Evolution of Shale Microstructure under in Situ Heat Treatment: Synchrotron Small-Angle X-ray Scattering
Linhao Zhang, Mengdi Sun, Qi Lv, Chima Finnian Ukaomah, Qinhong Hu, Bingsong Yu, Jiehui Zhang, Xing Liang, Gaocheng Wang, Shu Jiang
Abstract
Shale gas reservoirs are characterized by low porosity and low permeability which inhibits their large-scale commercial development. This has fueled research into the enhancement of gas recovery from shale reservoirs. In this study, a new method of increasing gas production by heating is proposed. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to analyze the mass loss curve and enthalpy change of shale during heating. The phase state changes of mineral composition during heating of organic-rich shale were also obtained. The pore distribution of shale samples during heat treatment was compared by using small-angle X-ray scattering technology, and the influence of heat on shale pore structure was analyzed. The results show that the thermal effect accelerates the increase in the number and size of micro-/nanopores in shale samples. This effectively improves the permeability of shale samples and induces the free migration of gas. In addition, the difference in the specific heat capacity of each mineral in shale samples will cause an inhomogeneous temperature distribution. Thermal stress causes the fracture of mineral crystals in shale, and the shrinkage between mineral particles causes the development of fractures in the shale matrix, which improves the shale gas reservoir permeability. Hence, in situ heat treatment is an efficient stimulation method for enhancing shale gas recovery.