The features, evolution and controlling factors of diagenesis within tight sandstone of Xujiahe formation in Sichuan foreland basin, China

The tight sandstone gas has become one of the research hotspots of unconventional resources, the diagenesis of tight sandstone attracted much attention of researchers. In the middle part of the foreland basin located in... [ view full abstract ]

The tight sandstone gas has become one of the research hotspots of unconventional resources, the diagenesis of tight sandstone attracted much attention of researchers. In the middle part of the foreland basin located in western Sichuan Province of China, as the major tight gas sandstone reservoirs, the sandstones of the Xujiahe Formation which belong to the ultra-tight sandstone deposited in braid-river delta sedimentary environment with the burial depth of 3000m-5000m and complicated diagenesis were mainly distributed in the second and fourth member of Xujiahe Formation.
Based on the thin-section examination, scanning electron microscope , cathode luminescence and imaging logging interpretation, the research indicates that the diagenesis occurred in the studied sandstones generally comprise mechanical compaction, pressure-solution, carbonate cementation, siliceous cementation, chlorite cementation, dissolution and cataclasis. Then the physical property measurement, X-ray diffraction analysis, homogenization temperatures of fluid inclusions, carbon and oxygen isotope analysis and Electron probe were used in analyzing the diagenetic sequence and the impacts of diagenesis on pores of sandstone.
Consequently, six patterns of diagenetic sequence and porosity evolution for the upper, middle and lower sub-members of the second and fourth member of Xujiahe Formation are constructed respectively. The compaction and cementation mostly destroyed pores of sandstone and resulted in the densification of sandstone. However, some primary pores were preserved by some early cements (early carbonate cements and chlorite rims), and some secondary pores were produced by the dissolution and cataclasis, both of which were beneficial for the formation of the gas reservoirs. In addition, the comprehensive research suggests that the diagenesis is obviously affected by the sedimentary microfacies, composition and texture characteristics of sandstones, diagenetic environment and tectonic activity.

This study was supported by the National Natural Science Foundation of China (No. 41202043) and the Innovation Foundation of China National Petroleum Corporation (No. 2014D-5006-0108).