CN117930359A - Method for correcting fault shadows in post-stack seismic data by establishing high-precision velocity fields - Google Patents
Method for correcting fault shadows in post-stack seismic data by establishing high-precision velocity fields Download PDFInfo
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Abstract
The invention relates to a method for correcting fault shadows in post-stack seismic data by establishing a high-precision velocity field, which comprises the following steps: manufacturing and calibrating the synthetic seismic records of all actual wells in the research area, and performing horizon interpretation according to the calibration result; determining the range of a fault shadow zone according to the seismic identification characteristics of the fault shadow; supplementing a virtual well in an area with the two sides not exceeding 200 meters inside and outside the boundary of the fault shadow area; making and calibrating the synthetic seismic record of the virtual well by means of the adjacent actual well data; taking the time domain interpretation horizon as space constraint, and obtaining a high-precision speed field with virtual well participation by adopting a well interpolation method; and performing time-depth conversion on the time-domain seismic data by using the high-precision velocity field to obtain accurate depth-domain seismic data. The invention adopts a mode of supplementing a virtual well to obtain a high-precision velocity field, and utilizes the velocity field to perform time-depth conversion on post-stack seismic data, so that an accurate depth-domain seismic data body and interpretation results can be obtained.
Description
Technical Field
The invention relates to the field of geophysical prospecting of petroleum and natural gas, in particular to a method for correcting fault shadows in post-stack seismic data by establishing a high-precision velocity field, which is applied to guiding marine prospecting and development.
Background
The seismic data is a data body formed by the fact that seismic waves excited by the earth surface propagate downwards, are reflected to the earth surface after encountering an underground geologic body interface and are recorded by a receiver, and the measurement unit is double-pass reflection time. In general, the stratum speed is relatively uniform, the time domain of the geologic body is approximately equivalent to the structural form of the depth domain, and the interpretation result of the time domain seismic data can reflect the structural form of the depth domain. The seismic data can be used for revealing the spread information of geologic bodies such as underground stratum, faults and the like through interpretation work.
If a velocity anomaly layer (such as thick mudstone, magma rock and the like) exists in the stratum and a large break fault is generated by breaking the stratum, the thickness of the velocity anomaly layer is suddenly changed, and the average velocity of the stratum is suddenly changed. Due to the variation of the average velocity, the time for the surface-excited seismic waves to reach a certain depth of formation will also vary during seismic data acquisition. At this time, the geologic body morphology (time domain morphology) revealed by the seismic data will not be identical to the true morphology (depth domain morphology). This phenomenon is caused by the fault fracture velocity anomaly layer, and is characterized in the seismic data by the occurrence of "pull-up and pull-down" of the same phase axis of the seismic in the triangular area below the fault, and the phenomenon is called "fault shadow". Sun Weizhao et al in forward modeling, recognition and correction of tomosynthesis: the formation principle of 'fault shadow' is researched by taking Nile Termit basin as an example, and the 'fault shadow' phenomenon is pointed out to be commonly existed in various oil-gas-containing basins, and is easily interpreted as a main fault associated minor fault in the interpretation process or interpreted as a anticline structure to deploy drilling, so that the accuracy of trap evaluation and well position deployment is seriously influenced. In recent years, a large amount of oil and gas resources are found in the ocean field in China, but because of high ocean exploration and development risks, the accuracy requirement on interpretation results of seismic data is higher, and accurate identification is particularly important to correct the fault shadow phenomenon.
The former considers that prestack depth migration imaging techniques can fundamentally suppress the "tomosynthesis" phenomenon. Forward modeling, recognition and correction of fault shadows as disclosed by Sun Weizhao et al in geophysical progress 2022: taking Nile Termit basin as an example ", it is pointed out that in areas with high precision velocity modeling conditions, developing prestack depth migration is the fundamental solution to eliminate" fault shadows ". "application research of 3D velocity modeling method based on fault and horizon constraint in eliminating fault shadows" by Peng Hailong et al, published in geophysical progress 2017, points out that the velocity field precision can be improved by utilizing horizons and faults to constrain the chromatographic velocity modeling. "Daqing chlamydospore field fault shadow seismic forward modeling and correction method" of Jiang Yan et al was disclosed in 2019 of petroleum geophysical exploration, indicating that a high-precision three-dimensional air-speed field can be established to correct "fault shadows" by means of well speed correction.
Although the former performs a series of researches on the prestack depth migration imaging technology, the actual work area is constrained by the well pattern density, a high-precision speed field is difficult to obtain, and a fault shadow phenomenon still exists in post-stack seismic data. And Jiang Yan proposes that the well speed correction mode is only suitable for a dense well pattern area, the established speed field for the dense well pattern area is not accurate enough, and a fault shadow correction method with higher precision for post-stack seismic data is to be proposed.
Disclosure of Invention
The invention aims to provide a method for correcting fault shadows in post-stack seismic data by establishing a high-precision velocity field, which is used for obtaining the true structural form of a stratum under a fault.
