Method for recovering original ancient bottom shape

Abstract

The invention discloses a method for recovering an original paleo-bottom shape. The method comprises the following steps: completing seismic reflection time difference diagrams of two target stratums through horizon interpretation; the seismic reflection time difference diagram is multiplied by the speed, and the thickness of the compacted stratum is obtained; then, the compaction rate of each well is calculated, and a plane distribution diagram of the stratum comprehensive compaction rate of the research area is drawn; and then multiplying the stratum thickness distribution diagram by the comprehensive compaction rate to obtain an original distribution characteristic diagram before compaction, and carrying out stereoscopic display to obtain an ancient bottom diagram. According to the method, a well-seismic combination technology is adopted, various factors influencing paleo-bottom shape recovery are comprehensively considered, and the paleo-bottom shape recovery method based on the three-dimensional seismic constraint and single well decompaction correction technology is systematically provided.

Description

Technical Field

[0001] The present invention belongs to the technical field of paleogeomorphology restoration methods, and relates to a method for restoring the original paleotopography. Background Art

[0002] Commonly used methods for paleotopography restoration mainly include: the impression method, the geophysical method, the sedimentological method, the residual thickness method, the sequence stratigraphy method, the horizon flattening method, and the computer simulation method, etc. Each restoration method has certain applicable conditions and advantages, and at the same time has certain deficiencies, which directly or indirectly affect the accuracy of paleotopography restoration. Therefore, it is difficult to meet the current oil and gas exploration requirements by using relatively single data and methods to restore the paleotopography.

[0003] (1) The impression method

[0004] The impression method is a semi - quantitative prediction of the paleogeomorphology in this area and is a widely used method. Its principle is to reflect the paleogeomorphology pattern of the erosion surface based on the thickness from the marker bed of the overlying filling sediment to the erosion surface by using the mirror image relationship. The detailed steps are as follows: flatten the strata with the nature of filling and leveling and the erosion interface in the overlying filling strata of the target horizon, and use it as the reference plane, count the thickness from the erosion interface to this reference plane, and compile a plane isogram, and then further divide the paleogeomorphology of the study area according to the criteria for karst paleogeomorphology division. The advantage of this method is that it can combine the situation of the drilled wells and further improve the division and restoration accuracy of the karst geomorphic unit. The disadvantage is that it is difficult to master the true thickness between the erosion interface and the reference plane.

[0005] (2) The sedimentological method

[0006] The sedimentological method uses various basic geological maps, and combines paleocurrent analysis, paleotectonic development characteristics, genetic analysis, calculation of topographic slope, and consideration of the differences in sedimentation rates of various sediments, etc., so as to qualitatively restore the karst paleogeomorphology characteristics and reproduce the evolution process of the karst paleogeomorphology on the time scale. It should be noted that the compaction differences of various lithologies should be considered, so that the calculation results obtained using the original sedimentation thickness are more accurate. The advantage of using the sedimentological method to restore the karst paleogeomorphology is that it is simple and easy to understand and can roughly restore the karst paleogeomorphology pattern. The disadvantage is that under various influencing factors, the accuracy of paleogeomorphology restoration is not high and a large number of basic maps are required.

[0007] (3) The residual thickness method

[0008] The principle of the residual thickness method is similar to but different from the impression method. The difference is that this method needs to find a reference plane below the isochronous interface and flatten it. After flattening, the ancient geomorphic form at that time is reflected by the thickness of the overlying strata. Then, an ancient geomorphic map is compiled. In the map, the area with a small sedimentary thickness is a depression, and vice versa is a highland. The advantage of this method is also relatively reliable and intuitive, and it can finely reflect the karst ancient geomorphology. The disadvantage is that due to the failure to consider the influence of erosion differences and tectonic topography on the sedimentary thickness, the final mapping error is relatively large.

