CN116243378B - A Shallow Velocity Modeling Method Based on the True Earth Surface - Google Patents

Abstract

This invention discloses a shallow velocity modeling method based on the true Earth surface, including steps such as obtaining the marker layer time plane map T _cmp starting from the CMP surface, obtaining the shallow marker layer thickness D _cmp-d starting from the offset surface, obtaining the shallow marker layer time T _cmp-d starting from the offset surface, obtaining the shallow marker layer velocity Vi starting from the offset surface, and establishing a shallow velocity model _. This invention achieves multi-dimensional constraints of points, lines, and surfaces by combining information from micrologging, drilling, and seismic data, which can solve the velocity constraint and smoothing error problems of conventional methods, improve the accuracy of the shallow velocity model, and thus improve the overall depth migration velocity model accuracy, ensuring the accuracy of depth migration imaging. This invention is applicable to shallow velocity modeling methods on the true Earth surface, and this method is used in the pre-stack depth migration processing of seismic data.

Description

Shallow speed modeling method based on true earth surface

Technical Field

The invention belongs to the technical field of petroleum and natural gas seismic exploration, relates to pre-stack deep bias processing of seismic data, and particularly relates to a shallow velocity modeling method based on true earth surface.

Background

Along with the high-speed development of national economy and the great demand for oil and gas resources, it is imperative to increase the strength of domestic oil and gas exploration. The detection area with geological conditions of the surface and underground double complex structures gradually becomes an important successor field of oil and gas exploration, the surface fluctuation and underground deformation of the double complex structure area are severe, so that the seismic wave propagation is severely distorted, compared with the time migration processing, the depth migration processing can better solve the complex wave field effect caused by the abnormal change of local speed, and only the depth migration using an accurate speed model can obtain the image optimally overlapped and positioned at the correct depth (from the depth migration of the complex structure, chr istof Stork and Advance Geophysical), so that the precision of the speed model is a key link for improving the imaging quality of the depth migration.

The influence analysis of the velocity model error on the pre-stack depth migration imaging is carried out, the influence of the shallow velocity error on the accurate imaging of the depth domain is larger than that of the middle-deep velocity error, and the method is mainly characterized in that 1, the velocity error of the shallow surface layer has larger influence on the middle-deep imaging range, the errors can be accumulated and irreversible, and 2, the velocity error of the shallow layer can cause poorer middle-deep imaging quality, so that how to establish an accurate shallow velocity model is one of key problems to be solved in the depth migration processing.

In the conventional processing process, the method for obtaining the shallow velocity model mainly comprises the following steps of 1, a micro-logging method, 2, a small refraction method, 3, a surface wave method, 4, a chromatographic inversion method, 5, a full waveform inversion method and the like. In addition, through research, chinese patent CN106249290B discloses a method for establishing a surface layer velocity structure model by using multi-level data fusion, which calculates multiple sets of shallow layer velocity models by using data with different scales, and then fuses the multiple sets of data according to an inverse distance weighting algorithm to form a new shallow layer velocity model. And splicing the near-surface velocity model obtained by the method with the near-surface subsurface velocity model obtained by utilizing prestack time migration processing to obtain a full-depth velocity model. The method has the following two problems that 1, in the establishment of a shallow surface velocity model, constraint is usually carried out by taking micro logging data as a basis, but the micro logging quantity is usually small, the planar trend is difficult to accurately control, and 2, before the depth migration treatment is carried out, the spliced full depth velocity model is required to be smoothed for use. Because the thickness and the speed value of the shallow surface layer speed model are smaller, the error between the smoothed speed and the actual speed is larger, and the error is difficult to eliminate, thereby seriously affecting the accuracy of the imaging of the underlying stratum.

Disclosure of Invention

In order to solve the defects in the prior art, the invention aims to provide a shallow speed modeling method based on a true earth surface, so as to achieve the effect of multidimensional constraint of points, lines and surfaces, improve the precision of a shallow speed model, further improve the precision of an integral depth migration speed model and ensure the imaging precision of depth migration.

