EA012059B1 - Method of minerals prospection - Google Patents

Abstract

Invention can be used for complex (electromagnetic and seismic) minerals prospection. Invention essence: in the known way of elastic waves shooting in the earth crust formation by the pulse electric discharge created between electrodes which are connected to the high-voltage condenser power source and placed in reservoir or hole in the earth, filled with a liquid, what is new is that, simultaneously with elastic magnetic waves are shot for which purpose loop or solenoid is used as one of electrodes or its continuation. Besides, the loop is made from separate sectors located on a circle and in parallel connected among them; solenoid is made multiple; solenoid is made of spring steel and chilled. Invention allows to raise reliability and speed of type and properties definition of geological environment.

Description

FIELD OF THE INVENTION

The invention relates to methods for exciting high-intensity seismic-acoustic and electromagnetic fields and can be used for complex (electromagnetic and seismic) mineral exploration.

State of the art

A known method and device for monitoring the environment (see application \ UO No. 926416, IPC 601U 3/10, prior, 12.19.95), according to which the medium is checked for the presence of zones with increased electrical conductivity and / or increased magnetic permeability by acting on pulsed magnetic field medium. The medium control device includes an inductor with a large quenching resistance. When an exciting signal is supplied, the coil generates damped oscillations. The oscillating magnetic field created by the coil interacts with the controlled medium. The voltage resulting from this interaction at another receiver coil causes a voltage to be applied to the receiver. The received signal is corrected and evaluated taking into account the components due to the electrical conductivity and magnetic permeability of the medium.

The disadvantage of this method is that it determines only conductive geological structures such as metal ores and coal. This limits its use.

There is also known a method of exciting elastic waves in the thickness of the earth's crust during seismic exploration (see AS USSR 106338, class 21d, authors L.A. Yutkin, L.I. Goltsova, publ. 13.07.53, publ. In B .I., 1957, No. 5), which consists in the fact that a pulsed electric discharge is applied between the electrodes connected to a high-voltage capacitor and immersed in a reservoir or in a well in the earth filled with liquid to excite elastic waves.

Using an electric discharge in a liquid, obtained using high-voltage electro-hydraulic devices, it is possible to obtain different types of seismic waves: ordinary (like a mixture of waves), surface, Rayleigh waves. Seismoacoustic pulses reflected from geological strata are then perceived by receiving piezoelectric or mechanical induction sensors and recorded on the tape of a multi-channel seismic station or computer screen. In this case, by the difference in time from the moment of discharge to the moment of arrival of the reflected wave, one can judge the depth of the formation, and the amplitude of the reflected pulse to assess the density of the reflected pulse of the formation, previously knowing the amount of attenuation of the pulse in the layers of overlying rocks (see L.A. Yutkin, “Electro-hydraulic effect and its application in industry.” L., Mechanical Engineering, Leningrad Branch, 1986, as well as the book “Electrospark source of elastic waves for ground-based seismic exploration.” Edited by A.V. Kalinin , Moscow, Moscow University Press, 1989).

The method of exciting elastic waves in the thickness of the earth's crust is the closest to the claimed invention and therefore adopted as a prototype.

The disadvantage of this method is that it determines only the mechanical constants of the geological environment, namely, the values of the longitudinal ν _ρ and transverse V, the propagation velocity of elastic waves in the geological section, and from them through the known relations:

Ur = l / (E + 4c / 3) / p; Y8 = ^ p / p; Uz / Ur = l / 2 (1-y) / (1-2y), where E is Young's modulus; μ is the shear modulus; ν is the Poisson's ratio; ρ is the density of the medium, which makes it possible to go to the moduli of compression and shear of the geological medium and the ratio of transverse to longitudinal strain. This method does not allow to determine what is in the geological trap - oil or just mineralized liquid.

SUMMARY OF THE INVENTION

The objective of the invention is the creation of integrated seismic and electromagnetic exploration methods on a single excitation device.

The technical result of the invention is to increase the reliability and speed of determining the type and properties of the geological environment by increasing the number of simultaneously excited and recorded wave fields and obtaining information about twice as many constants of the geological environment (about mechanical constants: Young's modulus, shear modulus; Poisson's ratio, density of the medium, as well as electrical constants: electrical conductivity, magnetic and dielectric constant).

To achieve a technical result, that in the inventive method of generating elastic waves in the thickness of the earth’s crust, where a pulsed electric discharge is used, created between the electrodes that are connected to a high voltage capacitor energy source and immersed in a reservoir or in a well in the earth filled with liquid, new that, as one of the electrodes or its continuation, a loop or a solenoid is used, through which magnetic waves are excited simultaneously with elastic waves.

