Shallow natural gas displacement adaptability evaluation method

Abstract

A shallow natural gas displacement adaptability evaluation method disclosed by the present invention comprises the following steps that an evaluation index factor set and a grading determination standard of each evaluation index are established, the evaluation index factor set comprises a target layer A and evaluation indexes, and the evaluation indexes comprise a first-level evaluation index criterion layer B and a second-level evaluation index object layer C; calculating the weight of each evaluation index; calculating the membership degree of the secondary evaluation indexes; performing evaluation factor fuzzy comprehensive operation based on the weight and the membership degree; and S4, establishing an evaluation model and a shallow natural gas displacement adaptability evaluation grade, substituting an operation result in the step S4 into the evaluation model to obtain an evaluation result, and determining the shallow natural gas displacement adaptability evaluation grade according to the evaluation result. According to the method, a fuzzy mathematics comprehensive evaluation method is introduced to establish a subway tunnel shallow natural gas displacement adaptability evaluation system, and the applicability of displacement measures to different projects is researched.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction engineering, and in particular to a method for evaluating the adaptability of shallow natural gas displacement. Background Art

[0002] The shallow natural gas displacement process is divided into three parts: first, the fracture seepage and pore diffusion of injected gas; second, the pore diffusion and fracture seepage of shallow natural gas; and third, the coupling process between the gas system and the solid system. The primary purpose of oil and gas displacement and coalbed methane extraction is to collect gas for energy utilization. Research focuses on the extraction volume of extraction holes. However, the shallow natural gas content in non-coal tunnels does not meet energy utilization standards. Shallow natural gas displacement aims to improve the formation environment and enable safe tunnel construction through shallow natural gas formations.

[0003] The impacts of displacement measures are numerous and complex. In practical engineering applications, adaptability evaluation is necessary to adjust subjective solutions and improve objective factors that influence displacement, so that the displacement can achieve the desired effect. Therefore, a shallow natural gas displacement adaptability evaluation method is urgently needed. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for evaluating the adaptability of shallow natural gas displacement.

[0005] The object of the present invention is achieved through the following technical solutions:

[0006] A shallow natural gas displacement adaptability evaluation method comprises the following steps:

[0007] S1. Establish an evaluation index factor set and a hierarchical judgment standard for each evaluation index, wherein the evaluation index factor set includes a target layer A and evaluation indexes, and the evaluation indexes include a first-level evaluation index criterion layer B and a second-level evaluation index object layer C;

[0008] S2. Calculate the weight of each evaluation index;

[0009] S3. Calculate the membership degree of the secondary evaluation indicators;

[0010] S4. Fuzzy comprehensive calculation of evaluation factors based on weights and membership: including evaluation from object level to indicator level, and from criterion level to target level;

[0011] S5. Establish an evaluation model and shallow natural gas displacement adaptability evaluation level, substitute the calculation result of step S4 into the evaluation model to obtain an evaluation result, and determine the shallow natural gas displacement adaptability evaluation level according to the evaluation result.

[0012] Furthermore, in step S1,

[0013] The criterion layer B includes B1: shallow natural gas occurrence factors, B2: displacement measure effectiveness factors, and B3: engineering benefit factors.

[0014] Furthermore, in step S1,

[0015] The target layer C includes: shallow natural gas occurrence factors: C1: fault distance, C2: core RQD value, C3: shallow natural gas detection concentration, C4: cap rock thickness;

[0016] Displacement effectiveness factors: C5: formation permeability, C6: water table depth, C7: gas injection pressure design value weight;

[0017] Engineering benefit factors: C8: tunnel burial depth, C9: displacement implementation period.

[0018] Furthermore, in step S2,

[0019] The weights of the criterion layer B are: B1: shallow natural gas occurrence factor, B2: displacement measure effectiveness factor, and B3: engineering benefit factor, with weight ratios of 0.2972, 0.5389, and 0.1638.