[0009] (4) Sequence stratigraphy method

[0010] Sequence stratigraphy emphasizes establishing an isochronous sequence framework of the overlying strata and flattening it, and using the isochronism of the sequence interface to reflect the ancient geomorphic form. The detailed steps are as follows: Analyze the development and evolution process of the overlying strata of the weathered crust using the sedimentation method to determine the time of filling and leveling, and conduct a reference cycle comparison in combination with the maximum flooding surface and the reference plane to reflect the ancient geomorphic form before sedimentation. The advantage of the sequence stratigraphy method is that the relative isochronism of the overlying reference plane is strong, and the research results are more reasonable. The disadvantage is that it is relatively difficult to select the reference plane. Summary of the invention

[0011] The purpose of the present invention is to provide a method for restoring the original ancient bottom topography, which solves the problem of low accuracy in restoring the ancient geomorphology in the existing methods for restoring the ancient bottom topography.

[0012] The technical solution adopted by the present invention is a method for restoring the original ancient bottom topography. Based on seismic data and well logging data, the well-seismic combination technology is adopted, and various factors affecting the restoration of the ancient bottom topography are comprehensively considered, and a method for restoring the ancient bottom topography based on three-dimensional seismic constraint and single-well decompaction correction technology is systematically proposed.

[0013] The characteristics of the present invention also lie in that

[0014] The method for restoring the original ancient bottom topography of the present invention has the following specific operation steps:

[0015] Step 1: Collection, sorting and analysis of basic data: Collect geological background data, well logging data, lithology descriptions of mud logging, seismic achievement data, drilling cores and thin sections, and stratification data, and sort and analyze the data;

[0016] Step 2: According to the geological background data, select the skeleton wells, and combine the core and well logging characteristic curves to find the marker beds in the area. Connect them horizontally and vertically to form a well-connected section. Based on the calibrated stratification data and taking the seismic interpretation data as the basis, trace the strata to establish a stratigraphic framework section;

[0017] Step 3: Conduct key horizon division and comparison on the completed wells in the area, count the sand-to-ground ratio and mud-to-ground ratio, calculate the compaction rate, and then obtain the restored formation thickness;

[0018] Step 4: Well-seismic integration: Establish seismic isochronous interfaces and marker beds, and establish regional seismic facies sequence interfaces through calibration of well horizons. These interfaces are stable and continuously traceable across the whole area, with obvious waveform reflection characteristics. Through reflection interfaces at different horizons, formation thickness data between different horizons can be calculated. After decompaction correction, the original thickness of the formation is restored.

[0019] Step 5: Combine the formation thickness data of known wells and the formation thickness data of seismic reflection horizons in the region, verify each other, and draw the present-day formation thickness isopach map. Then, through decompaction correction, restore the original thickness of the formation, and further obtain the original distribution map of the paleo-topography in that period.

[0020] Step 6: Decorate and color. Decorate and label each formation thickness unit according to the legend, improve the corresponding cartographic elements, and obtain the restored original paleo-topography map.

[0021] The specific steps for establishing the stratigraphic framework in Step 2 are as follows: First, select key wells, find marker beds in the region by combining core and logging characteristic curves, connect them horizontally and vertically to form a cross-well profile, and based on the calibrated stratification data and seismic interpretation data, trace the strata to establish a stratigraphic framework profile.

[0022] In Step 3, obtain the compaction rate of the target formation in known wells, and then obtain the original formation thickness: First, count the known sand-to-shale ratio and mud-to-shale ratio, calculate the compaction rate, and then obtain the restored formation thickness.

[0023] According to the compaction rate \(K = K\) 砂 *\(\varPhi\) 砂 +\(K\) 泥 *\(\varPhi\) 泥 , obtain the formation thickness \(H_0\) of the target layer in known wells after compaction correction as \(H_0 = H + H\times K\), and then restore the distribution pattern of the paleo-topography.

[0024] In the formula: \(K\): Comprehensive rock compaction rate;

[0025] \(K\) 砂 : Compaction rate of sandstone, with a test value of 0.2;

[0026] \(K\) 泥 : Compaction rate of mudstone, with a test value of 0.6;

[0027] \(\varPhi\) 砂 : Sand-to-shale ratio;

[0028] \(\varPhi\) 泥 : Mud-to-shale ratio;

[0029] \(H_0\): Original formation thickness before compaction;

[0030] \(H\): Present-day formation thickness;

[0031] Calibrate different lithologies in the formation respectively to obtain the original formation thickness H0 before compaction.

