Shallow natural gas displacement adaptability evaluation method

Abstract

This invention discloses a method for evaluating the adaptability of shallow natural gas displacement, comprising the following steps: establishing a set of evaluation index factors and a grading standard for each evaluation index; the set of evaluation index factors includes a target layer A and evaluation indicators, and the evaluation indicators include a first-level evaluation indicator criterion layer B and a second-level evaluation indicator object layer C; calculating the weight of each evaluation indicator; calculating the membership degree of the second-level evaluation indicators; performing fuzzy comprehensive calculation of the evaluation factors based on the weights and membership degrees; establishing an evaluation model and a shallow natural gas displacement adaptability evaluation level; substituting the calculation result of step S4 into the evaluation model to obtain the evaluation result; and determining the shallow natural gas displacement adaptability evaluation level based on the evaluation result. This invention introduces a fuzzy mathematical comprehensive evaluation method to establish a shallow natural gas displacement adaptability evaluation system for subway tunnels and studies the applicability of displacement measures to different projects.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction engineering technology, and in particular to a method for evaluating the adaptability of shallow natural gas displacement. Background Technology

[0002] The shallow natural gas displacement process consists of three parts: first, the fracture seepage-pore diffusion process of injected gas; second, the pore diffusion-fracture seepage process of shallow natural gas; and third, the coupling process between the gas system and the solid system. Oil and gas displacement extraction, along with coalbed methane extraction, primarily aims to extract and collect gas for energy utilization. Their research focus is also biased towards the extraction volume of the extraction wells. However, the shallow natural gas content in non-coal formation tunnels does not meet energy utilization standards. Therefore, the displacement of shallow natural gas aims to improve the formation environment and ensure the safe passage of tunnels through shallow natural gas formations.

[0003] The impact of displacement measures is multifaceted and complex. In practical engineering applications, adaptability evaluation is necessary to adjust subjective schemes affecting displacement and improve objective factors so that displacement can achieve the expected results. Therefore, a shallow natural gas displacement adaptability evaluation method is urgently needed. Summary of the Invention

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

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for evaluating the adaptability of shallow natural gas displacement includes the following steps:

[0007] 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 indicators. The evaluation indicators 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 indicator;

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

[0010] S4. Fuzzy comprehensive calculation of evaluation factors based on weights and membership degrees: including evaluation from the object layer to the indicator layer and evaluation from the criterion layer to the target layer in sequence;

[0011] S5. Establish an evaluation model and shallow natural gas displacement adaptability evaluation level. Substitute the calculation results of step S4 into the evaluation model to obtain the evaluation results, and determine the shallow natural gas displacement adaptability evaluation level based on the evaluation results.

[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: caprock thickness;

[0016] Factors affecting the effectiveness of displacement measures: C5: formation permeability, C6: water level depth, C7: design value of gas injection pressure;

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

[0018] Furthermore, in step S2,

[0019] The weights of the criterion layer B are as follows: 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, respectively.

[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, C4: caprock thickness weight ratio I1 = (0.125 0.125 0.625 0.125); C5: formation permeability, C6: water level depth, C7: gas injection pressure design value weight ratio I2 = (0.5813 0.1095 0.3091); C8: tunnel depth, C9: displacement implementation option weight ratio I3 = (0.3333 0.6667).

[0022] Furthermore, in step S3,

[0023] Establish an evaluation matrix from the indicator layer to the criterion layer:

[0024]

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

[0026] Membership functions are determined using triangular distribution functions, where fault distance, core RQD value, tunnel depth, and displacement implementation period are positive index membership functions, and their membership function expressions are as follows:

[0027]

[0028]

[0029] The remaining indicators are negative membership functions, expressed as follows:

[0030]

[0031] In the formula, a, b, c, and d represent the threshold values ​​for the grading criteria of each evaluation indicator; x represents the value of the evaluation indicator. 。 Furthermore, in step S4, the object layer evaluates the index layer as follows:

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

[0033] In the formula, I i For object layer weights, R i This 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] In the formula, I represents the weight of the criterion layer, and U... i This represents the result of the first-level fuzzy comprehensive evaluation.