[0020] Furthermore, in step S2,

[0021] The weights of the target layer C are as follows: C1: fault distance, C2: core RQD value, C3: shallow natural gas detection concentration, and C4: caprock thickness, with a weight ratio of I1 = (0.125 0.125 0.625 0.125); C5: formation permeability, C6: water table depth, and C7: design gas injection pressure, with a weight ratio of I2 = (0.5813 0.1095 0.3091); and C8: tunnel depth and C9: displacement implementation period, with a weight ratio of I3 = (0.3333 0.6667).

[0022] Furthermore, in step S3,

[0023] Establish an evaluation matrix of the indicator layer against the criterion layer:

[0024]

[0025] Where R i —is the indicator layer evaluation matrix; i—takes values ​​1, 2, and 3, representing the criterion layers B1, B2, and B3 respectively; r—is the membership degree; n—is the nth indicator in the indicator layer.

[0026] The membership function is determined by the triangular distribution function, where the fault distance, core RQD value, tunnel burial depth, and displacement implementation period are positive indicator membership functions, and their membership function expressions are as follows:

[0027]

[0028]

[0029] The remaining indicators are negative indicator membership functions, and the expressions are:

[0030]

[0031] Where a, b, c, d represent the threshold values ​​of the grading criteria for each evaluation index; x represents the value of the evaluation index. Further, in step S4, the object layer is evaluated to the index layer as follows:

[0032] U i =I i R i (i=1, 2, 3)

[0033] Where, I i is the object layer weight, R i is the indicator evaluation matrix.

[0034] Furthermore, in step S4, the criterion layer evaluates the target layer as follows:

[0035] U=IU t =(u1,u2,u3,u4)(i=1,2,3)

[0036] Where I is the criterion layer weight, U i It is the first-level fuzzy comprehensive evaluation result.

[0037] Furthermore, in step S5, the evaluation model establishment includes the following steps:

[0038] S51. The adaptability of shallow natural gas displacement is divided into four levels: I, II, III, and IV according to the evaluation indicators. The adaptability corresponds to the displacement measures being very adaptable, relatively adaptable, basically adaptable, and unadaptable, respectively.

[0039] S52. Assume that the evaluation set is: N = {N1, N2, N3, N4}, and assign values ​​of 4, 3, 2, and 1, respectively, indicating that the adaptability evaluation levels are I, II, III, and IV, corresponding to the four states of very adaptable, relatively adaptable, basically adaptable, and unadaptable;

[0040] S53. Calculate the adaptability evaluation of displacement measures. The calculation formula for the adaptability evaluation of displacement measures is:

[0041] Among them, when 3.5≤T≤4.0, the adaptability evaluation level is I; when 2.5≤T<3.5, the adaptability evaluation level is II; when 1.5≤T<2.5, the adaptability evaluation level is III; when 1.0≤T<1.5, the adaptability evaluation level is IV.

[0042] The beneficial effects of the present invention are:

[0043] 1) This paper introduces fuzzy mathematics comprehensive evaluation method to establish an adaptability evaluation system for shallow natural gas displacement in subway tunnels and studies the applicability of displacement measures to different projects.

[0044] 2) From the three aspects of shallow natural gas occurrence factors, displacement measures effectiveness factors, and engineering benefit factors, factors affecting the displacement effect, such as shallow natural gas detection concentration, formation permeability, and tunnel burial depth, were selected, and a fuzzy mathematical comprehensive evaluation method was used to construct an adaptability evaluation system for shallow natural gas displacement in subway tunnels.

[0045] 3) The present invention can accurately reflect the adaptability level of natural gas displacement in each section during tunnel construction, so as to accurately guide the selection of treatment methods for harmful gases in non-coal gas tunnels. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The figure is a flow chart of a shallow natural gas displacement adaptability evaluation method. DETAILED DESCRIPTION

[0047] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work shall fall within the scope of protection of the present invention.

