Dyes and Isotopes Track Groundwater from Sink to Spring

The hydraulic connection between a sinkhole and a natural spring—the longest and largest yet documented—could help reduce the guesswork in mapping karst aquifers.

Identification of Hydraulic Connection Points between Different Confined Aquifers in the Liyazhuang Coal Mine

Water inrush from coal seam floors is one major geological obstacle hindering safe and efficient production activities in mines. Determining the source of water inrush can facilitate its prediction and guide decisions regarding measures for prevention and control. The process of identifying the location of hidden hydraulic contact points in different confined aquifers forms the basis of hydrogeological explorations. It is also the basis for categorizing mine areas prone to water inrush and making qualitative decisions regarding the prevention and control of water inrush. In this study, the positions of hidden hydraulic contact points between the Ordovician Fengfeng and Shangmajiagou formations in the basement of the Liyazhuang coal mine were determined using numerical simulations of the flow fields. First, each node of the finite element grid was considered as a water inrush point to determine the water level at other nodes. Subsequently, the error between measured and simulated water levels, determined based on the flow fields, was determined using the least squares method. The node with the minimum error was then considered as the hidden hydraulic contact point. The simulation results for the flow field indicate a distance of 5000 m between the hydraulic connection and the water inrush points located between the peak formation and the Majiagou aquifer in the Liyazhuang coal mine. Furthermore, the hydraulic relationship between them is poor. Observational data of water inrush from the floor of the No. 2 coal seam and the water level of the confined aquifer in the Liyazhuang coal mine, including the water quality test data of different Ordovician ash aquifers, show that the source of water inrush from the floor of the No. 2 coal seam is the aquifer of the Fengfeng Formation. This finding is consistent with the results of the numerical simulations of the flow field. The results demonstrate that, in mining areas subjected to high pressures, numerical simulations of the flow field can serve as an effective tool for determining the location of hidden hydraulic contact points.

Analysis of the Karst Development Law Based on Multiple Exploration Technologies of Cambrian Limestone

Coal mine floor limestone aquifers are a major source of water inrush from the coal seam floor and a serious threat to the safety of coal mining. In order to reduce and avoid the occurrence of water inrush within the coal mine, we use multiple detection techniques, which are geophysical exploration technology , drilling technology, water inrush accidents and tracer test, to develop a multi-faceted exploration of karst development and analyze its development characteristics in the Chaochuan mine No. 1 well of Pingdingshan Coal Co.Ltd, Henan Province, China. The results show that, the Cambrian limestone (CL) karst water is poor; there is a certain hydraulic connection. Near faults F5, F1, and SF28, the area is less water-rich area, the water is weak, and the deep karst water forms a closed area; 61.54 % of shallow water inrush accidents in the Taiyuan limestone and CL karsts were caused by large tectonic and nearby shallow faults. The karst vertical zonation is shallow; the shallow water level decreased more in the West Wing of the No. 1 well than in the East Wing at elevations above 140 m and below -150 m. The F125 level decline is greater than that of the east, and the west fault is more than 170 m due to the hydraulic connection intrusive barrier wings of the karst water. the East Wing below -150 m F125 fault was weak and uneven on both sides of the hydraulic connection.

Potential influence of overpressurized gas on the induced seismicity in the St. Gallen deep geothermal project (Switzerland)

In July 2013, the city of St. Gallen conducted a deep geothermal project that aimed to exploit energy for district heating and generating power. A few days after an injection test and two acid stimulations that caused only minor seismicity, a gas kick forced the operators to inject drilling mud to combat the kick. Subsequently, multiple earthquakes were induced on a fault several hundred meters away from the well, including a ML 3.5 event that was felt throughout the nearby population centers. Given the occurrence of a gas kick and a felt seismic sequence with low total injected fluid volumes (∼1200 m3), the St. Gallen deep geothermal project represents a particularly interesting case study of induced seismicity. Here, we first present a conceptual model based on seismic, borehole, and seismological data suggesting a hydraulic connection between the well and the fault. The overpressurized gas, which is assumed to be initially sealed by the fault, may have been released due to the stimulations before entering the well via the hydraulic connection. We test this hypothesis with a numerical model calibrated against the borehole pressure of the injection test. We successfully reproduce the gas kick and spatiotemporal characteristics of the main seismicity sequence following the well control operation. The results indicate that the gas may have destabilized the fault during and after the injection operations and could have enhanced the resulting seismicity. This study may have implications for future deep hydrothermal projects conducted in similar geological conditions with potentially overpressurized in-place gas.