A method for testing in-situ permeability coefficient of rock formation

Abstract

The present disclosure provides a method for testing in-situ permeability coefficient of rock formation, comprising: drilling and forming a borehole along the depth direction of the rock formation by using a drilling device, and arranging a casing on the borehole wall; taking a cylindrical region of the rock formation at the bottom of the borehole as a test section; injecting flushing fluid to the bottom of the borehole by using a drill pipe, so that part of the flushing fluid flows back to the top orifice of the borehole along the gap between the drill pipe and the casing, and the rest of the flushing fluid permeates along the planar direction of the rock formation to the periphery of the test section; controlling the injection flow rate of the flushing fluid until the backflow of the flushing fluid stabilizes at the top orifice of the borehole, and calculating the permeability coefficient under the flushing fluid condition by using the injection flow rate of the flushing fluid when it is stable; and obtaining the in-situ permeability coefficient of the rock formation based on the permeability coefficient under the flushing fluid condition. In the method for testing in-situ permeability coefficient of rock formation, the preparation time before the test is greatly reduced, and the collapse accident caused by the sudden change of pressure and seepage environment due to the activity of the drill pipe is avoided.

Description

Technical Field

[0001] This disclosure relates to the field of permeability testing technology, and in particular to an in-situ permeability testing method for rock formations. Background Technology

[0002] Currently, the most commonly used permeability coefficient testing method in aquifer area management and geological exploration is the in-situ test. The principle involves injecting water into a borehole under a certain pressure, sealing the borehole with plugs at regular intervals. As the water level rises, water seeps from the borehole into the surrounding aquifer. The permeability of the rock formation is evaluated by measuring the injection volume per unit time. This method is simple to operate and highly adaptable. However, in practice, it requires removing the drill rod and replacing the water pump before testing, resulting in lengthy preparation time and significantly impacting testing efficiency. Furthermore, sudden changes in pressure and seepage environment within the borehole can easily lead to borehole collapse. Summary of the Invention

[0003] This disclosure aims to at least partially address one of the technical problems in the related art.

[0004] Therefore, the purpose of this disclosure is to provide a method for testing the in-situ permeability coefficient of rock formations.

[0005] To achieve the above objectives, this disclosure provides a method for testing the in-situ permeability coefficient of rock formations, comprising: drilling along the depth direction of the rock formation using drilling equipment to form a borehole, and arranging a casing on the borehole wall, wherein the drill rod of the drilling equipment is located inside the casing; using a cylindrical region of the rock formation at the bottom of the borehole as a test section; injecting flushing fluid into the bottom of the borehole using the drill rod, so that part of the flushing fluid flows back along the gap between the drill rod and the casing to the top orifice of the borehole, and the remaining flushing fluid permeates along the plane direction of the rock formation to the periphery of the test section; controlling the injection flow rate of the flushing fluid until the backflowing flushing fluid stabilizes at the top orifice of the borehole, and calculating the permeability coefficient under the flushing fluid conditions using the injection flow rate of the flushing fluid when stable; and obtaining the in-situ permeability coefficient of the rock formation based on the permeability coefficient under the flushing fluid conditions.

[0006] Optionally, calculating the permeability coefficient under the flushing fluid conditions using the injection flow rate of the flushing fluid at steady state includes: obtaining the height of the test section, the radius of the borehole, the hydrodynamic viscosity of water, the hydrodynamic viscosity of the flushing fluid, the fluid density of water, the fluid density of the flushing fluid, and the head height of the test section; calculating the permeability coefficient under the flushing fluid conditions based on a first formula and the injection flow rate of the flushing fluid at steady state; wherein, the first formula is: The K 冲The permeability coefficient under the flushing fluid conditions is given by , Q is the injection flow rate of the flushing fluid at steady state, L is the height of the test section, r is the radius of the borehole, and μ is... 水 The fluid dynamic viscosity of the water is μ. 冲 The hydrodynamic viscosity of the rinsing fluid is ρ. 水 The fluid density of the water, ρ 冲 The fluid density of the flushing fluid is denoted as H, and the head height of the test section is denoted as H.

