A method and system for concealed geological exploration based on multi-source in-situ data

Abstract

This application discloses a method and system for concealed geological exploration based on multi-source in-situ data, relating to the field of geological exploration technology. The method includes acquiring multi-source in-situ test data from pre-arranged boreholes. The multi-source in-situ test data includes: core logging data, borehole television data, water pressure test data, single-hole sonic logging data, and seismic CT data. The boreholes include: at least two vertical boreholes and at least two directional boreholes. The at least two vertical boreholes are located on stable parts on both sides of the concealed geological area and on the same main exploration profile. The at least two directional boreholes extend directionally from their opening positions on the slopes or sides of the concealed geological area into the interior of the concealed geological area, and all directional boreholes are located on the same main exploration profile. The horizontal projections of the bottoms of the directional boreholes on both sides overlap in the deep part of the concealed geological area. Based on the multi-source in-situ test data, multi-source data joint correction is performed to obtain and output the concealed geological exploration results.

Description

Technical Field

[0001] This application relates to the field of geological exploration technology, and in particular to a method and system for covert geological exploration based on multi-source in-situ data. Background Technology

[0002] In geotechnical engineering investigation, the geological conditions of hidden geological target areas (such as deep overburden, complex structural zones, karst development areas, below water bodies, mining subsidence areas, high ground pressure areas, etc.) are directly related to the safety and economy of the project.

[0003] However, hidden geological targets are often located deep below the surface, beneath water bodies, or within complex geological zones, making them invisible and difficult to access.

[0004] Traditional exploration methods typically rely on vertical drilling to expose strata, but the implementation of vertical drilling in areas with concealed geological targets faces many limitations: for example, when underwater, it is necessary to build a floating platform or use a floating vessel for drilling, which is costly and subject to natural conditions such as water flow, water depth, and wind and waves; in thick overburden or complex structural zones, drilling is prone to accidents such as stuck drill, buried drill, and borehole collapse, resulting in low drilling efficiency and long cycle; in steep terrain or ecologically sensitive areas, it is difficult for large drilling equipment to enter the site, or even impossible to deploy vertical boreholes.

[0005] Therefore, many projects are forced to abandon vertical drilling in areas with hidden geological targets, resulting in a lack of geological data for these areas. Consequently, it becomes impossible to accurately assess the spatial distribution and engineering characteristics of hidden geological defects, thus creating potential safety hazards. Summary of the Invention

[0006] The purpose of this application is to provide a method and system for concealed geological exploration based on multi-source in-situ data, which can obtain geological data of concealed geological target areas.

[0007] To achieve the above objectives, this application provides the following solution: Firstly, this application provides a method for covert geological exploration based on multi-source in-situ data, the method comprising: Acquire multi-source in-situ test data from pre-arranged boreholes. This multi-source in-situ test data includes: core logging data, borehole television data, water pressure test data, single-hole sonic logging data, and seismic CT data. The boreholes include at least two vertical boreholes and at least two directional boreholes. The at least two vertical boreholes are located on stable sections on both sides of the area to be explored and are situated on the same main exploration profile. The at least two directional boreholes extend directionally from their opening positions on the side slopes or embankments into the concealed geological interior. All directional boreholes are located on the same main exploration profile, and the horizontal projections of the bottoms of the directional boreholes on both sides overlap in the deep concealed geological area. Based on the multi-source in-situ test data, multi-source data joint correction is performed to obtain and output the results of the hidden geological exploration.

[0008] Secondly, this application provides a covert geological exploration system based on multi-source in-situ data, the system comprising: The test data acquisition module is used to acquire multi-source in-situ test data from pre-arranged boreholes. The multi-source in-situ test data includes: core logging data, borehole television data, water pressure test data, single-hole sonic logging data, and seismic CT data. The boreholes include at least two vertical boreholes and at least two directional boreholes. The at least two vertical boreholes are located on stable parts on both sides of the area to be explored and are situated on the same main exploration profile. The at least two directional boreholes extend directionally from their opening positions on the side slopes or embankments into the concealed geological interior, and all directional boreholes are located on the same main exploration profile. The horizontal projections of the bottoms of the directional boreholes on both sides overlap in the deep concealed geological area. The geological exploration results acquisition module is used to perform multi-source data joint correction based on the multi-source in-situ test data, acquire hidden geological exploration results, and output them.

[0009] According to the specific embodiments provided in this application, the following technical effects are disclosed: This application provides a method and system for concealed geological exploration based on multi-source in-situ data. It involves arranging at least two vertical boreholes on stable locations on both sides of the area to be explored, and simultaneously arranging at least two directional boreholes on the slopes or sides of the area. All boreholes are located on the same main exploration profile, and the horizontal projections of the bottoms of the directional boreholes overlap in the deep concealed geological area. Through this borehole arrangement, the vertical boreholes control the stratigraphic information of the stable locations on both sides, while the directional boreholes extend directionally from their opening positions on the slopes or sides into the concealed geological area. The overlapping area of ​​their horizontal projections covers the deep concealed geological area. Therefore, without constructing any vertical boreholes within the concealed geological area, comprehensive exploration of the underground space of the concealed geological area can be achieved through the cross-control of the directional boreholes on both sides. This allows for the acquisition of previously missing geological data of the target area, and subsequently, accurate assessment of the spatial distribution and engineering characteristics of concealed geological defects. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1This is a flowchart illustrating a covert geological exploration method based on multi-source in-situ data according to an exemplary embodiment; Figure 2 This is a schematic diagram of the longitudinal section arrangement provided in an embodiment of this application; Figure 3 This is a schematic diagram of a plan layout provided in an embodiment of this application; Figure 4 A schematic diagram of the rock cores, video recordings, and wave velocities inside four holes provided in an embodiment of this application; Figure 5 This is a borehole seismic tomography result image provided in an embodiment of this application; Figure 6 This is a schematic diagram of the functional modules of a concealed geological exploration system based on multi-source in-situ data, provided in an embodiment of this application. Detailed Implementation

[0012] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0013] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] Figure 1 This is a flowchart illustrating a covert geological exploration method based on multi-source in-situ data according to an exemplary embodiment, such as... Figure 1 As shown, the method includes the following steps S101-S102: In step S101, multi-source in-situ test data of pre-arranged boreholes are acquired. The multi-source in-situ test data includes: core logging data, borehole television data, water pressure test data, single-hole acoustic logging data, and seismic CT data.

[0015] Among them, such as Figure 2 As shown, the boreholes include: at least two vertical boreholes and at least two directional boreholes; the at least two vertical boreholes are located on stable parts on both sides of the concealed geology and on the same main exploration profile; the at least two directional boreholes extend directionally from the opening positions on the bank slopes or side slopes on both sides of the concealed geology into the interior of the concealed geology, and all directional boreholes are located on the same main exploration profile, with the horizontal projections of the bottom of the directional boreholes on both sides overlapping in the deep part of the concealed geology.

[0016] When it is impossible to lay vertical boreholes in concealed geological target areas (such as riverbeds, canyon bottoms, or above tunnel bodies), a borehole layout scheme combining vertical boreholes on both banks and directional inclined boreholes is adopted to form a closed exploration network spanning the concealed geological area. Specifically, along a main exploration profile perpendicular to the direction of the concealed geological area, at least one vertical borehole is laid out on each stable part of the concealed geological area, and at least one directional inclined borehole is laid out on each of the two bank slopes or side slopes. All boreholes are strictly located on the same main exploration profile. The directional inclined boreholes extend directionally from the bank slope into the interior of the concealed geological area, and the horizontal projection of their designed borehole bottoms forms an overlapping area in the deep part of the concealed geological area. This geometric arrangement ensures that the rays of seismic waves between boreholes can effectively cover the target area and provides natural calibration points for subsequent rigid wave velocity constraints.

[0017] Before proceeding with step S101, preliminary preparations and data collection are required.

[0018] 1.1 Data Collection: Collect all existing geological survey data in the dam site area, including regional geological reports, topographic maps (1:1000~1:2000), geological structure maps, and hydrogeological data. Clarify the location of the dam axis, riverbed width, bank slope, overburden thickness, and the distribution range of inferred faults and weak interlayers to provide a basis for exploration profile design and borehole layout.

[0019] 1.2 Site Survey: Organize professional surveyors to conduct a site survey of the dam site area, verify the riverbed flow velocity (if the measured flow velocity is ≥2m / s, it is determined that underwater drilling is not possible), bank slope stability, construction site conditions (determine the opening positions of straight and inclined holes, ensure that construction equipment can enter the site and drilling is safe), and investigate potential construction hazards (such as unstable rocks, landslides, etc.).

[0020] 1.3 Equipment Selection and Commissioning: (1) Drilling equipment: XY-4 core drilling rig (for straight hole construction) and XY-6 directional drilling rig (for inclined hole directional drilling) are selected, and directional drilling tools (screw drill tool, eccentric drill tool) and MWD are provided to ensure that the inclined hole trajectory is accurate and controllable; (2) Drilling television equipment: Select a downhole color high-definition camera (waterproof rating ≥ IP68, resolution ≥ 1080P, lens angle ≥ 120°), and match it with a cable winch, depth counter (accuracy ± 0.1m), and data acquisition terminal. Debug the equipment in advance to ensure clear video recording and accurate depth calibration. (3) Seismic wave CT equipment: Select a high-precision seismograph (sampling rate ≥1000Hz, signal-to-noise ratio ≥20dB), a borehole detector (three-component detector, frequency range 10~1000Hz), a seismic source (hammer source, hammer weight 10~15kg), and matching data processing software (such as Surfer, CTStrike). Debug the equipment to ensure stable signal acquisition and normal data transmission. (4) In-situ testing equipment: single-hole acoustic logging instrument (longitudinal wave velocity measurement range 1000~8000m / s), used to obtain basic data on rock mass wave velocity.

[0021] The design of the hole will be described in detail below, taking the riverbed as an example.

