Method for establishing three-dimensional velocity model of unconformity stratum

Abstract

The invention discloses a method for establishing a three-dimensional velocity model of an unconformity stratum, which realizes full coverage of velocity data by constructing a velocity surface three-dimensional mode, realizes strong coherence prediction of the unconformity stratum by establishing an unconformity stratum grid distribution mode, and realizes strong coherence prediction of the unconformity stratum in a special lithologic region grid independent calculation mode. And performing three-dimensional interpolation in a sequential interpolation mode from top to bottom to realize speed prediction in a three-dimensional space. According to the method, an effective technical means and a field implementation method are provided for unconformity formation velocity prediction, the technical problem that a velocity model in an unconformity formation is inaccurate can be solved, and important technical information is provided for research of reservoir distribution, pressure prediction and the like.

Description

Technical Field

[0001] The invention relates to the field of oil and gas exploitation, and in particular to a method for establishing a three-dimensional velocity model of an unconformity stratum. Background Art

[0002] Stratigraphic unconformity refers to the contact relationship between two sets of strata of different ages with sedimentary discontinuities or missing strata. Velocity is one of the key parameters in oil and gas exploration and development, and can provide important information for research on structural characteristics, reservoir distribution and pressure prediction. Due to the missing strata and lithology mutations in unconformable strata, the velocity changes greatly. Conventional horizontal interpolation of wellbore velocity often causes distortion of unconformity strata velocity without considering stratigraphic unconformity and lithology changes.

[0003] At present, the establishment of unconformity stratum velocity model requires overcoming the following technical difficulties:

[0004] (1) The problem of how to establish an unconformity stratigraphic framework model.

[0005] (2) How to use rock property changes to constrain the establishment of velocity models and improve the accuracy of velocity models. Summary of the invention

[0006] In view of the above technical problems, the present invention provides a method for establishing a three-dimensional velocity model of unconformity strata, which realizes full coverage of velocity data by constructing a three-dimensional mode of velocity surface, establishes a grid distribution mode of unconformity strata to realize strong coherence prediction of the whole strata, a separate calculation mode of grids in special lithology areas, and realizes velocity prediction in three-dimensional space by three-dimensional interpolation of a sequential interpolation mode from top to bottom.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for establishing a three-dimensional velocity model of an unconformity stratum, comprising the following steps:

[0008] (1) Using the calibration results of synthetic seismic records, the layered data of each well is converted into time and depth, calibrated in the seismic data volume, and each layer is tracked in the seismic data volume. The position of the pinch-out point must be accurate, and the stratigraphic unconformity model of each layer is established;

[0009] (2) Count the number of wells that encounter special lithology in the formation integration area and establish the distribution range of special lithology. The boundary of the special lithology area is half the distance between the wells that have not encountered special lithology and the wells that have encountered special lithology;

[0010] (3) Using the velocity data of synthetic seismic records, the seismic interpretation data of each layer is transformed into time-depth, and a depth domain structural map is established. The initial depth domain structural map is depth-corrected using the layered data of each well.

[0011] (4) Compensate for missing regional data in the time-domain seismic interpretation stratigraphic data and depth-domain structural maps to achieve full regional data coverage;

[0012] (5) using the time domain and depth domain data of the corresponding layers to obtain velocity data of each layer, the method of obtaining the velocity data is to divide the time domain seismic interpretation layer data by the depth domain structural map of the corresponding layer to obtain the velocity data of the corresponding layer;

[0013] (6) The study area is processed into three-dimensional grids. The three-dimensional grids of the integrated strata are established in equal proportions, and the three-dimensional grids of the unconformable strata are established by interpolation according to the stratigraphic trend to determine the three-dimensional grid range of the special lithology area;

[0014] (7) Based on the velocity data of each layer of the drilled well, the velocity change of the well with depth is predicted by a linear variable velocity formula, and the velocity data on the well is assigned to the three-dimensional grid passed by the well;

[0015] (8) Using the Kriging interpolation method, the three-dimensional grid cells are assigned values ​​along the layers from top to bottom and from the well points from near to far. The prediction results are used as the known values ​​of the next prediction process and participate in the next grid calculation. The velocity values ​​of each grid are predicted in sequence;

[0016] (9) The calculation reaches the grid area of ​​the unconformity formation. Wells that have not encountered the missing part of the unconformity formation are not included in the calculation until all grid velocity assignments are completed and a three-dimensional velocity model of the unconformity formation is established.

