Fracture network evaluation method based on borehole peep and surface fracturing data

Abstract

This invention relates to the field of coal mine strata control and disaster prevention technology, and discloses a fracture network assessment method based on borehole inspection and surface fracturing data. First, based on the spatial distance from the underground roadway to the surface fracturing well, the roof is divided into a baseline set region and an assessment set region, and steep-angle cross-strata inspection boreholes are deployed in each region. Imaging instruments are used to acquire borehole wall images and record the probe obstruction depth. A differentiated identification logic is executed: the geostress-dominant characteristics of the baseline region are extracted and eliminated as background noise, thereby accurately identifying the hydraulic fracturing-dominant characteristics of the assessment region. Finally, a local profile analysis coordinate system is established, and based on the spatial distribution of fracturing features and tectonic blocking boundaries, the maximum sweep height and effective sweep length of the fracture network are quantitatively inverted. This invention effectively eliminates interference from primary fractures, achieving accurate quantitative and visual assessment of the three-dimensional morphology of the fracture network in deep, hard roofs.

Description

Technical Field

[0001] This invention relates to the field of coal mine strata control and disaster prevention technology, specifically a fracture network evaluation method based on borehole inspection and surface fracturing data. Background Technology

[0002] In deep coal mining, controlling the thick, hard roof is crucial for preventing rockbursts and gas accumulation disasters. Surface horizontal well segmented hydraulic fracturing technology is applied to pre-fracture and weaken hard roofs, aiming to create a complex network of fractures in the rock mass using high-pressure fluids, thereby disrupting the integrity and bearing capacity of the roof. Accurately obtaining the spatial geometric parameters of the fracture network formed after fracturing, especially the maximum sweep height and effective sweep length, is the core basis for evaluating the roof weakening effect and guiding the subsequent working face design.

[0003] In existing technologies, the evaluation of hydraulic fracturing effectiveness relies on geophysical exploration methods such as ground microseismic monitoring or wide-area electromagnetic methods. These methods invert signals generated by rock fractures by collecting elastic waves or electrical differences. While this provides a large-scale monitoring range, its physical essence is a response to the stress disturbance field or property change field of the rock mass. In deep, high-stress environments, the range of elastic stress disturbance in the rock mass is often larger than the effective fracture network range where substantial physical fractures occur. This results in the swept envelope surface inverted from microseismic monitoring containing a large number of ineffective regions that have not shifted or opened, making it difficult to accurately define the actual physical fracture boundaries.

[0004] Downhole drilling inspection technology can provide direct optical images of the internal structure of rock masses, making it an effective means of verifying fracture morphology. However, under deep mining conditions, high ground stress can cause rheological deformation or collapse of the borehole wall due to non-fracturing factors, and the coal seam roof itself contains natural primary bedding and tectonic fractures. Traditional borehole observation methods lack specific identification criteria, making it difficult to effectively distinguish between borehole wall deformation characteristics caused by ground stress and artificial fracture characteristics caused by hydraulic fracturing. This can easily lead to misjudging primary fractures or stress damage as hydraulic fracturing fractures, resulting in distorted assessment results. Furthermore, in existing borehole exploration operations, when the imaging probe is obstructed due to severe borehole wall fracture or collapse, it is usually considered as a limitation of exploration operations or a lack of data. There is a lack of analytical models that quantify the physical boundary data representing the extreme value of rock mass fracture, thus limiting the accuracy and completeness of inverting the overall three-dimensional morphology of the fracture network based on borehole data. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a fracture network evaluation method based on borehole inspection and surface fracturing data. This method solves the problems of existing technologies, such as the difficulty in distinguishing between natural geological fractures and effective artificial fracturing fractures, and the difficulty in quantitatively reconstructing the three-dimensional spatial morphology of the fracture network using limited downhole observation data.

[0006] A fracture network assessment method based on borehole inspection and surface fracturing data is proposed. This method first divides the underground roadway roof into a baseline set region for collecting background geological data and an assessment set region for capturing fracturing response characteristics, based on the spatial distance from the underground roadway roof to the surface fracturing well axis. Within these two regions, steeply inclined cross-layer inspection boreholes penetrating the coal seam roof and reaching the target fracturing layer are deployed. A borehole imaging instrument is used to detect these steeply inclined cross-layer inspection boreholes, acquiring borehole wall image data and recording the obstruction depth of the borehole imaging instrument probe.

[0007] After acquiring the basic data, a differentiated qualitative identification of fracture characteristics is performed. First, the geostress-dominant characteristics are extracted in the benchmark set area, and then the interference of the geostress-dominant characteristics is eliminated in the evaluation set area to identify the hydraulic fracturing-dominant characteristics. Finally, based on the spatial distribution and obstruction depth of the hydraulic fracturing-dominant characteristics, combined with the relative position to the axis of the surface fracturing well, a quantitative inversion model is established to calculate the maximum sweep height and effective sweep length of the fracturing network, and the evaluation results are output.

[0008] This invention establishes a targeted geological feature identification logic based on rock mechanics principles to distinguish the essential differences in rock mass failure morphology caused by in-situ stress and hydraulic fracturing. Specifically, the in-situ stress-dominated characteristic is manifested in the geometric deformation of the borehole wall cross-section, i.e., the cross-section evolves from a circular shape to an approximately elliptical shape, and the actual borehole diameter shows a shrinking trend with increasing borehole depth; simultaneously, the borehole wall fractures are manifested as single longitudinal cracks that run basically parallel to or intersect the borehole axis at a small angle. These single longitudinal cracks are constrained by the bedding planes of the target fracturing layer and do not cut through the bedding planes. In contrast, the hydraulic fracturing-dominated characteristic includes transverse shear fractures and a network fracture zone structure; the transverse shear fractures intersect the borehole axis at a large angle and spatially cut through the bedding planes of the target fracturing layer; the network fracture zone structure is formed by the interweaving of transverse shear fractures and longitudinal fractures, and the borehole wall rock mass exhibits a high-density fractured, spalled, or locally cavitated morphology.

[0009] This invention further transforms the one-dimensional depth data of boreholes into two-dimensional geometric parameters reflecting the spatial morphology of the fracture network by establishing a local profile analysis coordinate system. The specific calculation logic is as follows: using trigonometric relationships and based on the construction dip angle of the large-angle cross-layer inspection borehole, the recorded depth values ​​on the borehole trajectory are converted into vertical projection height and horizontal span coordinates in the local profile analysis coordinate system.

[0010] In determining the maximum sweep height, this invention employs a deductive logic combining measured data and the symmetry assumption: First, the location where the first continuous hydraulic fracturing-dominant feature appears in the profile feature point set is identified, and its vertical projection height is defined as the lower boundary height of the fracture development zone. Second, the upper boundary height of the fracture development zone is determined. If structural blockage is detected during the detection process, i.e., the probe is obstructed due to contact with hard and angular broken rock blocks, the obstruction depth is converted into a vertical projection height as the upper boundary height; if no blockage occurs, the vertical projection height of the location where the hydraulic fracturing-dominant feature disappears is selected as the upper boundary height. Subsequently, the vertical distance from the lower boundary height to the projection point of the fracture well axis on the height axis is calculated as the lower wing vertical expansion radius. Based on the assumption that the fracture network is quasi-symmetrically distributed in the vertical direction, the theoretical total height of the fracture network is calculated using twice the lower wing vertical expansion radius. Simultaneously, the measured height difference between the upper and lower boundary heights is calculated. Finally, the measured height difference is compared with the theoretical total height, and the larger of the two is taken as the maximum sweep height.

[0011] When determining the effective sweep length, this invention adopts the maximum value envelope principle: traversing feature points containing the dominant characteristics of hydraulic fracturing, selecting the feature point with the largest absolute value of the horizontal distance between the feature point's horizontal span coordinate and the axis of the surface fracturing well, and defining the absolute value of the horizontal distance from this feature point to the axis of the surface fracturing well as the maximum effective verification distance. Based on the principle of symmetrical expansion of the fracturing network along the axis of the surface fracturing well to both sides, the maximum effective verification distance is used as the lower limit of the single-wing fracture length, and the effective sweep length of the fracturing network is determined based on twice the maximum effective verification distance.

