Exploring the vertical heterogeneity of extremely thick aquifers in coal mines through layered fine-scale pumping tests

ObjectiveExtremely thick aquifers in mining areas typically exhibit strong heterogeneity and high water yield. Therefore, they are prone to cause severe water inflow in mines and induce water disasters, representing a major factor affecting the mining safety of numerous mines in China. However, the vertical heterogeneity of these aquifers remains poorly understood, emerging as a primary bottleneck in the prevention and control of such water hazards. MethodsTo scientifically reveal the vertical heterogeneity characteristics of extremely thick aquifers, this study investigated the extremely thick Luohe Formation aquifer in a coal seam roof of a representative coal mine in the Huanglong coalfield, Shaanxi Province. Focusing on the core concept of layered fine-scale investigation and using methods including theoretical analysis, field experiment, and laboratory test, this study conducted pumping tests, as well as relevant analyses and testing, of the aquifer based on nine layers in a single borehole.Results and ConclusionsA new test method for equal-diameter, layered, fine-scale pumping using a single hydrological borehole was developed. Through generalization, a model of flow into a partially penetrating well was established for single-borehole, layered aquifer pumping. Furthermore, an analytical method for calculating hydrogeological parameters, tailored to layered pumping, was derived. Accordingly, the process and construction method for layered pumping tests on extremely thick aquifers were established. The permeability coefficients and unit water yield of the nine layers of the Luohe Formation aquifer were calculated based on field test results. Concurrently, the groundwater levels, temperatures, and hydrochemical characteristics of the layers were determined, followed by the analysis of layers with close hydraulic connections. Based on various calculated and analytical results, the Luohe Formation aquifer was divided into upper, middle, and lower segments, with the lower segment subdivided into lower sub-segments 1 and 2. Then, the equivalent permeability coefficients of these segments were calculated. The water inflow of a mining face in a representative mine of the Huanglong coalfield was predicted using relevant parameters. The prediction results were then compared with the actual water inflow to verify the reliability of the parameter estimation methods. The results of this study can provide significant guidance for gaining scientifically robust insights into the heterogeneous structure of extremely thick aquifers in mining areas and for assessing the degree of influence of these aquifers on water filling in mines.