SU1728813A1 - Method for quantitative analysis of rock lithologic composition - Google Patents

Abstract

The invention relates to methods for exploring subsoil by seismic survey by reflected waves and geophysical measurements in wells. The purpose of the invention is to improve the accuracy, reliability of the determination and reduce the volume of drilling to obtain the necessary reference data. For this purpose, the seismic survey is carried out with the reflected waves and the stable values of the angular coefficient are determined and the linear dependence of the interval seismic velocity in the layer bounded by reflective horizons on the depth of its occurrence. In zones of significant differences in a values, we drill or use two wells drilled earlier, in which the lithological composition of the layer is determined. On the basis of these data, the composition of the layer in areas not explored by drilling is determined from the value of the coefficient a. WITH S

Description

The invention relates to methods for exploring subsoil by seismic survey by reflected waves and geophysical measurements in wells, in particular, to methods for determining the material composition of rocks.

Methods are known for determining the lithological composition of rocks by the magnitude of the velocity of propagation of longitudinal and transverse elastic waves in them, which make it possible to classify the investigated complex of rocks enclosed between seismic reflecting horizons to a certain lithological type.

The disadvantages of these methods are their low accuracy and the need to register transverse elastic waves.

The closest to the proposed method is a method for quantifying the sandstone content in the sandy-argillaceous rock enclosed between seismic reflecting horizons, based on determining the quantitative relationship between the interval velocity and the depth of the studied layer in the drilled area and further predicting the content sandstone in the layer in the unexplored area according to the interval depth velocity values obtained as a result of the seismic survey of CDP.

The disadvantage of the known method is the low accuracy and reliability of the estimates, since the absolute values of the interval seismic velocity and S 00

with

Bins, on the basis of which quantitative estimates of sandiness are made, have a large error of determination; The obtained dependences of speed on depth and sandiness can be used only for small ranges of sandstone content, close to those used to establish reference dependencies (the relationship between speed values and sandstone is nonlinear and, for example, with differences in sandstone and sandstone). mudstone twice, the coefficient of linear dependence in different ranges of change of sandiness will be four times); in general, reference speeds versus depth do not have a physical meaning, do not take into account the effect on the interval velocity of other geological characteristics of rocks, as a result of which the parameters of reference dependencies can turn out to be completely arbitrary. In addition, the known method requires a large amount of a priori data, and therefore a high degree of knowledge of part of the study area.

The aim of the invention is to improve the accuracy, accuracy of determination of the lithological composition of rocks and reduce the volume of drilling.

This goal is achieved by the fact that the percentage composition of lithologic components in the layer under study is determined by the magnitude of the angular coefficient of the linear approximating dependence of the interval seismic velocity in the layer on its depth.

The method is carried out as follows.

A CDP seismic survey is conducted and, at each observation point, the interval seismic velocity and the depth of its midpoint are determined for the layer under study, which is enclosed between reflecting horizons. From these data, the stable values of the angular coefficients of the approximate linear velocity dependence on depth are calculated everywhere.

The stability of the quantity a excludes the influence on it of lateral-changing geological characteristics of the bed rocks. The coefficient a is a relative value, established over a large set of values of interval velocity and depth; therefore, it is not affected by systematic errors and the random ones are significantly weakened.

Estimation of the lithological composition of the rocks of the layer is carried out on the basis of stable values of the coefficient a, the value of which largely depends on the type of rocks.

In the zones of the greatest difference in the stable values of the coefficient a, two wells are drilled, which completely reveal the layer under study. Geophysical surveys in the area of the geological section corresponding to the layer in question are carried out in wells, and the percentage of lithological components in the layer is determined, characterizing the latter as a two-component one.

Calculate the reference values ai and 32, which are the values of the coefficient a for the components of the layer using the formulas

(C22-C2Ua2

ai

32

C22a2-C21a1 (Ci1-CiVa2

Where

. Ci1a1-d2a2 a and a2 - the value of the coefficient a in

the zones of its greatest difference;

Ci and C2 - the percentage of lithological components in the first zone of the layer (where a a1);

Ci2 and C2 - the same, in the second zone of the layer (where a a2).

The percentage of the considered components in the layer over the entire study area is determined by the values of the coefficient a by the formula

  1-c1. a (32 - ai)

Claims (1)

The invention The method of quantitative determination of the lithological composition of rocks, including seismic surveys of reflected waves, determining from its data the values of the interval velocity and the depth of the layer bounded by reflective horizons, drilling and geological and geophysical studies in the wells that determine the lithological composition of the layer, o characterized by the fact that, in order to increase accuracy, reliability and reduce the volume of drilling, according to the seismic survey data, On the approximate linear dependence of the interval velocity in the layer on the depth of its bedding, in the zones of greatest difference in the values of a, two wells are drilled, in which the percentage of lithological components in the layer is determined, characterizing the latter as a two-component one, and The coefficient a determines the percentage of the components in question in the layer over the entire area of the study.