A method for estimating gas emission at the face of a non-coal gas tunnel.

Abstract

The present invention discloses a method for estimating the gas emission volume of a non-coal gas tunnel face, comprising: obtaining the stratum permeability, porosity, borehole radius and physical parameters in the borehole of the face; wherein the physical parameters include: pressure, concentration and emission velocity in the borehole; based on the stratum permeability, porosity, borehole radius and pressure in the borehole, obtaining the pressure field distribution model of the face area; based on the pressure field distribution model of the face area, obtaining the fracture permeability; obtaining the face area and face fracture rate, and obtaining the gas emission volume based on the face area, face fracture rate, concentration and fracture permeability. Compared with the existing calculation method, the emission volume calculation method provided by the present invention takes into account the characteristics of gas emission from the fissures of the tunnel face and the gas seepage law, so as to more accurately guide the construction.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel engineering, and in particular relates to a method for estimating the gas emission amount of a non-coal gas tunnel face. Background Art

[0002] With the development of tunnel engineering construction, a large number of engineering problems have begun to emerge, especially the gas problem in non-coal tunnels. The face of non-coal tunnels is the first line of construction for tunnel construction. After blasting, many cracks are often formed, which becomes a high-frequency area for gas outburst. In the relevant specifications of railway and highway tunnels, the parameter of gas outburst at the tunnel face is also considered as the main basis for judging the gas level of the tunnel. There are two main methods for obtaining the gas outburst at the tunnel face in the existing technical means, one is on-site measurement, and the other is empirical formula calculation. On-site measurement is mainly based on the gas concentration and velocity at the return air volume. Since the gas concentration in the return air area is not uniform, the test method and operation specifications have a great impact on the experimental results, and it takes time and money. Most of the existing empirical formulas do not consider the influence of cracks and the seepage law of gas, so the calculated values ​​are quite different from the actual ones. Therefore, how to obtain the gas outburst at the face of non-coal tunnel economically and reasonably has become an urgent problem to be solved. Summary of the invention

[0003] In order to solve the above technical problems, the present invention proposes a method for estimating the gas outburst volume of the tunnel face of a non-coal gas tunnel, which overcomes the shortcomings of the prior art that when the non-coal gas tunnel is constructed by the mining method, the effective gas pressure of the gas bag and the permeability of the tunnel face construction cracks are difficult to directly measure, resulting in inaccurate prediction of the gas outburst volume of the tunnel face.

[0004] To achieve the above object, the present invention provides a method for estimating the gas emission amount of a non-coal gas tunnel face, comprising:

[0005] Obtaining the formation permeability, porosity, borehole radius and physical parameters in the borehole at the tunnel face; wherein the physical parameters include: pressure, concentration and outflow velocity in the borehole;

[0006] Based on the formation permeability, porosity, borehole radius and borehole pressure, a pressure field distribution model of the tunnel face area is obtained;

[0007] Based on the pressure field distribution model in the tunnel face area, obtaining fracture permeability;

[0008] The tunnel face area and the tunnel face crack rate are obtained, and the gas emission volume is obtained based on the tunnel face area, the tunnel face crack rate, the concentration and the crack permeability.

[0009] Optionally, obtaining the pressure field distribution in the tunnel face area includes:

[0010] Obtaining an effective gas convergence radius based on the formation permeability, porosity, borehole radius and borehole internal pressure;

[0011] Based on the gas convergence effective radius, gas pressure and outflow velocity, obtaining effective gas pressure;

[0012] Based on the effective gas convergence radius and the effective gas pressure, the pressure field distribution of the tunnel face area is obtained.

[0013] Optionally, obtaining the effective gas convergence radius further includes: obtaining a pressure range corresponding to the effective gas convergence radius;

[0014] It is determined whether the effective gas pressure satisfies the pressure range. If yes, the effective gas pressure is solved successfully. If no, the effective gas convergence radius is obtained again.

