A method for determining the direction of maximum horizontal principal stress based on borehole pore pressure ratio

Abstract

This invention discloses a method for determining the direction of the maximum horizontal principal stress based on borehole formation rate, relating to the field of mining engineering technology. The method includes: constructing a set of pressure-relief boreholes of the same diameter and target depth along a horizontal plane at a preset azimuth angle within the area to be measured; recording the actual drilling depth of each pressure-relief borehole based on its construction; calculating the formation rate of each pressure-relief borehole based on the actual drilling depth and target depth; and determining the direction of the maximum horizontal principal stress based on the distribution law of the formation rate. This invention clarifies the correlation between "drilling direction - formation rate - direction of the maximum horizontal principal stress," transforming common borehole formation obstacles in engineering into an effective way to acquire geological information. It achieves low-cost and high-efficiency acquisition of key geostress direction information without the need for additional specialized equipment and complex testing processes, providing a highly practical solution for rapid assessment and targeted engineering control of the geostress field in coal mines.

Description

Technical Field

[0001] This invention relates to the field of mining engineering technology, and in particular to a method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate. Background Technology

[0002] The orientation of the geostress field is one of the key geomechanical factors affecting the stability of the surrounding rock in roadways and the layout of mine engineering. Accurately determining the orientation of the maximum horizontal principal stress in a region is of significant engineering importance for optimizing working face layout, rationally determining roadway axis, guiding support design and parameter optimization, and preventing dynamic disasters such as rockbursts. Currently, obtaining the geostress orientation mainly relies on core experiments (such as wave velocity anisotropy, acoustic emission, differential strain analysis, etc.) and field tests (such as hydraulic fracturing, microseismic monitoring, wellbore imaging, etc.). However, these methods generally have the following limitations: core experiments are limited by the cost and quantity of core samples, resulting in a limited range of data representation; while field tests offer higher accuracy, they are complex and expensive, making large-scale, multi-point application difficult in underground coal mines.

[0003] In tunnel excavation and surrounding rock control practices, drilling is a crucial method for exposing the surrounding rock, implementing pressure relief, and detecting geological information. However, during drilling, stress concentration in the surrounding rock often leads to phenomena such as borehole collapse and stuck drill bits, severely impacting drilling depth and construction efficiency. Current technologies largely focus on improving drilling tools and optimizing processes to increase the borehole success rate. There is a lack of systematically revealing the intrinsic relationship between borehole success rate and geostress direction based on the fundamental mechanical mechanism of the spatial matching relationship between the direction of surrounding rock stress and the drilling direction. Furthermore, there is a lack of simple and economical methods to inversely determine the geostress direction based on the directly observable engineering indicator of borehole success rate.

[0004] Therefore, there is an urgent need for a low-cost, easy-to-implement in-situ method for determining the direction of the maximum horizontal principal stress. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate, so as to solve the problems of high cost and complex operation of current technology for determining the direction of geostress.

[0006] To achieve the above objectives, the present invention provides a method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate, comprising the following steps: S1. Within the area to be measured, construct a set of pressure relief boreholes with the same diameter and target depth along the horizontal plane at a preset azimuth angle. S2. Based on the construction of the pressure relief boreholes, record the actual drilling depth of each pressure relief borehole; S3. Calculate the hole formation rate of each pressure relief borehole based on the actual drilling depth and the target depth. S4. Determine the direction of the maximum horizontal principal stress based on the porosity distribution law.

[0007] Preferably, the preset azimuth angles are evenly distributed within the range of 0°-180° at fixed intervals.

[0008] Preferably, the fixed interval is 10°-30°.

[0009] Preferably, based on the construction status of the pressure relief boreholes, the specific details of recording the actual drilling depth of each pressure relief borehole include: When the pressure relief drilling operation encounters obstruction, the operation shall be stopped immediately, and the drilling depth at the point of cessation shall be recorded as the actual drilling depth. When the pressure relief drilling is unobstructed, proceed to the target depth and record the results.

[0010] Preferably, the obstruction conditions include: stuck drill, drill bit jamming, and stagnant progress.

[0011] Preferably, the specific details of determining the direction of the maximum horizontal principal stress based on the porosity distribution law include: Plot the porosity distribution curve as a function of the preset azimuth angle; Based on the distribution curve, determine the azimuth angle corresponding to the extreme value of porosity; the extreme value includes: the maximum value and the minimum value; The direction of the maximum horizontal principal stress in the region is determined based on the azimuth angle corresponding to the extreme value of porosity.

