A method and system for calculating an isobathic palaeogeomorphology map

Abstract

The application provides a method and system for calculating an isobath ancient landform map, which comprises the following steps: determining an upper datum plane and a lower datum plane of a target layer, and obtaining residual thickness data and impression thickness data; jointly determining an ancient structure map of the upper datum plane period according to the impression thickness data and the residual thickness data; correcting the ancient structure map by using lithological data of a standard well in a study area to obtain an ancient landform map; and uniformly correcting the depth of the ancient landform map to obtain an isobath ancient landform map. The application first jointly determines an ancient structure pattern by using residual thickness data and impression thickness data, and then corrects the ancient structure map by using lithological data and thickness parameters of the target layer to obtain an isobath ancient landform map, so as to obtain high-precision isobath ancient landform data. The method is suitable for analyzing the ancient landform pattern after the deposition of a carbonate rock stratum, and can provide a basis for karst ancient landform prediction and sedimentation pattern analysis, and can also meet the needs of oil and gas exploration.

Description

Technical Field

[0001] This invention belongs to the field of petroleum exploration technology, and specifically relates to a method and system for calculating paleogeographic maps of equal depth. Background Technology

[0002] The Dengying Formation of the Upper Sinian System in the Sichuan Basin contains a thick (approximately 300–1200 m) dolomite formation, rich in resources and possessing enormous potential. The Dengying Formation's resources amount to 2.8 trillion cubic meters, but the proven rate is low, indicating a very broad exploration prospect. Therefore, conducting paleokarst geomorphological calculations of the Dengying Formation in the Upper Sinian System of the Sichuan Basin is of significant guiding importance for predicting the distribution of karst reservoirs in the weathering crust of the Dengying Formation and for subsequent oil and gas exploration work in the Dengying Formation.

[0003] There is extensive research on paleokarst oil and gas reservoirs both domestically and internationally. Among the main research areas are paleogeography, groundwater activity, and fractures. Paleogeography is a major factor influencing karst development, and its calculation is a key focus. Many scholars have attempted to calculate paleogeography in different regions using various methods. Currently commonly used methods include: geophysical methods, impression methods, residual thickness methods, sedimentological methods, sequence stratigraphy, and stripping methods.

[0004] However, these methods all have drawbacks. For example, geophysical methods are significantly limited by objective conditions; surface conditions and technical means significantly affect their resolution, and the landforms they reflect are generally macroscopic, unable to depict landform units in detail. The imprint method suffers from the difficulty in determining the strata serving as the reference surface, and the compaction correction of strata between the reference surface and the stripping surface is difficult to perform. The residual thickness method does not consider the influence of pre-deposition topography and stripping differences, resulting in large errors. Sedimentological methods and sequence stratigraphy are not easy to finely depict landform units. The layer leveling method is difficult to select when filling and aligning the reference surface in actual operation, and the compaction correction is difficult. The stripping technique adopts the principle of sedimentary compaction, namely: as the burial depth increases, the soil cover load of the strata also increases, leading to decreased porosity and volume. It can be assumed that the lateral position of the strata remains unchanged during deposition, only the longitudinal position changes. Therefore, the decrease in stratum volume is attributed to a decrease in stratum thickness. Furthermore, based on the assumption that the skeleton density remains constant during settlement, the skeleton thickness (also known as solid thickness) of the stratum remains constant, which leads to a relatively large error in the operation of this method.

[0005] In the existing technology, Liu Hong et al., in "Calculation and Significance of Paleokarst Landforms of Dengying Formation in Sinian System of Sichuan Basin" (Petroleum Exploration and Development, June 2015, 283-293), through comprehensive analysis of the Sinian System in Sichuan Basin and adjacent areas, believe that compared with the "residual thickness method", using the top boundary of Canglangpu Formation as the reference surface of the "imprint method" to calculate the paleokarst landforms of Dengying Formation has the advantages of strong comparability, stable distribution and easy identification. The results are more reasonable. Therefore, it is more reasonable to use the "imprint method" to calculate the paleokarst landforms of Dengying Formation in Sichuan Basin and adjacent areas.Figure 1 For the framework model of the seismic strata in the Sichuan Basin, the above methods are currently aimed at... Figure 1 The paleogeographic map of the Dengying Formation still lacks quantitative data methods. Therefore, it is urgent to establish a set of paleogeographic maps with quantitative digital height. Summary of the Invention