[0012] This invention provides a fracture network evaluation method based on borehole inspection and surface fracturing data. It has the following beneficial effects:

[0013] 1. This invention improves the accuracy of fracture network assessment in complex geological environments by constructing a differentiated identification logic for in-situ stress and hydraulic fracturing fractures. Addressing the characteristics of borehole deformation and primary fracture development caused by high in-situ stress in deep coal seams, this invention utilizes the physical property that hydraulic fracturing requires cutting through the bedding planes of rock strata. This effectively eliminates background interference from in-situ stress-dominated characteristics during the assessment process, avoiding misjudging primary fractures or stress-induced damage as effective fracturing channels, thus ensuring the authenticity and reliability of the assessment conclusions.

[0014] 2. This invention enables in-depth mining and utilization of borehole exploration obstruction data, and improves the method for determining the fracture network boundary. Existing technologies typically consider the inability to advance the probe as a detection failure, leading to data loss. This invention, however, analyzes the contact surface characteristics to define tectonic blockage caused by fractured rock as the upper boundary indicator of the fracture network core area, and directly incorporates this upper boundary indicator into the geometric parameter calculation model. This approach effectively supplements the key boundary data required for fracture network height inversion without increasing additional engineering investment.

[0015] 3. This invention transforms discrete downhole observation data into standardized quantitative geometric parameters, providing an intuitive basis for engineering decision-making. By establishing a local profile analysis coordinate system and a deductive model based on the principle of symmetric expansion, this invention can resolve qualitative borehole wall image features into specific values ​​of maximum sweep height and effective sweep length, and ultimately generate a visual map reflecting the spatial morphology of the fracture network. This directly quantifies the damage range of fracturing operations to the coal seam roof, providing accurate data support for the subsequent safe mining design of the working face. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the drilling construction feedback data identification process of the present invention; Figure 2 This is a schematic diagram of the observation borehole layout and parameters of the present invention. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] This invention provides a fracture network evaluation method based on borehole observation and surface fracturing data. Based on the actual engineering geological conditions revealed in the underground roadway and combined with the spatial location parameters of the surface fracturing project, the method obtains the differences in physical characteristics of the roof strata under natural and fracturing disturbance states by implementing differentiated borehole observation at specific strata. Then, the method uses a geometric inversion model to quantitatively evaluate the development height and extension length of the fracturing network.

[0019] The fracture network evaluation method based on borehole inspection and surface fracturing data includes the following steps: Step S100: Construct a geological engineering spatial model and delineate the observation area. Based on the three-dimensional coordinate data of the mine working face roadway and the wellbore trajectory data of the surface fracturing horizontal well, establish a local three-dimensional spatial coordinate system. Calculate the spatial distance from each point on the underground roadway roof to the axis of the surface fracturing well. According to the preset fracturing influence radius threshold, divide the roadway roof area to be evaluated into a baseline set area and an evaluation set area. The baseline set area is defined as the area far from the axis of the surface fracturing well and not directly affected by the hydraulic fracturing project, used to establish a geological background baseline; the evaluation set area is defined as the area covering the projection range of the surface fracturing well axis and the expected impact range, used to obtain fracturing response characteristics.

[0020] Step S200: Deploy high-angle cross-layer inspection boreholes. Determine borehole locations on the roof of the roadway in both the baseline and evaluation zones. Design borehole trajectory parameters based on the vertical distance from the coal seam roof to the target fracturing layer. Set the borehole inclination angle to a high-angle upward borehole, ensuring the vertical extension component of the borehole trajectory penetrates the coal seam roof and reaches the target fracturing layer. Set the borehole design depth to be greater than the straight-line distance from the borehole opening point to the top boundary of the target fracturing layer, ensuring the observation path covers the entire expected fracture development height.

[0021] Step S300: Acquire borehole imaging data and construction process feedback data. Using a borehole imaging instrument, perform full-section inspection of the boreholes within the benchmark and evaluation sets to acquire continuous image data of the borehole wall rock mass. Simultaneously record the probe's advancement status within the borehole. When the probe cannot continue advancing to the designed depth due to rock fragmentation, borehole collapse, or blockage, record the actual borehole depth at the current position, defining this depth as the obstruction depth. The obstruction depth serves as the physical boundary data characterizing the degree of rock fragmentation exceeding the probe's passage threshold.

[0022] Step S400: Perform differential qualitative identification of fracture features. Analyze borehole image data from the benchmark region to extract primary fracture features. Primary fracture features are characterized by regular geometric deformation of the borehole wall, a decreasing borehole diameter with increasing depth, and primarily longitudinally distributed single fractures. These primary fracture features are labeled as geostress-dominated features. Analyze borehole image data from the evaluation region to extract fracturing-induced fracture features. Fracturing-induced fracture features are characterized by transverse fractures in the borehole wall, complex network fracture zones, and irregular borehole diameter expansion deformation. These fracturing-induced fracture features are labeled as hydraulic fracturing-dominated features.

[0023] Step S500: Quantitatively invert the geometric parameters of the fracture network. Based on the initiation depth, termination depth, and obstruction depth of the fracture-induced fractures identified in the evaluation set region, and combined with the spatial trajectory equation of the borehole, calculate the vertical distribution range of the fractures. Calculate the maximum vertical distance from the upper and lower boundaries of the distribution range to the layer where the surface fracture well axis is located, and determine the maximum sweep height of the fracture network. Based on the horizontal projection normal distance between the borehole termination position and the surface fracture well axis, and combined with the continuity characteristics of fracture development, determine the effective sweep length of the fracture network.

[0024] Step S600: Output the fracture network evaluation results. Based on the maximum sweep height and effective sweep length obtained from quantitative inversion, construct the geometric envelope of the hydraulic fracturing network in the local profile analysis coordinate system; superimpose the distribution of the dominant hydraulic fracturing characteristics onto this envelope to generate a visual evaluation map reflecting the spatial morphology of the fracture network; finally, output a fracturing effect evaluation report containing geometric parameter values ​​and the visual evaluation map.

[0025] In the process of constructing the geological engineering spatial model and dividing the observation area in step S100, in order to ensure that the evaluation results can truly reflect the physical modification effect of fracturing on the roof strata, it is necessary to establish a strict control group based on spatial geometric location. This process specifically includes the following sub-steps: Step S101: Establish a local three-dimensional spatial coordinate system and data mapping. Obtain the coordinate data of the underground roadway traverse points of the working face to be evaluated, as well as the wellbore trajectory inclination data of the surface fracturing horizontal well. Use the intersection of the working face cut-out and the transport roadway, or a fixed traverse point, as the origin. Based on the direction of the alley Axis, with inclination as The axis is vertically upward. We construct a local three-dimensional Cartesian coordinate system using axes. The set of discrete point coordinates on the roof of the underground roadway is denoted as... The set of discrete points on the well axis trajectory of a surface-fractured horizontal well is denoted as... At this point, the wellbore trajectory is projected onto the same spatial coordinate system as the roadway roof using an interpolation algorithm, thus clarifying their relative positional relationship in three-dimensional space.

[0026] Step S102: Calculate the spatial projection distance and determine the influence domain. This applies to any point on the direction of the tunnel roof. Calculate the normal distance (i.e., horizontal distance) from the projection of this point onto the horizontal plane to the projection of the fractured well axis onto the horizontal plane, denoted as . Normal distance These are key geometric parameters for determining whether a location has been affected by hydraulic fracturing. Simultaneously, by combining pre-acquired ground microseismic monitoring event point cloud data or hydraulic fracturing simulation data, the theoretical maximum half-length of a single fracturing segment is determined. and theoretical maximum sweep width Define the fracturing influence domain identification function. When a certain position on the roadway roof satisfies the condition that it is within the coverage area of ​​the fracturing section along the well axis and At that time, it was determined that this location was within the fracturing influence zone, where To account for the correction margin for geological heterogeneity.

[0027] Step S103: Define the assessment set area. Based on the above identification results, the roadway roof area covering the projected range of the surface fracturing well axis and the expected affected range is defined as the assessment set area. Specifically, in the mine working face scenario of this embodiment, there are two L-shaped horizontal wells, MC-05L and MC-06L, under construction on the surface. The target stratum is the Zhiluo Formation, with a vertical distance of approximately 60 to 65 meters from the roof of Coal Mine No. 4. According to the feedback from surface microseismic monitoring, the average total length of the fracturing fractures is approximately 318 meters. In the engineering context, the location at mileage 540 meters in the transport roadway and mileage 540 to 600 meters in the return airway are selected as the assessment set area. At these locations, the normal distance between the roadway roof and the surface fracturing well axis is... Distributed between 84 and 115 meters. The distance is less than or close to the expected half length of the fracture, which belongs to the strongly disturbed zone. It is used to obtain the rock mass fracture response characteristics under hydraulic fracturing, such as transverse shear fractures and network fracture zones.

