Quantitative Evaluation of Quality-Control Factors of a Tight Sandstone Reservoir: A Case Study of the Shihezi Formation of Permian in the Yanan Gas Field of the Southeast Ordos Basin of China

The Permian Shihezi Formation within the Yan’an Gas Field in the southeast Ordos Basin has garnered considerable attention from both academic and industry circles due to its significance as a major gas formation. However, the exploration and development of this formation have faced substantial challenges arising from the intricacies of sedimentation, intense diagenesis, pronounced heterogeneity, and the interplay of various factors within the Shihezi Formation. In this study, we combined thin section, scanning electron microscope, X-ray diffraction, and high-pressure mercury injection methods to analyze the reservoir characteristics and diagenesis of Shihezi Formation. In addition, a new model is proposed to quantitatively study the influencing factors of tight sandstone reservoirs and was further employed to predict the reservoir sweet spot in the study area. The results revealed that the physical property of the reservoir in Shihezi Formation changes from the south to the north. The reservoir has undergone pronounced diagenetic alterations, leading to the development of a reservoir space system primarily characterized by residual original pores, intergranular dissolution pores, and intragranular dissolution pores. Utilizing Scherer’s initial porosity recovery model in conjunction with thin section petrology, a quantitative assessment of diagenetic strength was conducted. The results indicate that porosity reduction due to compaction and cementation ranges from 7% to 27% and 7% to 23%, respectively, while porosity enhancement resulting from dissolution falls within the range of 1.21% to 8.55%. In tight sandstone reservoir, rock composition and diagenesis have obvious control effects on reservoir quality. The establishment of a reservoir quality parameter model by principal component analysis sets up a single standard for the evaluation of influencing factors of reservoir quality, which has higher reliability. Finally, based on reservoir quality parameters, the formation in the southern area has better quality, showing higher oil and gas development value.