Pore media characteristics of Jurassic weak cemented sandstone and its significance for water-preserved coal mining

Hami mining area of Xinjiang has the characteristic of little rainfall and strong evaporation,which is a seri- ous arid area. With the high-intensity coal resources mined in study area,the protection of aquifers is extremely impor- tant for coal mining. Due to the special diagenetic environment and migration conditions,Jurassic weak cemented sand- stone is a complex water-bearing rock system,which brings many hydrogeological problems to the water control of coal mine in the study area. Taking the Jurassic weak cemented sandstone in Hami mining area as a research topic,the evo- lution of micropore structure of weak cemented sandstone was studied through seepage experiment,laboratory test and theoretical analysis. The result shows that the weak cemented sandstone is characterized by its large pore and middle pore throat concentrated distribution and strong watery,belonging to high porosity rock,and a large amount of milky suspension is exuded in the seepage experiment. Due to the seepage action,the weak cemented sandstone shows an in- crease in permeability because of the dissolution of soluble salts and kaolinite and increases in porosity obviously. Through water quality and rock mineral identification analysis,the effect of soluble salt dissolution on the increase of porosity is 45. 80% -82. 28% ,and the effect of suspended solids exudation on the increase of porosity is 14. 78% -54. 20% after the seepage experiment. The dissolution of soluble salts and kaolinite are the main factors for the en- hancement of sandstone permeability. The concept of water-preserved coal mining was proposed based on the water storage spatial variability of pore structure and permeability mutation,and the idea of “protective mining and avoiding large-scale disturbances” for water-preserved coal mining should be followed below the weak cemented sandstone aqui- fer. The research results have significance for the development,utilization and protection of weak cemented sandstone aquifers in the western region. At the same time,it can provide a theoretical and practical basis for the study of water- preserved coal mining technology affected by the Jurassic weak cemented sandstone water damage in the western region in China.