WO2018107905A1 - Method for periodically measuring time thickness of sedimentary stratum using receiver function - Google Patents

Abstract

A method for periodically measuring the time thickness of a sedimentary stratum using a receiver function, belonging to the field of solid geophysical research. The method comprises: firstly selecting a vertical component Z, a radial component r and a tangential component t of three component seismic data, received by a seismic station, the magnitude thereof being more than four and the epicentral distance thereof being 30 degrees to 100 degrees, and selecting seismic events satisfying the condition; then respectively calculating normalized autocorrelation functions of the vertical component Z, the radial component r and the tangential component t for each of the seismic events; detecting whether each seismic event i is periodic and determining whether the periodicity of the seismic event i is a periodicity caused by a sedimentary stratum below a receiving station; and obtaining an average time thickness reflecting the thickness of the sedimentary stratum below the seismic station by using a mathematical average algorithm. The method provides a theoretical basis for the research of a sedimentary stratum.

Description

Method for periodically measuring the thickness of a sedimentary formation using a receiving function Technical field

The invention relates to the field of solid geophysical research, and is used for earth structure research and determination of basement depth of a sedimentary basin, and particularly relates to a method for determining the thickness of a sedimentary stratum.

Background technique

The time thickness of the sedimentary stratum refers to the time when the seismic wave propagates vertically downward from the surface to the bottom interface of the sedimentary layer and then propagates back up to the surface. This time can be used to characterize the relative thickness of the sedimentary stratum and the buried depth of the basin basement.

According to the theory of earth plate tectonics, the earth consists of the earth's crust, the mantle and the earth's core. The properties such as the nature and thickness of the crust are closely related to geological disasters such as natural earthquakes, and the sedimentary basins on it are closely related to the enrichment of mineral resources. Both the basement depth of the sedimentary basin and the thickness of the sedimentary stratum are very important physical quantities, both in the study of the crust and mantle structure of the Earth, and in the evolution of sedimentary basins and mineral resources.

At present, the commonly used sedimentary basin basement measurement methods are mainly drilling method, gravity exploration method and magnetotelluric sounding. Among them, the drilling method is not only expensive, but also provides only a little layer of information; the gravity exploration method and the magnetotelluric sounding method use the method of downward extension of the potential field, and its accuracy is affected by the depth of exploration. In addition, artificial seismic methods in oil and gas exploration can also be used to conduct research on sedimentary strata, which can obtain subsurface images, but also requires high costs and does not guarantee substrate reflection.

Therefore, a new method for measuring the thickness of a sedimentary formation time is to be provided.

Summary of the invention

The object of the present invention is to provide a method for periodically measuring the thickness of a sedimentary formation by using a receiving function, which utilizes a teleseismic signal with a magnitude above 4.0 in a natural earthquake, and analyzes the period in which the seismic wave is reflected multiple times in the sedimentary stratum. The time thickness of the sedimentary formation.

Its technical solutions include:

A method of measuring the thickness of a sedimentary formation, comprising the following steps in sequence:

a. Select the vertical component Z, the radial component r and the tangential component t of the three-component seismic data received by the seismic station with a magnitude greater than four or more and an epicenter distance of 30° to 100°, and select the seismic event that satisfies the condition. The selected earthquake events are i, i = 1, 2, 3...M;

和

并分别检测每个自相关函数的周期性，得到三个周期值分别记为T_z、T_r、T_t； b. Calculate the normalized autocorrelation function of the vertical component Z, the radial component r and the tangential component t of each seismic event

with

And the periodicity of each autocorrelation function is detected separately, and three period values are respectively recorded as T _z , T _r , T _t ;

c. detecting whether each earthquake event i has periodicity;

d. If the total number of periodic seismic events detected is K, the sedimentary formation time thickness T is:

As a preferred solution of the present invention, in step b, the periodic detection method of the autocorrelation function is:

The first four extreme points are selected on the autocorrelation function, and the corresponding time delays are τ _j , j=1...4, and the corresponding autocorrelation function values are a _j , j=1...4, according to which The characteristics of the normalized autocorrelation function are τ ₁ =0, a ₁ =1;

Use the following criteria to determine the periodicity of the autocorrelation function:

则自相关函数的周期为

否则该自相关函数没有周期性，并令T＝0。If |τ ₂ +τ ₄ -2τ ₃ | ≤ 2Δ, where Δ is the sampling interval, a ₂ <0, a ₃ >0, a ₄ <0, and

Then the period of the autocorrelation function is

Otherwise the autocorrelation function has no periodicity and T=0.

