Effective range evaluation method for in-situ test of permeability of engineering rock mass

Abstract

The invention discloses a method for evaluating an effective range of an engineering rock mass permeability in-situ test, which comprises the following steps of: on the basis of a pressure distribution function, an inner boundary condition and an outer boundary condition which are obtained in a derivation process of an engineering scale in-situ gas permeability test method, adding a pressure boundary condition of an observation hole to carry out formula derivation; and a more accurate effective test range of the in-situ gas permeability test of the engineering scale can be given, and engineering practice can be better guided.

Description

Technical Field

[0001] The invention relates to an effective range evaluation method for in-situ testing of engineering rock mass permeability, and belongs to the technical field of effective range evaluation for in-situ testing of engineering rock mass permeability. Background Art

[0002] In various deep geological engineering projects, accurate permeability measurement is crucial for evaluating the effectiveness of surrounding rock grouting reinforcement, deep rock fracturing, and the sealing properties of deep chamber barrier systems. In recent years, to address the limited representativeness of core-scale permeability test results, the difficulty in maintaining the original stress, temperature, and humidity states of the samples, and the inability to directly guide engineering practice, numerous researchers have devoted themselves to the study of engineering-scale permeability testing and developed a variety of permeability testing methods. Clarifying the effective range of in-situ testing of engineering rock permeability plays a crucial role in experimental design and the application of test results in practical engineering projects. Some researchers have studied the effective range of engineering-scale in-situ gas permeability testing. By establishing a pressure distribution function and a set of pressure boundary equations and solving them using the finite difference method, they can determine the gas pressure distribution in the rock mass. The outer boundary of the test is then determined, where the dimensionless pressure is 0.1. The effective test radius is then numerically equal to the test section length + 1 / 2 the expansion plug length.

[0003] However, relatively little research has been conducted on the effective test range of engineering-scale in-situ gas permeability testing, and many researchers have overlooked its impact on test results during their derivation. Existing studies often assume an artificially pre-defined outer pressure boundary and treat it as a known condition. The resulting effective test range is identical for rock masses of varying permeability, which is clearly unreasonable. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide an effective range evaluation method for in-situ testing of engineering rock permeability.

[0005] Preferably, the present invention provides a method for evaluating the effective range of in-situ testing of engineering rock mass permeability, which is characterized by comprising:

[0006] Obtain the average pressure of the test hole and the average pressure of the observation hole during the corresponding time;

[0007] The effective test range is calculated using formula (14) and formula (15):

[0008] r out =(r in ) 1-A′ (r′) A′ (14),

[0009]

[0010] Where, P mean P′ is the average pressure of the test hole during Δt time; mean is the average pressure of the observation hole during the corresponding Δt time; P0 is the atmospheric pressure; r out is the effective test radius; r in is the drilling radius, A' is the calculation parameter, and r' is the distance between the observation hole and the test hole.

[0011] 2. The method for evaluating the effective range of in-situ testing of engineering rock mass permeability according to claim 1 is characterized in that:

[0012] The average pressure P of the test hole within Δt time is calculated using the following formula: mean and atmospheric pressure P0:

[0013] P│r in =P mean ,

[0014] P│r out =P0,

[0015] P 2 =C1lnr+C2,

[0016]

[0017] C2=P mean 2 -C1lnr in ,

[0018] Where P is the pressure between rock masses, r in is the drilling radius, r out is the effective test range, r is the distance between a point in the rock mass and the center of the test hole;

[0019] 3. The method for evaluating the effective range of in-situ testing of engineering rock mass permeability according to claim 2 is characterized in that:

[0020] Formula (14) and formula (15) satisfy the following conditions:

[0021] Condition 1: Gas seepage in rock mass is laminar flow;

[0022] Condition 2: The gas in the rock mass satisfies the ideal gas state equation;

[0023] Condition 3: The ambient temperature is constant;

[0024] Condition 4: The rock mass is uniform and isotropic;

[0025] Condition 5: Gas seepage in rock mass is radial flow.

[0026] Prioritize obtaining the average pressure of the test hole and the average pressure of the observation hole during the corresponding time, including:

[0027] Drill test holes and observation holes in the rock mass to be tested, and clean the test holes and observation holes;

[0028] Install the gas injection pipe and expansion plug into the predetermined position of the test hole, use the inflation device to inject gas of the required pressure into the expansion plug, seal the test hole, and install the pressure gauge in the observation hole;

[0029] Gas with a pressure of P1 is injected into the test hole and the observation hole through the gas injection pipe at one time. During the test, the pressure value of the pressure drop process in the test hole and the pressure value of the pressure change process in the observation hole are recorded to obtain the pressure drop curve of the test hole and the pressure change curve of the observation hole.

[0030] Prioritize obtaining the average pressure of the test hole and the average pressure of the observation hole during the corresponding time, including:

[0031] Based on the pressure drop curve of the test hole and the pressure change curve in the observation hole, the average pressure of the test hole within the time Δt and the average pressure of the observation hole within the corresponding time are calculated.