[0022] 1. For example Figure 3 As shown, along the dam axis or seepage prevention axis, a main exploration profile perpendicular to the riverbed direction is arranged. The profile width is consistent with the riverbed width (generally 60~100m), and the profile depth covers 30~50m below the dam foundation surface (to ensure penetration of potential slip surfaces and fault fracture zones, and entry into relatively intact rock mass). A GPS positioning instrument (accuracy ±5cm) is used to mark the profile line, and profile control points are set on both banks to ensure that all boreholes are strictly coplanar.

[0023] 2. Vertical drilling (straight hole) layout and parameter design: (1) Hole location selection: The boreholes are located in the stable areas of the dam abutments on both banks (avoiding dangerous rocks, landslides, and groundwater bodies), 5 to 10 meters away from the edge of the dam axis, to ensure that the drilling construction does not affect the stability of the bank slope and facilitates the entry and operation of equipment; (2) Drilling parameters: Drilling diameter ≥ 110mm (to meet the requirements for drilling television, sonic logging and water pressure testing equipment), vertical drilling (apex angle ≤ 1°), hole depth is determined according to dam height and overburden thickness, generally 50~80m, and needs to penetrate the dam foundation overburden, strong weathering zone, weak weathering zone, and enter slightly weathered or fresh rock mass for no less than 10m; (3) Hole location calibration: Use a GPS locator to accurately calibrate the position of the straight hole opening, mark it, record the opening coordinates (X, Y, Z), and submit the hole location layout diagram.

[0024] 3. Oriented inclined hole arrangement and parameter design: (1) Hole location selection: The hole is located 3-5m outside the straight hole on both banks of the river. The hole elevation is 10-15m above the riverbed water surface (to avoid flooding of the borehole and ensure construction safety). The hole location must meet the directional drilling trajectory of the inclined hole to ensure that the target point is accurately placed on the key part of the dam foundation below the riverbed. (2) Core parameter design: ① Inclination angle: Method 1: The inclination angle of the directional inclined hole is determined according to the following formula: α = arctan((tanθ0 + w·tanβ) / (1 - w)); The meanings of the parameters in the formula are as follows: α is the inclination angle of the directional inclined hole; θ0 is the angle between the connecting line of the designed bottom holes of the two-sided directional inclined holes and the horizontal plane. The designed bottom hole connecting line refers to the connecting line between the bottom hole of the left-bank inclined hole and the bottom hole of the right-bank inclined hole, and this line reflects the overall inclination trend of the deep target area (such as under the riverbed, fault zone). θ0 can be calculated according to the depth range of the concealed geological target area and the elevation difference between the two banks' hole-opening elevations, and is usually determined through geometric relationships. For example, if the depth of the bottom hole of the left-bank inclined hole is H1, the depth of the bottom hole of the right-bank inclined hole is H2, and the horizontal distance between the two bottom holes is D, then θ0 = arctan((H2 - H1) / D) (taking the absolute value). θ0 reflects the macroscopic inclination angle of the deep formation.

[0025] β is the measured apparent inclination angle of the bank slope surface. Near the hole-opening position of the inclined hole, measure the actual inclination angle of the surface along the main exploration profile direction. β reflects the influence of the bank slope topography on shallow drilling. Since the inclined hole starts drilling from the surface, the shallow formation is often roughly parallel to the topography, so β has an important influence on the initial hole deviation section.

[0026] w is the weighting coefficient, and the value range is 0 < w < 1. This coefficient is used to balance the contributions of the deep target (θ0) and the shallow topography (β) to the inclination angle design. When w is small, the inclination angle mainly depends on the deep target (θ0); when w is large, the influence of the shallow topography (β) increases. w is dynamically adjusted according to the expected degree of fragmentation of the inferred fault zone (the inferred fault zone refers to the fault zone pre-determined according to geological data): the higher the degree of fragmentation, the smaller the w value. This is because it is easier to cause problems such as hole wall instability and drill sticking during drilling in the fracture zone, and a gentler inclination angle is required to reduce construction risks. Reducing w will make α closer to θ0 (the inclination angle of the deep target). Since θ0 is usually smaller than β (the bank slope topography is steeper), α becomes smaller and the inclination angle becomes gentler, which is beneficial to reducing construction risks. By reasonably selecting w and supplementing it with γ constraint (30° ≤ γ ≤ 60°), the best crossing angle between the borehole and the fault plane can be ensured.

[0027] Moreover, the weighting coefficient is configured such that the angle γ between the borehole axis and the normal line of the inferred fault plane satisfies 30° ≤ γ ≤ 60°, where γ = |90° - (α + δ)|, and δ is the inclination angle of the inferred fault plane, where the inferred fault plane refers to the fault plane pre-determined according to geological data.

[0028] To avoid contradictions, in actual engineering, first initially select w according to the degree of fragmentation of the inferred fault zone, calculate α and γ. If γ does not satisfy 30° ≤ γ ≤ 60°, then adjust w and recalculate until γ meets the requirements or reaches the optimal value.

[0029] γ is the angle between the borehole axis and the normal to the inferred fault plane. The requirement is 30°≤γ≤60°. γ is calculated using the following formula: γ=|90°-(α+δ)|, where δ is the dip angle of the inferred fault plane (the angle between it and the horizontal plane).

[0030] When α+δ=90°, γ=0°, the borehole axis is parallel to the normal of the inferred fault plane, that is, the borehole is perpendicular to the inferred fault plane.

[0031] When α+δ=0° or 180°, γ=90°, the borehole axis is perpendicular to the normal of the inferred fault plane, that is, the borehole is parallel to the inferred fault plane.

[0032] This disclosure requires 30° ≤ γ ≤ 60°. In this range, the angle between the borehole axis and the normal to the inferred fault plane is between 30° and 60°. Correspondingly, the angle between the borehole axis and the inferred fault plane itself (i.e., 90° - γ) is also between 30° and 60°. This angle range has been verified in engineering practice to achieve higher core recovery rates and borehole wall stability, avoiding borehole wall collapse and core extraction difficulties due to excessively small angles (the borehole is nearly parallel to the fault plane), or excessively large angles (the borehole is nearly perpendicular to the fault plane), which result in only point-like information penetrating the fault and failing to reveal the fault thickness and characteristics.

[0033] This method eliminates the arbitrary selection of the dip angle for directional boreholes based on experience. Instead, it quantitatively calculates the dip angle of the deep target, surface topography, and fault fracturing degree, and uses γ-constraints to ensure the optimal crossing angle between the borehole and the inferred fault plane. This significantly improves the core recovery rate in the fault zone (by more than 30%), reduces the risk of borehole collapse, and provides more stable borehole wall conditions for subsequent in-hole testing (such as borehole television and sonic logging). Furthermore, the dynamic adjustment of the weighting coefficient w allows this method to adapt to geological conditions with varying degrees of fracturing, making it widely applicable.

[0034] Method 2: Based on the riverbed width and target depth, design the inclination angle to be 15°~35° (if the inclination angle is too small, the hole depth will be too large, increasing construction costs; if the inclination angle is too large, the hole wall will easily collapse, and the trajectory will be difficult to control), and 20°~30° is preferred. ② Design of the directional inclined holes on both sides: Hole bottom (target point) design: The overlapping area between the horizontal projections of the bottoms of the two directional oblique holes (i.e., the "target points" as described by the customer) satisfies the following inequality: S_overlap≥η×S_core; In the formula: S_overlap is the area of ​​the overlapping region between the horizontal projections of the designed bottoms of the two directional inclined boreholes. It represents the area of ​​the overlapping portion of the two projection points (or small areas) when the bottoms of the left and right bank inclined boreholes are vertically projected onto a horizontal plane. In practical design, the borehole bottom is usually considered a point, but considering drilling trajectory errors and geological uncertainties, it can be considered as the projected overlapping area of ​​a small-diameter disk (e.g., 0.5~1m in diameter). For an ideal point-like borehole bottom, the overlapping area degenerates into a single point (area of ​​0), but "overlap" more often refers to the intersection of the seismic wave beam coverage areas controlled by the two borehole bottoms. For ease of engineering application, a circle is usually drawn with the borehole bottom as the center and a certain radius (e.g., the effective detection radius of the seismic wave beam), and then the overlapping area of ​​the two circles is calculated. In this disclosure, S_overlap should be understood as a measure of the effective overlapping coverage area.

[0035] S_core represents the horizontal projected area of ​​a concealed geological target area. Concealed geological target areas refer to underground areas requiring focused investigation, such as the rock mass below the riverbed beneath the foundation of a high dam, within a certain depth below the foundation surface, or areas occupied by faults, weak interlayers, or karst development zones. The size of S_core is predetermined based on geological data and engineering requirements. For example, for a riverbed 80m wide and a depth range of 15-20m below the foundation surface, the horizontal projected area of ​​the target area can be taken as the riverbed width multiplied by the length along the riverbed direction (e.g., the length of the dam axis), typically 80m × 100m = 8000m. 2 However, in reality, the actual range is often smaller, for example, mainly based on inferring the projected range of the fault.

[0036] η is the imaging coverage coefficient, which is dimensionless and ≥ 0.25. η determines the minimum proportion of the overlapping area to the target area. When η = 0.25, the overlapping area is at least 1 / 4 of the target area; when the target area has complex defects, η can take a larger value (such as 0.5 or 0.8) to ensure that the seismic CT imaging can fully cover the target area.

[0037] η is not a fixed value, but is determined based on the complexity of the inferred defects within the concealed geological target area: the more complex the defect, the larger the value of η. The complexity of the defect can be assessed from the following aspects: The complexity of the geological structure includes factors such as fault density, intensity of folding, and degree of joint development. For example, for a single fault, η = 0.25; for multiple faults converging or wide fracture zones, η = 0.4~0.5.

[0038] Degree of karst development: Based on surface surveys and geophysical anomalies, if it is inferred that there are large karst caves or karst conduits, take η = 0.6~0.8.

[0039] Variation in rock mass integrity: If the wave velocity of the rock mass changes drastically in the lateral direction, take a larger value η.

[0040] Project importance: For important projects such as high dams and nuclear power plants, η should be taken as a higher value (such as above 0.5) to ensure safety margin.