[0012] Preferably, determining the direction of the maximum horizontal principal stress in the region based on the azimuth angle corresponding to the extreme value of porosity includes the following: When the extreme value is the minimum value, the azimuth angle corresponding to the minimum porosity is determined. The direction indicated by the azimuth angle corresponding to the minimum value is the direction orthogonal to the direction of the maximum horizontal principal stress in the region. That is, the direction indicated by the azimuth angle corresponding to the minimum value is at a 90° angle to the direction of the maximum horizontal principal stress in the region. When the extreme value is at its maximum value, determine the azimuth angle corresponding to the maximum porosity. The direction indicated by the azimuth angle corresponding to the maximum value is the direction of the maximum horizontal principal stress in the region.

[0013] Preferably, the pressure relief borehole described in S1 is a large-diameter borehole constructed along the sidewall of the roadway.

[0014] Preferably, the diameter ranges from 100mm to 200mm.

[0015] Preferably, the target depth in S1 is in the range of 20m-50m.

[0016] In summary, the maximum horizontal principal stress direction determination method based on borehole formation rate provided by this invention offers the following advantages compared to traditional technologies: Through integrated in-situ testing encompassing "construction-observation-inversion," the determination of geostress direction is fully integrated into the conventional stress relief drilling process. Only the borehole orientation needs to be changed and the borehole depth recorded; the maximum horizontal principal stress direction can be directly determined through the borehole formation rate. This overcomes the limitations of traditional methods that rely on core samples or specialized testing, achieving a technological shift from "detection first, design later" to "construction and sensing simultaneously," demonstrating strong on-site operability and economy. By clarifying the correlation between "drilling direction - borehole formation rate - horizontal principal stress direction," common borehole formation obstacles in engineering are transformed into effective geological information acquisition methods. This enables the low-cost and high-efficiency acquisition of key geostress direction information without the need for additional specialized equipment and complex testing processes, providing a highly practical solution for the rapid assessment of underground geostress fields in coal mines and targeted engineering control.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the mechanical analysis model of the pressure relief drilling process in this invention; Figure 1 Part (a) in the diagram is a schematic diagram of the cutting forces; Figure 1 Part (b) is a schematic diagram of the forces acting on the drill bit; Figure 1 Part (c) in the diagram is a schematic diagram of the forces acting on the drill pipe; Figure 2 This is a schematic diagram showing the spatial distribution relationship between the direction of the maximum horizontal principal stress in the surrounding rock of the tunnel and the large-diameter pressure relief boreholes at different azimuth angles in this invention. Figure 3 This is a flowchart illustrating a method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate according to the present invention. Figure 4 This is a schematic diagram of the pressure relief drilling arrangement scheme used in Embodiment 1 of the present invention; Figure 5 This is a comparative schematic diagram showing the actual drilling depth measurement results of the pressure relief boreholes in various directions in Embodiment 1 of the present invention; Figure 6 This is a graph showing the hole formation rate distribution of the pressure relief drilling in Embodiment 1 of the present invention; Figure 7 This is a schematic diagram showing the result of determining the direction of the maximum horizontal principal stress in the roadway sidewall based on the extreme value of the borehole formation rate of the pressure relief borehole in Embodiment 1 of the present invention. Detailed Implementation

[0019] The technical method of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this application.

[0020] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the scope of this application and its application or use.

[0021] Techniques, systems, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the instruction manual.