[0032] Preferably, the present invention provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of any one of the methods described in the first aspect when executing the program.

[0033] Preferably, the present invention provides a computer-readable storage medium having a computer program stored thereon, which implements the steps of any one of the methods described in the first aspect when executed by a processor.

[0034] The beneficial effects achieved by the present invention are:

[0035] The present invention deduces the effective test range by taking the measured pressure of the observation hole as the pressure boundary condition, and uses the non-artificially preset pressure boundary condition as the deduction basis, which can more realistically reflect the seepage of gas between rock masses and provide a more scientific and reasonable effective test range, solving the drawback of the existing theory that the effective test range of rock masses with different permeabilities is consistent, and improving the scientificity and accuracy of the effective test range evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0037] Figure 1 Schematic diagram of the in-situ gas permeability test principle and pressure boundary in some embodiments of the present application;

[0038] Figure 2 It is a schematic diagram of the pressure drop curve of the test hole and the observation hole in some embodiments of the present application.

[0039] Meaning of the reference numerals: 1-gas injection eye tube; 2-test hole; 3-pressure gauge; 4-expansion plug; 5-inner pressure boundary; 6-outer pressure boundary; 7-observation hole pressure boundary; 8-gas seepage direction; 9-observation hole; 10-rock mass. DETAILED DESCRIPTION

[0040] See also Figure 1 The present invention proposes a method for evaluating the effective range of in-situ testing of engineering rock permeability. By utilizing the pressure distribution function, internal boundary conditions, and external boundary conditions obtained in the derivation process of the engineering-scale in-situ gas permeability test method, a new pressure boundary condition of an observation hole is added to derive the formula. This can provide a more accurate effective test range of the engineering-scale in-situ gas permeability test, which can better guide engineering practice.

[0041] The testing principle of the present invention:

[0042] Unlike the traditional in-situ gas permeability steady-state test method, it does not continuously inject gas into the test hole at the same flow rate, and a new observation hole is added on the basis of the original test design. The test method provided by the present invention is to extend the steady-state method based on the inlet pressure gradient at the core scale to the engineering scale. At the beginning of the test, gas with a pressure of P1 is injected into the test hole and the observation hole. The pressure changes in the test hole and the observation hole are then recorded, and the permeability is calculated based on the pressure gradient of the test hole. The derivation of the engineering-scale in-situ gas permeability test principle is carried out under the following five assumptions: ① The gas seepage in the rock mass is laminar, that is, it conforms to Darcy's law; ② The gas satisfies the ideal gas state equation; ③ The temperature condition of the test is constant temperature; ④ The rock mass satisfies uniform isotropy; ⑤ The gas seepage in the rock mass is radial flow.

[0043] The gas mass conservation equation in porous media is determined as:

[0044]

[0045] Where ρ is density and v is volume;

[0046] According to the assumption ②, the ideal gas state equation is determined as follows:

[0047] PV=nRT(2), where

[0048] P is the gas pressure, V is the volume of the space where the gas is located, n is the amount of substance, R is the molar gas constant, and T is the temperature;

[0049] Based on the relationship between the amount of substance, mass and molar mass, and the relationship between mass, volume and density, we have:

[0050] m=nM (3),

[0051] m=ρV (4),

[0052] In the formula, m is the mass of the gas, and V is the volume of the space where the gas is located;

[0053] Combining formula (2), formula (3), and formula (4), we can calculate the gas density:

[0054]

[0055] Based on assumption ①, the gas seepage velocity is calculated as follows:

[0056]

[0057] Where k is the effective permeability, μ is the gas dynamic viscosity coefficient, is the Hamiltonian operator; P is the gas pressure;

[0058] According to assumption ⑤, the experimental model can be further simplified into a one-dimensional radial model in the cylindrical coordinate system. According to assumptions ③ and ④, the gas permeability k, gas dynamic viscosity coefficient μ, and temperature T are all constants.

[0059] Substitute formula (5) and formula (6) into formula (1) and simplify formula (1) to:

[0060] ΔP 2 =0(7),

[0061] Where Δ is the Laplace operator;

[0062] The one-dimensional radial expression of formula (7) in cylindrical coordinate system is:

[0063]

[0064] From formula (8), we can get P 2 The pressure distribution function is obtained by analysis:

[0065] P 2 =C1lnr+C2 (9),

[0066] Since this test method is different from the traditional in-situ gas permeability steady-state test method, it does not continuously inject gas into the test hole at the same flow rate. At the beginning of the test, gas with a pressure of P1 is injected into the test hole and the observation hole. After Δt time, the gas pressure in the test section drops by ΔP, and the average gas pressure in the test section P is obtained. mean for:

[0067]

[0068] Therefore, the pressure boundary condition in the test hole is not the P1 mentioned in the traditional in-situ gas permeability steady-state test method, but the average gas pressure P obtained by the steady-state method based on the inlet pressure gradient at the core scale. mean ;

