A method and system for modeling a two-dimensional geological structure of an underground karst topography

Abstract

The application discloses a kind of karst landform area underground two-dimensional geological structure modeling method and system, belong to geophysical exploration technical field.For the problem that karst landform area seismic data signal-to-noise ratio is low, physical property is strong inhomogeneous, drilling data is deficient and leads to poor geological modeling precision, the present application obtains electrical property, seismic and geological multi-source information by magnetotelluric sounding, two-dimensional seismic and shallow surface geological survey;With well-by-side sounding constraint electrical property structure processing;Comprehensive electrical property gradient zone and seismic wave group difference identification fracture;Deep region is tracked stratum using electrical property marker layer and seismic wave group, and stratum morphology is restored based on surface occurrence and drilling thickness in shallow region;Whether stratum sequence and thickness meet regional rule is evaluated by block, and model is iteratively optimized.The present application can significantly improve the modeling precision and reliability of underground two-dimensional geological structure in karst landform area, and is low in cost, easy to operate, applicable to low exploration degree region.

Description

Technical Field

[0001] This invention relates to the field of geophysical exploration technology, specifically to a method and system for modeling the underground two-dimensional geological structure in karst landform areas. Background Technology

[0002] Subsurface geological structures are a fundamental aspect of geology and a primary vehicle for studying regional tectonic evolution and its resource and environmental effects. In recent years, with the decreasing availability of shallow geological resources and the gradual shift of mineral development towards deeper strata, the accuracy of subsurface geological structures, especially deep geological structures, has become particularly important for resource exploration and evaluation.

[0003] Because traditional methods such as route profiling reveal limited geological information, and because the geological structural characteristics of shallow and deep sections in complex tectonic zones differ significantly, the modeling of subsurface geological structures is highly dependent on geophysical methods. Currently, previous researchers have conducted extensive work on methods for modeling subsurface geological structures, resulting in a series of approaches. There are two main types: The first is a single geophysical interpretation under physical property or drilling constraints. For example, based on regional rock property analysis, marker layers are determined by constructing rock property columns or drilling calibration, followed by lateral tracing and integration with faults to ultimately establish a geological-geophysical model. This method is widely used in oil and gas basin areas with abundant deep well and high-precision reflection seismic data. The second type is a multi-method combined interpretation. By analyzing the physical properties of different strata, such as density, magnetic susceptibility, and resistivity, the resistivity, magnetic susceptibility, and gravity information are assigned to each stratum on the initially constructed geological model for fitting, continuously optimizing and iterating to obtain the optimal geological model.

[0004] The main drawbacks of existing technical solutions include: 1) The surface of the karst landform area in southern China is widely developed with carbonate rocks, karst formations, and fractures, making seismic acquisition a challenge. The low signal-to-noise ratio of seismic data makes it difficult to obtain reflection data that reflects the underlying geological structure, especially for strata shallower than 0.5-1.0 km, resulting in significant difficulties in geological structure modeling. 2) The sedimentary facies of marine sedimentary strata in southern China exhibit rapid lateral variations, strong heterogeneity of rock strata, and a large range of rock physical values. Furthermore, due to the volume effect of gravity, magnetic, and electrical methods, the accuracy of combined interpretation using these methods is low, leading to poor application results. 3) Three-dimensional structural modeling technology is primarily based on a large amount of deep drilling and high-precision seismic data. However, in areas with low exploration levels, there are often only 1-2 risk wells, resulting in relatively scarce data and making three-dimensional structural modeling technology difficult to apply.

[0005] In summary, current modeling of the underground two-dimensional geological structure in the southern karst landform region is mainly based on non-seismic geophysical methods with volume effects, such as gravity, magnetism, and electricity. The physical property data are highly heterogeneous, and there are few wells, resulting in low accuracy of the geological structure model.

