RU2721475C1 - Method for direct search for hydrocarbons using geoelectrics - Google Patents

Abstract

FIELD: physics.SUBSTANCE: invention relates to geoelectric prospecting by electromagnetic field formation methods and can be used to determine presence of hydrocarbons and outline of deposit. Summary: alternating electromagnetic field of transverse-magnetic (TM) polarization is formed. Magnetic and electric components of electromagnetic field are measured. Maps of the distributed polarization parameter determined by electrical components and a map of the measured signals of the magnetic component are plotted. In places where maxima of signals of magnetic component and polarization parameter coincide, presence of hydrocarbon deposits is determined. Formation of variable electromagnetic field of transverse-magnetic (TM) polarization can be performed by means of circular electric dipole (CED), vertical line or backward electric line.EFFECT: technical result is the possibility of detecting hydrocarbon deposits at depths of several kilometres in media with specific resistance of less than 50 Ohm⋅m.4 cl, 8 dwg

Description

FIELD OF THE INVENTION

The invention relates to geoelectrical exploration by the methods of formation of an electromagnetic field and can be used to determine the presence of hydrocarbons and contouring deposits. Determining the presence or absence of hydrocarbons in the identified seismic survey object is still an intractable task.

State of the art

A known method of electrical exploration (RF Patent No. 2454683 A device for direct search of geological objects / Balashov BP, Mogilatov VS, Pauli AI), in which an electric field is excited in the Earth by axisymmetric introduction of electric current into the Earth and parameters are measured electric field along profiles radially diverging from the point of introduction of an axisymmetric electric current into the Earth. In this case, the axisymmetric introduction of current into the Earth is ensured by a uniform arrangement of the external supply electrodes (grounding) around the circumference and by connecting them via radial lines to one pole of the current source. The radius of the circle is determined by the required depth of study. In this case, the internal supply electrode is earthed in the center of the circle formed by the external supply electrodes and connected to the other pole of the current source. Such a source since the publication of the method is called a circular electric dipole (QED).

Measurements of the electromagnetic response of the studied field medium are carried out over the area around the source at a distance of up to 7 QED radii. In this case, depending on the required depth and size of the source, the investigated area can be up to 400 square meters. km Based on the known method, the method of sounding by vertical currents (SEC) is developed and applied.

A known method of exciting an electromagnetic field in a medium is described in USSR author's certificate No. 150184 (SU No. 150184. Device for marine electrical exploration. Author Nazarenko OV), in which an electromagnetic field is excited in the Earth or in the sea using a vertical electric line.

Also known is a method of exciting an electromagnetic field in an environment described in the patent of the Russian Federation No. 2453872 for electrical exploration (No. 2453872. Method for geoelectrical exploration and a device for its implementation. Authors: Balashov BP, Mogilatov VS), in which the electromagnetic field is excited field using oncoming electric line. The oncoming electric line is a horizontal electric line located on the same line and connected towards each other.

Closest to the proposed invention is the device described in the patent of the Russian Federation No. 2454683 (Device for direct search of geological objects / Balashov BP, Mogilatov VS, Pauli A.I.). The patent describes a method for exciting a field of TM polarization in a medium. The patent does not describe which components of the electromagnetic field need to be measured and how to interpret the received signals.

The standard approach to the interpretation of materials in geoelectrics of a medium model conducted from the day surface takes into account only a change in the isotropic resistivity. As experience with the use of geoelectrics has shown, it is impossible to detect hydrocarbon deposits at depths of several kilometers in media with resistivity less than 50 Ohm * m by changing the electrical resistivity of the medium. The invention aims to provide such an opportunity.

The technique described in this invention allows to identify hydrocarbon deposits by the magnetization of the medium and the polarizability of the medium in electromagnetic fields of TM polarization. Only such an approach in a large number of provinces allows the identification and contouring of hydrocarbon deposits by ground-based methods.

SUMMARY OF THE INVENTION

In the direct hydrocarbon search method using geoelectrics, including the formation of an alternating electromagnetic field of transverse magnetic (TM) polarization, measuring the electromagnetic transition signal response of the medium under study and interpreting the measurements, it is proposed to measure the magnetic and electrical components of the electromagnetic field, to build maps of the distributed polarization parameter, determined by electric components, and maps of the measured signals of the magnetic component, and in places where the maximums of the signals of the magnetic component and the polarization parameter coincide, determine the presence of hydrocarbon deposits. The formation of an alternating electromagnetic field of transverse magnetic (TM) polarization can be carried out using a circular electric dipole (QED), a vertical line, or an oncoming electric line.

