Maturity-dependent thermodynamic and flow characteristics in continental shale oils

Understanding the phase behavior and flow characteristics of shale oil is crucial for optimizing exploration and development strategies. This study examines the thermodynamic properties and flow capacities of shale oils from a continental freshwater reservoir in northeastern China (GNE), comparing them with oils from a continental saline shale oil reservoir in northwestern China (JNW) and the marine Bakken reservoir in North America. Experiments, including degassing, constant composition expansion, and viscosity measurements, combined with phase behavior modeling and pore network simulations, reveal that high-maturity shale oils contain more light fractions, exhibit higher light-to-heavy ratios, elevated bubble point pressures, and gas-oil ratios, along with lower densities and viscosities. These characteristics result in superior flow capacities, as indicated by a shift to the upper left in P-T phase diagrams. Key physical properties such as gas-to-oil ratio, density, and flow rate are strongly correlated with the light-to-heavy ratio, making it a critical parameter for shale oil classification. Notably, JNW shale oil, characterized by an extremely low light-to-heavy ratio, shows markedly different properties compared to GNE and Bakken shale oils. These findings highlight the need for tailored development strategies, such as early pressure maintenance in high-maturity reservoirs, to enhance recovery efficiency.