Micro pore characteristics of Luohe aquifer sandstone in Binchang Mining Area typical roof water hazard mines

The mining of Huanglong Coalfield faces a serious threat from roof sandstone water disaster of the extremely thick Luohe Formation. A laboratory study on the microscopic pore characteristics of the sandstone of the Luohe Formation in the Gaojiapu Coal Mine, Binchang Mining Area were carried out using various methods. XRD diffraction, casting thin sections, and scanning electron microscopy were combined to study the pore types of the sandstone particles. Overburden porosimeter was used to illustrate the variation characteristics of porosity and permeability under different confining pressures. High-pressure mercury injection and nuclear magnetic resonance techniques were used to characterize the pore-throat radius of the sandstone core, and X-ray three-dimensional CT scanning was used to quantitatively characterize sandstone pores larger than 9 μm. The results show that, ①the sandstone particles of medium-grained sandstone are larger, and the pore types are mainly residual intergranular pores with a small amount of intergranular dissolved pores, while the particles of fine-grained sandstone are smaller, and the intergranular pores are mostly filled with clay minerals, secondary dissolution intergranular pores, and a smaller degree of pore development.; ②The pore throat radius of large pores in medium-grained sandstone ranges from 0.61 to 4.94 μm, with a cumulative distribution frequency of 48%, while in fine-grained sandstone, the pore-throat radius ranges from 0.188 to 0.683 um, with a cumulative distribution frequency of 47%, indicating that medium-grained sandstone has larger pore-throat radius, which are more conducive to groundwater storage and migration.; ③CT scanning shows that the average surface porosity of medium-grained sandstone is 7.081%, and that of fine grained sandstone is 2.032%. The highly developed macropores (equivalent pore diameter > 180 μm) and micropores contribute to a higher surface porosity. Combined with a larger pore throat radius, the medium-grained sandstone presents a higher permeability. The microscopic pore characteristics of the two types of sandstone are consistent with the on-site evaluation result of the water yield propertyof the corresponding aquifer. The research findings can provide a basic reference for the prevention and control of water disasters from the sandstone roof of the Luohe Formation.