Dynamic Evolution Mechanism of Reservoir Physical Properties during Oil Shale In Situ Conversion

Oil shale in situ conversion is a process where the generated crude oil and the unconverted solid organic matter in immature to lowly mature shales are converted to light oil and gas via artificial heating. The focus of this study was to solve the engineering problems in shale oil production and establish quantitative evaluation models of the dynamic physical properties of reservoirs during shale in situ conversion. Based on thermal pyrolysis experiments, it is concluded that the total organic carbon (TOC) coupled with temperature controls the dynamic reservoir physical properties during shale in situ conversion. After heating, the porosity and permeability can increase 4-fold and 10-fold, respectively. The physical properties of the shale reservoir at the same thermal pyrolysis temperature show a good power positive correlation with the TOC. In addition, the permeability anisotropy value showed that the horizontal permeability (Kh) is larger than the vertical permeability (Kv). Kh/Kv increased as the temperature increased. Furthermore, Kh/Kv shows a good positive exponential correlation with porosity. The evaluation model of porosity with the TOC and temperature has been established based on the thermal pyrolysis data. There is a good positive correlation between permeability and porosity, and the evaluation model of permeability and Kv has been established using porosity. The results provide models for reservoir dynamic physical property prediction during shale in situ conversion. Furthermore, the results provide guidance on shale mechanics anisotropy for furthering fracturing engineering.