[0015] Optionally, the pressure field distribution model is:

[0016]

[0017] Among them, P is the pressure at a distance of x meters from the tunnel face, P2 is the effective gas pressure, P3 is the tunnel face surface pressure, and r2 is the effective gas convergence radius.

[0018] Optionally, obtaining the fracture permeability includes:

[0019] Based on the pressure field distribution in the tunnel face area, the number of cracks, the average length of cracks, the width of the crack surface and the roughness of the cracks are obtained;

[0020] The fracture permeability is obtained based on the number of fractures, the average length of fractures, the width of fracture surfaces and the roughness of fractures.

[0021] Optionally, the fracture permeability is:

[0022]

[0023] Where n is the number of cracks, l is the average length of the cracks, is the effective width of the crack, is b / 2, b is the crack surface width, and e is the crack roughness.

[0024] Optionally, the gas outflow rate is:

[0025]

[0026] Where, Q is the gas outburst volume, n is the number of cracks, l is the average length of the cracks, b is the width of the crack surface, e is the crack roughness, P2 is the effective gas pressure, P3 is the face surface pressure, r2 is the effective gas convergence radius, A is the face area, is the crack rate of the tunnel face, t is the gas outburst time, θ is the concentration, and u is the dynamic viscosity coefficient of methane.

[0027] Compared with the prior art, the present invention has the following advantages and technical effects:

[0028] The present invention takes into account the influence of cracks, gas seepage and diffusion field on the gas emission, and the calculation result is reliable. It can effectively enhance the prediction accuracy of gas emission at the face of non-coal gas tunnel constructed based on the mining method, and can accurately guide construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0030] Figure 1 A curve diagram of pressure variation around a borehole according to an embodiment of the present invention;

[0031] Figure 2 Schematic diagram of the convergence radius (r2) solver interface of an embodiment of the present invention;

[0032] Figure 3 is a solver diagram of effective pressure (P2) according to an embodiment of the present invention;

[0033] Figure 4 The present invention is a schematic diagram of the flow chart of calculating the gas emission from the face of a non-coal tunnel constructed using the mining method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0035] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0036] This embodiment provides a method for estimating gas emission from a non-coal gas tunnel face, including:

[0037] Obtaining the formation permeability, porosity, borehole radius and physical parameters in the borehole at the tunnel face; wherein the physical parameters include: pressure, concentration and outflow velocity in the borehole;

[0038] Based on the formation permeability, porosity, borehole radius and borehole pressure, a pressure field distribution model of the tunnel face area is obtained;

[0039] Based on the pressure field distribution model in the tunnel face area, obtaining fracture permeability;

[0040] The tunnel face area and the tunnel face crack rate are obtained, and the gas emission volume is obtained based on the tunnel face area, the tunnel face crack rate, the concentration and the crack permeability.

[0041] Furthermore, obtaining the pressure field distribution in the tunnel face area includes:

[0042] Obtaining an effective gas convergence radius based on the formation permeability, porosity, borehole radius and borehole internal pressure;

[0043] Based on the gas convergence effective radius, gas pressure and outflow velocity, obtaining effective gas pressure;

[0044] Based on the effective gas convergence radius and the effective gas pressure, the pressure field distribution of the tunnel face area is obtained.

[0045] Further, obtaining the effective gas convergence radius also includes: obtaining a pressure range corresponding to the effective gas convergence radius;

[0046] It is determined whether the effective gas pressure satisfies the pressure range. If yes, the effective gas pressure is solved successfully. If no, the effective gas convergence radius is obtained again.

[0047] Furthermore, the pressure field distribution is:

[0048]

[0049] Among them, P is the pressure at a distance of x meters from the tunnel face, P2 is the effective gas pressure, P3 is the tunnel face surface pressure, and r2 is the effective gas convergence radius.

[0050] Further, obtaining the fracture permeability includes:

[0051] Based on the pressure field distribution in the tunnel face area, the number of cracks, the average length of cracks, the width of the crack surface and the roughness of the cracks are obtained;

[0052] The fracture permeability is obtained based on the number of fractures, the average length of fractures, the width of fracture surfaces and the roughness of fractures.

