RU1833825C - Method of acoustic logging - Google Patents

Abstract

Usage: in geophysical studies of wells by acoustic methods, including for assessing the reservoir properties of rocks in the near-wellbore space. SUMMARY OF THE INVENTION: At each observation point, pulses of the same type of wave with low and high amplitudes are excited and recorded. The latter are selected from the condition that in the rocks crossed by the well the relative deformations exceeding. Registration is carried out by at least two receivers. The properties of the rocks crossed by the well are judged by the magnitude of the absorption coefficient.

Description

The invention relates to geophysical exploration of wells by acoustic methods and can be used for lithological dissection of sections and assessment of reservoir properties of mountainous rocks. genus in the near-wellbore space,

The aim of the invention is to increase the information content and accuracy of the method.

The goal is achieved in that a low-amplitude acoustic pulse, and additional excitation, is excited and recorded at two or more different points of reception of the well in the well and a high-amplitude pulse is recorded at the same points, the amplitude of which is selected so that when it passes through the rocks composing the walls wells, deformations occurred with amplitudes exceeding 10. From the amplitude-time characteristics of the pulses of the same type of waves recorded at the receiving points in low and high amplitude modes, the amplitude-dependent component of the absorption of seismic waves is determined.

The dependence of the decrement of absorption of seismic waves v on the strain amplitude Ј is approximately described by the expression

Y (E) To + Kr (1)

where v0 is the amplitude independent absorption component;

K is the coefficient of amplitude dependence.

Coefficient K depends on the type of rock, changing by several orders during the transition from dense to highly porous rocks.

The method is based on Ngrt, that the amplitude-dependent Kg absorption component, which is practically not manifested at strain amplitudes of Ј 106, typical of traditional methods of acoustic logging, becomes noticeable for most rocks at e. Acoustic Log Measurement DecremenS

absorption at relatively small Ј and large e 10 strain amplitudes, we can determine the coefficient K for the studied interval:

) -1 / (Ј) / ((2)

Since the strain amplitude during the propagation of pulses along the borehole wall changes, their average values based on the measurements are used as estimates of Ј.

At sufficiently small strain amplitudes in the low-amplitude mode (e, in addition, all parameters obtained by traditional methods of acoustic logging can be measured. In this

case v (e) v0, and K is defined by the approximate formula

K v (e) -v (Ј) (3)

The method is carried out as follows.

A low-amplitude acoustic pulse is excited in the well and oscillations are recorded at two or more points of reception at the measuring base of the probe; in addition, a high-amplitude pulse is excited and oscillations are recorded at the same points. From the amplitude-time characteristics of the pulses of the selected wave recorded at the reception points in the low and high amplitude modes, strain amplitudes e1, e and absorption decrements v (, v (ЈM) in two modes are determined by any of the known methods, according to which formula (2) calculates the coefficient of the amplitude dependence of the absorption K.

The obtained dependence of the coefficient K (z) on depth is used to lithologically separate the section and evaluate the reservoir properties of the rocks by comparison with data from standard wells or based on relationships established by laboratory experiments.

If it is impossible to quantify the strain amplitudes, for example, when working with non-tariff sensors. measuring the relative amplitudes A and A of the signals recorded in the two modes, and calculating the parameter K proportional to the coefficient K;

) -1 (e) / ()

, -,

(4)

Dependence K (z) on well depth is used for lithological dissection

sections and revealing strata with increased porosity.

. In particular, for a three-element probe, K can be estimated by the formula

I / -,

2ln (Ai A2 / A2 fnp (t2-ti) (Ai + A2

,

twenty

25

thirty

35

40

45

fifty

10

fifteen

where fnp is the predominant pulse frequency of the wave being studied; / /

TI, t2 — arrival times, Ai, Aa — relative amplitudes in the low-amplitude mode, and A, A2 / g — relative amplitudes in the high-amplitude mode, measured on two channels.

Obtaining an additional parameter characterizing the amplitude-dependent component of the absorption increases the information content of the proposed method in comparison with the known ones. In addition, the method has increased resistance to amplitude distortion caused by the influence of uncontrolled geometric factors and the difference in the characteristics of the receiving channels, since they are largely compensated by calculating the parameters K and K. This increases the accuracy of the measurements.

Claims (1)

SUMMARY OF THE INVENTION An acoustic logging method comprising sequential excitation and registration of acoustic pulses with different amplitudes and evaluation of rock properties by the nature of their variation, characterized in that, in order to increase the information content and accuracy of the method, sequential excitation and registration are performed at each observation point at least two pulse receivers of the same type of waves with low and high amplitudes, the latter being chosen from the condition of creating rocks from the well intersected by weights of deformations exceeding are determined by the absorption) (e1) and 9 () for respectively low and high strain amplitudes e1 and E, and the properties of the rocks are judged by the value of the coefficient K, determined by the formula (e) -v (Ј) / (Ј-е)