An inclination-domain seismic imaging method

Abstract

The present invention relates to a dip-domain seismic imaging method, which comprises the following steps: Step 1, prepare a post-stack migrated seismic data volume generated by an offset-domain imaging method, display the data volume in the time domain, perform low-pass filtering on it, retain the signals within the main frequency, and remove the high-frequency part with relatively low signal-to-noise ratio; Step 2, calculate the true formation dip corresponding to all imaging points on the main survey line; Step 3, calculate the true formation dip corresponding to all imaging points on the connecting survey line; Step 4, during migration imaging, for each input pre-stack seismic data trace, calculate the magnitude of the formation dip of each imaging point in the direction of the main survey line according to the spatial coordinates of the shot point, geophone point and imaging point; Step 5, complete the calculation of all imaging points to obtain the final seismic imaging profile. The present invention utilizes the existing seismic data volume, generates a formation dip field through a set of high-precision and fast algorithms, without manual participation, and has the advantages of high efficiency and high precision.

Description

Technical field:

[0001] The invention relates to the technical field of reflection seismic data processing in seismic exploration, and in particular to a dip domain seismic imaging method. Background technology:

[0002] Different from the conventional offset range imaging method, the dip domain migration imaging method is based on the formation dip gather, which uses manual means to pick up the formation dip, constructs the formation dip field of the entire imaging domain, and then uses the formation dip field as an offset parameter to participate in the migration imaging. For the dip domain migration imaging method, the accuracy of the formation dip determines the accuracy of the aperture size of the migration method, which in turn affects the final migration imaging quality. For the determination of the formation dip in the dip domain migration imaging method, the industry currently mostly uses the formation dip gather for manual picking. However, the generation of the dip gather will take up a lot of memory, and the application of the method has limitations. In addition, the manual picking of the formation dip using the formation dip gather has the disadvantages of low efficiency and poor accuracy. In response to these problems, the industry has not yet proposed an effective solution. Summary of the invention:

[0003] The purpose of the present invention is to provide a dip domain seismic imaging method, which is used to solve the problems of low efficiency, poor accuracy and great limitations caused by manual picking of formation dip gathers when obtaining formation dip in existing dip domain imaging methods.

[0004] The technical solution adopted by the present invention to solve its technical problem is:

[0005] Step 1: prepare a post-stack migration seismic data volume generated by an offset range domain imaging method, the data volume has M main survey lines, N contact survey lines, each main survey line has N CDP points, each contact survey line has M CDP points, and the time length of each seismic trace is T. Display the data volume in the time domain, perform low-pass filtering on it, retain the signal within the main frequency, and remove the high-frequency part with low signal-to-noise ratio;

[0006] Step 2: Calculate the true formation dip angle X corresponding to all imaging points on the main survey line;

[0007] Step 3: Calculate the true formation dip angle Y corresponding to all imaging points of the contact survey line;

[0008] Step 4: During migration imaging, for each pre-stack seismic data input, the formation dip angle of each imaging point in the direction of the main survey line is calculated based on the spatial coordinates of the shot point, the receiver point and the imaging point, and is recorded as a x , calculate the formation dip angle of each imaging point in the direction of the connecting survey line, denoted as a y, and then compare it with the true formation dip angle X of the main survey line of this imaging point obtained in Step 2 and the true formation dip angle Y of the connecting survey line of this imaging point obtained in Step 3. If both satisfy a x <= X and a y <= Y, then continue to calculate the travel time and amplitude of this imaging point to complete the imaging; otherwise, repeat this step for the next imaging point;

[0009] Step 5: Complete the calculation of all imaging points to obtain the final seismic imaging profile.