[0069] Assume that the hole wall of the test section is r in The gas pressure at P mean ; Distance from the axis of the test section r out The pressure at the point is P0; hence the boundary condition P│r in =P mean , P│r out =P0 and substituting into formula (9) we get:

[0070]

[0071] Substituting formula (11) and formula (12) into formula (9), we get:

[0072]

[0073] At this time, P 2 is expressed as a function of r, and r out is an unknown quantity; if we can obtain the average pressure of the observation hole at a distance r' from the center of the borehole within the time Δt, it is P' mean That is, we get another boundary condition P│ r’ =P′ mean , the boundary condition P│ r’ =P′ mean Substitute into formula (13) to obtain the effective test radius r out ;

[0074] r out =(r in ) 1-A′ (r′) A′ (14)

[0075]

[0076] Where, P mean is the average pressure of the test hole during Δt time (Pa); P′ meanis the average pressure of the observation hole during the corresponding Δt time (Pa); P0 is the atmospheric pressure, the specific value is 1×10 5 (Pa); r out is the effective test radius (m); r in is the drilling radius (m);

[0077] The testing steps of the present invention include:

[0078] ① Drill test holes and observation holes in the rock mass to be tested, and complete the cleaning operations of the test holes and observation holes;

[0079] ②Install the gas injection pipe and expansion plug into the predetermined position in the test hole, use the inflation device to inject the required pressure of gas into the expansion plug to complete the sealing operation of the test hole, and install the pressure gauge in the observation hole;

[0080] ③Inject gas with a pressure of P1 into the test hole and the observation hole through the gas injection pipe at one time. During the test, record the pressure value of the test hole during the pressure drop process and the pressure value of the observation hole during the pressure change process;

[0081] ④ Process the pressure drop curve of the test hole and the pressure change in the observation hole recorded in ③ to obtain the average pressure (Pa) of the test hole within the Δt time and the average pressure of the observation hole within the corresponding time. Substitute the average pressure (Pa) of the test hole and the average pressure of the observation hole within the corresponding time into formula (14) and formula (15) to obtain the effective test range of this test.

[0082] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0083] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention as disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not invented herein, and the description and examples are to be considered merely as exemplary.

[0084] The above specific implementation methods further illustrate the purpose, technical solutions and beneficial effects of this application in detail. It should be understood that the above are only specific implementation methods of this application and are not intended to limit the scope of protection of this application. Any modifications, equivalent replacements, improvements, etc. made on the basis of the technical solutions of this application should be included in the scope of protection of this application.

Claims

1. A method for evaluating the effective range of in-situ testing of engineering rock mass permeability, characterized in that: include: Obtain the average pressure of the test hole and the average pressure of the observation hole during the corresponding time; The effective test range is calculated using formula (14) and formula (15): Where, P mean P′ is the average pressure of the test hole during Δt time; mean is the average pressure of the observation hole during the corresponding Δt time; P0 is the atmospheric pressure; r out is the effective test radius; r in is the drilling radius, A' is the calculation parameter, and r' is the distance between the observation hole and the test hole.

2. The method for evaluating the effective range of in-situ testing of engineering rock mass permeability according to claim 1, characterized in that: The average pressure P of the test hole within Δt time is calculated using the following formula: mean and atmospheric pressure P0: Where P is the pressure between rock masses, r in is the drilling radius, r out is the effective test range, and r is the distance between a point in the rock mass and the center of the test hole.

3. The method for evaluating the effective range of in-situ testing of engineering rock mass permeability according to claim 2, characterized in that: Formula (14) and formula (15) satisfy the following conditions: Condition 1: Gas seepage in rock mass is laminar flow; Condition 2: The gas in the rock mass satisfies the ideal gas state equation; Condition 3: The ambient temperature is constant; Condition 4: The rock mass is uniform and isotropic; Condition 5: Gas seepage in rock mass is radial flow.

4. The method for evaluating the effective range of in-situ testing of engineering rock mass permeability according to claim 1, characterized in that: Obtain the average pressure of the test hole and the average pressure of the observation hole during the corresponding time, including: Drill test holes and observation holes in the rock mass to be tested, and clean the test holes and observation holes; Install the gas injection pipe and expansion plug into the predetermined position of the test hole, use the inflation device to inject gas of the required pressure into the expansion plug, seal the test hole, and install the pressure gauge in the observation hole; Gas with a pressure of P1 is injected into the test hole and the observation hole through the gas injection pipe at one time. During the test, the pressure value of the pressure drop process in the test hole and the pressure value of the pressure change process in the observation hole are recorded to obtain the pressure drop curve of the test hole and the pressure change curve of the observation hole.

5. The method for evaluating the effective range of in-situ testing of engineering rock mass permeability according to claim 4, characterized in that: Obtain the average pressure of the test hole and the average pressure of the observation hole during the corresponding time, including: Based on the pressure drop curve of the test hole and the pressure change curve in the observation hole, the average pressure of the test hole within the time Δt and the average pressure of the observation hole within the corresponding time are calculated.

6. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the method according to any one of claims 1 to 5 are implemented.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 5 are implemented.

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