Characteristics and classification evaluation of tight sandstone reservoirs in the Shuixigou Group of the Taibei Sag, Turpan-Hami Basin

This study focuses on the Xishanyao and Sangonghe Formation tight sandstone reservoirs within the Shuixigou Group of the Taibei Sag in the Turpan-Hami Basin. Using thin section identification, scanning electron microscopy (SEM) observations, and high-pressure mercury injection (HPMI) tests, we systematically analyzed the petrophysical properties, reservoir space features, and diagenetic characteristics of these tight sandstone reservoirs. The interrelationships between reservoir parameters and petrophysical indicators were thoroughly investigated, finally establishing a comprehensive evaluation system tailored to tight sandstone reservoirs in this area. The results indicate that the tight sandstone in the study area is primarily lithic sandstone, characterized by relatively poor particle sorting and rounded grains. The reservoir porosity and permeability are both low, and the storage space is primarily composed of secondary pores. The study area has undergone diagenetic processes, including compaction, cementation, dissolution, and replacement. Among these, compaction has had the most destructive impact on reservoir properties, cementation has had a dual effect, while dissolution has improved reservoir quality. Porosity is positively correlated with sandstone grain size, permeability, median radius, average throat radius, and maximum mercury saturation, but negatively correlated with cement content, bound water saturation, and displacement pressure. Based on mercury injection curves, the reservoirs can be classified into four types according to porosity intervals. Using the above evaluation indicators, a classification and evaluation standard for tight sandstone reservoirs in the Shuixigou Group of the Taibei Sag is established.