[0032] In step 4, to obtain the formation thickness of different seismic reflection interfaces, according to the different seismic reflection characteristics of different formations, establish seismic isochronous interfaces and marker beds, and then use the known well horizons for calibration to further refine the horizon division and establish seismic sequence interfaces that are stable in distribution and can be continuously traced in the region; select formation reflection interfaces using seismic wave characteristics, and obtain the formation thickness H = Δt0 * V by the reflection velocity and time of seismic waves between two interfaces; and Δt0 = Tp1 - Tp2, and the original formation thickness H0 = H + H * K is obtained after decompaction calibration. 砂 *Φ 砂 + H * K 泥 *Φ 泥 , and further obtain the distribution characteristics of the paleotopography;

[0033] In the formula:

[0034] H0: The original formation thickness before compaction;

[0035] Δt0: The seismic reflection time difference;

[0036] V: The seismic interlayer reflection velocity;

[0037] Tp1: The seismic reflection target layer 1;

[0038] Tp2: The seismic reflection target layer 2.

[0039] In step 5, combine the formation thickness data of the known wells and the formation thickness data of the seismic reflection horizons in the region, verify each other, draw the isopach map of the current formation thickness, and then through decompaction calibration, restore the original thickness of the formation, and further obtain the original distribution characteristic map of the paleotopography in that period.

[0040] The beneficial effects of the present invention are:

[0041] Based on seismic data and known well data, the present invention adopts a technical method of combining wells and seismic data, and systematically proposes a method for decompaction restoration of the original paleotopography, effectively using well-seismic data to quantitatively restore the paleotopography, not only improving the accuracy of paleotopography restoration, but also providing an accurate basis for the distribution of sand bodies, thereby enhancing the economic benefits of exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments:

[0043] Figure 1 is the flow chart of the paleotopography restoration method of the present invention;

[0044] Figure 2 Schematic diagram of the restoration process of the original paleo-topography of the present invention; Specific implementation manners

[0045] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

[0046] Embodiment 1

[0047] A method for restoring the original paleo-topography, based on seismic data and well logging data, adopts the technology of combining well and seismic data, comprehensively considers various factors affecting the restoration of paleo-topography, and systematically proposes a method for restoring paleo-topography based on three-dimensional seismic constraint and single-well decompaction correction technology.

[0048] Embodiment 2

[0049] The difference from Embodiment 1 is that

[0050] The method for restoring the original paleo-topography of the present invention has a process as Figure 1-2 shown, and the specific operation steps are as follows:

[0051] Step 1: Collection, sorting and analysis of basic data: Collect geological background data, well logging data, lithology descriptions of mud logging, seismic achievement data, drilling cores and thin sections, and stratification data, and sort and analyze the data;

[0052] Step 2: According to the geological background data, select the key wells, and combine the core and well logging characteristic curves to find the marker beds in the area, connect them horizontally and vertically to form a well-connected profile respectively. Based on the calibrated stratification data and taking the seismic interpretation data as the basis, trace the strata and establish a stratigraphic framework profile;

[0053] Step 3: Divide and compare the key horizons of the drilled wells in the area, count the sand-to-shale ratio and mud-to-shale ratio, calculate the compaction rate, and then obtain the restored formation thickness;

[0054] Step 4: Combine well and seismic data: Establish seismic isochronous interfaces and marker beds, establish regional seismic facies sequence interfaces through known well horizon calibration, which are stable and continuously traceable throughout the area and have obvious waveform reflection characteristics; through the reflection interfaces of different horizons, the formation thickness data between different horizons can be calculated, and through decompaction correction, the original thickness of the formation is restored;

[0055] Step 5: Combine the formation thickness data of the known wells and the formation thickness data of the seismic reflection horizons in the area, verify each other, draw the present-day formation thickness contour map, and then through decompaction correction, restore the original thickness of the formation, and then obtain the original distribution characteristic map of the paleo-topography in that period;

[0056] Step 6: Decorate and color, decorate and mark each formation thickness unit according to the legend, improve the corresponding cartographic elements, and obtain the restored original paleo-topography map.

