A method for risk assessment of leakage of deep underground mine water and its application

Abstract

This invention belongs to the field of geophysics and provides a method and application for assessing the leakage risk of deep underground mine water. First, the physical parameters of the rock mass within the target layer are obtained. Then, the resistivity of the underground rock mass before and after mine water sealing is measured using a wide-area electromagnetic method. After identifying the low-resistivity anomaly, the total volume of the low-resistivity anomaly within the target layer is calculated. Based on the Archie formula, a formula for calculating the water-bearing volume of the rock mass is derived, thereby obtaining the calculated volume of the sealed mine water. The leakage risk of the sealed mine water within the target layer is assessed based on the relationship between the calculated volume and the actual volume. This invention uses a wide-area electromagnetic method to detect the resistivity of the target layer, calculates the volume of sealed mine water based on the Archie formula, and compares the difference between the sealed mine water volume and the actual sealed volume to assess the leakage risk. It has advantages such as high detection efficiency, simple and reliable calculation method, and high reliability of risk assessment. It has a wide range of applications and is environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of geophysics, specifically relating to a method and application for assessing the risk of leakage of deep underground sealed mine water. Background Technology

[0002] The deep transfer and storage method for high-concentration mine water can effectively alleviate problems such as groundwater depletion and land subsidence in central and western my country. However, this method also has problems such as insufficient means of detecting the migration range of the sealed mine water, leakage of mine water due to surrounding rock fracture leading to groundwater pollution, and lack of supervision methods.

[0003] In 2010, He Jishan [1] A "wide-area electromagnetic method" was proposed, which achieves deep electromagnetic detection by transmitting high-power pseudo-random currents into the ground. This method uses high-power pseudo-random electromagnetic signals instead of traditional frequency electromagnetic detection methods, significantly increasing the detection depth. Based on this, He Jishan... [2] A 1.5km shale gas exploration operation was conducted in northwestern Hunan, validating the deep-penetration capability of the wide-area electromagnetic method. (Li Diquan) [3] A comparative study of the detection effects of wide-area electromagnetic methods and CSAMT methods was conducted in areas with strong interference to verify and demonstrate that the wide-area electromagnetic method has advantages over the traditional frequency domain electromagnetic method, such as stronger anti-interference capability and greater detection depth. (Li Diquan) [4] Wide-area electromagnetic fine exploration was carried out in Xinyuan Coal Mine to achieve fine detection of the electrical structure of the target layer, proving that wide-area electromagnetic method can be used for fine detection in water-rich areas of coal mines.

[0004] Currently, research on deep storage of high-concentration mine water mainly focuses on groundwater chemistry, hydrodynamic field simulation, and deep well exploration. Traditional monitoring of high-concentration mine water storage primarily relies on well logging and drilling, and uses formation lithology analysis for pseudo-fluid simulation. However, existing technologies lack rapid and effective methods for monitoring the water-bearing capacity of the target layer, making it difficult to determine the volume of stored mine water and whether large-scale leakage has occurred. Therefore, how to apply wide-area electromagnetic methods to assess the leakage risk of deep underground mine water storage is one of the urgent technical problems to be solved in this field.

[0005] References:

[0006] [1] He Jishan. Research on wide-area electromagnetic sounding method [J]. Journal of Central South University (Natural Science Edition), 2010, 41(03):1065-1072.

[0007] [2] He Jishan, Li Diquan, Dai Shikun Application of wide-area electromagnetic method in shale gas detection in northwestern Hunan[J]. Petroleum Geophysical Exploration, 2014, 49(05):1006-1012+824.

[0008] [3] Li Diquan, Xiao Jiaoyu, Zhang Jifeng, et al. Comparison of detection effects of WFEM and CSAMT in water-rich areas of Xinyuan Coal Mine [J]. Geophysical and Geochemical Exploration, 2021, 45(05): 1359-1366.

[0009] [4] Li Diquan, Wang Zhongle, Liu Zijie, et al. Fine detection of water-rich areas in Xinyuan Coal Mine using wide-area electromagnetic method [J]. Progress in Geophysics, 2024, 39(01):174-182. Summary of the Invention

[0010] The purpose of this invention is to provide a method for assessing the risk of leakage of deep underground mine water, which solves the problem that it is difficult to detect the migration range and volume of mine water and to determine whether large-scale leakage has occurred.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] This invention provides a method for assessing the risk of leakage of deep underground mine water, comprising the following steps:

[0013] S1. Obtain the physical parameters of the rock mass within the target layer:

[0014] The formula for calculating the water saturation of rock mass is derived based on the Archie formula; the rock mass physical parameters within the target layer are obtained based on well logging data and literature data of the target layer for mine water sealing; the rock mass physical parameters include apparent resistivity, porosity, saturation index, porosity index, and the proportionality coefficient in the Archie formula;

[0015] S2. Measure the volume of the low-resistivity anomaly within the target layer:

[0016] Wide-area electromagnetic method was used to detect the target rock mass before mine water sealing, and the resistivity data of the target rock mass before mine water sealing was obtained.

