Densification Mechanisms and Pore Evolution Analysis of a Tight Reservoir: A Case Study of Shan-1 Member of Upper Paleozoic Shanxi Formation in SW Ordos Basin, China

Abstract

This comprehensive analysis investigated the causes of formation densification in the Shan-1 Member tight reservoir in the southwestern Ordos Basin. The study aimed to mitigate exploration and development risks by examining petrological characteristics, reservoir performance, pore characteristics, and pore evolution. Various techniques were employed, including thin-section casting, scanning electron microscopy, and analysis of porosity and permeability. By establishing the relationship between visualized reservoir porosity and thin slice porosity, along with employing mechanical compaction correction methods and the principle of “back stripping by inversion,” the recovery of paleophysical properties in tight sandstone reservoirs was conducted. Additionally, the research integrated diagenetic evolution sequences and the recovery of paleophysical properties to analyze the origins of reservoir densification and pore evolution in the Shan-1 Member. The results suggest that compaction is the primary factor contributing to reservoir densification, with burial depth playing a crucial role in determining the intensity of compaction. Cementation, particularly associated with illite, emerged as a significant influence on reservoir densification, while low dissolution also contributed to the densification process. The densification of the Shan-1 reservoir in the study area was estimated to have occurred during the Early Jurassic, approximately 195 Ma. These research findings not only enhance the understanding of the Shan-1 reservoir but also provide valuable insights for predicting tight reservoirs and improving the efficiency of oil and gas production.