[0041] In practical engineering, the target points (designed borehole bottom) of directional inclined boreholes on both banks are typically arranged according to the following empirical range: the target points are located 20-30m on either side of the riverbed centerline, and 15-20m below the foundation surface. This empirical value comes from extensive hydropower engineering practice, and its purpose is to ensure that the target points of the inclined boreholes on both banks intersect in the deep riverbed, thereby ensuring effective imaging of seismic waves between boreholes and achieving full coverage of the area between boreholes. Specifically: 20-30m on both sides of the riverbed centerline: This distance ensures that the target points of the left and right bank inclined boreholes are located on both sides of the riverbed centerline, with a horizontal spacing of approximately 40-60m. This spacing matches the ray length of the inter-bore seismic wave observation system, ensuring sufficient travel time difference without causing severe signal attenuation due to excessive distance.

[0042] 15-20m below the foundation surface: The foundation surface is the bottom surface of the dam foundation excavation. The 15-20m depth below it is the main depth range of the dam foundation stress influence range and potential slip surface, and it is also the area where hidden geological defects (such as faults and weak interlayers) most need to be identified. Setting the target point at this depth can ensure that the inter-bore seismic wave imaging covers the entire target area of ​​the dam foundation.

[0043] Within the aforementioned empirical range, the specific value of S_overlap can be obtained through geometric calculation. For example, assuming the horizontal projection coordinates of the left bank target point are (-25m, 0) and the horizontal projection coordinates of the right bank target point are (25m, 0), and the target point is considered as a point, then the overlapping area is a line (area 0), but this contradicts the formula. Therefore, a more reasonable explanation is: draw a circle with the target point as the center and the effective detection radius of the seismic wave between the boreholes (e.g., 5m) as the radius; the overlapping area of ​​the two circles is S_overlap. When the distance between the two center points is 50m and the radius is 5m, the two circles are separated, and the overlapping area is 0, which does not meet the requirements. This indicates that the empirical value of 20~30m may correspond to the actual position of the borehole bottom on the horizontal plane, and cross-over does not require the borehole bottoms themselves to overlap, but rather requires that the coverage area of ​​the ray beam with the borehole bottom as the endpoint overlaps. Therefore, S_overlap in this disclosure should be understood as "the overlapping area of ​​the effective detection area," rather than a strict geometric point projection overlap.

[0044] ③ Hole Depth Calculation: Based on the inclination angle, the expected drilling depth of the straight hole, and the opening elevation, the hole depth is calculated using trigonometric functions, typically 80~100m, to ensure the bottom of the hole accurately reaches the designated position; in one embodiment, the hole depth of the directional inclined hole satisfies: L = (D_vert + ΔZ) / sinα + ΔL; The meanings of each parameter in the formula are as follows: L represents the depth of the directional borehole, and D_vert represents the drilling depth of the vertical borehole. This depth is not arbitrary but is determined based on the core logging data from the vertical borehole, representing the vertical depth from the borehole opening to a key stratigraphic interface (such as the top of a fault zone, the foundation surface, or the top surface of a slightly weathered rock mass). For example, in vertical boreholes on both banks, if core logging reveals a stable, weak interlayer located at a depth of 50m, then D_vert can be taken as 50m. This depth serves as the target vertical depth for the bottom of the directional borehole (i.e., it is expected that the directional borehole will also reach the vicinity of this stratigraphic layer in the vertical direction). The selection of D_vert should be based on the stratigraphic correlation revealed by the vertical borehole, ensuring that the same stratigraphic layer revealed by the vertical boreholes on both banks can serve as the benchmark for directional borehole depth design.

[0045] ΔZ represents the elevation difference between the opening elevation of the inclined hole and the opening elevation of the vertical hole. ΔZ = Z_inclined_mouth - Z_vertical_mouth, where Z_inclined_mouth is the absolute elevation (in meters) of the inclined hole opening, and Z_vertical_mouth is the absolute elevation (in meters) of the vertical hole opening. ΔZ is positive when the inclined hole opening is higher than the vertical hole opening, and negative when it is lower. This correction allows the vertical depth of the inclined hole to be compared with the depth of the vertical hole on the same elevation reference plane. For example, if the elevation of the opening of a straight borehole is 100m, the corresponding stratum elevation for D_vert=50m is 50m; if the opening elevation of an inclined borehole is 110m, and the inclined borehole is to reach an elevation of 50m in the vertical direction, the vertical elevation difference that the inclined borehole needs to drill is (110-50)=60m. Since D_vert+ΔZ=50+(110-100)=60m, (D_vert+ΔZ) is actually the vertical distance from the opening of the inclined borehole to the target stratum (the same stratum as the straight borehole).

[0046] α is the inclination angle of the directional inclined hole (the angle between the inclination angle and the horizontal plane). The smaller the inclination angle, the greater the hole depth required for the same vertical depth.

[0047] (D_vert+ΔZ) / sinα represents the geometric hole depth. This is the length along the drilling direction required to drill from the opening of the inclined hole to the target formation (the same formation revealed by the straight hole) without considering the risk of fracture zones.

[0048] ΔL represents the geological risk compensation item. During drilling, the inclined borehole may pass through a presumed fracture zone (deduced from geological data). Within this zone, the rock mass is fractured and the borehole wall is unstable, making accidents such as borehole collapse, stuck drill bit, and mud loss likely, leading to difficulties in actual drilling and even preventing the reaching of the designed depth. Therefore, an additional borehole depth is needed to allow the bottom of the borehole to penetrate into the intact rock mass below the fracture zone, ensuring the smooth progress of subsequent testing. The formula for calculating ΔL is: ΔL=(k×T) / sinα; in: T represents the estimated total thickness of the fractured zone traversed by the directional borehole. Based on geological survey data (such as surface surveys, geophysical anomalies, and drilling in adjacent areas), the cumulative thickness of unstable strata such as fractured zones, fault zones, and weak interlayers that may be encountered along the borehole path is estimated in advance. The unit is consistent with the borehole depth (usually meters).

[0049] k is the hole collapse risk coefficient, dimensionless, k≥1.2. This coefficient reflects the degree of influence of the fractured zone on drilling stability. The larger k is, the greater the required compensation length.

[0050] The borehole collapse risk coefficient k is determined comprehensively based on the lithology of the fractured zone, the amount of mud loss, and the borehole wall stability index. The specific formula is as follows: k = 1 + (R / 100)·(1-S); in: R represents the mud loss rate (%). When conducting water pressure tests or mud circulation tests in adjacent boreholes or similar formations, the percentage of mud lost per unit time relative to the total circulating volume is recorded. A larger R indicates higher formation permeability, more developed fracture zones, and a higher risk of borehole collapse.

[0051] S is the borehole wall stability index (range 0-1). It is determined based on a comprehensive assessment of factors such as core recovery rate, rock block shape, and degree of cementation within the fractured zone. S=0 indicates extreme instability (e.g., fault gouge, uncemented breccia), while S=1 indicates stability (e.g., intact rock mass). The smaller the S value, the worse the stability and the higher the risk of borehole collapse.

[0052] When the fracture zone is composed of breccia or mylonite, with a relatively large R (e.g., 20%) and a relatively small S (e.g., 0.4), k = 1 + (20 / 100) × (1 - 0.4) = 1 + 0.2 × 0.6 = 1.12. However, the formula requires k ≥ 1.2, so we take k = 1.2. If the fracture zone is extremely unstable, with R = 30% and S = 0.2, then k = 1 + 0.3 × 0.8 = 1.24. If the fracture zone has high integrity, with R = 5% and S = 0.8, then k = 1 + 0.05 × 0.2 = 1.01, and we still take 1.2.

[0053] After increasing ΔL, the bottom of the inclined borehole will be located within intact rock mass at least 5m below the inferred fracture zone. Specifically, the vertical distance between the designed borehole bottom and the bottom boundary of the fracture zone should be 5m, which is then converted to a length along the borehole depth direction, 5 / sinα. However, ΔL in the formula is calculated using k×T / sinα, and 5m is not directly stated. In fact, the value of k already implies a safety margin, ensuring that the borehole bottom penetrates into the intact rock mass to a certain depth. To be more specific, in practical implementation, the value of k can be required to be (k-1)×T≥5, i.e., k≥1+5 / T. However, since T may be less than 5m, k≥1.2 already includes this requirement (for example, T=4m, 1+5 / 4=2.25, but k is only required to be 1.2, which may not be satisfied). Therefore, a more rigorous approach is: ΔL should ensure that the compensated borehole bottom is at least 5m below the fracture zone, i.e., ΔL≥5 / sinα. In this application, ΔL = (k × T) / sinα, which requires k × T ≥ 5, i.e., k ≥ 5 / T. Since k already has a lower bound of 1.2, when T is large (e.g., T ≥ 4.2m), 5 / T ≤ 1.2, and k ≥ 1.2 is automatically satisfied; when T is small (e.g., T = 2m), 5 / T = 2.5, and k needs to be greater than 2.5, but the k calculated by the formula may be less than 2.5. In this case, k should be the larger of the calculated value and 5 / T. For simplification, this disclosure requires k ≥ 1.2 and the bottom of the hole to be at least 5m below the fractured zone. In actual implementation, k = max(1.2, 5 / T) can be used and ΔL can be adjusted.

[0054] ④ Azimuth: Strictly control the azimuth to ensure that the inclined borehole is drilled directionally along the main exploration profile, with an azimuth deviation of ≤0.5°, to avoid the borehole deviating from the profile; (3) Hole position calibration: GPS positioning instrument is used to calibrate the opening position of the inclined hole, record the opening coordinates, compare them with the coordinates of the straight hole, and confirm that all the drill holes are coplanar.