[0017] Seal volume into the target layer The target rock mass after the mine water was sealed was detected using the wide-area electromagnetic method, and the resistivity data of the target rock mass after the mine water was sealed were obtained.

[0018] Import the obtained resistivity data of the target layer rock mass into a three-dimensional data visualization software (such as Voxler software), construct three-dimensional electrical structure models of the target layer rock mass before and after mine water sealing, compare the resistivity of the three-dimensional electrical structure models before and after mine water sealing, extract the rock mass with a resistivity decrease of at least 50% from the three-dimensional electrical structure model after mine water sealing as a low-resistivity anomaly, and obtain the resistivity and volume of each low-resistivity anomaly.

[0019] S3. Calculate the volume of mine water to be sealed in the target layer:

[0020] Based on the physical parameters of the target layer rock mass obtained from S1, the resistivity of the low-resistivity anomaly obtained from S2 is substituted into the formula for calculating the water saturation of the rock mass to calculate the water saturation of each low-resistivity anomaly. Then, the water-bearing volume of each low-resistivity anomaly is calculated based on its volume, and the water-bearing volume of all low-resistivity anomalies is obtained as the calculated volume of mine water sealed within the target layer. ;

[0021] S4. Assess the risk of leakage from sealed mine water:

[0022] The calculated volume of the sealed mine water obtained from S3 Actual volume of mine water Based on the relationship, the risk of leakage of sealed mine water at the current moment is assessed using the following method:

[0023] when They concluded that no leakage had occurred in the sealed mine water at the current moment.

[0024] when They believe that the sealed mine water may leak at this time;

[0025] when They believe that the sealed mine water has already begun to leak at this moment.

[0026] Furthermore, in S1, the formula for calculating the water saturation of the rock mass is as shown in equation (1):

[0027] (1)

[0028] In the formula: ρ is the apparent resistivity of the target rock mass; ρ is the resistivity of the target rock mass, which is the resistivity of the formation obtained by frequency domain electromagnetic inversion in this study; Ф is the porosity of the rock mass, which is the porosity of the target layer in the well logging in the example; S is the water saturation of the rock mass (the ratio of water to pores); n is the saturation index (the ratio of water to pores); m is the porosity index (cementation coefficient), which is greatly affected by the lithology of the rock mass and is related to the measured stratigraphic age (1.3 for Tertiary, 1.95 for Paleozoic); a is the proportionality coefficient in the Archie formula.

[0029] Furthermore, in S2, the process of obtaining the resistivity of the target layer rock mass using the wide-area electromagnetic method is as follows:

[0030] A survey network is constructed on the surface with the well as the center. The survey network includes several parallel survey lines. Each survey line contains several measuring electrodes. All measuring electrodes are connected to a signal receiver. Two power supply electrodes are set up outside the surface survey network. Both power supply electrodes are connected to a signal transmitter. The line connecting the two power supply electrodes is parallel to the survey line.

[0031] A coordinate system Oxy is established with the midpoint of the line connecting the two power supply electrodes as the center O, the normal of the line connecting the two power supply electrodes as the y direction, and the direction of the measuring line as the x direction, so as to obtain the coordinates of the two power supply electrodes and each measuring electrode.

[0032] The signal transmitter transmits signals in the frequency range of 0.01~6144Hz via two power supply electrodes. n The sequence frequency domain current signal is sent underground. The signal receiver receives the current signal through each measuring electrode and simultaneously measures the potential difference between different measuring electrodes. Based on the coordinates of each measuring electrode, the coordinates of the two power supply electrodes, the obtained potential difference, the transmitted current signal, and the received current signal, the resistivity of the target layer rock mass is inverted using numerical analysis.

[0033] Furthermore, the distance between the measuring electrode and the sealing well is less than or equal to the influence radius R of the surface affected by the mine water sealing, and the influence radius R is calculated according to formula (2):

[0034] (2)

[0035] In the formula: Where is the radius of the sealing well, K is the average permeability coefficient of the formation within the depth range of the sealing well, M is the thickness of the target layer, and Q is a parameter related to the original water level of the aquifer and the water level of the sealing well in the circular island model assumption.

[0036] Furthermore, the distance between the measuring electrodes is not less than 50m; the distance between the two power supply electrodes is 900~1200m; and the emission current is not less than 20A.

[0037] Furthermore, the ratio of the transmit / receive distance (the distance between the midpoint of the line connecting the measuring electrode and the two power supply electrodes) to the detection depth in the wide-area electromagnetic method is greater than or equal to 3:1.

[0038] Furthermore, when using the frequency domain electromagnetic method, the resistivity of the target layer rock mass is obtained by numerical analysis according to equation (3):

[0039] (3)

[0040] In the formula: The apparent resistivity of the target rock mass; To calculate the observation coefficients for higher-order apparent resistivity; It is the electromagnetic effect function; To measure the potential difference between electrodes M and N; E x Let be the component of the electric field generated by the two power supply electrodes in the x-direction; I is the emission current; The imaginary unit is k; the wave number is k.

