Response model of fluid–rock ratio to reservoir space in primary formation of shale oil during hydrous pyrolysis

Abstract

Due to the presence of geological fluid under actual geological conditions, water–rock interaction will occur between the fluid and reservoir. Thus, to analyse the influence of the water–rock interaction on storage space during the organic matter evolution stages, this study conducted a series of simulation experiments on shales by using a closed autoclave: four temperatures, 250°C, 300°C, 350°C, 400°C, and five fluid–rock ratios (FRRs), 0:20, 4:20, 10:20, 15:20, and 20:20. Low pressure N2 adsorption measurement was conducted on the solid residues. The experimental results show that the effect of temperature on the yield and pore structure of oil shale was the same as the result when the FRR was = 0:20, 4:20 and = 10:20, 15:20, 20:20, respectively. This result showed that temperature remained the main factor that affected the thermal evolution of hydrocarbon generation. Additionally, temperature was beneficial to the generation and storage of shale oil within a certain range, but only occupied the storage space of shale oils or connected a certain storage space beyond a certain range. The variation trend of shale oil yield with increasing FRR under the same simulated temperatures, 250°C and 400°C, was most affected by the FRR, but little change occurred at 300°C and 350°C. This further proved that the ratio of fluid to rock was an indirect acting factor, which affected the evolution of organic matters and then the development of pore structures. Before the oil window (350°C), the lower evolution degree, the higher water content and the more significant effect. In the higher evolution stage, the higher the water content, and the more complete the kerogen reaction, which was also more conducive to the development of pore structures. Therefore, this study promotes the establishment of linear equations on FRR to the gas adsorption capacity, which further provides a theoretical basis and guidance for the exploration and development of shale oil.