In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:

a shallow speed modeling method based on true earth surface comprises the following steps in sequence:

s1, obtaining a time plane diagram T of a mark layer calculated by a cmp plane _cmp

Determining a shallow low-speed conglomerate mark layer and a shallow high-speed conglomerate mark layer by using time domain seismic data and drilled data, finely explaining the mark layer near the surface of the sleeve on a seismic section, obtaining a mark layer time plane graph T ₀ through gridding, and obtaining a mark layer time plane graph T _cmp calculated by a cmp surface according to T ₀;

S2, calculating the thickness D of the shallow marker layer calculated by the offset surface _cmp-d

S21, calculating the layer-by-layer speed of the mark by using a T _cmp and an earthquake velocity spectrum, and carrying out constraint correction on the change of the speed by using drilling and micro-logging data to obtain the layer-by-layer speed V _iq of the mark;

S22, performing time-depth conversion by using T _cmp and a layer speed V _iq to obtain a marking layer thickness D _cmp-d;

S3, calculating shallow layer mark layer time T calculated by offset surface _cmp-d

S31, obtaining filling quantity delta T ₀ from a horizontal reference surface to an offset surface by using predictable offset surface data, filling speed and horizontal reference surface data;

S32, obtaining static correction stripping quantity delta T _0b by using predictable static correction data and delta T ₀;

S33, obtaining the time T _cmp-d of the offset surface through DeltaT _0b and T _cmp;

S4, calculating the shallow marker layer speed V of the offset surface _i

Using D _cmp-d and T _cmp-d to obtain the sign layer speed V _i calculated by the offset plane;

s5, establishing a shallow layer speed model by using the time T _cmp calculated by the cmp surface and the marker layer speed V _i, and fusing the shallow layer speed model with a middle-deep layer speed model established by combining earthquake geology to obtain a full-depth speed model.

As a limitation of the present invention, in step S1, the calculation formula of the time plan view T _cmp of the marker layer calculated on the cmp plane is as follows:

T _cmp＝T₀ -cmp' - - -type (i)

In the formula (i), cmp is a low-frequency static correction amount in seismic data processing, T ₀ is a marker layer time plane diagram obtained by gridding, and T _cmp is a marker layer time plane diagram calculated from a cmp surface.

As another limitation of the present invention, in step S22, the calculation formula of the thickness D _cmp-d of the marker layer is:

D _cmp-d＝T_cmp*V_iq/2000 @ D @ -formula (ii)

In formula (ii), T _cmp is the time of the marker layer calculated on the cmp side, and V _iq is the speed of the marker layer calculated on the cmp side.

As a third limitation of the present invention, in step S31, the calculation formula of the filling amount Δt ₀ is:

DeltaT ₀＝(H_p-H_d)/V_c x 2000-a step of: - - -type (iii)

In the formula (iii), H _p is a horizontal reference plane elevation, H _d is an offset plane elevation, and V _c is a filling rate.

As a fourth limitation of the present invention, in step S32, the calculation formula of the static correction peeling amount Δt _0b is:

DeltaT _0b＝cmp-△T₀' -a step of: - -type (iv)

In the formula (iv), Δt _0b is the static correction peeling amount, cmp is static correction data provided by the process, and Δt ₀ is the filling amount between the horizontal reference surface and the offset surface obtained in step S31.

As a fifth limitation of the present invention, in step S33, the calculation formula of the time T _cmp-d from the offset plane is:

t _cmp-d＝△T_0b+T_cmp - -type (v)

In the formula (v), Δt _0b is the static correction peeling amount, and T _cmp is the marker layer time from the cmp surface.

As a sixth limitation of the present invention, in step S4, the calculation formula of the sign layer speed V _i calculated on the offset plane is:

V _i＝D_cmp-d/T_cmp-d x 2000' - - -type (vi)

In the formula (vi), D _cmp-d is the shallow marker layer thickness from the offset plane, and T _cmp-d is the time from the offset plane.

The technical scheme of the invention is characterized in that the method for establishing the shallow layer speed model from the offset surface comprises the following steps:

Through comprehensive research of multiple information, the shallow layer mark is precisely interpreted and accurately calculated and restrained; calculating the stripping amount of static correction and the time of a mark layer calculated by the offset surface by processing low-frequency static correction data, offset surface data and filling speed;

the invention relates to a method for improving depth migration imaging precision by utilizing fine speed modeling so as to realize construction form details, which provides reasonable and reliable basis for well position deployment, and the related thought and implementation process specifically comprises the following aspects:

① Based on the processed low-frequency static correction data, the offset surface data and the filling rate, the static correction stripping amount is obtained by using the processed low-frequency static correction data and the calculated offset surface static correction data.