[0041] in, Determine according to equations (4) to (6):

[0042] (4)

[0043] (5)

[0044] (6)

[0045] In the formula: dL is the distance between the two power supply electrodes; To measure the angle between the electrode and the y-direction in the Oxy coordinate system; To measure the distance between electrodes M and N.

[0046] Furthermore, in S3, the calculated volume of mine water sealed within the target layer is calculated according to formula (7):

[0047] (7)

[0048] In the formula: The calculated volume of mine water sealed within the target layer (the calculated volume refers to the water-bearing volume of the rock mass obtained from the calculation, which is used to replace the actual volume of mine water sealed within the rock mass); Let J be the volume of the j-th low-resistivity anomaly in the target layer; Let be the water saturation of the j-th low-resistivity anomaly.

[0049] Furthermore, the application of the method for assessing the leakage risk of deep underground mine water sealing according to the present invention is as follows: The resistivity of the target rock mass during the mine water sealing process is detected multiple times using a wide-area electromagnetic method, and the calculated volume of the sealed mine water is calculated based on the rock mass resistivity for each detection. Based on the volume of mine water sealed during each exploration Assess the leakage risk of the target rock mass sealing mine water at the current moment, and determine whether to continue sealing mine water into the target rock mass based on the leakage risk assessment results.

[0050] The underlying principle of the method described in this invention is as follows: the mine water to be sealed is a high-concentration ionic solution with good conductivity. After the mine water is sealed in the underground rock mass, the rock mass resistance will decrease and the conductivity will increase. Based on the above characteristics, this invention uses a deep wide-area electromagnetic method to measure the resistivity change of the target layer rock mass before and after sealing the mine water. Based on the measurement results, the low-resistivity anomaly after sealing the mine water is determined. The volume of the low-resistivity anomaly in the target layer is calculated using the three-dimensional visualization software Voxler. Then, the water saturation of the low-resistivity anomaly in the target layer is calculated using the Archie formula to obtain the calculated volume of the sealed mine water in the target layer. The leakage risk of the sealed mine water is judged based on the difference between the calculated volume and the actual sealed volume.

[0051] This invention innovatively proposes a method for assessing the risk of leakage of deep underground mine water. Compared with existing technologies, this invention has the following beneficial technical effects:

[0052] ① High working efficiency: The wide-area electromagnetic method used can efficiently and accurately detect the resistivity of the target layer, which greatly improves the working efficiency compared with traditional methods;

[0053] ② The volume of sealed mine water is calculated using the derived formula of Archie's formula, which is simple and has improved reliability;

[0054] ③This method is applicable to various tasks, including the storage of high-concentration mine water, underground storage of urban wastewater, and long-term underground storage of highly polluted water bodies, and has a wide range of applications;

[0055] ④ It can accurately calculate the volume of sealed mine water, which is highly reliable when used to assess the risk of underground leakage of mine water, thereby reducing the pollution of groundwater caused by underground mine water sealing and protecting the natural environment. Attached Figure Description

[0056] Figure 1 This is a flowchart illustrating the method of the present invention.

[0057] Figure 2 This is a schematic diagram of the geological structure of the coalfield in the study area in Embodiment 1 of the present invention.

[0058] Figure 3 This is a schematic diagram of the arrangement of the field source and measurement network in the wide-area electromagnetic method in Embodiment 1 of the present invention.

[0059] Figure 4 This is a vertical cross-sectional schematic diagram of the resistivity inversion results of the target layer rock mass of survey lines 2 and 8 in the survey network in Embodiment 1 of the present invention; wherein, Figure (a) is the 2nd survey line and Figure (b) is the 8th survey line.

[0060] Figure 5 This is the frequency domain electromagnetic resistivity inversion result corresponding to the depth of the sealed target layer in Embodiment 1 of the present invention.

[0061] Figure 6 This is a schematic diagram of the low-resistivity anomaly volume of the target layer in Embodiment 1 of the present invention; wherein, Figure (a) is a top view; Figure (b) is a right view; and Figure (c) is a left view.

[0062] Figure 7 This is a statistical chart of the porosity of the target layer in the well logging in Embodiment 1 of the present invention. Detailed Implementation

[0063] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0064] Figure 1 This is a schematic flowchart of the method of the present invention;

[0065] This invention provides a method for assessing the risk of leakage of deep underground mine water, comprising the following steps:

[0066] S1. Obtain the physical parameters of the rock mass within the target layer:

[0067] The formula for calculating the water saturation of rock mass is derived based on the Archie formula. Based on the well logging data and literature of the target layer for mine water sealing, the physical parameters of the target layer rock mass are determined. The physical parameters of the rock mass include apparent resistivity, porosity, saturation index, porosity index, and the proportionality coefficient in the Archie formula. Generally, the average value of the measured physical parameters of the rock mass in the target layer is taken.