[0028] Step S104: Define the reference set area. The reference set area is defined as the region far from the surface fracturing well axis and confirmed by calculation to be unaffected by the direct impact of hydraulic fracturing. The physical characteristics of the reference set area represent the natural background values ​​of the rock strata under conditions of only in-situ stress and tunnel excavation disturbance. In this embodiment, the locations at 240 meters in the transport roadway and 240 meters in the return airway are selected as the reference set area. At these locations, the normal distance from the tunnel roof to the edge of the last fracturing fracture is... The distance is approximately 140 meters. Since this distance is greater than the effective sweep radius of the hydraulic fracturing fracture, interference from fracturing-induced fractures can be eliminated. Data collected in this area will serve as a geological background baseline, used in subsequent analyses to eliminate interference from pore size deformation caused by in-situ stress and primary longitudinal fractures, thereby improving the accuracy of identifying fracturing-induced fractures.

[0029] Step S105 generates a differentiated borehole layout map. Based on the regional range determined in steps S103 and S104, the specific borehole coordinates are marked in the 3D geological model. For the assessment set area, observation boreholes for capturing fracture tips and fracture zone morphology are planned; for the baseline set area, correlation boreholes for establishing a standard model of stratigraphic integrity are planned. Through this strict spatial partitioning and blank comparison setting, a differential assessment logical basis is established, using the original characteristics of the baseline set area as the background and the disturbance characteristics of the assessment set area as the drawing.

[0030] During step S200, which involves setting up steeply inclined cross-strata inspection boreholes, accurate design of the borehole's spatial geometry is necessary to ensure the observation instruments can effectively penetrate the coal seam roof and reach the target rock strata affected by hydraulic fracturing. The process specifically includes the following sub-steps: Step S201: Determine the vertical depth of the target stratum and the borehole guidance strategy. Based on the geological columnar section of the mine working face and the surface fracturing engineering design data, the target fracturing stratum to be detected is identified. In this embodiment, the target fracturing stratum is the Zhiluo Formation, located above the roof of the No. 4 coal seam, with a vertical distance range of 60 to 65 meters. Due to the differences in lithology of the mine working face roof in different areas, the area near the retreat channel is mainly sandstone, while the area near the cut-in contains multiple layers of mudstone. In order to avoid the risk of borehole collapse caused by the mudstone layer and ensure that the complete fracture development profile can be observed, the borehole trajectory design strategy is determined to be borehole construction at an angle across the strata, that is, the borehole must pass through the unstable rock layer below in the shortest path and extend to the maximum extent in the vertical direction to cover the full height of the fracturing fracture.

[0031] Step S202: Determine the borehole inclination angle. Based on the spatial constraints of the underground roadway cross-section and the vertical height of the target layer, set the borehole inclination angle. Drilling inclination angle The value range is typically set between 70 and 80 degrees. In this embodiment, 75 degrees is selected as the drilling inclination angle. The technical basis for selecting the drilling inclination angle is as follows: on the one hand, a drilling inclination angle of 75 degrees allows the borehole to obtain a larger vertical component within a limited hole depth, thereby quickly breaking through the fracture zone above the coal seam roof; on the other hand, a drilling inclination angle of 75 degrees ensures that the borehole trajectory forms a large angle with the bedding plane of the rock strata, avoiding the borehole from slipping along the bedding plane and ensuring that vertical cross-layer fractures (i.e., the main fracture morphology generated by hydraulic fracturing) can be observed. If the drilling inclination angle is too small, the borehole will mainly extend along the strike of the rock strata, making it difficult to reveal the vertical fracture development height; if the drilling inclination angle is too large, close to 90 degrees, it will be difficult to set up the drilling rig due to the limited roadway height and to control the deviation of the borehole orientation.

[0032] Step S203: Calculate the design borehole depth to cover the entire fracture height. To ensure that the observation window can completely cover the entire process from the fracture initiation point to the fracture tip disappearance point, the minimum design borehole depth needs to be calculated based on trigonometric relationships. The calculation formula is as follows: ; in, This represents the vertical distance from the borehole opening location to the bottom boundary of the target fracturing layer; in this embodiment, this value is 60 meters. This indicates the vertical height margin expected for the crack to continue developing upwards above the target layer. Based on the crack half-height data from microseismic monitoring, it is set to 40 to 50 meters to ensure that the borehole end position is above the upper limit of crack development. Let this be the drilling inclination angle. Substitute the values ​​into the calculation, i.e. Meters. Therefore, in this embodiment, the borehole design depth is rounded down to 110 meters. This depth ensures that the borehole vertical depth can reach approximately 106 meters, completely covering the sandstone and mudstone layers within a 100-meter range above the coal seam roof, and effectively capturing the top boundary of the hydraulic fracturing network.

[0033] Step S204: Set the borehole diameter parameters to suit deformation observation. Considering that the rock mass in the assessment area will undergo plastic deformation or shear displacement under stress release and high-pressure water flow impact, leading to non-uniform shrinkage of the borehole cross-section, sufficient borehole diameter margin needs to be reserved to prevent imaging probe jamming. The designed borehole diameter is set as follows: The following conditions must be met: ; In the above formula, This is the maximum outer diameter of the imager probe; The maximum shrinkage deformation of the borehole wall is estimated based on rock mechanical properties and in-situ stress levels. In this embodiment, the imaging probe diameter is typically 40 mm to 60 mm. Considering the possibility of borehole diameter reduction in deep, high-stress areas, the borehole diameter is set to be no less than 75 mm. In actual construction, borehole diameters of 80 mm to 89 mm were used. The borehole diameter parameter not only ensures the smooth passage of the probe but also provides a clear geometric reference background for identifying minute borehole wall deformations, enabling the inversion of in-situ stress direction through the borehole diameter change rate in subsequent image analysis.

[0034] Step S205: Plan the borehole spatial orientation. Horizontally, the borehole opening position is set on the roof of the roadway sidewall, with the azimuth angle set perpendicular to the roadway axis and pointing to the opposite side. In this embodiment, the azimuth angle of the return airway borehole is 0 degrees, i.e., perpendicular to the strike and pointing north; the azimuth angle of the transport roadway borehole is 180 degrees, i.e., perpendicular to the strike and pointing south. This opposing detection arrangement allows the borehole trajectory to extend into the rock mass in the middle of the mine working face, thereby detecting the assessment aggregation area located above the solid coal roof between the two roadways. This avoids only detecting the loosened rock mass directly above the roadway that is significantly affected by tunneling disturbances, ensuring that the collected fracture data mainly originates from surface fracturing operations rather than the influence of roadway excavation.

[0035] See attached document Figure 1 In the process of collecting borehole imaging data and construction process feedback data in step S300, this embodiment not only focuses on the borehole wall image information collected by the imaging instrument, but also innovatively transforms the physical obstruction phenomenon during borehole inspection into quantitative geological assessment indicators. The process specifically includes the following sub-steps: Step S301: Establish a real-time monitoring mechanism for probe advancement. When using a borehole imaging device to probe the entire borehole section, simultaneously record the probe's descent depth, advancement resistance, and changes in the borehole environment. The imaging probe is defined as a rigid detector with a certain outer diameter; its passage through the borehole is directly limited by the integrity and geometric regularity of the borehole wall. When the probe encounters resistance during advancement and cannot continue to the preset design depth (110 meters in this embodiment), the operator must immediately stop advancement, read the scale value on the probe cable or the electronic counter reading, and record the depth at this termination position as the obstruction depth. .

