关键词: 低渗透砾岩, 二氧化碳驱, 分形理论, 动用规律, 动用下限

Abstract: This paper is a case study of the low-permeability conglomerate reservoirs of Kexia Formation in the Well Block M of Xinjiang Oilfield, aiming to investigate the dynamic laws and lower limit of oil production by CO₂ flooding in the study area. Base on nuclear magnetic resonance and high-pressure mercury intrusion experiments, an investigation was performed on the laws of multi-staged pore-scale production by CO₂ flooding in distributary channel conglomerate and interdistributary bay sandy fine conglomerate reservoirs. Further, the formulae for calculating the porosity and lower limit of oil saturation during production by CO₂ flooding were derived based on the fractal theory of porous media. The results show that compared with CO₂ near-miscible flooding, CO₂ miscible flooding can displace oil from more submicron pores and mesopores in the distributary channel conglomerate reservoirs. Consequently, the technical lower limit for effective pore utilization is reduced from 6.8 % to 5.2 %, and the lower limit of oil saturation is reduced from 27.8 % to 19.4 %. It can also display oil from more mesopores and nanopores in the interdistributary bay sandy fine conglomerate reservoirs, Correspondingly, the technical lower limit for effective pore utilization is reduced from 4.8 % to 3.2 %, and the lower limit of oil saturation is reduced from 36.9 % to 25.1 %. Following the reperforation operation in Well A of the pilot area, the daily oil production has increased by 3.0 tons, thus effectively verifying the reliability of the model calculation results. These findings can provide effective guidance for the subsequent industrialized development of low-permeability conglomerate reservoir by CO₂ miscible flooding.

Key words: low-permeability conglomerate, carbon dioxide flooding, fractal theory, dynamic law of oil production, lower limit of oil production