[0007] Optionally, calculating the permeability coefficient under the flushing fluid conditions using the injection flow rate of the flushing fluid at a stable state further includes: obtaining a fourth formula corresponding to the total permeation flow rate and permeability coefficient of the test section based on a second formula corresponding to the seepage velocity and permeability coefficient, and a third formula corresponding to the total permeation flow rate and seepage velocity; obtaining the first formula based on the fourth formula; wherein, the second formula is: The third formula is: The fourth formula is: The v represents the seepage velocity of the flushing fluid, and the i and the The hydraulic gradient of the test section is given by A, where A is the cross-sectional area of ​​the test section.

[0008] Optionally, obtaining the first formula based on the fourth formula includes: separating the first variable h and the second variable x in the fourth formula and integrating them to obtain the fifth formula, wherein the boundary conditions for integration are: the starting point of x is r, the ending point of x is the influence radius R of the test section, the initial water head of h is the water head height H of the test section, and the ending water head of h is the original groundwater level 0; determining the influence radius of the test section based on the sixth formula, and substituting the influence radius of the test section into the fifth formula to obtain the first formula; wherein the fifth formula is: The sixth formula is: .

[0009] Optionally, calculating the permeability coefficient under the flushing fluid conditions using the injection flow rate of the flushing fluid at steady state further includes: converting the units of each parameter in the first formula to standard units to obtain a seventh formula; wherein, the seventh formula is: .

[0010] Optionally, obtaining the in-situ permeability coefficient of the rock stratum based on the permeability coefficient under the flushing fluid conditions includes: obtaining an eighth formula corresponding to the permeability coefficient under the flushing fluid conditions and the in-situ permeability coefficient under the water conditions based on the permeability coefficient ratio of the flushing fluid and the water; and obtaining a ninth formula based on the eighth formula and the seventh formula; wherein, the eighth formula is: The ninth formula is: The K 水 is the in-situ permeability coefficient under the aforementioned water conditions.

[0011] Optionally, calculating the permeability coefficient under the flushing fluid conditions using the injection flow rate of the flushing fluid at a stable state includes: recording the injection flow rate of the flushing fluid according to a preset time interval; obtaining a preset ratio value of the current injection flow rate, and a first difference between the two injection flow rates adjacent to the current injection flow rate; and calculating the permeability coefficient under the flushing fluid conditions using the current injection flow rate when the preset ratio value is not less than the first difference.

[0012] Optionally, the step of calculating the permeability coefficient under the flushing fluid conditions using the injection flow rate of the flushing fluid at a stable state further includes: obtaining a second difference between the current injection flow rate and the previous injection flow rate adjacent to the current injection flow rate; and calculating the permeability coefficient under the flushing fluid conditions using the current injection flow rate when the preset ratio value is not less than the first difference and the second difference is not greater than the preset difference.

[0013] Optionally, controlling the injection flow rate of the flushing fluid until the backflowing flushing fluid stabilizes at the top orifice of the borehole includes: reducing the injection flow rate of the flushing fluid when the backflowing flushing fluid overflows from the top orifice of the borehole; and increasing the injection flow rate of the flushing fluid when the backflowing flushing fluid is below the top orifice of the borehole by a preset distance.

[0014] Optionally, the method further includes: obtaining the corresponding permeability of the rock stratum, as well as the rock mass characteristics and soil characteristics of the rock stratum based on the in-situ permeability coefficient of the rock stratum.

[0015] The technical solution provided in this disclosure may include the following beneficial effects: There is no need to remove the drill rod and replace the water pump before testing, which greatly reduces the preparation time before testing, effectively improves testing efficiency, and avoids hole collapse accidents caused by sudden changes in pressure and seepage environment due to drill rod movement.

