RU2030768C1 - Method of mapping of rocks - Google Patents

Abstract

FIELD: geophysical prospecting. SUBSTANCE: electric field is excited successively by two pairs of point supply electrodes A $\genfrac{}{}{0ex}{}{\text{+}}{\text{I}}$ _I, B $\genfrac{}{}{0ex}{}{\text{-}}{\text{I}}$ _I, A $\genfrac{}{}{0ex}{}{\text{+}}{\text{┴}}$ , B $\genfrac{}{}{0ex}{}{\text{+}}{\text{┴}}$ located perpendicular relative to each other. Difference of potentials of each pair of supply electrodes is measured with the help of receiving dipole MN with point groundings which center is located on straight line passing through supply electrodes of one pair. Dipole itself is oriented in parallel to second pair of supply electrodes. Difference of potentials is measured in external zone of point groundings at different distances to the left and to the right from them. Method of special points is used to determine electrical properties and structural parameters of medium. EFFECT: expanded application field and enhanced authenticity of method. 1 dwg

Description

 The invention relates to geophysical methods of exploration by direct electric current, which allows to determine the shape of geoelectric heterogeneities, the depth, strike and angle of incidence of their boundaries with respect to the earth's surface and the electrical resistivity (resistivity) of rocks composing the heterogeneities and the surrounding space. The proposed measurement method can be widely used in deep geological and structural mapping of platform and folded areas, the search and exploration of oil, gas and thermal waters.

A known method of geoelectrical exploration by the method of two components (MDS), which is designed to study shallow depths and consists in studying the field of one or two point sources of current in two mutually perpendicular directions on the earth's surface using two receiving lines, the centers of which are located on a straight line connecting the bipolar supply electrodes. At each profile point during electrical profiling by the two-component method (EP MDS) or each spacing of the supply electrodes in the case of vertical electric sounding by the two-component method (VES MDS), the current I in the supply circuit, the axial potential difference ΔU _t on the electrodes of the receiving line oriented along the installation axis, and the azimuthal potential difference ΔU _p on the electrodes of the orthogonal receiving line. Multiple inspections in experimental and production conditions showed high reliability and satisfactory accuracy of the results of MDS electrical exploration (the relative error does not exceed 20% when assessing the resistivity of rocks and the depth of geoelectric boundaries).

 A known method of mapping rocks in which an electric field is alternately excited by a pair of supply electrodes, one of which is each of the electrodes of the cruciform installation, lying on the profile line, and a remote electrode, for each pair of supply electrodes, measure the potential difference between the remaining electrodes of the cruciform installations that determine the parameters of rock anisotropy and the direction of shale.

 The disadvantages of the methods are the need for a large number of wires, difficulties with laying supply lines on the ground and large losses of current power in the wires when mapping rocks at great depths.

 The objective of the invention is to achieve the required depths of research without loss of information and accuracy of the results with a minimum of wires and power losses in them.

The problem is solved by using two parallel receiving dipoles with a common center point in combination with the interpretation of the measurement results by the method of singular points. The method is illustrated in the drawing, which shows a diagram of the arrangement of dipoles. Through the supply dipoles AB _I and AB _II, alternately, a constant electric current is supplied to the ground, the strength of which (I) is measured. The field strengths of the parallel (ΔU _II ) and orthogonal (ΔU _t ) supply dipoles are measured using a receiving dipole MN, the center of which is located to the right (MN _pr ) and to the left (MN _lion ) from the center of the supply dipoles on a straight line passing through the electrodes of the orthogonal dipole (AB _I ). The receiving dipole MN _lion or MN _{rights are} oriented perpendicular to the orthogonal (AB _I ) and parallel to the equatorial (AB _II ) supply dipoles.

The invention is accompanied by a drawing, which shows the relative position of the receiving electrodes (MN _lion and MN _rights ) and supply (AB _I and AB _II ) dipoles.

K и отношения

- для левого и правого положения приемного диполя относительно центра питающих, где К - коэффициент экваториальной дипольной установки. Строение геологической среды и удельное электрическое сопротив- ление (УЭС) пород определяют по координатам экстремумов и точек перегиба на графиках ρ_к и

- двустороннего дипольного ЭП или ВЭЗ с помощью номограмм, изображающих аналитические и эмпирические зависимости параметров аномалий на графиках ЭП МДС и ВЭЗ МДС от строения и электрических свойств среды в следующей последовательности:
- находят на графиках ЭП МДС и ВЭЗ МДС экстремумы и точки перегиба, определяют их координаты и вычисляют интерпретационные соотношения;
- по знакам и абсолютным значениям интерпретационных соотношений с помощью номограмм определяют значения УЭС и параметров анизотропии, глубины залегания, простирание и истинные углы падения геоэлектрических границ.The measurement results are presented in the form of graphs of the apparent resistance ρ _to =

K and relationship

- for the left and right positions of the receiving dipole relative to the center of the supply, where K is the coefficient of the equatorial dipole setup. The structure of the geological environment and the electrical resistivity (resistivity) of the rocks are determined by the coordinates of the extrema and inflection points on the graphs ρ _to and

- a two-sided dipole EP or VES using nomograms depicting the analytical and empirical dependences of the parameters of anomalies on the graphs of the EP MDS and VES MDS on the structure and electrical properties of the medium in the following sequence:
- find on the graphs of the EP MDS and VES MDS extrema and inflection points, determine their coordinates and calculate the interpretation ratios;
- the signs and absolute values of the interpretation ratios using nomograms determine the values of resistivity and anisotropy parameters, depth, strike and true angles of incidence of the geoelectric boundaries.

 Using the proposed method of mapping rocks allows you to reach depths of several kilometers with minimum lengths of the supply and receiving lines and the real power of the sources of supply current.

Claims (1)

 ROCK MAPPING METHOD, in which the electric field is alternately excited by two pairs of point supply electrodes located perpendicular to one another and having a common central point, for each pair of supply electrodes, a potential difference is measured using a receiving dipole, and the apparent resistance values are calculated from the obtained potential differences and the relationship of the azimuthal and axial potential differences, which determine the electrical resistivity, coefficient of electric anisotropy and structural parameters of the medium under study, characterized in that, when measuring the potential difference, the center of the receiving dipole is located on a straight line passing through the supply electrodes of one pair, and the receiving dipole itself is oriented parallel to the second pair of supply electrodes, while measurements are made in the outer region of the supply dipoles at various distances from their center, and the electrical resistivity, electrical anisotropy coefficient and structural parameters of the medium under study are determined by the method special points.

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