In addition, the loop is made of separate sectors arranged in a circle and parallel connected to each other; the solenoid is made multi-start; the solenoid is made of spring steel and hardened.

The use of one of the electrodes or its extension as a loop or solenoid ensures that the discharge current flows simultaneously through the liquid and through the loop or solenoid simultaneously and almost at the same point of the seismic-acoustic pulse and the magnetic field pulse, which then with their velocities ( shock and elastic waves - with the speed of sound in water or in rocks - is about 1.6 km / s or 3-6.5 km / s, magnetic - with a speed close to the speed of light - it is 100-150 thousand km / s ) are distributed over rocks and s can be taken with a hydrophone and the piezoelectric or magnetic antennas at neighboring wells or on the surface. As a result, two can be obtained quickly and immediately: seismic and electrical sections of the geological environment (oil or gas field). In addition to seismic and electrical sections, additional information on rock permeability can be obtained. As is known, the resistivity of a rock is determined not so much by the resistivity of individual grains of the mineral, but by the resistivity of the fluid filling the intergranular space. Geophysicists have long tested and successfully applied to determine the porosity of the medium the Archie equation, which relates resistivity and porosity. According to him

where p _VP - specific resistance of water-saturated rock; p _in - the resistivity of the water filling the pores; k _p is the porosity coefficient (the fraction of the mountain space occupied by the pores); 8 _{Into a} part of the pore space filled with water; t = 1.3-1.95 - constant, the value of which depends on the type of rock.

Due to the generation of seismoacoustic and magnetic pulses from a single high-voltage capacitor source, the efficiency is almost doubled electrical discharge and efficiency the capacitor source itself (40% of the electric energy goes to the shock wave and high-speed hydroflow and about 50% of the electric energy goes to the magnetic field).

Due to the significantly higher propagation velocity of the magnetic field pulse in the rocks, increasing the accuracy of launching of the receiving seismic station and reducing the error in determining the longitudinal and transverse propagation velocities of elastic waves in the geological environment.

Due to the formation of a solenoidal and sufficiently intense magnetic field, the intensity lines of which are parallel to the axis of the interelectrode gap, creating obstacles to the development of leaders in the radial direction and facilitating the formation of a through-conduction channel with minimal losses for pre-discharge losses, as well as increasing the length of the punched gap and the amplitude of the seismic acoustic pulse.

The manufacture of a loop from separate circularly located and parallel connected sectors provides a reduction of η times, where η is the number of sectors, the inductance of the loop and, accordingly, the possibility of obtaining several times the large discharge currents, amplitudes and frequencies of the magnetic field in the loop. Accordingly, in this case, it can be ensured that the loop impedance does not exceed the active resistance of the discharge channel and the loop will have little effect on the amplitude of the shock (near the discharge channel) and elastic (at large distances) waves. In addition, by increasing the frequency of the magnetic field, it is possible to increase the detail (spatial resolution) of the electric section of the field.

The implementation of the multi-start solenoid (in the form of several spirals wound with an azimuth shift and connected in parallel) provides the ability to:

passing high currents through the solenoid and a sharp decrease in the inductance of the solenoid (the dependence on η is weakened). Accordingly, the inductance of the solenoid up to 2 μH on the parameters of the electric discharge in water and the amplitude of the shock (near the discharge channel) and elastic (at large distances) waves does not affect (see Fig. 5 and 6 of the application description);

increasing the stability of the solenoid to the action of shock waves emanating from the discharge channel, due to the equidistant and symmetrical arrangement of the solenoid spirals relative to the discharge channel, as well as the mechanical attachment of the beginning and end of each spiral (the solenoid inlet) to the metal cathode and reverse current path.

The implementation of the spring steel solenoid and its hardening provide an even greater increase in the mechanical stability and strength of the solenoid to the effects of shock waves and high-speed hydraulic flow generated during a discharge in water and passing through the turns of the solenoid. Thus, it becomes possible to repeatedly excite elastic and magnetic waves from one point, accumulate the signals transmitted from these two waves through rocks, filter out noise and increase the reliability of determining rock parameters.

Thus, due to new distinctive features in the claimed method, two different physical fields are excited (generated) simultaneously, namely, elastic and magnetic waves (or seismic-acoustic and magnetic pulses). This means that it is possible to combine seismic and electrical exploration methods in time and space, on one source of excitation and on one field under study, and to more clearly interpret (determine) the type and properties of rocks and fluids in the field.