The technical scheme adopted for solving the technical problems is as follows: the method for correcting fault shadows in post-stack seismic data by establishing a high-precision velocity field comprises the following steps:
step one, manufacturing and calibrating synthetic seismic records of all actual wells in a research area, and performing horizon interpretation according to calibration results;
Step two, determining the range of a fault shadow zone according to the earthquake identification characteristics of the fault shadow; the seismic identification features of fault shadows include:
In the time domain seismic data, a speed abnormal layer exists on an overlying stratum and is broken by faults; a stratum earthquake event under the fault is locally pulled up and pulled down; vertical dislocation or distortion phenomenon occurs on stratum earthquake phase axis below the fault; on the plane of the coherence attribute, a false fault which is parallel to the main fault appears on the fault lower disc;
Supplementing a virtual well in an area with the two sides not exceeding 200 meters inside and outside the boundary of the fault shadow area;
step four, manufacturing and calibrating the synthetic seismic record of the virtual well by means of the adjacent actual well data;
Step five, taking the speed of each well as a benchmark, taking a time domain interpretation horizon as a space constraint, and obtaining a high-precision speed field with virtual well participation by adopting a well interpolation method;
and step six, performing time-depth conversion on the time-domain seismic data by using the high-precision velocity field to obtain accurate depth-domain seismic data.
The method for manufacturing and calibrating the synthetic seismic record in the step one of the scheme specifically comprises the following steps:
and (3) acquiring seismic data and well curve data of a research area, utilizing a sound wave time difference curve and a density curve to manufacture synthetic seismic records of all actual wells of the research area, matching and calibrating according to the similarity of the synthetic seismic records and the actual seismic records beside the well, ensuring that the well earthquake achieves the best matching effect, establishing a time-depth relation of each actual well, and determining the corresponding positions of geological layers on a time domain seismic section.
The method for supplementing the virtual well in the scheme step three comprises the following steps:
(1) Well position setting: establishing a virtual well at the positions of the inner side and the outer side of the boundary of the fault shadow zone and lacking well control;
(2) Curve data for virtual wells: and adopting the acoustic time difference curve and the density curve of the adjacent well as the curve data of the virtual well.
The scheme comprises the following steps:
When the virtual well synthetic seismic record is manufactured, the initial speed is consistent with that of the adjacent actual well, and the acoustic time difference curve and the density curve also adopt the adjacent actual well curve; during calibration, matching the synthetic seismic record of the virtual well with the actual seismic record beside the virtual well; for a virtual well in a fault shadow region, the single well speed obtained after matching is an abnormal speed in the fault shadow region; for the virtual wells outside the fault shadow area, the single well speed obtained after matching is the normal speed outside the fault shadow area; this results in a single well velocity at each virtual well that matches the actual velocity.
Advantageous effects
1. The invention adopts a mode of supplementing the virtual well to obtain a high-precision velocity field, and the velocity field is utilized to carry out time-depth conversion on the post-stack seismic data, so that an accurate depth domain seismic data body and interpretation results can be obtained.
2. The invention corrects the shadow of the post-stack seismic data interrupt layer by establishing the high-precision velocity field, improves the accuracy of seismic data interpretation, and is suitable for seismic data interpretation work in the field of marine and land petroleum and natural gas exploration.
Drawings
FIG. 1 is a well A synthetic seismic record calibration diagram;
FIG. 2 is an example study area "tomosynthesis" impact range;
FIG. 3 is a position diagram of a virtual well replenishment;
FIG. 4 is a high precision velocity field profile;
FIG. 5 is a depth domain profile after time-depth conversion using a velocity field without supplementing a dummy well;
fig. 6 is a depth domain profile after time-depth conversion using a high precision velocity field after replenishing a virtual well.
Detailed Description
The invention is further described below with reference to the accompanying drawings:
this method of correcting "fault shadows" in post-stack seismic data by creating high-precision velocity fields, the method comprising the steps of:
Step one, as shown in fig. 1, making and calibrating synthetic seismic records of all wells in an example research area, wherein the making of the synthetic seismic records uses a sound wave time difference curve and a density curve, and matching operation is carried out through the synthetic seismic records and the real seismic records beside the wells to obtain the time-depth relation of each well, and the positions of well layering on a time domain seismic section are clarified, so that the paraxial horizon interpretation of seismic data is developed.
Step two, determining the range of a shadow zone according to the earthquake recognition characteristics of 'fault shadows': and extracting coherence properties from the seismic data to obtain a layer-along coherence slice. And determining the influence range of the fault shadow zone according to the position of the pseudo fault on the plane coherent slice, the 'pull-up and pull-down' range of the seismic event below the fault on the section and the position of the dislocation or distortion of the seismic event. As shown in fig. 2, the left graph is a slice along the layer, the distribution of faults is visible on the slice, the right graph is a seismic reflection section, the triangle area below the faults has the characteristic of "pull-up", and the right boundary of the triangle area has the characteristic of dislocation of the same phase axis, so that the range of "fault shadows" is identified.