All three sources — a circular electric dipole, a vertical electric line, and a counter electric line — have in common the field excitation of only or predominantly TM polarization. Over the entire area around a circular electric dipole and a vertical electric line, an electromagnetic field of only TM polarization is excited. On the straight line, on which the rays of the oncoming electric line are located, an electromagnetic field of predominantly TM polarization is excited. By excitation of an electromagnetic field of only or predominantly TM polarization in a medium, these three sources differ from other sources widely used in electrical prospecting with artificial sources. See FIG. 1.

It is known that any electromagnetic field excited in the earth by artificial or natural sources can be represented as a superposition of the fields of TM polarization and TE polarization. If a pure electromagnetic field of TM polarization is excited in the medium under study by introducing a pulsed or harmonic electric current into the earth, then above the horizontally layered medium all three magnetic components of the electromagnetic field will be zero. On the other hand, if the field above the medium in which the electromagnetic field is excited only by TM polarization is not zero, this is evidence of the presence of three-dimensional inhomogeneities in the medium with respect to some electrodynamic parameter. See FIG. 1.

It has been experimentally shown that upon excitation in the medium of an electromagnetic field of TM polarization, an anomalous magnetic field is fixed over hydrocarbon deposits. If the magnetic field is measured, then there are three-dimensional inhomogeneities in electrodynamic parameters. Calculations of three-dimensional models have shown that heterogeneity in resistivity and polarization cannot cause signals fixed over hydrocarbon deposits. This means that over hydrocarbon deposits there is a change in other electrodynamic parameters, possibly the magnetization of the medium. Examples of a number of work performed using one of the sources of the electromagnetic field of TM polarization - circular electric dipole, are shown in FIG. 2. In FIG. Figure 2 shows the anomalous signals of the measured magnetic component ∂B _z / ∂t over hydrocarbon deposits at different times. The removal of observation points from the center of the source is taken into account by formula 1.

It has been experimentally shown that elevated parameter values of the induced polarization of the medium are recorded over hydrocarbon deposits. When conducting electrical exploration, most of all, a change in the polarization parameter affects the measured electrical signals when excited in the medium of an electromagnetic field of TM polarization.

This patent proposes a method for identifying hydrocarbon deposits during electrical exploration. Electrical exploration is carried out with excitation in the medium of an electromagnetic field of TM polarization. By measuring the magnetic components on the surface of the medium, the electrodynamic parameter characteristic of hydrocarbon deposits is determined. By measuring the electrical components, an increase in the polarization parameter is detected. The places of accumulation of hydrocarbons are characterized by a signal above the field when measuring the magnetic components of the electromagnetic field and an increase in the polarizability parameter, a change which manifests itself when measuring the electrical components of the electromagnetic field. The patent describes how to determine the presence of hydrocarbons in the medium when excited in an environment of an electromagnetic field of TM polarization by measuring the magnetic and electrical components of an electromagnetic field.

Details, features, and advantages of the present invention are explained using the drawings, which show:

FIG. 1 - Current lines excited in the medium by a classical source of electromagnetic field of TE polarization in Figure 1a. Current lines excited in a medium by a source of an electromagnetic field of TM polarization - a vertical electric line in Figure 1b. Current lines excited in a medium by an electromagnetic field source of TM polarization — a circular electric dipole in Figure 1c.

Figure 2 - Signals of the magnetic component of the electromagnetic field ∂B _z / ∂t upon excitation of the medium by a circular electric dipole, in different areas, above hydrocarbon deposits. FIG. 2a - section of Chico-Martinez, California. T = 31 ms. Fig.2b - Shadkinskoye field, Tatarstan. T = 201 ms. Figv. - Shia field, Suenglinsky site, Tatarstan. T = 201 ms. Fig.2g - Shugansk deposit, Tatarstan. T = 9 ms. Fig.2d - Akbyazovskaya deposit, Tatarstan. T = 31 ms. Fig.2e - Vinokurovsky site, Tatarstan. T = 43 ms.

FIG. 3-Diagram of the excitation and measurement of the electromagnetic field during the excitation of the electromagnetic field in the medium by a circular electric dipole.

FIG. 4 - Scheme of excitation and measurement of the electromagnetic field during the excitation of the electromagnetic field in the medium by a vertical electric line.