[0006] To address the above problems, this invention proposes a method for calculating iso-depth paleomorphology, the method comprising the following steps:

[0007] Determine the upper and lower reference planes of the target layer, and obtain residual thickness data and impression thickness data;

[0008] The paleotectonic map of the upper reference surface period was determined based on the impression thickness data and the residual thickness data.

[0009] Paleotectonic maps were corrected using lithological data from standard wells in the study area to obtain paleogeomorphic maps;

[0010] By setting the highest point of the paleogeographic map to sea level 0, and uniformly correcting the depth of the paleogeographic map, an equal-depth paleogeographic map is obtained.

[0011] Furthermore, the residual thickness data is the thickness data between the target layer and the lower reference surface; the impression thickness data is the thickness data between the target layer and the upper reference surface.

[0012] Furthermore, the determination of the upper and lower reference planes needs to satisfy the following two conditions:

[0013] The reference plane is an isochronous surface;

[0014] The reference surface is easy to track and identify in earthquakes.

[0015] Furthermore, the paleotectonic map of the upper reference surface period, determined jointly based on the impression thickness data and the residual thickness data, is performed using the following method:

[0016] Calculate the maximum thickness data and correction coefficient between the upper and lower reference planes based on the impression thickness data and residual thickness data;

[0017] The corrected relative height is calculated based on the maximum thickness data, the correction coefficient, and the residual thickness data.

[0018] Furthermore, the maximum thickness data is calculated using the following formula:

[0019] H max = m(i) + h(i)

[0020] In the formula, H maxrepresents the maximum thickness data, m represents the impression thickness data, h represents the residual thickness data, and i represents each virtual well data point;

[0021] The correction factor is calculated using the following formula:

[0022]

[0023] G represents the correction factor. This represents the average residual thickness data. This represents the average impression thickness data;

[0024] The relative height of the ancient tectonic map is calculated using the following formula:

[0025] y(i)=[H max -h(i)]×(1-G

[0026] In the formula, h represents the residual thickness data; G represents the correction coefficient; y represents the relative height of the paleostructure; and H represents the relative height of the paleostructure. max This represents the maximum thickness data, and i represents the data point in each virtual well.

[0027] Furthermore, the paleotectonic map correction based on the lithological data includes: correcting the paleotectonic map by the ratio of the total thickness of the mudstone and siltstone at the bottom of the overlying strata to the total thickness of the overlying strata.

[0028] Furthermore, the correction of the paleotectonic diagram includes the following steps:

[0029] Calculate the lithological benchmark value j in the standard well p :

[0030] j p =k p / m p

[0031] In the formula, k represents the thickness of the fine-grained sedimentary section at the bottom of the overlying strata above the target layer, m represents the imprint thickness data, and P is the standard well in each study area;

[0032] Calculate the lithological correction values ​​for data points on the structural map:

[0033] j(i)=k(i) / m(i)

[0034] In the formula, j is the lithology correction value, k represents the thickness of the fine-grained sedimentary section at the bottom of the overlying strata above the target layer, m represents the imprint thickness data, and i represents the data point in each virtual well.

[0035] Based on the lithological correction value and the lithological benchmark value, the relative paleogeomorphological map height data is calculated to obtain the paleogeomorphological map:

[0036] χ(i)=y(i)×{1-(j(i)-jp )}

[0037] χ represents the relative height of the paleogeographic map, y represents the relative height of the paleotectonic structure, and j represents the relative height of the paleotectonic map. p denoted as the lithological baseline value, j as the lithological correction value, and i as the data point in each virtual well.

[0038] Furthermore, the calculation formula for obtaining the aforementioned paleogeographic map of equal depth is as follows:

[0039] f(i)=χ(i)-H max

[0040] In the formula, f represents the paleogeographic elevation data, χ represents the relative paleogeographic map elevation data, and H... max This represents the maximum thickness data, and i represents the data point in each virtual well.