[0016] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this disclosure. Attached Figure Description

[0017] The above and / or additional aspects and advantages of this disclosure will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, in which: Figure 1This is a schematic flowchart of an embodiment of the in-situ permeability coefficient testing method for rock formations proposed in this disclosure; Figure 2 This is a schematic diagram of the structure during flushing fluid injection in an embodiment of the rock stratum in-situ permeability coefficient testing method proposed in this disclosure. Detailed Implementation

[0018] Embodiments of this disclosure are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are used only to explain this disclosure, and should not be construed as limiting this disclosure. Rather, embodiments of this disclosure include all variations, modifications, and equivalents falling within the spirit and scope of the appended claims.

[0019] like Figure 1 As shown in the embodiments of this disclosure, a method for in-situ permeability testing of rock formations is proposed, including: S1: Drilling equipment is used to drill along the depth direction of the rock strata to form a borehole, and a casing is arranged on the borehole wall, wherein the drill rod of the drilling equipment is located inside the casing. S2: The cylindrical area where the rock strata are located at the bottom of the borehole is used as the test section; S3: Use the drill pipe to inject flushing fluid into the bottom of the borehole, so that some of the flushing fluid flows back to the top of the borehole through the gap between the drill pipe and the casing, and the remaining flushing fluid permeates around the test section along the plane of the rock strata. S4: Control the injection flow rate of the flushing fluid until the backflowing flushing fluid stabilizes at the top of the borehole, and calculate the permeability coefficient under the flushing fluid conditions using the injection flow rate of the flushing fluid when it stabilizes. S5: Obtain the in-situ permeability coefficient of the rock formation based on the permeability coefficient under flushing fluid conditions.

[0020] Understandably, by injecting flushing fluid into the bottom of the borehole using the drill pipe, some of the flushing fluid flows back towards the top of the borehole through the gap between the drill pipe and the casing and stabilizes at the top of the borehole. The remaining flushing fluid then permeates around the test section along the plane of the rock strata. Thus, the permeability coefficient of the rock strata under flushing fluid conditions can be calculated using the injection flow rate of the flushing fluid when it is stable. Furthermore, the in-situ permeability coefficient of the rock strata under groundwater conditions can be calculated using the permeability coefficient under flushing fluid conditions. Moreover, this method of testing permeability coefficients does not require removing the drill pipe or replacing the water pump before the test, thereby significantly reducing the preparation time before the test and effectively improving the test efficiency. At the same time, it also avoids borehole collapse accidents caused by sudden changes in pressure and seepage environment due to drill pipe movement.

[0021] It should be noted that the drilling equipment can be a drilling rig, and the flushing fluid can be mud. Specifically, after the drilling equipment drills a borehole in the rock formation, the mud pump of the drilling equipment transports the mud from the external mud pool to the bottom of the borehole through the drill pipe. Valves, electromagnetic flow meters, etc. can be installed on the conveying pipeline between the mud pool and the drill pipe.

[0022] In this embodiment, the cylindrical area at the bottom of the borehole is used as the test section, which realizes the generalization of the "well" model. Specifically, the test section is regarded as a cylindrical "well" with a radius of r (the radius of the borehole) and a height of L placed in an infinitely large homogeneous isotropic aquifer, with liquid seeping from the well wall into the surrounding rock mass.

[0023] In addition, some of the flushing fluid flows back towards the top of the borehole along the gap between the drill pipe and the casing. When the backflowing flushing fluid stabilizes at the top of the borehole, so that the injection flow rate and the flow rate into the test section reach equilibrium, the permeability coefficient of the test section rock mass is calculated by measuring the stable injection flow rate and based on the corresponding seepage theory model (the formula below).

[0024] Compared to traditional testing methods, the method in this embodiment is less difficult to implement, requires less preparation, and has less impact on construction.