② And calculating the mark layer time calculated by the offset surface by using the static correction stripping amount and the shallow mark layer time data.

③ And (3) calculating the speed of the shallow marker layer by correcting the thickness data calculated by the offset surface and the shallow marker layer time calculated by the offset surface.

By adopting the technical scheme, compared with the prior art, the invention has the following beneficial effects:

according to the shallow speed modeling method based on the true earth surface, the bottom interface is extended downwards, multi-dimensional constraint of points, lines and planes is realized through the mode of multi-information combination of micro-logging, drilling, earthquake and the like, the problems of speed constraint and errors after smoothing in the conventional method can be solved, the precision of a shallow speed model is improved, the precision of an integral depth migration speed model is further improved, and the imaging precision of depth migration is guaranteed.

The method is suitable for a shallow velocity modeling method of a true earth surface, and the method is used for a pre-stack depth deviation processing process of seismic data.

Drawings

The invention will be described in more detail below with reference to the accompanying drawings and specific examples.

FIG. 1 is a schematic view of the low velocity conglomerate bottom interface seismic reflection axis;

FIG. 2 is a time plan view of the low-speed conglomerate bottom interface time and cmp surface;

FIG. 3 is a schematic diagram of acoustic data for drilling and micro-logging speed data (G is drilling, S is deep micro-logging);

FIG. 4 is a layer-by-layer velocity plan view of a marker;

FIG. 5 is a plan view of a marker layer thickness;

FIG. 6 is a plan view of the fill level from the horizontal reference plane to the offset plane;

FIG. 7 is a static correction data plan;

FIG. 8 static corrects the amount of peel;

FIG. 9 is a time plan view of the offset surface starting with the logo layer;

FIG. 10 is a plan view of the layer velocity of the sign from the offset surface;

FIG. 11 is a cross-sectional view showing the imaging effect before and after the implementation of the method according to the embodiment of the present invention.

Detailed Description

The following description of the preferred embodiments of the present invention is provided in connection with the accompanying drawings, and it is to be understood that the preferred embodiments described herein are for the purpose of illustration and understanding only and are not intended to limit the invention.

Embodiment is a shallow speed modeling method based on true earth surface

The embodiment is a shallow layer speed modeling method based on true earth surface in a high spring area of a Pascal basin, the earth surface of the test area selected in the embodiment develops huge thick gravels, farmlands, loess and the like, the thickness and the speed of the shallow layer gravels are changed severely, and the accurate establishment of a shallow layer speed model is extremely difficult;

According to the actual conditions of a work area, 3 deep micro-logs with the depth of 450m are respectively deployed in a gravel gobi area in the south of the work area, a farmland area in the north and a transition zone, shallow surface speed changes are implemented, and drilling by the deep micro-logs reveals that 1, low-speed conglomerates and high-speed conglomerate strata exist in the south and the middle of the work area, and surface loess and normal strata develop in the farmland area in the north;

Based on the knowledge, the shallow speed modeling is performed according to the following steps:

s1, obtaining a time plane diagram T of a mark layer calculated by a cmp plane _cmp

The bottom interface (figure 1) of the low-speed conglomerate is taken as a shallow layer mark layer, a corresponding seismic reflection axis is determined through fine well seismic calibration, fine explanation is carried out, gridding is carried out, a low-speed conglomerate bottom interface time plane diagram T ₀ (figure 2 a) is obtained, the time plane diagram T ₀ is corrected to the cmp surface starting time, namely the mark layer time plane diagram T _cmp (figure 2 b) starting from the cmp surface,

T_cmp＝T₀-cmp

Wherein cmp is a low-frequency static correction amount in seismic data processing, T ₀ is a marker layer time plane diagram obtained by gridding, and T _cmp is a marker layer time plane diagram calculated by cmp surface;

S2, calculating the thickness D of the shallow marker layer calculated by the offset surface _cmp-d