[0022] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0023] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0024] The core principle and technical basis of the maximum horizontal principal stress direction discrimination method based on borehole formation rate proposed in this invention are as follows: Figure 1 and Figure 2 As shown, the details are as follows: (1) The main control mechanism of deep drilling hole formation rate Tunnel excavation induces a typical zonal structure in the surrounding rock, successively including a shallow plastic zone, a deep elastic zone, and a pre-existing rock stress zone. Within the shallow plastic zone, the mechanical behavior of the surrounding rock is similar to the post-peak strain softening stage at a laboratory scale. Its internal stress is significantly reduced due to pressure relief, and the coal and rock mass is in a fractured and loose state, with significantly deteriorated strength. When constructing large-diameter pressure-relief boreholes in the shallow plastic zone, the drilling process is relatively smooth due to the lower resistance of the surrounding rock, requiring significantly less thrust and torque, making it easier for the drilling rig to achieve efficient and stable drilling. As the pressure-relief borehole extends deeper, the construction area gradually transitions from a plastic zone to an elastic stress concentration zone and even a pre-existing rock stress zone. Especially in shallow strata, controlled by tectonic stress, horizontal stress is often generally higher than vertical stress, with the maximum horizontal principal stress often becoming the dominant factor affecting the mechanical response and stability of the surrounding rock. When the drill bit moves from the low-stress, weakly structured plastic zone into the high-stress, intact rock mass-dominated elastic zone, its working mechanical environment undergoes a fundamental change. Under high confining pressure, especially in a stress field dominated by high-level principal stress, intense circumferential stress concentration occurs around the pressure relief borehole. This can easily lead to compression failure of the borehole wall, borehole collapse, and diameter reduction, and significantly increase the frictional resistance between the drill pipe and the borehole wall, resulting in construction obstacles such as "drill sticking" and "drill jamming." These adverse mechanical responses directly limit the borehole depth and significantly reduce the borehole formation rate, severely affecting the pressure relief effect.

[0025] Therefore, the stress concentration characteristics around the pressure relief borehole directly control its borehole stability and porosity. In geological environments, the geostress field generally exhibits significant anisotropy, with the direction of the maximum horizontal principal stress often dominating the mechanical response of the surrounding rock. By systematically comparing the differences in borehole performance of pressure relief boreholes in different orientations, the spatial distribution characteristics of the stress concentration degree in the surrounding rock can be indirectly inverted, thus providing important field evidence for determining the dominant direction of the maximum horizontal principal stress in the region.

[0026] (2) Control mechanism of surrounding rock stress on drilling mechanical behavior In an infinitely large flat plate, when a circular pressure relief borehole is subjected to mutually perpendicular maximum and minimum horizontal principal stresses at a distance, the stress distribution around the borehole can be given by the Kirsch solution in elasticity mechanics. In polar coordinates (r, θ) (with the origin at the borehole center and θ measured from the direction of the maximum horizontal principal stress), the radial stress components are: ; in, σ r For radial stress components, σ 1 represents the maximum horizontal principal stress. σ 3 represents the minimum horizontal principal stress. a Let r be the radius of the pressure relief borehole, and θ be the polar coordinate angle.

[0027] The tangential stress components are: ; in, This represents the tangential stress component.

[0028] The shear stress components are: ; in, This represents the shear stress component.

[0029] On the borehole wall of the pressure relief drill ( At point ), both the radial stress component and the shear stress component are zero, and the circumferential stress simplifies to: ; in, This is circumferential stress.

[0030] As derived from the above theory, the maximum and minimum horizontal principal stresses in the far field together constitute the controlling parameters for the circumferential stress distribution of the borehole wall in pressure-relief boreholes. The larger these values ​​are, the more significantly the circumferential stress around the borehole caused by the elastic concentration effect increases, especially at the borehole wall perpendicular to the direction of the maximum horizontal principal stress, where extremely high circumferential compressive stress concentration will occur. This high-stress environment will significantly reduce the stability of the surrounding rock of the borehole wall, thus mechanically explaining the inherent mechanism of borehole wall instability phenomena such as borehole collapse, drill bit sticking, and drill bit jamming that easily occur during drilling operations.

[0031] Based on the analysis of the rock-breaking mechanics model, the shear body mechanics model when the cutting teeth cut the rock is as follows: Figure 1 As shown in part (a), its force equilibrium is referenced by the following equation: ; in, This represents the total reaction force exerted by the rock mass on the cutting teeth during cutting. The angle of the cutting teeth. The angle between the shear plane and the cutting plane. The internal friction angle of the rock. Shear reaction force The reaction force of the unbroken rock mass c For cohesion, h For cutting depth, The cutting width of the cutting tooth is the projected width of the cutting tooth in the cutting direction.

[0032] Figure 1 In part (a) of the This refers to the normal force exerted by the coal and rock mass on the cutting and shearing surface.