[0041] This invention also proposes a calculation system for iso-depth paleomorphology, the system comprising:

[0042] The acquisition module is used to determine the upper and lower reference surfaces of the target layer, and acquire residual thickness data and impression thickness data; the residual thickness data is the thickness data between the target layer and the lower reference surface; the impression thickness data is the thickness data between the target layer and the upper reference surface.

[0043] The construction module is used to jointly determine the paleotectonic map of the upper reference surface period using impression thickness data and residual thickness data;

[0044] The correction module is used to correct paleotectonic maps using lithological data from standard wells in each study area to obtain paleogeomorphological maps; the lithological data is the ratio of the total thickness of mudstone and siltstone to the total thickness of the overlying strata.

[0045] The quantization module sets the highest point of the ancient geomorphological map to sea level 0, uniformly corrects the depth of the ancient geomorphological map, and obtains an iso-depth ancient geomorphological map.

[0046] Furthermore, the correction module performs correction using the following formula:

[0047] χ(i)=y(i)×{1-(j(i)-j p )}

[0048] Where χ represents the relative height of the paleogeographic map, y represents the relative height of the paleotectonic structure, and j p denoted as the lithological baseline value, j as the lithological correction value, and i as the data point in each virtual well.

[0049] The beneficial effects of this invention are:

[0050] This invention first uses residual thickness data and impression thickness data to jointly determine the paleotectonic pattern. In order to obtain high-precision paleogeomorphic data of equal depth, the paleotectonic map is corrected by the overlying lithology data and thickness parameters of the target layer to obtain an equal-depth paleogeomorphic map. This method is suitable for analyzing the paleogeomorphic pattern after the deposition of carbonate strata, laying the foundation for karst paleogeomorphic prediction and sedimentary pattern analysis, and also meeting the needs of oil and gas exploration.

[0051] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 This diagram illustrates a pre-existing structural framework for the seismic formations of the Danian system in the Sichuan Basin.

[0054] Figure 2 A schematic diagram of a stratigraphic profile is shown in an embodiment of the present invention;

[0055] Figure 3 A flowchart illustrating the calculation method for equal-depth valley topographic maps in an embodiment of the present invention is shown;

[0056] Figure 4 The following is a contour map of the residual thickness within the study area in an embodiment of the present invention;

[0057] Figure 5 The following is a contour map of the impression thickness within the study area in an embodiment of the present invention;

[0058] Figure 6 This invention illustrates a paleogeographic relative height map of the study area before correction in an embodiment of the invention.

[0059] Figure 7 This invention presents a corrected paleogeographic relative height map of the study area in an embodiment of the invention.

[0060] Figure 8 An isohyetal geomorphological map of the study area in an embodiment of the present invention is shown. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0062] The Sichuan Basin is rich in marine carbonate oil and gas resources with enormous potential. Exploration practice shows that the intensity of carbonate reservoirs is closely related to karst, and the superposition and modification of shoal facies reservoirs by karst processes is the main formation mechanism of high-quality carbonate reservoirs in the Sichuan Basin. Previous studies have conducted relatively systematic research on the karstification stages and distribution of hill-shoal bodies in the weathering crust of the Dengying Formation, but paleogeomorphological research is relatively weak. The residual thickness method or imprint method is usually used to reflect its sedimentary paleogeomorphology, which has many irrationalities and restricts scientific research and exploration deployment, and urgently needs to be addressed.

[0063] To this end, this invention proposes a method for calculating paleogeomorphism of equal depth. This method uses the residual thickness data of the overlying strata and the underlying residual strata to determine the paleotectonic pattern. It uses the parameters of the overlying lithology and thickness of the target layer to correct the paleotectonic structure and obtain a high-precision paleogeomorphism map of equal depth. This method is suitable for analyzing the paleogeomorphic pattern after the deposition of carbonate strata and meets the needs of oil and gas exploration.