[0017] In step (1), the wells in the study area that have completed synthetic seismic records are used to perform time-to-depth conversion on each well layer according to the principle of closest distance, and each layer is calibrated in the time domain seismic data volume; according to the position of each well layer in the seismic data volume, the tracking of each layer is completed, especially for unconformable oil and gas reservoirs, where there are generally missing strata. The position tracking of the pinch-out point must be accurate, and finally the stratigraphic contact model of the study area is established to prepare for the establishment of the velocity framework.

[0018] In step (3), the velocity data of the wells of the completed synthetic seismic records are used to perform time-depth conversion on the data of each layer. The wells of the synthetic seismic records should be selected by region to establish the initial depth domain structural map of each layer; the initial depth domain structural map is depth-corrected using the layered data of each well to overcome the inaccuracy of the initial depth domain structural map caused by local stratigraphic missing and large lithological changes, and to ensure that the corrected depth domain structural map is completely matched with the layered data of the well.

[0019] In step (4), for areas where some strata are missing, the time domain seismic interpretation stratigraphic data and the depth domain structural map data are compensated to achieve stratigraphic overlap.

[0020] In step (5), the velocity surface of each layer is obtained using the time domain and depth domain data of each corresponding layer, that is, the velocity data of each layer is obtained by dividing the time data by the depth data, so as to prepare for obtaining the velocity data of the entire spatial model.

[0021] In step (6), the special lithology area must also be accurately located in the three-dimensional grid.

[0022] In step (7), the linear variable velocity formula is used to predict the change of the velocity of the well with depth based on the velocity of each well passing through the layer site, and the complete velocity data of the well is obtained; the number of velocity data on each grid is analyzed, the average of the data is calculated, and the value is assigned to the grid, and finally the grid assignment of all wells passing through is completed.

[0023] In step (8), when the velocity difference between the special lithology area and the ordinary lithology area reaches more than 100%, the velocity of the three-dimensional grid range where the special lithology distribution range exists is calculated separately; wells that have not encountered special lithology do not participate in the calculation of grid velocity within the special lithology distribution range; grid velocity outside the special lithology distribution range is calculated for all wells according to the Kriging interpolation formula.

[0024] The beneficial effects of the present invention are: providing effective technical means and field implementation methods for unconformity formation velocity prediction, solving the technical problem of inaccurate velocity models in unconformity formations, and providing important technical information for research on reservoir distribution and pressure prediction. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The method of the present invention is a map of the locations of pinch-out points of unconformities in seismic data volumes.

[0026] Figure 2 It is a diagram of the formation contact model of the method of the present invention.

[0027] Figure 3 It is a distribution range map of special lithology of the present invention.

[0028] Figure 4 It is a method level speed establishment method diagram of the present invention.

[0029] Figure 5 This is a diagram of establishing a grid pattern of unconformable formations using the method of the present invention.

[0030] Figure 6 It is a schematic diagram of assigning wellbore velocity data to a grid according to the method of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments, and all other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative work are within the scope of protection of the present invention.

[0032] The method for establishing a three-dimensional velocity model of an unconformity stratum of the present invention comprises the following steps:

[0033] (1) Using the calibration results of synthetic seismic records, the layered data of each well is converted into time and depth, calibrated in the seismic data volume, and each layer is tracked in the seismic data volume. The position of the pinch-out point must be accurate, and the stratigraphic unconformity model of each layer is established;

[0034] (2) Count the number of wells that encounter special lithology in the formation integration area and establish the distribution range of special lithology. The boundary of the special lithology area is half the distance between the wells that have not encountered special lithology and the wells that have encountered special lithology;

[0035] (3) Using the velocity data of synthetic seismic records, the seismic interpretation data of each layer is transformed into time-depth, and a depth domain structural map is established. The initial depth domain structural map is depth-corrected using the layered data of each well.