[0033] During drilling, the reaction force of the rock mass on the drill bit is directly affected by its in-situ stress state. For example... Figure 1 As shown in section (b), the lateral pressure acting on the drill bit The stress field is mainly determined by the normal component of the surrounding rock stress field on the cross-section of the pressure relief borehole. This component is closely related to the direction of the maximum horizontal principal stress in the far field and the angle between the borehole axis and the stress field. This is the frictional torque acting on the drill bit sidewall. The thrust acting on the drill bit, This represents the rotational resistance torque experienced by the bottom cutting teeth when breaking rock. When the stress relief borehole direction is perpendicular to the direction of the maximum horizontal principal stress, the projected component on the stress relief borehole normal plane reaches its maximum value. At this point, the surrounding rock exhibits the highest stress concentration state, leading to lateral pressure... The cutting resistance increases significantly. This results in greater cutting resistance for the drill bit, requiring higher torque and thrust to achieve effective drilling, thus directly affecting hole formation efficiency and drilling stability.

[0034] In addition, the stress condition of the drill pipe is as follows Figure 1 As shown in part (c), refer to the following formula: ; in, For the total thrust of drilling, For chip removal force, This refers to the reaction force of the coal and rock mass on the cutting teeth of the drill bit when the drill bit is breaking the coal and rock mass (which is only affected by the magnitude of the internal stress when drilling into the rock mass). For friction, For total torque, The torque required to agitate coal dust from the bottom of the hole and discharge it outside the hole. This is the resistance torque generated by the coal and rock mass on the drill bit (which is positively correlated with the stress in the coal mass). This is the frictional resistance torque (affected by both the drilling depth and internal stress).

[0035] in addition, Figure 1 In part (c) This refers to the drilling length. This is the chip removal distance.

[0036] Based on the above drilling mechanics model, the total drilling thrust and total torque are composed of the chip removal force, torque, and friction components, respectively. The chip removal force and torque are directly positively correlated with the internal stress of the coal body; the friction force and frictional resistance torque are simultaneously affected by the coupling effect of drilling depth and internal stress. The mechanism is that under high ground stress, the borehole wall convergence deformation intensifies, the amount of drill cuttings increases, leading to an increase in the normal pressure on the borehole wall of the drill pipe-pressure relief borehole and the flow resistance of the chip removal. Furthermore, the effective stress acting on the cross-section of the pressure relief borehole is determined by the maximum horizontal principal stress in the far field and its angle with the axis of the pressure relief borehole: when the direction of the pressure relief borehole is perpendicular to the maximum horizontal principal stress, the circumferential stress generated by the maximum horizontal principal stress around the pressure relief borehole is... The maximum value makes the coal body exhibit higher breaking resistance and borehole wall convergence tendency, thereby significantly improving the chip removal force, torque and friction components; conversely, by adjusting the included angle of the pressure relief borehole axis, the effective stress can be reduced, thereby systematically reducing the various mechanical components in the thrust and torque, and improving drilling stability.

[0037] (3) Quantitative correlation between periphery stress and maximum horizontal principal stress like Figure 2 As shown, under the influence of geological structure and environment, the maximum horizontal principal stress and the maximum horizontal principal stress in the elastic zone of the pressure relief borehole (large diameter borehole) have an angle α, where σ1=σ H ×sinα, where α ranges from 0° to 180°. When the axial direction of the pressure relief borehole is on the same straight line as the direction of the maximum horizontal principal stress, the stress component of the maximum horizontal principal stress around the borehole is 0. When the direction of the pressure relief borehole is perpendicular to the direction of the maximum horizontal principal stress, the stress component of the maximum horizontal principal stress is the maximum horizontal principal stress. On the one hand, this can severely lead to compression failure of the borehole wall, borehole collapse, and diameter reduction, and significantly increase the frictional resistance between the drill pipe and the borehole wall, resulting in construction obstacles such as "drill sticking" and "drill jamming". On the other hand, this can also increase the chip removal force, torque, and friction components, increasing the thrust and torque required for drilling.