[0010] In the above solution, the method for calculating the true formation dip angle X corresponding to the imaging point of the main survey line in Step 2: For any main survey line e, for the f-th CDP on it, at the imaging point at the time-depth t, where e is a positive integer not greater than M, f is a positive integer not greater than N, and t is a positive number not greater than T, scan the coherence values corresponding to several dip angles between the minimum formation dip angle and the maximum formation dip angle in the main survey line direction, and fit the coherence values corresponding to these dip angles using the least squares method. φ represents the magnitude of the main survey line formation dip angle, and C X (e, f, t, φ) represents the magnitude of the coherence value. The fitting curve is in the form of a quadratic curve, and the specific expression is:

[0011] C X (e, f, t, φ) = α3 + α2φ + α1φ 2

[0012] α1, α2, α3 are fitting coefficients. Then, find the derivative of the curve C X (e, f, t, φ) with respect to φ. When , the corresponding φ is the true formation dip angle X of the imaging point in the main survey line direction at this time-depth.

[0013] In the above solution, the method for calculating the true formation dip angle Y corresponding to the imaging point of the connecting survey line in Step 3: For any connecting survey line p, for the q-th CDP on it, at the imaging point at the time-depth t, where p is a positive integer not greater than N, q is a positive integer not greater than M, and t is a positive number not greater than T, scan the coherence values corresponding to several dip angles between the minimum formation dip angle and the maximum formation dip angle in the connecting survey line direction, and fit the coherence values corresponding to these dip angles using the least squares method. η represents the magnitude of the connecting survey line formation dip angle, and C Y (p, q, t, η) represents the magnitude of the coherence value. The fitting curve is in the form of a quadratic curve, and the specific expression is:

[0014] C Y (p, q, t, η) = β3 + β2η + β1η 2

[0015] β1, β2, β3 are fitting coefficients. Then, find the derivative of the curve CY (p, q, t, η)'s derivative with respect to η, when the corresponding η is the true formation dip angle Y of the imaging point in the direction of the connecting survey line at this time depth.

[0016] The calculation of the formation dip angle of the imaging point in the main survey line direction and the formation dip angle of the imaging point in the connecting survey line direction in step four of the above solution is realized as follows: For each input prestack seismic data trace, define the horizontal coordinate of the shot point as s, the horizontal coordinate of the receiving point as g, the azimuth angle as θ, the coordinates of the imaging point as (x, y, τ), and the migration velocity of the imaging point as vel rms ;

[0017] Define the following variables, u1 = s - x, u2 = s + g - 2x, and calculate the distance variables

[0018] w1 = u1 cosθ; w2 = u1u2 + 2(vel rms ) 2 ; w3 = u2 cosθ; x is the abscissa of the X-axis, then then the formation dip angle a of the imaging point in the main survey line direction x is arctan[(u1 + w5cosθ) / (vel rms τ)]; where: u1, u2, w1, w2, w3, w4, w5 are all intermediate variables and have no real meaning;

[0019] Define the following variables, v1 = g - y, v2 = s + g - 2y, and calculate the distance variables r1 = v1 cosθ; r2 = v1v2 + 2(vel rms ) 2 ; r3 = v2 cosθ;

[0020] y is the abscissa of the Y-axis, then then the formation dip angle a of the imaging point in the connecting survey line direction y is arctan[(v1 + r5cosθ) / (vel rms τ)]; where: v1, v2, r1, r2, r3, r4, r5 are all intermediate variables and have no real meaning.

[0021] The present invention has the following beneficial effects:

[0022] 1. The present invention uses the existing post-stack migration seismic data volume in the offset domain to calculate the formation dip angles of the main survey line and the connecting survey line, avoiding the problems of low efficiency, poor accuracy, and large limitations caused by manual picking through formation dip angle gathers in the existing dip angle domain imaging methods.

[0023] 2. When the present invention performs migration imaging, first calculate the formation dip angles in the main survey line direction and the connecting survey line direction at the imaging point for each input prestack seismic trace, then compare the magnitudes with the formation dip angles at this point in the main survey line and the connecting survey line calculated in advance, and further determine the imaging area, thereby improving the quality of seismic imaging.