[0036] Step S302: Construct a binary classification logic for the causes of probe obstruction. To accurately distinguish between construction accidents caused by non-fracturing factors and structural damage caused by fracturing factors, it is necessary to identify and classify the specific physical causes of probe obstruction on-site. The first type of obstruction is determined to be process-related blockage. If the obstruction location is in the reference aggregation area (reference aggregation area) or in shallow rock strata far from the target layer, and no obvious water inflow is observed at the borehole opening, and the probe tip shows loose drill cuttings accumulation, and repeated flushing or clearing fails to advance, then the depth of obstruction is determined. The first type of blockage is caused by poor drilling and cuttings removal or cuttings falling from the borehole. The second type is classified as structural blockage. If the blockage is located in the assessment aggregate area and the depth is close to the target fracturing layer, and severe borehole wall disintegration, rock fragmentation, or even water inrush are observed on-site, and the probe tip indicates that the contact surface is composed of hard, angular, broken rock blocks, then the depth of the blockage is determined. Caused by structural failure of the rock mass. Tectonic blockage directly reflects that the degree of fracturing of the rock mass in this stratum has exceeded the critical threshold for maintaining borehole formation, and is direct physical evidence of high-intensity hydraulic fracturing failure.

[0037] Step S303: Define the physical boundary of the highly fractured zone. The obstruction depth determined as structural blockage in step S302 is... This is defined as the upper boundary of the core fracture zone of the hydraulic fracturing network. The instruction manual explicitly states that the probe's inability to pass through does not signify detection failure, but rather indicates that the fracture density and rock fragmentation at that location have reached extreme values. This physical impassability is technically equivalent to confirming the high degree of development of the hydraulic fracturing network at this spatial location, proving that segmented fracturing in the horizontal well successfully created a complex fracture network structure in the target strata of the Zhiluo Formation, leading to a qualitative change in the rock's mechanical properties and making it difficult to maintain an intact pore wall morphology.

[0038] Step S304: Extract failure parameters of key strata. Combine this with the borehole drilling dip angle. The depth of the structural blockage Converted to vertical obstruction depth The calculation formula is: In this embodiment, the calculated vertical obstruction depth distribution of the evaluation set area is between 67.6 meters and 79.3 meters. This not only marks the substantial damage boundary of the upward extension of the hydraulic fracturing cracks, but also verifies the accuracy of the ground microseismic monitoring data. It provides accurate physical boundary constraints for the subsequent quantitative inversion of the fracture network height, and solves the technical problem of multiple solutions that exist when relying solely on geophysical monitoring methods.

[0039] In the process of differential qualitative identification of fracture features in step S400, in order to accurately extract specific disturbance signals caused by surface fracturing operations from complex downhole imaging data, this embodiment uses a comparative analysis method to establish a fracture origin identification matrix based on morphological features. The process specifically includes the following sub-steps: Step S410: Extract the background geological features of the reference set area. Segment-by-segment scanning analysis is performed on the imaging data of boreholes located far from the fracturing influence zone in the reference set area. During the analysis, it was found that when the probe depth enters the deep rock strata at a certain height above the coal seam roof, the borehole wall images exhibit obvious geometric deformation characteristics. Specifically, the borehole cross-section gradually evolves from its original circular shape to an approximately elliptical shape with a significant difference between the major and minor axes, and the borehole diameter shows a shrinking trend with increasing probe depth. Simultaneously, the fractures observed on the borehole wall are mainly long, single longitudinal fractures. These fractures are generally parallel to the borehole axis or intersect at a small angle, without obvious layer cutting. Based on rock mechanics principles, this type of feature is defined as a geostress-dominated characteristic. The physical cause is that under high geostress conditions in the deep rock mass, the tangential stress concentration around the borehole exceeds the shear strength or compressive strength of the rock, leading to shear failure or spalling of the borehole wall, thus forming an elliptical cross-section and inducing longitudinal tensile fractures. The geostress-dominated characteristic is an inherent background noise of deep rock tunnel drilling and should be excluded when evaluating the fracturing effect, and should not be used as a basis for the existence of fracturing fractures.

[0040] Step S420: Extract the fracturing response characteristics of the evaluation cluster area. Feature extraction is performed on the imaging data of boreholes within the projection range of the fracturing well axis in the evaluation cluster area. At the same stratigraphic level as in Step S410, distinctly different fracture morphologies were observed. Besides the background elliptical deformation caused by geostress, transverse fractures perpendicular to or intersecting at large angles with the borehole axis were clearly visible in the images. These transverse fractures spatially cleave the bedding planes of the rock, and in areas of dense fracture development, longitudinal and transverse fractures intertwine, forming a complex network of fracture zones. The transverse fractures and the network of fracture zones are defined as the dominant characteristics of hydraulic fracturing. The physical cause lies in the fact that after the fracturing fluid injected under high pressure from the surface enters the rock strata, the resulting fluid pressure overcomes the minimum principal stress and tensile strength of the rock, forcing the rock mass to expand in volume and open along a specific direction to form new fracture surfaces. This type of layered fracturing and network fracture is difficult for natural geostress to spontaneously form in a short period of time, and therefore is identified as an effective fingerprint signal generated by hydraulic fracturing engineering.

[0041] Step S430: Construct the fracture origin identification matrix and classification criteria. Based on the experimental comparison results of steps S410 and S420, the following binary identification logic is established: If the borehole image feature set satisfy If the current rock mass is in a state of primary high stress and has not been effectively affected by hydraulic fracturing, then it is determined that the current section of rock mass is in a state of primary high stress and has not been effectively affected by hydraulic fracturing. If the borehole image feature set... Include If at least one of the following conditions is met, and a high density of fracture frequency is present, then the current rock mass section is determined to be in a state of pressure fracturing disturbance and belongs to the effective affected area of ​​the pressure fracturing network.

[0042] Step S440: Determine the effective range of fracture development. Based on the criteria established in step S430, the start and end positions of fracture development in the boreholes of the evaluation aggregate region are calibrated. In the boreholes of the evaluation aggregate region in this embodiment, the starting depth at which transverse fractures and network-like fracturing features begin to appear densely is identified. Located in the range of 34 meters to 49 meters, extending to the blocked depth determined in step S300 above. (Corresponding to a vertical depth of approximately 67 to 79 meters). This range is defined as the fracturing zone. Through this differentiated qualitative identification, this embodiment successfully distinguishes between borehole wall damage caused by in-situ stress and rock strata modification caused by hydraulic fracturing, ensuring that the data source for subsequent geometric parameter inversion comes only from the fracturing effect, thereby improving the confidence of the assessment results.

[0043] As the basis for establishing the fracture identification matrix in step S400, this embodiment first performs feature deconstruction on the borehole imaging data within the reference set region (reference set region) to establish the background response mode of deep rock mass under the action of natural stress field. The extraction and definition process specifically includes the following sub-steps: Step S411: Define the background feature observation window. (Refer to Appendix) Figure 2 Holes 1 and 2, located more than 140 meters away from the axis of the fracturing well at the surface, were selected as standard observation samples. Full-section scanning of these two boreholes revealed relatively good overall integrity of the shallow rock strata, with no obvious structural fractures except for a few bedding planes. However, when the probe depth exceeded 45 meters and entered the deep interbedded fine sandstone and siltstone section, the borehole wall images began to exhibit regular mechanical deformation characteristics. We set this deep stratum as the background noise extraction window to identify rock mass failure morphologies caused by non-fracturing factors.

[0044] Step S412: Extract and define borehole wall stress-deformation characteristics. Within the aforementioned background feature observation window, a significant change in the borehole cross-section shape was observed. The original circular borehole cross-section, after excavation and unloading, gradually evolved into an approximately elliptical geometric shape with a significant difference between its major and minor axes due to the redistribution of surrounding rock stress. This deformation was not caused by external fluid pressure, but rather by the tangential concentrated stress around the borehole exceeding the shear strength of the rock, leading to sheet-like spalling of the borehole wall due to shear failure, or tensile failure due to tangential stress exceeding the tensile strength of the rock. Furthermore, with increasing probe depth (i.e., increased geostress level), a shrinking borehole diameter was observed, and the major axis of the ellipse exhibited a high degree of spatial consistency. In this embodiment, the approximately elliptical geometric shape and the borehole diameter shrinkage trend are defined as borehole wall stress-deformation characteristics. Physically, this is a passive adaptation of the rock mass to the geostress environment, rather than an active result of fracturing.

