A method for determining the groundwater mixing mode and ratio in a multi-aquifer system of a mine

Abstract

The present invention relates to the technical field of water control in coal mines, and discloses a method for determining the groundwater mixing mode and ratio of a multi-aquifer system in a mine, comprising the following steps: S1. Collect and collate the hydrochemical data, water level data of each water-inrush aquifer during the mine production period, and the mineral composition of each water-inrush aquifer, and draw a water level trend chart before and after the mine exploitation; S2. Analyze the water level changes of the mine aquifers according to the water level trend chart, combine the water level change characteristics and mixing characteristics of each water-inrush aquifer to obtain the recharge relationship between each aquifer, and finally determine the groundwater mixing mode of the multi-aquifer system in the mine. The method proposed by the present invention can comprehensively determine the groundwater mixing mode and ratio, and at the same time, the present invention combines hydrogeological data such as the actual water level change data and hydrochemical data of the mine, effectively improving the accuracy of groundwater mixing identification.

Description

Technical Field

[0001] The present invention relates to the technical field of water control in coal mines, and particularly to a method for determining the groundwater mixing mode and ratio in a multi-aquifer system of a mine. Background Technique

[0002] Coal is the main energy source in China. Coal mining activities have changed the hydrochemical and hydrodynamic conditions of the multi-aquifer system in the mine. With the increase in mining depth and intensity, human activities such as coal mining and drainage have damaged the groundwater occurrence state of the mine aquifer system to varying degrees, resulting in a decline in the aquifer water level and groundwater mixing. In order to prevent major water inrush accidents during coal mine exploitation, it is necessary to drain the mine before exploitation. The drainage activities will cause changes in the groundwater level and strengthen the hydraulic connection between aquifers. Therefore, determining the groundwater mixing mode and ratio in the multi-aquifer system is of great significance for water control in coal mines. Accurately obtaining the groundwater mixing mode and ratio has the following functions in mine production: 1. It can be used to identify the water inrush source; 2. Judge the impact of mining on the aquifer and indicate the scale of the mine water conduction channel; 3. Determine the hydraulic connection and hydrochemical source of the multi-aquifer system in the mine. At present, the identification of groundwater mixing modes mainly includes the fuzzy comprehensive evaluation method, support vector machine, and artificial neural network, etc., which mostly focus on qualitative analysis. The calculation methods for the mixing ratio are cumbersome to operate and have a greater technical difficulty, and the errors in determining the mixing mode and ratio are relatively large. Therefore, the present invention provides a method for determining the groundwater mixing mode and ratio that is simple to operate and combines qualitative and quantitative analysis for this problem. Summary of the Invention

[0003] To solve the technical problems proposed in the background technique, the present invention provides a method for determining the groundwater mixing mode and ratio in a multi-aquifer system of a mine.

[0004] The present invention is realized by adopting the following technical solutions: A method for determining the groundwater mixing mode and ratio in a multi-aquifer system of a mine includes the following steps:

[0005] S1. Collect and sort out the hydrochemical data, water level data of each water-filled aquifer during the mine production period, and the mineral composition of each water-filled aquifer, and draw the water level trend diagram before and after the mine exploitation;

[0006] S2. Analyze the water level changes of the mine aquifers based on the water level trend diagram, combine the water level change characteristics and mixing characteristics of each water-filled aquifer to obtain the recharge relationship between each aquifer, and finally determine the groundwater mixing mode of the multi-aquifer system in the mine;

[0007] S3. Based on the analysis of the aquifer mixing model, select the mixed-source water sample as the initial water sample, the mixed water sample as the final water sample, and select the mineral phase according to the mineral composition of the aquifer. Input the corresponding hydrochemical data and mineral phase in the water sample into the PHREEQC software for hydrogeochemical inverse simulation, and obtain several groups of mixing ratios after simulation;

[0008] S4. Select the optimal groundwater mixing ratio according to the mineral composition and proportion characteristics of each aquifer.