[0024] 3. Compared with the conventional method, the present invention utilizes the existing seismic data volume and generates a formation dip angle field through a set of high-precision and fast algorithms. The entire process consumes little memory and has no manual participation, with the advantages of high efficiency and high precision. Brief Description of the Drawings:

[0025] Figure 1 Schematic diagram of the scanning dip angle and coherence at the imaging point in the main survey line or connecting survey line direction.

[0026] Figure 2 Post-stack migration seismic data profile in the main survey line direction in the offset distance domain. Well A is a deviated well passing through the seismic profile.

[0027] Figure 3 Figure 2 Formation dip angle profile corresponding to the seismic profile.

[0028] Figure 4 Seismic imaging profile generated by the conventional migration method.

[0029] Figure 5 Seismic imaging profile obtained after adopting the method of the present invention. Detailed Embodiment:

[0030] The following further describes the present invention with reference to the drawings:

[0031] Taking a certain seismic data in an eastern oilfield as an example, this dip angle domain imaging method specifically includes the following steps:

[0032] 1. Perform conventional noise suppression processing on the prestack seismic data. The data sampling interval is 2 ms, the recording duration of the seismic signal is 5000 ms, the CDP interval is 25 m, the minimum offset distance is 100 m, the maximum offset distance is 5400 m, and the offset distance interval is 50 m.

[0033] Step 1. Prepare a post-stack migration seismic data volume generated by an offset distance domain imaging method. This data volume has 500 main survey lines and 1000 connecting lines. There are 1000 CDP points (Common Depth Point) on each main survey line and 500 CDP points on each connecting survey line. The time length of each seismic trace is 3.5 s. Let this data volume be displayed in the time domain, perform low-pass filtering on it, retain the signals within the main frequency, and remove the high-frequency part with a relatively low signal-to-noise ratio.

[0034] Step 2: Calculate the true formation dip angle for all imaging points on each main survey line. The principle is as follows Figure 1 shown. When the coherence value is the largest, the corresponding dip angle is the formation dip angle. The main survey line seismic profile is as shown in Figure 3 . Figure 3 The right scale represents the relationship between the seismic profile grayscale and the seismic replication.

[0035] Method for calculating the true formation dip angle X corresponding to the imaging points on the main survey line: For any main survey line e, for the f-th CDP on it, at the imaging point at the time-depth t, where e is a positive integer not greater than M, f is a positive integer not greater than N, and t is a positive number not greater than T, scan the coherence values corresponding to several dip angles between the minimum formation dip angle and the maximum formation dip angle in the main survey line direction, and fit the coherence values corresponding to these dip angles using the least squares method. φ represents the magnitude of the main survey line formation dip angle, and C X (e, f, t, φ) represents the coherence value magnitude. The fitting curve is in the form of a quadratic curve, and the specific expression is:

[0036] C X (e, f, t, φ) = α3 + α2φ + α1φ 2

[0037] α1, α2, α3 are fitting coefficients. Then, find the derivative of the curve C X (e, f, t, φ) with respect to φ. When , the corresponding φ is the true formation dip angle X in the main survey line direction at this time-depth of the imaging point.

[0038] Step 3: Calculate the true formation dip angle corresponding to all imaging points on each connecting survey line.

[0039] Method for calculating the true formation dip angle Y corresponding to the imaging points on the connecting survey line: For any connecting survey line p, for the q-th CDP on it, at the imaging point at the time-depth t, where p is a positive integer not greater than N, q is a positive integer not greater than M, and t is a positive number not greater than T, scan the coherence values corresponding to several dip angles between the minimum formation dip angle and the maximum formation dip angle in the connecting survey line direction, and fit the coherence values corresponding to these dip angles using the least squares method. η represents the magnitude of the connecting survey line formation dip angle, and C Y (p, q, t, η) represents the coherence value magnitude. The fitting curve is in the form of a quadratic curve, and the specific expression is:

[0040] C Y (p, q, t, η) = β3 + β2η + β1η 2

[0041] β1, β2, β3 are fitting coefficients. Then, find the derivative of the curve C YThe derivative of (p, q, t, η) with respect to η, when the corresponding η is the true formation dip angle Y of the imaging point in the direction of the connecting survey line at this time depth.