[0025] In some embodiments, calculating the permeability coefficient under flushing fluid conditions using the injection flow rate of the flushing fluid at steady state includes: The height of the test section, the radius of the borehole, the hydrodynamic viscosity of water, the hydrodynamic viscosity of the flushing fluid, the fluid density of water, the fluid density of the flushing fluid, and the head height of the test section were obtained. The permeability coefficient under flushing fluid conditions was calculated based on the first formula and the injection flow rate of the flushing fluid at steady state. The first formula is: ; K 冲 Let be the permeability coefficient under flushing fluid conditions, Q be the injection flow rate of the flushing fluid at steady state, L be the height of the test section, r be the radius of the borehole, and μ be the permeability coefficient. 水 Let μ be the hydrodynamic viscosity of water. 冲 ρ is the hydrodynamic viscosity of the flushing fluid. 水 ρ is the fluid density of water. 冲 H is the fluid density of the flushing fluid, and H is the head height of the test section.

[0026] Understandably, when the backflowing flushing fluid stabilizes at the top of the borehole, the injection flow rate Q of the flushing fluid at this time is collected. The collected injection flow rate is substituted into the first formula and combined with other known parameters to accurately calculate the permeability coefficient under the flushing fluid conditions.

[0027] It should be noted that K 冲The permeability coefficient under flushing fluid conditions is expressed in m / s, and Q is the injection flow rate of the flushing fluid at steady state, expressed in m³ / s. 3 / s.

[0028] In addition, L is the height of the test section, r is the radius of the borehole, and H is the water head height of the test section (the difference between the equivalent experimental water head and the original groundwater level), all in meters.

[0029] μ 水 Let μ be the hydrodynamic viscosity of water. 冲 The fluid dynamic viscosity is expressed in Pa·s.

[0030] ρ 水 ρ is the fluid density of water. 冲 The fluid density of the flushing fluid is expressed in kg / m³. 3 .

[0031] All parameters are known parameters obtained directly or indirectly. When the injection flow rate Q of the flushing fluid at a steady state is measured, it can be substituted into the first formula to obtain the permeability coefficient K under the flushing fluid conditions. 冲 .

[0032] In some embodiments, calculating the permeability coefficient under flushing fluid conditions using the injection flow rate of the flushing fluid at steady state further includes: Based on the second formula corresponding to seepage velocity and permeability coefficient, and the third formula corresponding to total seepage flow rate and seepage velocity, the fourth formula corresponding to total seepage flow rate and permeability coefficient of the test section is obtained; The first formula is derived from the fourth formula; The second formula is: The third formula is: ; The fourth formula is: ; v is the seepage velocity of the flushing fluid, i and Let A be the hydraulic gradient of the test section and A be the cross-sectional area of ​​the test section.

[0033] It is understandable that the seepage velocity in the second formula is substituted into the third formula, thereby forming a fourth formula corresponding to the total seepage flow and permeability coefficient of the test section, in conjunction with the hydraulic gradient and cross-sectional area of ​​the test section. The first formula is then obtained using the fourth formula.

[0034] It should be noted that the second formula is based on Darcy's law, where v is the seepage velocity of the flushing fluid in m / s, and i = , where is the hydraulic gradient of the test section, and A is the cross-sectional area of ​​the test section in m². 2 .

[0035] In some embodiments, obtaining the first formula based on the fourth formula includes: Separate the first variable h and the second variable x in the fourth formula and integrate them to obtain the fifth formula. The boundary conditions for integration are: the starting point of x is r, the ending point of x is the influence radius R of the test section, the initial water head of h is the water head height H of the test section, and the ending water head of h is the original groundwater level 0. The influence radius of the test section is determined based on the sixth formula, and then the influence radius of the test section is substituted into the fifth formula to obtain the first formula. The fifth formula is: The sixth formula is: .

[0036] It is understandable that the first variable h and the second variable x in the fourth formula are separated and integrated to obtain the fifth formula, and the influence radius of the test section determined based on the sixth formula is substituted into the fifth formula to obtain the first formula.

[0037] Specifically, separating the first variable h and the second variable x in the fourth formula, we get: .

[0038] Integrating both sides, we get: .

[0039] Then we get the fifth formula: .