[0068] The Archie formula was first used to calculate the resistivity variation of sandstone, and later gradually applied to the calculation of rock and mineral resistivity. It effectively analyzes the relationship between formation rock resistivity and lithological parameters such as formation porosity, water saturation, oil saturation, rock mass cementation, and mineral content. The expression for the Archie formula for calculating rock resistivity is as follows:

[0069]

[0070] In the formula: ρ is the apparent resistivity of the target rock mass; ρ is the resistivity of the target rock mass, which is the resistivity of the formation obtained by frequency domain electromagnetic inversion in this study; Ф is the porosity of the rock mass, which is the porosity of the target layer in the well logging in the example; S is the water saturation of the rock mass (the ratio of water to pores); n is the saturation index (the ratio of water to pores); m is the porosity index (cementation coefficient), which is greatly affected by the lithology of the rock mass and is related to the measured stratigraphic age (1.3 for Tertiary, 1.95 for Paleozoic); a is the proportionality coefficient in the Archie formula.

[0071] Based on Archie's formula, the water saturation of the rock mass is calculated according to equation (1):

[0072] (1)

[0073] The water-bearing volume of the rock mass is calculated using the following formula:

[0074]

[0075] In the formula: The target layer's water-bearing volume (the water-bearing volume of the rock mass refers to the volume of mine water sealed within the rock mass); The volume of the low-resistivity anomaly in the target layer.

[0076] S2. Measured volume of low-resistivity anomaly within the target layer:

[0077] Wide-area electromagnetic method was used to detect the target rock mass before mine water sealing, and resistivity data of the target rock mass before mine water sealing were obtained.

[0078] Seal volume into the target layer The target rock mass after the mine water was sealed was detected using the wide-area electromagnetic method, and the resistivity data of the target rock mass after the mine water was sealed were obtained.

[0079] The obtained resistivity data of the target rock mass was imported into a 3D data visualization software (such as Voxler 4.0.476 software produced by Golden Software Corporation, USA). Three-dimensional electrical structure models of the target rock mass before and after mine water sealing were constructed. The two 3D electrical structure models were compared, and rock masses with a resistivity decrease of at least 50% were extracted from the 3D electrical structure model after mine water sealing as low-resistivity anomalies. The resistivity and volume of each low-resistivity anomaly were obtained. A low-resistivity anomaly is defined as a rock mass whose resistivity decreases by at least 50% after mine water sealing compared to before sealing.

[0080] The process of detecting the resistivity of the target rock mass using the wide-area electromagnetic method is as follows:

[0081] A survey network is constructed on the surface with the well as the center. The survey network includes several parallel survey lines. Each survey line contains several measuring electrodes. All measuring electrodes are connected to a signal receiver. Two power supply electrodes are set up outside the surface survey network. Both power supply electrodes are connected to a signal transmitter. The line connecting the two power supply electrodes is parallel to the survey line.

[0082] Establish a coordinate system Oxy with the midpoint of the line connecting the two power supply electrodes as the center O, the normal of the line connecting the power supply electrodes as the y direction, and the direction of the measuring line as the x direction, and obtain the coordinates of the two power supply electrodes and each measuring electrode.

[0083] The signal transmitter transmits signals in the frequency range of 0.01~6144Hz through two power supply electrodes. nThe sequence frequency domain current signal is sent underground, and the signal receiver receives the current signal through each measuring electrode. At the same time, the potential difference between different measuring electrodes is measured. Based on the coordinates of each measuring electrode, the coordinates of the two power supply electrodes, the obtained potential difference, the transmitted current signal, and the received current signal, the resistivity of the underground rock mass is inverted using numerical analysis, and the resistivity of the target layer rock mass is obtained.

[0084] The distance between the measuring electrode and the sealing well is less than or equal to the radius R of influence of the mine water sealing on the surface. The radius R is calculated according to formula (2):

[0085] (2)

[0086] In the formula: Where is the radius of the sealing well, K is the average permeability coefficient of the formation within the depth range of the sealing well, M is the thickness of the target layer, and Q is a parameter related to the original water level of the aquifer and the water level of the sealing well in the circular island model assumption.

[0087] The distance between the measuring electrodes shall not be less than 50m. The distance between the two power supply electrodes shall be 900~1200m. The emission current shall not be less than 20A.

[0088] In the wide-area electromagnetic method, the ratio of the transmit / receive distance (the distance between the midpoint of the line connecting the measuring electrode and the two power supply electrodes) to the detection depth is greater than or equal to 3:1, and the detection depth is the depth of the target layer.