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

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

[0039] S52. Let the evaluation set be: N = {N1, N2, N3, N4}, and assign values ​​of 4, 3, 2, and 1 respectively, representing the fitness evaluation levels of I, II, III, and IV, corresponding to four states: very adapted, relatively adapted, basically adapted, and maladapted.

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

[0041] When 3.5≤T≤4.0, the stress evaluation level is I; 当The stress evaluation level is II when 2.5≤T<3.5; the stress evaluation level is III when 1.5≤T<2.5; and the stress evaluation level is IV when 1.0≤T<1.5.

[0042] The beneficial effects of this invention are:

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

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

[0045] 3) This 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-series gas tunnels. Attached Figure Description

[0046] Figure 1 This is a flowchart of a method for evaluating the adaptability of shallow natural gas displacement. Detailed Implementation

[0047] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are 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 method for evaluating the adaptability of shallow natural gas displacement 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 classification judgment standard for each evaluation index. The evaluation index factor set includes a target layer A and evaluation indexes. The evaluation indexes include a first-level evaluation index criterion layer B and a second-level evaluation index object layer C.

[0052]

[0053]

[0054] Table 1 - Set of Evaluation Indicators and Factors

[0055]

[0056] Table 2 - Evaluation Indicator 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: caprock thickness;

[0059] Factors affecting the effectiveness of displacement measures: C5: formation permeability, C6: water level depth, C7: design value of gas injection pressure;

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

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

[0062] The weights of each evaluation factor were calculated using the analytic hierarchy process (AHP). First, a judgment matrix was constructed using the Saaty scale of the pairwise comparison method. Then, the consistency of the judgment matrix was verified. Finally, the weights of the criteria layer and the object layer were calculated separately. The weights of the criteria layer B are as follows: 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, respectively.

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

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

[0065] Establish an evaluation matrix for the indicator layer on the criterion layer:

[0066]

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

[0068] Membership functions are determined using triangular distribution functions, where fault distance, core RQD value, tunnel depth, and displacement implementation period are positive index membership functions, and their membership function expressions are as follows:

[0069]

[0070]

[0071] The remaining indicators are negative membership functions, expressed as follows:

[0072]

[0073] In the formula, a, b, c, and d represent the threshold values ​​for the grading criteria of each evaluation indicator; x represents the value of the evaluation indicator. It should be noted that r... n1 For example: regardless of whether it is a positive or negative index membership function, r n1 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 degrees: A two-level fuzzy comprehensive evaluation method is adopted, using a weighted average evaluation model for calculation. The evaluation is first performed from the object layer to the indicator layer.

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

[0076] In the formula, I i For object layer weights, R i This is the indicator evaluation matrix.

[0077] Then the evaluation proceeds from the criteria layer to the target layer:

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

[0079] In the formula, I represents the weight of the criterion layer, and U... i This represents the result of the first-level fuzzy comprehensive evaluation.

[0080] S5. Establish an evaluation model and shallow natural gas displacement adaptability evaluation level. Substitute the calculation results of step S4 into the evaluation model to obtain the evaluation results, and determine the shallow natural gas displacement adaptability evaluation level based on the evaluation results.

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

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

[0083] S52. Let the evaluation set be: N = {N1, N2, N3, N4}, and assign values ​​of 4, 3, 2, and 1 respectively, representing the fitness evaluation levels I, II, III, and IV, corresponding to four states: very adapted, relatively adapted, basically adapted, and maladapted.

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

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

[0086]

[0087] Table 3 - Adaptability Evaluation Results

[0088] Example 2:

[0089] This embodiment is an adaptability analysis of shallow natural gas displacement measures for the Chengmei Line project.

[0090] Based on the actual geological conditions and stratigraphic parameters of the Chengmei Line project, as well as the research on the displacement range and displacement time of shallow natural gas mentioned above, the YCK63+300~YCK63+970 section, which is more seriously affected by shallow natural gas, is evaluated. The displacement layer is the shield tunnel mudstone layer, and the evaluation index values ​​are shown in Table 4 below.