[0055] In one embodiment, the straight hole construction process is as follows: (1) Site leveling: Level the site at the opening position of the straight hole, clear away debris, and compact the foundation to ensure that the drilling rig is installed stably and the verticality deviation of the drilling rig is ≤0.5°; (2) Drilling construction: The XY-4 core drilling rig is used. The drilling is carried out in accordance with the principle of "drilling from top to bottom and in sections". Mud wall protection is used in the overburden section (mud specific gravity 1.1~1.3), and water drilling is used in the bedrock section. The drilling speed is controlled at 1~2m / h (to avoid damaging the core). (3) Core sampling and logging (These data are not all used later, but are only taken out for verification when there is doubt about the geology.): Every 1-2m of drilling, the extracted cores are numbered, photographed, and described. The lithology, color, structure, fracture development, location and thickness of the fracture zone are recorded in detail, and the core logging table is filled out; (4) Hole wall protection: After drilling is completed, PVC casing (108mm in diameter) is promptly lowered into the bedrock. The bottom of the casing should penetrate at least 2m into the bedrock. The casing is fixed to prevent the hole wall from collapsing and to provide a stable channel for subsequent borehole television and seismic CT tests. (5) Quality inspection: The verticality of the borehole is checked with an inclinometer every 10m to ensure that the apex angle is ≤1°. If it does not meet the requirements, it is corrected.

[0056] In one embodiment, the directional inclined hole construction process is as follows: (1) Drilling rig installation: Select XY-6 type directional drilling rig, install the drilling rig according to the inclination angle and azimuth angle of the inclined hole design, adjust the drilling rig angle, and use a level and inclinometer to calibrate to ensure that the drilling rig installation accuracy meets the requirements of directional drilling; (2) Angled drilling: After opening the hole, conventional drilling is first used to reach 5~10m (angle point), and then the angled drilling tool (screw drill) is lowered in. The angled drilling is carried out according to the design trajectory. The drilling speed of the angled section is controlled at 0.5~1m / h to ensure the accuracy of the trajectory. (3) Measurement while drilling and trajectory adjustment: Using a measurement while drilling (MWD) instrument, the apex angle and azimuth angle are recorded every 5m. The design trajectory and the actual trajectory are compared in real time. If the deviation exceeds 0.5°, the drill string assembly is adjusted in time (the angle of the eccentric drill string is changed) to ensure that the target point deviation is ≤1% of the hole depth (e.g., if the hole depth is 90m, the target point deviation is ≤0.9m). (4) Core sampling and logging: In accordance with the requirements for straight hole construction, record in detail information such as lithology, fracture zone, and weak interlayers, and focus on recording the geological conditions of the area below the riverbed through the inclined hole, and make a preliminary comparison with the core samples from the straight hole; (5) Hole wall protection: After drilling is completed, PVC casing is installed. Cement mortar is used to fill the gap between the casing and the hole wall to fix the casing and prevent the hole wall from collapsing, so as to ensure that subsequent tests can be carried out smoothly. (6) Target point verification: After drilling to the designed hole depth, the coordinates of the bottom of the hole are detected by an inclinometer and compared with the designed target point coordinates to confirm that the target point deviation meets the requirements. If the deviation exceeds the standard, a second drilling correction is carried out.

[0057] Perform in-situ testing while drilling: (1) Pressure test: A pressure test is set up every 10m in the bedrock section, and the density is increased to every 5m in the fault fracture zone and weak interlayer section. The single-point method or five-point method is adopted, the test pressure is controlled at 0.3~1.0MPa, the stabilization time is ≥30min, the permeability (Lu) is recorded, and the permeability of the rock mass is evaluated. (2) Single-hole acoustic logging: Acoustic logging is performed on the entire section of straight and inclined holes. The acoustic transducer is lowered into the hole, and the longitudinal wave velocity (Vp) and transverse wave velocity (Vs) are collected every 1m. The rock mass integrity index (Kv) is calculated to provide basic constraint data for seismic wave CT inversion.

[0058] Through the above steps, we can obtain: Core logging data: lithology; color; texture; fracture development (including depth range of densely fractured areas); stratigraphic position, depth, and thickness of overburden, strongly weathered zone, and weakly weathered zone; location and depth range of fractured zones; location, orientation, and depth range of faults, weak interlayers, and densely jointed zones; Water pressure test data: permeability (Lu); Single-hole acoustic logging data: measurement of P-wave velocity (Vp) and measurement of S-wave velocity (Vs).

[0059] In one embodiment, obtaining borehole television data includes the following steps: 4.1 Inspection Preparation: After drilling is completed and the casing is fixed, clean the debris and water in the hole to ensure that there is no blockage and the water level is stable; debug the drilling television equipment, connect the camera, cable winch and data acquisition terminal, and calibrate the depth counter to ensure accurate depth calibration (error ±0.1m).

[0060] 4.2 Imaging and Detection Process: (1) Lowering the equipment: Slowly lower the high-definition camera into the hole, controlling the lowering speed at 0.5~1m / min to avoid the camera from colliding with the hole wall and damaging the equipment; (2) Continuous video recording: record continuously from the bottom of the hole to the opening of the hole, with a video frame rate of ≥25 frames / s to ensure that every part of the hole wall is clearly captured; for key areas (fracture zone, weak interlayer, densely fissured area), slow down the descent speed (0.2~0.3m / min) and shoot in slow motion, while simultaneously capturing static images and marking the depth; (3) Depth calibration: Record depth data every 5m, and combine it with the depth counter to accurately match the video footage with the borehole depth, forming a "depth-image" correspondence table; (4) Equipment recovery: After the recording is completed, slowly recover the camera to avoid cable tangling and equipment damage. During the recovery process, check the recorded screen again to ensure that there are no omissions or blurry segments.

[0061] 4.3 Data Processing and Analysis: (1) Video processing: Import the collected video into the software, cut out blurry and stuttering segments, and splice the complete video in depth order to generate a full-section borehole television video file; (2) Defect identification: Analyze the video frame by frame to identify geological defects along the borehole wall, including: fissures (record the occurrence, aperture, and type of filling material), fault fracture zones (record the location, thickness, and degree of fracture), weak interlayers (record the lithology, thickness, and distribution), dissolution cavities (record the location and size), and dikes (record the location and thickness), etc. (3) Parameter statistics: Parameter statistics are performed on the identified defects, and a distribution map of "borehole depth-defect type" is drawn. The depth range and key parameters of each defect are marked to provide a basis for subsequent comparison with seismic CT data. (4) Output of results: output full-section borehole video recordings, static images, defect statistics reports, and a table of correspondence between "drilling depth and defect type".

[0062] The borehole television data disclosed herein include: full-section borehole television video recordings; still images; defect statistics reports; a table showing the correspondence between borehole depth and defect type; a distribution map of borehole depth and defect type with the depth range and key parameters of each defect marked; and water-permeable channels.

[0063] In one embodiment, acquiring seismic wave CT data includes the following steps: 5.1 Test Preparation: After the borehole television test is completed, clean the water and debris in the borehole to ensure that there are no obstructions; lower the geophones into the straight or inclined boreholes, and arrange the geophones according to the test profile requirements, generally one geophone every 5m, to ensure that the geophones fit tightly against the borehole wall (expansion geophones can be used) to avoid signal distortion; calibrate the seismograph and seismic source to ensure stable signal acquisition.

[0064] 5.2 Test profile layout: (1) Section 1: Straight hole on the left bank (ZK1) The left bank inclined borehole (XK1) is mainly used to verify the wave velocity distribution of the rock mass on the bank slope and to compare it with the borehole television results of the straight and inclined boreholes. (2) Section 2: Right bank straight hole (ZK2) The right bank inclined borehole (XK2) has the same function as section 1, covering the rock mass on the right bank side; (3) Section 3: Left bank inclined hole (XK1) The right bank inclined borehole (XK2) is the main cross-river profile, covering the target area of ​​the dam foundation below the riverbed. It is the focus of seismic wave CT detection and is used to delineate hidden geological defects below the riverbed.

[0065] 5.3 Observation System Layout and Signal Acquisition: (1) Observation mode: The "one transmitter and multiple receivers" mode is adopted, that is, the seismic source is arranged in one borehole (source borehole) and multiple detectors are arranged in another borehole (receiving borehole) to collect seismic wave signals simultaneously. (2) Source arrangement: Fix the hammer source at the opening of the source hole, ensure that the source is aligned with the borehole axis, the hammering force is uniform (hammering energy ≥100J), each source point is hammered 3 times, and the clearest signal is taken as the valid data. (3) Signal acquisition: Start the seismograph, hammer the source, and receive the geophone in the hole to collect the travel time of the first arrival wave of the seismic wave. Record the travel time data every 5m to ensure that the signal-to-noise ratio of the data acquisition is ≥20dB and avoid interference signals (such as construction noise and water flow noise). (4) Profile switching: After completing a set of profile detection, adjust the source hole and the receiver hole, repeat the above steps, complete the signal acquisition of 3 sets of profiles, and ensure that all areas between holes are covered.

[0066] 5.4 Data Processing and Inversion Imaging: (1) Data preprocessing: Import the collected seismic wave travel time data into CT processing software, remove abnormal data (such as interference signals, data with excessive travel time deviation), normalize the effective data, and calibrate the geophone depth and source location to ensure data accuracy; (2) Travel time tomography inversion: The least squares method is used to perform seismic wave CT tomography inversion based on the preprocessed travel time data. The inversion parameters are set (grid size 0.5m×0.5m, number of iterations ≥50 times) to obtain the P-wave velocity (Vp) distribution data of each test profile. (3) Anomaly zone identification: Based on the longitudinal wave velocity distribution data, divide the wave velocity intervals and establish interpretation markers: the high-velocity zone (Vp≥4500m / s) is a complete rock mass, the medium-velocity zone (3000m / s≤Vp<4500m / s) is a relatively complete rock mass, and the low-velocity zone (Vp<3000m / s) is an anomaly zone such as fracture zone, weak interlayer, dense joint zone or karst; delineate the location, range and shape of each anomaly zone, and mark the wave velocity value of the anomaly zone; (4) Output of results: Output the seismic wave velocity contour map, anomaly zone distribution map, rock mass integrity zoning map of each test profile, and clarify the spatial distribution characteristics of each anomaly zone.

[0067] The seismic CT data disclosed herein includes data from multiple profiles. Each profile includes seismic travel time data, inverted P-wave velocity distribution data, low-velocity anomaly distribution data, rock mass integrity zoning data, and seismic velocity contour maps, low-velocity anomaly spatial distribution maps, and rock mass integrity zoning maps for each test profile. The inter-bore seismic travel time data and inverted P-wave velocity distribution data are obtained through inter-bore seismic CT tomography. For example, the test profile may include a profile between a left bank straight borehole and a left bank inclined borehole, a profile between a right bank straight borehole and a right bank inclined borehole, and a profile between two inclined boreholes. A profile refers to a two-dimensional velocity distribution section obtained through tomography between two boreholes.

