Study on the movable fluid saturation and its influencing factors in the tight sandstones of the Sangonghe Formation, Junggar Basin

Movable fluid saturation is a key parameter for describing the reservoir capacity of tight sandstones, and clarifying its influencing factors is essential for understanding the occurrence of movable fluid in such formations. This study focuses on the reservoir of the Sangonghe Formation in the Junggar Basin, China. Using nuclear magnetic resonance (NMR) test, the movable fluid saturation of tight sandstone samples in the study area was quantitatively characterized. Additionally, qualitative and quantitative analyses of mineral composition, pore types and morphology, and pore throat distribution were conducted through X-ray diffraction (X-RD) test, scanning electron microscopy (SEM) test, and high-pressure mercury intrusion (MICP) test. Based on these analyses, the relationships between various parameters and movable fluid saturation were investigated, and the influencing factors were discussed from the perspective of microscopic pore structure. The results indicate that the tight sandstones in the study area can be classified into four categories based on displacement pressure and pore throat size. Each type exhibits significant differences in movable fluid saturation, which can be attributed to factors such as diagenesis, clay minerals, pore shape, pore throat distribution and connectivity, and pore throat sorting. Specifically, the degree of mineral dissolution, the content of ellipsoidal (oblate) pores, pore throat connectivity, pore throat sorting coefficients, and permeability show positive correlations with movable fluid saturation. In contrast, mechanical compaction, cementation, and the content of illite, illite–smectite mixed layers, and chlorite are negatively correlated with movable fluid saturation. The content of kaolinite, porosity, and pore volume show no significant correlation with movable fluid saturation.