Evolutionary characteristics of sandstone pore-fracture structure under the action of high and low temperature cyclic impact

WANG Jiachang; KANG Jianting; KANG Tianhe; ZHENG Yawei; YAN Jiaxin; ZHANG Huihui; LIANG Xiaomin

doi:10.13199/j.cnki.cst.2022-1774

Abstract：China is rich in coal-measure gas reserves.However,the complex geological conditions of coal-measure gas reservoirs make it costly and inefficient to mine a single gas-bearing system,and difficult to co-mine multiple gas-bearing systems.How to improve the per-meability and compatibility of coal reservoirs is the key issue in development of coal-measure gas.In order to explore effective methods to improve the structure of coal reservoirs,the evolution characteristics of sandstone pore-fracture in the top plate of coal seams under the cyclic impacts of high temper-ature(200℃)and low temperature(-196℃)were investigated.The development of sandstone pore-frac-ture before and after high-and low-temperature impacts was characterized using industrial micro-CT.The CT data of the specimens be-fore and after impact were filtered and homogenized using digital image and three-dimensional reconstruction techniques.The changes of volume,surface area,porosity and fractal dimension of distribution complexity of sandstone pore-fracture after 0,1,5,10 and 15 high-and low-temperature impacts were qualitatively and quantitatively analyzed.The results shown that:①High-and low-temperature cyclic im-pacts promoted the development,expansion and connectivity of pore-fracture,and the sprouting of secondary fracture in sandstone.The impacts contributed to the expansion of micro pore-fracture to form larger macro fracture;②The volume,surface area,porosity and fractal dimension of distribution complexity of sandstone pore-fracture varied logarithmically with the increase of the number of temperat-ure impacts,and the growth tended to increase first and then decrease.The increase of its area and porosity reached a maximum of 15.48%and 20.98%,respectively,after the 5th impact effect;③High-and low-temperature cyclic impacts weakened the binding force between the sandstone matrix and broke the original static equilibrium.The variation curve of sandstone porosity with the number of scanned lay-ers evolved into a"C-like"shape,which indicated that the binding force at the ends of the sandstone was more attenuated.