阅读说明：本技术 一种考虑倾角时差的反射点位置确定方法 (Reflection point position determination method considering dip angle time difference ) 是由 李启成 孙敬雯 刘倩 郑新娟 于 2021-10-25 设计创作，主要内容包括：本发明属于地震勘探技术领域,具体涉及一种考虑倾角时差的反射点位置确定方法。目前地震反射波勘探都用到偏移归位方法确定反射面,但偏移归位需要绘制公切线,这一定会存在较大的误差。本发明在用地震勘探确定反射面倾角的基础上,首次提出用反射面倾角确定反射点的位置,并准确实现；本发明还首次提出用理论数据检验勘探理论的方法,理论数据具有实际地震记录不具备的准确性。无论对地震勘探的实践,还是对地震勘探的理论或教学,都具有深刻的理论和实践价值。(The invention belongs to the technical field of seismic exploration, and particularly relates to a method for determining the position of a reflection point by considering dip angle time difference. At present, the seismic reflection wave exploration uses an offset homing method to determine a reflecting surface, but the offset homing needs to draw a common tangent line, which has a larger error. On the basis of determining the inclination angle of the reflecting surface by seismic exploration, the invention firstly provides the method for determining the position of the reflecting point by using the inclination angle of the reflecting surface and accurately realizes the method; the invention also provides a method for detecting the exploration theory by using theoretical data for the first time, wherein the theoretical data has accuracy which is not possessed by actual seismic records. The method has profound theoretical and practical values for the practice of seismic exploration and the theory or teaching of seismic exploration.)

1. A reflecting point position determining method considering dip angle time difference is characterized in that the position of a reflecting point is determined by using the dip angle of a reflecting surface and is accurately realized, and the specific flow is as follows:

step 1: establishing a multi-covering observation system, recording position coordinates of an excitation point and a receiving point, grasping the seismic wave velocity of a medium above a reflecting target layer and the normal depth variation range of the target layer, and calculating the self-excited self-receiving time (t) of the target layer by using a formula (1)₀) The variation range of (a);

in the formula (1), v is the wave velocity of seismic waves, and h is the normal depth of a target layer;

step 2: exciting seismic waves, and recording seismic wave travel time t at a receiving point;

and step 3: and (3) channel extraction collection: gathering the seismic records of the common midpoint gather together;

and 4, step 4: dynamic correction and horizontal superposition: selecting a common midpoint gather, determining wave speed and self-excited self-receiving time (t)₀) Based on the variation range, the wave speed and the self-excited self-receiving time (t) are increased from small to large according to a certain step length₀) Calculating the dynamic correction value by using a formula (2);

Δ t in formula (2)_φTaking the dynamic correction value as x, the offset distance and the seismic wave velocity as v;

at seismic wave velocity and self-excited self-collecting time (t)₀) On the basis of the change ofSeismic wave velocity and self-excited time (t)₀) Determining the self-excited self-receiving time (t) of different common-center points by the formula (3)_0M) Time of self-excitation and self-collection for all common center points (t)_0M) The sections are horizontally overlapped, and the time corresponding to the maximum amplitude is used as the optimal self-exciting and self-receiving time (t) of the common center point_0M)；

t_0M＝t-Δt_φ (3)

At present, a multiple coverage observation system is commonly used in seismic exploration work to determine the normal depth of a common central point, and the specific method for determining the common central point is as follows: after wave speed and self-excited self-receiving time (t) are determined₀) Based on the variation range, the wave speed and the self-excited self-receiving time (t) are increased from small to large according to a certain step length₀) Arranging and combining them in a certain order, determining the dynamic correction value, and further determining the self-excited self-receiving time (t) of each record in the common central point_0M) On the basis of the above-mentioned work, the self-excited time (t) is equal to the self-excited time₀) The obtained self-excited self-receiving time (t) of the common central point_0M) Performing horizontal superposition, wherein the maximum amplitude after superposition is the optimal wave speed and the optimal self-excited time (t)₀) On the basis, the self-excited self-receiving time (t) of the actual common central point is calculated by the formula (11)_0M)；