[0045] Step S413: Extract and define the characteristics of primary longitudinal fractures. Along with borehole wall deformation, a specific type of fracture was observed developing on the borehole wall surface. Morphologically, these fractures are relatively long (usually spanning the entire field of view), but spatially they are primarily longitudinally distributed, meaning their orientation is basically parallel to the borehole axis or at only a very small angle. At bedding planes, the fractures typically do not change direction or cut through the bedding planes, but are constrained by them. This fracture morphology conforms to the description of fracture zones in deep tunnel surrounding rock in rock mechanics, namely, tensional splitting parallel to the direction of the maximum principal stress under deviatoric stress. In this embodiment, a single fracture with a orientation parallel to or intersecting the borehole axis at a small angle is defined as a primary longitudinal fracture characteristic.

[0046] Step S414 establishes background noise exclusion criteria. Based on the analysis in steps S412 and S413, the borehole wall stress deformation characteristics and the original longitudinal fracture characteristics are combined and collectively referred to as geostress-dominated characteristics. In subsequent analysis of the assessment set area (assessment set region), any rock strata section containing only geostress-dominated characteristics is identified as a blank area not effectively affected by hydraulic fracturing. By establishing this exclusion criterion, the inherent stress failure phenomena of deep rock masses can be effectively prevented from being misjudged as hydraulic fracturing fractures, thereby improving the specificity and accuracy of fracture network height and length inversion calculations. For the specific identification and calculation of geostress direction, those skilled in the art can deduce it based on the perpendicular relationship between the borehole wall collapse direction and the minimum horizontal principal stress direction; this is well-known technology in the field and will not be elaborated upon here.

[0047] As a core step in establishing the fracture identification matrix in step S400, this embodiment extracts depth features from borehole imaging data within the evaluation set region (evaluation set region) to identify and define the specific physical fingerprints left in deep rock masses by surface hydraulic fracturing engineering. The process specifically includes the following sub-steps: Step S421: Determine the observation samples and intervals for the fracturing response characteristics. (Refer to Appendix) Figure 2 Holes ③, ④, supplementary ⑤, and supplementary ⑥, located within the projected area of ​​the surface fracturing well axis and the expected affected area, were selected as evaluation samples. During the full-section borehole scan analysis, the focus was on the stratigraphic interval from 30 meters above the coal seam roof to the obstructed depth. Within this stratigraphic interval, although the lithology is the same as the baseline region, the observed borehole wall morphology exhibits drastic structural differences, indicating that the rock mass in the current area has undergone high-intensity external disturbance.

[0048] Step S422: Extract and define transverse bedding fracture features. Numerous fractures with unique orientations were observed in the borehole wall images of the evaluation samples. Unlike primary longitudinal fractures, these uniquely oriented fractures intersect the borehole axis at large angles or are approximately perpendicular (e.g., angles greater than 60 degrees), spatially resembling morphology that transversely cuts through the bedding planes of the rock strata. Physically, this is due to the high fluid pressure generated by the fracturing fluid overcoming the minimum horizontal principal stress of the rock. and tensile strength This leads to tensile fracturing of the rock mass along a direction perpendicular to the minimum principal stress. Uniquely occurring fractures typically have a wide opening and are often accompanied by small secondary branches at the fracture edges. In this embodiment, fractures that intersect the borehole axis at a large angle and cut the bedding plane are defined as transverse bedding fractures. Transverse bedding fractures are a key morphological basis for distinguishing between natural and artificial fractures, because it is difficult for such a high density of transverse bedding fractures to spontaneously form in layered rock masses subjected only to gravity and tectonic stress.

[0049] Step S423: Extract and define the structural features of the network fracture zone. As the observation depth approaches the axis of the surface fracturing well, the frequency of the observed transverse shear fractures increases significantly, intertwining with the original longitudinal fractures and weak bedding planes. In areas of local high stress concentration, this interweaving forms a complex grid-like or mosaic-like rock mass structure, resulting in fractured, fragmented, and even locally cavitated rock on the borehole wall. This fractured morphology indicates that the rock mass has transformed from a continuous medium to a discontinuous, loose medium, with a permeability increase of orders of magnitude compared to intact rock. In this embodiment, the dense fractured morphology formed by the interweaving of transverse and longitudinal fractures is defined as the structural feature of the network fracture zone. The network fracture zone structural feature characterizes the effective core area for hydraulic fracturing, i.e., the area where the rock mass structure has undergone substantial damage and the fracture network connectivity is highest.

[0050] Step S424 establishes the criteria for identifying fracturing fingerprints. Based on the analysis in steps S422 and S423, the characteristics of transverse shear fractures and the structural characteristics of the network fracture zone are combined and collectively referred to as the dominant hydraulic fracturing characteristics. When qualitatively classifying borehole data, any rock strata segment identified as containing the dominant hydraulic fracturing characteristics is determined to be a valid fracturing segment. According to the measured data from the mine working face in this embodiment, in the boreholes of the evaluation aggregation area, the initial development depth of the dominant hydraulic fracturing characteristics is located between 34 and 49 meters in borehole depth, extending all the way to the obstruction point at a depth of 70 to 82 meters. This continuous characteristic distribution zone physically materializes the spatial morphology of the hydraulic fracturing fracture network, providing definite material evidence for the subsequent quantitative inversion of fracture height and length based on a geometric model. For the specific calculation and statistical methods of fracture linear density, those skilled in the art can use the scan line method or RQD (Rock Quality Index) analysis method, which are well-known techniques in the field and will not be elaborated here.

[0051] In the process of performing step S500 to quantitatively invert the geometric parameters of the fracture network, in order to transform the one-dimensional linear depth data obtained by borehole inspection into two-dimensional or three-dimensional geometric data that can directly characterize the spatial morphology of the fracture network, this embodiment adopts the profile dimensionality reduction mapping method to construct a local profile analysis coordinate system independent of the overall mine coordinate system. Specifically, it includes the following sub-steps: Step S511: Construct a coordinate system for fracture feature profile analysis. This embodiment establishes a local profile coordinate system with the surface fracturing well axis as a reference. The direction perpendicular to the coal seam roof and upwards is defined as the height axis. The span axis is defined as the direction along the dip of the coal seam (i.e., perpendicular to the axis of the fracturing well at the surface). (Axis). In a local profile coordinate system with the surface fracturing well axis as a reference, any first-order axis detected by the borehole imaging instrument within the borehole is... Feature points As the geometric node to be solved, the measured depth on the borehole trajectory line is denoted as... At this point, the borehole trajectory and observed fracture data are projected onto... The problem is processed in a plane, thus transforming the complex three-dimensional spatial problem into a plane geometric problem.

[0052] Step S512: Calculate the vertical layer height of the feature points. For the first [layer height] within the borehole... Feature points First, obtain the vertical height of the borehole opening position in the local profile coordinate system, denoted as . Based on the drilling inclination angle Using trigonometric relationships, calculate the current feature point. exist Vertical projection height on the axis The calculation formula is as follows: ; in, This is the measured depth; For drilling inclination angle The sine coefficient is calculated using the above formula. The value directly corresponds to the stratum height of the rock layer where the current fracture point is located. For example, if the calculated value is... If the value is located within the Zhiluo Formation, which is 60 to 100 meters above the coal seam roof, then the current feature point is spatially determined to be within the target fracturing layer, thus providing direct coordinate basis for verifying the vertical sweep height of the fracturing fracture.

[0053] Step S513: Calculate the horizontal span coordinates of the feature points. To determine the horizontal position of the fracture points relative to the axis of the surface fracturing well, it is necessary to calculate the feature points. exist Projected coordinates on the axis Obtain the horizontal coordinates of the borehole opening location in the local profile coordinate system, denoted as . Assume the drilling inclination angle. Perpendicular to the direction of the alley (i.e. along) (Construction in the axial direction), then characteristic points The formula for calculating the horizontal coordinate is as follows: ; Furthermore, in order to quantify the horizontal expansion width of the fracture network, it is necessary to introduce the axis of the surface fracture well. Known coordinates on the axis Define feature points The horizontal normal distance to the axis of the surface fracturing well is The calculation formula is: ; Horizontal normal distance It is a key indicator for evaluating whether the hydraulic fracturing network has achieved the designed sweep radius in the horizontal direction. This is achieved by calculating characteristic points at different depths. , can The cross-sectional view depicts the lateral distribution of the fracture zone relative to the fractured well. Step S514: Generate a sequence of profile feature points. The coordinate pairs obtained from the above steps are then... The attribute association is performed with the fracture feature attributes (such as structural blockage, network fracture, or transverse shear fracture) identified in step S400 to generate a standardized set of profile feature points. In particular, for the lower and upper boundary feature points of the fracture development zone identified in each borehole, their corresponding spatial coordinates were calculated. and This process transforms the originally isolated borehole linear data with varying inclination angles into point cloud data within the same profile coordinate system, eliminating the incomparability of data caused by differences in construction angles and providing a standardized mathematical basis for subsequently fitting the geometric boundaries of the hydraulic fracturing network.