[0053] Furthermore, the fracture permeability is:

[0054]

[0055] Where n is the number of cracks, l is the average length of the cracks, is the effective width of the crack, is b / 2, b is the crack surface width, and e is the crack roughness.

[0056] Furthermore, the gas outflow rate is:

[0057]

[0058] Where, Q is the gas outburst volume, n is the number of cracks, l is the average length of the cracks, b is the width of the crack surface, e is the crack roughness, P2 is the effective gas pressure, P3 is the face surface pressure, r2 is the effective gas convergence radius, A is the face area, is the crack rate of the tunnel face, t is the gas outburst time, θ is the concentration, and u is the dynamic viscosity coefficient of methane.

[0059] The method for estimating the gas emission amount of a non-coal gas tunnel face of the present invention is mainly implemented by the following technical scheme, including the following steps:

[0060] S1. Test the gas pressure (P1), concentration (θ) and outflow velocity (V) in the exploration borehole or the gas advance borehole at the tunnel face;

[0061] S2. Test formation permeability (K) and porosity Drilling radius (r);

[0062] S3, bringing the parameters such as permeability, porosity, borehole pressure, borehole radius into the effective radius (r2) solver, and selecting the effective radius (r2) of the appropriate pressure range;

[0063] S4, bringing r2 into the effective pressure finder to find the effective pressure P2;

[0064] S5. Determine the pressure field distribution form in the tunnel face area based on P2 and r2;

[0065] S6. Determine the values ​​of n (number of cracks), l (average length of cracks), b (effective width of cracks), and e (crack roughness) according to the condition of the tunnel face or the design grade of the surrounding rock, and calculate the crack permeability;

[0066] S7. Measurement of face area (A) and face crack rate Substitute the above parameters into the formula to obtain the outflow volume.

[0067] When constructing non-coal gas tunnel projects, it is necessary to identify the gas level of the tunnel in order to formulate corresponding construction methods and preventive measures, so as to effectively ensure the safety of tunnel construction. According to the requirements of the technical specifications for the design and construction of highway or railway gas tunnels, the gas level of the tunnel is mainly determined by the size of the gas outflow at the face. If the value of the face outflow is calculated too small, the gas prevention measures will not be in place and affect the safety of construction. If the value of the face outflow is calculated too large, the gas level of the tunnel will be judged too high, which will lead to excessive gas prevention measures and increase construction costs. The rapid migration of shallow natural gas mainly depends on various fault structures and artificial cracks, and the gas outflow at the face of non-coal tunnels also mainly occurs in the development of these cracks. Since a pressure gradient will be formed in the exit area when gas seepage occurs, the pressure measured in the gas borehole is not the true pressure of the gas bag. Due to the difficulty in obtaining the permeability of the cracks and the effective pressure of the gas bag, it is difficult to calculate the gas outflow at the face of non-coal tunnels based on the mining method. In this technical solution, the inventors consider the influence of the width, number, and cross-sectional roughness of the cracks on the permeability of the cracks based on the actual situation of gas outburst at the face; through the self-developed effective pressure solver, under the conditions of known formation permeability, gas exploration borehole pressure, concentration, etc., the effective pressure of the gas bag in front of the face is automatically solved; by simplifying the gas seepage behavior at the face cracks into a plane unidirectional stable seepage, according to parameters such as the face surface pressure and the front gas bag pressure, the pressure distribution characteristic equation on the gas seepage path is solved. Then the pressure distribution characteristic equation and the fracture permeability are introduced into the Darcy seepage equation to obtain the final outburst formula. This formula takes into account the influence of cracks, gas seepage and diffusion field on the outburst, and the calculation results are reliable. It effectively enhances the prediction accuracy of the gas outburst at the face of non-coal gas tunnels constructed based on the mining method, and can accurately guide construction.

[0068] It should be noted that the effective pressure in this embodiment is the pressure of the gas bag in front of the tunnel face that has not been disturbed or damaged.

