RU1819354C - Method of marine electric survey - Google Patents

Abstract

Usage: search and exploration of mineral deposits in the waters. SUMMARY OF THE INVENTION: at each sounding point, the magnitude of the first sounding spacing is chosen to be equal to the two thicknesses of the Sea water layer, measured with the help of an acridometer, and the magnitude of the last raanos is selected by reaching the asymptotic conductivity value. 2 ill.

Description

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AND

The present invention relates to electrical prospecting, namely, marine electrical prospecting with alternating current, and can also be used when conducting electrical surveys in any area from a moving vessel.

The purpose of the invention is to increase the productivity and reliability of measurements.

The invention consists in a method of selecting the optimal set of spacings, taking into account changes in the structure of the seabed and the thickness of the water layer when conducting electrical exploration work on a moving vessel:

In FIG. Figure 1 shows an apparatus for studying the structure of a sea section; Fig. 2 is a graph illustrating changes in the behavior of the effective resistance (inverse effective conductivity / bf 1% f) for various thicknesses of the section layers.

The installation consists of a carrier vessel equipped with an echo sounder, which allows determining the thickness of water layer 1 (Fig. 1). which tows the source of the floor - a horizontal electric dipole 2 and receiving dipoles 3i (from 31 to 3b).

The soundings are performed over the sea sections, each layer of which is characterized by the following parameters: pi - thickness of the water layer pb - beats. water resistance Ll - thickness of the precipitation layer RSP - beats. precipitation layer resistance - beats. resistance of the underlying base (bedrock).

Figure 1 shows two sections I and II, differing from each other by the layer thicknesses hb hb and Nel Nel.

On Fig, 2 schematically shows the curves of the effective resistance of the ref depending on the separation of the installation g, constructed

for sections I and II. An example with curves is presented for one of the modifications of frequency-remote sensing and isoparametric sounding.

The spacing intervals - A for section I and B for section II are shown, which are necessary to obtain complete sounding curves / Eef (g). The curve is considered complete from the horizontal left asymptote characterizing the resistivity of water pb to the right, inclined (in the case of infinite) or horizontal (in the case of finite resistance of the base) asymptote. The left asymptote of the curves is characteristic of the spacing values of r 2. The output of the curves /% φ (r) to the right asymptote begins at the distances of r 3 (n + r | s). Changing the parameters of the Hb and Hel layers causes a significant shift of the / Oeff (g) curves along the z axis, i.e., obtaining a complete curve requires a certain choice of spacing.

The method of marine electrical exploration is carried out as follows.

When the vessel 1 moves along the profile, the depth hb of water at a given location is measured with an echo sounder. From the condition g / np 2, select the minimum separation from which the measurement of the signal at the receiving dipole 36 begins. Depending on the technique used, a current of the selected frequency is included in source 2. The signal is measured and its effective resistance (conductivity) is recalculated in a known manner. The transition to the next spacing and the 3i + i sensor measures the signal while maintaining or changing the frequency of the source, and the effective resistance value is calculated. The transitions to new spacings are repeated until an asymptotic value of the effective resistance is obtained. This ends the cycle of obtaining the sounding curve and everything repeats in a new place, starting with measuring the depth and electrical resistance of the water layer. A vessel moving forward continuously displaces the installation along the profile and the point at which the depth measurement was carried out with an echo sounder is always between the source of the floor and the receiving dipole. Thus, despite the movement of the vessel during the entire sensing cycle, the same volume of medium is excited. Wherein

the optimum number of spacing is used for each sounding, which increases the number of soundings per unit length of profile. Using the Do / A curve (phi), a geoelectric section in each section of the profile is determined.

The method can be implemented using a station for marine frequency-remote sensing developed in

Laboratory of Geoelectrics, Department of Earth Physics, NIIF Leningrad State University. The station is designed to conduct studies of the geoelectric structure of the seabed in waters with sea depths of 5 to 30 meters at

thickness of sedimentary cover up to 50m. The source of the electromagnetic field is a horizontal electric dipole with a moment of 60 Am. On the receiving spit - 20 receivers of the electrical component of the floor at distances from 15 to

250 m. The range of sounding frequencies is 2 - 1500 Hz. An integrated computer automates the measurement, processing and presentation of sounding results. The method is tested in water x

Baltic and White Seas.

Claims (1)

SUMMARY OF THE INVENTION A marine electrical prospecting method for generating an alternating current electric using a horizontal electric dipole, measuring the electric field in the direction of the observation profile when changing the separation and frequency of excitation, determining effective conductivity and judgments about the structure of the seabed by the value of effective conductivity, characterized in that, in order to increase the productivity and reliability of measurements, an electric field is created using a horizontal electric dipole oriented along the observation profile, the thickness of the water layer is measured at each sounding point choose the value of the first separation is equal to twice the thickness of the water layer, the value of the effective conductivity at each separation is determined by the value of the measured electrical component, and the value of the last separation is selected by the output of the values of the effective conductivity to the asymptote. yy - (i i f Г t t i i i i I it i i | i i Kt e i i i i t, 1 U L i i g d t i t i i,, i “Ч 9ь (/} V // J /////////////////, ..,. -w - f ---- - -r - I-- i - f - F - 7l 7 V. It i 40 I . at Och & g / 8.2