US3537542A - Sparking devices suitable for seismic prospecting - Google Patents

Description

United States Patent [72] lnventors lqlgglgqde puhois [51] Int. Cl m, G0lv 1/06 Ryan, and 50 Field of Search .1 340/l2(ARC) AndreIamesJe Verdon, Met, France '1 2; l8l/.5(EM),5/(IC [21 Appl. No. 783,586 [22] Filed Dec. 13, 1968 References Cited [45] Patented Nov. 3, 1970 v UNITED STATES PATENTS 1 Assisnee 1mm"! Francflis Parole, des 3,286,226 11/1966 Kearsley et al. 340/12 Carburants 91 Luhriflants 3,369,217 2/1968 Lulhrmann etal. 18 1/5 de Seine, France 5,458,858 7/1969 Wright 181/5 [32] Priority Dec. 14, 1967 [33] France Primary Examiner-Rodney D. Bennett [3 I] 132,353 Assistant Examiner-Brian L. R bando i [54] SPARKING DEVICES SUITABLE FOR SEISMIC A ttomey Craig, Antonelli, Stewartand Hill 2 ABSTRACT: A sparking device for underwater seismic prospecting comprising at least two immersed electrodes and means for suddenly discharging a high electrical energy, in combination with a burner supplied with an inflammable gaseous mixture adapted to produce a conducting ionized flame.

Patented Nov. 3, 1970 Sheet INVENTORY 10 W i \i k L a a G rn W \\\n\ x 2 U Jew c4000: bow: F I G: 2

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ATTORNEY? Patented Nov. 3, 1970 m g P 4 g 2 xxx xx INVENTORS AUDEDUBO/S' JAMES JEAN CL ANDRE Patented Nov. 3, 1970 Sheet INVENTORS JI W (Ml/06 061806 ATTORNFY$ SPARKING DEVICES SUITABLE FOR SEISMIC PROSPECTING A known method for emitting acoustic waves in a liquid medium consists of generating sonic energy from sparks induced by means of an immersed sparking device. Such a method is used particularly in the field of seismic prospecting.

The sparking devices which have been used heretofore are for example of the type including electrodes through which is produced a sudden discharge of electric current, for example by means of a capacitor, so as to create in the vicinity of these electrodes a high intensity electrical field which causes a sudden electrolysis followed with an intense ionization.

Another type of prior art sparking device comprises an insulating enclosure perforated with orifices at the respective levels at which sparks are generated according to the abovedescribed process.

Another known type of sparking device includes an explosive wire placed between two electrodes through which is produced a sudden discharge of electric current.

A sparking device of the last-mentioned type provides for a higher acoustic efficiency than the other types, and in contrast thereto, can be operated in a liquid medium which is little or not at all electrically conductive, such as for example fresh water.

An object of the present invention is to provide a new sparking device in which the electrolyte or the explosive wire is replaced by a preionized medium constituted by a very high temperature flame, for example a flame having an elongated shape such as that produced by a burner of the type used in a blowpipe.

According to the invention, this flame is produced between two electrodes and a sudden discharge of electric current, provided for example by capacitors is produced through the electrodes and this flame.

The plasma, which is partly preestablished, is then of cylindrical shape, similar to that produced by the explosion of a wire.

The acoustic efficiency of this new sparking device is comparable to that obtained with a sparking device using an explosive wire.

One ofthe main advantages of the new sparking device is to make possible a rapid rate of successionof the shots, while maintaining a high efficiency, this efficiency being independent from the conductivity of the liquid medium.

The range of utilization of the sparking device according to the invention is very wide, i.e. from a few Joules to more than 100,000 Joules.

As a result of the preexistence of a plasma, the major part of the energy stored in the capacitors is used in the adiabatic expansion of the plasma.

In the prior art devices, a substantial part of this energy is absorbed either by the electrolysis, or by the volatilization of the explosive wire.

Some embodiments of the new sparking device according to the invention will now be described more in detail with reference to the attached drawings wherein:

FIG. 1 diagrammatically illustrates a sectional view of a first embodiment of this sparking device;

FIG. 2 is a sectional view along line A-B of FIG. 1;

FIG. 3 is a sectional view along line c-d of FIG. 1.

FIG. 4 is a sectional view of a second embodiment of the sparking device;

FIG. 5 is a sectional view of a third embodiment of the sparking device according to the invention;

P10. 6 is a sectional view of a fourth embodiment of the sparking device according to the invention.

The sparking device shown in cross section by FIG. 1 in cludes a burner constituted of a tube 1 made of a conducting material able to withstand high temperatures, such as for example tungsten. One end of this tube is connected with a device not shown supplying an inflammable gaseous mixture under pressure, while the other end, which is immersed, terminates with a nozzle 10. The tube 1 provided with this nozzle is connected by a conducting wire to a source of electric energy located on a mobile installation and is used as an electrode.