[0069] Furthermore, the exploration drilling in S1 refers to the drilling hole located in front of the tunnel face to be calculated for special gas exploration before construction, or the gas advance drilling hole in the tunnel face.

[0070] In order to ensure the effectiveness and accuracy of the calculation in this embodiment, it is necessary to test the gas pressure, outflow rate and concentration in the exploration borehole or advance borehole so as to solve the effective gas pressure in the next step.

[0071] Furthermore, S3 uses an effective radius finder to solve the gas convergence radius r2 around the borehole, and plots the gas pressure changes under different effective pressures, saving calculations and making the pressure changes around the borehole visible. The parameters required include formation permeability K(md), formation porosity Borehole pressure P1 (MPa), borehole radius r (mm).

[0072] Since there is a pressure reduction funnel formed by gas seepage between the gas pressure in the exploration hole or the advance hole and the effective gas pressure in the formation, such as Figure 1 As shown in a, Figure 1 b is the isobaric line around the borehole. Therefore, the pressure P1 tested in the borehole is less than the gas pressure P2 in the formation. According to Darcy's law, to solve the value of P2 under the condition of known pressure and velocity in the exploration hole, the convergence radius of the gas pressure around the exploration hole must be solved first. Based on the above concept, according to the control equations of gas seepage field and diffusion field, an APP for solving r2 was developed ( Figure 2 ), using this APP to calculate, the gas pressure convergence radius value under different effective gas pressures in specific physical parameter formations can be obtained.

[0073] In the APP for solving r2, the migration process of gas in rock mass is divided into two steps. The first step is that the gas in the rock matrix diffuses into the cracks, and the second step is that the gas seeps from the cracks into the borehole. Based on Fick's first diffusion law and Darcy's law, the diffusion field control equation of gas in rock mass is expressed as follows:

[0074]

[0075] where p m is the rock mass pore pressure (MPa); D is the gas diffusion coefficient (m 2 / s);δ S is the matrix shape factor (m -2 );p f is the gas pressure in the fracture system (MPa).

[0076] The governing equation of the seepage field is as follows:

[0077]

[0078] Where V is the gas seepage velocity (m / s), (k e is the fracture permeability, md; μ is the gas dynamic viscosity coefficient, CH4 is 1.08×10 -5 Pa·s), and the meanings of other symbols are the same as above.

[0079] The flux formula for mass exchange from the gas diffusion system to the gas seepage system is:

[0080]

[0081] In the above formula, m m M is the mass of gas stored in unit volume of rock matrix (kg); c is the molar mass of methane molecule; R is the ideal gas constant, J / (mol·k); T is the temperature (K), and other symbols are the same as before.

[0082] Finite element analysis software is used to simulate the migration process of gas in rock mass based on the above control equations, and secondary APP development is carried out based on the secondary development platform of the software, with the input sources selected as formation permeability K(md), formation porosity The borehole pressure P1 (MPa), the borehole radius r (mm), and the calculation results are presented in a graphical form ( Figure 2 ).

[0083] Furthermore, in S4, based on the test pressure and test speed in the exploration hole, an APP developed by the inventor himself is used to calculate the effective pressure P2 at the point where the gas pressure converges around the borehole, and a pressure distribution diagram within the convergence radius is drawn. The maximum pressure value in the diagram is the effective pressure P2.

[0084] In order to meet the accuracy of calculation in this embodiment, an effective pressure finder is developed based on Darcy seepage theory to calculate the effective pressure P2 at the convergence radius. Since the gas mainly flows out through the cracks after the tunnel face blasting, the gas diffusion process is not considered in this APP, and the gas seepage process is mainly considered. The control equation is as follows:

[0085]