[0064] Specifically, with Figure 3 Using the flowchart shown as an example, the calculation method for an iso-depth paleogeographic map proposed in this invention will be described in detail:

[0065] S1: The reference plane above and below the preferred target plane.

[0066] A reference plane is selected above and below the target level for data calculation;

[0067] The selection of the reference surface should conform to the principles of isochronism and ease of tracking and identification on earthquakes. It is best to choose the lithology-facies transition surface.

[0068] S2: Obtain thickness data.

[0069] The thickness data between the target layer and the upper reference surface is obtained as the impression thickness data, and the thickness data between the target layer and the lower reference surface is obtained as the residual thickness data.

[0070] In one embodiment of the present invention, standard wells (usually one well per 400 square kilometers) are selected and evenly distributed within the mapping area. The thickness data of the target layer and the reference surface of each well are statistically analyzed to obtain the corresponding residual thickness data and impression thickness data. The maximum and minimum values ​​of these data are then statistically analyzed.

[0071] Secondly, using deep seismic data, a large number of virtual wells are established between standard wells. Typically, the grid density for basin-level maps is 1km×1km.

[0072] The residual thickness data of the study area in the embodiments of the present invention are as follows: Figure 4 As shown, the impression thickness data is as follows: Figure 5 As shown.

[0073] S3: Calculate the paleostructure data of the upper reference surface period.

[0074] The maximum thickness between the upper and lower reference planes is calculated using the impression thickness data and residual thickness data. Then, the paleotectonic height data of the upper reference plane period is calculated and corrected to obtain the paleotectonic height data of the upper reference plane period.

[0075] A paleotectonic profile of the study area in one embodiment of the present invention can be referred to. Figure 4 In the figure, m represents the impression thickness data, h represents the residual thickness data, wells A, B, and P represent standard wells in different areas, and k represents the thickness of the fine-grained sedimentary section at the bottom of the overlying strata above the target surface (the fine-grained sedimentary section includes mudstone and siltstone). Figure 2 The stratigraphic profile diagram shown illustrates the calculation method.

[0076] S3-1: Calculate the maximum thickness between the upper and lower reference surfaces based on the impression thickness data and the residual thickness data. The maximum thickness data is calculated using the following formula:

[0077] H max = m(i) + h(i)

[0078] In the formula, H max The maximum thickness data between the upper and lower reference planes is represented by m, the impression thickness data is represented by h, the residual thickness data is represented by i, and each variable corresponds to each virtual well data point.

[0079] S3-2: Calculate the correction coefficient based on the impression thickness data and residual thickness data, and correct the coefficient according to the following formula:

[0080]

[0081] In the formula, This represents the average residual thickness data. This represents the average impression thickness data, where G is the correction coefficient;

[0082] S3-3: Calculate the corrected relative height of the paleostructure based on the correction coefficient, maximum thickness data, and residual thickness data, using the following formula:

[0083] y(i)=[Hmax -h(i)]×(1-G

[0084] In the formula, y represents the relative height of the paleotectonic structure, and H... max represents the maximum thickness data, h represents the residual thickness data; G represents the correction coefficient; i represents each variable, that is, each data point in the virtual well.

[0085] S4: Calculate paleogeographic height data.

[0086] Paleotectonic maps were further corrected using lithological data (such as lithological benchmark values) from standard wells in each area to obtain paleogeomorphic maps. The lithological benchmark value is the ratio of the total thickness of the fine-grained sedimentary section (including mudstone and siltstone) at the bottom of the overlying strata to the total thickness of the overlying strata. In other words, correction was performed using the ratio of the thickness of the overlying fine-grained rock section to the impression thickness; the greater the thickness of the fine-grained rock section, the lower the paleogeomorphic profile, and vice versa, thus obtaining relative paleogeomorphic data.

[0087] Select a standard well to correct the relative height of the remaining well points, use lithology to correct the paleotectonic map data, and obtain the relative paleogeographic map height data.

[0088] Specifically, follow these steps:

[0089] S4-1: Calculation of lithological benchmark value j p

[0090] j p =k p / m p

[0091] In the formula, j p The value represents the lithological baseline, k represents the thickness of the fine-grained sedimentary section at the bottom of the overlying strata above the target surface, m represents the imprint thickness data, and P is the standard well.

