Process and Controlling Factors of Pore Evolution in Marine-Continental Transitional Black Shale—An Example From Permian Shanxi Formation in the Eastern Margin of Ordos Basin

Pore and pore network evolution of shale is critical for the evaluation system in gas reservoirs. Thermal maturation effect acts as an indispensable role porosity evolution. In this paper, high-temperature high-pressure in-situ thermal simulation experiments were conducted to investigate process controlling factors marine-continental transitional shale. Multiple methods, including scanning electron microscopy (SEM), X-ray diffraction, helium porosimetry low-pressure N2 CO2 adsorption used mineral composition structure at different stages maturity. The results showed that type III organic matter (OM) generated petroleum with maturity increasing. total carbon ( TOC ) decreased by 13.3% when temperature reached 607°C. At same time, it produced numerous pores during hydrocarbon generation. Besides, some changes have occurred, especially illite (from 11% 31%) kaolinite 89% 69%). general, can divide into 3 (maturity, high over maturity) low period, large amounts pyrolytic bitumen oil fill pores, causing diminish; a number cracked gas, resulting rapid expansion system; over-maturity cracking pyrolysis slowed down, allowing stabilize. Shale primarily controlled OM, conversion inorganic minerals contributes less compared matter. period (1.2% < Ro 2.0%) was extensive Shanxi Formation shale, which contributed mostly generation accumulation gas.