Characteristics and main controlling factors of the tight sandstone reservoirs around the paleo-uplift in the southern Tianshan area, Tarim Basin

Objective The main controlling factors and densification genesis of sandstone reservoirs around the paleo-uplift in the southern Tianshan area of the Tarim Basin have always restricted the increase in reserves and production in this area. Methods By using thin section and cathode luminescence (CL) observations, physical property testing, mercury injection analysis, and other related methods, the characteristics of sandstone reservoirs in the Lower Cretaceous Baxigai and Shushanhe Formations were studied, and the main factors controlling the reservoir properties were also summarized. Results The study draws the following conclusions: The porosity of the target layer in the study area is mostly less than 10%, and the permeability is less than 1×10-3 μm2, which is a typical tight sandstone reservoir. Among them, the braided river delta sandstones exhibit the best physical properties (φ=12.3%, k=60.4×10-3 μm2) and pore structure, followed by the fan delta sandstones (φ=6.9%, k=1.9×10-3 μm2), while the lacustrine sand bar facies features the worst physical properties (φ=6.7%, k=0.34×10-3 μm2). The evolution of paleo-uplift controlled the differences between sedimentary facies and diagenetic processes. The sedimentary environment of braided river deltas and fan deltas has strong hydrodynamic forces, coarser particles, and weak cementation, so the porosity and permeability are high. In contrast, the lacustrine sand bar facies are far away from terrigenous input, the grains are fine, and the underwater paleo-uplift controlled the formation of carbonate cement with high contents in the diagenetic stage, which blocked the pore throat and reduced the physical properties of the sandstone reservoir. Conclusion These results provide a reference for petroleum exploration and development of the Lower Cretaceous successions in the southern Tianshan area.