And thirdly, supplementing the virtual well in an area with the two sides not exceeding 200 meters inside and outside the boundary of the fault shadow area. As shown in fig. 3, the actual well positions of the example study area are unevenly distributed, so that virtual wells need to be supplemented at positions which are on the inner side and the outer side of the boundary of the shadow area and lack of well control, and an acoustic time difference curve and a density curve of adjacent wells are adopted as curve data of the virtual wells.
Step four, manufacturing and calibrating the synthetic seismic record of the virtual well by means of the adjacent actual well data; and (3) making a synthetic seismic record of the virtual well, wherein the initial speed is consistent with that of an adjacent actual well, and an adjacent well curve is adopted by the acoustic time difference and density curve. And matching the synthetic seismic record of the virtual well with the actual seismic record beside the virtual well, wherein the speed of the virtual well is the speed of the real stratum. The adjacent well is an adjacent actual well.
And fifthly, taking the speeds of all the wells as references, taking a time domain interpretation horizon as a space constraint, adopting a well interpolation method to obtain a high-precision speed field with participation of the virtual wells, and as shown in fig. 4, uniformly changing the high-precision speed field along a same phase axis, generating speed mutation at a shadow boundary, and generating abnormal high speed at a shadow region, so as to meet the speed change rule of a fault shadow phenomenon. Each well includes an actual well and a dummy well, in which a well is a well in a hatched area and B well is a well in a hatched area.
And step six, performing time-depth conversion on the time-domain seismic data by using the high-precision velocity field to obtain accurate depth-domain seismic data. As shown, FIG. 5 is a depth domain profile after a time-depth transition using velocity fields without supplementing the pseudo well, with "fault shadowing" phenomena uncorrected, and with the seismic reflection axis indicated by the arrows still having a distortion. And FIG. 6 is a depth domain section after time-depth conversion by using a high-precision velocity field after supplementing a virtual well, the common phase axis and the horizon of the earthquake are smooth, the correction effect of the 'fault shadow' phenomenon is good, and the real geological situation is met.
Claims (4)
1. A method for correcting fault shadows in post-stack seismic data by establishing a high-precision velocity field, comprising the steps of:
step one, manufacturing and calibrating synthetic seismic records of all actual wells in a research area, and performing horizon interpretation according to calibration results;
Step two, determining the range of a fault shadow zone according to the earthquake identification characteristics of the fault shadow; the seismic identification features of fault shadows include:
In the time domain seismic data, a speed abnormal layer exists on an overlying stratum and is broken by faults; a stratum earthquake event under the fault is locally pulled up and pulled down; vertical dislocation or distortion phenomenon occurs on stratum earthquake phase axis below the fault; on the plane of the coherence attribute, a false fault which is parallel to the main fault appears on the fault lower disc;
Supplementing a virtual well in an area with the two sides not exceeding 200 meters inside and outside the boundary of the fault shadow area;
step four, manufacturing and calibrating the synthetic seismic record of the virtual well by means of the adjacent actual well data;
Step five, taking the speed of each well as a benchmark, taking a time domain interpretation horizon as a space constraint, and obtaining a high-precision speed field with virtual well participation by adopting a well interpolation method;
and step six, performing time-depth conversion on the time-domain seismic data by using the high-precision velocity field to obtain accurate depth-domain seismic data.
2. The method of correcting fault shadows in post-stack seismic data by establishing a high-precision velocity field as recited in claim 1, wherein: the method for manufacturing and calibrating the synthetic seismic record in the first step comprises the following steps:
and (3) acquiring seismic data and well curve data of a research area, utilizing a sound wave time difference curve and a density curve to manufacture synthetic seismic records of all actual wells of the research area, matching and calibrating according to the similarity of the synthetic seismic records and the actual seismic records beside the well, ensuring that the well earthquake achieves the best matching effect, establishing a time-depth relation of each actual well, and determining the corresponding positions of geological layers on a time domain seismic section.
3. The method of correcting fault shadows in post-stack seismic data by establishing a high-precision velocity field as recited in claim 2, wherein: and step three, supplementing a virtual well:
(1) Well position setting: establishing a virtual well at the positions of the inner side and the outer side of the boundary of the fault shadow zone and lacking well control;
(2) Curve data for virtual wells: and adopting the acoustic time difference curve and the density curve of the adjacent well as the curve data of the virtual well.
4. A method of correcting fault shadows in post-stack seismic data by establishing a high-precision velocity field as recited in claim 3, wherein: the fourth step is as follows:
When the virtual well synthetic seismic record is manufactured, the initial speed is consistent with that of the adjacent actual well, and the acoustic time difference curve and the density curve also adopt the adjacent actual well curve; during calibration, matching the synthetic seismic record of the virtual well with the actual seismic record beside the virtual well; for a virtual well in a fault shadow region, the single well speed obtained after matching is an abnormal speed in the fault shadow region; for the virtual wells outside the fault shadow area, the single well speed obtained after matching is the normal speed outside the fault shadow area; this results in a single well velocity at each virtual well that matches the actual velocity.
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