FIG. 5 - Diagram of the excitation and measurement of the electromagnetic field upon excitation of the electromagnetic field in the medium by an oncoming electric line.

FIG. 6 - Measurement results of the magnetic component ∂B _z / ∂t in the form of signal isolines at a time of 55.7 ms upon excitation of the electromagnetic field by a circular electric dipole.

FIG. 7 - Polarization parameter obtained by the inversion of the measurement data of electrical components upon excitation of the electromagnetic field by oncoming electric lines.

FIG. 8 - Areal results of measurements of the magnetic component ∂B _z / ∂t in the form of isolines of the signal at a time of 32.2 ms when the electromagnetic field is excited by a circular electric dipole ZVT-M and the isoline band of the polarization parameter, aligned along the profile of the measurement of electrical components when the electromagnetic components are excited by counter electric lines.

Disclosure of invention

The geophysical work is divided into 3 stages: preparing the source (s), conducting measurements of magnetic and electric fields, processing (interpretation) of the measurement results.

The first stage is the preparation of sources. To excite the field of TM polarization in the medium, one of three methods is used:

1) A circular electric dipole is installed on the day surface, see fig. 3. Based on the research area, the depth of the objects, the level of interference, the grounding parameters, determine the size and number of beam segments 4 of the circular electric dipole and the amplitude of the current pulses of the generators 1. The size of the source and current strength only affects the distance at which the useful signal exceeds the level of interference . In accordance with FIG. 3 make arrangement of a circular electric dipole on the ground. In this case, the supply electrode 2 is earthed in the center of the circle formed by uniformly grounded supply electrodes 3. The supply electrodes 3, the number of which must be at least 6, are connected to one end of the beam segments 4 of the supply lines, which are arranged along the radii of the circle through the same angle. A current generator 1 is included in each beam segment 4. The second ends of the beam segments 4 are connected to each other and connected to one of the poles of the power source U. The other pole of the power source U is connected to the supply electrode 2. In FIG. 4 shows 6 ray segments 4 by a solid line, this is the minimum required number of lines. The number of lines can be increased based on the need to carry out certain works. In FIG. 4 shows 6 ray segments 4 by a dashed line, i.e. if we organize another 6 ray segments 4, then there will be 12 rays in a circular electric dipole.

2) One grounding of the vertical line 3 is installed on the day surface or at some deepening and the second grounding 3 of the vertical line is installed strictly vertically under the overlying ground, see FIG. 4. The second grounding is installed either in the reservoir or in the well, strictly vertically under the first grounding. The dimensions of the vertical line are determined based on the specific geophysical problem being solved, the area of research, the sounding depth, as well as the depth of the reservoir or the depth of the well. The size and strength of the current in the source only affects the distance at which the useful signal exceeds the interference level. A current generator 1 is included in the vertical line 4. One end of the vertical line 4 is connected to one of the poles of the power source U. The other pole of the power source U is connected to the supply electrode 3.

3) A counter electric line is installed on the day surface. Both supply lines are on one straight line. Based on the research area, the depth of the objects, the level of interference, the grounding parameters, the sizes of the beam segments 4 of the oncoming electric line and the amplitude of the current pulses of the generators are determined 1. The size and current strength in the source only affects the distance at which the useful signal exceeds the noise level. In accordance with FIG. 5 make the arrangement of the device on the ground. In this case, ground the supply electrode 2 in the center of the oncoming electric line. The supply electrodes 3 are connected to one end of the beam segments. A current generator 1 is included in each beam segment 4. The second ends of the beam segments 4 are connected to each other and connected to one of the poles of the power source U. The other pole of the power source U is connected to the supply electrode 2.

The second stage is signal measurement. In one of the three sources of electromagnetic field above, an electric current is passed. The current in the source should change, when the current in the source changes in the medium, transients begin, at this time, changes in the magnetic field and changes in the electric field are measured on the day surface. The signals of the dependence of the magnetic and electric fields on time contain information on the electrodynamic parameters of the medium. The current pulses in the above sources are excited by a variable shape - rectangular, triangular, sinusoidal, etc.

After the change in current in the generator complex begins, measurements of the components of the electromagnetic field begin. Magnetic and electrical components are measured. Measurements are taken on an arbitrary grid around the sources when using a circular electric dipole or vertical electric line as sources. The signal at each point is measured at all times at which the signal exceeds noise interference. The places of observations are determined based on the geophysical problem being solved, the availability of observation points, the level of interference, and the distance from the field source. When using an oncoming electric line as a source, measurements are taken on the same straight line where the oncoming electric line is located.