[0006] To address the aforementioned issues, there is an urgent need for a method and system for modeling the underground two-dimensional geological structure in karst landform areas, which can solve the problems existing in traditional methods. Summary of the Invention

[0007] The purpose of this invention is to provide a method and system for modeling the underground two-dimensional geological structure in karst landform areas, which can significantly improve the modeling accuracy and reliability of the underground two-dimensional geological structure in karst landform areas, and is low in cost, easy to operate, and suitable for areas with low exploration level.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for modeling the underground two-dimensional geological structure in karst landform areas includes:

[0010] Step 1: Select the marine sedimentary strata outcrop area, collect regional geological maps and drilling data from adjacent areas, statistically analyze the occurrence of the main faults, determine the main structural trends in the region, and clarify the sequence structure of the strata, the range of strata thickness, and the macroscopic variation trend;

[0011] Step 2: Select an area where multiple strata are continuously exposed, and deploy a magnetotelluric sounding device and a shallow surface geological profile drawing device perpendicular to the structural strike of the same profile to obtain electrical structural profiles and shallow surface geological profiles.

[0012] Step 3: Conduct well-side sounding, using resistivity logging as a constraint, determine the main frequency bands and electrical principal axis parameters for magnetotelluric sounding data processing, obtain the regional electrical structure, and extract the center point depth of significant resistivity anomalies below the measuring point;

[0013] Step 4: Deploy a two-dimensional seismic measurement device along the same profile, and conduct fine processing of seismic data based on geological guidance, guided by the characteristics of shallow surface geological profiles, to obtain stacking time profiles and stacking depth profiles;

[0014] Step 5: Under the constraint of surface faults, refer to the position of electrical gradient zones or electrical discontinuities on the electrical structure profile, and identify the location and attitude of the main faults and secondary faults on the seismic profile based on the continuity of the seismic phase axis and the transverse differences of wave groups, and draw them on the seismic profile to form a fault structure profile.

[0015] Step 6: Overlay the elevation profile and stratigraphic boundary onto the seismic profile. For deep regions with a depth greater than a preset threshold, project the location of the low-resistivity body onto the seismic overlay depth profile. Compare and determine the seismic reflection wave group characteristics of the low-resistivity marker layer. Use the low-resistivity marker layer as the first marker layer, and the layers located below the low-resistivity marker layer as the second and third marker layers. The amplitude of the second and third marker layers is greater than that of the first marker layer, the continuity of the second and third marker layers is better than that of the first marker layer, and the second and third marker layers have layered reflections. According to the regional stratigraphic thickness variation trend, mark the geological strata of the second and third marker layers. Based on the location and attitude variation characteristics of the marker layers, trace them laterally and match them with the fault structures.

[0016] Step 7: For shallow areas with a depth less than the preset threshold, determine the boundary of the strata on the surface along the profile, calculate the apparent dip angle of the strata along the profile, calculate the bottom boundary depth of the strata based on the strata thickness revealed by drilling, perform lateral tracking and connection according to the trend of strata attitude changes, and match it with faults.

[0017] Step 8: Repeat step 7 to determine the bottom interface and lateral distribution trend of each stratum exposed on the surface from top to bottom, and draw a preliminary geological-geophysical integrated model.

[0018] Step 9: Based on the location of the main fault, divide the profile into different segments, obtain the stratigraphic sequence structure and single-layer thickness of each segment, and evaluate whether it conforms to the regional variation range and lateral variation trend. If it does not conform locally, adjust the fault occurrence and stratigraphic superposition in the stratigraphic thickness anomaly area, and finally obtain a geological model that conforms to the constraints of geological and geophysical multi-source information.

[0019] Furthermore, in step 1, when extracting surface fault information, geological maps at a scale of 1:200,000 or larger are used; when statistically analyzing the strike of the main faults in the region, rose diagrams are created at 5° intervals; when statistically analyzing the changing trend of the thickness of the strata in the region, contour maps are drawn using the Kriging interpolation method.

[0020] Furthermore, in step 2, the magnetotelluric sounding device uses a five-component tensor observation, with a sampling point distance of 500–1000 m, a sampling frequency band of 320–0.001 Hz, an electrode distance of 100 m, and a recording duration of more than 24 hours.