[0009] The method for determining the groundwater mixing model and ratio of the multi-aquifer system in the mine proposed in this solution combines the hydrochemical data, water level data of each water-inrush aquifer and the mineral composition of each water-inrush aquifer, and draws a trend chart of water level changes. Combine the trend of water level changes to judge the water recharge relationship between aquifers, and finally determine the mixing model. And this solution can, based on the analysis of the aquifer mixing model, select the mixed-source water sample as the initial water sample, the mixed water sample as the final water sample, and select the mineral phase according to the mineral composition of the aquifer. Input the corresponding hydrochemical data and mineral phase in the water sample into the PHREEQC software for hydrogeochemical inverse simulation, obtain several groups of mixing ratios after simulation, and finally screen out the best and most accurate mixing ratio.

[0010] As a further improvement of the above solution, the hydrochemical data is obtained by collecting the water samples flowing from the underground discharge holes or water outlets during the mine production period and sealing and testing them. The hydrochemical data includes the concentrations of Na + , Ca 2+ , Mg 2+ , Cl - , SO4 2- , HCO3 - and the pH value.

[0011] As a further improvement of the above solution, the water level data is taken from the water level observation holes of each water-inrush aquifer during the mine production period. And in order to increase the intuitiveness and accuracy of the water level data, the average value of the water level data of each observation hole per quarter is selected to establish a water level database for different aquifers over the years.

[0012] As a further improvement of the above solution, the mine multi-aquifer system is, from top to bottom, a loose aquifer, a coal measure aquifer and a confined aquifer.

[0013] As a further improvement of the above solution, the determination of the mixing model is based on the following method:

[0014] If the water level of the loose layer aquifer shows a downward trend, the groundwater mixing model is the mixing of the loose layer aquifer into the coal measure aquifer;

[0015] If the water level of the confined aquifer shows a downward trend, the groundwater mixing mode is the mixing from the confined aquifer to the coal measure aquifer;

[0016] If the water level decline characteristics of the confined aquifer and the unconsolidated aquifer are the same, it indicates that there is a certain hydraulic connection between the two aquifers, and the mixing mode is the mixing from the confined aquifer to the unconsolidated aquifer.

[0017] As a further improvement of the above solution, in step S1, the sampling location of the water chemical data should be within the mine range and close to the water level observation hole.

[0018] As a further improvement of the above solution, in step S3, during the simulation, the sampling time of the initial water sample should be before the sampling time of the final water sample.

[0019] As a further improvement of the above solution, after selecting the initial water sample and the final water sample in step S3, input the water chemical data, set the mineral phases according to the mineral composition of the aquifer, perform hydrogeochemical simulation using the PHREEQC software, and calculate the mixing ratio.

[0020] As a further improvement of the above solution, among the several groups of mixing ratios obtained in step S3, first, according to the principle that the sum of the percentages of the mixing ratios of the initial water samples is less than or equal to 1, and then combined with the mineral phase characteristics of the aquifer for screening.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. The method proposed by the present invention can comprehensively determine the groundwater mixing mode and ratio, and at the same time, the present invention combines the actual water level change data and water chemical data and other hydrogeological data of the mine, effectively improving the accuracy of groundwater mixing identification.

[0023] 2. The present invention uses the water level data to qualitatively judge the groundwater mixing mode and quantitatively simulate and calculate the groundwater mixing ratio with the water chemical data, fully considering the changes in the actual hydrodynamic and hydrochemical conditions of the multi-aquifer system in the mine under the influence of coal mining, making the calculation results more accurate and in line with the actual situation.

[0024] 3. By comparing this method with other methods in the prior art, it provides a new solution idea for determining the groundwater mixing mode and ratio of the multi-aquifer system in the mine.