The places of observations are determined based on the geophysical problem being solved, the availability of observation points, the level of interference, and the distance from the field source. The distance between the observation points affects the accuracy of determining the boundaries of the object and is a compromise between the desire to determine the boundaries of the object as accurately as possible and economic feasibility.

Measurement of the magnetic components is carried out using a meter 8 connected to the sensor 9 or using a meter 6 connected to the magnetometer 7. Measurement of the electrical components is carried out using a meter 10 connected to the measuring line 5, see FIG. 3, 4, 5.

3rd stage - processing (interpretation) of the measurement results, restoration of the electrodynamic parameters of the medium. Maps of the observed magnetic signal are constructed from the results of measurements of the magnetic signal. When building maps, the observation point is removed from the center of the source. To account for the remoteness of the observation points, the signals are multiplied by the ratio of the distance between the observation point and the center of the source to the radius of the source. Alternatively, the degree of this relationship is used, for example, the square of the relationship, see formula 1.

To visualize areal maps of the magnetic components of the VEC, we use the following normalization:

where ε _i - EMF value, measured at the i picket,

r is the distance between the center of QED and the measurement point,

d is the diameter of the QED,

n is the normalization degree, which varies with time (usually from 1 to 3), but constant at a given time for the entire area.

Measurements of the electrical component fit into the existing theory, widely used in geoelectrics. Using the measured electric components of the electromagnetic field, the polarization parameter of the medium is restored. The so-called inverse problem is being solved. To take into account all the electrodynamic parameters of the medium, formulas for calculating the electric signal are used taking into account the polarization parameter according to one of the signal calculation formulas. When calculating the signal, the parameters of the generator set and the measuring system, as well as their relative position, are taken into account. Most polarization accounting formulas are interdependent, the Cole-Cole formula is most often used, see formula 2. Given the polarization using this formula, the signal from a polarizing medium is most often calculated.

The phenomenological approach to describing induced polarization (VP) as a Cole-Cole model has become widespread:

where η, τ and c are the polarization parameters of the medium,

η is the polarization parameter,

τ is the polarization time constant,

c is a power constant

ρ (ω) ^_ resistivity of the medium at a frequency ω,

ρ ₀ is the specific resistance of the medium in direct current.

After calculating the signal for the electrical component, the calculated curve is compared with the measured signal. Choose a value of the polarization parameter at which the calculation results are the least different from the observed curve. The selected polarization parameter is considered to correspond to the real parameter. This is the solution to the so-called inverse problem.

After processing the magnetic signals and electrical signals, maps of the distributed polarization parameter determined by the electrical components and maps of the measured signals of the magnetic component are constructed. In places where the maximums of the signals of the magnetic component and the polarization parameter coincide, hydrocarbon deposits are located.

An example implementation of the claimed method.

An example of the practical application of the proposed method is the work carried out with the participation and according to the methodology of the authors in the Republic of Tatarstan.

The aim of the work was to assess the presence of hydrocarbons in the positive structure identified by seismic exploration, and to delineate the oil reservoir, if hydrocarbons are detected. The work was carried out near the well-known oil field, we took advantage of this circumstance to compare the signals over the oil field and the seismic uplift under study.

The work was carried out by the following methods:

Sounding Method by vertical currents, the source of the electromagnetic field is a circular electric dipole. Periodic rectangular current pulses were passed through the source. The measurements were carried out of the magnetic component ∂B _z / ∂t with a different observation grid. Signal maps were constructed at various measurement times from 10 ms to 100 ms. In carrying out these works, we used a sounding installation, GTE-10c current stabilizers, a network power supply, a control unit, and nine ballast resistor blocks. The measuring sets consisted of meters for measuring the magnetic component and sensors for fixing the magnetic component ∂B _z / ∂t.

Sounding Method by oncoming lines, electromagnetic field sources - oncoming electric lines. Periodic rectangular current pulses were transmitted in the sources. The measurements were carried out of the electrical component along a straight line on which oncoming electric lines were located with a step between the measurement points of 375 meters. In carrying out these works, we used a sounding installation, GTE-10c current stabilizers, a network power supply, a control unit, and nine blocks of ballast resistors. The measuring kits consisted of meters for measuring the electrical component and the measuring line.