Toward the end of the tube 1, on its external wall, is secured a cylindrical part 2 of the electrode, made of a nonconducting material, on which is secured in turn, such as by screwing, a sleeve 3 provided with a ring-shaped part which surrounds the part 2 and is extended by rods 3a the length of which is such that their free ends project beyond the end of .the nozzle la of the tube 1.

The sleeve 3 and the rods 3a are made of an electrically conducting material. A ring 4, also made of a conducting material is secured to the free ends of the rods 3a and carries bars made of a conducting material which can withstand high temperatures, such as tungsten or a conducting material coated with tungsten, these bars crossing one another in a plane which is substantially perpendicular to the rods 3a (HO. 2), so as to form a grid 5 constituting another electrode.

The sleeve 3 is connected through a conductive cable 7 to the source of electric energy located on the mobile installa tion. external wall is coated with a layer of insulating material 6, like the external wall of the tube 1 and that of the cable 7 on their parts located outside this sleeve.

The rods 3a may also be provided with an insulating coat- Such a sparking device operates as follows:

The device is immersed and the burner, supplied with a gaseous mixture, is tired. The flame thus produced generates between the electrodes 1 and 5 a substantially cylindrical volume of ionized gas constituting a plasma of high electrical conductivity.

A sudden discharge of current under very high voltage is generated through electrode 1 and 5 for example by means of capacitors. The electrical circuit is closed between electrodes 1 and 5 through the interval mode conductive by the plasma.

A sudden discharge of current heats the plasma adiabatically, thereby subjecting it to a sudden expansion which generates an intense acoustic shock wave.

This operation may be repeated without any limitation, the time interval between two successive shock waves only depending on the time required for recharging the capacitors in this selected embodiment.

The efficiency of the flame emanating from the burner may be improved for example by incorporating an ionizing seed to the gases, for example in the form of powders or fine metallic particles, in such proportions as to control the conductivity of the plasma and its density.

In a second embodiment of the sparking device according to the invention, illustrated by FIG. 4, the burner includes a tube 1 provided with a nozzle 1a, constituting one of the electrodes connected with a terminal of a source of electric energy, not shown, through an electrically. insulated conductor 8.

This electrode-burner is surrounded with a streamlined hull made of an insulating material or coated with an insulating material including a streamlined annular part 9 the internal wall of which, forming a venturi, is extended by rods 10 which are secured to the end part 11 of the streamlined hull. This end part is provided, toward the interior of the streamlined hull and substantially in front of the nozzle 1a, with an electrode 12 connected with the other terminal of the source of electric energy through an electrically insulated conductor 13. The end part 11 of the streamlined hull may be provided with stabilizing fins 14.

The operation of this sparking device is similar to that of the above-described sparking device.

Moreover the design of the sparking device shown by FIG. provides for the protection of the flame of the burner 1 by means of the water current which is created around this flame when the device is being towed in the water. The direction of this water current is indicated by the arrows 17 on FIG. 4.

In a third embodiment of the sparking device according to the invention, shown by FIG. 5, this device includes two electrode-burners 1 and 15, respectively provided with nozzles 1a and 15a, connected through conductors to a source of electric energy.

The other elements of the sparking device are identical to those of the embodiment illustrated by FIG. 1. The electrodegrid 5 may also include teeth 16 directed toward the nozzles 1a and a and located substantially in front of the latter, so as to improve the electrical connection.

The operation of such a sparking device is substantially similar to that of the sparking device according to the first embodiment.

However, this sparking device produces an additional effect, called blowing effect" similar to that generated by a sparking device of the type described in French Pat. Specification No. 1,549,176.

The electric current which for example leaves the electrodes 1 and 15, flows through the plasma and the teeth 16, then through the electrode-grid 5 and the rods 3a, the direction of the current (indicated by arrows 18 in H6. 5) through these rods being opposite to the direction of the current through the plasma (indicated by the arrows 19).

There is thus produced an acceleration of the plasma, as a result of the action of the magnetic fields created by currents of opposite directions flowing through the conducting elements.

in the embodiment of FIG. 5, there are two identical systems which at the instant of the explosion promote this acceleration of the plasma.

This device could also be housed in a streamlined hull ofthe type illustrated by FIG. 4.

FIG. 6 illustrates a fourth embodiment of a sparking device according to the invention, provided with improvements intended to increase the stability of the flame to the blowing effect created by an electric discharge.

This sparking device operates with a steady flame, free from pulsations, little sensitive to variations in the percentages of the components of the gaseous mixture, and to acoustic shocks, in particular to the effects of an electric discharge, and

also insensible to the effects of gravity.