[0048] See Figure 1 , the present invention provides a technical solution:

[0049] Example 1:

[0050] like Figure 1 As shown, a shallow natural gas displacement adaptability evaluation method includes the following steps:

[0051] S1. Use the fuzzy comprehensive evaluation method to evaluate the adaptability of shallow natural gas displacement, establish an evaluation index factor set (as shown in Table 1 below), and a grading judgment standard for each evaluation index. The evaluation index factor set includes a target layer A and evaluation indicators. The evaluation indicators include a first-level evaluation index criterion layer B and a second-level evaluation index object layer C.

[0052]

[0053]

[0054] Table 1 - Evaluation index factor set

[0055]

[0056] Table 2 - Evaluation index grading criteria

[0057] The criterion layer B includes B1: shallow natural gas occurrence factors, B2: displacement measure effectiveness factors, and B3: engineering benefit factors.

[0058] The target layer C includes: shallow natural gas occurrence factors: C1: fault distance, C2: core RQD value, C3: shallow natural gas detection concentration, C4: cap rock thickness;

[0059] Displacement effectiveness factors: C5: formation permeability, C6: water table depth, C7: gas injection pressure design value weight;

[0060] Engineering benefit factors: C8: tunnel burial depth, C9: displacement implementation period.

[0061] S2. Calculate the weight of each evaluation index;

[0062] The analytic hierarchy process was used to calculate the weights of the evaluation factors. First, the judgment matrix was constructed using the Saaty scale of the paired comparison method. Then, the consistency of the judgment matrix was verified. Finally, the weights of the criterion layer B were calculated as follows: B1: shallow natural gas occurrence factor, B2: displacement measure effectiveness factor, B3: engineering benefit factor, with weight ratios of 0.2972, 0.5389, and 0.1638.

[0063] The weights of the target layer C are as follows: C1: fault distance, C2: core RQD value, C3: shallow natural gas detection concentration, and C4: caprock thickness, with a weight ratio of I1 = (0.125 0.125 0.625 0.125); C5: formation permeability, C6: water table depth, and C7: design gas injection pressure, with a weight ratio of I2 = (0.5813 0.1095 0.3091); and C8: tunnel depth and C9: displacement implementation period, with a weight ratio of I3 = (0.3333 0.6667).

[0064] S3. Calculate the membership degree of the secondary evaluation indicators;

[0065] Establish an evaluation matrix of the indicator layer against the criterion layer:

[0066]

[0067] Where R i—is the indicator layer evaluation matrix; i—takes values ​​1, 2, and 3, representing the criterion layers B1, B2, and B3 respectively; r—is the membership degree; n—is the nth indicator in the indicator layer.

[0068] The membership function is determined by the triangular distribution function, where the fault distance, core RQD value, tunnel burial depth, and displacement implementation period are positive indicator membership functions, and their membership function expressions are as follows:

[0069]

[0070]

[0071] The remaining indicators are negative indicator membership functions, and the expressions are:

[0072]

[0073] Where a, b, c, d—represent the threshold value of each evaluation index classification standard; x—is the value of the evaluation index. n1 For example: Regardless of whether it is a positive indicator membership function or a negative indicator membership function, r n1 They both represent elements in the evaluation matrix, with the same meaning but different calculation methods.

[0074] S4. Fuzzy comprehensive calculation of evaluation factors based on weights and membership: This is done using a two-level fuzzy comprehensive evaluation method and a weighted average evaluation model. First, the evaluation is done from the object layer to the indicator layer:

[0075] U i =I i R i (i=1,2,3)

[0076] Where, I i is the object layer weight, R i is the indicator evaluation matrix.

[0077] Then evaluate from the criterion layer to the target layer:

[0078] U=IU t =(u1,u2,u3,u4) (i=1,2,3)

[0079] Where I is the criterion layer weight, U i It is the first-level fuzzy comprehensive evaluation result.

