Developmental characteristics and genetic model of Ordovician karst porosity in the southern margin of Northern China.

Ordovician carbonate rocks are not only important reservoirs for oil, gas, and water but also important targets for water hazard prevention and control in the coal mining process. However, the developmental characteristics and distribution laws of the Ordovician karst in the southern margin of Northern China are still unknown, causing frequent karst water disasters and poor water blocking effect by grouting. This study focused on such issues based on field investigation, core analysis, thin section observation, conventional logging, and 3D seismic data analysis of Ordovician karst in the Huainan Coalfield in the southern margin of Northern China. The results indicate that the Ordovician karst porosity in the Huainan Coalfield consists mainly of fractures, vugs, and caves and that the fractures are primarily structural fractures. The degree of filling varies greatly among karst porosity types, with fractures and caves mostly filled, followed by semi-filled and unfilled. The vugs are mainly semi-filled, followed by unfilled, and rarely filled. In planes, fractures and caves are mainly distributed on both sides of the faults and decrease exponentially with the distance from the faults. In the cross section, fractures, vugs, and caves are widespread from 0 to 80 m above the Ordovician weathered crust, indicating that they serve as major reservoirs and migration channels for karst groundwater. On the other hand, the depth below 80 m is a weak karst development zone, with undeveloped fractures, vugs, and caves. The Ordovician weathered crust and faulting mainly control the development and distribution of Ordovician karst in the Huainan Coalfield. This phenomenon is thought to be the result of multi-stage karstification succession and superposition. This study promotes an understanding of the developmental characteristics and genetics of Ordovician karst in the southern margin of Northern. It also provides important suggestions and guidelines for preventing and controlling Ordovician karst water hazards in the study area. [ABSTRACT FROM AUTHOR]