Abstract: In order to address the coexistence of inorganic and organic pores in shale reservoirs, a dual-continuum approach was developed to establish a percolation mathematical model for the flow of oil and water phases in shale. This model takes into consideration the wetting and flow characteristics of oil and water phases within both inorganic and organic pores in shale. By employing the proposed model, we obtained matching results from oil-water spontaneous imbibition experiments conducted on shale and determined both the inorganic and organic pore permeability, facilitating accurate calculation of oil content within shale reservoirs. Furthermore, a comprehensive study was carried out to investigate the dynamic characteristics and influential laws of the permeation process in shale. The study results indicate that the permeability of inorganic pores ranges from 10^-8 to 10^-5 D, while that of organic pores ranges from 10^-10 to 10^-7 D. As the permeability through inorganic pores increases, the rate of spontaneous imbibition in shale also increases. However, when the ratio of organic pore permeability to inorganic pore permeability is less than 10^-3, the impact of organic pore permeability on self-imbibition rate is insignificant. These findings have significant implications for a thorough assessment of permeability and reserves in shale reservoirs.

Key words: shale, dual-continuum media, inorganic pore permeability, organic pore permeability, reserve evaluation