[0042] Step 4: During migration imaging, for each input prestack seismic data trace, calculate the formation dip angles of each imaging point in the main survey line and connecting survey line directions based on the spatial coordinates of the shot point, receiver point, and imaging point, denoted as a x and a y , respectively, and compare them with the previously calculated formation dip angles of the main survey line and connecting survey line of this imaging point. If both a x ≤ X and a y ≤ Y are satisfied, then continue to calculate the travel time and amplitude of this imaging point to complete the imaging; otherwise, repeat this step for the next imaging point.

[0043] The calculation of the formation dip angle of the imaging point in the main survey line direction and the formation dip angle of the imaging point in the connecting survey line direction is achieved as follows: For each input prestack seismic data trace, define the horizontal coordinate of the excitation point as s, the horizontal coordinate of the receiving point as g, the azimuth angle as θ, the coordinates of the imaging point as (x, y, τ), and the migration velocity of the imaging point as vel rms ;

[0044] Define the following variables: u1 = s - x, u2 = s + g - 2x, and calculate the distance variables w1 = u1 cosθ; w2 = u1u2 + 2(vel rms ) 2 ; w3 = u2 cosθ; x is the abscissa of the X-axis, then then the formation dip angle a x of the imaging point in the main survey line direction is arctan[(u1 + w5 cosθ) / (vel rms τ)]; where: u1, u2, w1, w2, w3, w4, w5 are all intermediate variables with no real meaning;

[0045] Define the following variables: v1 = g - y, v2 = s + g - 2y, and calculate the distance variables r1 = v1 cosθ; r2 = v1v2 + 2(vel rms ) 2 ; r3 = v2 cosθ;

[0046] y is the abscissa of the Y-axis, then then the formation dip angle a y of the imaging point in the connecting survey line direction is arctan[(v1 + r5 cosθ) / (vel rms τ)]; where: v1, v2, r1, r2, r3, r4, r5 are all intermediate variables with no real meaning.

[0047] Step Five: Complete the calculation of all imaging points to obtain the final seismic imaging profile.

[0048] Figure 1 It is a schematic diagram of the scanning dip angle and coherence of imaging points in the main survey line or connecting survey line direction. When the coherence value is the largest, the corresponding dip angle is the dip angle of the formation. Figure 2 It is a post-stack migration seismic data profile in the main survey line direction in the offset domain. Well A is a deviated well passing through the seismic profile. Figure 3 It is Figure 2 The formation dip angle profile corresponding to the seismic profile. Figure 4 It is a seismic imaging profile generated by the conventional migration method. Figure 5 It is the seismic imaging profile obtained after adopting the method of the present invention. It can be seen that Figure 4 For the conventional seismic imaging profile shown, due to the adoption of a unified imaging aperture, the imaging accuracy is insufficient and the signal-to-noise ratio of the seismic profile is relatively low. Figure 5 By using the formation dip angle generated by the method herein as the migration parameter, the obtained seismic imaging profile has a high signal-to-noise ratio and the seismic imaging quality is improved to a certain extent.

Claims

1. An inclination domain seismic imaging method, characterized in that The method includes the following steps: Step 1: Prepare a post-stack migrated seismic data volume generated by an offset-domain imaging method. The data volume has M main survey lines and N connecting survey lines. There are N CDP points on each main survey line and M CDP points on each connecting survey line. The time length of each seismic trace is T. Display the data volume in the time domain, perform low-pass filtering on it, retain the signals within the main frequency, and remove the high-frequency part with relatively low signal-to-noise ratio; Step 2: Calculate the true formation dip angle X corresponding to all imaging points on the main survey lines; Step 3: Calculate the true formation dip angle Y corresponding to all imaging points on the connecting survey lines; Step 4: During migration imaging, for each input prestack seismic data trace, calculate the formation dip angle of each imaging point in the main survey line direction based on the spatial coordinates of the shot point, receiver point, and imaging point, denoted as a x , calculate the formation dip angle of each imaging point in the connecting survey line direction, denoted as a y , then compare it with the true formation dip angle X of the main survey line of this imaging point obtained in Step 2 and the true formation dip angle Y of the connecting survey line of this imaging point obtained in Step 3. If both a x <= X and a y <= Y are satisfied, then continue to calculate the travel time and amplitude of this imaging point to complete the imaging; otherwise, repeat this step for the next imaging point Step 5: Complete the calculation of all imaging points to obtain the final seismic imaging profile.