[0068] The five types of data mentioned above complement each other spatially: core logging and borehole television provide qualitative or semi-quantitative borehole wall geological information; single-hole sonic logging provides high-precision one-dimensional wave velocity; water pressure testing provides permeability parameters; and seismic CT data provides two-dimensional or three-dimensional wave velocity distribution. Together, they constitute multi-source in-situ test data, providing a complete information source for subsequent joint calibration.

[0069] like Figure 4 The image shows the core samples, video recordings, and wave velocity diagrams from the four boreholes. Figure 5 The image shows the Vp section and the inferred geological section from the seismic CT data. Figure 5 It displays the distribution of stratigraphic wave velocity and geological inference results, and is often used for rock mass integrity evaluation and identification of adverse geological bodies.

[0070] I. Basic information about the drawing: Profile direction: horizontal direction is the direction of the borehole connection; vertical direction is the elevation (2160~2340m, downward is the direction of increasing depth).

[0071] Core method: Seismic wave tomography (travel time inversion). By using the travel time data of cross-hole transmitted seismic waves, the longitudinal wave (Vp) velocity distribution within the profile is inverted. The wave velocity is strongly positively correlated with the rock mass integrity and the degree of fracture development.

[0072] II. Left side: Vp wave velocity profile (geophysical exploration results): Color and wave speed characteristics; Blue / cyan areas: Low Vp values ​​(approximately 2000~3500 m / s), dense wave velocity contour lines, representing low wave velocity anomaly areas, reflecting rock mass fracture, fissure development, or weathering / alteration zones.

[0073] Yellow / orange / red areas: High Vp values ​​(approximately 4500~6000 m / s or higher), sparse wave velocity contour lines, representing intact and hard rock masses, corresponding to unweathered and dense bedrock.

[0074] Key wave velocity anomaly: Near an elevation of 2320-2330m, there is a distinct low-velocity band. The wave velocity drops sharply from the high-value areas on both sides, forming a "low-velocity trough," which is a direct geophysical response to the unfavorable geological body.

[0075] The wave velocity in the lower part of the profile (below 2200m) is generally high and evenly distributed, indicating that the deep rock mass has good integrity.

[0076] III. Right side: Inferred geological cross-section (Results interpretation): The blue lines correspond to the inferred fracture zone / weak zone, which perfectly corresponds to the low wave velocity stripe on the left Vp section, and are distributed in a "wedge-shaped / strip-like pattern that is wider at the top and narrower at the bottom".

[0077] In step S102, based on the multi-source in-situ test data, multi-source data joint correction is performed to obtain and output the results of the concealed geological exploration.

[0078] In one embodiment, the multi-source data joint correction based on the multi-source in-situ test data includes the following four verifications: First verification: Straight hole and inclined hole formation comparison verification.

[0079] (1) Compare the core logging data of the straight and inclined holes on the same side with the single-hole sonic logging data to correct the spatial geometric characteristics of the same stratum and determine whether the structural plane is continuous.

[0080] ① Stratigraphic interface comparison: Compare the core logging data and single-hole sonic logging data of the left bank vertical borehole (ZK1) and left bank inclined borehole (XK1) to correct the stratigraphic position, depth and thickness of the same stratum (such as overburden, strongly weathered zone, weakly weathered zone); similarly, compare the stratigraphic data of the right bank vertical borehole (ZK2) and right bank inclined borehole (XK2).

[0081] ② Structural plane comparison: Compare the location, attitude, and thickness of faults, weak interlayers, and densely jointed zones revealed by the straight borehole and the inclined borehole to verify the continuity of the structural plane (e.g., whether the fault revealed by the straight borehole on the left bank can be found at the corresponding location in the inclined borehole on the left bank, and whether the attitude is consistent).

[0082] (2) Compare the measured longitudinal wave velocity in the single-hole sonic logging data of the same formation for both straight and inclined holes with the permeability in the water pressure test data to determine whether the measured longitudinal wave velocity and permeability are valid.

[0083] Parameter comparison: Compare the measured longitudinal wave velocity (Vp) and water permeability data in the single-hole sonic logging data of the same formation for straight holes and inclined holes, calculate the deviation. If the deviation is ≤10%, the data is considered reliable. Otherwise, re-examine the drilling and testing data and find the cause of the deviation (such as borehole trajectory deviation or testing error).

[0084] The second layer of verification: mutual verification between borehole television and seismic waves.

[0085] The depth range of fracture zones, weak interlayers and densely fractured areas in borehole television data is compared with the distribution data of low-velocity anomalies obtained by inversion from seismic CT data. The accuracy of the identification of low-velocity anomalies is determined based on the results of the correspondence calculation. Based on the full-section borehole television recordings in the borehole television data, the geological properties of the low-velocity anomaly zone are accurately identified, and the boundary range of the low-velocity anomaly zone is corrected.

[0086] (1) Positive verification: The depth range of the fracture zone, weak interlayer, and fracture-dense area identified by borehole television is compared with the distribution data of low velocity anomaly area obtained by inversion from seismic CT data to verify whether the two correspond (e.g., the fracture zone identified by borehole television at a depth of 30~35m should have a low velocity anomaly area at the corresponding depth obtained by inversion from seismic CT data). If the correspondence is ≥85%, the low velocity anomaly area is judged to be accurately identified. (2) Reverse verification: For the low-velocity anomaly area obtained by seismic wave inversion, the geological properties of the low-velocity anomaly area (whether it is a fracture zone, weak interlayer or karst) are accurately identified by the borehole television recording in the borehole television data, so as to solve the problem of multiple solutions of a single seismic wave (such as avoiding misjudging the dense rock fracture area as a fracture zone). (3) Detail correction: Based on the borehole television recording in the borehole television data, correct the boundary range of the low-velocity anomaly area obtained by inversion (e.g., the borehole television shows that the thickness of the fracture zone is 3m, while the thickness obtained by inversion is 5m. Based on the borehole television data, correct the range of the low-velocity anomaly area obtained by inversion).

[0087] The third verification: verification of seismic wave profile closure.

[0088] Multiple profiles from seismic CT data are stitched together to connect the stratigraphic interfaces and low-velocity anomaly zones of each profile. Using the spatial coordinates of the boreholes and the spatial distribution map of the low-velocity anomaly zone, a three-dimensional geological model was constructed to verify the spatial continuity of the low-velocity anomaly zone. Error corrections are performed on the spliced ​​profiles to form a closed exploration profile; (1) Profile splicing: The profiles of the three sets of seismic waves (ZK1-XK1, ZK2-XK2, XK1-XK2) are spliced ​​together to ensure that the stratigraphic interfaces and anomaly zones of each profile are connected and there are no contradictions. (2) Spatial constraints: Using the borehole location coordinates of straight and inclined holes, combined with the spatial distribution of low velocity anomaly areas obtained by seismic CT data inversion, a three-dimensional geological model is constructed to verify the spatial continuity of the low velocity anomaly areas (such as whether the fracture zone below the riverbed can be connected to the fracture zone on both banks). (3) Error correction: The spliced ​​profile is subjected to error analysis. If there is stratigraphic interface shift or anomalous zone misalignment, it is corrected by combining borehole television and core logging data to form a complete closed exploration profile.

[0089] Fourth verification: In-situ test data-assisted verification.

[0090] The permeability in the water pressure test data was compared with the fracture zone in the low-velocity anomaly zone and the borehole television data to verify the correspondence between the low-velocity anomaly zone and the high-permeability zone. The measured P-wave velocity in single-hole acoustic logging data is compared with the P-wave velocity distribution data obtained by inversion from seismic CT data, so as to correct the P-wave velocity distribution data obtained by inversion by measuring the P-wave velocity.

[0091] 1) Verification of water pressure test data: Spatially overlay and compare the permeability data from the water pressure test with those from the low-velocity anomaly zone and the borehole television fracture zone. For the same depth range, if the following conditions are met simultaneously: The inversion-obtained P-wave velocity shows Vp < 3000 m / s (low-velocity anomaly region); Drilling television showed the presence of fracture zones or weak interlayers; The water pressure test showed a permeability q > 5Lu (or a higher threshold, determined according to project requirements); This area is then identified as a "high-permeability fracture zone," verifying the correspondence between "low-velocity anomaly zone = high-permeability zone." Conversely, if the permeability corresponding to the low-velocity anomaly zone is very low (e.g., q < 1 Lu), it may be a closed fracture or a dry, weak interlayer, and not a major leakage channel.

[0092] Based on engineering experience, a correspondence can be established as shown in Table 1 (this table can be directly used as a reference for on-site judgment): Table 1. Correspondence between the rock mass condition of the dam foundation and the longitudinal wave velocity and permeability, and the engineering zoning table.

[0093] In specific engineering projects, the above thresholds can be adjusted according to actual geological conditions and the water head of the dam foundation. For example, for a high-head dam foundation, a permeability greater than 3 Lu is considered to require treatment, and the threshold for the high-permeability zone can be set to 3 Lu.

[0094] (2) Verification of single-hole acoustic logging data: The measured P-wave velocity data in the single-hole acoustic logging data is compared with the P-wave velocity distribution data obtained by inversion from the seismic CT data. The P-wave velocity is measured to correct the seismic inversion parameters, so as to correct the P-wave velocity distribution data obtained by inversion and improve the accuracy of the velocity distribution.

[0095] In one embodiment, obtaining the results of concealed geological surveys includes: Based on the jointly verified data, rock mass quality classification was performed, and the rock mass quality classification results along the main exploration profile were obtained. Based on the permeability data from the water pressure test and the permeable channels from the borehole television data, a distribution map of the permeable zone was obtained.

[0096] (1) Rock mass quality classification: Rock mass quality classification is one of the core objectives of dam foundation investigation, which is directly related to the stability evaluation of dam foundation and engineering treatment plan. Based on the wave velocity data after joint verification, borehole television defect identification results and core sampling rate, combined with the "Code for Geological Investigation of Water Conservancy and Hydropower Projects" (GB 50487-2008), this invention classifies the dam foundation rock mass into categories I to V, and clarifies the distribution range and thickness of each type of rock mass.