[0036] (4) Compensate for missing regional data in the time-domain seismic interpretation stratigraphic data and depth-domain structural maps to achieve full regional data coverage;

[0037] (5) using the time domain and depth domain data of the corresponding layers to obtain velocity data of each layer, the method of obtaining the velocity data is to divide the time domain seismic interpretation layer data by the depth domain structural map of the corresponding layer to obtain the velocity data of the corresponding layer;

[0038] (6) The study area is processed into three-dimensional grids. The three-dimensional grids of the integrated strata are established in equal proportions, and the three-dimensional grids of the unconformable strata are established by interpolation according to the stratigraphic trend to determine the three-dimensional grid range of the special lithology area;

[0039] (7) Based on the velocity data of each layer of the drilled well, the velocity change of the well with depth is predicted by a linear variable velocity formula, and the velocity data on the well is assigned to the three-dimensional grid passed by the well;

[0040] (8) Using the Kriging interpolation method, the three-dimensional grid cells are assigned values ​​along the layers from top to bottom and from the well points from near to far. The prediction results are used as the known values ​​of the next prediction process and participate in the next grid calculation. The velocity values ​​of each grid are predicted in sequence;

[0041] (9) The calculation reaches the grid area of ​​the unconformity formation. Wells that have not encountered the missing part of the unconformity formation are not included in the calculation until all grid velocity assignments are completed and a three-dimensional velocity model of the unconformity formation is established.

[0042] In step (1), the wells in the study area that have completed synthetic seismic records are used to perform time-to-depth conversion on each well layer according to the principle of closest distance, and each layer is calibrated in the time domain seismic data volume; according to the position of each well layer in the seismic data volume, the tracking of each layer is completed, especially for unconformable oil and gas reservoirs, where there are generally missing strata. The position tracking of the pinch-out point must be accurate, and finally the stratigraphic contact model of the study area is established to prepare for the establishment of the velocity framework.

[0043] In step (3), the velocity data of the wells of the completed synthetic seismic records are used to perform time-depth conversion on the data of each layer. The wells of the synthetic seismic records should be selected by region to establish the initial depth domain structural map of each layer; the initial depth domain structural map is depth-corrected using the layered data of each well to overcome the inaccuracy of the initial depth domain structural map caused by local stratigraphic missing and large lithological changes, and to ensure that the corrected depth domain structural map is completely matched with the layered data of the well.

[0044] In step (4), for areas where some strata are missing, the time domain seismic interpretation stratigraphic data and the depth domain structural map data are compensated to achieve stratigraphic overlap.

[0045] In step (5), the velocity surface of each layer is obtained using the time domain and depth domain data of each corresponding layer, that is, the velocity data of each layer is obtained by dividing the time data by the depth data, so as to prepare for obtaining the velocity data of the entire spatial model.

[0046] In step (6), the special lithology area must also be accurately located in the three-dimensional grid.

[0047] In step (7), the linear variable velocity formula is used to predict the change of the velocity of the well with depth based on the velocity of each well passing through the layer site, and the complete velocity data of the well is obtained; the number of velocity data on each grid is analyzed, the average of the data is calculated, and the value is assigned to the grid, and finally the grid assignment of all wells passing through is completed.

[0048] In step (8), when the velocity difference between the special lithology area and the ordinary lithology area reaches more than 100%, the velocity of the three-dimensional grid range where the special lithology distribution range exists is calculated separately; wells that have not encountered special lithology do not participate in the calculation of grid velocity within the special lithology distribution range; grid velocity outside the special lithology distribution range is calculated for all wells according to the Kriging interpolation formula.

[0049] The calculation formula involved in the present invention is as follows.

