Quantitative calculation of tight sandstone reservoir porosity evolution based on different diagenesis:A case study of Chang 6₃ reservoir in Huaqing area, Ordos Basin

The Chang 6₃ tight sandstone reservoirs in Huaqing area of the Ordos Basin was deposited in delta front and stable,semi-deep lake environments. A simulation equation corresponding to porosity was established according to the characteristics of diagenetic evolution or the comprehensive geological effect of a clastic reservoir. Mineral components and porosity types were described by using casting thin section and SEM analyses. Granularity images were applied to get the structural characteristics and sorting features of clastic particles. Sedimentary microfacies, well logging, normal physical characteristics and depth analyses were applied to determine the depositional environment, burial depth and physical characteristics. Simultaneously,we tested paleotemperature, vitrinite reflectance, the highest pyrolysis temperature and clay minerals to study diagenesis, porosity evolution and relatively high permeability formation. Burial history analysis of the study area provided a theoretical reference for oil-and-gas exploration and development of tight sandstone reservoirs. According to the analysis of four typical samples, we consi-dered that the properties were mainly controlled by compaction, and differentiated diagenetic evolution was the root cause that led to different physical characteristics and porosity structures.