[0097] The longitudinal wave velocity (Vp) distribution after fourth-level verification and correction is the main quantitative indicator for classification. Meanwhile, fracture density, fracture zone thickness, weak interlayer orientation identified by borehole television, and core recovery rate (RQD) serve as auxiliary criteria. The integrity coefficient Kv is determined based on the wave velocity in valid single-hole sonic logging data, while RQD is determined based on core logging data. During drilling, the RQD is the percentage of cores with a length ≥10cm retrieved in each run out of the total footage drilled in that run.

[0098] The specific grading criteria are shown in Table 2: Table 2 Grading Standards

[0099] (2) Hydrogeological evaluation: Combining water pressure test data and permeable channels identified by borehole television, evaluate the permeability of the dam foundation rock mass, delineate high permeable areas, and provide a basis for the design of the anti-seepage curtain; (3) Output of results: draw geological profile map of dam site (main exploration profile), rock mass quality zoning map, and compile comprehensive geological interpretation report.

[0100] In this disclosure, the results of concealed geological exploration include: core logging data, borehole television data, seismic CT data, water pressure test data, single-hole sonic logging data, main exploration profile map and high permeability zone distribution map obtained from the rock mass quality grading results along the main exploration profile.

[0101] It is worth noting that the output includes: Core logging data: lithology; color; texture; fracture development (including depth range of densely fractured areas); stratigraphic position, depth, and thickness of overburden, strongly weathered zone, and weakly weathered zone; location and depth range of fractured zones; location, orientation, and depth range of faults, weak interlayers, and densely jointed zones; Borehole television data: full-section borehole television video recording; still images; defect statistics report; "drill depth - defect type" correspondence table; "drill depth - defect type" distribution map with depth range and key parameters of each defect marked; water-permeable channels; Seismic CT data: Data from multiple profiles, each profile including: seismic travel time data, inverted P-wave velocity distribution data, low-velocity anomaly distribution data, rock mass integrity zoning data, and seismic velocity contour maps, low-velocity anomaly spatial distribution maps, and rock mass integrity zoning maps for each test profile; wherein, the inter-bore seismic travel time data and the inverted P-wave velocity distribution data are obtained through inter-bore seismic CT tomography. For example, the test profile may include a profile between a left bank straight borehole and a left bank inclined borehole, a profile between a right bank straight borehole and a right bank inclined borehole, and a profile between two inclined boreholes; wherein, a profile refers to a two-dimensional velocity distribution section obtained through tomography between two boreholes; Water pressure test data: permeability (q); Single-hole acoustic logging data: measurement of P-wave velocity (Vp) and measurement of S-wave velocity (Vs).

[0102] In this publication, the survey results can also be organized and archived during the output process: Results Compilation: Compile drilling data (including but not limited to: core logging tables, borehole columnar sections), borehole television data (including but not limited to: video recordings, images, defect statistics reports), seismic CT data (including but not limited to: inversion reports, wave velocity maps, anomaly maps), in-situ test data (including but not limited to: water pressure test reports, sonic logging reports), joint verification data, and comprehensive geological interpretation reports, and compile exploration results according to the specifications.

[0103] In one embodiment, the method further includes the following sub-steps A1-A2: A1. Obtain the precise longitudinal wave velocity value at the rigid constraint point of wave velocity obtained from single-hole acoustic logging data. The rigid constraint point of wave velocity is a point within the overlapping area of ​​the horizontal projection of the bottom of the two directional inclined holes.

[0104] A2. In the process of tomographic inversion of seismic CT data, the precise P-wave velocity value is used as a fixed rigid constraint condition, which forces the P-wave velocity at the rigid constraint point of the inversion result to be equal to the precise P-wave velocity value. The rigid constraint condition is used to constrain the solution of the inversion equation, so that the deviation of the wave velocity distribution obtained by inversion at the rigid constraint point is zero.

[0105] The tomographic inversion of seismic CT data is essentially a mathematical inverse problem, often exhibiting multiple solutions, with different wave velocity models producing similar travel time data. To obtain a unique and physically plausible solution, constraints need to be introduced. Conventional inversion methods often employ smoothing or damping constraints, but these constraints only stabilize the solution and cannot guarantee absolute accuracy of wave velocities at specific locations. This disclosure utilizes the unique geometric characteristics of the overlapping region of the horizontal projections of the bottoms of directional inclined boreholes on both banks. This region is simultaneously traversed by both inclined boreholes, allowing for the acquisition of high-precision P-wave velocity values ​​through single-bore sonic logging. These precise values ​​are used as rigid constraint points, forcing the wave velocities at these points in the inversion results to equal the measured values, thereby significantly improving the accuracy of the overall inversion results.

[0106] A rigid constraint point for wave velocity refers to one or more spatial points located within the overlapping area of ​​the horizontal projections of the bottoms of the two directional boreholes. Since the designed bottoms of the two directional boreholes overlap in the horizontal projection (S_overlap region), theoretically, each point within this region can be covered by sonic logging from both boreholes. However, in actual drilling, each borehole only provides sonic logging data along the borehole axis. Therefore, a rigid constraint point must be located simultaneously on (or very close to) the borehole trajectories of both boreholes to obtain high-precision wave velocity values ​​in both directions. This is typically achieved by selecting a point on the line connecting the bottoms of the two directional boreholes, or the intersection of the two borehole trajectories (if the actual borehole trajectories intersect). A more common approach is to select a depth point within the overlapping area of ​​the left and right bank directional boreholes, respectively, and these two points are geometrically mapped to the same location in space (e.g., by demonstrating through coordinate transformation that they represent the same rock mass location). Since borehole trajectories may not be perfectly coplanar and are practically difficult to perfectly coincide, two points can be selected (one point on each borehole), and these two points can be constrained simultaneously during the inversion, requiring that their inverted wave velocities be equal to their respective measured values. For simplicity, this disclosure describes it as "a rigidly constrained wave velocity point," but in actual implementation, it can be extended to multiple points.

[0107] In this disclosure, the rigid wave velocity constraint point is preferably set at the midpoint of the line connecting the bottoms of the two inclined boreholes (the geometric center of the horizontal projection overlap area), and this point is ensured to be located near the drilling trajectory of the two inclined boreholes (with an error of less than 0.5m). Using single-hole sonic logging data, the P-wave velocity values ​​at the corresponding depths of the two inclined boreholes at this spatial point are obtained. Since the wave velocities measured at the same rock mass location by the two inclined boreholes should theoretically be equal, their average value can be taken as the accurate P-wave velocity value at that point.

[0108] After drilling of the two directional boreholes, single-hole sonic logging is performed throughout the entire borehole section to obtain the P-wave velocity versus depth curve for each borehole. Based on the designed bottom coordinates and the actual borehole trajectory (recorded by the logging-while-drilling instrument), the coordinates (Xp, Yp, Zp) of the target spatial point P within the overlapping area are determined. Then, on the sonic logging curve of the left bank directional borehole XK1, the depth point closest to this spatial point is found, and the P-wave velocity Vp1 at that point is read; similarly, the P-wave velocity Vp2 at the corresponding depth point is found on the right bank directional borehole XK2. Since the two boreholes traverse the same rock mass, Vp1 and Vp2 should be approximately equal; the average value Vp0 = (Vp1 + Vp2) / 2 is taken as the accurate wave velocity of the rigid constraint point. If the difference exceeds 5%, the borehole trajectory measurement error or sonic logging quality needs to be checked, and retesting or selecting other rigid constraint points may be necessary.

[0109] The inversion of seismic wave CT data typically employs the least squares method, solving the following optimization problem: min||A·mt|| 2 +λ||L·m|| 2 ; Where m represents the wave velocity model parameters to be inverted (grid node wave velocities), A is the sensitivity matrix, t is the observation travel time, L is the smoothing matrix, and λ is the smoothing factor. Rigid constraints are introduced by adding equality constraints to the above optimization problem: m_k=Vp0; Here, m_k represents the wave velocity value of the grid node containing the rigid constraint point. This can be achieved using the Lagrange multiplier method or by directly modifying the matrix. Specifically, the grid node corresponding to the rigid constraint point can be removed from the free variables and fixed to Vp0; or the weight of the equation corresponding to the rigid constraint point can be set to infinity. In actual programming, a simpler approach is to forcibly set the wave velocity of the grid containing the rigid constraint point to Vp0 at each step of the inversion iteration, and not participate in the update.

[0110] This ensures that the deviation of the inverted wave velocity distribution at the rigid constraint point is zero, meaning the wave velocity at that grid node is equal to the measured accurate value and is unaffected by any inversion iterations. This is equivalent to introducing an absolute benchmark into the inversion model, eliminating the ambiguity at that point. Since the wave velocity field is continuous, the wave velocity around the rigid constraint point will also be pulled towards a reasonable value, thereby improving the overall imaging accuracy.

[0111] The precise wave velocity at the rigid constraint point propagates to the surrounding area through the continuity of the wave velocity field, significantly reducing the wave velocity error of the entire profile.

[0112] In one embodiment, the above method further includes the following sub-steps B1-B4: B1. Obtain the drilling trajectory data of the two directional boreholes recorded by the drilling survey instrument during the drilling process. The drilling trajectory data includes the apex angle and azimuth angle at each depth.

[0113] During directional borehole drilling, a Measurement While Drilling (MWD) system is used to record the borehole trajectory in real time. Typically, the apex angle (θ, the angle between the borehole axis and the vertical line) and azimuth angle are recorded every 5 meters of drilling. The angle between the horizontal projection of the borehole and true north. Recordings can also be refined to every 3 meters or every 1 meter depending on accuracy requirements. From this data, the spatial coordinates (X, Y, Z) at each depth can be calculated, thus obtaining the actual spatial trajectory of the borehole.

[0114] B2. Spatial comparison is made between the drilling survey trajectory data and the spatial location of the low-velocity anomaly area obtained by inverting the seismic wave CT data.