[0050] Formula 1 Linear speed change formula

[0051]

[0052] Where: Z is the depth of the target layer, Z 0 is the initial depth, V 0 is the average velocity, V is the velocity of the layer, t is the target layer time, t 0 is the initial time, K is the coefficient of linear velocity;

[0053] Formula 2 Kriging interpolation formula

[0054] Let x 1 ,...,x n is a series of observation points on the region, z(x 1 ),...,z(x n ) is the corresponding observed value. The regionalized variable is in x 0 The value z * (x 0 ) can be estimated using a linear combination:

[0055]

[0056] where λ i is the weight coefficient.

[0057] From the above formula, we can know that z * (x 0 ) is to use statistical models to determine λ i The unbiasedness and minimum estimated variance are used as the factors to select λ. i Standards:

[0058] E[Z*(x 0 )-Z(x 0 )]=0

[0059]

[0060] From these two relations, we can deduce that i The Kriging equations.

[0061] First, starting from the second-order stationary assumption, we know that E[Z(x)] is a constant, and we have

[0062]

[0063] The relationship can be obtained:

[0064]

[0065] Starting from the minimum estimated variance, the Lagrange multiplier method can be used to obtain:

[0066]

[0067] Further deduction can obtain the n+1 order linear equation system, namely the Kriging equation system:

[0068]

[0069] When the random function does not satisfy the second-order stationarity but satisfies the intrinsic assumption, the Kriging equations can be expressed by the variogram r(h) as follows:

[0070]

[0071] By solving the above equations, we can obtain a series of λ i (i=1,...,n), based on which the Kriging estimate of the estimated point can be solved. The minimum estimated variance, that is, the Kriging variance, can be solved using the following formula:

[0072]

[0073] Or expressed as a variogram:

[0074]

[0075] The present invention establishes an unconformity stratigraphic framework model based on seismic interpretation layer data, adopts stratigraphic deposition model to establish a stratigraphic grid model, and then interpolates the velocity along the stratigraphic model through the uphole velocity, while referring to the lithology changes in the stratum, thereby improving the rationality of the interpolation velocity along the interpreted horizon.

[0076] Example

[0077] A method for establishing a three-dimensional velocity model of an unconformity stratum. Establishing a velocity model for an unconformity stratum can be regarded as an effective method for using the technology. The specific implementation method is as follows:

[0078] (1) Complete the tracking of each layer in the seismic data volume, especially ensure the accuracy of the location of the pinch-out point, and establish the stratigraphic unconformity model of each layer

[0079] Using the wells in the study area that have completed synthetic seismic records, we transform the time-depth of each well layer according to the principle of the closest distance, and mark each layer in the time domain seismic data volume. According to the position of each well layer in the seismic data volume, we complete the tracking of each layer. Especially for unconformable oil and gas reservoirs, there are generally missing strata, and the position tracking of the pinch-out point must be accurate ( Figure 1 ), and finally establish the stratigraphic contact model of the study area ( Figure 2 ), in preparation for establishing the speed grid.

[0080] (2) The number of wells drilling into special lithology in the formation integration zone was counted, and the distribution range of special lithology was established. The boundary of the special lithology area was half the distance between the wells that did not encounter special lithology and the wells that encountered special lithology ( Figure 3 ).

[0081] (3) Using the velocity data of synthetic seismic records to perform time-depth conversion on each layer data of seismic interpretation, a depth domain structural map is established.

[0082] The velocity data of the wells with completed synthetic seismic records are used to perform time-to-depth conversion on the data of each layer. The wells with synthetic seismic records should be selected by region, and not all completed synthetic seismic records should be used in the calculation. Since the velocity difference between adjacent wells is too large, the depth domain structural map after conversion is distorted. Therefore, the initial depth domain structural map of each layer should be established.

[0083] The initial depth domain structural map is depth-corrected using the layered data from each well to overcome the problem of inaccurate initial depth domain structural map caused by local stratigraphic missing and large lithological changes, and to ensure that the corrected depth domain structural map fully matches the layered data from the well.

[0084] (4) Compensate for missing regional data in the time domain seismic interpretation stratigraphic data and depth domain structural maps to achieve full regional data coverage

[0085] For areas where some strata are missing, the time domain seismic interpretation stratigraphic data and depth domain structural map data are used to compensate, such as Figure 1 In the figure, there are some missing layers in the eastern area of ​​T2 and T3 layers, which need to be compensated according to the position of T1 layer to achieve layer overlap.