[0021] Furthermore, in step 2, the number of control points of the shallow surface geological profile drawing device is greater than 1.2 times the number of stratigraphic boundaries in the profile.

[0022] Furthermore, in step 3, during well-side sounding, the magnetotelluric sounding device uses a five-component tensor observation, with a distance of less than 100m from the well, a sampling frequency band of 320–0.01Hz, an electrode distance of 100m, and a recording duration of more than 20 hours.

[0023] Furthermore, in step 4, the two-dimensional seismic measurement device adopts a three-line, one-shot wide-line two-dimensional seismic observation system with a trace spacing of 20m, a shot spacing of 80m, a well depth of 14-18m, and a charge of more than 12kg.

[0024] Furthermore, in step 6, the preset threshold ranges from 0.5km to 1.0km.

[0025] This invention also provides a system for modeling the underground two-dimensional geological structure in karst landform areas, applied to the aforementioned method for modeling the underground two-dimensional geological structure in karst landform areas, comprising:

[0026] The data acquisition and preprocessing unit is used to collect regional geological maps and drilling data, statistically analyze the occurrence of main faults, determine the main structural trends in the region, and clarify the sequence structure of strata, the range of strata thickness, and macroscopic variation trends.

[0027] The geophysical data acquisition unit is deployed perpendicular to the structural trend to acquire magnetotelluric sounding data, two-dimensional seismic data, and simultaneously conduct shallow surface geological profile measurements to obtain electrical structural profiles, reflection seismic profiles, and shallow surface geological profiles.

[0028] The integrated modeling and evaluation unit, connected to the data acquisition and preprocessing unit and the geophysical data acquisition unit, is used to construct and evaluate a two-dimensional underground geological structure model based on multi-source data.

[0029] The integrated modeling and evaluation unit includes:

[0030] The fracture structure identification module is used to identify and draw the main fractures and secondary fractures on the seismic profile based on the continuity of the phase axis and the lateral difference of the wave group, under the constraint of surface fractures and in combination with the electrical gradient zone or electrical discontinuity zone on the electrical structure profile, thus forming a fracture structure profile map.

[0031] The deep strata tracking module is used to determine the marker layer for areas with a depth greater than a preset threshold by combining the depth of the low-resistivity interface and the seismic wave group characteristics of the corresponding strata, and to perform lateral tracking in conjunction with the fault structure.

[0032] The shallow strata tracking module is used to determine the bottom interface and lateral variation trend of each stratum from top to bottom, based on the surface strata occurrence and the strata thickness revealed by drilling, for areas with a depth less than a preset threshold, and to match it with faults.

[0033] The model evaluation and optimization module is used to divide the profile into different segments based on the location of the main faults, evaluate whether the stratigraphic sequence structure and single-layer thickness of each segment conform to the regional variation range and macro-variation trend, and adjust the fault occurrence and stratigraphic superposition relationship in the stratigraphic thickness anomaly area if there is a local discrepancy.

[0034] In summary, the present invention has at least one of the following beneficial technical effects:

[0035] 1. Significantly improves the modeling accuracy of underground two-dimensional geological structures in karst landform areas: This invention abandons the limitations of single geophysical methods and adopts a collaborative strategy of "multi-method, multi-attribute, and mutual constraint". By organically combining magnetotelluric sounding, two-dimensional seismic surveys, and shallow surface geological surveys, and using drilling data for calibration, it achieves multi-dimensional and multi-level constraints on fault locations, stratigraphic attitudes, and deep interfaces, effectively overcoming the problems of insufficient or non-unique information from single methods, making the final geological model more consistent with the actual underground conditions.