And 5: calculating the depth of the common center point normal by using a formula (4);

in the formula (4), h_MNormal depth to a common center point;

step 6: repeating the step 4 to complete the calculation of all the common center point normal depths;

and 7: exciting seismic waves by taking the common center point as an excitation point, receiving the seismic waves at positions with equal shot-geophone distances on two sides, and recording the shot-geophone distances and the seismic wave travel time;

and 8: calculating the inclination angle phi of the reflecting surface by using a formula (5), and calculating the position coordinates of all reflecting points by using a formula (6) or (7);

phi is the inclination angle of the reflecting surface and is the inclination angle time difference;

when Δ t is reached_dWhen the absolute value is more than 0, the reflection point is positioned on the left side of the common central point, and the absolute value of the position coordinate of the reflection point is as follows:

z＝x₀-x₁ y＝y₁＝hcosφ (6)

in the formula (6), x₀Is the absolute value of the horizontal coordinate of the common center point M, y₁Is the absolute value of the vertical coordinate, x, of the reflection point₁The absolute value of the horizontal distance between the reflection point and the common center point is shown, and z is the absolute value of the horizontal coordinate of the reflection point;

when Δ t is reached_dWhen the absolute value is less than 0, the reflection point is positioned on the right side of the common central point, and the absolute value of the position coordinate of the reflection point is as follows:

z＝x₀+x₁ y＝y₁＝hcosφ (7)

and step 9: and drawing a depth profile of the reflecting surface in the ray plane.

2. A reflection point position determination method taking into account a tilt moveout according to claim 1, wherein the formula (6) and the formula (7) accurately determine the coordinates of the reflection point.

3. The method as claimed in claim 1, wherein it is almost impossible to find a known reflecting surface in nature, and the patent proposes to obtain data by theoretical model for accurate seismic travel, which can provide a verification method for future seismic exploration theory.

Technical Field

The invention belongs to the technical field of seismic exploration, and particularly relates to a method for determining the position of a reflection point by considering dip angle time difference.

Background

In seismic exploration, dynamic correction is needed when the position of a reflecting surface is determined by a reflected wave method, and after the common center point normal depth is determined by the dynamic correction, the position of the reflecting surface needs to be determined by an offset homing method.

Reference documents: land-based mondson, wang-yonggang, seismic exploration principle [ M ]. third edition, eastern Shandong-Yingo, China oil university Press, 2011, page 35, page 201.

The method for determining the position of the reflecting surface by the offset homing method comprises the following steps:

as shown in FIG. 1, the normal depth h of the common center point is calculated according to the correlation formula_MAt a common center point M₁Is used as the center of a circle,at a corresponding normal depth h_MAn arc is drawn for a radius, a semi-arc as in fig. 1 can be obtained, and any point on the semi-arc, such as a, B, c. But may be based on multiple concentric point data, such as M₁，M₂，M₃.., etc., centered on the respective corresponding normal depth h_M1，h_M2，h_M3.., the radii are plotted as arcs, resulting in a series of arcs, as shown in FIG. 2, whose envelopes, or common tangents, are the locations of the reflecting surfaces, and which envelopes are essentially the result of smoothing the depth curve to normal.

From the above analysis, it can be seen that the common tangent line needs to be drawn when the reflection surface is determined by the offset homing method, and the drawing of the common tangent line has large human factors, so that the existence of large errors is inevitable.

Disclosure of Invention

To reduce the error, we introduce the concept of dip moveout. As shown in FIG. 3, O is the seismic wave excitation point, the normal depth of the excitation point is h, two receiving points S and S 'with equal offset X on the horizontal ground, RR' is the seismic wave reflection surface, the inclination angle of the reflection surface is phi, the propagation speed of the seismic wave of the medium above the reflection surface is v, and for the receiving point S, the down wave travel time t is_sCalculating by using a formula (1);

when x/2h < <1, the formula (1) is expanded by Taylor series, and high-order terms above the power of 2 are omitted:

in the formula (2)Is the time of self-excitation and self-acceptance at the excitation point (point O);

for point S', its upwave travel time t_s'Comprises the following steps:

similarly, when x/2h < <1, the formula (3) is expanded by Taylor series, and high-order terms above the power of 2 are omitted:

the travel time of reflected waves of two observation points which are equidistant on two sides of the seismic source is subtracted to obtain the dip angle time difference delta t_dComprises the following steps:

after the time difference of the inclination angle is measured on two points with offset distances x on two sides of the point O, the inclination angle phi of the inclined plane can be estimated by using a formula (6), wherein the formula (6) is the deformation of the formula (5);

thus, when the reflecting surface is determined, the normal depth of the common central point can be determined by using the current reflected wave exploration method, the inclination angle of the reflecting surface is determined by using the formula (6), and finally, the coordinates of the reflecting point corresponding to the common central point are determined by using the formulas (7) and (8).