[0086] (5) The velocity surface of each layer is obtained by using the time domain and depth domain data of each layer respectively. That is, the velocity data of each layer is obtained by dividing the time data by the depth data ( Figure 4 ), in preparation for obtaining the velocity data of the entire space model.

[0087] (6) The study area is processed into three-dimensional grids. The three-dimensional grids of the integrated strata are established in a proportional manner, and the three-dimensional grids of the unconformable strata are established by interpolation according to the stratigraphic trend to determine the three-dimensional grid range of the special lithology area.

[0088] The study area is processed into a three-dimensional grid to prepare for the final three-dimensional velocity model. The three-dimensional grid of the integrated strata is established in a proportional manner, and the three-dimensional grid of the unconformable strata is established by interpolation according to the stratum trend. The special lithology area must also determine the exact position in the three-dimensional grid ( Figure 5 ).

[0089] (7) Based on the velocity data of each layer of the well, the linear variable velocity formula is used to predict the change of the velocity of the well with depth, and the velocity data on the well is assigned to the three-dimensional grid through which the well passes.

[0090] Using the linear variable velocity formula (Formula 1), the velocity variation of each well with depth is predicted according to the velocity of each well passing through the layer site, and the complete velocity data of the well is obtained.

[0091] Analyze how many speed data there are on each grid, find the average of several data, and assign them to the grid ( Figure 6 ), and finally complete the grid assignment for all wells passing through.

[0092] (8) The Kriging interpolation method is used to assign values ​​to the three-dimensional grid cells from top to bottom and from the well points from near to far.

[0093] A. The three-dimensional grid units are assigned values ​​along the layers from top to bottom and from the well points from near to far. The assignment method is the Kriging interpolation method (Formula 2). The prediction results are used as the known values ​​for subsequent predictions and participate in subsequent grid calculations. The velocity values ​​of each grid are predicted in sequence.

[0094] B. The three-dimensional grid range in the area with special lithology is calculated separately, and the wells that have not encountered special lithology are not involved in the velocity calculation;

[0095] When the velocity difference between the special lithology area and the ordinary lithology area reaches more than 100%, it is necessary to calculate the velocity of the three-dimensional grid range where the special lithology distribution range exists separately. For example, at a depth of 2000 meters, when the vertical average velocity of ordinary lithology is 2500 meters / second and the vertical evaluation velocity of special lithology is more than 5000 meters / second, wells that have not encountered special lithology do not participate in the calculation of grid velocity within the special lithology distribution range; grid velocity outside the special lithology distribution range participates in the calculation of all wells according to the Kriging interpolation formula.

[0096] C. Calculate to the unconformity formation grid area. Wells that have not encountered this formation will not be included in the calculation until all grid velocity assignments are completed.

[0097] The calculation reaches the unconformity formation grid area, and the wells that have not encountered the unconformity missing part of the formation are not included in the calculation to avoid interference between different formation velocities until all grid velocity assignments are completed.

[0098] In summary, the content of the present invention is not limited to the above-mentioned embodiments, and people with insight in the same field can easily propose other embodiments within the technical guiding ideology of the present invention, but such embodiments are all included in the scope of the present invention.

