Research on the Control Mechanism of Mixed-Type Shale Laminar Structure on Shale Oil Reservoir and Storage Properties

As the fundamental constituent units of hybrid shale oil reservoirs, laminae exhibit complex structures and diverse combination types, leading to strong reservoir heterogeneity. Therefore, revealing the structural characteristics of laminae and their controlling mechanisms is crucial for understanding the storage and occurrence properties of such reservoirs. This study focuses on the shale reservoirs of the Fengcheng Formation in Mabei, Xinjiang, integrating methods such as cast thin sections, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and nitrogen adsorption to characterize the storage properties of laminae. On this basis, laser scanning confocal microscopy was used to accurately analyze the oil-bearing properties and occurrence differences within individual laminae. Furthermore, nuclear magnetic resonance (NMR) technology was applied to elucidate the controlling effects of complex laminae combinations on storage and occurrence. The results indicate that: (1) The Fengcheng Formation contains diverse laminae types, including felsic clastic laminae, tuff laminae, dolomite laminae, limestone laminae, siliceous laminae, borax laminae, and organic matter laminae. (2) The primary storage spaces consist of dissolution pores in felsic clastic/tuff laminae, intragranular and intercrystalline pores in dolomite laminae, and intercrystalline pores in limestone/siliceous/borax laminae. Strong dissolution, conducive to the development of high-quality reservoirs, occurs when the proportion of felsic clastic laminae is 50%-60% or dolomite laminae is 20%-40%. (3) Confocal microscopy characterization reveals that dolomite, micritic siliceous, and felsic clastic laminae exhibit superior oil-bearing properties. The differences in oil-bearing properties are mainly controlled by two key factors: ① The interbedded distribution of source and reservoir rocks without barriers; the closer a lamina is to the source, the better its oil-bearing properties. ② A coordinated source-to-reservoir ratio; the optimal oil-bearing properties occur when the ratio of source laminae to reservoir laminae is 1:3 to 2:1, with the poorest properties when the ratio exceeds 6:1. NMR core-scale testing further validates these controlling patterns. The conclusion is that the key to efficient storage and occurrence of shale oil lies in the optimal spatial configuration and coordinated proportion between high-quality source rocks and effective reservoirs.