As shown in FIG. 4, phi is the inclination angle of the reflecting surface, x₀Is the absolute value of the horizontal coordinate of the common center point M, y₁Is the absolute value of the vertical coordinate, x, of the reflection point₁Is the absolute value of the horizontal distance between the reflection point and the common center point, and z is the absolute value of the horizontal coordinate of the reflection point.

When Δ t is reached_dWhen the absolute value is more than 0, the reflection point is positioned on the left side of the common central point, and the absolute value of the position coordinate of the reflection point is as follows:

z＝x₀-x₁ y＝y₁＝hcosφ (7)

in the formula (7), z is the absolute value of the horizontal coordinate of the reflection point, and y is the absolute value of the vertical coordinate of the reflection point;

when Δ t is reached_dWhen the absolute value is less than 0, the reflection point is positioned on the right side of the common central point, and the absolute value of the position coordinate of the reflection point is as follows:

z＝x₀+x₁ y＝y₁＝hcosφ (8)

the method of determining the reflecting surface by the equations (7) and (8) is called a reflecting point position determining method considering the inclination time difference and determines the reflecting surface based on the reflecting point position.

In view of the completeness of the description, the theory of determining the reflecting surface by using the improved method is realized and verified on the basis of the method for determining the reflecting surface by using the offset homing method.

In order to verify the accuracy of the improved method we propose to determine the reflecting surface, a known reflecting surface is necessary. But it is almost impossible to find a reflecting surface in nature where the information is exactly known. In order to obtain accurate seismic wave travel time data, data are obtained through a theoretical model, and a verification method can be provided for future seismic exploration theories. For example, as shown in fig. 5, the inclined angle of the inclined reflecting surface R is phi, and the variation relation of t along with the position coordinate x during seismic wave travel can be obtained through theoretical calculation. Calculating the travel time t of seismic waves received in the uplink direction by using a formula (3) by taking the point O as an excitation point, the normal depth of the point O as h, the wave velocity of the seismic waves as v and x as coordinates of an observation point; the normal depth of the point D is h', if the point D is taken as an excitation point, the travel time t of the seismic waves received in the downlink direction is calculated by the formula (1).

A method for determining the position of a reflection point by considering the time difference of inclination angle is disclosed, and the flow chart of the implementation mode is shown in figure 7. The specific process is as follows:

step 1: establishing a multi-covering observation system, recording position coordinates of an excitation point and a receiving point, grasping the seismic wave velocity of a medium above a reflecting target layer and the normal depth variation range of the target layer, and calculating the self-excited self-receiving time (t) of the target layer by using a formula (9)₀) The variation range of (a);

in the formula (9), v is the wave velocity of the seismic waves, and h is the normal depth of the target layer;

step 2: exciting seismic waves, and recording seismic wave travel time t at a receiving point;

the calculation equation of the upward reflected wave travel time in fig. 5 obtained by the theoretical model is formula (10):

and step 3: and (3) channel extraction collection: gathering the seismic records of the same common midpoint gather;

and 4, step 4: dynamic correction and horizontal superposition: selecting a common midpoint gather, determining wave speed and self-excited self-receiving time (t)₀) Based on the variation range, the wave speed and the self-excited self-receiving time (t) are increased from small to large according to a certain step length₀) Calculating a dynamic correction amount by using the formula (11);

delta t in formula (11)_φIs a dynamic correction value;

at seismic wave velocity and self-excited self-collecting time (t)₀) Within the variation range of (a), the wave velocity and the self-excited time (t) of the seismic waves are changed₀) Calculating the self-excited self-receiving time (t) of the common center point by the formula (12)_0M) Self-excited self-receiving time (t) for the common center point_0M) The sections are horizontally overlapped, and the self-excitation and self-collection time of the common center point corresponding to the maximum amplitude is adopted as the actual self-excitation and self-collection time (t) of the common center point_0M)；

t_0M＝t-Δt_φ (12)