[0086] Similar to the development process of the effective half-pound solver, this APP is also based on the above control equations. A basic model is established in the finite element simulation software. Based on the APP secondary development platform of the finite element simulation software, r1, formation porosity, formation permeability, gas outflow velocity in the borehole, and gas pressure in the borehole are used as input sources, and the calculation results are presented in the form of graphics. The software interface is as follows Figure 3 As shown in the figure, the calculation process needs to measure and calculate the gas pressure, outflow velocity and gas pressure convergence radius at the tunnel face or in the exploration hole in advance, bring the above parameters into the solver, and the maximum value obtained is the effective pressure at the convergence point of the formation gas pressure. In order to ensure the reliability of the results, the effective pressure obtained by the solution is compared with the result of the r2 solver. In the pressure change curve result of the r2 solver, each effective radius corresponds to a pressure range. If the result obtained in the P2 solver is within this pressure range, the solution is completed. Otherwise, repeat steps S3 and S4 until the solution is successful.

[0087] Furthermore, in S5, the pressure distribution form of the tunnel face area is solved according to the effective pressure P2 and the face surface pressure P3, and the calculation formula is as follows: In the formula, P2 is the effective pressure (Pa), which is the calculation result in step S4; P3 is the surface pressure of the tunnel face (Pa); and P is the pressure at a distance of x meters from the tunnel face (Pa).

[0088] The research object in this technical solution is gas, so the effect of pressure on gas density should be considered during the seepage process. Substituting into the fluid continuity equation, we can get In order to simplify the solution formula and reduce the amount of calculation, the process of gas seepage from the crack to the tunnel surface is regarded as a plane unidirectional stable seepage, then the fluid continuity equation can be simplified to a one-dimensional form: By integrating it, the gas pressure field distribution in the non-coal tunnel face area can be obtained as follows: By further derivation of the pressure, the gas gradient distribution formula in the non-coal tunnel face area can be obtained as follows: In the above expression, ρ g Indicates the density of methane gas (kg / m 3 ); M is the molecular mass of methane (g / mol); R is the gas state constant (J / mol / K); T is the formation temperature (K); is the formation porosity (%); μ is the dynamic viscosity coefficient of methane (P*s).

[0089] Furthermore, in S6, the gas emission from the non-coal tunnel face is calculated based on the permeability of the cracks rather than the permeability of the rock. The calculation formula is as follows: Where n is the number of cracks, l is the average length of cracks (m), is the effective width of the crack (m), and e is the crack roughness.

[0090] In actual engineering, due to the small pore diameter and permeability of the rock matrix at the face, the gas seepage rate is slow. Therefore, the channels for gas outbursts at the face of non-coal gas tunnels constructed based on the mining method are mainly various artificial or structural cracks. When calculating the crack permeability in the present invention, the influencing factors such as the length, width, and number of cracks are considered, and the calculation results are more consistent with the phenomenon of gas outbursts at the face in actual engineering. It can also be seen from the formula that the permeability of the crack is proportional to the number, length, and width of the cracks, and inversely proportional to the surface roughness of the cracks, among which the crack width has the greatest impact on the crack permeability. Since the artificial cracks at the face are usually wedge-shaped spatial bodies that develop radially along the blastholes, and their cross-sectional area is a triangle, in order to comprehensively consider the influence of the crack width on the permeability, take In the formula, b is the surface width of the tunnel face crack (m). Since the tunnel face cracks are usually wedge-shaped spatial bodies that develop radially along the blastholes, half of the tunnel face surface width is taken.

[0091] Furthermore, the calculation formula for calculating the gas emission from the face of a non-coal gas tunnel constructed based on the mining method in S7 is as follows: In the formula, t refers to the duration of gas outburst (s), and the meanings of other symbols are the same as above.

[0092] According to the solution formula of S7 gas outburst, it can be seen that the formula takes into account the influence of factors such as fracture permeability, actual outburst area, gas seepage characteristics, outburst time, etc. The factors considered are relatively comprehensive and the settlement results are relatively reliable.