[0089] The wide-area electromagnetic method uses a high-power frequency domain electromagnetic transmitter covering the entire region to transmit 2 n The sequence frequency domain signal overcomes the problem that traditional electromagnetic methods cannot detect in the near and transition regions. The calculation formula strictly follows the calculation formula of the entire region of the electric dipole source. Reference [1] records the E of a horizontal electric dipole source on a uniform earth surface. x The precise calculation formula is as follows:

[0090]

[0091] The formula for calculating the higher-order apparent resistivity of the entire region is derived from the above formula as shown in equation (3):

[0092] (3)

[0093] in, Determine according to equations (4) to (6):

[0094] (4)

[0095] (5)

[0096] (6)

[0097] In the formula: The apparent resistivity of the target rock mass; To calculate the observation coefficients for higher-order apparent resistivity; It is the electromagnetic effect function; To measure the potential difference between electrodes M and N; E x dL represents the x-component of the electric field generated by the two power supply electrodes; I is the emission current; dL is the distance between the power supply electrodes AB. is the angle between the actual measuring point and the power supply electrode AB; k is the wavenumber; r is the transmit / receive distance, i.e., the distance between the actual measuring point (measuring electrode) and the midpoint of the power supply electrode AB; It is the imaginary unit.

[0098] Currently, the target strata for mine water sealing in the Ordos region of central and western my country are mainly the Liujiagou Formation. The selection is based on the permeability of this stratum and its surrounding rock. The fractures generated in the target stratum are mainly longitudinal or transverse fractures. After the mine water is sealed underground from the sealing well, it will gradually flow into the fractures of the target stratum rock mass. Because the resistivity of the target stratum will decrease significantly within the range affected by high concentrations of mine water, a significant low resistivity phenomenon will be found in the affected area when the wide-area electromagnetic method is used for detection.

[0099] S3. Calculate the volume of mine water to be sealed in the target layer:

[0100] Based on the physical parameters of the target layer rock mass obtained from S1, the resistivity of the low-resistivity anomaly obtained from S2 is substituted into the formula for calculating the water saturation of the rock mass to calculate the water saturation of each low-resistivity anomaly. Then, the water-bearing volume of each low-resistivity anomaly is calculated based on its volume, and the water-bearing volume of all low-resistivity anomalies is obtained as the calculated volume of mine water sealed within the target layer. ;

[0101] According to step S1, the water saturation of each low-resistivity anomaly is calculated using the following formula:

[0102] (8)

[0103] In the formula: Let be the water saturation of the j-th low-resistivity anomaly; The resistivity of the j-th low-resistivity anomaly (generally the average value is taken); Φ represents the apparent resistivity of the target layer rock mass; Ф represents the porosity of the rock mass; m represents the porosity index.

[0104] Ignoring the slight changes in the resistivity of some rock masses caused by mine water, the saturated water-bearing volume within the low-resistivity anomaly is taken as the water-bearing volume of the target rock mass. Therefore, the water-bearing volume of the target rock mass is equal to the volume of all low-resistivity anomalies multiplied by the water saturation of the corresponding low-resistivity anomaly. The volume of mine water sealed within the target layer is calculated according to formula (7):

[0105] (7)

[0106] In the formula: The volume of mine water sealed within the target layer; Let be the volume of the j-th low-resistivity anomaly in the target layer.

[0107] The volume of sealed mine water calculated by this invention It is a calculated volume, not the actual volume, but the actual volume cannot be obtained. This invention replaces the actual volume with the calculated volume and assesses the risk of leakage of sealed mine water based on the calculated volume.

[0108] S4. Assess the risk of leakage from sealed mine water:

[0109] The calculated volume of the sealed mine water obtained from S3 Actual volume of sealed mine water Based on the relationship, the risk of leakage of sealed mine water at the current moment is assessed using the following method:

[0110] when They concluded that no leakage had occurred in the sealed mine water at the current moment.

[0111] when It is believed that the sealed mine water may leak at this moment;

[0112] when They believe that the sealed mine water has already begun to leak at this moment.

[0113] Geophysical methods are subject to a certain volume effect, which can lead to the resistivity of detected low-resistivity anomalies being higher than the actual resistivity. This results in an underestimation of the water saturation of the target layer, causing the calculated volume of sealed mine water to be lower than the actual volume. However, the influence of the volume effect will not exceed 10% of the actual volume. Considering that the sealed mine water undergoes some migration during the actual sealing process, resulting in the volume of sealed mine water within the detection range being slightly smaller than the actual sealed volume, this invention uses 80% as the threshold value for no leakage of sealed mine water. At that time, it was considered that no leakage had occurred, meaning that the mine water was completely sealed within the target layer; when In situations where it is difficult to accurately determine whether leakage has occurred, this invention uses 50% as the threshold for judging the degree of leakage of sealed mine water in order to avoid excessive leakage of mine water and cause groundwater pollution, while also considering economic efficiency. At that time, it was believed that the sealed mine water might leak at the current moment, which could also be understood as the small-scale leakage or migration of mine water having little impact on groundwater pollution. At that time, it was believed that the sealed mine water had already leaked, and that the leakage was on a large scale, seriously threatening the quality of the groundwater.

