Thermal simulation experiment of organic matter-rich shale and implication for organic pore formation and evolution

A thermal simulation experiment of diagenesis, hydrocarbon generation and evolution of the organic matter-rich shale was carried out to investigate formation and evolution of organic pores under the constraint from immature, low mature, mature, high mature to overmature geological conditions. The argon ion polishing–field emission scanning electron microscope was used to analyze microscopic features of original samples and simulated samples of various evolution stages. Results showed organic pores could be formed during hydrocarbon generation from biochemical and hypothermal processes in the immature and low mature stages, and the shale shallow-buried depth might be favorable for preservation of organic pores; the generation and evolution of organic pores were of heterogeneity, and the maturity was not a decisive factor which controlled formation and development of organic pores, while the difference in physiochemical structure of organic matter played an important role in formation and evolution of organic pores; the organic pore development was obviously related with the retained oil, and the organic pores formed in the oil generation stage were easily filled by pyrolysis asphalt; organic contraction fractures/organic marginal pores might be important storage spaces for shale gas occurrence, and their development was mainly controlled by the physiochemical structure and evolution degree of organic matters when the chemical adsorbed organic matter was converted into the physical adsorbed organic matter and the free organic matter. Keywords: Thermal simulation experiment, Organic pores, Thermal evolution stage, Heterogeneity, Plane porosity, Retained oil, Shale