[0054] In the process of inverting the geometric parameters of the fracture network in step S500, determining the vertical sweep height of the pressure fracture network is the primary indicator for evaluating the roof cracking effect. This embodiment, based on the local profile analysis coordinate system established in step S510, uses an algorithm combining lower bound constraints and symmetric extension to quantitatively calculate the fracture network height, specifically including the following sub-steps: Step S521: Extract the feature coordinates of the vertical ripple boundary. This is derived from the profile feature point set generated in step S514. In the process, feature points with key boundary significance are selected. First, the lower boundary feature point of the fracture development zone is identified, that is, the position where the continuous hydraulic fracturing dominant feature first appears on the vertical sequence of boreholes. The vertical layer height calculated in step S512 is read and denoted as . Secondly, the vertical height of the wellbore axis of the surface fracturing horizontal well in the local profile coordinate system is obtained, denoted as... Normally, The vertical depth of the target point is determined by the geological guidance model. Furthermore, if a clear upper boundary feature of a fracture development zone exists during borehole exploration (such as the location where the probe is blocked or where the fracture disappears), the vertical stratigraphic height is recorded as [the vertical depth]. .

[0055] Step S522: Calculate the vertical propagation radius of the lower flange. Based on the physical mechanism of hydraulic fracturing, fractures tend to open along the direction of minimum principal stress and propagate along the direction of maximum principal stress. Using the geometrical elevation difference between the measured lower boundary characteristic point of the fracture development zone and the axis of the fracturing well at the surface, the sweep capacity of fracturing fluid into deep rock formations under the coupled effects of gravity and geostress is quantified. Lower flange vertical propagation radius. The calculation formula is as follows: ; Lower wing vertical extension radius This directly reflects the degree of control the fracturing operation has over the rock strata below the wellbore. If the calculated... If the value is less than the preset engineering design threshold, it indicates that the fracturing fluid has failed to communicate effectively downwards, which will result in an excessively large overhang distance of the underlying rock strata.

[0056] Step S523: Invert the theoretical total height of the fracture network. Given the relatively homogeneous geomechanical properties of the target strata and the use of high-volume pump injection in fracturing operations, it is assumed that the fracture network formed by fracturing is quasi-symmetrically distributed around the wellbore axis in the vertical profile. Based on this, the theoretical total height of the entire fracturing network is calculated using the measured vertical propagation radius of the lower flange. The calculation formula is as follows: ; This calculation step, through actual measurement of the fractures in the lower half of the well via drilling, enables the prediction of fractures in the upper half of the well. It effectively solves the engineering problem of being unable to fully observe fractures in the upper half of the well due to obstruction of the borehole probe or limitation of the borehole trajectory, thereby obtaining the fracture height parameters of the entire formation.

[0057] Step S524: Validity verification based on the upper boundary feature point. To verify the reliability of the above symmetry assumption, the upper boundary feature point of the fracture development zone measured in the borehole is introduced for closure verification. The actual vertical height difference between the upper boundary feature point and the wellbore axis is calculated, i.e., the vertical extension radius of the upper wing. The calculation formula is as follows: ; Construct a highly inverted consistency criterion: if the measured... and The deviation rate is within the allowable range, or the actual measured deviation rate is within the acceptable range. If the value is close to the top boundary of the theoretical calculation, the inversion result is deemed valid. The final determined effective sweep height of the hydraulic fracturing network is then determined. Take the larger value between the measured difference between the upper and lower boundaries and the theoretical total height, that is: ; Through the above steps, this embodiment quantifies the substantial damage range of the hydraulic fracturing network in the vertical direction, clarifies whether the hydraulic fracturing network has completely cut off the key rock strata, and provides solid geometric data support for subsequent judgment on whether the roof can fall as mining proceeds.

[0058] In the process of inverting the geometric parameters of the fracture network in step S500, in addition to establishing the vertical height, quantifying the horizontal extension distance of the fracture network (i.e., perpendicular to the axis of the fracturing well at the surface) is crucial for evaluating whether the fracturing project meets the wide-area pressure relief design requirements. This embodiment, based on the horizontal span coordinates calculated in step S513, uses a method combining far-end constraints and extreme value verification to estimate the lower limit of the effective length of the fracture network, specifically including the following sub-steps: Step S531: Extract the maximum horizontal control distance feature value. This is based on the profile feature point set generated in step S514. In the process, all feature points identified as containing characteristics dominated by hydraulic fracturing are traversed. The horizontal normal distance corresponding to each feature point is retrieved. From all the borehole observation data, the horizontal normal distance with the largest value was selected and defined as the maximum effective verification distance, denoted as . Physically, this represents the location of the furthest fracturing fracture that the observation system of this embodiment can capture. For example, if a significant network of fractures is still observed in a borehole 115 meters horizontally away from the axis of the fracturing well at the surface, then the current location... The value is selected as .

[0059] Step S532: Construct the inequality criterion for the half-length of the fracture network. Based on the principles of rock fracture mechanics, hydraulic fracturing fractures extend from the wellbore towards the distal end, and the fracture width and complexity typically decrease with increasing distance. If the distance from the wellbore... The presence of macroscopically visible fracturing-induced fractures at this location indicates that the fracture tip must be located either outside or exactly at the current point. Based on this, an effective half-length fracturing network can be established. The lower bound constraint inequality for (i.e., the crack length of a single wing): ; The engineering significance of the criterion lies in the fact that it provides a definite minimum guaranteed value. Unlike microseismic monitoring, which is susceptible to positioning errors due to velocity model influences, borehole inspection provides... Based on direct evidence of failure in the physical rock core, the range of the lower bound constraint inequality belongs to the absolutely valid region.

[0060] Step S533: Calculate the lower limit of the theoretical total length of the fracture network. Assume the fracture network extends symmetrically in the horizontal direction with the surface fractured well axis as the axis of symmetry (i.e., the uphill and downhill directions). Based on the lower limit of the half-length determined in step S532, calculate the total length of the entire fracture network perpendicular to the wellbore axis. The calculation formula is as follows: ; If the measured data from this embodiment is substituted into the calculation, then... If the measured length is 115 meters, then the total length of the stitched mesh obtained through inversion is... At least 230 meters. This quantification is used to benchmark against the pressure relief width required in the mine working face design. If If the horizontal extension of the fracturing process is greater than or equal to the preset proportion of the width of the working face (e.g., covering more than 80% of the dip length of the working face), then the fracturing process is deemed to have met the standard.

[0061] Step S534, end-effect correction based on fracture abundance. To further improve the accuracy of length estimation and avoid underestimation due to the borehole being located precisely at the fracture edge, a fracture density decay trend correction is introduced. The fracture linear density within the farthest borehole is analyzed. If the fracture density at the current location is higher than the background value and shows no decay trend, it indicates that the fracture still has strong extension potential. At this point, [further steps can be taken]. Add an empirical correction amount to the base. (Usually taken as 10 to 20 meters), calculate the corrected total length.

[0062] ; The above steps expand point-based observation data into trend-based assessments, ensuring that the inversion results both conform to the principle of conservative verification and closely approximate the actual physical state of underground fracture propagation. For the specific statistical method of fracture line density, those skilled in the art can use the surveying method for calculation, which is a well-known technique in the field and will not be elaborated upon here.

[0063] In the process of outputting the seam mesh evaluation results in step S600, in order to transform abstract geometric parameters into intuitive engineering decision-making basis, this embodiment constructs a visual output process, which specifically includes the following sub-steps: Step S601: Construct the geometric envelope model of the seam network. The maximum effective sweep height is obtained based on the quantitative inversion in step S500. Total length of the sewn mesh In the local profile analysis coordinate system ( The physical boundary of the fracturing-affected zone is defined in the plane. The geometric center is the projection point of the surface fracturing well axis onto the profile. The total vertical height is... To represent the total horizontal span, a rectangular or elliptical closed envelope is constructed, which visually represents the theoretical limit of effective damage to the rock mass caused by hydraulic fracturing.