[0038] Under the control of geological structure and occurrence environment, the in-situ stress field usually exhibits obvious directionality. Among them, the maximum horizontal principal stress, as the dominant component of regional tectonic stress, has a decisive influence on the mechanical behavior of the borehole surrounding rock. In actual engineering, due to the combined influence of local structure, topography, and mining disturbance, the actual direction of the maximum horizontal principal stress in the elastic zone where the pressure relief borehole is located is often inconsistent with the direction of the regional maximum horizontal principal stress, and there is a spatial angle α (0°≤α≤180°) between the two. According to the stress projection principle, the effective stress component of the maximum horizontal principal stress on the pressure relief borehole plane can be expressed as σ1=σ H×sinα. When the axis of the pressure relief borehole is parallel to the direction of the maximum horizontal principal stress (α=0° or 180°), the projection component of the maximum horizontal principal stress in the radial plane of the pressure relief borehole is zero. The pressure relief borehole mainly bears the effect of the minimum principal stress, and the stress concentration in the surrounding rock is relatively low. When the axis of the pressure relief borehole is perpendicular to the direction of the maximum horizontal principal stress (α=90°), the maximum horizontal principal stress acts completely on the cross-section of the pressure relief borehole, and its normal component reaches its maximum value of the maximum horizontal principal stress. At this time, the borehole wall of the pressure relief borehole bears extremely high circumferential compressive stress concentration, which significantly induces instability phenomena such as borehole wall compression failure, borehole collapse, and continuous diameter reduction. At the same time, the high stress state exacerbates the convergence deformation of the borehole wall and the friction effect of the fractured coal and rock, resulting in a significant increase in the normal pressure between the drill rod and the borehole wall, a sharp increase in frictional resistance, and easy to cause construction obstacles such as "drill sticking" and "drill jamming". In terms of drilling dynamics, the high confining pressure greatly enhances the fracture resistance and cutting difficulty of the coal and rock, resulting in the chip removal force and chip removal torque The frictional resistance increased significantly, and the increased amount of drill cuttings and the obstruction of the cuttings removal channel further increased the frictional resistance. and frictional resistance torque Ultimately, this manifests as the total drilling thrust. With total torque The systemic increase in power places higher demands on the thrust and torque of drilling rigs.

[0039] This invention provides a method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate, such as... Figure 3 As shown, it includes the following steps: S1. Within the area to be measured, construct a set of pressure-relief boreholes with the same diameter and target depth along the horizontal plane at a preset azimuth angle. The preset azimuth angles are evenly distributed within the range of 0°-180° at fixed intervals of 10°-30°; the pressure-relief boreholes are large-diameter boreholes constructed along the sidewalls of the roadway, with a diameter ranging from 100mm to 200mm; the target depth ranges from 20m to 50m.

[0040] S2. Based on the construction of the pressure relief boreholes, record the actual drilling depth of each pressure relief borehole.

[0041] Furthermore, the specific content of step S2 includes: When the pressure relief drilling operation encounters obstruction, the operation should be stopped immediately, and the drilling depth at the point of cessation should be recorded as the actual drilling depth.

[0042] When the pressure relief drilling is unobstructed, proceed to the target depth and record the results.

[0043] The obstruction situations include: stuck drill, drill bit jamming, and stagnant progress.

[0044] S3. Calculate the hole formation rate for each pressure relief borehole based on the actual drilling depth and the target depth.

[0045] S4. Determine the direction of the maximum horizontal principal stress based on the porosity distribution law.

[0046] Furthermore, step S4 specifically includes the following steps: S401. Draw the distribution curve of porosity as a function of preset azimuth angle.

[0047] S402. Based on the distribution curve, determine the azimuth angle corresponding to the extreme value of porosity. The extreme values ​​include the maximum and minimum values.

[0048] S403. Determine the direction of the maximum horizontal principal stress in the region based on the azimuth angle corresponding to the extreme value of the porosity.

[0049] Furthermore, the specific content of step S403 includes: When the extreme value is at its minimum, the azimuth angle corresponding to the minimum porosity is determined. The direction indicated by the azimuth angle corresponding to the minimum value is orthogonal to the direction of the maximum horizontal principal stress in the region. That is, the direction indicated by the azimuth angle corresponding to the minimum value forms a 90° angle with the direction of the maximum horizontal principal stress in the region.

[0050] When the extreme value is at its maximum value, determine the azimuth angle corresponding to the maximum porosity. The direction indicated by the azimuth angle corresponding to the maximum value is the direction of the maximum horizontal principal stress in the region.

