SU1689900A1 - Method of seismic prospecting - Google Patents

Abstract

The invention relates to seismic exploration and can be used in oil and gas exploration using multi-wave research methods. The purpose of the invention is to increase the efficiency of multi-wave seismic survey on reflected SvP exchange waves. To do this, the seismic survey method, which excites longitudinal P and transverse Sv waves, records the reflected seismic vibrations by vertical seismic receivers on linear profiles and the resulting seismograms with a common excitation point (TSS) are subjected to subsequent processing, the seismic vibrations are recorded with the removal B, satisfying the condition 0,, 8Н, and on the base B, the length of which lies within 0, where Н is the normal distance from the excitation point to the boundary under study. During processing, they summed using the similar operator as the additional summation of the path of the indicated base along a straight line with a slope that coincides with the slope of the OTV-PP hodograph. In this case, the linear linear summation starts from the arrival time of the reflected PP-radius from the studied boundary and periodically repeated with temporary shifts Find the absolute maximum of the similar operator, which is used to identify the SvP wave from the boundary under study, and the parameters of the selected SvP wave, complex them with data from other waves, are judged by and the material composition of the geological section. 2 Il. G L O 00 th

Description

The invention relates to seismic survey methods and can be used when conducting multi-wave surveys using reflected SvP exchange waves.

The aim of the invention is to increase the efficiency of multi-wave seismic survey on reflected exchange waves.

SvP.

Figure 1 shows the scheme for implementing the method; Fig. 2 shows simulation results with a similarity operator as the sum kernel.

FIG. Figures 1 and 2 show the daytime surface 1, excitation point 2, groups 3.1-З.п of seismic receivers connected by a seismic oblique to an onboard station 4 which is connected to the computer 5, the reflecting boundary 6 under study, the beam 7 of the incident wave, the reflected reflected wave, the carry-out of 9 point 2 excitation base 10 of location of observation points, distance 11 along the normal from the point of excitation to the boundary under study 6, dependence of the similarity factor on time.

The method is carried out as follows.

about

t- &

The field work is carried out according to the method of multiple overlaps on reflected longitudinal waves, which is typical for the geological region under study, and the observation system must satisfy the following conditions: the offset is 0, ..., 8H, the base of the seismogram with a common excitation point (TSS) -0 ,, 0 Н, where Н is the normal distance from the point of excitation to the boundary under study.

The essence of the method is based on the physical properties of the reflected exchange waves SvP. The reflection coefficient with a change in the direction of polarization of the waves at small angles of incidence on the boundary is almost zero, therefore the interference system of receiving exchange waves should be flank with the removal. In this case, the traceability of SvP exchange waves will increase due to the reduction of interference of exchange and monotypic waves in the plane xt (x is the distance between the source and the receiver, t is the time),

In addition, the locus OTV - SvP earlier comes to the asymptote than the locus OTV-PP, i.e. the first with a smaller offset and, therefore, on a larger base is approximated by a straight line. Thus, it is advisable to extract the SvP-wave by summing along the direct paths of the GSP. To do this, it is necessary to determine the optimal values of the offset and the base of reception, at which the SvP waves can be considered flat, and the linear summation - an effective way to isolate them. This problem can be solved using numerical simulation performed on synthetic seismograms obtained for various effective seismic section models. At the same time, on the seismograms there are both monotypic reflected waves of both types and exchange reflected of both types. The simulation results show that on the offset, lying in the range of 0.7-0.8-H, and on the base in the range of 0.8: 1.0 N, the SvP wave reflected from the subhorizontal boundary can be considered flat, propagating along a linear profile with an apparent velocity VSP equal to the apparent velocity Vpp of the reflected longitudinal wave PP generated at the boundary under study and recorded on the same base, which is in direct accordance with the theory of the SvP and PP properties in the far zone.

The coincidence of the slopes of the SvP hodographs makes it possible to avoid the selection of the SvPwave brute force by the slope of the summation line, if the slope is known, otherwise speaking Vpp of the hodograph of the PP wave. The reflected SvP wave arrives later than the reflected PP

from the same horizon, therefore, the search and selection of the first one begin after the time of entry of the PP wave.

Another significant physical property of SvP waves, which distinguishes them from the monotypic and exchangeable PSv waves, is the significantly smaller size of the reflecting area with the same sizes of receiving apertures. Consequently, the Roughness of the reflecting boundary leads to less

largest phase and amplitude spreads between the observed and approximating hodographs, which increases the signal-to-noise ratio when SvP waves are emitted by means of a straight line

the summation, as well as the accuracy of anchoring the wave to the reflecting horizon.

Specific values of the parameters of the reception system are based on the requirements

geological problem, surface conditions, channel seismic station, etc.