[0091]

[0092] Based on the values ​​obtained from the evaluation index survey, the following primary evaluation matrix is ​​established:

[0093]

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

[0095]

[0096] The results of the second-order fuzzy evaluation, U3 = I3R3 = (0.5555 0.4445 0 0), 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 of the Chengmei Line project is well-suited for shallow natural gas treatment using displacement measures.

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

Claims

1. A method for evaluating the adaptability of shallow natural gas displacement, characterized in that: Includes the following steps: S1. Establish an evaluation index factor set and a grading judgment standard for each evaluation index: The evaluation index factor set includes a target layer A and evaluation indicators, and the evaluation indicators 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 indicator; S3. Calculate the membership degree of the secondary evaluation indicators; S4. Fuzzy comprehensive calculation of evaluation factors based on weights and membership degrees: including evaluation from the object layer to the indicator layer and evaluation from the criterion layer to the target layer in sequence; S5. Establish an evaluation model and shallow natural gas displacement adaptability evaluation level. Substitute the calculation results of step S4 into the evaluation model to obtain the evaluation results. Determine the shallow natural gas displacement adaptability evaluation level based on the evaluation results. In 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: caprock thickness; Factors affecting the effectiveness of displacement measures: C5: formation permeability, C6: water level depth, C7: design value of gas injection pressure; Engineering benefit factors: C8: tunnel depth; C9: displacement implementation period; In step S2 The weights of the target layer C are: C1: fault distance, C2: core RQD value, C3: shallow natural gas detection concentration, and C4: caprock thickness. C5: Formation permeability, C6: Water level depth, C7: Design value of gas injection pressure (weighted ratio) C8: Tunnel depth; C9: Weighting ratio of displacement implementation options. ; In step S3 Establish an evaluation matrix from the indicator layer to the criterion layer: In the formula — This is the evaluation matrix for the indicator layer; i — takes values ​​of 1, 2, and 3, representing criteria layers B1, B2, and B3 respectively; r — is the membership degree; n — is the nth indicator in the indicator layer; Membership functions are determined using triangular distribution functions, where fault distance, core RQD value, tunnel depth, and displacement implementation period are positive index membership functions, and their membership function expressions are as follows: The remaining indicators are negative membership functions, expressed as follows: In the formula, x represents the value of the evaluation index; , , , , , , , , , These are the threshold values ​​for the grading criteria of each evaluation indicator, corresponding to the four levels: I, II, III, and IV.

2. The shallow natural gas displacement adaptability evaluation method according to claim 1, characterized in that: In 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 2, characterized in that: In step S2 The weights of the criterion layer B are as follows: 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, respectively.

4. The shallow natural gas displacement adaptability evaluation method according to claim 1, characterized in that: In step S4, the object layer evaluates the index layer as follows: In the formula, For object layer weights, This is the indicator evaluation matrix.

5. The shallow natural gas displacement adaptability evaluation method according to claim 4, characterized in that: In step S4, the criterion layer evaluates the target layer as follows: In the formula, For the criterion layer weights, This represents the result of the first-level fuzzy comprehensive evaluation.

6. The shallow natural gas displacement adaptability evaluation method according to claim 5, characterized in that: In step S5, the evaluation model establishment includes the following steps: S51. The adaptability level of shallow natural gas displacement is classified into four levels: I, II, III and IV according to the evaluation index. Their adaptability corresponds to the displacement measures being very adaptable, the displacement measures being relatively adaptable, the displacement measures being basically adaptable, and the displacement measures being unsuitable, respectively. S52. Let the evaluation set be: The values ​​are assigned to 4, 3, 2, and 1 respectively, representing the fitness evaluation levels I, II, III, and IV, corresponding to four states: highly adapted, relatively adapted, basically adapted, and maladapted. S53. Calculate the adaptability evaluation of displacement measures. The formula for calculating the adaptability evaluation of displacement measures is: The stress evaluation level is as follows: when 3.5≤T≤4.0, the stress evaluation level is I; when 2.5≤T<3.5, the stress evaluation level is II; when 1.5≤T<2.5, the stress evaluation level is III; and when 1.0≤T<1.5, the stress evaluation level is IV.

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