[0093] like Figure 4 As shown, this embodiment takes the Miyaluo No. 3 Tunnel of the C18 section of the Wenchuan-Maerkang Expressway in Sichuan Province as an example to calculate the outflow volume. The starting and ending mileage of the right tunnel of Miyaluo No. 3 Tunnel is K161+723~K165+980, and the total length of the tunnel is 4257m. The tunnel site is located in the staggered contact zone between the eastern edge of the Qinghai-Tibet Plateau and the northwestern edge of the Sichuan Basin. The terrain is complex, with high terrain in the northwest and low terrain in the southeast. The working area is mostly high mountain canyon areas with well-developed gullies. The tunnel site is covered with artificial filling layers, landslide deposits, slope alluvial layers and alluvial layers, and the cover layer is well developed. The underlying Triassic Upper System Juwo Formation is mainly composed of metamorphic sandstone, slate, and phyllite, with good hydrocarbon generation conditions. In addition, the Miyaluo compression-torsion fault is developed in the site, and structural fissures are developed. It has strong representativeness and can better reflect the advantages of this embodiment.

[0094] Based on the non-coal tunnel harmful gas hazard assessment method, the following steps were implemented in the Miyaluo Tunnel:

[0095] S1. Test the gas pressure (P1), concentration (θ) and outflow velocity (V) in the exploration borehole or the gas advance borehole at the tunnel face;

[0096] S1.1: Field work arrangement: advanced deep hole arrangement, pre-test preparation, equipment installation and instrument test operation during the actual test. The blasthole depth in step S3.1 is 30m and the radius is 75mm.

[0097] After the leading hole was sealed, the pressure and gas concentration in the hole were tested using the M-Ⅱ gas pressure tester, and the speed of the gas overflow point was measured using the air compressor comprehensive parameter tester. The test results showed that the gas pressure P1 = 0.24MPa, θ = 15.76%, V = 0.0057cm / s.

[0098] S2. Test formation permeability (K) and porosity Drilling radius (r);

[0099] Through indoor experiments and drilling parameter inquiries, we found that the formation permeability K = 0.606mD, porosity Drilling radius r=37.5mm.

[0100] S3, bringing the parameters such as permeability, porosity, borehole pressure, borehole radius into the effective radius (r2) solver, and selecting the effective radius (r2) of the appropriate pressure range;

[0101] Substitute the parameters obtained from S1 and S2 into the effective radius finder, and the solution is as follows Figure 2 As shown in the result diagram, when the effective pressure is 0.26-0.27MPa, the gas convergence radius r1 is 2.5m; when the effective pressure is 0.27-0.28MPa, the gas convergence radius r1 is 3m; and so on, the convergence radius of other effective pressure ranges can also be obtained from the diagram. Since the gas pressure in the borehole is only 0.24MPa, the gas pressure convergence radius value of 3m in the range of 0.27-0.28MPa is temporarily taken.

[0102] S4, bringing r2 into the effective pressure finder to find the effective pressure P2;

[0103] Substitute the convergence radius r1=3m in the range of 0.27-0.28MPa into the effective pressure solver, and the solution is as follows: Figure 3 As shown. From the pressure distribution diagram, it can be seen that along the height direction of the cylinder, the maximum pressure is 0.279MPa in the xy plane, and this pressure value is within the range of [0.27MPa, 0.28MPa], so the solution is reasonable. The effective gas pressure in front of the right line face of the entrance of Miyaluo No. 3 Tunnel is 0.279MPa.

[0104] S5. Determine the pressure field distribution form in the tunnel face area based on P2 and r2;

[0105] When solving the pressure field distribution form in the tunnel face area, since the tunnel face surface is exposed to the air, P3 = 0.1MPa is taken. Substituting r1 and P2 into the formula, we can obtain: Taking the derivative with respect to x, we get

[0106] S6. Determine the values ​​of n (number of cracks), l (average length of cracks), b (effective width of cracks), and e (crack roughness) according to the condition of the tunnel face or the design grade of the surrounding rock, and calculate the crack permeability;

[0107] After on-site investigation, it was found that there were multiple gas leakage points after the face blasting at K162+380 in the right tunnel of Miyaluo No. 3 Tunnel. After measurement, there were 15 cracks with an average length of 1.8m and A=66m. 2 , b = 2 mm, e = 3.2, and substituting them into the crack permeability solution formula, we can get:

[0108] S7. Measurement of face area (A) and face crack rate Substitute the above parameters into the formula to obtain the outflow volume.