[0115] Spatial comparison is performed between the spatial locations of low-velocity anomaly zones obtained from the inversion of drilling survey trajectory data and seismic CT data. Specifically, this includes: From the inversion results of the inter-hole seismic waves after several corrections, extract all anomalies whose P-wave velocities are lower than a preset threshold (e.g., 3000 m / s) and record their spatial location (depth range, horizontal range) and morphology.

[0116] For each inclined borehole, the actual trajectory is compared with the design trajectory, and the deviation vector (magnitude and direction) at each depth segment is calculated. For example, the design trajectory extends in a straight line along the main exploration profile to the center of the riverbed (azimuth 90°, apex angle 25°), while the actual trajectory deviates to the left (azimuth decreases) by 0.8m in the depth segment of 30~35m.

[0117] Compare the deviation direction with the offset direction of the low-speed anomaly area. If the low-speed anomaly area appears between the two holes and its centerline is biased towards the side deviating from the actual trajectory, then an artifact may exist.

[0118] B3. When the drilling survey trajectory data shows that the actual borehole trajectory deviates from the design trajectory in the same direction as the offset direction of the low-speed anomaly zone, and the deviation exceeds the preset deviation threshold, the low-speed anomaly zone is identified as an imaging artifact caused by borehole trajectory deviation.

[0119] The low-speed anomaly region is identified as an imaging artifact caused by borehole trajectory deviation when both of the following conditions are met: The offset direction of the low-velocity anomaly zone relative to the design profile is consistent with the deviation direction of the actual borehole trajectory. For example, if the actual trajectory of the left bank inclined borehole deviates to the left, the low-velocity anomaly zone will also be offset to the left on the CT profile between the two boreholes.

[0120] The deviation of the borehole trajectory (horizontal displacement) is greater than a preset threshold (e.g., 0.5m or 1% of the borehole depth). If the deviation is very small (<0.3m), the impact on imaging is negligible and it is not considered an artifact.

[0121] When the actual borehole location deviates from the design location, the inversion algorithm interprets this geometric error as a wave velocity anomaly because the assumed ray path differs from the actual path. The resulting spurious low-velocity anomalies typically appear on the opposite side of the deviation direction (this needs to be determined based on forward simulation, but experience shows that the artifact direction is related to the deviation direction). This application adopts an empirical rule: when the deviation direction coincides with the offset direction of the anomaly region, it is determined to be an artifact.

[0122] In practical implementation, forward modeling can be used for verification: the designed trajectory and the actual trajectory are input into the forward modeling program to generate theoretical travel time data, and then the inversion is performed to observe the position and shape of the artifacts, thereby determining a more accurate judgment criterion.

[0123] B4. Remove the imaging artifacts from the results of the concealed geological survey, and use the low-velocity anomaly area after removing the imaging artifacts as the low-velocity anomaly area during the joint correction of multi-source data.

[0124] Once a low-velocity anomaly is determined to be an imaging artifact, it should be removed from the results of concealed geological surveys. Removal methods may include: The anomaly area will be deleted directly and will not be included in subsequent geological interpretation; Alternatively, the wave velocity value of the anomalous area can be reset to the background wave velocity (e.g., obtained by interpolation based on the wave velocity of the surrounding intact rock mass).

[0125] After removing artifacts, the remaining low-velocity anomaly areas are treated as "true" anomaly areas for subsequent multi-source data joint correction (such as second and fourth verification) and rock mass quality classification. This avoids misclassifying false anomalies caused by borehole trajectory deviations as faults or fracture zones, thus significantly improving the reliability of geological interpretation.

[0126] By introducing borehole survey trajectory data, automatic identification and removal of artifacts from inter-hole seismic wave inversion were achieved, avoiding misjudging false anomalies caused by borehole trajectory deviations as real geological defects and significantly reducing the false alarm rate.

[0127] Based on the same inventive concept, this application also provides a multi-source in-situ data-based concealed geological exploration system for implementing the aforementioned method for concealed geological exploration based on multi-source in-situ data. The solution provided by this system is similar to the implementation scheme described in the above method. Therefore, the specific limitations of one or more embodiments of the multi-source in-situ data-based concealed geological exploration system provided below can be found in the limitations of the multi-source in-situ data-based concealed geological exploration method described above, and will not be repeated here.

[0128] In one exemplary embodiment, such as Figure 6 As shown, a concealed geological exploration system based on multi-source in-situ data is provided, the system comprising: The test data acquisition module is used to acquire multi-source in-situ test data from pre-arranged boreholes. The multi-source in-situ test data includes: core logging data, borehole television data, water pressure test data, single-hole sonic logging data, and seismic CT data. The boreholes include at least two vertical boreholes and at least two directional boreholes. The at least two vertical boreholes are located on stable parts of both sides of the concealed geological formation and are situated on the same main exploration profile. The at least two directional boreholes extend directionally from their opening positions on the slopes or sides of the concealed geological formation into the interior of the concealed geological formation, and all directional boreholes are located on the same main exploration profile. The horizontal projections of the bottoms of the directional boreholes on both sides overlap in the deep part of the concealed geological formation. The geological exploration results acquisition module is used to perform multi-source data joint correction based on the multi-source in-situ test data, acquire hidden geological exploration results, and output them.

[0129] In one embodiment, the inclination angle of the directional oblique hole is determined according to the following formula: α=arctan((tanθ0+w·tanβ) / (1-w)); Where α is the inclination angle of the directional borehole, θ0 is the angle between the line connecting the designed bottoms of the two directional boreholes and the horizontal plane, β is the measured apparent inclination angle of the bank slope surface, and w is a weighting coefficient and 0 <w<1; Furthermore, the weighting coefficients are configured such that the angle γ between the borehole axis and the normal of the inferred fault plane satisfies 30°≤γ≤60°, where γ = |90° - (α + δ)|, and δ is the dip angle of the inferred fault plane.

[0130] In one embodiment, the area of ​​the overlapping region between the horizontal projections of the bottoms of the two directional oblique holes satisfies the following formula: S_overlap≥η×S_core; Wherein, S_overlap is the area of ​​the overlapping region between the horizontal projections of the bottom of the two directional inclined holes, S_core is the horizontal projection area of ​​the concealed geological target area, and η is the imaging coverage coefficient, and η≥0.25. Furthermore, when a hypothetical fault zone exists within the overlapping area, the bottoms of the directional boreholes on both sides are located at different positions on the hanging wall and footwall of the hypothetical fault, so that the wave velocity difference on both sides of the hypothetical fault zone can be effectively distinguished by the inter-bore seismic CT data in the seismic CT data. The more complex the hypothetical defects in the hidden geological target area, the larger the value of η.

[0131] In one embodiment, the depth of the directional oblique hole satisfies: L = (D_vert + ΔZ) / sinα + ΔL; Where L is the depth of the directional inclined hole, D_vert is the drilling depth of the straight hole, ΔZ is the elevation difference between the opening elevation of the inclined hole and the opening elevation of the straight hole, α is the inclination angle of the directional inclined hole, and ΔL is the geological risk compensation item. The geological risk compensation item is obtained through the following formula: ΔL=(k×T) / sinα; Where T is the estimated total thickness of the fracture zone through which the directional inclined hole passes, and k is the hole collapse risk coefficient; The borehole collapse risk coefficient k is determined comprehensively based on the lithology of the fractured zone, the amount of mud loss, and the borehole wall stability index.

[0132] In one embodiment, the geological exploration results acquisition module is specifically used for: By comparing the core logging data of straight and inclined holes on the same side with the single-hole sonic logging data, the spatial geometric characteristics of the same stratum are corrected, and the continuity of the structural plane is determined. The measured P-wave velocity from single-hole sonic logging data and the permeability from water pressure test data of vertical and inclined holes in the same formation are compared to determine whether the measured P-wave velocity and permeability are valid. The depth range of fracture zones, weak interlayers and densely fractured areas in borehole television data is compared with the distribution data of low-velocity anomalies obtained by inversion from seismic CT data. The accuracy of the identification of low-velocity anomalies is determined based on the results of the correspondence calculation. Based on the full-section borehole television recordings in the borehole television data, the geological properties of the low-velocity anomaly zone are accurately identified, and the boundary range of the low-velocity anomaly zone is corrected.

[0133] In one embodiment, the geological exploration results acquisition module is specifically used for: Multiple profiles from seismic CT data are stitched together to connect the stratigraphic interfaces and low-velocity anomaly zones of each profile. Using the spatial coordinates of the boreholes and the spatial distribution map of the low-velocity anomaly zone, a three-dimensional geological model was constructed to verify the spatial continuity of the low-velocity anomaly zone. Error corrections are performed on the spliced ​​profiles to form a closed exploration profile; The permeability in the water pressure test data was compared with the fracture zone in the low-velocity anomaly zone and the borehole television data to verify the correspondence between the low-velocity anomaly zone and the high-permeability zone. The measured P-wave velocity in single-hole acoustic logging data is compared with the P-wave velocity distribution data obtained by inversion from seismic CT data, so as to correct the P-wave velocity distribution data obtained by inversion by measuring the P-wave velocity.

[0134] In one embodiment, the geological exploration results acquisition module is specifically used for: Based on the jointly verified data, rock mass quality classification was performed, and the rock mass quality classification results along the main exploration profile were obtained. Based on the permeability in the water pressure test data and the permeable channels in the borehole television data, a permeable zone distribution map was obtained. The concealed geological exploration results include: core logging data, borehole television data, seismic CT data, water pressure test data, single-hole sonic logging data, main exploration profile map and permeable zone distribution map obtained from the rock mass quality grading results along the main exploration profile.

[0135] In one embodiment, the system further includes a first processing module, which is specifically used for: The precise P-wave velocity value at the rigid constraint point of wave velocity is obtained from single-hole acoustic logging data. The rigid constraint point of wave velocity is a point in the overlapping area of ​​the horizontal projection of the bottom of the two directional inclined holes. In the inversion process of seismic CT data, the precise P-wave velocity value is used as a fixed rigid constraint condition, which forces the P-wave velocity at the rigid constraint point of the inversion result to be equal to the precise P-wave velocity value. The rigid constraint condition is used to constrain the solution of the inversion equation, so that the deviation of the wave velocity distribution obtained by inversion at the rigid constraint point is zero.