[0036] 2. Effectively solves the modeling challenges of low signal-to-noise ratio seismic data: Addressing the issues of low signal-to-noise ratio and difficulties in shallow imaging in karst landforms, this invention proposes a differentiated modeling method based on depth and strategy. For deep regions with high signal-to-noise ratios, lateral tracing is fully utilized using seismic wave groups and electrical marker layers; for shallow regions with extremely low signal-to-noise ratios, the reliance on low-quality seismic reflections is bypassed, and instead, surface attitude measurements and well thickness data are used to geometrically reconstruct the stratigraphic floor. This strategy of "deep geophysical dominance and shallow geostatistical dominance" allows for effective control of the entire profile, significantly improving the completeness and reliability of the modeling.

[0037] 3. Provides an efficient and low-cost modeling solution for areas with low exploration levels: This invention does not rely on a large number of densely distributed deep wells or high-precision 3D seismic exploration; it only requires a small number of risk wells and conventional 2D geophysical surveys. All data is acquired through ground surveys, the operation process is standardized, highly targeted, and cost-controllable. Furthermore, through a step-by-step modeling process and a built-in evaluation-optimization mechanism, models can be quickly built and validated, making it highly suitable for regional geological structure surveys and resource potential assessments in karst landform areas with limited funding and scarce basic data.

[0038] 4. Enhanced Model Rationality and Reliability: This invention incorporates an evaluation and feedback optimization step based on regional geological patterns at the end of the modeling process. By interpreting the model into different fault blocks, it verifies whether their stratigraphic sequence and thickness conform to regional variation trends. If not, it backtracks and adjusts faults or stratigraphic attitudes. This closed-loop process ensures that the final model not only matches measured data in terms of geophysical properties such as physical properties and wave groups, but also fundamentally conforms to the regional tectonic evolution patterns, avoiding errors that might arise from a "geophysical theory" that violates geological common sense. Attached Figure Description

[0039] Figure 1 This is a flowchart illustrating the method of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0041] like Figure 1 As shown, this invention provides a method for modeling the underground two-dimensional geological structure in karst landform areas, including:

[0042] Step 1: Select the marine sedimentary strata outcrop area, collect regional geological maps and drilling data from adjacent areas, statistically analyze the occurrence of the main faults, determine the main structural trends in the region, and clarify the sequence structure of the strata, the range of strata thickness, and the macroscopic variation trend;

[0043] Step 2: Select an area where multiple strata are continuously exposed, and deploy a magnetotelluric sounding device and a shallow surface geological profile drawing device perpendicular to the structural strike of the same profile to obtain electrical structural profiles and shallow surface geological profiles.

[0044] Step 3: Conduct well-side sounding, using resistivity logging as a constraint, determine the main frequency bands and electrical principal axis parameters for magnetotelluric sounding data processing, obtain the regional electrical structure, and extract the center point depth of significant resistivity anomalies below the measuring point;

[0045] Step 4: Deploy a two-dimensional seismic measurement device along the same profile, and conduct fine processing of seismic data based on geological guidance, guided by the characteristics of shallow surface geological profiles, to obtain stacking time profiles and stacking depth profiles;

[0046] Step 5: Under the constraint of surface faults, refer to the position of electrical gradient zones or electrical discontinuities on the electrical structure profile, and identify the location and attitude of the main faults and secondary faults on the seismic profile based on the continuity of the seismic phase axis and the transverse differences of wave groups, and draw them on the seismic profile to form a fault structure profile.

[0047] Step 6: Overlay the elevation profile and stratigraphic boundary onto the seismic profile. For deep regions with a depth greater than a preset threshold, project the location of the low-resistivity body onto the seismic overlay depth profile. Compare and determine the seismic reflection wave group characteristics of the low-resistivity marker layer. Use the low-resistivity marker layer as the first marker layer, and the layers located below the low-resistivity marker layer as the second and third marker layers. The amplitude of the second and third marker layers is greater than that of the first marker layer, the continuity of the second and third marker layers is better than that of the first marker layer, and the second and third marker layers have layered reflections. According to the regional stratigraphic thickness variation trend, mark the geological strata of the second and third marker layers. Based on the location and attitude variation characteristics of the marker layers, trace them laterally and match them with the fault structures.

