SU272450A1 - METHOD OF DIELECTRIC ELECTROMAGNETIC CARTRIDGE - Google Patents

Description

This invention relates to a geophysical field survey method.

A dielectric logging method is known, in which the dielectric constant of rocks is determined by measuring the phase difference of a high-frequency (of the order of tens of megahertz) magnetic fraction. The high-frequency magnetic field is excited in the borehole using a vertical magnetic dipole, the phase difference is measured by the malad of two spaced-apart receiving coils, separated by a distance from the hetero-dipole. The method makes it possible to eliminate or substantially reduce the influence of the resistivity of the medium (at a value of at least 20-25 ohm-m) on the results of measurements of the dielectric constant of rocks.

In order to gain accuracy in determining the electrical properties of rocks, according to the proposed method, the ratios of the amplitudes of the fields at the same points are measured simultaneously with the difference between the phases of the Af field, and

tatam measurements; rhenium calculates the values of dielectric constant and resistance of rocks.

In proportion, the proportion in the air is determined by the following compaction.

L, K (1 + br, Y + (.

where au and b are real and imaginary parts of the wave number.

K. a - {- ib.

At a distance ha from the generator dipole, the amplitude will be

A, (+ br, f + (ar.Y.

The ratio of the amplitudes at two points on the distance x ri and ha from the generator, taking into account that / 2 r1 + Ar, where Ar is the distance to the receiving coils, will be

   K (1 + bri) + (ari) A e- Y (I + Lg ,, (

 ydg / (1 -t- briY- + (arif Y (i + + {ar.)) The ratio is mainly determined by

It is a member characterizing the attenuation of the wave at a distance from the first to the second receiving coil. The value of b at the ratio - 1 is determined / m 2 by the expression, 1887 yi is the conductivity of the medium, co is the frequency of the field, it is relative dielectric 10-9 as the permeability S -, 1J, is the mag (, the zenith permeability of the medium. that p, | .. Thus, the value of 6, and hence the ratio, is mainly determined by the value of the conductivity of the rock and is much less dependent on the value of e. In actual practice, when the well is filled b ;; {solution with specific syrupivne less than the resistance surround W, their sweating, attitude - will also be op Determined by the attenuation in space, their rocks at a distance between the receiving coils and in practice will not depend on the specific resistance of the solution and small changes in the borehole diameter. This is due to the fact that although the amplitude of the field induced in each coils depends on the resistance of the drilling fluid, with respect to this influence is excluded, since the well equally affects the signal in the first and second coils, because the wave’s lead coming from the source to the first and the second pick-up coils .kov and distinguishing It is only an interval in the surrounding rocks length Az G1-G2. Since the measurement of the ratio does not give exact conductivity values, the determination of the true value of s should be carried out using a nomogram of the form shown in the drawing. The nomogram is designed for a frequency of 60 MHz and a probe with a distance between the Topoai generator and receivers of 0.8 and 1 m. On the nomogram there are two families of curves. One family corresponds to different values of the phase difference Df, the other to different values of the ratio of amplitudes -. To determine the true value of the rock, the observed values of Df and с are removed from the well log and - and on the nomogram L they find the point of intersection of the corresponding lines - Df and -. The abscissa of this point characterizes the value of rock e, the value of p is taken from the ordinate axis. Thus, this method allows, along with the value of e., To determine the value of the resistivity of the rock at a high frequency. Subject of the Invention A method of dielectric electromagnetic logging, which involves exciting an electromagnetic field in a well with a frequency of about tens of megahertz and measuring the phase difference of the field at its two points, characterized in that, in order to improve the accuracy of determining the electrical properties of rocks, it is also measured the ratio of the amplitudes of the field at the same points and the results of the measurements calculate the dielectric constant and the resistance of the rocks.

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