At present, a multi-time coverage observation system is commonly used in seismic exploration work to determine the normal depth of a common central point; the multiple covering observation system is at different excitation points and different connectionsThe same reflection point is explored by the receiving point; one such purpose is to reduce the occasional error caused by a single survey; another object is to accurately determine the amount of fluctuation in formula (11); the calculation of the dynamic correction value in equation (11) requires accurate grasping of the seismic wave velocity and the spontaneous excitation time (t)₀) When wave velocity (v) and self-excited self-receiving time (t)₀) Under the condition that the exploration cannot be accurately mastered, the exploration is dynamically corrected by using the common central point;

the principle of determining the reflection point by using the common center point dynamic correction is as follows: selecting seismic wave velocity and self-excited self-collecting time (t) in a certain range for the same common central point exploration record (three records are available in the exploration), wherein the three records are available in the exploration₀) Calculating the dynamic correction value of each exploration record, and enabling each exploration record after dynamic correction to be in the self-excitation self-collection time (t) of the common central point_0M) Are all equal; the self-excitation and self-collection time of each exploration record at the common central point after dynamic correction is necessarily equal, because each record is explored by the same reflection point;

specifically, the wave speed and the self-excited self-receiving time (t) are determined₀) Based on the variation range, the wave speed and the self-excited self-receiving time (t) are increased from small to large according to a certain step length₀) Arranging and combining them in a certain order, determining the dynamic correction value, and further determining the self-excited self-receiving time (t) of each record in the common central point_0M) (ii) a On the basis of the above-mentioned work, the wave speed is the same and the self-excited time (t) is the same₀) The obtained self-excited self-receiving time (t) of the common central point_0M) Performing horizontal superposition, wherein the maximum amplitude after superposition is the optimal wave speed and the optimal self-excited time (t)₀) On the basis, the self-excitation and self-collection time (t) of the actual common central point is calculated by the formula (12)_0M) Detailed steps refer to fig. 7;

and 5: calculating the depth of the common center point normal by using a formula (13);

in the formula (13), h_MNormal depth being common to the center point；

Step 6: repeating the step 4 to complete the calculation of all the common center point normal depths;

and 7: exciting seismic waves by taking the common center point as an excitation point, receiving the seismic waves at positions with equal shot-geophone distances on two sides, and recording the shot-geophone distances and the travel time of the seismic waves;

and 8: calculating the inclination angle phi of the reflecting surface by using a formula (6), and calculating the position coordinates of all reflecting points by using a formula (7) or (8);

in the formula (6), phi is the inclination angle of the reflecting surface, Δ t_dIs the dip angle time difference;

as shown in FIG. 4, φ is the reflective surface tilt angle;

when Δ t is reached_dWhen the absolute value is more than 0, the actual reflection point is positioned on the left side of the common central point, and the absolute value of the position coordinate of the reflection point is as follows:

z＝x₀-x₁ y＝y₁hicos phi and (7)

In the formula (7), x₀As absolute value of coordinate of excitation point, y₁Is the absolute value of the vertical coordinate, x, of the reflection point₁The absolute value of the horizontal distance between the reflection point and the excitation point is obtained, z is the absolute value of the horizontal coordinate of the reflection point, and y is the absolute value of the vertical coordinate of the reflection point;

when Δ t is reached_dWhen the absolute value is less than 0, the actual reflection point is positioned on the right side of the common central point, and the absolute value of the position coordinate of the reflection point is as follows:

z＝x₀+x₁ y＝y₁hicos phi and (8)

And step 9: and drawing a depth profile of the reflecting surface in the ray plane.

The beneficial technical effects are as follows:

the invention belongs to the technical field of seismic exploration, and particularly relates to a method for determining the position of a reflection point by considering dip angle time difference. At present, the seismic reflection wave exploration uses an offset homing method to determine a reflecting surface, but the offset homing needs to draw a common tangent line, which has a larger error. On the basis of determining the inclination angle of the reflecting surface by seismic exploration, the invention firstly provides the method for determining the position of the reflecting point by using the inclination angle of the reflecting surface and accurately realizes the method; the invention also provides a method for detecting the exploration theory by using theoretical data for the first time, wherein the theoretical data has accuracy which is not possessed by actual seismic records. The method has profound theoretical and practical values for the practice of seismic exploration and the theory or teaching of seismic exploration.