[0051] Example 1 This embodiment was implemented in a coal mine roadway. By systematically changing the azimuth angle of the pressure relief borehole (large diameter borehole), the variation law of the hole formation rate was analyzed, thereby inverting and verifying the direction of the maximum horizontal principal stress of the surrounding rock.

[0052] A field test of a method for determining the direction of the maximum horizontal principal stress based on borehole formation rate is conducted, and the steps are as follows: S1. Design a set of large-diameter pressure relief boreholes on the right side of the roadway. The diameter of the pressure relief boreholes is set at 150mm, and the rated output torque of the drilling rig is 500N·m. (The rest of the text appears to be unrelated and possibly machine-translated gibberish.) Figure 4 As shown, all pressure relief boreholes were constructed horizontally, with the starting point remaining consistent. To investigate the directional effect, the preset azimuth angle of the pressure relief boreholes was varied in 10° increments within the range of 0°-180°. The target depth of the pressure relief boreholes was uniformly set at 30m.

[0053] S2. Pressure Relief Drilling Construction and Data Acquisition: Each pressure relief borehole is constructed sequentially according to the preset azimuth and target depth. During the construction of the pressure relief borehole, if the drill gets stuck, jammed, or the drilling progress stops, work is immediately stopped, and the drilling depth at the time of cessation is recorded as the actual drilling depth. After the construction of each pressure relief borehole is completed, the actual drilling depth is accurately measured and recorded.

[0054] S3. Test Results and Analysis: After the pressure relief drilling was completed, the actual depths of each pressure relief borehole were 30m, 22.2m, 15.7m, 12.1m, 7.0m, 16.0m, 16.7m, 20.1m, 21.4m, 23.2m, 25.4m, 27.8m, 28.5m, 30m, 28.4m, 26.7m, and 30m, respectively. Figure 5 As shown, there are significant differences in azimuth. The shallowest pressure relief borehole, with a preset azimuth angle of 50°, is only 7.0m, while the pressure relief boreholes with preset azimuth angles of 10°, 140°, and 170° all reached the target depth of 30m.

[0055] For quantitative evaluation, the porosity is defined as the ratio of the actual drilling depth to the target depth, as shown in the following formula: ; in, Porosity H n This represents the actual drilling depth. H 0 represents the target depth.

[0056] The calculated porosity distribution of each pressure relief borehole is as follows: Figure 6 As shown. According to Figure 6 The variation law and mechanical mechanism of porosity with preset azimuth angle are analyzed as follows: In the 0°-50° range: the hole formation rate increases significantly as the preset azimuth angle decreases. This phenomenon is mainly attributed to two aspects: First, as the angle between the maximum horizontal principal stress and the maximum horizontal principal stress in the elastic zone of the pressure relief borehole decreases, the effective maximum horizontal principal stress component acting on the cross-section of the pressure relief borehole decreases accordingly. According to the theory of elasticity, the circumferential stress concentration of the borehole wall weakens. Second, the trajectory of the pressure relief borehole in the 0° to 50° range is more likely to be located in the shallow plastic zone formed by roadway excavation. The stress release in the shallow plastic zone and the deterioration of the coal and rock mass strength significantly reduce the drilling difficulty.

[0057] Within the 50°-140° range, the hole formation rate shows a continuous upward trend with the increase of the preset azimuth angle, reaching 100% at 140°. This pattern clearly reveals the strong control of the horizontal principal stress direction over the drilling process. As the angle changes from 50° to 140°, the angle between the axial direction of the pressure-relief borehole and the direction of the maximum horizontal principal stress gradually decreases, causing the projection component of the maximum horizontal principal stress on the radial plane of the borehole (i.e., the effective stress) to continuously decrease. This directly leads to a reduction in the circumferential stress at key locations on the borehole wall, effectively suppressing the risks of instability such as hole collapse and diameter reduction, while also reducing the frictional resistance between the drill rod and the borehole wall, thereby avoiding construction obstacles such as "drill sticking" and "drill jamming," and significantly improving the hole formation rate.

[0058] In the 140° to 160° range, the hole formation rate decreased slightly. This is because the angle between the preset azimuth angle and the direction of the maximum horizontal principal stress increased again due to the continued increase in the angle of the pressure relief borehole axis, which caused the effective stress component to rebound and the construction difficulty of the pressure relief borehole to increase accordingly.