[0057] The specific steps for establishing the stratigraphic framework in Step 2 are as follows: First, select the skeleton wells, find the marker beds in the region by combining core and logging characteristic curves, connect them horizontally and vertically to form a well-to-well section, and based on the calibrated stratification data and seismic interpretation data, trace the strata to establish the stratigraphic framework section.

[0058] In Step 3, calculate the compaction rate of the target formation in the known wells, and then calculate the original formation thickness: First, count the sand-to-shale ratio and shale-to-sand ratio of the known wells, calculate the compaction rate, and then obtain the restored formation thickness.

[0059] According to the compaction rate K = K 砂 *Φ 砂 +K 泥 *Φ 泥 , calculate the thickness H0 of the target formation in the known wells after compaction correction as H0 = H + H * K, and then restore the distribution pattern of the ancient paleotopography;

[0060] In the formula: K: Comprehensive rock compaction rate;

[0061] K 砂 : Compaction rate of sandstone, experimental value is 0.2;

[0062] K 泥 : Compaction rate of mudstone, experimental value is 0.6;

[0063] Φ 砂 : Sand-to-shale ratio;

[0064] Φ 泥 : Shale-to-sand ratio;

[0065] H0: Original formation thickness before compaction;

[0066] H: Current formation thickness;

[0067] Correct different lithologies in the strata respectively to obtain the original formation thickness H0 before compaction.

[0068] In Step 4, calculate the formation thickness of different seismic reflection interfaces. According to the different seismic reflection characteristics of different strata, establish seismic isochronous interfaces and marker beds, and then use the well location calibration of known wells for further fine layer division to establish seismic sequence interfaces that are stable in distribution and can be continuously traced in the region; select formation reflection interfaces using seismic wave characteristics, and calculate the formation thickness H = Δt0 * V through the reflection velocity and time of seismic waves between two interfaces; and Δt0 = Tp1 - Tp2, and obtain the original formation thickness H0 = H + H * K after decompaction correction 砂 *Φ 砂 +H*K 泥 *Φ 泥 , and further obtain the distribution characteristics of the ancient paleotopography;

[0069] In the formula:

[0070] H0: Original formation thickness before compaction;

[0071] Δt0: Seismic reflection time difference;

[0072] V: Seismic interlayer reflection velocity;

[0073] Tp1: Seismic reflection target layer 1;

[0074] Tp2: Seismic reflection target layer 2.

[0075] Step 5 combines the formation thickness data of known wells and the formation thickness data of seismic reflection layers in the region, verifies each other, and draws the present-day formation thickness contour map. Then, through decompaction correction, the original thickness of the formation is restored, and the original distribution characteristics map of the paleo-topography in that period is obtained.

[0076] Example 3

[0077] The interpretation of this seismic data involves a total of 6516 km of five 3D blocks 2 , and 2520 km of 2D. Among them, the key horizons in the five 3D blocks are represented by Ttl, Tpq, TP8, TP9, and Tp respectively. The interpretation density of the key horizons in the 3D area is 32*32, which lays a good foundation for the later restoration of the paleo-topography.

