A numerical study of fluids desorption and phase behavior in shale oil reservoir using a chemical reaction model

Oil transfer in shale formation is different from conventional reservoirs due to the abundant nanopores and organic matters. The various storage states of shale oil make the available models not valid. A model considering fluids desorption and phase behavior, which are the major differences from flow in other types of reservoirs, is important for shale oil reservoir development. Based on experimental studies and theoretical analysis, a chemical reaction model is introduced coupling Darcy flow in the pores, fluids desorption in organic matters and on pore surfaces, and phase behavior of confined fluids. The relation between the concentrations of reactants and the physical properties of shale is established to make the chemical reaction model extend to shale oil simulation. Then the model is verified by experimental results and the influences of different mechanisms on oil production are systematically analyzed. The results show that the organic matter retards the transfer of sorption fluids and the existence of solution gas significantly enhances the oil-displacement efficiency. A higher TOC and a larger pressure difference make the ultimate production of dead oil higher. An optimal pressure difference and a reasonable solution gas-oil ratio could help to improve the ultimate production for solution gas drive. This work provides a more convenient approach to imitate the flow characteristics of shale oil, and the result agrees better with the field data.