Drawings

FIG. 1 is a schematic diagram of a common midpoint determination of reflection points according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of the determination of the position of a reflecting surface by offset homing according to an embodiment of the present invention;

FIG. 3 is a schematic view of the time difference between the dip angles of the embodiment of the present invention;

FIG. 4 is a schematic diagram of position coordinates of a reflection point according to an embodiment of the present invention;

FIG. 5 is a schematic view of a reflection surface for obtaining seismic records according to an embodiment of the invention;

FIG. 6 is a common center point survey observation system according to an embodiment of the present invention;

FIG. 7 is a flowchart illustrating a common center point dynamic calibration process according to an embodiment of the present invention;

FIG. 8 shows the results of the common midpoint dynamic correction and horizontal stacking according to an embodiment of the present invention;

FIG. 9 illustrates a common midpoint kinematic correction of survey results according to an embodiment of the present invention;

FIG. 10 is a comparison of survey results with actual reflective surfaces according to embodiments of the invention.

Detailed Description

The method comprises the following specific steps:

step 1: establishing a multi-coverage observation system, as shown in FIG. 6; recording position coordinates of the excitation point and the receiving point, grasping the seismic wave velocity of the medium above the reflecting target layer and the normal depth variation range of the target layer, and calculating the self-excitation and self-collection time (t) of the target layer by using a formula (9)₀) The variation range of (a);

as shown in fig. 6, a survey line of a common center point exploration multiple coverage observation system; AB is an exploration line, and BC is a reflecting surface; for simplicity, only four common center points, M, are set on the survey line₁、M₂、M₃、M₄Wherein M is₁The position coordinates of the points are 30M, M₂The position coordinates of the points are 110M, M₃The position coordinates of the points are 190M, M₄The position coordinates of the points are 290 m; the exploration adopts three times of coverage; calculating the seismic wave velocity v of 400.0m/s in the traveling process of the seismic upgoing wave by using a formula (3); h is the normal depth of the target layer at the excitation point, with a value equal to the distance of AC in FIG. 6; the normal depth of the point A on the exploration line is 300m, which is the maximum normal depth in the exploration range, and the normal depths of the rest excitation points are specifically calculated according to the positions of the excitation points; the inclination angle phi of the reflecting surface is 5 degrees; obtaining seismic wave travel time t through calculation of a formula (3), namely obtaining seismic records;

the information cannot be accurately mastered before exploration, but the variation range of the wave velocity of seismic waves and the normal depth of a target layer can be mastered, the variation range of the normal depth of the target layer of the current exploration is h-250 m-300m, the variation range of the wave velocity is v-350 m/s-450m/s, and the self-excitation and self-collection time t₀The variation range is 0.01s-2.00 s;

at a common center point M₁Exploration is taken as an example to illustrate an exploration method; exciting seismic waves at the position of 0m, receiving the seismic waves at the position of 60m, and recording the travel time of the seismic waves; then, seismic waves are excited at a position of 10m, the seismic waves are received at a position of 50m, and the seismic wave travel time is recorded; finally, seismic waves are excited at a position of 20m, the seismic waves are received at a position of 40m, and the seismic wave travel time is recorded; method for exploring other common central points and M₁The method of spotting is the same;

step 2: exciting seismic waves, and recording seismic wave travel time t at a receiving point;

the record of seismic wave travel time comes from the theoretical calculation of formula (3), and the survey line for exploration is shown in figure 6; to M₁，M₂，M₃And M₄The survey is conducted at four common central points, and the obtained seismic wave travel time records are shown in the first column from table 1 to table 4,The second and three columns of data;

