Method of geological prospecting

FIELD: geoelectrical prospecting.

SUBSTANCE: invention relates to geoelectrical prospecting by the electrical resistance method. The method uses two fixed supplying grounding circuits, the first of them being located in practical infinity, the other one along with two fixed reception grounding circuits being arranged nearby the observation profile, two additional movable grounding circuits located at equal distance from the second supplying grounding circuit. In measurements, in every position of the movable grounding circuits, the latter are connected in turns to a power source or an instrument. On connecting them to the power source, a voltage drop between the fixed reception grounding circuits is measured. On connecting them to instrument and measuring the voltage drop between them, the fixed supplying grounding circuits are connected to electric power source. The aforesaid operations are effected for all preset positions of the movable grounding circuits. Proceeding the measurement results, sections of apparent electrical resistance and voltage drop are plotted to estimate the availability of geoelectrical irregularities in the section.

EFFECT: higher efficiency of revealing geoelectrical irregularities and lower ambiguity in experimental data interpretation.

1 dwg

 

The present invention relates to an electrical exploration method of electrical resistivity and improves the efficiency study of the upper part of the section, identify local geoelectric inhomogeneities in the bedrock.

The field of application of the proposed method: geological engineering; detection tectonically fragmented, permeable rocks; identification of ore-bearing objects covered by unconsolidated sediments; the study of the spread in the geological environment of human-contaminated groundwater; study of the conditions of the soil hydraulic structures and other

The known method of vertical electrical sounding (VES), which uses four ground located on the same line (profile), two of which - foster - are at the same distance from the center of the installation and connected to the terminals of the measuring instrument, and the other two feeding - related at the same distance from the center of the installation and connected to the terminals of a source of electric current. After performing the measurements at one position of the feeding ground they move to the next preset distance from the center of the installation, etc. On the results of electrical sensing define the values of the apparent resistivity of rocks for the each position of the feeding ground and change of the electrical resistance depending on the distance between the supply grounding judge available in the context of geoelectric inhomogeneities [1].

The known method has significant drawbacks: first, it is designed to explore the horizontally layered media, so when inhomogeneous structure of the upper part of the section, the presence of deep not horizontal surfaces section the results of VES are not amenable to direct quantitative interpretation; secondly, the experimental materials significantly distorted when the rough terrain [2].

The known method the dipole electric sensing using supply dipole (grounding a and b) and the receiving dipole (ground M and N), the centers are at the beginning of the measurement is placed at a specified distance (spacing). In the process of one of the dipoles remains stationary, and the second is moved along the profile of observations with a given step, i.e. increase the spacing of the probe installation. Each spacing determine the value of the apparent resistivity ρto. On the dependence of the electrical resistivity from scattering judge geoelectric structure of the studied section [3].

The known method has the following major disadvantages: first, the results of the soundings with dipole installation is greatly distorted when the inhomogeneous structure of the environment in horizontal directions (especially in subsurface formations); secondly, a small inaccuracy in the determination of the orientation roaming dip the La lead to significant errors [3].

The closest in technical essence to the present invention is the method of differential elektroregulirovki, in which the first power supply ground (In) refer to practical infinity, and the second power supply ground (a) and two foster grounding (M and N) are placed on the same line (the profile) so that adoptive grounding are arranged symmetrically relative to the Central supply ground (A). Three-electrode differential installation to be moved along the profile of observations with a given step. At each Parking supply ground is connected to a source of electrical current, and receiving the measuring device and measure the voltage drop between foster grounding (ΔUMN). When electrical profiling over a homogeneous half-space ΔUMN=0, and if in the context of geoelectric inhomogeneities ΔUMNtakes non-zero values [4].

Prototype method has a significant drawback: when the electrical profiling over geoelectric inhomogeneities anomalous values ΔUMNproportional to the resistivity of rocks, accommodating heterogeneity. This leads to the fact that no information about the resistivity of the host rocks apparent anomaly is uncertain.

The aim of the proposed method is to increase the effektivnosti identify geoelectric inhomogeneities in the geological environment and the reduction of ambiguity in the interpretation of the experimental data with inhomogeneous structure of the upper part of the section.

