Evaluation of movability of shale oil in organic matter in depletion production by REV-scale simulations

Abstract

The oil transfer in shale oil formations includes the oil flow in inorganic and organic pores, and the diffusion in the organic matter (OM). A novel triple-continuum model (OM matrix, organic pores, inorganic matrix) is proposed coupling the oil flow (in organic and inorganic pores) and diffusion (in OM matrix). The proposed model is further validated by three-dimensional (3D) numerical simulations. The simulation results show that the proportion of oil production of the absorbed oil from OM matrix in the total shale oil production is small due to the relatively slow diffusion process. However, the diffusion of oil from OM matrix to the organic pores can provide extra energy for the oil expansion in inorganic pores, and thus can greatly increase the oil production in the depletion process. The high OM content can prolong the timespan of oil production. More absorbed oil in OM provides more elastic energy for oil depletion in organic and inorganic pores, and thus leads to higher flow rate in the late period of shale oil production. Smaller size of OM means shorter distance for oil transfer from OM to inorganic matrix, and thus accounts for higher movability of oil in OM.