Optimization of Water Pumping and Injection for Underground Coal Gasification in the Meiguiying Mine,China

The Meiguiying mine is a famous underground coal gasification (UCG) mine in China, but there has been a potential safety hazard since it began operating, that groundwater in the overlying aquifer might enter the mine and even extinguish the gasifier. A 3-D hydrogeological model was developed to explore the characteristics of the seepage field of the aquifer and determine an optimal water pumping and injection option for the UCG. The results indicate that more attention should be paid to control induced fractures of the roof due to the increasing water level of the aquifer, and that a pumping rate of 160 m³/day would decrease the water level to a reasonable elevation. Moreover, to maintain the groundwater table and mine safety, 120 m³/day was recommended as a reasonable and economical recharge (re-injection) rate in the study area.     

Numerical Simulation of Mine Water Inflow with an Embedded Discrete Fracture Model: Application to the 16112 Working Face in the Binhu Coal Mine,China

Properly accounting for the effect of heterogeneity of aquifers and accurately predicting mine water inflow during the mining process is still a challenging problem in China. We developed a stochastic modelling methodology that considers a large range of possible multi-scale fracture configurations and heterogeneous porous rock to predict mine water inflow close to the observed data. The coupled discrete fracture–rock matrix models were built for the Binhu coal mine 16,112 working face with the Monte Carlo method. The models were solved using the embedded discrete fracture model to calculate groundwater inflow from the aquifer beneath the coal seam floor. The calculated results and the observed groundwater inflows in the field agreed well. Sensitivity analysis indicates that groundwater inflow increases with increased fracture length and fracture density. The effect of natural fractures introduces a large uncertainty for the models, due to the existence of long fractures that could act as conduits between the Ordovician limestone and no. 14 aquifers. The results highlight the importance of multi-scale fractures on modeling and simulating flow in the mine area.

     

Geothermal Water at a Coal Mine: From Risk to Resource

Geothermal water from a Cambrian limestone aquifer presented a flooding risk at the No. 8 coal 2₁ mine near Pingdingshan City, China. The water-bearing zones were identified using the mine transient electromagnetic method and direct current prospecting, and a groundwater drainage system was installed. After water drainage was implemented, the water level in the limestone near the haulway dropped 17.2 m in 277 days, greatly reducing the risk of a mine water inrush. The water quality, quantity, and temperature allowed it to be used for mineral baths, resulting in energy savings and emission reductions.     

Using Multiple Methods to Predict Mine Water Inflow in the Pingdingshan No. 10 Coal Mine,China

To ensure safe mining of the no. 2 coal seam in the Pingdingshan No. 10 coal mine, three methods (analogue, big well, and numerical simulation) were used to forecast mine water inflow and their performance. The big well method predicted the largest water inflow: 233.8 m³/h in the ?230 m level and 281.1 m³/h in the ?300 m level. The numerical simulation predicted the least inflow, 205.7 and 228.6 m³/h respectively for the 230 and ?300 m levels; this was closest to the measured values. Based on this work, it appears that combining numerical simulations with other methods are a good way to accurately forecast mine water inflow.     

Geochemistry,Hydraulic Connectivity and Quality Appraisal of Multilayered Groundwater in the Hongdunzi Coal Mine,Northwest China

This study assessed the geochemistry and quality of groundwater in the Hongdunzi coal mining area in northwest China and investigated the mechanisms governing its hydrogeochemistry and the hydraulic connectivity between adjacent aquifers. Thirty-four groundwater samples were collected for physicochemical analyses and bivariate analyses were used to investigate groundwater quality evolution. The groundwater in the mine was determined to be neutral to slightly alkaline, with high levels of salinity and hardness; most samples were of SO₄·Cl–Na type. Fluoride and nitrate pollution in the confined aquifers were identified, primarily sourced from coals. Natural geochemical processes, such as mineral dissolution, cation exchange, and groundwater evaporation, largely control groundwater chemistry. Anthropogenic inputs from agricultural and mining activities were also identified in both shallow unconfined aquifers and the deeper confined aquifers, respectively. It was determined that the middle confined aquifer has a high hydraulic connectivity with the lower coal-bearing aquifer due to developed fractures. Careful management of the overlying aquifers is required to avoid mine water inrush geohazards and groundwater quality deterioration. The groundwater in the mining area is generally of poor quality, and is unsuitable for direct human consumption or irrigation. Na⁺, SO₄^2?, Cl^?, F^?, TH, TDS, NO₃^?, and COD_Mn are the major factors responsible for the poor quality of the phreatic water, while Na⁺, SO₄^2?, F^?, and TDS are the major constituents affecting the confined groundwater quality. This study is beneficial for understanding the impacts of coal mine development on groundwater quality, and safeguarding sustainable mining in arid areas.     