[0048] Step 7: For shallow areas with a depth less than the preset threshold, determine the boundary of the strata on the surface along the profile, calculate the apparent dip angle of the strata along the profile, calculate the bottom boundary depth of the strata based on the strata thickness revealed by drilling, perform lateral tracking and connection according to the trend of strata attitude changes, and match it with faults.

[0049] Step 8: Repeat step 7 to determine the bottom interface and lateral distribution trend of each stratum exposed on the surface from top to bottom, and draw a preliminary geological-geophysical integrated model.

[0050] Step 9: Based on the location of the main fault, divide the profile into different segments, obtain the stratigraphic sequence structure and single-layer thickness of each segment, and evaluate whether it conforms to the regional variation range and lateral variation trend. If it does not conform locally, adjust the fault occurrence and stratigraphic superposition in the stratigraphic thickness anomaly area, and finally obtain a geological model that conforms to the constraints of geological and geophysical multi-source information.

[0051] In step 1, when extracting surface fault information, geological maps at a scale of 1:200,000 or larger are used. When statistically analyzing the strike of the main faults in the region, rose diagrams are created at 5° intervals. When statistically analyzing the variation trend of the stratum thickness in the region, contour maps are drawn using the Kriging interpolation method.

[0052] In step 2, the magnetotelluric sounding device uses a five-component tensor observation, with a sampling point distance of 500–1000 m, a sampling frequency band of 320–0.001 Hz, an electrode distance of 100 m, and a recording duration of more than 24 hours.

[0053] The number of control points in the shallow surface geological profile drawing device is more than 1.2 times the number of stratigraphic boundaries in the profile.

[0054] In step 3, during well-side sounding, the magnetotelluric sounding device uses a five-component tensor observation, with a distance of less than 100m from the well, a sampling frequency band of 320–0.01Hz, an electrode distance of 100m, and a recording duration of more than 20 hours.

[0055] In step 4, the two-dimensional seismic measurement device adopts a three-line, one-shot wide-line two-dimensional seismic observation system (3L1S500T observation system), in which each line receives 500 channels, the channel spacing is 20m, the shot spacing is 80m, the well depth is 14-18m, and the charge is more than 12kg.

[0056] In step 6, the elevation profile and stratigraphic boundaries are superimposed on the seismic profile. For deep regions with a depth greater than a preset threshold, the location of the low-resistivity body is projected onto the seismic stacking depth profile. The seismic reflection wave group characteristics of the low-resistivity marker layer are compared and determined. The low-resistivity marker layer is designated as the first marker layer, and the strata located below the low-resistivity marker layer are designated as the second and third marker layers. The amplitudes of the second and third marker layers are greater than those of the first marker layer, and the continuity of the second and third marker layers is better than that of the first marker layer. The second and third marker layers exhibit layered reflection. Based on the regional stratigraphic thickness variation trend, the geological strata of the second and third marker layers are marked. Based on the location and attitude variation characteristics of the marker layers, lateral tracking is performed and matched with fault structures. Specifically:

[0057] Project the low-resistivity body location obtained in step 3 onto the fracture structure profile obtained in step 5, compare and determine the seismic reflection wave group characteristics of the strata with low resistivity characteristics (first marker layer), trace them laterally and match them with the fracture; at the same time, for the part with a depth greater than 0.5-1.0 km and a relatively high signal-to-noise ratio, based on the first marker layer and according to the regional stratum thickness, infer the strata with relatively clear seismic activity and a high signal-to-noise ratio on the profile (second marker layer, third marker layer, etc.), trace them laterally and match them with the fracture structure.

