Influence of different thermal evolution stages on shale pore development

Different thermal evolution degrees on pore development were studied by cryogenic nitrogen adsorption experiment and microscopic photometric analysis. The organic matter Ro, the pore volume, and the proportion of different pore types are different in the Qingshankou Formation, Longmaxi Formation, and Niutitang Formation. However, the relationship between pore development and thermal evolution is consistent. With increasing the degree of the thermal evolution of organic matter holes appear three different change rules. When the organic matter Ro is less than 1.2, shale porosity is mainly influenced by physical compaction and cementation, shale organic hole filling. With the increase of Ro, the porosity tends to decrease, and when Ro is between 1.2 and 3.0, the organic matter of pyrolysis hydrocarbon generation and organic matter hydrocarbon generation hole and corrosion hole a lot of development, the stage total shale porosity is lower before the rising trend, organic matter porosity increased with the increase of Ro. When Ro is greater than 3.0 (overmaturity stage), graphitization occurs. Under the influence of deep burial and slow compaction, the porosity is decreasing continuously.