Claims

1. A method for establishing a three-dimensional velocity model of unconformity strata, characterized in that: The following steps are involved: (1) Using the calibration results of synthetic seismic records, the layered data of each well is converted into time and depth, calibrated in the seismic data volume, and each layer is tracked in the seismic data volume. The position of the pinch-out point must be accurate, and the stratigraphic unconformity model of each layer is established; (2) Count the number of wells that encounter special lithology in the formation integration area and establish the distribution range of special lithology. The boundary of the special lithology area is half the distance between the wells that have not encountered special lithology and the wells that have encountered special lithology; (3) Using the velocity data of synthetic seismic records, the seismic interpretation data of each layer is transformed into time-depth, and a depth domain structural map is established. The initial depth domain structural map is depth-corrected using the layered data of each well. (4) Compensate for missing regional data in the time-domain seismic interpretation stratigraphic data and depth-domain structural maps to achieve full regional data coverage; (5) using the time domain and depth domain data of the corresponding layers to obtain velocity data of each layer, the method of obtaining the velocity data is to divide the time domain seismic interpretation layer data by the depth domain structural map of the corresponding layer to obtain the velocity data of the corresponding layer; (6) The study area is processed into three-dimensional grids. The three-dimensional grids of the integrated strata are established in equal proportions, and the three-dimensional grids of the unconformable strata are established by interpolation according to the stratigraphic trend to determine the three-dimensional grid range of the special lithology area; (7) Based on the velocity data of each layer of the drilled well, the velocity change of the well with depth is predicted by a linear variable velocity formula, and the velocity data on the well is assigned to the three-dimensional grid passed by the well; (8) Using the Kriging interpolation method, the three-dimensional grid cells are assigned values ​​along the layers from top to bottom and from the well points from near to far. The prediction results are used as the known values ​​of the next prediction process and participate in the next grid calculation. The velocity values ​​of each grid are predicted in sequence; (9) The calculation reaches the grid area of ​​the unconformity formation. Wells that have not encountered the missing part of the unconformity formation are not included in the calculation until all grid velocity assignments are completed and a three-dimensional velocity model of the unconformity formation is established.

2. The method for establishing a three-dimensional velocity model of unconformity strata according to claim 1, characterized in that: In step (1), using the wells in the study area that have completed synthetic seismic records, time-depth conversion is performed on each well layer according to the principle of closest distance, and each layer is marked in the time domain seismic data volume; According to the position of each well layer in the seismic data body, the tracking of each layer is completed. In particular, unconformity oil and gas reservoirs generally have missing strata, and the position tracking of the pinch-out point must be accurate. Finally, the stratigraphic contact model of the study area is established to prepare for the establishment of the velocity framework.

3. The method for establishing a three-dimensional velocity model of unconformity strata according to claim 1, characterized in that: In step (3), the velocity data of the wells of the completed synthetic seismic records are used to perform time-depth conversion on the data of each layer. The wells of the synthetic seismic records should be selected by region to establish the initial depth domain structural map of each layer; the initial depth domain structural map is depth-corrected using the layered data of each well to overcome the inaccuracy of the initial depth domain structural map caused by local stratigraphic missing and large lithological changes, and to ensure that the corrected depth domain structural map is completely matched with the layered data of the well.

4. The method for establishing a three-dimensional velocity model of unconformity strata according to claim 1, characterized in that: In step (4), for areas where some strata are missing, the time domain seismic interpretation stratigraphic data and the depth domain structural map data are compensated to achieve stratigraphic overlap.

5. The method for establishing a three-dimensional velocity model of unconformity strata according to claim 1, characterized in that: In step (5), the velocity surface of each layer is obtained using the time domain and depth domain data of each corresponding layer, that is, the velocity data of each layer is obtained by dividing the time data by the depth data, so as to prepare for obtaining the velocity data of the entire spatial model.

6. The method for establishing a three-dimensional velocity model of unconformity strata according to claim 1, characterized in that: In step (6), the special lithology area must also be accurately located in the three-dimensional grid.

7. The method for establishing a three-dimensional velocity model of unconformity strata according to claim 1, characterized in that: In step (7), the linear variable velocity formula is used to predict the change of the velocity of the well with depth based on the velocity of each well passing through the layer site, and the complete velocity data of the well is obtained; the number of velocity data on each grid is analyzed, the average of the data is calculated, and the value is assigned to the grid, and finally the grid assignment of all wells passing through is completed.

8. The method for establishing a three-dimensional velocity model of unconformity strata according to claim 1, characterized in that: In step (8), when the velocity difference between the special lithology area and the ordinary lithology area reaches more than 100%, the velocity of the three-dimensional grid range where the special lithology distribution range exists is calculated separately; wells that have not encountered special lithology do not participate in the calculation of grid velocity within the special lithology distribution range; grid velocity outside the special lithology distribution range is calculated for all wells according to the Kriging interpolation formula.

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