[0025] The method proposed by the present invention is simple, easy to operate, economical and reliable, and can guide the water prevention and control work in coal mines in production practice, and has an indicative effect on judging the water-conducting channel and the hydraulic connection of the aquifer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1A flow chart of a method for determining groundwater mixing patterns and proportions in a multi-aquifer system of a mine;

[0027] Figure 2 A graph showing changes in the borehole water level in a mine from 2018 to 2021;

[0028] Figure 3 A cross-section of the aquifer in a mine. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0030] Example 1:

[0031] This example uses a mine as an example. Coal mining and drainage operations in the mine cause changes in the hydraulic connections between different aquifers, resulting in mixing of groundwater from multiple aquifer systems. Due to the complex hydrogeological conditions of the mine, the groundwater mixing pattern and proportion remain to be determined. According to relevant data from the mine, the mine's primary aquifers include the Cenozoic unconsolidated stratum fourth aquifer (hereinafter referred to as "fourth aquifer"), the Permian coal-bearing sandstone fissure aquifer (hereinafter referred to as "coal-bearing water"), and the Carboniferous Taiyuan Formation karst aquifer (hereinafter referred to as "Taiyuan gray water").

[0032] Reference Figure 1 A method for determining the chemical composition and proportions of water in a multi-aquifer system comprises the following steps:

[0033] S1: Data collection: Collect and organize the hydrochemical data, water level data and mineral composition of each water-filled aquifer during mine production, and draw a water level trend chart before and after mine mining.

[0034] The water chemical data of the main water-filled aquifer in the mine is the water sample collected from the underground water hole or outlet during the mine production and sealed and tested. The water chemical data includes Na + , Ca 2+ Mg 2+ 、Cl - 、SO4 2- 、HCO3 - The water chemical data are shown in Table 1, including 3 groups of tetrahedral water, 2 groups of coal-bearing water, and 2 groups of Taihu ash water.

[0035] Table 1

[0036]

[0037] The water level data are from the water level observation holes of the main water - filling aquifers during the mine production. To enhance the intuitiveness and accuracy of the water level data, the average value of each quarter is selected and sorted. The data of 3 water level observation holes from the first quarter of 2018 to the first quarter of 2021 are collected, including 2 Taihui water level observation holes (2005 - Observation 1 and 2012 - Observation 1) and 1 Sihe water level observation hole (2006 - Water 1). Each observation hole has 13 data, totaling 39 data. The positions where the water level data and the hydrochemical data are collected are close to each other.

[0038] S2: Determination of the mixing mode; Analyze the water level changes of the mine aquifers based on the water level trend chart, and combine the water level change characteristics and mixing characteristics of each water - filling aquifer to obtain the recharge relationship between each aquifer. Finally, determine the mixing mode of the groundwater in the multi - aquifer system of the mine.

[0039] From Figure 2 It can be seen that since the first quarter of 2018, the water level of the Sihe observation hole 2006 - Water 1 has gradually decreased. Although the water level rebounded in 2020, the overall water level is still in a downward trend and dropped to the lowest value in the first quarter of 2021.

[0040] From the first quarter of 2018 to the first quarter of 2021, the water levels of the observation holes 2005 - Observation 1 and 2012 - Observation 1 both showed a downward trend. It can be seen that activities such as coal mining and drainage lead to floor mining fissures, causing the water level of the Taihui aquifer to gradually decrease.

[0041] [[ID=|14]]The schematic diagram of the mine aquifer profile is as Figure 3 shown. The judgment basis of the mixing mode is the change trend of the groundwater level during the mining period. There are the following three situations:

[0042] If the water level of the unconsolidated aquifer shows a downward trend, the groundwater mixing mode is the mixing from the unconsolidated aquifer to the coal - measure aquifer;

[0043] If the water level of the confined aquifer shows a downward trend, the groundwater mixing mode is the mixing from the confined aquifer to the coal - measure aquifer;

[0044] If the water level decline characteristics of the confined aquifer and the unconsolidated aquifer are the same, it indicates that there is a certain hydraulic connection between the two aquifers, and the mixing mode is the mixing from the confined aquifer to the unconsolidated aquifer.