[0059] In the 160° to 180° range: the hole formation rate rebounded to 100%. The main reason is that the stress relief drilling trajectory within this preset azimuth angle range is again mainly located in the plastic zone of the roadway, and the low stress and low strength characteristics of the surrounding rock become the dominant factors, thus ensuring a high hole formation rate.

[0060] S4. Conclusion and Stress Direction Judgment: Based on the comprehensive analysis of step S3, it can be seen that when the hole formation rate reaches a minimum of 23.3% (corresponding to a preset azimuth angle of 50°), it indicates that the direction of the pressure relief borehole is perpendicular to the direction of the maximum horizontal principal stress of the surrounding rock. At this time, the stress concentration effect on the cross section of the pressure relief borehole is the strongest.

[0061] When the hole formation rate reaches the maximum value of 100% (corresponding to a 140° azimuth angle), it indicates that the direction of the pressure relief borehole is basically parallel to the direction of the maximum horizontal principal stress of the surrounding rock. At this time, the stress component of the maximum horizontal principal stress in the borehole radial direction is almost zero, and the borehole construction conditions are most favorable.

[0062] Therefore, it can be clearly determined that the direction of the maximum horizontal principal stress in the roadway sidewall of the test area is approximately 140°. Figure 7 As shown.

[0063] Example 1, through field tests, directly verified the intrinsic relationship between the borehole formation rate of pressure relief drilling and the direction of in-situ stress, providing a reliable methodology and practical basis for inverting the direction of in-situ stress based on construction results.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate, characterized in that, Includes the following steps: S1. Within the area to be measured, construct a set of pressure relief boreholes with the same diameter and target depth along the horizontal plane at a preset azimuth angle. S2. Based on the construction of the pressure relief boreholes, record the actual drilling depth of each pressure relief borehole; S3. Calculate the hole formation rate of each pressure relief borehole based on the actual drilling depth and the target depth. S4. Determine the direction of the maximum horizontal principal stress based on the porosity distribution law.

2. The method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate according to claim 1, characterized in that, The preset azimuth angles are evenly distributed at fixed intervals within the range of 0°-180°.

3. The method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate according to claim 2, characterized in that, The fixed interval is 10°-30°.

4. The method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate according to claim 1, characterized in that, Based on the construction of the pressure relief boreholes, the specific details of the actual drilling depth of each pressure relief borehole should be recorded, including: When the pressure relief drilling operation encounters obstruction, the operation shall be stopped immediately, and the drilling depth at the point of cessation shall be recorded as the actual drilling depth. When the pressure relief drilling is unobstructed, proceed to the target depth and record the results.

5. The method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate according to claim 4, characterized in that, The obstruction conditions include: stuck drill, drill bit jamming, and stagnant progress.

6. The method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate according to claim 1, characterized in that, The specific content for determining the direction of the maximum horizontal principal stress based on the porosity distribution law includes: Plot the porosity distribution curve as a function of the preset azimuth angle; Based on the distribution curve, determine the azimuth angle corresponding to the extreme value of porosity; the extreme value includes: the maximum value and the minimum value; The direction of the maximum horizontal principal stress in the region is determined based on the azimuth angle corresponding to the extreme value of porosity.

7. The method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate according to claim 6, characterized in that, The specific details for determining the direction of the maximum horizontal principal stress in the region based on the azimuth angle corresponding to the extreme value of porosity include: When the extreme value is the minimum value, the azimuth angle corresponding to the minimum porosity is determined. The direction indicated by the azimuth angle corresponding to the minimum value is the direction orthogonal to the direction of the maximum horizontal principal stress in the region. That is, the direction indicated by the azimuth angle corresponding to the minimum value is at a 90° angle to the direction of the maximum horizontal principal stress in the region. When the extreme value is at its maximum value, determine the azimuth angle corresponding to the maximum porosity. The direction indicated by the azimuth angle corresponding to the maximum value is the direction of the maximum horizontal principal stress in the region.

8. The method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate according to claim 1, characterized in that, The pressure relief borehole described in S1 is a large-diameter borehole constructed along the sidewall of the roadway.

9. The method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate according to claim 8, characterized in that, The diameter ranges from 100mm to 200mm.

10. The method for determining the direction of the maximum horizontal principal stress based on the borehole formation rate according to claim 1, characterized in that, The target depth mentioned in S1 ranges from 20m to 50m.

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