- 2 012059

List of figures of drawings and other materials

In FIG. 1 and 2 show a variant of the device (in section and plan) for implementing the proposed method with a flat loop.

In FIG. 3 and 4 show variants of a device for implementing the inventive method with a conical solenoid and a cylindrical solenoid.

In FIG. 5 and 6 show the amplitude-time dependences of the discharge current for a device with a cylindrical solenoid according to FIG. 4, connected to a borehole electro-hydraulic apparatus with an operating voltage of 30 kV and an energy intensity of 1 kJ, when the apparatus operates in water and the solenoid has different inductances.

Information confirming the possibility of carrying out the invention

A device for implementing the inventive method with a loop (see Fig. 1 and 2) is intended for ground and river integrated exploration of minerals. It contains two coaxial and gap-mounted electrodes: anode 1 and cathode 2 and a conductive loop 3 made of four sectors distributed in a circle.

Loop 3 is made of insulated high-voltage wire (ignition wire) of the EPZ 614 mark. The beginnings of conductors in each sector of the loop are connected to cathode 2, and the ends of the conductors in each sector of the loop are connected to the braid 4 of the high-voltage coaxial cable of the RK-75-11-17 or IR -2.

The core 5 of the coaxial cable at one end is connected to the anode 1. The second end of the coaxial cable is connected to a high voltage capacitor energy source 6. The high voltage capacitor energy source 6 can be located on board a boat or a car. The electrodes 1, 2 and the conductive loop 3 are immersed in a pond 7.

Devices for implementing the proposed method with a conical (see Fig. 3) and cylindrical (see Fig. 4) solenoids are designed for downhole integrated exploration of minerals.

A device with a conical solenoid (see Fig. 3) is a coaxial electrode system containing a central anode 1, cathode 2 and a cylindrical solenoid 3. Anode 1 and cathode 2 are located on the same axis and with a gap of 15-20 mm relative to each other. The anode 1 is insulated with a conical polyurethane insulator 4. The conical solenoid 3 is oriented with its apex toward the central anode 1, i.e. the top of the conical solenoid is actually the cathode 2. The base of the conical solenoid 3 is connected to the return conductor 5, made in the form of a rigid metal bus. The central anode 1 and the return conductor 5 are connected through a special adapter (not shown in the figure) to the downhole capacitor energy source 6.

A device with a cylindrical solenoid (see Fig. 4) also represents a coaxial electrode system containing a central anode 1, cathode 2 and a cylindrical solenoid 3. Anode 1 and cathode 2 are located on the same axis and with a gap of 15-20 mm relative to each other. The anode 1 is insulated with a conical polyurethane insulator 4. The end of the solenoid 3 is connected to the return conductor 5. The start of the solenoid 3 is connected through the metal disk 7 to the cathode 2. The anode 1 and the return conductor 5 are connected through a special adapter (not shown) to the borehole condenser energy source 6. To exclude screening of the magnetic field in the metal disk 7, several radial slots are made. A conical insulator 8, also made of polyurethane, is dressed at the cathode 2.

The coaxial arrangement of the anode 1 and cathode 2, as well as the conical shape of the insulators 4 and 8, ensures the direction of the shock and elastic waves along the radius of the electrode system (in the direction transverse from the well axis). The cylindrical shape of the solenoid 3 provides the emission of a magnetic wave also mainly in the transverse direction from the axis of the well.

Anode 1 and anode 2 have a diameter of 8-12 mm and are made of tungsten or a special erosion-resistant material AMB30.

Solenoid 3 is a cylindrical spiral with an outer diameter of 102 mm, a length of 100 mm and a pitch of 25 mm. The spiral is made of spring steel - wire with a diameter of 6-10 mm and hardened. The number of turns of the spiral is 4-5. The inductance of the helix is 1.1-1.72 μH.

A device with a cylindrical solenoid (see Fig. 4) is mechanically more durable and stable than a device with a conical solenoid (see Fig. 3), so in the first device the beginning and end of the cylindrical solenoid are securely fixed, and in the second device a conical spiral It would “hang” on the reverse current lead and under each electric discharge (electro-hydraulic shock) it experiences high mechanical stresses, which are concentrated at the point of attachment of the base of the conical spiral to the reverse current lead.

Devices with a conical and cylindrical solenoid can be manufactured as separate modules for a high-voltage borehole electro-hydraulic apparatus and lowered together with it to the bottom of an oil well. As a process fluid that is pumped into the well and into which the devices of FIG. 3 and 4, you can use fresh (technical) water or non-ionized hydrocarbon liquids, such as ethanol, acetone, kerosene.

