Shale Pore Evolution Characteristics Based on Semi-Closed Pyrolysis Experiment

The microscopic pore structure of organic-rich shale is an important factor affecting the enrichment of shale gas, but the characteristics of pore structure change during thermal evolution are not clear, which is difficult for the current research.Taking the low-mature oil shale samples of the Middle Permian Lucaogou Formation in the Santanghu Basin, Xinjiang as an example, a high-temperature and high-pressure semi-closed pyrolysis experiment was carried out, and the thermal simulation samples at various temperature stages were extracted, using low-temperature adsorption technique to characterize the pore structure of the un-extracted and extracted sample and to reveal the pore evolution characteristics of the low mature to over mature shale samples.The results show that in the low-mature to mature stage, the content of mesopores decreases with the increase of thermal simulation temperature, and the micropore content decreases first and then rises.High pressure and residual oil/bitumen have certain inhibitory effect for all pores.While at the high maturity stage, the pore content increases significantly, and the micropore and mesopore are generated in the residual bitumen.It indicates that temperature and pressure conditions have important influence on pore structure in thermal simulation experiments.The thermal evolution of organic matter and its evolution products are closely related to the evolution trend of shale pores.