Diagenesis and pore evolution of tight sandstone reservoir is one of the most important issues surrounding clastic reservoirs. The tight sandstone of the Shanxi Formation is an important oil and gas producing layer of the Upper Paleozoic in Ordos Basin, and its densification process has an important impact on reservoir quality. This study determined the physical properties and diagenetic evolution of Shanxi Formation sandstones and quantitatively calculated the pore loss in the diagenetic process. Microscopic identification, cathodoluminescence, and a scanning electron microscope were used identify diagenesis, and the diagenesis evolution process was clarified along with inclusion analysis. In addition, reservoir quality was determined based on the identification of pore types and physical porosity. Results show that rock types are mainly sublitharenite and litharenite. The reservoir has numerous secondary pores after experiencing compaction, cementation, and dissolution. We obtained insight into the relationship between homogenous temperature and two hydrocarbon charges. The results indicated that there were two hydrocarbon charges in the Late Triassic–Early Jurassic (70–90 °C) and Middle Jurassic–Early Cretaceous (110–130 °C) before reservoir densification. The quantitative calculation of pore loss shows that the average apparent compaction, cementation, and dissolution rates are 67.36%, 22.24%, and 80.76%, respectively. Compaction directly affected the reservoir tightness, and intense dissolution was beneficial to improve the physical properties of the reservoir.

The deposition of the Lower Cambrian argillaceous rocks on the Kongquehe slope provides a good opportunity to reconstruct the paleoenvironmental conditions of the Tarim Basin. To explore the paleoredox conditions, paleoclimate, and provenance of this deposit, 21 samples were collected from Well A, and the concentrations of major and trace elements were analyzed. The V/(V + Ni), V/Cr, Ni/Co, U/Th, Uau, and V/Sc ratios indicated that the sediments in the water body from the Lower Cambrian were in a reducing environment, and the degree of reduction weakened from the bottom to the top. The Sr/Cu, Mg/Ca, and Fe/Mn ratios in the sediments revealed that the Lower Cambrian was mainly characterized by a warm and humid paleoclimate, and there may be a paleoclimatic transition toward drought conditions as recorded by the sediments of Xidashan Formation. The chemical alteration index, compositional variation index, plagioclase alteration index values, and Th/U and K/Rb ratios of the Lower Cambrian mudstone all reflected that the parent rock in the study area was mainly subject to low- to medium-degree chemical weathering. Longitudinally, the Lower Cambrian gradually increased and then weakened from Xishanbulake Formation to Xidashan Formation. The ratios of trace elements and rare earth elements as well as Th–Sc–Zr/10, Th–Co–Zr/10, and ∑REE–La/Yb diagrams all showed that the mudstones of Xishanbulake and Xidashan Formations of the Lower Cambrian in the study area have a common parent rock type, mainly sedimentary rocks rich in felsic minerals. Additionally, the structural setting discrimination diagrams of SiO₂–K₂O/Na₂O, Th–Sc–Zr/10, Th–Co–Zr/10, and La–Th–Sc showed that the structural setting of the Lower Cambrian mudstone deposition is mainly a continental island arc environment and has the characteristics of an active continental margin.