[0045] From the above analysis of the aquifer water level data and the types of aquifer mixing patterns, it can be seen that the water levels of the fourth aquifer and the Taiyuan Group limestone aquifer in this mine are gradually decreasing. Since the fourth aquifer is above the coal measure strata and is a loose aquifer, and coal mining activities are carried out in the coal measure strata, the water-richness of the coal measure aquifer is poor and mainly static reserves, so the water in the fourth aquifer mixes with the coal measure water. At the same time, the Taiyuan Group limestone aquifer is above the coal measure aquifer and belongs to a confined aquifer, indicating that the water in the Taiyuan Group limestone aquifer mixes with the coal measure water due to the mining-induced fractures in the floor. In addition, the water level change trends of the water level observation well 2006-Shui 1 in the fourth aquifer and the water level observation well 2012-Guan 1 in the Taiyuan Group limestone aquifer are significantly consistent, which indicates that in the area where the coal measure strata are missing, the lower Taiyuan Group limestone water mixes with the upper fourth aquifer water.

[0046] S3: Establish the inverse model to obtain the preliminary mixing ratio; based on the analysis of the aquifer mixing pattern, select the original mixed source water sample as the initial water sample and the mixed water sample as the final water sample, select the mineral phases according to the aquifer minerals, and input the corresponding hydrochemical data and mineral phases into the PHREEQC software for hydrogeochemical inverse simulation;

[0047] S4: Screen and finally determine the accurate mixing ratio; select the best groundwater mixing ratio according to the mineral composition and proportion characteristics of each aquifer.

[0048] According to the above qualitative analysis of the groundwater mixing pattern in the multi-aquifer system, the hydrochemical data of the aquifers are collected close to the positions of the water level observation wells in this mine, as listed in Table 1. According to Table 1, the hydrochemical data of the fourth aquifer water and the coal measure water are selected, which are Si17, Sha3, and Sha7 respectively. Among them, Sha3 and Si17 are used as the initial water samples, and Sha7 is used as the final water sample. Complete the input of the main ions and pH values of the water samples. Select the possible mineral phases, conduct hydrogeochemical inverse simulation and calculation, and the final mixing ratios are statistically shown in Table 2. It can be seen from Table 2 that in the results, Sha3 accounts for 86.19%, Si17 is mixed in at 13.78%, meeting the requirement that the sum of the proportions is less than 1. Therefore, this ratio is the groundwater mixing ratio at this place.

[0049] Table 2

[0050]

[0051] According to Table 3, the hydrochemical data of the limestone water and the coal measure water are selected, which are Tai9, Sha3, and Sha7 respectively. Among them, Sha3 and Tai9 are used as the initial water samples, and Sha7 is used as the final water sample. Complete the input of Na + , Ca 2+ , Mg 2+ , Cl - , SO4 2- , HCO3 -For the input of the concentration and pH value, select the possible mineral phases, conduct hydrogeochemical inverse simulation, and finally select the appropriate mixing ratio from the operation results as shown in Table 2. It can be seen from Table 2 that in Result A, Sand 3 accounts for 89.13%, and Tai 9 is mixed in at 10.84%; in Result B, Sand 3 accounts for 87.84%, and Tai 9 is mixed in at 12.16%. Based on the mineral characteristics of the Taihuai and coal-bearing aquifers in this mine, the rock salt content is less, and there is CO2 entering the aquifer, so Result A is determined as the final mixing ratio.