[0058] It should be noted that, based on the processed seismic stacking time profiles and migration time profiles, low signal-to-noise ratio (SNR) is characterized by "weak amplitude energy and poor continuity of seismic phase axes, exhibiting overall blank reflections and chaotic reflections"; relatively high SNR is characterized by "strong amplitude energy and good continuity of seismic phase axes, exhibiting overall layered reflection characteristics." Strata located below low-resistivity marker layers, exhibiting strong amplitude, good continuity, and layered reflections with relatively high SNR, are designated as second and third grade marker layers. Based on the regional stratigraphic thickness variation trend, the geological strata of the second and third grade marker layers are determined. Then, based on the location and attitude variation characteristics of the marker layers, lateral tracking is performed and matched with fault structures.

[0059] In step 7, for shallow areas with a depth less than a preset threshold, the boundaries of the strata at the surface are determined along the profile, the apparent dip angle of the strata along the profile is calculated, the bottom boundary depth of the strata is calculated based on the strata thickness revealed by drilling, and lateral tracing and connection are performed according to the trend of strata attitude changes, and matched with faults. Specifically:

[0060] For the portion with a depth of less than 0.5-1.0 km and a low signal-to-noise ratio, the elevation profile is overlaid on the seismic profile based on the reference surface and replacement velocity during processing. The location of the stratigraphic boundary is marked, and the apparent dip angle of the strata along the profile is calculated. The bottom boundary depth of the strata is calculated based on the stratigraphic thickness revealed or inferred from drilling. Lateral tracing and connection are performed according to the changing trend of the attitude of the same set of strata in the lateral direction, and the tracing is matched with the fault.

[0061] In step 9, based on the location of the main fault, the profile is divided into different segments. The stratigraphic sequence structure and single-layer thickness of each segment are obtained, and their conformity with the regional variation range and lateral variation trend is assessed. If they do not conform locally, the fault attitude and stratigraphic superposition in the stratigraphic thickness anomaly area are adjusted. Finally, a geological model that conforms to the constraints of multi-source geological and geophysical information is obtained, specifically:

[0062] Based on the location of the main fault, the profile is divided into different parts, and the stratigraphic sequence structure and thickness of individual strata in each part are obtained. The stratigraphic thickness is evaluated to determine whether it conforms to the regional variation range and its lateral variation trend. If it is consistent with the regional variation trend and the error is within 5%, the geological structural model is considered to be completed. If it does not conform locally, the fault occurrence and stratigraphic superposition in the stratigraphic thickness anomaly area are adjusted to finally obtain a geological model that conforms to multi-source information such as geology and geophysics (electricity, wave group).

[0063] This invention also provides a system for modeling the underground two-dimensional geological structure in karst landform areas, applied to the aforementioned method for modeling the underground two-dimensional geological structure in karst landform areas, comprising:

[0064] The data acquisition and preprocessing unit is used to collect regional geological maps and drilling data, statistically analyze the occurrence of main faults, determine the main structural trends in the region, and clarify the sequence structure of strata, the range of strata thickness, and macroscopic variation trends.

[0065] The geophysical data acquisition unit is deployed perpendicular to the structural trend to acquire magnetotelluric sounding data, two-dimensional seismic data, and simultaneously conduct shallow surface geological profile measurements to obtain electrical structural profiles, reflection seismic profiles, and shallow surface geological profiles.

[0066] The integrated modeling and evaluation unit, connected to the data acquisition and preprocessing unit and the geophysical data acquisition unit, is used to construct and evaluate a two-dimensional underground geological structure model based on multi-source data.

[0067] The integrated modeling and evaluation unit includes:

[0068] The fracture structure identification module is used to identify and draw the main fractures and secondary fractures on the seismic profile based on the continuity of the phase axis and the lateral difference of the wave group, under the constraint of surface fractures and in combination with the electrical gradient zone or electrical discontinuity zone on the electrical structure profile, thus forming a fracture structure profile map.

[0069] The deep strata tracking module is used to determine the marker layer for areas with a depth greater than a preset threshold by combining the depth of the low-resistivity interface and the seismic wave group characteristics of the corresponding strata, and to perform lateral tracking in conjunction with the fault structure.

