Investigation on differentiation behaviors of multiple hydrocarbon components in intra-source migration within matrix-type shale oil reservoirs

Shale oil development is key to global energy security and better fossil energy use. China’s continental shale oil (mostly matrix-type) differs fundamentally from global marine shale oil. Current studies on its intra-source migration lack analysis of multi-factor coupled controls. They also fail to systematically characterize differential migration and synergistic-competitive relationships between hydrocarbon components. This study investigates matrix-type shale oil reservoirs of the Qingshankou Formation, Songliao Basin, using a multi-component multi-field coupled numerical simulation. It explores intra-source hydrocarbon fractionation, clarifies coupled migration controls, quantifies component-dependent migration features, and analyzes the evolution of spatial differentiation under in-situ conditions. Our results demonstrate that light, medium, and heavy hydrocarbons exhibit pronounced differential fractionation and follow a three-stage evolutionary pattern during intra-source migration, ultimately forming a stable spatial zonation characterized by distal enrichment of light components, middle-proximal accumulation of medium components, and in-situ retention of heavy components. We further distinguish and quantify the hierarchical controlling factor system: initial hydrocarbon composition and mixed fluid viscosity are the primary internal factors governing migration efficiency, while matrix particle size and bedding characteristics are the key external factors controlling migration heterogeneity. The orientation of bedding relative to the migration direction dominates pore-throat connectivity and overall migration efficiency. This study advances the theoretical framework of intra-source hydrocarbon accumulation in continental shale oil systems. It offers valuable reference for cost-effective exploration and efficient development of continental shale oil in China.