As another preferred solution of the present invention, in step c, it is determined whether the periodicity of each seismic event i is a periodicity caused by a sedimentary formation below the receiving station, and the specific determination method is:

If T _z +T _r +T _t =0, the earthquake event i has no periodicity;

If T _z +T _r +T _t >0, T _z =0, the seismic event i has periodicity; when min(T _r , T _t )=0, the period size is T _i =max(T _r ,T _t ), otherwise T _i =min(T _r ,T _t );

If T _z +T _r +T _t >0, T _z >0, T _r +T _t >0, and |T _z -T _t |>2Δ or |T _z -T _r |>2Δ, earthquake event i It has periodicity; when min(T _r , T _t )=0, the period size is T _i =max(T _r ,T _t ), otherwise T _i =min(T _r ,T _t ).

The beneficial technical effects brought by the invention are:

The invention selects the recorded fourth-order teleseismic data with an epicenter distance of 30°-100°, and extracts the periodicity of the receiving function by using an autocorrelation function, and the seismic wave at this distance is incident at a close vertical angle on the shell-ankle interface. The seismic wave reaches the seismic station almost vertically. In the sedimentary basin, since the seismic wave velocity of the sedimentary layer is much lower than the seismic wave velocity of the crust, the seismic wave propagates almost vertically in the sedimentary layer. Since the earth's surface is the contact surface of the sedimentary layer with the air, it is a good reflective interface. At the same time, the sedimentary layer is the interface between the sedimentary stratum and the earth's crust, and it is also a good interface. After the seismic wave enters the sedimentary layer, the two interfaces are at the interface. It is reflected back and forth multiple times to form a sound.

The present invention utilizes the period of the sounding of the receiving function to obtain the time thickness of the deposited formation, that is, the vertical two-way travel of seismic waves in the sedimentary formation. The invention automatically recognizes the periodicity of the receiving function by using the adjacent amplitude extreme value ratio and the amplitude extreme point delay time double discriminating condition on the autocorrelation function curve of the receiving function, after obtaining the period of the plurality of receiving functions of the same seismic station. The periodicity caused by the sedimentary stratum below the seismic station is identified by the periodic difference of the different components of the receiving function. Finally, the mathematical mean value algorithm is used to obtain the average time thickness reflecting the thickness of the sediment stratum below the seismic station.

DRAWINGS

The present invention will be further described below in conjunction with the accompanying drawings:

Figure 1 is a flow chart of the method of the present invention;

Figure 2 is a diagram of a receiver function with periodicity;

Figure 3 is a diagram of a periodic autocorrelation function;

Figure 4 is a diagram of a receiving function without periodicity;

Figure 5 is a diagram of an autocorrelation function without periodicity;

Figure 6 is a graph showing the time thickness of a sedimentary stratum in the Williston Basin, USA, in accordance with an embodiment of the present invention.

detailed description

The present invention proposes a method for periodically measuring the thickness of a deposited formation using a receiving function. In order to make the advantages and technical solutions of the present invention clearer and clearer, the present invention will be described in detail below with reference to specific embodiments.

As shown in the flow chart of Figure 1, the method of the present invention for measuring the thickness of a deposited formation comprises the following steps:

The first step is to select the teleseismic earthquake with a seismic station above 4.0 in the sedimentary basin (the epicentral distance is 30° to 100°);

The second step is to calculate an autocorrelation function of three receiving functions for each seismic event;

The third step is to detect whether each event has periodicity;

The fourth step is to calculate the mean of all periodic functions as the time thickness of the sedimentary formation.

The detailed description will be given below in conjunction with the specific embodiment 1.

Example 1:

The method of the invention is used in the Williston Basin in North America. The basin is rich in oil and gas resources and is a typical Karatun basin. The area of the basin is in the range of latitude 41° to 50° and longitude -111° to -95°. Select a total of 307 seismic stations in the area. From the data processing center of IRIS (Incorporated Research Institutions for Seismology), the data of 2,459 earthquakes with more than four earthquakes since 1980 have been obtained. After the basic processing of these data, the receiver function is obtained, which is 2459&*307. = 754,913. In the process, the time when the converted wave generated by the seismic wave on the Moho surface reaches the station is set to 0, and the receiving function usable for the research of the present invention is selected according to whether there is a significant converted wave at time 0. Figures 2 and 4 show the selected receive function, which shows that the attachment has a significant strong amplitude at time zero. According to this basic requirement of the receiving function, the number of matching receiving functions is 19462 in this example.