[0052] Table 3

[0053]

[0054] According to Table 4, select the hydrochemical data of the limestone water and the fourth aquifer, namely Tai 10, Si 1, and Si 2. Among them, Si 1 and Tai 10 are used as the initial water samples, and Si 2 is used as the final water sample. Complete the input of the concentrations of Na + , Ca 2+ , Mg 2+ , Cl - , SO4 2- , HCO3 - and the pH value, and select the possible mineral phases to conduct the results of hydrogeochemical inverse simulation. Finally, select the appropriate results from the operation results as shown in Table 2. It can be seen from Table 2 that in Result A, Tai 10 accounts for 13.11% and Si 1 accounts for 78.84%; Result B is slightly different from Result A, with Tai 10 accounting for 31.98% and Si 1 accounting for 60.19%. Based on the characteristics of the Taihuai aquifer in this mine containing carbonate minerals such as calcite and dolomite, Result B is selected as the final mixing ratio.

[0055] Table 4

[0056]

[0057] The above embodiments are only the preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention fall within the scope of protection required by the present invention.

Claims

1. A method for determining the groundwater mixing pattern and ratio in a multi-aquifer system of a mine, characterized in that It includes the following steps: S1. Collect and collate the hydrochemical data, water level data of each water - filled aquifer during the mine production period, and the mineral composition of each water - filled aquifer, and draw the water level trend chart before and after the mine exploitation; The water chemical data is obtained by collecting water samples flowing from underground water discharge holes or water outlets during mine production and conducting sealed tests. The water chemical data includes the concentrations of Na + , Ca 2+ , Mg 2+ , Cl - , SO4 2- , HCO3 - and the pH value; The water level data is taken from the water level observation holes of each water - filled aquifer during the mine production period. In order to increase the intuitiveness and accuracy of the water level data, the average value of the water level data of each observation hole per quarter is selected to establish the water level database of different aquifers over the years; S2. Analyze the water level changes of the mine aquifers based on the water level trend chart, combine the water level change characteristics and mixing characteristics of each water - filled aquifer to obtain the recharge relationship between each aquifer, and finally determine the mixing mode of groundwater in the multi - aquifer system of the mine; S3. Based on the analysis of the aquifer mixing mode, select the mixed - source water sample as the initial water sample, the mixed water sample as the final water sample, and select the mineral phase according to the aquifer mineral composition. Input the corresponding hydrochemical data and mineral phase in the water sample into the PHREEQC software for hydrogeochemical inverse simulation, and obtain several groups of mixing ratios after simulation; S4. Select the optimal groundwater mixing ratio according to the mineral composition and proportion characteristics of each aquifer; In step S3, after selecting the initial water sample and the final water sample, complete the input of hydrochemical data, set the mineral phase according to the aquifer mineral composition, use the PHREEQC software for hydrogeochemical simulation, and calculate the mixing ratio; Among the several groups of mixing ratios obtained in step S3, first, according to the principle that the sum of the percentages of the mixing ratios of the initial water sample is less than or equal to 1, and then screen in combination with the mineral phase characteristics of the aquifer; The multi - aquifer system of the mine is, from top to bottom, the unconsolidated aquifer, the coal - measure aquifer, and the confined aquifer; The determination of the mixing mode is based on the following method: If the water level of the unconsolidated aquifer shows a downward trend, the groundwater mixing mode is that the unconsolidated aquifer mixes into the coal - measure aquifer; If the water level of the confined aquifer shows a downward trend, the groundwater mixing mode is that the confined aquifer mixes into the coal - measure aquifer; If the water level decline characteristics of the confined aquifer and the unconsolidated aquifer are the same, it indicates that there is a certain hydraulic connection between the two aquifers, and the mixing mode is that the confined aquifer mixes into the unconsolidated aquifer.

2. The method for determining the groundwater mixing mode and ratio in a multi-aquifer system of a mine according to claim 1, characterized in that In step S1, the sampling location of the hydrochemical data should be within the mine range and close to the water level observation hole.

3. The method for determining the groundwater mixing mode and ratio of a multi-aquifer system in a mine according to claim 1, wherein In step S3, during the simulation, the sampling time of the initial water sample should be before the sampling time of the final water sample.

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