S21, calculating the low-speed conglomerate layer speed by using a low-speed conglomerate bottom interface time plane diagram T _cmp and seismic speed spectrum data obtained in a time domain seismic data processing process, correcting the layer speed by using drilling sound wave data obtained in a well logging process and micro-logging speed data (figure 3) obtained in a collecting process, and obtaining a mark layer-by-layer speed V _iq (figure 4), wherein the calculation of V _iq is realized in the existing software, and the basic principle is a known dix formula:

Wherein V _R,i is root mean square velocity of the 1 st to i th layers, and t _0,i is self-excitation self-time of the 1 st to i th layers;

S22, obtaining a low-speed conglomerate bottom interface thickness map through time-depth conversion, correcting the thickness D _cmp-d (figure 5) by using drilling layering data obtained in the well logging process and micro well logging thickness data obtained in the acquisition process, wherein the time-depth conversion process is that,

D_cmp-d＝T_cmp*V_iq/2000

Wherein T _cmp is the time of the marker layer calculated on the cmp surface, and V _iq is the speed of the marker layer calculated on the cmp surface;

S3, calculating shallow layer mark layer time T calculated by offset surface _cmp-d

S31, calculating filling quantity DeltaT ₀ (figure 6) from the horizontal reference surface to the offset surface by using offset surface elevation data (800 m-160 m) provided in the depth domain seismic data processing process and filling speed (2500 m/s) and horizontal reference surface data (2000 m) obtained in the time domain seismic data processing process,

△T₀＝(H_p-H_d)/V_c*2000

Wherein H _p is the horizontal reference plane elevation, H _d is the offset plane elevation, and V _c is the filling rate;

S32, subtracting the static correction data (figure 7) obtained in the time domain seismic data processing process from the DeltaT ₀ to obtain static correction stripping quantity DeltaT _0b (figure 8), wherein,

△T_0b＝cmp-△T₀

Wherein Δt _0b is the static correction stripping amount, cmp is the static correction data provided by the process, and Δt ₀ is the filling amount from the horizontal reference surface to the offset surface obtained in step S31;

S33. adding the corrected lift-off quantity Δt _0b to the low-speed conglomerate bottom interface time T _cmp, to obtain a time T _cmp-d (fig. 9) from the offset surface determined by the depth offset,

T_cmp-d＝△T_0b+T_cmp

Wherein DeltaT _0b is static correction stripping amount, and T _cmp is mark layer time calculated on a cmp surface;

S4, calculating the shallow marker layer speed V of the offset surface _i

The corrected thickness D _cmp-d is divided by the time T _cmp-d from the offset surface, and the low-velocity conglomerate layer velocity V _i (fig. 10) from the offset surface is obtained, wherein,

V_i＝D_cmp-d/T_cmp-d*2000

Wherein D _cmp-d is the thickness of the shallow marker layer calculated on the offset surface, and T _cmp-d is the time calculated on the offset surface;

S5, establishing a shallow layer speed model by using the time T _cmp calculated by the cmp surface and the marker layer speed V _i, and fusing the shallow layer speed model with a middle-deep layer speed model established by combining earthquake geology to obtain a full-depth speed model;

The pre-stack depth migration data after speed modeling by the method has obviously improved imaging quality compared with the imaging quality before the implementation of the method, and the imaging effect comparison section results before and after the implementation of the method are shown in FIG. 11, wherein FIG. 11a is a section before the implementation of the method, and FIG. 11b is a section after the implementation of the method;

As can be seen from fig. 11, the imaging effect in shallow, medium and deep is obviously improved after the implementation of the method;

After the main purpose layer (K) is high in matching degree with drilling depth, the drilling layering error of the well 1 well is 12m, the newly deployed drilling wells 2,3 and 4 wells are comprehensively calibrated, the prestack depth migration data and the drilling layering error of the new drilling well are within +/-50 m, the relative error is less than 0.8%, and specific data are shown in the table 1;

TABLE 1 comparison of measured and imaged burial depths for drilling in work area and error analysis

As can be seen from table 1, the method can effectively improve imaging quality and precision of prestack depth migration;

It should be noted that the foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but the present invention is described in detail with reference to the foregoing embodiment, and it will be apparent to those skilled in the art that modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for some of the technical features thereof. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (7)