According to the present invention, the autocorrelation functions of the 19462 receiving functions are respectively calculated, and two types of autocorrelation functions are obtained. One class is shown in FIG. 3, which is a typical periodic receiving function autocorrelation function; one class is shown in FIG. Is an autocorrelation function of a typical aperiodic receiver function. Using the third step of the test, the periodic data of the receiving function of 307 stations is finally obtained.

Taking the H31Axx_TA station as an example, as shown in Table 1, the latitude and longitude of the station are: 44.4795° and -98.4772°, respectively, and the effective seismic events connected are 372. The following table shows the periodicity of the detected partial seismic events, and the validity of the rule according to the third step of the present invention is given. These valid period data are used to calculate the time thickness of the deposited formation below the site to be 1.0209 s.

Table 1 HAxx_TA station part receiving function test result

Source latitude (°) Source longitude (°) Z component period (s) R component period (s) T component period (s) Earthquake code Effectiveness -7.454 -75.146 0 1.0667 0 EQ102390440 no 51.451 -175.87 0 0.9667 1.0083 EQ102461116 Yes -43.522 171.83 2.475 2.9917 2.125 EQ102461635 no -23.825 179.975 2.3417 2.2167 2.2167 EQ102482348 no -20.671 169.818 0 0 0 EQ102511137 no 44.588 149.724 0 1.05 0 EQ102511739 no -37.034 -73.412 0 1.05 0 EQ102520728 no 59.405 -30.226 2.3167 1.0667 1.0667 EQ102521031 Yes 41.497 141.986 0 1.075 0 EQ102560547 Yes -14.612 -70.777 0 1.025 1.0417 EQ102560715 Yes 36.443 70.774 0 1.0583 0 EQ102601921 Yes 52.233 179.754 0 0 0 EQ102660528 no -7.809 -74.373 2.1667 1.0083 0 EQ102671901 Yes 62.854 -149.512 0 1.025 0 EQ102681205 no -20.999 -179.02 0 0 0 EQ102691720 no 52.438 179.732 0 0.95 0 EQ102691827 Yes 57.688 -32.762 0 1.0583 0 EQ102700008 Yes 57.727 -32.679 0 0.9583 0 EQ102700016 Yes -36.249 -74.256 0 0 0 EQ102730026 no 19.706 121.472 0 0 0 EQ102730900 no -7.926 -71.324 0 0 0 EQ102732330 no -17.818 -173.989 0 1.8833 0 EQ102791943 Yes 51.374 -175.361 1.9583 1.025 1.075 EQ102810326 Yes 51.287 -175.18 8.2333 8.0917 0 EQ102810349 no 10.211 -84.293 0 1.025 0 EQ102820154 Yes 42.311 142.871 0 1.1417 0 EQ102871358 Yes -20.414 -173.846 0 0 0 EQ102892008 no -34.737 -73.726 0 1.0417 0 EQ102940249 Yes -20.878 -68.372 0 0 0 EQ102951931 no -29.593 -71.112 2.3333 0 0 EQ102960138 no -6.385 150.161 2.7167 0 0 EQ103041638 no

According to the fourth step of the present invention, time thickness data of the deposited formation below each station is obtained. Of the 307 stations, 264 stations received valid time thicknesses. The data of some stations is shown in Table 2. According to this data, the time thickness map shown in Fig. 6 can be drawn. In order to compare with the general method, the contours obtained by the conventional method are given in Fig. 6, which are basically similar, but the method is more reliable. It does not require special geophysical observations, and existing natural seismic detection data can be used.

