SU544925A1 - Acoustic logging method - Google Patents

Description

one

The invention relates to geophysical methods of mineral exploration, in particular to methods of acoustic well logging.

The known method of acoustic well logging, condition n1, ir} is that an acoustic probe is lowered into the well under study, oscillations of the probe emitter are excited, head waves generated by the emitter are received, and the time delay of the first arrival of the signal at the receiver is measured relative to the moment of the emitter excitation, the so-called interval time.

However, the known method is characterized by the ambiguity of interpretation of the data obtained, since the interval time depends not only on the porosity of the rocks, but also on many other factors — the modulus of bulk compression, density, fracturing, pore filling properties, and uneven walls of the well, etc.

A more accurate interpretation is allowed by the method consisting in placing the d-probe into the well, exciting head waves in the fluid, and recording the phase correlation diagrams of the signal received by the probe receiver. The use of phase-correlation diagrams makes it possible to discern the influence of such additional factors as cavernosity,

fractures, etc. on the value of interval time, which makes it possible to more accurately judge the porosity of rocks.

However, it should be pointed out that the coefficient of absorption of the will | - of their will is much more sensitive to porosity. There is a method of acoustic carotal with the measurement of the coefficient of elastic wave input. The method consists in that the well waves excite head waves with an acoustic knot of the probe projectile, receive these waves by two receivers of elastic waves spaced apart along the axis of the well and, by comparing the amplitudes of signals on the receivers, judge the absorption of elastic waves: In rocks.

However, the absorption of elastic waves is measured with a larger error, which significantly reduces the advantages of the method. The increase in measurement errors is associated with the inevitable changes in the probe axis from the borehole axis, its misalignment, the uneven boundaries of the borehole, the presence of a mudcake, etc.

The closest to the invention is the acoustic logging method, which measures the frequency shift of the maximum spectral density of signals received by the Iriemiyk ynjiyrnx snapshot wave, relative to the frequency of the maximum spectral density of the signals emitted by its radiator. Specified Smears

the frequencies of the maximum spectral density are due to the fact that in most rocks the absorption increases linearly with frequency, and the rapidity of this growth significantly depends on the size and nature of the porosity, since the relative length of the wavelength and pore size varies with frequency, which leads to an increase in the energy dispersion of the surgeons waves with increasing frequency. A shift in the frequency of the maximum of the spectral density, depending on the rate of growth of the absorption, is more than 100% and can be measured with a higher accuracy than the absorption itself. It contains significant information about the porosity of the medium and its nature. At the same time, this method of porous porosity has low sensitivity and is difficult to implement in the form of automatic devices.

The proposed method allows to increase the sensitivity and reduce the bluntness of the measurements by eliminating the influence of irregularities and the surface of the well. This is achieved by filtering the head waves, which are received by the receiver, by filtering, for example, treble, measuring the power of the high-frequency part of the spectrum and the power of the unfiltered signal, and adjusting the cut-off power to a predetermined value, for example, 1/2, and according to the cut-off frequency of the filter, the porosity of the medium and the nature of its filling are judged. Example. A well-drilled device, having a wide-band acoustic emitter and receiver, is placed in the well under study. The electroacoustic exciter p) the transmitter of the probe is powered by a pulse generator or a noise generator, whereby the latter emits a wide-band signal in the form of elastic waves into the surrounding frame. In the medium under study, immersion excitation of elastic waves occurs, which propagate along the axis of the well and, in turn, cause side waves in the fluid, recorded by the receiver of the probe. The received signal through a time selector suppressing the interfering types of waves is fed to filtering; a high or low pass filter with an adjustable cutoff frequency is used as a filter. After filtering, the filtered signal carries only a high-frequency signal or a low-frequency part of the spectrum with frequencies higher or lower than the cut-off frequency of the filter. The signal after filtering is detected by a square detector with a detector, at the output of which a signal is obtained that is penetrated by the power of the signal with spectral components whose frequencies are .5 or lower than the cutoff frequency of the filter. Similarly, a quadratic detector generates a signal proportional to the monolithic character of the entire received signal. This signal is attenuated by the attenuator at the specified location, and then compared with the signal of the filtered signal detector. Then, the cut-off frequency of the filter is changed to as long as the compared signals: a signal irrational to the power of all the power of that signal, divided by the attribute B at a given number of times, and a signal proportional to the power of the signal with frequencies higher or lower than the cut-off frequency of the filter rabbi among themselves. The cutoff frequency of the filter will be the frequency that separates

20 energy spectrum of sigial in given relation.

Due to the growth of legs, the number of other waves in mountainous mountains, with an increase in the frequency of high frequencies, the first component of the signal weakens

5 is stronger than low frequencies, which leads to a redistribution of the energy of the signal over the spectrum and its concentration in the low frequency region, but at a given emission from the compared energy the separation frequency will decrease depending on the rate of absorption growth with frequency. The latter depends on the porosity of the medium and its nature, and in the high-quality range on the viscosity of the aggregate.

Claims (1)

Invention Formula Acoustic logging method based on immersio radiation of uirugi waves 0 in the test environment and in the acceptance of the head will, in order to increase the sensitivity and reduce the errors introduced by the uneven surfaces of the wells, the acoustic signal of the head waves 5 filter, for example, phi.higher frequencies, measure the power of the high-frequency part of the spectrum and the monotony of the unfiltered signal, and adjust the ratio of the indicated powers by changing the cut-off frequency of the filter. up to a given value, for example 1/2, and but the cutoff frequency of the filter is judged on the porosity of the medium and the nature of the filling of the pores.