[0040] A widely used approximation in hydrology is that when l / r is greater than 8 (which aligns with most engineering practices), the radius of influence R is approximately equal to the length of the test section L. This is corrected using a formula that considers variations in fluid viscosity. .

[0041] Will Substituting =L into the formula yields the sixth equation, where the radius of influence under the rinsing fluid condition is R ( )for: .

[0042] Substituting the influence radius R of the test section into the fifth formula yields the first formula.

[0043] In some embodiments, calculating the permeability coefficient under flushing fluid conditions using the injection flow rate of the flushing fluid at steady state further includes: By converting the units of each parameter in the first formula to standard units, we obtain the seventh formula. The seventh formula is: .

[0044] For example, Q is calculated in meters. 3 / s, after unit conversion, the unit of Q is L / min.

[0045] In some embodiments, obtaining the in-situ permeability coefficient of a rock formation based on the permeability coefficient under flushing fluid conditions includes: Based on the ratio of the permeability coefficients of the flushing fluid and water, the eighth formula is obtained corresponding to the permeability coefficient under the flushing fluid condition and the in-situ permeability coefficient under the water condition. Based on formulas eight and seven, we arrive at formula nine; The eighth formula is: ; The ninth formula is: ; K 水 is the in-situ permeability coefficient under water conditions.

[0046] It is understandable that, based on the correspondence between the permeability coefficient under flushing fluid conditions and the in-situ permeability coefficient under water conditions in Formula 8, the formula for calculating the in-situ permeability coefficient is obtained by substituting it into Formula 7, which is Formula 9.

[0047] It should be noted that the method in this embodiment has minimal impact on construction, meaning it does not require removing the drill rod or changing the water. Therefore, viscosity correction is necessary.

[0048] According to Hagen-Poiseuille's law: K = .

[0049] Where k is the intrinsic permeability, which depends only on the porous medium itself, and ρ is the fluid density (kg / m³). 3 g is the acceleration due to gravity (m / s²). 2 μ is the fluid dynamic viscosity (Pa·s).

[0050] The ratio of the permeability coefficients of the two fluids in the same formation is: .

[0051] After conversion, we get the eighth formula, which is: .

[0052] K obtained from the seventh formula 冲 Substituting into the eighth formula, we obtain the final in-situ permeability coefficient calculation model for rock strata.

[0053] Furthermore, the viscosity of the added water is 1×10⁻⁶. -3 Pa·s, the density of water is 1 kg / m³ 3 We can obtain: .

[0054] In some embodiments, calculating the permeability coefficient under flushing fluid conditions using the injection flow rate of the flushing fluid at steady state includes: Record the injection flow rate of the flushing fluid according to a preset time interval; Get the preset ratio value of the current injected traffic, and the first difference between the two injected traffic adjacent to the current injected traffic; When the preset ratio is not less than the first difference, the permeability coefficient under the flushing fluid conditions is calculated using the current injection flow rate.

[0055] For example, the preset time could be 1 minute, and the preset percentage could be 10%. This means that the injection flow rate of the flushing fluid is recorded every minute. When 10% of the current injection flow rate is not less than the first difference between the two consecutive injection flow rates adjacent to the current flow rate, the permeability coefficient under the flushing fluid conditions is calculated using the current injection flow rate. In other words, during the injection flow rate recording process, the difference between two consecutive injection flow rates (the first difference) is not greater than 10% of the last injection flow rate.

[0056] In some embodiments, calculating the permeability coefficient under flushing fluid conditions using the injection flow rate of the flushing fluid at steady state further includes: Get the second difference between the current injected flow and the previous injected flow adjacent to the current injected flow; When the preset ratio is not less than the first difference and the second difference is not greater than the preset difference, the permeability coefficient under the flushing fluid condition is calculated using the current injection flow rate.

[0057] It is understandable that when the second difference is not greater than the preset difference, it means that the injection flow rate of the flushing fluid does not have a continuous increasing or decreasing trend and the injection flow rate is in a stable state. Therefore, the permeability coefficient under the flushing fluid conditions can be accurately calculated using the current injection flow rate.