Hydrochemical Characteristics and Groundwater Source Identification of a Multiple Aquifer System in a Coal Mine

Hydrochemical analysis and Bayesian discrimination were used to identify groundwater sources for multiple aquifers in the Panyi Coal Mine, Anhui, China. The results showed that the Cenozoic top aquifer water were HCO₃?Na+K?Ca and HCO₃?Na+K?Mg types, which distinguished it from the other aquifers due to its low Na⁺?+?K⁺ and Cl^? concentrations. The Cenozoic middle and Cenozoic bottom aquifer waters were mainly Cl?Na+K and SO₄?Cl?Na+K types. The water types in the Permian fractured aquifer changed from Cl?Na+K to HCO₃?Cl?Na+K and HCO₃?Na+K moving away from the Panji anticline. In addition, HCO₃ ^? concentrations increased and Ca²⁺ concentrations decreased with depth in the aquifer. The Taiyuan limestone aquifers were of Cl?Na+K, SO₄·Cl?Na+K, and HCO₃·Cl?Na+K types, and are very difficult to distinguish from the other aquifers. The precision of the Bayesian discrimination based on groundwater chemistry was 86.09%. Water chemistry indicators in the Permian fractured aquifer were moderately to highly variable and moderately to strongly correlated, spatially. The water chemistry spatial distribution indicates that the Permian fractured aquifer is recharged by the Cenozoic bottom aquifer near the Panji anticline, which reduces the accuracy of Bayesian discrimination in that area.     

Hydrogeochemical Processes of Carboniferous Limestone Groundwater in the Yangzhuang Coal Mine,Huaibei Coalfield,China

We examined the primary mechanisms controlling water quality evolution in the Carboniferous aquifer in the Yangzhuang coal mine (Huaibei coalfield). Q-mode factor analysis explained how the Na⁺ and SO₄^2? concentrations gradually increase and the hydrochemical type transforms from Ca-HCO₃ to Ca·Na-HCO₃ and Ca·Na-HCO₃·SO₄ along the flow path. The high bicarbonate concentration appears to be due to dissolution of calcite and dolomite and an open carbonate system, while frequent water inrushes and the declining water level provide evidence for the relative closure of the Carboniferous limestone aquifer. Gypsum dissolution is the main SO₄^2? source. Inverse geochemical modeling sufficiently explained the hydrogeochemical processes that control the water quality evolution. These findings should aid the interpretation of groundwater hydrochemical evolution and groundwater quality management in the study area and other north China coalfields.

     

Prevention of Groundwater Disasters in Coal Seam Floors Based on TEM of Cambrian Limestone

We analyzed the abundance and connectivity of Cambrian limestone aquifers (CL) using data from geological and hydrogeological boreholes, groundwater tracer tests, groundwater temperature monitoring, and surface transient electromagnetic exploration (TEM). Our results demonstrate that extremely well-developed small faults with an average density of number 73 per square km control the groundwater abundance and flow of the CL. The hydraulic conductivity of the CL aquifers estimated by tracer tests lies between 13,511 and 38,738 m/d, suggesting good connectivity. The surface TEM result of 4.91 km² shows that areas with an apparent resistivity value less than 30 Ωm can be treated as an anomalous low-resistivity zone. This has been proven to be reliable by experience at the working face and can be used to determine water control measures for future mining. Using these data, we developed a series of preventive measures to mitigate potential floor water ingress related to future mining in the eastern area of the Pingdingshan coalfield No. 2 mine.     

