Development Scale and Reservoir Characteristics of Sand Bodies in the Qian 5 Member of the Shiqianfeng Formation of the Shenmu Gas Field in the Ordos Basin

The Shiqianfeng Formation, as the top natural gas reservoir in the Permian of the Ordos Basin, has the characteristics of large sandstone thickness and wide distribution. Based on the analysis of outcrop, drilling and logging data, and core sedimentary facies, the outcrop measurement method, empirical formula method, and dense well network dissection method were used to evaluate the development scale of sand bodies in the Qian5 member. Combining microscopic thin sections, scanning electron microscopy, mercury intrusion, nuclear magnetic resonance, and other analytical methods, the study and classification evaluation of reservoir characteristics in the Qian5 member are conducted, providing clues for subsequent high-precision development. Research suggests that the Qian5 section of the Shenmu area is a braided river delta plain deposit, mainly composed of braided distributary channels and flood plain subfacies, with locally developed flood crossing sand deposits. During the sedimentation period, the average depth of braided river channels is 5-6 m, with a width of 800-1200 m in the upper section of Qian5 and a width of 1200-1600 m in the lower section of Qian5. Thick layers of lithic sandstone, feldspathic lithic sandstone, and lithic feldspathic sandstone reservoirs were formed, characterized by high rock debris content and high intergranular pore content. It is manifested as four types of sandstone reservoirs: type I, micron level fracture pore type; Class II micron-nano interconnected pore type; Class III nano-micron level connected to isolated pore type; Class IV nanoscale isolated pore type. The local enrichment of laumontite in the sandstone of Qian5 member has created potential material conditions for searching for reservoirs with high porosity and permeability.