TABLE 1 common center point M₁Survey records and survey results

TABLE 2 common center point M₂Survey records and survey results

TABLE 3 common center point M₃Survey records and survey results

TABLE 4 common center point M₄Survey records and survey results

And step 3: and (3) channel extraction collection: gathering the seismic records of the same common midpoint gather;

the exploration adopts a triple coverage observation system, as shown in figure 6, four common central points M to be explored are arranged₁，M₂，M₃And M₄The common center point seismic records of (a) are collectively put together;

and 4, step 4: dynamic correction and horizontal superposition: selecting a common midpoint gather, determining wave speed and self-excited self-receiving time (t)₀) On the basis of the variation range, the step length of the wave velocity v is taken as 1 and is increased from 350m/s to 450 m/s; time of self-excitation and self-receiving (t)₀) The step size of (1) is taken to be 0.01 and is increased from 0.01s to 2.00 s; calculation of the amount of fluctuation Deltat using equation (11)_φDetermining the self-excited self-receiving time (t) of different common-center points by the formula (12)_0M) Time of self-excitation and self-collection for all common center points (t)_0M) The sections are horizontally overlappedThe optimal self-excited self-receiving time (t) with the time corresponding to the maximum amplitude as the common center point_0M)；

Delta t in formula (11)_φTaking the dynamic correction value as x, the offset distance and the seismic wave velocity as v;

t_0M＝t-Δt_φand (12)

Optimal self-excited self-receiving time (t) of common center point obtained in calculation process_0M) Optimal velocity v and optimal t₀See the fourth, fifth and sixth columns in tables 1-4; in FIG. 8, a-d are respectively common center points M₁、M₂、M₃And M₄The result of the concentric dynamic correction and the horizontal superposition result; wherein, the three graphs positioned at the lower part are respectively three common center point dynamic correction results, and the graph at the top part is a horizontal superposition result;

and 5: calculating the depth of the common center point normal by using a formula (13);

in the formula (13), h_MNormal depth to a common center point; the common center point normal depth h is obtained by calculation_MSee seventh columns of tables 1 through 4;

as can be seen from Table 1, the corrected speeds obtained from the common center points are different from the preset speed of 400 m/s; the reason for the analysis is that when the reflecting surface is horizontal, the common reflection point is a real reflection point, namely, the reflection points excited for multiple times occur at the same point, and the corrected speed should be approximately equal to the actual speed; when the reflecting surfaces are inclined, the so-called common center points do not coincide, the motion-corrected speed and the motion-corrected (t) are obtained₀) The method has no clear physical meaning, is the result of mathematical processing, and is the average effect of the same parameters of a plurality of adjacent reflection points;

step 6: repeating the step 4 to complete the calculation of all the common center point normal depths;

four common center points M₁，M₂，M₃And M₄The correlation calculation results are shown in tables 1 to 4, respectively; because the common-center point dynamic correction is the average effect among a plurality of adjacent reflection points, and the realization of the dynamic correction needs a plurality of assumptions, the reflection surface of exploration is greatly different from the actual reflection surface;

according to the existing offset homing method for determining the reflecting surface, the common-center point dynamic correction exploration result can be obtained, as shown in fig. 9, the common-center point dynamic correction exploration result is compared with the real reflecting surface, and the difference between the common-center point dynamic correction exploration result and the real reflecting surface is large;

and 7: exciting seismic waves with the common center point of FIG. 6 as the excitation point, wherein the common center point includes M₁，M₂，M₃，M₄The method comprises the steps that four points are total, seismic waves are received at positions with equal offset distances (30m) on two sides, the offset distances and seismic wave travel time are recorded, the down wave travel time is calculated by a formula (1), and the up wave travel time is calculated by a formula (3); the first, second, third and fourth columns specifically recorded in table 5;

TABLE 5 calculation of reflecting surface parameters using reflecting point coordinates determination of reflecting surface taking into account tilt time differences

And 8: calculating the inclination angle phi of the reflecting surface by using a formula (6), and calculating the coordinates of a reflecting point by using formulas (7) and (8); specific values are in the fifth, sixth and seventh columns of table 5;

and step 9: drawing on the basis of the coordinates of the reflection points to obtain a depth profile in a ray plane; as shown in FIG. 10, in which the results of the survey using the offset homing method are shown by thin black lines and the results of the survey using the modified method are shown by thick black lines, it can be seen that the difference between the two is large; the dotted line in the figure represents the actual reflecting surface, and the exploration result is well matched with the actual position where the seismic wave energy arrives by using the improved method;

the improved method, as shown in fig. 10, shows that the surveyed part is completely overlapped with the real reflecting surface, and the current method, namely the offset homing method, shows that the surveyed part is greatly different from the real reflecting surface, thus the improved method has obvious progress.