[0109] After on-site investigation and calculation, the post-blasting crack development rate of the tunnel face at K162+380 in the right tunnel of Yaluo No. 3 Tunnel was 0.05243%. Since the gas outburst volume at the tunnel face was to be solved, the gas pressure gradient at the tunnel face was obtained as follows: Substituting it into the gas outflow solution formula, we can get:

[0110] According to the on-site construction test, the average gas outflow of the three shifts at the face is 1.656m 3 / min. By comparing the results in the technical solution, it can be seen that the result of the calculation formula for the gas emission of the tunnel face is basically consistent with the construction conclusion, and its accuracy rate reaches 85.2%. It can be seen that the calculation method of the present invention has good practicality in predicting the gas emission of the tunnel face of non-coal gas tunnels during mining method construction. The result is reliable and accurate, and it can scientifically, reasonably and effectively predict the gas emission of the tunnel face of non-coal gas tunnels based on the mining method, providing a feasible and applicable basis for tunnel design and construction.

[0111] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for estimating gas emission from a non-coal gas tunnel face, characterized in that: include: Obtaining the formation permeability, porosity, borehole radius and physical parameters in the borehole at the tunnel face; wherein the physical parameters include: pressure, concentration and outflow velocity in the borehole; Based on the formation permeability, porosity, borehole radius and borehole pressure, a pressure field distribution model of the tunnel face area is obtained; Based on the pressure field distribution model in the tunnel face area, obtaining fracture permeability; Obtaining the fracture permeability includes: Based on the pressure field distribution in the tunnel face area, the number of cracks, the average length of cracks, the width of the crack surface and the roughness of the cracks are obtained; Based on the number of cracks, the average length of cracks, the width of crack surfaces and the roughness of cracks, the crack permeability is obtained; The fracture permeability is: Where n is the number of cracks, l is the average length of the cracks, is the effective width of the crack, which is b / 2, b is the crack surface width, and e is the crack roughness; The gas outflow rate is: Among them, Q is the gas outburst volume, n is the number of cracks, P2 is the effective gas pressure, P3 is the surface pressure of the tunnel face, r2 is the effective gas convergence radius, A is the tunnel face area, is the crack rate of the tunnel face, t is the gas outburst time, θ is the concentration, and u is the dynamic viscosity coefficient of methane; The tunnel face area and the tunnel face crack rate are obtained, and the gas emission volume is obtained based on the tunnel face area, the tunnel face crack rate, the concentration and the crack permeability.

2. The method for estimating gas emission from a non-coal gas tunnel face according to claim 1 is characterized in that: Obtaining the pressure field distribution in the tunnel face area includes: Obtaining an effective gas convergence radius based on the formation permeability, porosity, borehole radius and borehole internal pressure; Obtaining effective gas pressure based on the effective gas convergence radius, gas pressure and outflow velocity; Based on the effective gas convergence radius and the effective gas pressure, the pressure field distribution of the tunnel face area is obtained.

3. The method for estimating gas emission from a non-coal gas tunnel face according to claim 2 is characterized in that: Obtaining the effective gas convergence radius further includes: obtaining a pressure range corresponding to the effective gas convergence radius; It is determined whether the effective gas pressure satisfies the pressure range. If yes, the effective gas pressure is solved successfully. If no, the effective gas convergence radius is obtained again.

4. The method for estimating gas emission from a non-coal gas tunnel face according to claim 1 is characterized in that: The pressure field distribution model is: Among them, P is the pressure at a distance of x meters from the tunnel face, P2 is the effective gas pressure, P3 is the tunnel face surface pressure, and r2 is the effective gas convergence radius.

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