SU811168A1 - Method of determining elastic wave propagation speed in basin bottom ground - Google Patents

Description

The water-bottom interface and, based on the data obtained, determine the speed of propagation of elastic waves in the rocks of the bottom of the reservoir.

The drawing shows a scheme for determining the speed of propagation of elastic waves by the proposed method.

The diagram shows: emitter 1 for exciting elastic oscillations, receiver 2 located in close proximity to the emitter, and receiver 3 remote from the emitter by a known or detectable distance.

All these elements are located in the B first medium (water), which has the speed of propagation of elastic waves Ci, and can be towed by the vessel. The following operations are carried out to implement the proposed method.

A pulse of elastic oscillations is emitted in water, for example, by means of radiator 1, and these oscillations propagate both along the normal to the bottom surface and in other directions.

A receiver 2 accepts oscillations that propagate and are reflected along the normal to the bottom surface at a point near the emission point, measuring the propagation time of the reflected wave 1 and the reflection coefficient KL. Accelerate through the receiver 3 oscillations that propagate and are reflected at an angle to the surface the bottom, different from the normal PadePI, at a point at some distance from the first receiving point, with measurement of the propagation time of the reflected wave E and the reflection coefficient KL Measurement dissolved time propagation forward Volpe second reception point t.

The angle of incidence of the elastic wave at the interface of the first and second media (water-bottom) ai is determined by the formula

 + 4 - 12

COS "1 -

The rate of propagation g of elastic oscillations in the rocks of the bottom of a reservoir is determined by the formula

1/1

+ 1) M / S, -1)

WITH,

W.- (Cr -l) (K, 55

Slnai

where Ci is the speed of propagation of the elastic wave in the first medium (for example, water).

The ratio for the propagation velocity of the elastic wave in the rocks of the bottom of the reservoir (Cz) is obtained by the authors from the known formulas for determining the reflection coefficients of elastic waves from the water-bottom interface at normal incidence of waves (Kj) and at an angle less than the critical (KL) also using Snell's law.

To determine the Cz velocity, knowledge of the kinematic or dynamic characteristics of an elastic wave propagating or reflected from the bottom of the upper layer is not required.

The speed Ci, depending on the required accuracy, is calculated from the known distance between the radiator and receiver 2 or 3 and the corresponding measured time, or is determined by the tables of the dependence of the velocity in water on salinity, temperature and hydrostatic pressure, or is equal to an average value of 1500 m / c (with a maximum deviation from 1450 to 1550 m / s), or measured with a special device.

Accordingly, the pulse propagation time t by the shortest distance between the emitter 1 and the receiver 3 can be directly measured or calculated (from the known speed Ci and distance 1-3).

The advantage of this method is to use for determining the kinematic (arrival times of waves) and dynamic (reflection coefficients) dependences of signals (waves) that propagate only in the first medium (water), i.e. coming in the first arrivals, and not signals Reflected or refracted on the bottom of the second layer (bottom bottoms).

This circumstance simplifies the selection of signals and their processing both in the degree of complexity of the applied technical means (computers) and in the costs of time.

Claims (2)

1. US Patent No. 2952834, cl. 340-15, published. 1961. 2. US patent number 3372369, cl. 340-7, published. 1965 (prototype).