Prediction Reliability of Water Inrush Through the Coal Mine Floor

Inrush of Ordovician limestone karst water through the mine floor occurs frequently in the Carboniferous-Permian coalfield in northern China. A probability index method was proposed to predict water inrushes using five indices: an aquifer water-bearing index, a structural index, an aquifuge index, an aquifer water pressure index, and an underground pressure index. Expert input was used to obtain weights for these five factors. Expert evaluation and statistical probability were then used to determine weights of the subsidiary factors, allowing the calculation of a water inrush probability index (I) and a threshold water inrush value for the Feicheng coalfield of 0.65. The Dempster-Shafer evidence theory was then used to determine a 74% degree of confidence for this prediction. Finally, the method was applied to the No. 9901 working face of the Taoyang coal mine. A subsequent 1,083 m³/h water inrush that occurred there aligned with the statistical results.     

Study of Mine Water Inrush from Floor Strata through Faults

The mechanism of mine water inrushes in coal mines in China differs considerably from that in other countries. In China, most water inrushes occur from floor strata, the source of water inrush being karstic limestone aquifers. This paper describes the mechanism of mine water inrushes through a fault in the mine floor using principles of strata mechanics, and the path of water inrush from an aquifer to the working face. A criterion to judge whether the ground water inrush will occur through a fault or not is also described, together with a case history of water inflow in Feicheng Coalfield, China.     

Hydrogeochemical Processes and Inverse Modeling for a Multilayer Aquifer System in the Yuaner Coal Mine,Huaibei Coalfield,China

Coal mining can dramatically change hydrogeological conditions and induce serious environmental problems. Fifty groundwater samples were collected from the main aquifers in the Yuaner coal mine (Anhui Province, China). The results show that the main hydrogeochemical processes in the mine include dissolution, precipitation, pyrite oxidation, desulfurization, and cation exchange. The Neogene porous aquifer is affected by groundwater flow conditions; its main hydrogeochemical processes are dissolution of carbonate minerals and gypsum, and cation exchange. The Permian coal measure’s fractured sandstone aquifer was confirmed to be controlled by the region’s geological structure; its main hydrogeochemical processes are desulfurization and cation exchange. The Carboniferous Taiyuan limestone aquifer was determined by both groundwater flow conditions and regional geological structure; its main hydrogeochemical processes are dissolution of carbonate minerals and gypsum, pyrite oxidation, and cation exchange. Additionally, hydrogeochemical inverse modeling of the groundwater flow path confirm the hydrochemistry results and principal component analysis.

     

乌东煤矿地下水水化学特征及其指示

为了研究乌东煤矿煤层顶板含水层之间的水力联系,采用了统计分析、Piper三线图、Gibbs图等方法定性分析了基岩地下水、第四系地下水以及地表水之间的水力联系。利用不同水体的Cl-浓度差异性,计算了相邻含水层之间的水力联系度,定量判别了它们之间的水力联系程度。结果发现,所有地下水样品的pH介于7.1～8之间,都为弱碱性水。随着含水层埋深的加大,地下水TDS逐渐增大,地表水和第四系地下水TDS均低于基岩含水层地下水。基岩地下水、第四系地下水和地表水主要的水化学类型分别为Cl·SO4-Na、HCO3·SO4-Na·Ca、SO4·Cl·HCO3-Na和SO4·Cl·HCO3-Na·Ca。基岩地下水样品受到浓缩作用影响,地表水和第四系地下水受到岩石风化-蒸发影响。同时研究区地下水和地表水中还发生了阳离子反交换作用。第四系地下水和地表水的联系度为0.361,联系程度为中等|第四系和基岩地下水之间的联系度为0.404,联系程度为低。此结果可为后期矿井涌水量预计及防治水工作提供参考依据。     

Relevance Between Hydrochemical and Hydrodynamic Data in a Deep Karstified Limestone Aquifer: a Mining Area Case Study