[0114] Therefore, when leakage is suspected, mine water sealing is immediately stopped; when potential leakage is suspected, the detection frequency is increased and mine water sealing continues; when no leakage is suspected, the detection frequency is maintained and mine water sealing continues. The detection frequency is generally once every 0.5-1 years.

[0115] The underlying principle of the method described in this invention is as follows: the mine water to be sealed is a high-concentration ionic solution with good conductivity. Sealing the mine water in underground rock mass will reduce the rock mass's resistivity and increase its conductivity. This invention defines rock mass with a resistivity reduction of at least 50% after sealing as a low-resistivity anomaly, disregarding changes in water-bearing volume within rock mass with a resistivity reduction of less than 50%. The saturated water-bearing volume of all low-resistivity anomalies is taken as the target layer's sealed mine water volume. Based on the above characteristics, this invention employs a deep, wide-area electromagnetic method to measure... The resistivity change of the target rock mass before and after mine water sealing is measured. The rock mass with a rapid decrease in resistivity is the rock mass in the target layer that can effectively seal mine water (low-resistivity anomaly). Based on the measurement results, the low-resistivity anomaly after mine water sealing can be determined. The volume of the low-resistivity anomaly in the target layer is calculated using the 3D visualization software Voxler. The water saturation of the target layer is calculated using the Archie formula, and then the volume of mine water sealed in the target layer is calculated. The leakage risk of the sealed mine water is judged based on the difference between the volume of sealed mine water and the actual sealed volume.

[0116] This invention has the following advantages: ① High working efficiency: The wide-area electromagnetic method used can efficiently and accurately detect the resistivity of the target layer, significantly improving working efficiency compared to traditional methods; ② The derivation formula of the Archie formula is used to calculate the volume of sealed mine water, which is simple and reliable; ③ This method is applicable to various tasks including the sealing of high-concentration mine water, underground sealing of urban wastewater, and long-term underground sealing of highly polluted water bodies, with a wide range of applications; ④ It can accurately calculate the volume of sealed mine water, which is highly reliable when used to assess the risk of underground leakage of mine water, reducing the pollution of groundwater caused by underground mine water sealing and protecting the natural environment.

[0117] The application of the method for assessing the leakage risk of deep underground mine water sealing in this invention is as follows: the resistivity of the target rock mass during the sealing process of mine water is detected multiple times using the wide-area electromagnetic method. The volume of mine water sealed at each detection is calculated based on the resistivity. Based on the volume of mine water sealed at each detection, the leakage risk of the mine water sealed in the target rock mass at the current moment is assessed. Based on the leakage risk assessment results, it is determined whether to continue sealing mine water into the target layer.

[0118] Example 1; see also Figure 1-7 ;

[0119] The survey area is located on the southern edge of the Dongsheng Coalfield, which is a fully covered concealed coalfield. The geological structure of this area belongs to the Dongsheng Uplift of the Ordos Syncline of the North China Platform. In this embodiment, the target strata for sealing mine water are the Triassic Liujiagou Formation (T1l) to the Permian Shiqianfeng Formation (P3s), located at a depth of 1500m~2200m. The lithology of this stratum is mainly grayish-white or light pinkish-red fine sandstone, with local development of transverse or vertical fractures. The strata have high porosity and large storage space, and the rock mass has low permeability.

[0120] S1. Obtain the physical parameters of the rock mass within the target layer;

[0121] Based on the well logging data and Chen Ge's (2020) lithological study of this area, the Archie parameter values ​​for this area were determined as follows: ① Regional porosity, statistically analyzed from the well logging data of this area as follows: Figure 7 As shown, the porosity of the target layer within the range of 1500~2200m is 3%~5%, and the average porosity within the region is 4%; ② The resistivity of the target layer for sealing mine water Based on the study of the physical properties of high-concentration mine water in this region by Sun Yajun (2022) and Zhao Yuling (2014), the mineralization degree (TDS) of the sealed mine water in the Pingshuo area of ​​Ordos is approximately 1.5 g / L to 4.5 g / L. It is inferred that the resistivity of the target layer in this region is... The range is from 0.1 Ω·m to 10 Ω·m. The lower limit is set to 0.1Ω·m; ③ The parameters such as saturation index n, porosity index m, and proportional coefficient a in the Archie formula are rock mass physics parameters. Based on the analysis results of the lithology, porosity, and cementation form of the Liujiagou Formation in the Ordos area by Chen Ge (2020) et al., combined with the well logging data of the area, the regional average saturation coefficient n is set to 0.7, the regional average porosity index m is set to 1, and the regional average proportional coefficient a is set to 1.

[0122] S2. Measure the volume of the low-resistivity anomaly within the target layer.

[0123] In this embodiment, the sealing well is used as the center of the measurement network, and 10 measurement lines are laid out, with a total length of 4km and a total length of 40km. The point-to-line spacing is 200m (i.e., the distance between adjacent measuring electrodes is 200m). A 2D measurement network with 39 frequency points is used. n Sequence signal, measurement frequency 0.5~6144Hz, field source AB ( Figure 3 The length is approximately 1.2km, the transmission current is 90A, and the transmit / receive distance is 7.7km~9.7km; the maximum distance between the measuring electrode and the sealing well is 2250m, and the influence radius of the sealing well is 1000m.