[0058] In some embodiments, controlling the injection flow rate of the flushing fluid until the backflowing flushing fluid stabilizes at the top orifice of the borehole includes: When the backflowing flushing fluid overflows from the top of the borehole, reduce the injection flow rate of the flushing fluid to prevent overflow. Additionally, when the backflowing flushing fluid is below the top of the borehole by more than a preset distance, the injection flow rate of the flushing fluid is increased to prevent the flushing fluid level from becoming too low.

[0059] For example, by adjusting the injection flow rate of the flushing fluid, the liquid level variation of the backflow flushing fluid can be ≤2cm.

[0060] Before collecting the flushing fluid injection flow rate, the test section needs to be flushed using the flushing fluid circulation method until the flushing fluid returning from the orifice is clear.

[0061] In some embodiments, the method further includes: Based on the in-situ permeability coefficient of the rock strata, the corresponding rock permeability, rock mass characteristics, and soil characteristics of the rock strata are obtained.

[0062] For example, the permeability classification of soil and rock is shown in the table below, and K can be calculated. 水 The permeability q is obtained by referring to the table, which is the result of the conventional water injection test / pressure test.

[0063]

[0064] The method in this embodiment solves the problem that conventional water injection / pressure tests require removing the drill rod and replacing the water pump, which greatly affects normal construction. It achieves the goal of in-situ permeability coefficient testing without any preparation work. In addition, considering the pipe head loss caused by the drill rod in the casing, the equivalent head height of the orifice backflow, and the viscosity and density changes of the flushing fluid and clean water, the permeability coefficient of the target layer can be obtained more accurately. At the same time, it has the advantages of high construction efficiency and minimal impact on construction progress.

[0065] It should be noted that in the description of this disclosure, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this disclosure, unless otherwise stated, "a plurality of" means two or more.

[0066] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of preferred embodiments of this disclosure includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the function involved, as will be understood by those skilled in the art to which embodiments of this disclosure pertain.

[0067] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0068] Although embodiments of the present disclosure have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure.

Claims

1. A method for in-situ testing the permeability coefficient of rock strata, characterized in that, include: Drilling equipment is used to drill along the depth direction of the rock stratum to form a borehole, and a casing is arranged on the borehole wall, wherein the drill rod of the drilling equipment is located inside the casing; The cylindrical area at the bottom of the borehole where the rock strata are located is used as the test section; Flushing fluid is injected into the bottom of the borehole using the drill rod, so that part of the flushing fluid flows back towards the top opening of the borehole along the gap between the drill rod and the casing, and the remaining flushing fluid permeates around the test section along the plane of the rock stratum. The injection flow rate of the flushing fluid is controlled until the backflowing flushing fluid stabilizes at the top orifice of the borehole, and the permeability coefficient under the flushing fluid conditions is calculated using the injection flow rate of the flushing fluid when it stabilizes. The in-situ permeability coefficient of the rock stratum is obtained based on the permeability coefficient under the aforementioned flushing fluid conditions; The calculation of the permeability coefficient under the flushing fluid conditions using the injection flow rate of the flushing fluid at a stable state includes: The height of the test section, the radius of the borehole, the hydrodynamic viscosity of the water, the hydrodynamic viscosity of the flushing fluid, the fluid density of the water, the fluid density of the flushing fluid, and the head height of the test section are obtained. The permeability coefficient under the flushing fluid conditions is calculated based on the first formula and the injection flow rate of the flushing fluid at steady state. The first formula is: ; The K 冲 The permeability coefficient under the flushing fluid conditions is given by , Q is the injection flow rate of the flushing fluid at steady state, L is the height of the test section, r is the radius of the borehole, and μ is... 水 The fluid dynamic viscosity of the water is μ. 冲 The hydrodynamic viscosity of the rinsing fluid is ρ. 水 The fluid density of the water, ρ 冲 The fluid density of the flushing fluid is denoted as H, and the head height of the test section is denoted as H.