Safe coal mining in a karst region requires that mining operations assess any disturbances in the hydrogeological functioning of local aquifers and flow systems, and determine if disruptions are likely in the mine. We studied the geologic, hydraulic, and geochemical characteristics of the deep Ordovician karstified aquifer in the Xinglongzhuang and Dongtan mines of the Yanzhou coal mining district (China). The presence of a 100 m deep research borehole in the Ordovician limestone aquifer nearby facilitated hydrochemical and hydrodynamic data collection. The buried depth affected karst rock porosity, and the reduced porosity increased karst development. This, in turn, affected the abundance of water in the karst fissure. In addition to calcite and dolomite, the Ordovician limestone contains gypsum, which dissolves to form sulfate ions. Hydraulic data revealed that the water abundance in the research area is comparatively low, except for the C8 syncline zone. The Ordovician strata in this area is located in the deep, slow-flow zone of a vertical karst aquifer system, and the drilling unit water inflow is very low, which could represent the water abundance of the aquifer. Understanding this complex flow system is critical to appropriately assess the area’s deep groundwater resources and guide decision making regarding coal extraction.     

Evaluating Induced Fractures Between a Large Artificial Lake and an Aquifer-Coal Seam System: A Case Study in Tangshan Coal Mine,China

The hydrogeology of the Tangshan coal mine is extremely complicated. There are at least 20 major faults, with the offset exceeding 50 m. A large artificial lake was created where mining-induced subsidence occurred; it was filled with groundwater pumped from the adjacent aquifers near the coal seams. In addition, there are two nearby rivers that are also believed to have significant groundwater and surface water interactions. Both the river system and the large lake could be a potential threat to a new mining operation in the deep no. 5 coal seam. An in-situ hybrid packer system was designed to measure the thickness of the fracture zone and a 3-D hydrogeological model of the coal seam, associated aquifers, artificial lake, and surface water was established to simulate the groundwater flow field to evaluate the potential impact of induced fractures between the lake and the aquifers and coal seams. The results indicated that the lake has an insignificant impact on the aquifers and coal seams, though it does influence the shallow quaternary aquifer in the study area. Further study is suggested to monitor the groundwater and surface water interactions between the lake and the shallow aquifer system.     

深层地下水氢氧稳定同位素组成与水循环示踪

利用任楼井田及所在临涣矿区地表水与生产矿井的长观孔、矿井出水点,从上而下分别取第四系第四含水层、二叠系煤系砂岩含水层、石炭系太原组岩溶含水层及奥陶系岩溶含水层30个水样,测试δD与δ¹⁸O,分析D与¹⁸O组成并对含水层水循环进行示踪.研究表明：临涣矿区深部地下水样点δ值在δD－δ¹⁸O关系图上绝大部分均落在中国大气降水线和矿区地表水线下部,大气降水或地表水为各类含水层的补给主体.任楼井田煤炭采动影响第四系第四含水层明显,地表水补给第四系第四含水层速度快;临涣矿区的临涣、海孜与童亭四含水与大气降水未构成良好的水力联系.煤系砂岩地下水就整个临涣矿区来说,任楼井田埋藏相对较新.石炭系太原组岩溶含水层及奥陶系岩溶含水层在临涣矿区地下水径流速度相对较快,¹⁸O或D漂移不明显.     

小屯煤矿无机和有机水化学特征及水源判别研究

为了准确判别小屯煤矿井下突水水源,在小屯矿区开展了无机和有机水化学特征研究。结果表明,研究区内玉龙山灰岩水、长兴灰岩水与第四系水或地表水存在密切水力联系,夜郎组玉龙山段含水层与长兴灰岩含水层之间水力联系密切;大气降水与玉龙山灰岩水联系密切,采空区水与地表、地下水区别较大;大气降水直接补给长兴组灰岩含水层,经含水层涌入矿井,可以根据突水中DOM特征,判别采空区水突水水源。     