[0124] To effectively invert the formation resistivity of the test area, the electrical structure of the formation within the sealed area was statistically analyzed using actual well logging data from the sealed area. The statistical structure of the well logging resistivity in the sealed area is shown in Table 1.

[0125]

[0126] The resistivity inversion results of the wide-area electromagnetic method are as follows: Figure 4 The electromagnetic profile resistivity inversion results and regional logging data further narrowed the target layer for geological sealing of high-concentration mine water to the Triassic Liujiagou Formation to the Permian Shiqianfeng Formation within a depth range of 1500m to 2000m.

[0127] The results of the electrical inversion of the target layer are as follows Figure 5 As shown, the survey area is located in the Dongsheng Uplift zone of the Ordos Platform syncline. The strata are layered, with no obvious folds or faults. The overall structural morphology of the area is a monocline dipping southwest. The Triassic Liujiagou Formation to the Permian Shiqianfeng Formation in the area generally dip southwestward, with a dip angle of approximately 1-5°. In this sealing operation, the high-concentration mine water was mainly affected by the strata dip and diffused southwestward. The inversion results were imported into the 3D data visualization software Voxler. Based on the inversion results, 3D structural models of the target layer rock mass before and after mine water sealing were constructed. By comparing the resistivity of the two 3D electrical structural models before and after mine water sealing, rock masses with a resistivity decrease of at least 50% can be extracted as low-resistivity anomalies. The volume of each low-resistivity anomaly in the target layer of the sealing area was calculated as follows: Figure 6 When high-concentration mine water is injected, the resistivity of sandstone will drop to about 20 Ω·m, which is 80% lower than before sealing. The resistivity is relatively concentrated. Using gridded data, the volume of resistivity anomaly in the target layer can be calculated to be about 545.707 million cubic meters, denoted as V1.

[0128] S3. Calculate the volume of mine water to be sealed in the target layer:

[0129] The average resistivity of the low-resistivity anomaly is 1 Ω·m. According to equation (8), the water saturation of each low-resistivity anomaly is 4%. According to equation (7), the sum of the water volumes of all low-resistivity anomalies is obtained. It is approximately 555,000 to 645,000 cubic meters.

[0130] S4. Assess the risk of leakage from sealed mine water:

[0131] Target rock mass mine water volume Approximately 555,000 to 645,000 cubic meters. Actual sealed volume. The calculated storage volume is 500,000 to 600,000 cubic meters, slightly larger than the actual storage volume. Greater than or equal to 80% of the data indicate that the sealed mine water has not leaked at the current moment.

[0132] There are two main reasons why the calculated volume of sealed mine water is slightly larger than the actual volume of sealed mine water: first, because the target layer itself contains some formation water, which will affect the sealing of mine water; and second, because the volume effect of the wide-area electromagnetic method itself leads to the reflected low-resistivity anomaly volume being larger than the actual volume.

[0133] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for assessing the risk of leakage of deep underground mine water, characterized in that: Includes the following steps: S1. Obtain the physical parameters of the rock mass within the target layer: The formula for calculating the water saturation of rock mass is derived based on the Archie formula; the rock mass physical parameters within the target layer are obtained based on well logging data and literature data of the target layer for mine water sealing; the rock mass physical parameters include apparent resistivity, porosity, saturation index, porosity index, and the proportionality coefficient in the Archie formula; S2. Measure the volume of the low-resistivity anomaly within the target layer: Wide-area electromagnetic method was used to detect the target rock mass before mine water sealing, and resistivity data of the target rock mass before mine water sealing were obtained. Seal volume into the target layer The target rock mass after the mine water was sealed was detected using the wide-area electromagnetic method, and the resistivity data of the target rock mass after the mine water was sealed were obtained. Import the resistivity data of the target rock mass into a three-dimensional data visualization software, and construct three-dimensional electrical structure models of the target rock mass before and after mine water sealing. After comparing the rock resistivity of the three-dimensional electrical structure models before and after mine water sealing, extract the rock mass with a resistivity decrease of at least 50% from the three-dimensional electrical structure model after mine water sealing as a low-resistivity anomaly, and obtain the resistivity and volume of each low-resistivity anomaly. S3. Calculate the volume of mine water to be sealed in the target layer: Based on the physical parameters of the target layer rock mass obtained from S1, the resistivity of the low-resistivity anomaly obtained from S2 is substituted into the rock mass water saturation calculation formula to calculate the water saturation of each low-resistivity anomaly. Then, the water-bearing volume of each low-resistivity anomaly is calculated based on its volume, and the water-bearing volume of all low-resistivity anomalies is taken as the calculated volume of mine water sealed within the target layer. ; S4. Assess the risk of leakage from sealed mine water: according to With mine water storage volume Based on the relationship, the risk of leakage of sealed mine water at the current moment is assessed using the following method: when They concluded that no leakage had occurred in the sealed mine water at the current moment. when They believe that the sealed mine water may leak at this time; when They believe that the sealed mine water has already begun to leak at this moment.