[0092] S4-2: Calculate the lithological correction values ​​for data points on the structural map.

[0093] j(i)=k(i) / m(i)

[0094] In the formula, j represents the lithology correction value, k represents the thickness of the fine-grained sedimentary section at the bottom of the overlying strata above the target surface, m represents the imprint thickness data, and i represents the data point in each virtual well.

[0095] S4-3: Calculate the relative paleogeomorphic map height data based on the lithological correction value, paleotectonic relative height, and lithological benchmark value at any point:

[0096] χ(i)=y(i)×{1-(j(i)-j p )}

[0097] In the formula, χ represents the relative paleogeographic height, y represents the relative paleotectonic height, and j represents the relative height of the paleotectonic structure.p denoted as the lithological baseline value, j represents the lithological correction value, and i represents the data point in each virtual well.

[0098] In this embodiment, the relative height of other well points is corrected by selecting a standard well; that is, paleotectonic data is corrected using lithology to obtain relative paleogeographic height data. For example... Figure 6 The image shown is a relative height map of the paleotopography before correction in an embodiment of the present invention. Figure 7 This is a relative height map of paleogeography after lithological correction.

[0099] S5: Subtract the maximum thickness data from the corrected data points to obtain an equal-depth paleogeographic map.

[0100] The highest point of the paleogeographic map is set to sea level 0, which means the area with the thinnest residual carbonate rock and the thinnest overlying fine-grained segment has an elevation of 0. The overall height data is then uniformly corrected to obtain an iso-depth paleogeographic map.

[0101] f(i)=χ(i)-H max

[0102] In the formula, f represents the paleogeographic elevation data; χ represents the relative paleogeographic elevation data; and H... max This indicates the maximum thickness data.

[0103] In this embodiment, the final paleogeographic map obtained can be referred to Figure 8 As shown.

[0104] It should be noted that the above steps do not necessarily have to be strictly followed in the above order, and other steps may be performed between each step.

[0105] Based on the above calculation method, this invention proposes a calculation system for iso-depth paleomorphology, which specifically includes an acquisition module, a construction module, a correction module, and a quantization module.

[0106] in,

[0107] The acquisition module is used to determine the upper and lower reference surfaces of the target layer, and acquire residual thickness data and impression thickness data; the residual thickness data is the thickness data between the target layer and the lower reference surface; the impression thickness data is the thickness data between the target layer and the upper reference surface.

[0108] The construction module is used to jointly determine the paleotectonic map of the upper reference surface period using impression thickness data and residual thickness data;

[0109] The correction module is used to correct paleotectonic maps using lithological data from standard wells in each study area to obtain paleogeographic maps. The lithological data is the ratio of the total thickness of mudstone and siltstone to the total thickness of the overlying strata.

[0110] The quantization module sets the highest point of the ancient geomorphological map to sea level 0, uniformly corrects the depth of the ancient geomorphological map, and obtains an iso-depth ancient geomorphological map.

[0111] Practice has proven that the calculation method and system for iso-depth paleogeographic maps proposed in this invention are feasible in establishing paleogeographic models, realizing the transformation from qualitative analysis to quantitative analysis, and achieving good results in front-line production applications.

[0112] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating paleomorphic features of equal depth, characterized in that, The method includes the following steps: Determine the upper and lower reference planes of the target layer, and obtain residual thickness data and impression thickness data; The paleotectonic diagram of the upper reference surface period is determined by combining the impression thickness data and the residual thickness data; wherein, the maximum thickness data and correction coefficient of the thickness data between the upper and lower reference surfaces are calculated based on the impression thickness data and the residual thickness data; the corrected relative height is calculated based on the maximum thickness data, the correction coefficient, and the residual thickness data; Paleotectonic maps were corrected using lithological data from standard wells in the study area to obtain paleogeomorphic maps, including: correcting the paleotectonic maps by the ratio of the total thickness of mudstone and siltstone at the bottom of the overlying strata to the total thickness of the overlying strata. By setting the highest point of the paleogeographic map to sea level 0, and uniformly correcting the depth of the paleogeographic map, an equal-depth paleogeographic map is obtained.