薛湖煤矿矿井充水主控因素与矿井涌水量预测研究

河南薛湖煤矿在开采过程中受到了水害的影响,为了确保煤矿安全、高效生产,分析了矿井水文地质条件,研究了矿井冲水的主控因素,并对矿井涌水量进行预测计算。研究结果表明,薛湖煤矿矿区发育六大含水层（组）和三大隔水层（组）,煤系地层的二叠系砂岩裂隙含水层是危害矿井生产的主要含水层,随着生产的进行,顶板砂岩水多被疏干,对生产的安全不会造成很大的影响。二2主采煤层的直接充水水源为二叠系二2煤层顶板砂岩裂隙承压水,间接充水水源为二2煤层底板和奥陶系灰岩岩溶裂隙承压水,矿井的自身采空区积水是薛湖矿的充水水源之一。二2煤的导水途径主要有裂隙、断层和封闭不良钻孔3种,高角度正断层可能成为导水通道。越往深部开采水压将会越大,构造和裂隙的发育增加了底板水涌入矿井的危险。选取比拟法和稳定流解析法对采区矿井涌水量进行计算,比拟法计算的全矿井正常涌水量656 m 3/h、最大涌水量787 m 3/h比较符合近年来矿井充水的实际情况,可以作为下一步矿井开采的依据。但随着开采水平的不断延深,太灰岩溶水向矿井突水的概率也将大大提高,若出现短期内多点突水情况,将会超过比拟法预算的最大涌水量。     

Environmental Isotope Investigation of Groundwater in the Sarcheshmeh Copper Mine Area,Iran

Precipitation, surface, and groundwater samples were collected during 2009–2010 in the Sarcheshmeh copper mine drainage basin, Kerman Province, Iran. Groundwater samples were collected from both shallow and deep aquifers. All of the samples were analyzed for stable isotopes, deuterium (²H), and oxygen-18 (¹⁸O), and some were analyzed for tritium (³H). The results show a more restricted range of isotopic composition in groundwater samples than in precipitation samples based on the isotopic composition of the precipitation. The isotopic composition of surface and groundwater samples plot to the right of the local meteoric water line of the Sarcheshmeh area and around the evaporation line, indicating that the groundwater within the study area originates from meteoric water that has undergone secondary evaporation before or during recharge. Tritium was below the detection limit in the deep groundwater samples while shallow groundwater samples had tritium concentrations between 1.2 and 1.7 TU, which indicates a longer residence time for deep groundwater.     

皖北桃源矿深部含水层地下水地球化学数理统计分析

为查明皖北桃源煤矿煤系砂岩和灰岩含水层的水文地球化学特征及其主要控制因素,进而为深部水岩相互作用研究和水源识别提供信息,对22个水样品（10个煤系砂岩水、12个太灰水）的常规水化学组成进行了测试,并进行了包括因子、聚类和判别分析在内的多种数理统计以及离子相关性分析。结果表明：煤系砂岩和太灰水在离子含量上存在区别,前者水化学类型为SO4-Na型,而后者为SO4-Ca型。两个含水层的地下水样品化学组成与碳酸盐、硫酸盐及氯盐矿物的溶解以及硅酸盐矿物的风化有关。聚类分析结果表明,桃源矿煤系砂岩含水层部分样品在水化学特征上与太灰含水层相关,表明其可能受到了灰岩含水层的影响。此外,通过判别分析建立了识别煤系砂岩水和太灰水的判别方程,该方程不仅可以用于识别典型的煤系砂岩水和太灰水,也可以用于计算两者混合水的相对比例。     

张村矿断层突水特征分析研究

 针对张村矿断层突水问题,分析了矿区断层分布规律。基于距离判别法对张村矿主要影响断层突水等级进行了判别分析,结果表明：因煤层与太原组石灰岩之间的隔水层太薄,小于底板采动破坏深度,太原组石灰岩水比寒武系石灰岩水更容易发生突水;断层落差越大,在高水压作用下突水或涌水量会增大,因为断层的落差大小决定了其切割深度,其富水性会越强。分析结果与矿区实际情况和瞬变电磁探测结果是吻合的。根据研究结果提出矿区断层突水防治措施,对于矿井安全生产具有一定的指导意义。