[0080] S5. Establish an evaluation model and shallow natural gas displacement adaptability evaluation level, substitute the calculation result of step S4 into the evaluation model to obtain an evaluation result, and determine the shallow natural gas displacement adaptability evaluation level according to the evaluation result.

[0081] The establishment of the evaluation model includes the following steps:

[0082] S51. The adaptability of shallow natural gas flooding in subway tunnels is divided into four levels: I, II, III, and IV based on the evaluation indicators. The adaptability corresponds to the following: very adaptable flooding measures, relatively adaptable flooding measures, basically adaptable flooding measures, and unadaptable flooding measures, respectively.

[0083] S52. Assume that the evaluation set is: N = {N1, N2, N3, N4}, and assign values ​​of 4, 3, 2, and 1, respectively, representing the adaptability evaluation levels I, II, III, and IV, corresponding to the four states of very adaptable, relatively adaptable, basically adaptable, and unadaptable;

[0084] S53. Calculate the adaptability evaluation of the displacement measures: Defuzzify the evaluation vector using the following formula to calculate the adaptability evaluation of the displacement measures. The corresponding relationship of the T value evaluation results is shown in Table 3 below.

[0085] Among them, when 3.5≤T≤4.0, the adaptability evaluation level is Ⅰ; 当 When 2.5≤T<3.5, the adaptability evaluation level is II; when 1.5≤T<2.5, the adaptability evaluation level is III; when 1.0≤T<1.5, the adaptability evaluation level is IV.

[0086]

[0087] Table 3 - Adaptability evaluation results

[0088] Example 2:

[0089] This example is an analysis of the adaptability of shallow natural gas displacement measures in the Chengmeixian Project.

[0090] Based on the actual geological conditions and formation physical parameters of the Chengmei Line project, as well as the above studies on the shallow natural gas displacement range and displacement time, the YCK63+300 to YCK63+970 section, where the shallow natural gas hazard is more serious, was evaluated. The displacement layer is the shield mudstone layer, and the evaluation index values ​​are shown in Table 4 below.

[0091]

[0092] Based on the survey and research values ​​of the evaluation indicators, the following first-level evaluation matrix is ​​established:

[0093]

[0094] U1=I1R1=(0.3468 0.3824 0.1742 0.0967)

[0095]

[0096] U3=I3R3=(0.5555 0.4445 0 0) The secondary fuzzy evaluation results are as follows:

[0097] U=IU t =(0.4447 0.4747 0.0518 0.0158)

[0098] Evaluation result calculation:

[0099]

[0100] The shield tunnel section from YCK63+300 to YCK63+970 in the Chengmei Line Project is more suitable for adopting displacement measures to manage shallow natural gas.

[0101] The foregoing description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein and should not be construed as excluding other embodiments. Rather, the present invention can be used in various other combinations, modifications, and environments and can be modified within the scope of the concept described herein through the above teachings or techniques or knowledge in the relevant field. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention are intended to be protected by the appended claims.

Claims

1. A method for evaluating the adaptability of shallow natural gas flooding, characterized by: The steps include: S1. Establish an evaluation index factor set and a hierarchical judgment standard for each evaluation index: the evaluation index factor set includes a target layer A and evaluation indexes, and the evaluation indexes include a first-level evaluation index criterion layer B and a second-level evaluation index object layer C; S2. Calculate the weight of each evaluation index; S3. Calculate the membership degree of the secondary evaluation indicators; S4. Fuzzy comprehensive calculation of evaluation factors based on weights and membership: including evaluation from object level to indicator level, and from criterion level to target level; S5. Establish an evaluation model and shallow natural gas displacement adaptability evaluation level, substitute the calculation result of step S4 into the evaluation model to obtain an evaluation result, and determine the shallow natural gas displacement adaptability evaluation level according to the evaluation result.

2. The shallow natural gas displacement adaptability evaluation method according to claim 1, characterized in that: In the step S1, The criterion layer B includes B1: shallow natural gas occurrence factors, B2: displacement measure effectiveness factors, and B3: engineering benefit factors.