Table 2 Partial station time thickness data

Station name Latitude (°) Longitude (°) Time thickness (S) A18Axx_TA 48.9198 -109.8459 2.3414 A19Axx_TA 48.9286 -108.7429 2.7845 A20Axx_TA 48.8799 -107.9257 2.4267 A26Axx_TA 48.8973 -102.038 2.4017 A27Axx_TA 48.9533 -101.2407 2.1591 A28Axx_TA 48.9096 -100.2669 2.2114 A29Axx_TA 48.9228 -99.2321 1.5108 A30Axx_TA 48.9402 -98.3009 1.0746 A31Axx_TA 48.932 -97.1888 0.7057 A32Axx_TA 48.9172 -96.4935 2.1525 A33Axx_TA 48.9371 -95.3904 1.9343 B18Axx_TA 48.3943 -109.7775 2.2743 B19Axx_TA 48.4551 -108.9443 2.3986 B20Axx_TA 48.4389 -108.0209 2.3725 H18Axx_TA 44.6769 -109.6641 2.1474 H19Axx_TA 44.6704 -108.9857 1.8303 H20Axx_TA 44.4868 -107.999 2.0351 H21Axx_TA 44.6277 -107.0423 2.05 H23Axx_TA 44.562 -105.4007 2.9358 H26Axx_TA 44.6168 -102.7739 2.2167 H27Axx_TA 44.6329 -102.0775 2.1025 H28Axx_TA 44.6751 -101.0206 1.7944 H29Axx_TA 44.6261 -100.2125 1.6927 H31Axx_TA 44.4795 -98.4772 1.0209 H32Axx_TA 44.5041 -97.4363 1.5524 H33Axx_TA 44.6812 -96.7434 1.3954 H34Axx_TA 44.6673 -95.777 2.0047 I18Axx_TA 43.7013 -109.8171 1.1107 I19Axx_TA 44.0363 -108.9943 2.0962

I20Axx_TA 43.9496 -108.1283 2.1655 I21Axx_TA 43.8122 -107.292 2.2132 B21Axx_TA 48.4278 -107.0166 2.1807 B22Axx_TA 48.3008 -105.9964 2.5905 B23Axx_TA 48.4643 -104.9909 2.7212 B25Axx_TA 48.2716 -103.1613 2.7557 B26Axx_TA 48.3762 -102.2341 2.7335 B27Axx_TA 48.4044 -101.26 2.3684 B28Axx_TA 48.4492 -100.3616 2.0659 B29Axx_TA 48.4649 -99.3535 1.6749 B30Axx_TA 48.4505 -98.3286 1.347 B31Axx_TA 48.4236 -97.6495 0.7507 B32Axx_TA 48.3951 -96.5363 2.1644 B33Axx_TA 48.2722 -95.588 2.0757

It should be noted that any equivalents or obvious modifications made by those skilled in the art in the teachings of the present invention are intended to be within the scope of the present invention.

Claims (3)

A method of measuring the thickness of a sedimentary formation, characterized in that it comprises the following steps in sequence: a. Select the vertical component Z, the radial component r and the tangential component t of the three-component seismic data received by the seismic station with a magnitude greater than four or more and an epicenter distance of 30° to 100°, and select the seismic event that satisfies the condition. The selected earthquake events are i, i = 1, 2, 3...M; b. Calculate the normalized autocorrelation function of the vertical component Z, the radial component r and the tangential component t of each seismic event

with

And the periodicity of each autocorrelation function is detected separately, and three period values are respectively recorded as T _z , T _r , T _t ; c. detecting whether each earthquake event i has periodicity; d. If the total number of periodic seismic events detected is K, the sedimentary formation time thickness T is:

The method of measuring the thickness of a deposition formation according to claim 1, wherein in step b, the periodic detection method of the autocorrelation function is: The first four extreme points are selected on the autocorrelation function, and the corresponding time delays are τ _j , j=1...4, and the corresponding autocorrelation function values are a _j , j=1...4, according to which The characteristics of the normalized autocorrelation function are τ ₁ =0, a ₁ =1; Use the following criteria to determine the periodicity of the autocorrelation function: If |τ ₂ +τ ₄ -2τ ₃ | ≤ 2Δ, where Δ is the sampling interval, a ₂ <0, a ₃ >0, a ₄ <0, and

Then the period of the autocorrelation function is

Otherwise the autocorrelation function has no periodicity and T=0. The method for measuring the thickness of a sedimentary formation according to claim 1, wherein in step c, it is determined whether the periodicity of each seismic event i is a periodicity caused by a sedimentary formation below the receiving station, and the specific determination method is : If T _z +T _r +T _t =0, the earthquake event i has no periodicity; If T _z +T _r +T _t >0, T _z =0, the seismic event i has periodicity; when min(T _r , T _t )=0, the period size is T _i =max(T _r ,T _t ), otherwise T _i =min(T _r ,T _t ); If T _z +T _r +T _t >0, T _z >0, T _r +T _t >0, and |T _z -T _t |>2Δ or |T _z -T _r |>2Δ, earthquake event i It has periodicity; when min(T _r , T _t )=0, the period size is T _i =max(T _r ,T _t ), otherwise T _i =min(T _r ,T _t ).

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