2. The method for calculating iso-depth paleomorphology according to claim 1, characterized in that, The residual thickness data is the thickness data between the target layer and the lower reference surface; the impression thickness data is the thickness data between the target layer and the upper reference surface.

3. The method for calculating isohyetal landforms according to claim 1 or 2, characterized in that, The determination of the upper and lower reference planes requires the following two conditions to be met: The reference surface is an isochronous surface; The reference surface is easy to track and identify in earthquakes.

4. The method for calculating isohyetal landforms according to claim 1 or 2, characterized in that, The maximum thickness data is calculated using the following formula: In the formula, H max The maximum thickness data is represented by m, the impression thickness data is represented by h, the residual thickness data is represented by i, and each virtual well data point is represented by i. The correction factor is calculated according to the following formula: G represents the correction factor. This represents the average residual thickness data. This represents the average impression thickness data; The relative height of the ancient tectonic map is calculated using the following formula: In the formula, h represents the residual thickness data; G represents the correction coefficient; y represents the relative height of the paleostructure; and H represents the relative height of the paleostructure. max This represents the maximum thickness data, and i represents the data point in each virtual well.

5. The method for calculating isohyetal landforms according to claim 1, characterized in that, Correcting paleotectonic maps involves the following steps: Calculate the lithological benchmark value j in the standard well p : In the formula, k represents the thickness of the fine-grained sedimentary section at the bottom of the overlying strata above the target layer, m represents the imprint thickness data, and P is the standard well in each study area; Calculate the lithological correction values ​​for data points in the structural map: In the formula, j represents the lithology correction value, k represents the thickness of the fine-grained sedimentary section at the bottom of the overlying strata above the target layer, m represents the imprint thickness data, and i represents the data point in each virtual well. Based on the lithological correction value and the lithological benchmark value, the relative paleogeomorphological map height data is calculated to obtain the paleogeomorphological map: χ represents the relative height of the paleogeographic map, y represents the relative height of the paleotectonic structure, and j represents the relative height of the paleotectonic map. p denoted as the lithological baseline value, j represents the lithological correction value, and i represents the data point in each virtual well.

6. The method for calculating iso-depth paleomorphology according to claim 1, characterized in that, The formula for obtaining the aforementioned paleogeographic map of equal depth is as follows: In the formula, f represents the paleogeographic elevation data, χ represents the relative paleogeographic map elevation data, and H... max This represents the maximum thickness data, and i represents the data point in each virtual well.

7. A calculation system for iso-depth paleomorphology, characterized in that, The system includes, The acquisition module is used to determine the upper and lower reference planes of the target layer and acquire residual thickness data and impression thickness data; the residual thickness data is the thickness data between the target layer and the lower reference plane. The impression thickness data is the thickness data between the target layer and the upper reference surface; The construction module is used to jointly determine the paleostructural diagram of the upper reference surface period using the impression thickness data and the residual thickness data; wherein, the maximum thickness data and correction coefficient of the thickness data between the upper and lower reference surfaces are calculated based on the impression thickness data and the residual thickness data; and the corrected relative height is calculated based on the maximum thickness data, the correction coefficient, and the residual thickness data. The correction module is used to correct paleotectonic maps using lithological data from standard wells in each study area to obtain paleogeomorphological maps; the lithological data is the ratio of the total thickness of mudstone and siltstone to the total thickness of the overlying strata. The quantization module is used to set the highest point of the ancient geomorphological map to sea level 0, uniformly correct the depth of the ancient geomorphological map, and obtain an iso-depth ancient geomorphological map.

8. The calculation system for iso-depth paleomorphology according to claim 7, characterized in that, The correction module performs correction using the following formula: Where χ represents the relative height of the paleogeographic map, y represents the relative height of the paleotectonic structure, and j p denoted as the lithological baseline value, j represents the lithological correction value, and i represents the data point in each virtual well.

Images