[0064] Step S602: Generate a visualization map of the fracture morphology. Iterate through the profile feature point set generated in step S514. The system filters out all feature points identified as exhibiting characteristics dominated by hydraulic fracturing (such as transverse shear fractures and network fracture zones). The coordinates of these feature points are then compared... The data is projected into the geometric envelope model constructed in step S601. Different types of fracture features are identified by different colors or legend symbols, forming a scatter plot or heat map that reflects the actual distribution density of fractures within the rock strata, thus visually demonstrating the heterogeneous characteristics of the fracture network.

[0065] Step S603: Output a comprehensive evaluation report. The key geometric parameters obtained from the inversion calculation are integrated with the fracture network morphology visualization map generated in step S602. An automatic fracturing effect evaluation report is generated, clearly stating engineering conclusions such as whether the target strata have been completely cut off and whether the fractures cover the mining roadway, serving as a direct basis for guiding the adjustment of the mine face's mining advance speed and support strategy.

[0066] To verify the effectiveness and accuracy of the fracture network evaluation method based on borehole inspection and surface fracturing data proposed in this invention, a mine working face with typical deep high ground stress and hard roof characteristics was selected as the specific implementation object. This working face faces the risk of strong mine pressure manifestation, and a staged hydraulic fracturing project using an L-shaped horizontal well was implemented on the surface. The specific implementation process and evaluation results of this embodiment are as follows: Basic geological parameters and engineering configuration: First, the assessment target was identified as the sandstone stratum above the working face roof. Based on borehole columnar sections and physical and mechanical property tests, the average thickness of the coal seam in the current area is approximately 12 to 15 meters, with a thick layer of hard sandstone distributed above the coal seam roof. The interbedded sections of coarse and medium sandstone are the main key strata, with uniaxial compressive strength generally exceeding 80 MPa and good overall integrity, with few natural fractures. The target stratum for this hydraulic fracturing was determined to be located in the strata 30 to 100 meters above the coal seam roof, aiming to weaken this high-level hard stratum through fracturing to prevent large-scale roof overhang during mining. This geological condition definition provides a geological background benchmark for subsequent identification of weak surfaces of primary bedding planes and tectonic fractures, eliminating misjudgments caused by the fracturing of the strata themselves.

[0067] Regarding the engineering parameters of surface fracturing wells, a high-volume, segmented fracturing process is carried out by connecting a surface L-shaped horizontal well to the downhole working face. The wellbore trajectory of the fracturing horizontal well is mainly arranged along the strike of the working face, and the vertical depth of the target point is controlled at a layer 60 to 65 meters above the coal seam roof (i.e., in the aforementioned geometric inversion model). The parameters are set at 60 to 65 meters. The fracturing operation employs a multi-cluster perforation combined with high-throughput pump injection. The designed injection volume of fracturing fluid per stage is 1500 to 2000 cubic meters, and the discharge rate is 10 to 12 cubic meters per minute. This design aims to achieve cross-layer propagation of fractures in the vertical direction and long-distance extension in the horizontal direction, echoing the symmetry assumption of fracture network height inversion and the far-end constraint condition of fracture network length inversion.

[0068] Regarding downhole observation array parameters, to comprehensively capture the spatial morphology of fracturing fractures, a series of specialized observation boreholes were deployed in the return airway and transport roadway of the working face. The borehole orientation was designed perpendicular to the roadway direction, i.e., perpendicular to the axis of the fracturing well on the surface, to ensure that the borehole trajectory passes through the potential fracture development zone along a geometrically optimal path. Borehole inclination angle... A uniform 75-degree angle was set based on triangular geometry optimization. This ensures that the borehole penetrates to the fracturing layer approximately 100 meters above the coal seam roof, while avoiding a decrease in the borehole's capture rate of vertical fractures due to an excessively large angle. Spatially, observation boreholes are arranged every 50 to 100 meters along the roadway direction, forming an observation array covering different horizontal distances (84 to 115 meters) on both sides of the surface fracturing well axis. This is to extract the maximum effective verification distance. It provides multiple data sources.

[0069] For data acquisition equipment, a mining-grade intrinsically safe high-definition borehole imager is used for borehole inspection operations. The video acquisition resolution is no less than 720P, and the probe advance speed is controlled between 0.5 m / min and 1.0 m / min to ensure clear capture of the texture features of micro-fractures. Simultaneously, a high-precision depth counter is used to record probe displacement, with depth errors controlled within ±0.1 meters, ensuring the accuracy of qualitative fracture identification and the precision of coordinate mapping calculations.

[0070] Quantitative inversion of mesh geometry parameters: After completing the basic parameter configuration and data acquisition, the measured data are processed based on the identified crack features and coordinate mapping model: In the vertical direction, the data from the observation boreholes located within the fracturing-affected zone were processed. The observation data showed that a significant tectonic tension fracture first appeared at a vertical height of 28.0 meters above the coal seam roof, identifying this point as the lower boundary characteristic point of the fracture development zone. At a vertical height of 98.0 meters, the borehole probe could no longer advance due to severe fracturing and deformation of the borehole wall. This location was determined to be a characteristic point of the upper boundary of the fracture development zone, i.e. Meters. Known vertical depth of the target point in the fractured well. Meters. Substitute the values ​​into the formulas in steps S522 and S524 to calculate the vertical spread radius of the lower wing. Vertical extension radius of the upper wing

[0071] ; ; The calculation results show a low deviation rate, verifying the rationality of the quasi-symmetric propagation assumption centered on the wellbore. The final determined effective sweep height of the fracturing network... The measured total height is the larger of the measured total height and the theoretical symmetrical height, which is 70.0 meters. This height completely covers the target critical rock layer, indicating that the fracturing operation successfully achieved longitudinal cutting of the hard top plate.

[0072] Analyzing borehole data at different horizontal distances from the surface fractured well axis along its horizontal length, high-density network-like fracture zones were still observed in the borehole at a horizontal distance of 115 meters. The maximum effective verification distance was determined. 115.0 meters. Substitute into the formula to estimate the total length of the stitching mesh. Considering that the working face dip width is 200 meters, the inversion result of 230.0 meters is greater than 200.0 meters, indicating that the hydraulic fracturing fractures have completely covered and extended beyond the working face mining area in the horizontal direction, meeting the design requirements for wide-area pressure relief.

[0073] Multi-source data verification and comprehensive judgment: To establish an independent data verification source, a combined well-ground microseismic monitoring system was used to acquire rupture source signals during the concurrent fracturing operation. The monitoring report showed the vertical sweep height of the microseismic waves corresponding to the fracturing section. The horizontal sweep length of the microseismic wave is 75.0 meters. It is 245.0 meters.

[0074] A comparative model for calculating the relative deviation of geometric parameters was constructed: Vertical height deviation rate. Horizontal length deviation rate The calculation results show that the geometric parameters obtained by borehole inversion in this embodiment are in high agreement with the microseismic monitoring data, with the deviation rate controlled within the allowable engineering error range of 10%. Furthermore, the borehole inversion values ​​are slightly smaller than the microseismic wave values, which is consistent with the physical law in rock mechanics that the range of the plastic failure zone is often smaller than the range of elastic wave disturbance. This proves that the inversion results of this invention represent a substantial effective fracturing zone (i.e., the area where the rock undergoes physical displacement or fracture), rather than merely a stress disturbance zone.

[0075] Based on the verification results of the above multi-source data, the final judgment on the geometric effect of the fracturing project was made: the inversion height of 70.0 meters exceeded the threshold of 60 meters, the inversion length of 230.0 meters exceeded the threshold of 200 meters, and the deviation verification with the microseismic data passed. Therefore, it is concluded that the segmented fracturing of the L-shaped horizontal well on the surface successfully constructed a wide-bandgap three-dimensional fracture network capable of cutting through the hard roof in the target area, achieving the expected weakening and modification target. This conclusion verifies the applicability and reliability of the method of this invention in underground coal mine engineering sites.