The inventive method is implemented as follows:

a) make two electrodes 1 and 2, while the first electrode is isolated, and the second of the electrodes

- 3 012059 or its continuation is non-insulated and performed in the form of a loop or solenoid 3;

b) immerse the above electrodes 1 and 2 and loop 3 in a reservoir 4 or in a well in the ground filled with liquid;

c) connect the above electrodes 1 and 2 by means of a coaxial cable line 5 or a special coaxial adapter to a pulse voltage or current generator 6;

d) a high voltage pulse is applied to electrodes 1 and 2, and a breakdown of water or well fluid in the gap between the electrodes occurs;

e) during an electric discharge that passes through water or a well fluid, the electric energy stored in the capacitors of a ground or borehole capacitor energy source is rapidly released and a plasma channel is formed between the electrodes. A high-temperature plasma channel promotes rapid (explosive) overheating and evaporation of water or well fluid, as a result of which a vapor-gas cavity is formed around the electric discharge channel, which first expands to a certain radius and then begins to pulsate. Depending on the size of the vapor-gas cavity, the excess pressure in the liquid is defined as ('41 · where m = p _o 4pK <) ² 8o is the mass of the fluid that moved from the source when the displacement of the cavity was 8 _o ; p _{about the} density of the liquid; c is the phase velocity of an acoustic wave in a liquid (see book A. A. Kaufman, A. L. Levshin. Introduction to the theory of geophysical methods. Part 3. Acoustic and elastic wave fields in geophysics. Transl. from English. Moscow. Subsoil. 2001.S. 169-180).

In other words, a shock wave departs from the discharge channel in water, passing through a certain distance into an elastic wave.

f) at the same time, the discharge current flows through the loop or solenoid 3. The loop or solenoid 3 with the current is a magnetic dipole with a moment M = M ₀ -e ^- “-k, where Μ ₀ = Ι · 8 · η is the amplitude of the magnetic moment; Ι = Ι ₀ · δίηωΐ is the complex function that describes the current in the dipole; ω is the circular frequency; η is the number of turns; 8 - the area of one turn; k is the unit vector directed along the ζ axis.

This dipole creates a primary electromagnetic field with two components:

_5Sh 0 and ⁰ 4tgK ^{2 0} 2lYa ³ (see the book by A. A. Kaufman, A. L. Levshin. Introduction to the theory of geophysical methods. Part 2. Electromagnetic fields. Translated from English by Moscow. Nedra. 2000. p. 161-164).

In other words, a magnetic field is emitted from the loop or solenoid in the form of a single pulse or a damped sinusoid.

The author calculated the device — the electrode system with a cylindrical solenoid according to FIG. 4 for a downhole electro-hydraulic apparatus with a voltage of 30 kV and an energy consumption of 1 kJ. The calculations showed (see Figs. 5 and 6) that when the apparatus operates on an electrode system with a cylindrical solenoid with a diameter of 102 mm, the number of turns 4-6 and an inductance of up to 2 μH immersed in fresh water, the solenoid has practically no effect on the amplitude and duration discharge current in water (they remain at the level of 10-10.5 kA and 7 μs, respectively). In other words, a solenoid with an inductance of up to 2 μH does not affect the energy release in the discharge channel and the amplitude of the shock and elastic waves extending from the discharge channel, and at the same time provides the generation of magnetic field pulses of about 7 μs duration and a magnetic moment of about 1000 A-m ² . At large values of the inductance of the solenoid, its effect on the discharge in water increases, the shape of the discharge current does not become aperiodic, but turns into a damped sinusoid. However, this does not limit the possibilities of the proposed method. It can be used in such a well-known mineral exploration method as the transient method.

Claims (4)

CLAIM 1. A method of mineral exploration, in which elastic waves in the earth's crust are excited by a pulsed electric discharge created between electrodes that are connected to a high-voltage capacitor energy source and immersed in a reservoir or in a well in the earth filled with liquid, characterized in that simultaneously with magnetic waves are excited by elastic waves, for which a loop or a solenoid is used as one of the electrodes or its continuation. 2. The method according to claim 1, characterized in that they use a loop made of individual sectors arranged in a circle and connected in parallel. 3. The method according to claim 1, characterized in that the multi-way solenoid is used. 4. The method according to claim 1, characterized in that they use a solenoid made of spring steel and hardened.