodes in order to transmit voltage pulses to them. 12. Spark drill according to claim 11, characterized by an equal number of rectifier circuits (21, 21a, 21b), each of which is connected with its input to an alternating current source (20) and by the same Number of trigger circuits (27) whose input with connected to the output of one of the plurality of rectifier circuits, the output of each trigger circuit being connected to one of the plurality of second electrodes (12, 12a-12d) and the first electrode (11) is connected. 2Ü9881 / 0442 Read 11 e