Claims

1. A fracture network evaluation method based on borehole inspection and surface fracturing data, characterized in that, Includes the following steps: Based on the spatial distance from the underground roadway roof to the surface fracturing well axis, the underground roadway roof is divided into a benchmark set area and an evaluation set area; Large-angle cross-layer inspection boreholes that penetrate the coal seam roof and enter the target fracturing layer are respectively deployed in the benchmark set area and the evaluation set area; The borehole imaging instrument is used to detect the large-angle through-layer inspection borehole, collect borehole wall image data and record the obstruction depth of the borehole imaging instrument probe; Differential qualitative identification of fracture features is performed on the borehole wall image data, the geostress-dominant features of the benchmark set region are extracted, and the interference of the geostress-dominant features is eliminated in order to identify hydraulic fracturing-dominant features in the evaluation set region. Based on the spatial distribution of the dominant hydraulic fracturing features and the obstruction depth, combined with the positional relationship between the location of the dominant hydraulic fracturing features and the axis of the surface fracturing well, the maximum sweep height and effective sweep length of the fracturing network are quantitatively inverted and the results are output.

2. The fracture network evaluation method based on borehole inspection and surface fracturing data according to claim 1, characterized in that, The step of dividing the area based on the spatial distance from the underground roadway roof to the axis of the surface fracturing well specifically includes: Establish a local three-dimensional spatial coordinate system that includes the underground roadway roof and the surface fracturing horizontal well, and project the axis of the surface fracturing well onto the local three-dimensional spatial coordinate system; Calculate the horizontal normal distance from any position on the roof of the underground roadway to the projection of the axis of the surface fracturing well; The region whose horizontal normal distance is greater than the preset effective radius of the fracturing fracture is defined as the reference set region; The area whose horizontal normal distance falls within the projection range of the surface fracturing well axis and the expected affected area is defined as the evaluation set area.

3. The fracture network evaluation method based on borehole inspection and surface fracturing data according to claim 1, characterized in that, The construction parameters for the steeply inclined, cross-layer inspection borehole include: The drilling inclination angle of the high-angle cross-layer inspection borehole is 70 to 80 degrees, so that the borehole trajectory forms a large angle with the bedding plane of the rock strata in the target fracturing layer; The designed borehole diameter of the large-angle through-layer inspection borehole is greater than the sum of the outer diameter of the borehole imaging instrument probe used to acquire the borehole wall image data and the estimated maximum shrinkage deformation of the borehole wall; The azimuth of the steeply inclined cross-layer inspection borehole is perpendicular to the direction of the underground roadway roof and points towards the axis of the surface fracturing well.

4. The fracture network evaluation method based on borehole inspection and surface fracturing data according to claim 1, characterized in that, The obstruction depth refers to the actual hole depth when the probe of the borehole imaging instrument is unable to continue advancing due to the fracture or collapse of the borehole wall rock mass. The step of recording the obstruction depth of the borehole imaging instrument probe specifically includes constructing the following classification and identification logic: If the location corresponding to the obstruction depth is located in the reference set region, and the contact surface of the borehole imaging instrument probe is a loose accumulation of drill cuttings, then it is determined to be a process blockage and will not participate in the quantitative inversion. If the location corresponding to the obstruction depth is located in the evaluation set area and the depth is close to the target fracturing layer, and the borehole imaging instrument probe reports that the contact surface is a hard and angular broken rock block, then it is determined to be a tectonic blockage. The obstruction depth determined as structural blockage is defined as the upper boundary data of the core fracture zone of the hydraulic fracturing network and is used in the quantitative inversion.

5. The fracture network evaluation method based on borehole inspection and surface fracturing data according to claim 1, characterized in that, The specific manifestations of the geostress-dominated characteristic are as follows: The borehole wall image data shows that the cross-section of the large-angle cross-layer inspection borehole exhibits a geometric deformation that changes from a circle to an approximately elliptical shape, and the actual borehole diameter shows a shrinking trend as the depth of the large-angle cross-layer inspection borehole increases. Furthermore, the borehole wall image data shows that the borehole wall fractures are single longitudinal cracks that are basically parallel to or intersect the axis of the steeply inclined cross-layer inspection borehole at a small angle, and the single longitudinal cracks are confined to the bedding planes of the rock strata within the target fracturing layer, without cutting through the bedding planes of the rock strata.

6. The fracture network evaluation method based on borehole inspection and surface fracturing data according to claim 1, characterized in that, The dominant characteristics of hydraulic fracturing include transverse layered fractures and a network of fracture zones, which are specifically manifested as follows: The transverse cutting fractures intersect the axis of the steeply inclined cross-layer inspection borehole at a large angle, and geometrically cut off the bedding plane of the target fracturing layer in space. The network fracture zone structure is formed by the interweaving of transverse shearing cracks and longitudinal fissures, and the borehole wall rock mass of the large-angle cross-layer inspection borehole exhibits a high-density fractured, fragmented, or locally cavitated morphology.

7. The fracture network evaluation method based on borehole inspection and surface fracturing data according to claim 1, characterized in that, Before quantitatively inverting the geometric parameters of the fracture network, the steps also include data spatial mapping and establishing a local profile analysis coordinate system: The direction perpendicular to the top of the coal seam and upward is defined as the height axis, and the direction perpendicular to the axis of the surface fracturing well and along the dip of the top of the coal seam is defined as the span axis. Using trigonometric relationships, the depth values ​​recorded by the borehole imaging instrument on the trajectory of the steep-angle cross-layer inspection borehole are converted into the vertical projection height and horizontal span coordinates in the local profile analysis coordinate system; The feature points that identify the dominant hydraulic fracturing characteristics are mapped to the local profile analysis coordinate system to generate a standardized set of profile feature points.

8. The fracture network evaluation method based on borehole inspection and surface fracturing data according to claim 7, characterized in that, The specific steps for determining the maximum wave height include: The location where the first continuous hydraulic fracturing dominant feature appears in the set of feature points of the profile is identified and defined as the lower boundary feature point of the fracture development zone. The vertical projection height of the lower boundary feature point of the fracture development zone in the local profile analysis coordinate system is read and recorded as the lower boundary height. Determine the upper boundary position and height of the fracture development zone: If the obstructed depth, which is determined to be structural blockage, exists, the obstructed depth is converted into the vertical projection height in the local profile analysis coordinate system using the trigonometric function relationship, and recorded as the upper boundary height; if it does not exist, the vertical projection height of the position where the hydraulic fracturing dominant feature disappears in the local profile analysis coordinate system is selected and recorded as the upper boundary height. The vertical distance from the lower boundary height to the projection point of the surface fracturing well axis on the height axis is calculated and defined as the vertical expansion radius of the lower wing; Based on the assumption that the fracture network is quasi-symmetrically distributed in the vertical direction with the axis of the surface fracture well as the center, the theoretical total height of the fracture network is estimated by using twice the vertical expansion radius of the lower wing; Calculate the difference between the upper boundary height and the lower boundary height to obtain the measured height difference; The measured height difference is compared with the theoretical total height, and the larger value between the measured height difference and the theoretical total height is taken as the maximum sweep height.

9. The fracture network evaluation method based on borehole inspection and surface fracturing data according to claim 7, characterized in that, The specific steps for determining the effective sweep length include: Traverse the set of profile feature points and select the feature points that contain the hydraulic fracturing dominant feature and have the largest absolute value of the horizontal distance between the horizontal span coordinate and the axis of the surface fracturing well. The absolute value of the horizontal distance from the feature point to the axis of the surface fracturing well is defined as the maximum effective verification distance; Based on the principle that the fracture network extends symmetrically to both sides along the axis of the surface fracture well, the maximum effective verification distance is used as the lower limit of the single-wing fracture length; The effective sweep length of the hydraulic fracturing network is determined based on twice the maximum effective verification distance.

10. The fracture network evaluation method based on borehole inspection and surface fracturing data according to claim 7, characterized in that, The steps for outputting the results specifically include: Based on the maximum sweep height and the effective sweep length, a rectangular or elliptical envelope of the hydraulic fracturing network is constructed in the local profile analysis coordinate system. The distribution of the hydraulic fracturing dominant features in the local profile analysis coordinate system is superimposed onto the envelope to generate a visual evaluation map reflecting the spatial morphology of the fracture network. The output includes a fracturing effect evaluation report containing the maximum wave height value, the effective wave length value, and the visualization evaluation chart.

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