2. The method for assessing the risk of leakage of deep underground mine water as described in claim 1, characterized in that: In S1, the formula for calculating the water saturation of the rock mass is derived from the Archie formula as shown in equation (1): （1） In the formula, ρ is the apparent resistivity of the target layer rock mass; Ф is the rock mass porosity; S is the rock mass water saturation; n is the saturation index; m is the porosity index; a is the proportionality coefficient in the Archie formula.

3. The method for assessing the risk of leakage of deep underground mine water as described in claim 1, characterized in that: In S2, the process of obtaining the resistivity of the target layer rock mass using the wide-area electromagnetic method is as follows: A survey network is constructed on the surface with the well as the center. The survey network includes several parallel survey lines, and each survey line contains several measuring electrodes. All measuring electrodes are connected to a signal receiver. Two power supply electrodes are set up outside the surface survey network. Both power supply electrodes are connected to a signal transmitter, and the line connecting the two power supply electrodes is parallel to the survey line. A coordinate system Oxy is established with the midpoint of the line connecting the two power supply electrodes as the center O, the normal of the line connecting the two power supply electrodes as the y direction, and the direction of the measuring line as the x direction, so as to obtain the coordinates of the two power supply electrodes and each measuring electrode. The signal transmitter transmits signals in the frequency range of 0.01~6144Hz via two power supply electrodes. n The sequence frequency domain current signal is transmitted underground, and the signal receiver receives the current signal through each measuring electrode, while simultaneously measuring the potential difference between different measuring electrodes; Based on the coordinates of each measuring electrode, the coordinates of the two power supply electrodes, the obtained potential difference, the transmitted current signal, and the received current signal, the resistivity of the target layer rock mass is inverted using numerical analysis.

4. The method for assessing the risk of leakage of deep underground mine water as described in claim 3, characterized in that: The distance between the measuring electrode and the sealing well is less than or equal to the influence radius R of the surface affected by the mine water sealing. The influence radius R is calculated according to formula (2): (2) In the formula: Where is the radius of the sealing well, K is the average permeability coefficient of the formation within the depth range of the sealing well, M is the thickness of the target layer, and Q is a parameter related to the original water level of the aquifer and the water level of the sealing well in the circular island model assumption.

5. The method for assessing the risk of leakage of deep underground mine water as described in claim 3, characterized in that: The distance between the measuring electrodes is not less than 50m; the distance between the two power supply electrodes is 900~1200m; the emission current is not less than 20A.

6. The method for assessing the risk of leakage of deep underground mine water as described in claim 3, characterized in that: The ratio of the transmit / receive distance to the detection depth in the wide-area electromagnetic method is greater than or equal to 3:

1.

7. The method for assessing the risk of leakage of deep underground mine water as described in claim 3, characterized in that: The resistivity of the target layer rock mass was obtained by numerical analysis using equation (3): (3) In the formula: The apparent resistivity of the target rock mass; To calculate the observation coefficients for higher-order apparent resistivity; It is the electromagnetic effect function; To measure the potential difference between electrodes M and N; E x Let be the component of the electric field generated by the two power supply electrodes in the x-direction; I is the emission current; k is the imaginary unit; k is the wave number; in, Determine according to equations (4) to (6): (4) (5) (6) In the formula: dL is the distance between the two power supply electrodes; To measure the angle between the electrode and the y-direction in the Oxy coordinate system; To measure the distance between electrodes M and N.

8. The method for assessing the risk of leakage of deep underground mine water as described in claim 1, characterized in that: Calculated volume of mine water sealed within the target layer Calculate according to formula (7): (7) In the formula: Let be the volume of the j-th low-resistivity anomaly within the target layer; Let be the water saturation of the j-th low-resistivity anomaly.

9. The application of the risk assessment method for leakage of deep underground mine water as described in any one of claims 1-8, characterized in that: The resistivity of the target rock mass during the sealing of mine water was measured multiple times using the wide-area electromagnetic method. Based on the rock mass resistivity, the calculated volume of sealed mine water was calculated for each measurement. Based on the actual volume of mine water sealed during each exploration. Assess the leakage risk of the target rock mass sealing mine water at the current moment, and determine whether to continue sealing mine water into the target rock mass based on the leakage risk assessment results.

10. The application of the risk assessment method for leakage of deep underground mine water as described in claim 9, characterized in that: If it is determined that no leakage has occurred in the sealed mine water, the detection frequency should be maintained and the mine water sealing should continue; the detection frequency is once every 0.5-1 years. If it is suspected that the mine water being sealed may leak at the current moment, the detection frequency is increased and the mine water sealing continues; If it is believed that leakage has occurred in the sealed mine water, the sealing of the mine water shall be stopped immediately.

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