Migration mechanism of pyrolysis oil during oil shale in situ pyrolysis exploitation

In situ pyrolysis exploitation is an ideal method for the utilization of oil shale. The migration of pyrolysis oil has significant effects on the in situ exploitation process, such as reservoir permeability and oil quality; it further determines the feasibility and economy of this technology. However, the migration mechanism of pyrolysis oil components in the reservoir after hydraulic fracturing has not been fully revealed, so the exploitation process still lacks comprehensive theoretical guidance. In this study, visual experiments of pyrolysis oil migration were carried out, and simulations were also performed based on the adjusted reaction model including the behaviors of asphaltene. Experiment and simulation results collectively indicated that the separation of oil components was evident in the reservoir with a higher temperature, and the alternate cycle of volatilization-migration-condensation was the primary migration pattern of pyrolysis oil. Due to asphaltene deposition and high-viscosity oil accumulation, reservoir permeability was significantly reduced in the middle stage of exploitation. In addition, the asphaltene content in the produced oil decreased to ∼2.8%, the produced oil quality and energy conversion ratio improved markedly when the temperature of injected nitrogen was 500 °C. Results obtained could guide the oil shale in situ pyrolysis exploitation.