2. The dip-domain seismic imaging method according to claim 1, wherein: The method for calculating the true formation dip angle X corresponding to the imaging point of the main survey line in step 2: For any main survey line e, for the f-th CDP on it, at the imaging point with time-depth t, where e is a positive integer not greater than M, f is a positive integer not greater than N, and t is a positive number not greater than T, scan the coherence values corresponding to several dip angles between the minimum formation dip angle and the maximum formation dip angle in the main survey line direction, and use the least squares method to fit the coherence values corresponding to these dip angle values. φ represents the magnitude of the main survey line formation dip angle, and C X (e, f, t, φ) represents the magnitude of the coherence value, and the fitting curve is in the form of a quadratic curve. The specific expression is: C X (e, f, t, φ) = α3 + α2φ + α1φ 2 α1, α2, and α3 are fitting coefficients, and then the curve C is obtained. X The derivative of (e, f, t, φ) with respect to φ. When the corresponding φ is the true formation dip angle X of the imaging point in the main survey line direction at this time depth.

3. The dip-domain seismic imaging method according to claim 2, wherein: The method for calculating the true formation dip angle Y corresponding to the imaging point of the connecting survey line in step three: For any connecting survey line p, for the q-th CDP on it, at the imaging point with time depth t, where p is a positive integer not greater than N, q is a positive integer not greater than M, and t is a positive number not greater than T, scan the coherence values corresponding to several dip angles between the minimum formation dip angle and the maximum formation dip angle in the connecting survey line direction, and fit the coherence values corresponding to these dip angle values by the least squares method. η represents the formation dip angle size of the connecting survey line, and C Y (p, q, t, η) represents the coherence value size, and the fitting curve is in the form of a quadratic curve. The specific expression is: C Y (p, q, t, η) = β3 + β2η + β1η 2 β1, β2, and β3 are fitting coefficients, and then the curve C is obtained. Y The derivative of (p, q, t, η) with respect to η. When the corresponding η is the true formation dip Y of the imaging point in the direction of the connecting survey line at this time depth.

4. The dip-domain seismic imaging method according to claim 3, characterized in that: In Step 4, the formation dip angle of the imaging point in the main survey line direction and the formation dip angle of the imaging point in the connecting survey line direction are realized as follows: For each input prestack seismic data trace, define the horizontal coordinate of the shot point as s, the horizontal coordinate of the receiver point as g, the azimuth angle as θ, the imaging point coordinates as (x, y, τ), and the migration velocity of the imaging point as vel rms ; Define the following variables: u1 = s - x, u2 = s + g - 2x, and calculate the distance variable w1 = u1 cosθ; w2 = u1u2 + 2(vel rms ) 2 ; w3 = u2 cosθ; If x is the abscissa of the X-axis, then then the formation dip angle α of the imaging point in the main survey line direction x is arctan[(u1 + w5cosθ) / (vel rms τ)]; where: u1, u2, w1, w2, w3, w4, w5 are all intermediate variables with no real meaning; Define the following variables, v1 = g - y, v2 = s + g - 2y, and calculate the distance variables r1 = v1 cosθ; r2 = v1v2 + 2(vel rms ) 2 ; r3 = v2 cosθ; If y is the abscissa of the Y-axis, then the formation dip angle α of the imaging point in the direction of the connecting survey line y is arctan[(v1 + r5cosθ) / (vel rms τ)]; where: v1, v2, r1, r2, r3, r4, r5 are all intermediate variables and have no real meaning.

Images