[0070] The shallow strata tracking module is used to determine the bottom interface and lateral variation trend of each stratum from top to bottom, based on the surface strata occurrence and the strata thickness revealed by drilling, for areas with a depth less than a preset threshold, and to match it with faults.

[0071] The model evaluation and optimization module is used to divide the profile into different segments based on the location of the main faults, evaluate whether the stratigraphic sequence structure and single-layer thickness of each segment conform to the regional variation range and macro-variation trend, and adjust the fault occurrence and stratigraphic superposition relationship in the stratigraphic thickness anomaly area if there is a local discrepancy.

[0072] Embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0073] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0074] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0075] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0076] Contents not described in detail in this specification are prior art known to those skilled in the art. It is hereby indicated that the above description is intended to help those skilled in the art understand this invention, but does not limit the scope of protection of this invention. Any equivalent substitutions, modifications, improvements, or simplifications of the above descriptions that do not depart from the essential content of this invention fall within the scope of protection of this invention.

Claims

1. A method for modeling the underground two-dimensional geological structure in karst landform areas, characterized in that, include: Step 1: Select the marine sedimentary strata outcrop area, collect regional geological maps and drilling data from adjacent areas, statistically analyze the occurrence of the main faults, determine the main structural trends in the region, and clarify the sequence structure of the strata, the range of strata thickness, and the macroscopic variation trend; Step 2: Select an area where multiple strata are continuously exposed, and deploy a magnetotelluric sounding device and a shallow surface geological profile drawing device perpendicular to the structural strike of the same profile to obtain electrical structural profiles and shallow surface geological profiles. Step 3: Conduct well-side sounding, using resistivity logging as a constraint, determine the main frequency bands and electrical principal axis parameters for magnetotelluric sounding data processing, obtain the regional electrical structure, and extract the center point depth of significant resistivity anomalies below the measuring point; Step 4: Deploy a two-dimensional seismic measurement device along the same profile, and conduct fine processing of seismic data based on geological guidance, guided by the characteristics of shallow surface geological profiles, to obtain stacking time profiles and stacking depth profiles; Step 5: Under the constraint of surface faults, refer to the position of electrical gradient zones or electrical discontinuities on the electrical structure profile, and identify the location and attitude of the main faults and secondary faults on the seismic profile based on the continuity of the seismic phase axis and the transverse differences of wave groups, and draw them on the seismic profile to form a fault structure profile. Step 6: Overlay the elevation profile and stratigraphic boundary onto the seismic profile. For deep regions with a depth greater than a preset threshold, project the location of the low-resistivity body onto the seismic overlay depth profile. Compare and determine the seismic reflection wave group characteristics of the low-resistivity marker layer. Use the low-resistivity marker layer as the first marker layer, and the layers located below the low-resistivity marker layer as the second and third marker layers. The amplitude of the second and third marker layers is greater than that of the first marker layer, the continuity of the second and third marker layers is better than that of the first marker layer, and the second and third marker layers have layered reflections. According to the regional stratigraphic thickness variation trend, mark the geological strata of the second and third marker layers. Based on the location and attitude variation characteristics of the marker layers, trace them laterally and match them with the fault structures. Step 7: For shallow areas with a depth less than the preset threshold, determine the boundary of the strata on the surface along the profile, calculate the apparent dip angle of the strata along the profile, calculate the bottom boundary depth of the strata based on the strata thickness revealed by drilling, perform lateral tracking and connection according to the trend of strata attitude changes, and match it with faults. Step 8: Repeat step 7 to determine the bottom interface and lateral distribution trend of each stratum exposed on the surface from top to bottom, and draw a preliminary geological-geophysical integrated model. Step 9: Based on the location of the main fault, divide the profile into different segments, obtain the stratigraphic sequence structure and single-layer thickness of each segment, and evaluate whether it conforms to the regional variation range and lateral variation trend. If it does not conform locally, adjust the fault occurrence and stratigraphic superposition in the stratigraphic thickness anomaly area, and finally obtain a geological model that conforms to the constraints of geological and geophysical multi-source information.