3. The shallow natural gas displacement adaptability evaluation method according to claim 1, characterized in that: In the step S1, The target layer C includes: shallow natural gas occurrence factors: C1: fault distance, C2: core RQD value, C3: shallow natural gas detection concentration, C4: cap rock thickness; Displacement effectiveness factors: C5: formation permeability, C6: water table depth, C7: gas injection pressure design value weight; Engineering benefit factors: C8: tunnel burial depth, C9: displacement implementation period.

4. The shallow natural gas displacement adaptability evaluation method according to claim 2, characterized in that: In the step S2, The weights of the criterion layer B are: B1: shallow natural gas occurrence factor, B2: displacement measure effectiveness factor, and B3: engineering benefit factor, with weight ratios of 0.2972, 0.5389, and 0.1638.

5. The shallow natural gas displacement adaptability evaluation method according to claim 3, characterized in that: In the step S2, The weights of the target layer C are as follows: C1: fault distance, C2: core RQD value, C3: shallow natural gas detection concentration, and C4: caprock thickness, with a weight ratio of I1 = (0.125 0.125 0.625 0.125); C5: formation permeability, C6: water table depth, and C7: design gas injection pressure, with a weight ratio of I2 = (0.5813 0.1095 0.3091); and C8: tunnel depth and C9: displacement implementation period, with a weight ratio of I3 = (0.3333 0.6667).

6. The shallow natural gas displacement adaptability evaluation method according to claim 5, characterized in that: In the step S3, Establish an evaluation matrix of the indicator layer against the criterion layer: Where R i —is the indicator layer evaluation matrix; i—takes values ​​1, 2, and 3, representing the criterion layers B1, B2, and B3 respectively; r—is the membership degree; n—is the nth indicator in the indicator layer. The membership function is determined by the triangular distribution function, where the fault distance, core RQD value, tunnel burial depth, and displacement implementation period are positive indicator membership functions, and their membership function expressions are as follows: The remaining indicators are negative indicator membership functions, and the expressions are: Where a, b, c, d represent the threshold values ​​of the grading criteria for each evaluation index; x is the value of the evaluation index.

7. The shallow natural gas displacement adaptability evaluation method according to claim 6, characterized in that: In step S4, the object layer is evaluated to the indicator layer as follows: U i =I i R i (i=1,2,3) Where, I i is the object layer weight, R i is the indicator evaluation matrix.

8. The shallow natural gas displacement adaptability evaluation method according to claim 7, characterized in that: In step S4, the criterion layer evaluates the target layer as follows: U=IU t =(u1,u2,u3,u4)(i=1,2,3) Where I is the criterion layer weight, U i It is the first-level fuzzy comprehensive evaluation result.

9. The shallow natural gas displacement adaptability evaluation method according to claim 8, characterized in that: In step S5, the evaluation model is established by: S51. The adaptability of shallow natural gas displacement is divided into four levels: I, II, III, and IV based on the evaluation indicators. The adaptability corresponds to the following: very adaptable displacement measures, relatively adaptable displacement measures, basically adaptable displacement measures, and unadaptable displacement measures, respectively. S52. Assume that the evaluation set is: N = {N1, N2, N3, N4}, and assign values ​​of 4, 3, 2, and 1, respectively, representing the adaptability evaluation levels I, II, III, and IV, corresponding to the four states of very adaptable, relatively adaptable, basically adaptable, and unadaptable; S53. Calculate the adaptability evaluation of displacement measures. The calculation formula for the adaptability evaluation of displacement measures is: Among them, when 3.5≤T≤4.0, the adaptability evaluation level is Ⅰ; 当 When 2.5≤T<3.5, the adaptability evaluation level is II; when 1.5≤T<2.5, the adaptability evaluation level is III; when 1.0≤T<1.5, the adaptability evaluation level is IV.

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