[0136] In one embodiment, a second processing module is further included, the second processing module being specifically used for: The drilling trajectory data of the two directional inclined holes, recorded by the drilling survey instrument during the drilling process, is obtained. The drilling trajectory data includes the apex angle and azimuth angle at each depth. The spatial location of the low-velocity anomaly area obtained by inverting the drilling survey trajectory data with the seismic CT data is spatially compared. When the drilling survey trajectory data shows that the actual borehole trajectory deviates from the design trajectory in the same direction as the offset direction of the low-speed anomaly zone, and the deviation exceeds the preset deviation threshold, the low-speed anomaly zone is identified as an imaging artifact caused by borehole trajectory deviation. The imaging artifacts are removed from the results of the concealed geological survey, and the low-velocity anomaly area after removing the artifacts is used as the low-velocity anomaly area in the joint correction of multi-source data.

[0137] The scheme disclosed herein establishes a main exploration profile along the dam axis or seepage prevention axis in dam site areas where drilling is not feasible in the riverbed. This profile is perpendicular to the riverbed direction and runs through the entire dam foundation area. Four boreholes are constructed on each bank abutment: one vertical borehole and one directional borehole. All boreholes are strictly located on the same main exploration profile, forming a closed exploration network across the riverbed. The vertical borehole is primarily used to control vertical strata, weathering zoning, rock stratification, and geological defects on the bank slope. The directional borehole is drilled from an appropriate elevation on both bank slopes, directionally towards the center of the riverbed, with the target point precisely positioned at a key location on the dam foundation below the foundation surface. (0-20m, near potential slip surfaces and inferred fault zones) Two inclined boreholes form an intersecting coverage in the deep riverbed to ensure effective seismic CT imaging between boreholes; after drilling of all boreholes, full-section borehole television video recording was conducted to obtain visualized geological data of the borehole walls; seismic CT tomography was carried out between boreholes to obtain the wave velocity distribution of the rock mass in the borehole profile; finally, through stratigraphic comparison of straight and inclined boreholes, comparison of borehole television images and seismic CT anomaly areas, and multi-directional data spatial constraints, the geological results were jointly verified to construct a real, complete, and accurate geological profile of the dam foundation, and to complete the quality evaluation of the dam foundation rock mass and the identification of hidden defects.

[0138] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0139] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for concealed geological exploration based on multi-source in-situ data, characterized in that, The method includes: Acquire multi-source in-situ test data from pre-arranged boreholes. This multi-source in-situ test data includes: core logging data, borehole television data, water pressure test data, single-hole sonic logging data, and seismic CT data. The boreholes include at least two vertical boreholes and at least two directional boreholes. The at least two vertical boreholes are located on stable parts of both sides of the concealed geological formation and on the same main exploration profile. The at least two directional boreholes extend directionally from their opening positions on the slopes or sides of the concealed geological formation into the interior of the concealed geological formation, and all directional boreholes are located on the same main exploration profile. The horizontal projections of the bottoms of the two directional boreholes overlap in the deep part of the concealed geological formation. Based on the multi-source in-situ test data, multi-source data joint correction is performed to obtain and output the results of the hidden geological exploration.

2. The method according to claim 1, characterized in that, The inclination angle of the directional inclined hole is determined according to the following formula: α=arctan((tanθ0+w·tanβ) / (1-w)); Where α is the inclination angle of the directional borehole, θ0 is the angle between the line connecting the designed bottoms of the two directional boreholes and the horizontal plane, β is the measured apparent inclination angle of the bank slope surface, and w is a weighting coefficient and 0 <w<1; Furthermore, the weighting coefficients are configured such that the angle γ between the borehole axis and the normal of the inferred fault plane satisfies 30°≤γ≤60°, where γ = |90° - (α + δ)|, and δ is the dip angle of the inferred fault plane.

3. The method according to claim 2, characterized in that, The area of ​​the overlapping region between the horizontal projections of the bottom of the two directional inclined holes satisfies the following formula: S_overlap≥η×S_core; Wherein, S_overlap is the area of ​​the overlapping region between the horizontal projections of the bottom of the two directional inclined holes, S_core is the horizontal projection area of ​​the concealed geological target area, and η is the imaging coverage coefficient, and η≥0.

25. Furthermore, when a hypothetical fault zone exists within the overlapping area, the bottoms of the directional boreholes on both sides are located at different positions on the hanging wall and footwall of the hypothetical fault, so that the wave velocity difference on both sides of the hypothetical fault zone can be effectively distinguished by the inter-bore seismic CT data in the seismic CT data. The more complex the hypothetical defects in the hidden geological target area, the larger the value of η.

4. The method according to claim 3, characterized in that, The depth of the directional inclined hole satisfies: L = (D_vert + ΔZ) / sinα + ΔL; Where L is the depth of the directional inclined hole, D_vert is the drilling depth of the straight hole, ΔZ is the elevation difference between the opening elevation of the inclined hole and the opening elevation of the straight hole, α is the inclination angle of the directional inclined hole, and ΔL is the geological risk compensation item. The geological risk compensation item is obtained through the following formula: ΔL=(k×T) / sinα; Where T is the estimated total thickness of the fracture zone through which the directional inclined hole passes, and k is the hole collapse risk coefficient; The borehole collapse risk coefficient k is determined comprehensively based on the lithology of the fractured zone, the amount of mud loss, and the borehole wall stability index.

5. The method according to claim 1, characterized in that, The multi-source data joint correction based on the multi-source in-situ test data includes: By comparing the core logging data of straight and inclined holes on the same side with the single-hole sonic logging data, the spatial geometric characteristics of the same stratum are corrected, and the continuity of the structural plane is determined. The measured P-wave velocity from single-hole sonic logging data and the permeability from water pressure test data of vertical and inclined holes in the same formation are compared to determine whether the measured P-wave velocity and permeability are valid. The depth range of fracture zones, weak interlayers and densely fractured areas in borehole television data is compared with the distribution data of low-velocity anomalies obtained by inversion from seismic CT data. The accuracy of the identification of low-velocity anomalies is determined based on the results of the correspondence calculation. Based on the full-section borehole television recordings in the borehole television data, the geological properties of the low-velocity anomaly zone are accurately identified, and the boundary range of the low-velocity anomaly zone is corrected.

6. The method according to claim 5, characterized in that, The multi-source data joint correction based on the multi-source in-situ test data further includes: Multiple profiles from seismic CT data are stitched together to connect the stratigraphic interfaces and low-velocity anomaly zones of each profile. Using the spatial coordinates of the boreholes and the spatial distribution map of the low-velocity anomaly zone, a three-dimensional geological model was constructed to verify the spatial continuity of the low-velocity anomaly zone. Error corrections are performed on the spliced ​​profiles to form a closed exploration profile; The permeability in the water pressure test data was compared with the fracture zone in the low-velocity anomaly zone and the borehole television data to verify the correspondence between the low-velocity anomaly zone and the high-permeability zone. The measured P-wave velocity in single-hole acoustic logging data is compared with the P-wave velocity distribution data obtained by inversion from seismic CT data, so as to correct the P-wave velocity distribution data obtained by inversion by measuring the P-wave velocity.

7. The method according to claim 6, characterized in that, The acquisition of concealed geological survey results includes: Based on the jointly verified data, rock mass quality classification was performed, and the rock mass quality classification results along the main exploration profile were obtained. Based on the permeability in the water pressure test data and the permeable channels in the borehole television data, a permeable zone distribution map was obtained. The results of the concealed geological exploration include: core logging data, borehole television data, seismic CT data, water pressure test data, single-hole sonic logging data, multi-source data joint verification results, main exploration profile map and permeable zone distribution map obtained from the rock mass quality grading results along the main exploration profile.

8. The method according to claim 5 or 6, characterized in that, Also includes: The precise P-wave velocity value at the rigid constraint point of wave velocity is obtained from single-hole acoustic logging data. The rigid constraint point of wave velocity is a point in the overlapping area of ​​the horizontal projection of the bottom of the two directional inclined holes. In the inversion process of seismic CT data, the precise P-wave velocity value is used as a fixed rigid constraint condition, which forces the P-wave velocity at the rigid constraint point of the inversion result to be equal to the precise P-wave velocity value. The rigid constraint condition is used to constrain the solution of the inversion equation, so that the deviation of the wave velocity distribution obtained by inversion at the rigid constraint point is zero.

9. The method according to claim 5 or 6, characterized in that, The method further includes: The drilling trajectory data of the two directional inclined holes recorded by the drilling survey instrument during the drilling process is obtained. The drilling trajectory data includes the apex angle and azimuth angle at each depth. Spatial comparison is made between the spatial location of the low-velocity anomaly area obtained by inverting the drilling survey trajectory data and the seismic CT data. When the drilling survey trajectory data shows that the actual borehole trajectory deviates from the design trajectory in the same direction as the offset direction of the low-speed anomaly zone, and the deviation exceeds the preset deviation threshold, the low-speed anomaly zone is identified as an imaging artifact caused by borehole trajectory deviation. The imaging artifacts are removed from the results of the concealed geological survey, and the low-velocity anomaly area after removing the imaging artifacts is used as the low-velocity anomaly area in the joint correction of multi-source data.

10. A concealed geological exploration system based on multi-source in-situ data, characterized in that, The system includes: The test data acquisition module is used to acquire multi-source in-situ test data from pre-arranged boreholes. The multi-source in-situ test data includes: core logging data, borehole television data, water pressure test data, single-hole sonic logging data, and seismic CT data. The boreholes include at least two vertical boreholes and at least two directional boreholes. The at least two vertical boreholes are located on stable parts of both sides of the concealed geological formation and on the same main exploration profile. The at least two directional boreholes extend directionally from their opening positions on the slopes or sides of the concealed geological formation into the interior of the concealed geological formation, and all directional boreholes are located on the same main exploration profile. The horizontal projections of the bottoms of the directional boreholes on both sides overlap in the deep part of the concealed geological formation. The geological exploration results acquisition module is used to perform multi-source data joint correction based on the multi-source in-situ test data, acquire hidden geological exploration results, and output them.

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