This goal is achieved by the fact that in the proposed geoelectroprospecting that uses the first power supply ground reserved in practical infinity, and three ground along the profile of observations with the same distance between the extreme and the Central one, of which the Central is used as the second power supply ground, and the other two are foster grounding and is used to measure the voltage drop between them, namely, that in addition to the four main grounding use two additional ground along the profile observations at the same distance from the Central feeding ground, and each of their the installation process, connect the additional ground or to a source of electric current and measure the voltage drop between the main stationary receiving ground or to the measuring device and to a source of electrical current connected major stationary feeding ground, measure the drop in voltage between the complementary receiving grounding, perform these operations for a given provisions of the additional grounding, find the dependence of the electrostatic voltage between the additive is suspended foster grounding, the apparent electrical resistance between the main receiving ground with all the provisions of the additional supply of earthing and their distribution is judged on the presence and position in the context of geoelectric inhomogeneities.

The performed calculations show that the differential profiling over the vertical seam graph of voltage drop along the observation profile has characteristic features: zero-crossing over the center of the reservoir; the alternating extrema in the contact area of the reservoir with the host environment. If the layer has a high resistivity compared to the host environment, the extrema are fixed in the contact areas. For the formation of low resistivity compared to the enclosing environment of extreme values of the voltage drop observed in the host environment, and their position depends on the distance between the second supply grounding and foster grounding [5].

The drawing shows a diagram of the proposed installation. Signal ΔUMNmeasure when used as a feeding ground a and B. the Signal ΔUM1N1measure when used as a feeding ground And1and In1.

The proposed method is carried out with serial electrical equipment (e.g., ERA, ERA-ZN IS K) as follows. On the profile observations place the two main reception rooms ground (M1N1and the second power supply ground (A), and the grounding of M1and N1have symmetrically with respect to the supply grounding A. the First power supply ground (In) refer to practical infinity (must comply with the condition: AB 10-15 times more AM1=AN1). In addition, the profile of observations symmetrically with respect to the feeding ground And have two ground M, And1and N, B1(see drawing). When measuring above ground alternately connect: feeding ground A1and In1- stable source of electric current, and the foster grounding M1and N1- the measuring device and measure the drop in voltage ΔUM1N1; the first (a) and second (B) supply ground to the stable source of electric current, and the adoptive ground M and N to the measuring device and measure the drop in voltage ΔUMN. After performing the measurements at one position for additional grounding (M1) and (N, B1their move at the same given distance from the supply ground and the measurement process repeated. These operations repeat for all the specified provisions of the additional grounding. Doobsledovanie profile observations by the values Δ UM1N1calculate values of apparent resistivity (ρtoand building sections ρtoand ΔUMN. In the section of the drop voltage allocate geoelectric inhomogeneities, and the section of apparent resistivity are classified heterogeneity related objects either low or high electrical resistance.

Thus, the advantage of the proposed method is to increase the efficiency of detection of inhomogeneities in the upper part of the section in various geoelectric conditions, as the end result of measurement takes into account not only the spatial location of inhomogeneities, but also the ratio of their electrical resistance and the electrical resistance of the enclosing environment.

Sources of information

1. Jakubowski J.V. Electromagnetics. - M.: Nedra, 1973, p.56-57.

2. Matveev B.K. Electromagnetics. - M.: Nedra, 1990, s.

3. Alpin L.M. Theory of dipole soundings. - M., L.: Costoptimized, 1950, p.6; S. 88-89.

4. Tarkhov A.G. About electrical methods pure anomaly. Izvestiya an SSSR. Ser. geophysical No. 8, 1957, s-982.

5. Ulitin W., I. Fedorov, Harus R.L. TO the method of geoelectric mapping when geoelectric studies// theory and practice of geoelectric studies. Sat. the scientific. works, vol. 2. Ekaterinburg: Uralotha RAS, 2000, p.48-49, 4, 5.

Geoelectroprospecting that uses the first power supply ground is connected to one terminal of a source of electrical current and is related to practical infinity, and three ground located on one line profile observations with the same distance between the extreme and the Central one, of which the Central grounding is connected to the other terminal of the source of electric current as the second power supply ground, and the remaining two are used as receiving ground to measure the voltage drop between them, characterized in that in addition to the four main grounding use two additional ground available on the profile of the observations at the same distance from primary Central feeding ground and move in process measurements along profile observations at the same given distance from the Central grounding and every installation connecting additional grounding or to the terminals of a source of electric current and measure the voltage drop between the main stationary receiving ground or to a recording device, and to the terminals of a source of electric current connected major stationary feeding ground, measure the drop elektricheska the voltage between the secondary receiver ground perform these operations for a given provisions of the additional grounding, find the dependence of the electrostatic voltage between the additional foster grounding and apparent electrical resistance between the main receiving ground with all the provisions of the additional grounding and their distribution is judged on the presence and position in the section jelektricheskikh inhomogeneities.



 

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