[0078] For the restoration of the paleo-topography in the Shan 1 period, first, the interpretation of the two horizons of TP8 and TP9 in the 2D and 3D joint interpretation is completed through interpretation, and the seismic reflection time difference map (Δt0 山1 = Tp9 - Tp8) of the two target formations of TP8 and TP9 is contoured; then, the seismic reflection time difference map Δt0 is multiplied by the interlayer seismic velocity of TP8 and TP9 to obtain the compacted formation thickness ΔH 山1 ; Then, by combining more than 40 wells selected in the early stage, the compaction rate K of each well is calculated 山1 = Φsand 山1 *(1 + Ksand 山1 ) + Φmud 山1 *(1 + Kmud 山1 ), and the plane distribution map of the comprehensive formation compaction rate K 山1 of the study area is contoured, where Ksand 山1 refers to the compaction rate of sandstone, generally taking 0.6, Kmud 山1 refers to the compaction rate of mudstone, generally taking 0.6 - 0.7 for pure mudstone, and taking 0.6 in this calculation, Φsand 山1 refers to the percentage of sandstone content in the target formation of the target well, and Φmud 山1 refers to the percentage of mudstone content in the target formation of the target well; then, the pre-compaction thickness ΔH0 of each well is calculated and restored山1 , using ΔH0 山1 to correct ΔH 山1 distribution map, the original formation ΔH0 before compaction can be obtained 山1 thickness distribution map, and the paleotopography map can be obtained through gradient color display.

[0079] Example 4

[0080] For the paleotopography restoration of the Box 8 period, first, through interpretation, the two-dimensional and three-dimensional continuous interpretation of the two horizons of TP7 and TP8 is completed. Through horizon interpretation, the seismic reflection time difference map (Δt0 盒8 = Tp7 - Tp8) of the target formation is contoured; then, the seismic reflection time difference map Δt0 is multiplied by the velocity to obtain the thickness ΔH of the compacted formation 盒8 ; then, by combining more than 40 wells preferably selected in the early stage, the compaction rate K of each well is calculated 盒8 = Φsand 盒8 * (1 + Ksand 盒8 ) + Φmud 盒8 * (1 + Kmud 盒8 ), and the plane distribution map of the comprehensive formation compaction rate K of the study area is contoured, where Ksand 盒8 refers to the compaction rate of sandstone, generally taking 0.6, Kmud 盒8 refers to the compaction rate of mudstone, generally taking 0.6 - 0.7 for pure mudstone, and taking 0.6 in this calculation. Φsand 盒8 refers to the percentage of sandstone content in the target formation of the target well, and Φmud 盒8 refers to the percentage of mudstone content in the target formation of the target well; then, the thickness ΔH0 before compaction of each well is calculated and restored 山1 , using ΔH0 盒8 to correct ΔH 盒8 distribution map, the original formation ΔH0 before compaction can be obtained 盒8 thickness distribution map, and the paleotopography map can be obtained through gradient color display. 盒8

[0081] The present invention completes the contouring of the seismic reflection time difference map (Δt0 = Tpa - Tpb) of the target formation through horizon interpretation; then, the seismic reflection time difference map Δt0 is multiplied by the velocity to obtain the thickness ΔH of the compacted formation; then, the compaction rate K of each well is calculated as K = Φ 砂 * (1 + K 砂 ) + Φ 泥 * (1 + K 泥 ), and the plane distribution map of the comprehensive formation compaction rate K of the study area is contoured, where K 砂 refers to the compaction rate of sandstone, generally taking 0.6, K 泥 refers to the compaction rate of mudstone, generally taking 0.6 - 0.7 for pure mudstone, and taking 0.6 in this calculation. Φ 砂Refers to the percentage of sandstone content in the target formation of the target well, Φ 泥 Refers to the percentage of mudstone content in the target formation of the target well; then multiply the ΔH distribution map by the comprehensive compaction rate K to obtain the original formation ΔH0 thickness distribution map before compaction, and the paleotopography map can be obtained through three-dimensional display.

Claims

1. Method for restoring the original paleo - topography, Characterized in that, Based on seismic data and exploration well data, using the well - seismic combination technology, comprehensively considering various factors affecting the restoration of paleo - topography, a method for restoring paleo - topography based on 3D seismic constraint and single - well decompaction correction technology is systematically proposed.