The special performances of this new sparking device are a result of the following improvements: the use of a combustion chamber, of a device for mixing the gases in this chamber and of means of preventing any back-fire and providing a predetermined expansion of the gaseous mixture through elongated nozzles.

A protection of the combustion chamber may also be achieved by means of a perforated diaphragm which gives passage to only a part of the flame toward the exterior of this chamber. Thus during the electric discharge the blowing of the external part of the flame does not stop the combustion inside the chamber where the flame is initiated. When the excess of pressure outside the diaphragm disappears the flame spreads again through the aperture of this diaphragm.

Another improvement consists in a circulation of water under pressure through the annular space surrounding'the burner. v

The expelling of the combustible gasses at a high speed into a substantially stationary fluid (surrounding water) creates turbulences which cause pulsations of the flame. A jacket of water under pressure around the burner at a speed substantially equal to or greater than that of the expelled combustible gasses improves the regularity of the flame, the apparent speed of the gases being thus substantially reduced to a value corresponding to the difference of the respective speeds of the burning gaseous flow and of the water flow.

Moreover this water flow tends to keep the flame directed along the burner axis, while this flame has normally a tendency to become strongly bent toward the vertical under the action of forces due to gravity, when the burner takes an horizontal position.

This embodiment will be described more in detailwith reference to the attached drawing FIG. 6 which represents a cross-sectional view of this new sparking device.

This sparking device includes an electrode-burner provided with a first tube 1 having an end 1a, and a second tube 20 with the same axis and the diameter of which is greater than that of the first tube, so as to let an annular space 21 between the two tubes. The tube 20 extends over a certain length beyond the end 1a ofthe tube 1.

A combustion chamber 22 is limited laterally by the wall of that part of the tube 20 which extends beyond the tube 1. The extremity of the tube 20 is provided with a diaphragm 23 perforated in its center with an aperture 24. This diaphragm made of a substantially conducting material, for example a graphite washer, constitutes an end wall of the combustion chamber 22.

The opposite end wall of this chamber is constituted by an end of an annular element 25 which is secured internally to the tube 20. so that one of its ends be substantially located at the level of the end 1a of the tube 1.

The internal diameter of this annular element is slightly greater than the external diameter of the tube 1, so as to provide an annular passage 26 between these elements.

Another annular element 27 the internal diameter of which is substantially equal to that of the tube 20 extends this tube beyond the diaphragm 23. This element must serve as a deflector. It may be secured to the tube 20, as also the diaphragm 23, bymeans of a clamping ring 28.

The assembly of the above-indicated elements constitutes the properly so-called burner. The tube 20 is connected through a conducting cable to a source of electric energy located on a mobile installation (not shown). The burner thus serves as an electrode, the active parts of which are mainly the deflector 27 and the diaphragm 23.

The electrode-burner is surrounded, up to its end located on the side of the combustion chamber, with a sleeve 29 coaxial with the tubes 1 and 20 and the diameter of which is greater than that of the tube 20. The extremity of this sleeve most remote from the combustion chamber is closed with an end wall 30 and secured to the tube 20. The end of this sleeve located at the level of the deflector 27 is provided with an annular diaphragm 31 the central aperture of which has n diameter greater than the external diameter ofthe deflector 27, so as to provide an annular passage between these two elements. This diaphragm may be secured to the sleeve 29 by means ofa clamping ring 32.

The ring 29 is furthermore provided on its lateral wall with a mouthpiece 33 for a tube supplying water under pressure.

The second electrode of the sparking device is constituted by a conductive element 34 made ofa conducting material resistant to high temperatures, such as cast iron, preferably provided with a tapered end directed toward the burner, at a suitable distance from the latter. This second electrode is connected with the source of electric energy through a conductor 35 surrounded with an insulating material 36.

The assembly of the so-eonstituted sparking device can be housed in a streamlined hull so designed as to support the different elements, in an analogous way as in the embodiment illustrated by F IG. 4, the new burner being then substituted for the burner l.

The tube 1 and the annular space 21 between the tubes 1 and 20 are respectively supplied with the components under pressure of an inflammable-gaseous mixture. For example the tube 1 is supplied with oxygen and the annular space 21 with acetylene.

The annular space 38 between the sleeve 29 and the tube 20 is supplied with a stream of water under pressure.

This sparking device operates as follows: the combustion chamber is supplied with an inflammable gaseous mixture and the burner is lighted in the open air. The flame escapes through the aperture 24 of the diaphragm 23, this aperture being so calibrated as to let a passage only to the fraction of the flame which is necessary for the operation of the burner. The annular element 25 is so dimensioned as to efficiently regulate the flow rate of combustible gas and to prevent a backfire or return of the flame from the combustion chamber to the gas supplying pipe.