2. The method for testing the in-situ permeability coefficient of rock strata according to claim 1, characterized in that, The calculation of the permeability coefficient under the flushing fluid conditions using the injection flow rate of the flushing fluid at a stable state also includes: Based on the second formula corresponding to the seepage velocity and the permeability coefficient, and the third formula corresponding to the total seepage flow rate and the seepage velocity, the fourth formula corresponding to the total seepage flow rate and the permeability coefficient of the test section is obtained; The first formula is obtained based on the fourth formula; The second formula is: The third formula is: ; The fourth formula is: ; v is the seepage velocity of the flushing fluid, and i and the The hydraulic gradient of the test section is given by A, where A is the cross-sectional area of ​​the test section.

3. The method for testing the in-situ permeability coefficient of rock strata according to claim 2, characterized in that, The process of obtaining the first formula based on the fourth formula includes: Separate the first variable h and the second variable x in the fourth formula and integrate them to obtain the fifth formula. The boundary conditions for integration are: the starting point of x is r, the ending point of x is the influence radius R of the test section, the initial head of h is the head height H of the test section, and the ending head of h is the original groundwater level 0. The influence radius of the test section is determined based on the sixth formula, and the influence radius of the test section is substituted into the fifth formula to obtain the first formula; The fifth formula is as follows: The sixth formula is: .

4. The method for testing the in-situ permeability coefficient of rock strata according to claim 1, characterized in that, The calculation of the permeability coefficient under the flushing fluid conditions using the injection flow rate of the flushing fluid at a stable state also includes: By converting the units of each parameter in the first formula to standard units, we obtain the seventh formula. The seventh formula is as follows: .

5. The method for testing the in-situ permeability coefficient of rock strata according to claim 4, characterized in that, The method of obtaining the in-situ permeability coefficient of the rock formation based on the permeability coefficient under the flushing fluid conditions includes: Based on the ratio of the permeability coefficients of the flushing fluid and the water, an eighth formula is obtained corresponding to the permeability coefficient under the flushing fluid condition and the in-situ permeability coefficient under the water condition. Based on the eighth formula and the seventh formula, the ninth formula is obtained; The eighth formula is as follows: ; The ninth formula is: ; The K 水 is the in-situ permeability coefficient under the aforementioned water conditions.

6. The method for testing the in-situ permeability coefficient of rock strata according to claim 1, characterized in that, The calculation of the permeability coefficient under the flushing fluid conditions using the injection flow rate of the flushing fluid at a stable state includes: The injection flow rate of the flushing fluid is recorded at preset time intervals; Obtain a preset ratio value of the current injected flow, and a first difference between the two previous injected flows adjacent to the current injected flow; When the preset ratio value is not less than the first difference, the permeability coefficient under the flushing fluid conditions is calculated using the current injection flow rate.

7. The method for testing the in-situ permeability coefficient of rock strata according to claim 6, characterized in that, The calculation of the permeability coefficient under the flushing fluid conditions using the injection flow rate of the flushing fluid at a stable state also includes: Obtain the second difference between the current injected flow and the previous injected flow adjacent to the current injected flow; When the preset ratio is not less than the first difference and the second difference is not greater than the preset difference, the permeability coefficient under the flushing fluid condition is calculated using the current injection flow rate.

8. The method for testing the in-situ permeability coefficient of rock strata according to claim 1, characterized in that, Controlling the injection flow rate of the flushing fluid until the backflowing flushing fluid stabilizes at the top orifice of the borehole includes: When the backflowing flushing fluid overflows from the top opening of the borehole, reduce the injection flow rate of the flushing fluid; Furthermore, when the backflowing flushing fluid is below the top opening of the borehole by more than a preset distance, the injection flow rate of the flushing fluid is increased.

9. The method for testing the in-situ permeability coefficient of rock strata according to claim 1, characterized in that, The method further includes: Based on the in-situ permeability coefficient of the rock strata, the corresponding water permeability of the rock strata, as well as the rock mass characteristics and soil characteristics of the rock strata, are obtained.

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