Over the waves, PP is determined by standard digital processing, including the calculation and correction of kinematic corrections, the time tpp of the arrival of the PP wave reflected from the boundary under study at the beginning of the registration base, and its apparent speed Vpp.

Subsequently, the work according to the method consists in processing the OTV-SvP seismograms on a computer using a special program that implements an algorithm for searching for the reflected exchange wave SvP.

The essence of the algorithm is as follows. Input data is entered: arrival time tpp and apparent velocity PP of the Vpp wave, determined at the processing stage of the HTS-PP seismograms, DT summation interval along the coordinate t, which is recommended to take

equal in magnitude to the time interval containing the main energy of the wave pulse and approximately 100 ms in mid-frequency seismic exploration. Select the SvPA wave search interval.

on t, Recommended Value

 Atpp (1 + y) / 2y,

where Atpp is the average difference in the tracking time of the target boundaries in a time section built on reflected longitudinal PP waves;

Y Vs / Vp - a priori value of the ratio of the transverse and longitudinal velocities

waves for the object under study, if it is unknown, then about 0.5.

Calculate in the search interval Ds by step At the operator of the similarity P (r, t.) Using the formula

n (, t)

G: ((x;)}

.) 2

to - (/ 1 L-

where AH is the number of runs involved in the summation;

AH is the distance between the channels;

r (Xi) Xi / Vpp is the increment of time along the line of analysis at a point, 7V + i AX;

and AT / (5t is the summation parameter specifying the number of samples of the trace along the t axis;

AT is a summation window;

5t is the sampling step in t;

A (tK) is the amplitude of the path at the moment of time IK;

to tpp + At, tpp is the time of entry of the PP wave from the studied horizon;

At - step search in the t axis.

Calculate the operator of the similarity of Ts.o) at the points (l-1) A / At-5t, 1,2, .. when the values of tpp, Vpp, AT specified at the point and the values of OTV selected from the label of the TOV - SvP AX, 5t. The iteration step At recommends setting no more than 0.5 LT.

The time for which the absolute maximum of the coefficient of similarity is reached is determined.

C1m3x) max (P (to)), (i-1) A / At.

In the time interval containing 1 max, for example, 1 max-A1, then 1 max + Dts, increments of At (2–3) (5t, CT0 is again calculated), to -Xmax-j AT /, j, 0,1,2,., . and determine the time at which the similarity coefficient reaches the absolute maximum

IXtsv p) max (P (t0)),

At the output of the program, a tsv P numerical value is obtained. The time of registration of the SvP wave reflected from the boundary under study is fixed at the initial reception point.

Figure 2 shows the results of the SvP wave extraction by the indicated and software-implemented algorithm. The tsv P values obtained are used for typical calculations of the effective integral parameters Vs, J Vs / Vp, which are used as initial data for subsequent deep processing, making it possible to estimate the lithology of the geological section from the position of the presence of hydrocarbons more likely than the bright spot. .

The use of the proposed seismic survey method as compared to the known method provides an increase in the efficiency of research on reflected SvP 5 waves due to the following advantages: Improves the noise immunity and, therefore, the informativity of the SvP waves research, which is due to the optimal (for these waves) parameters of the observation system and a way to isolate these waves. In addition, in contrast to the well-known, SvP-BOLN is attached to the object under study and, more precisely, the accuracy of the construction of parameters (for example, Vs, y) that characterize the lithology and structure of the geological section is improved. Nickname ip is a circular force, and a source of transverse waves Sv is sufficient.

Claims (1)

Claims The seismic exploration method, in which longitudinal P- and transverse S-waves are excited at a common driving point with carry-over, record reflected seismic vibrations by vertical seismic receivers located on a linear profile section, the obtained seismogram is subjected to processing using summation of the paths, according to the results of processing, they identify the desired wave from the reflecting boundary under investigation and judge about the parameters of the selected wave 5 of the structure and material composition of the geologic section, characterized in that, in order to increase the efficiency of multiwave seismic exploration on reflected SvP exchange waves, 0 seismic vibrations were made by setting the length of the removal of the excitation point in the range from 0.7N to 0.8N and the size of the recording base in the range from 0.8N to H, where H is the normal distance from the point of excitation to the reflecting boundary under study, and the seismogram tracks are summed along a straight line with a slope that coincides with the slope of the hodograph of the reflected longitudinal wave PP, using the similar operator 0 as a summation kernel, with a straightline summation starting from the arrival time of the PP wave reflected from the test boundary and periodically repeated with time shifts, we find the absolute maximum of the similar operator, which identifies the SvP wave reflected from the test boundary. at f.9 f.9f 2.0 2.05 2.15 t, c FIG. 2 FIG. I