A flow of water under pressure is established through the annular space 21. The water follows the path indicated by the arrows 39 and escapes through the annular passage between the deflector 27 and the diaphragm 31, thereby forming an enclosure around the flame. The system formed by the deflector 27 and the diaphragm 31 carries this water enclosure in contact with the flame and increase its speed of ejection.

Moreover it could also be possible to use the speed of displacement of the device in the water in the way indicated above.

The sparking device is immersed and the gas flow rate as well as the velocity of the water stream are brought to their respective optimum values.

At this time an elongated zone of plasma connects the end of the electrode-burner with the other electrode 34. At the instant selected for shooting, the energy stored in a battery of capacitors (or in any other energy storing device, such as for example an electric coil .'..etc...) is switched to the circuit constituted by the two above-described electrodes and the zone of plasma.

The discharge current flows through the plasma. Therefrom results a period of substantially adiabatic heating of the plasma, followed by a phase of expansion of this plasma at the end of the discharge.

During the first phase which is characterized by a substantial pressure rise and a sudden radial expansion of the plasma, the active part of the flame is spread.

The remainder of the flame reenters the combustion chamber 22 where the combustion process continues, shel tered from the excess of external pressure, due to the small section of the aperture 24.

At the end of the period of expansion, the pressure in the zone between the electrodes becomes again equal to the hydrostatic pressure.

The flame then appears again outside the combustion through the aperture 24 and occupies again the space between the electrodes.

The device is then ready for a new shooting.

The burner may be provided with a device limiting the gas flow rate to a value which is justsufflcient for keeping up the flame during the time intervals between the shots, whereas the pressure is fully restored only at the instant of the shooting.

Such a device may be constituted in simple manner by means of a two-way valve with manual, pneumatic or electromechanical control.

It will obviously be possible to change the number of burners and electrodes or their respective arrangement without departing from the spirit and scope of the present invention.

We claim:

1. A sparking device for underwater seismic prospecting, comprising at least two immersed electrodes and means for suddenly discharging a high electrical energy across said electrodes, in combination with a burner supplied with an inflammable gaseous mixture for producing a conducting ionized flame between said electrodes, so as to form a plasma when an abrupt discharge of current is effected between said electrodes.

2. A sparking device in accordance with claim 1, wherein said burner constitutes one of said electrodes.

3. A sparking device in accordance with claim 1, wherein said burner is used as a central electrode and is surrounded with a conductive element having substantially the shape of a sleeve, comprising a cylindrical part secured to said central electrode by means of an insulating element, said cylindrical part being extended by rods having free ends projecting beyond the free end of the central electrode and connected with a conductive ring, bars carried by said ring, said bars forming a grid in a plane substantially perpendicular to said rods, said grid constituting another electrode.

4. A sparking device in accordance with claim 3, wherein said rodsare surrounded with an insulating coating.

5. A sparking device in accordance with claim 3, wherein said g1 id is provided with a tooth located in the extension of each burner.

6. A sparking device in accordance with claim 1, wherein said burner is surrounded with a streamlined hull providing for a circulation of water around said burner,

7. A sparking device in accordance with claim 1, including at least two burners constituting two electrodes, said device having other electrodes and at least one conducting clement supplying electric current to said other electrodes wherein the electric current flowing through the respective flames of said burners has a direction opposite to the current flowing through said conducting elements.

8. A sparking device in accordance with claim 2, wherein said electrode-burner is provided with a combustion chamber for the gaseous mixture.

9. A sparking device in accordance with claim 8, wherein said combustion chamber opens out in the space between the electrodes through an aperture of limited section.

10. A sparking device in accordance with claim 8, wherein said electrode-burner includes a first tube supplied with a component of the gaseous mixture, a second tube coaxial with said first tube and having a greater diameter than said first tube, said first and second tubes limiting an annular space supplied with another component of the gaseous mixture, said second tube having a greater length than said first tube, said combustion chamber being limited by the wall of said second tube, in the part thereof extending beyond said first tube, by a diaphragm having an aperture substantially in its center and located at the end of said second tube. and by an annular element integral with the internal wall of said second tube, said annular element being located substantially at the level of the end of said first tube and having an internal diameter which is slightly greater than the external diameter of said first tube.

11. A sparking device in accordance with claim 10, wherein said second tube is surrounded substantially over its whole length with a sleeve coaxial with said second tube and having a diameter substantially greater than that of said second tube, said second tube and said sleeve limiting an annular channel closed against the surrounding water on its side opposite to the combustion chamber, said annular channel being supplied with water under pressure.

12. A sparking device in accordance with claim 10, wherein the end of said second tube is provided with an annular deflector and the end of said sleeve is provided, substantially at the level of said deflector, with an annular diaphragm having an internal diameter greater than the external diameter of said deflector.

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