2. The method for modeling the underground two-dimensional geological structure in karst landform areas according to claim 1, characterized in that, In step 1, when extracting surface fault information, geological maps at a scale of 1:200,000 or larger are used. When statistically analyzing the strike of the main faults in the region, rose diagrams are created at 5° intervals. When statistically analyzing the variation trend of the stratum thickness in the region, contour maps are drawn using the Kriging interpolation method.

3. The method for modeling the underground two-dimensional geological structure in karst landform areas according to claim 1, characterized in that, In step 2, the magnetotelluric sounding device uses a five-component tensor observation, with a sampling point distance of 500–1000 m, a sampling frequency band of 320–0.001 Hz, an electrode distance of 100 m, and a recording duration of more than 24 hours.

4. A method for modeling the underground two-dimensional geological structure in a karst landform area according to claim 2, characterized in that, In step 2, the number of control points of the shallow surface geological profile drawing device is more than 1.2 times the number of stratigraphic boundaries in the profile.

5. A method for modeling the underground two-dimensional geological structure in a karst landform area according to claim 1, characterized in that, In step 3, during well-side sounding, the magnetotelluric sounding device uses a five-component tensor observation, with a distance of less than 100m from the well, a sampling frequency band of 320–0.01Hz, an electrode distance of 100m, and a recording duration of more than 20 hours.

6. A method for modeling the underground two-dimensional geological structure in a karst landform area according to claim 1, characterized in that, In step 4, the two-dimensional seismic measurement device adopts a three-line, one-shot wide-line two-dimensional seismic observation system with a trace spacing of 20m, a shot spacing of 80m, a well depth of 14-18m, and a charge of more than 12kg.

7. A method for modeling the underground two-dimensional geological structure in karst landform areas according to claim 1, characterized in that, In step 6, the preset threshold ranges from 0.5km to 1.0km.

8. A system for modeling the underground two-dimensional geological structure in karst landform areas, applied to the method for modeling the underground two-dimensional geological structure in karst landform areas as described in any one of claims 1-7, characterized in that, include: The data acquisition and preprocessing unit is used to collect regional geological maps and drilling data, statistically analyze the occurrence of main faults, determine the main structural trends in the region, and clarify the sequence structure of strata, the range of strata thickness, and macroscopic variation trends. The geophysical data acquisition unit is deployed perpendicular to the structural trend to acquire magnetotelluric sounding data, two-dimensional seismic data, and simultaneously conduct shallow surface geological profile measurements to obtain electrical structural profiles, reflection seismic profiles, and shallow surface geological profiles. The integrated modeling and evaluation unit, connected to the data acquisition and preprocessing unit and the geophysical data acquisition unit, is used to construct and evaluate a two-dimensional underground geological structure model based on multi-source data. The integrated modeling and evaluation unit includes: The fracture structure identification module is used to identify and draw the main fractures and secondary fractures on the seismic profile based on the continuity of the phase axis and the lateral difference of the wave group, under the constraint of surface fractures and in combination with the electrical gradient zone or electrical discontinuity zone on the electrical structure profile, thus forming a fracture structure profile map. The deep strata tracking module is used to determine the marker layer for areas with a depth greater than a preset threshold by combining the depth of the low-resistivity interface and the seismic wave group characteristics of the corresponding strata, and to perform lateral tracking in conjunction with the fault structure. The shallow strata tracking module is used to determine the bottom interface and lateral variation trend of each stratum from top to bottom, based on the surface strata occurrence and the strata thickness revealed by drilling, for areas with a depth less than a preset threshold, and to match it with faults. The model evaluation and optimization module is used to divide the profile into different segments based on the location of the main faults, evaluate whether the stratigraphic sequence structure and single-layer thickness of each segment conform to the regional variation range and macro-variation trend, and adjust the fault occurrence and stratigraphic superposition relationship in the stratigraphic thickness anomaly area if there is a local discrepancy.

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