In FIG. Figure 6 shows the results of measurements of the magnetic component ∂B _z / ∂t in the form of signal isolines at a time of 55.7 ms. The electromagnetic field was excited by a circular electric dipole, variable rectangular pulses were used to excite. Large circles indicate the pickets of the profile, in which the electrical component was measured when the electromagnetic field was excited by oncoming electric lines. The distance between the measurement points is 375 m. The well-known oil field is located south of the pipeline - indicated by a straight line passing through well 141. Four wells and one borehole fell into the measurement zone. Wells 1, 2, 3 with a flow rate of more than 20 cubic meters. meters per day, and well 4 with a flow rate of 2 cubic meters. meters per day, the seismic uplift and the license area were located northeast of the circular electric dipole. In the licensed area, the grid of measurements of the magnetic component ∂B _z / ∂t when working from a circular electric dipole was 150 × 300 m above the well-known oil deposit, the grid of measurements of the magnetic component ∂B _z / ∂t when working from a circular electric dipole was 10 times less approximately 500 × 700 m. In FIG. 6 schematically depicts several generators at once. Two of the five oncoming electric lines are depicted by a dashed line.

Wells 1, 2, 3 with a flow rate of more than 20 cubic meters. meters per day are in the zone of confident large positive signal, well 4 with a flow rate of 2 cubic meters. meters per day is in the zone of a small positive signal. The licensed area (surveyed seismic elevation) fell into the negative signal zone, which indicates the absence of hydrocarbons. Since the network of observations of the known oil reservoir was too rare, the map south of the pipeline turned out to be insufficiently complete (Fig. 8).

In FIG. 7, a polarization parameter is constructed along the profile, obtained by solving the inverse problem for the electric component from the oncoming electric line. In FIG. 7 below schematically shows the location of wells 1, 2, 3, 4. FIG. 8 shows that the data for the electric component from the oncoming electric line are consistent with the measurement data of the magnetic component ∂B _z / ∂t from the circular electric dipole and with a priori data. In the north, where the studied object is located, the polarization parameter is small, which indicates the absence of hydrocarbons. On the contrary, in the south, where the well-known oil field is located, the polarization parameter is large, which indicates the presence of hydrocarbons. It is impossible to explain the measured electrical signals from the oncoming electric line by the change in the resistivity of the medium, since the signal when working with identical oncoming electric lines changes 10 times, which, of course, cannot be explained by the change in conductivity.

In FIG. Figure 8 combines the areal results of measurements of the magnetic component ∂B _z / ∂t from a circular electric dipole at a time of 32.2 ms and the isoline band of the polarization parameter, which is aligned along the measurement profile from oncoming electric lines. This figure demonstrates that the boundary of the deposit obtained from two measurements — measurements of the magnetic component ∂B _z / ∂t when working from a circular electric dipole and measurements of the electric component from an oncoming electric line coincide well during these works.

Thus, the proposed method for direct search for oil deposits allows us to draw a conclusion about the presence of oil in the seismic elevation by the presence of a polarizing object, and to measure the object and make a final conclusion about the prospect of the search object by measuring the magnetic component ∂B _z / ∂t when working from a circular electric dipole give recommendations for exploratory drilling.

Claims (4)

1. A method for the direct search for hydrocarbons by geoelectrics, including the formation of an alternating electromagnetic field of transverse magnetic (TM) polarization, measuring the electromagnetic transient response signal of the test medium and interpreting the measurements, characterized in that the magnetic and electrical components of the electromagnetic field are measured and maps of the distributed parameter are measured the polarization determined by the electrical components, and a map of the measured signals of the magnetic component, and in places where the maximums of the signals of the magnetic component and the polarization parameter coincide, determine the presence of hydrocarbon deposits. 2. A method for the direct search for hydrocarbons by geoelectrics methods according to claim 1, characterized in that the formation of an alternating electromagnetic field of transverse magnetic (TM) polarization is carried out using a circular electric dipole (QED). 3. A method for the direct search for hydrocarbons by geoelectrics methods according to claim 1, characterized in that the formation of an alternating electromagnetic field of transverse magnetic (TM) polarization is carried out using a vertical line. 4. A method for the direct search for hydrocarbons by geoelectrics methods according to claim 1, characterized in that the formation of an alternating electromagnetic field of transverse magnetic (TM) polarization is carried out using an oncoming electric line.

Images