Pore Fractal and Structure Analysis of Pore-Filling Chlorite in Continental Shales: A Case Study from the Qingshankou Formation in the Gulong Sag

The successful exploration and development of shale oil in the clay-rich Gulong shale have sparked increased research into the influence of clay minerals on shale reservoirs. However, compared to chlorite in sandstones, limited studies have focused on the occurrence of chlorite in continental shales and its effects on shale reservoir properties. This study offers a comprehensive analysis of chlorite in Gulong shale samples from three wells at different diagenetic stages. Four primary chlorite occurrences are identified in the Gulong shale: Type I, which is chlorite filling dissolved pores in carbonate; Type II, which is isolated chlorite; Type III, which is chlorite filling organic matter; and Type IV, which is chlorite filling authigenic microquartz. Types I and III chlorites exhibit higher porosity, offering more storage space for shale reservoirs. Chlorites of Types I, III, and IV, filled with other substances, display higher fractal dimensions, indicating more complex pore structures. These complex pores are favorable for oil adsorption but hinder oil seepage. The processes of organic matter expulsion and dissolution, which intensify with increasing diagenesis, promote the development of Types I and III chlorites, thereby positively influencing the shale reservoir porosity of Gulong shale. This study underscores the influence of chlorite occurrences on shale reservoir properties, providing valuable insights for the future exploration and development of shale oil and gas.