2. The method for restoring the original paleo - topography according to claim 1, Characterized in that, The specific operation steps are as follows: Step 1: Collection, sorting and analysis of basic data: Collect geological background data, logging data, lithology descriptions of mud logging, seismic achievement data, drilling cores and thin sections, and stratification data, and sort and analyze the data; Step 2: According to the geological background data, select the key wells, combine the core and logging characteristic curves to find the marker beds in the area, connect them horizontally and vertically to form a well - connected profile respectively. Based on the calibrated stratification data and taking the seismic interpretation data as the basis, trace the strata to establish a stratigraphic framework profile; Step 3: Divide and compare the key horizons of the drilled wells in the area, count the sand - to - shale ratio and mud - to - shale ratio, calculate the compaction rate, and then obtain the restored formation thickness; Step 4: Well - seismic combination: Establish seismic isochronous interfaces and marker beds, establish seismic facies stratigraphic interfaces in the area through well - layer calibration of known wells, which are stable and continuously traceable throughout the area and have obvious waveform reflection characteristics; Calculate the formation thickness data between different horizons through the reflection interfaces of different horizons, and restore the original thickness of the formation through decompaction correction; Step 5: Combine the formation thickness data of known wells and the formation thickness data of seismic reflection horizons in the area, verify each other, draw the isopach map of the current formation thickness, and then restore the original thickness of the formation through decompaction correction, and further obtain the original distribution characteristic map of the paleo - topography in that period; Step 6: Decorate and color, decorate and mark each formation thickness unit according to the legend, improve the corresponding mapping elements, and obtain the restored original paleo - topography map.

3. The method for restoring the original paleo - topography according to claim 1, Characterized in that, The specific steps for establishing the stratigraphic framework in step 2 are as follows: First, select the key wells, combine the core and logging characteristic curves to find the marker beds in the area, connect them horizontally and vertically to form a well - connected profile respectively. Based on the calibrated stratification data and taking the seismic interpretation data as the basis, trace the strata to establish a stratigraphic framework profile.

4. The method for restoring the original paleo - topography according to claim 1, Characterized in that, For calculating the compaction rate of the target formation of the known well in step 3 and then obtaining the original formation thickness: First, count the known sand - to - shale ratio and mud - to - shale ratio, calculate the compaction rate, and then obtain the restored formation thickness.

5. The method for restoring the original paleo - topography according to claim 4, Characterized in that, According to the compaction rate K = K 砂 *Φ 砂 +K 泥 *Φ 泥 , the formation thickness H0 = H + H*K of the target layer of the known well after compaction correction is obtained, and then the ancient landform distribution pattern is restored and completed; In the formula: K: Comprehensive rock compaction rate; K 砂 : Sandstone compaction rate, test value is 0.2; K 泥 : Shale compaction rate, the test value is 0.6; Φ 砂 : Sand ratio; Φ 泥 : Mud ratio; H0: Original formation thickness before compaction; H: Current formation thickness; Correct different lithologies in the formation respectively to obtain the original formation thickness H0 before compaction.

6. The method for restoring the original paleo - topography according to claim 5, Characterized in that, In step 4, to obtain the formation thickness of different seismic reflection interfaces, based on the different seismic reflection characteristics of different formations, seismic isochronous interfaces and marker beds are established. Then, using the calibration of known well horizons, the horizons are further refined, and a seismic sequence interface that is stable in distribution and can be continuously traced in the region is established. The formation reflection interface is selected using the seismic wave characteristics, and the formation thickness H = Δt0 * V is obtained by the reflection velocity and time of the seismic wave at two interfaces. And Δt0 = Tp1 - Tp2, and the original formation thickness H0 = H + H * K is obtained after decompaction correction 砂 *Φ 砂 +H*K 泥 *Φ 泥 , and the distribution characteristics of the paleo-topography are further obtained; In the formula: H0: Original formation thickness before compaction; Δt0: Seismic reflection time difference; V: Seismic inter - layer reflection velocity; Tp1: Seismic reflection target layer 1; Tp2: Seismic reflection target layer 2.

7. The method for restoring the original paleo-topography according to claim 5, characterized in that in step 5, the present-day formation thickness contour map is drawn by combining the known well formation thickness data and the regional seismic reflection layer formation thickness data, which are mutually corroborated, and then the original thickness of the formation is restored through decompaction correction, and further the original distribution characteristic map of the paleo-topography of this period is obtained.

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