1. The shallow speed modeling method based on the true earth surface is characterized by comprising the following steps of:

s1, obtaining a time plane diagram T of a mark layer calculated by a cmp plane _cmp

Determining a shallow low-speed conglomerate mark layer and a shallow high-speed conglomerate mark layer by using time domain seismic data and drilled data, finely explaining the mark layer near the surface of the sleeve on a seismic section, obtaining a mark layer time plane graph T ₀ through gridding, and obtaining a mark layer time plane graph T _cmp calculated by a cmp surface according to T ₀;

S2, calculating the thickness D of the shallow marker layer calculated by the offset surface _cmp-d

S21, calculating the layer-by-layer speed of the mark by using a T _cmp and an earthquake velocity spectrum, and carrying out constraint correction on the change of the speed by using drilling and micro-logging data to obtain the layer-by-layer speed V _iq of the mark;

S22, performing time-depth conversion by using T _cmp and a layer speed V _iq to obtain a marking layer thickness D _cmp-d;

S3, calculating shallow layer mark layer time T calculated by offset surface _cmp-d

S31, obtaining filling quantity delta T ₀ from a horizontal reference surface to an offset surface by using predictable offset surface data, filling speed and horizontal reference surface data;

S32, obtaining static correction stripping quantity delta T _0b by using predictable static correction data and delta T ₀;

S33, obtaining the time T _cmp-d of the offset surface through DeltaT _0b and T _cmp;

S4, calculating the shallow marker layer speed V of the offset surface _i

Using D _cmp-d and T _cmp-d to obtain the sign layer speed V _i calculated by the offset plane;

s5, establishing a shallow layer speed model by using the time T _cmp calculated by the cmp surface and the marker layer speed V _i, and fusing the shallow layer speed model with a middle-deep layer speed model established by combining earthquake geology to obtain a full-depth speed model.

2. The method for modeling shallow velocity based on true surface according to claim 1, wherein in step S1, the calculation formula of the time plane map T _cmp of the mark layer calculated on the cmp surface is:

T _cmp＝T₀ -cmp' - - -type (i)

In the formula (i), cmp is a low-frequency static correction amount in seismic data processing, T ₀ is a marker layer time plane diagram obtained by gridding, and T _cmp is a marker layer time plane diagram calculated from a cmp surface.

3. The method for modeling shallow velocity based on true surface as defined in claim 1, wherein in step S22, the calculation formula of the marker layer thickness D _cmp-d is:

D _cmp-d＝T_cmp*V_iq/2000 @ D @ -formula (ii)

In formula (ii), T _cmp is the time of the marker layer calculated on the cmp side, and V _iq is the speed of the marker layer calculated on the cmp side.

4. The method for modeling shallow velocity on a true surface according to claim 1, wherein in step S31, the calculation formula of the filling quantity DeltaT ₀ is:

DeltaT ₀＝(H_p-H_d)/V_c x 2000-a step of: - - -type (iii)

In the formula (iii), H _p is a horizontal reference plane elevation, H _d is an offset plane elevation, and V _c is a filling rate.

5. The method for modeling shallow velocity on a true surface according to claim 1, wherein in step S32, the calculation formula of the static correction stripping amount DeltaT _0b is:

DeltaT _0b＝cmp-△T₀' -a step of: - -type (iv)

In the formula (iv), Δt _0b is the static correction peeling amount, cmp is static correction data provided by the process, and Δt ₀ is the filling amount between the horizontal reference surface and the offset surface obtained in step S31.

6. The method for modeling shallow velocity on a true surface according to claim 1, wherein in step S33, the calculation formula of the time T _cmp-d from the offset surface is:

t _cmp-d＝△T_0b+T_cmp - -type (v)

In the formula (v), Δt _0b is the static correction peeling amount, and T _cmp is the marker layer time from the cmp surface.

7. The method for modeling shallow velocity on a true surface according to claim 1, wherein in step S4, the calculation formula of the marker layer velocity V _i calculated by the offset surface is:

V _i＝D_cmp-d/T_cmp-d x 2000' - - -type (vi)

In the formula (vi), D _cmp-d is the shallow marker layer thickness from the offset plane, and T _cmp-d is the time from the offset plane.