致密油藏不同CO_2注入方式下微观驱油机理

Microscopic mechanism of oil displacement under different CO_2 injection modes in tight oil reservoirs

注CO_2补充地层能量已成为提高致密油藏开发效果的重要手段之一。本文将致密油藏物理模拟实验方法和低磁场核磁共振技术相结合,对大庆外围致密岩芯分别进行了CO_2驱、水驱转CO_2驱和周期注CO_2驱3种方式下的物理模拟实验,探讨了不同CO_2注入方式下的微观驱油机理。研究结果表明:大于0.1μm的亚微米级和微米级孔隙是致密储层原油的主要储集空间,大于1μm的微米级孔隙是可采原油的主要赋存空间,不同CO_2注入方式下亚微米级孔隙空间原油动用规律不同,周期注CO_2驱下亚微米级孔隙空间对原油采收率贡献最大。从不同CO_2注入方式的最终原油采收率来看,周期注CO_2驱原油采收率最高,其次为注水后转CO_2驱,CO_2驱开采方式下采收率最低。该研究为CO_2补充能量技术在致密油藏的推广应用提供理论指导。

CO2 flooding has been one of the key technologies to boost the development of tight oil reservoirs. Through combining the physical experiments with the nuclear magnetic resonance technique, experiments on oil displacement under different gas injection modes such as CO2 flooding, water injection converting to CO2 injection, and cyclic CO2 injection in tight oil reservoir of Daqing city were carried out, and the microscopic mechanism of oil displacement was discussed. The results indicate that the micron pores and the submicron pores with the size over 0.1 μm are the main storage spaces of tight oil reservoir, and the pores with the size over 1 μm are the main space for the recoverable crude oil. Laws of oil displacement in submicron pores are different under different CO2 injection modes, and the largest contribution on the oil recovery rate comes from the submicron pores under cyclic CO2 injection mode. In comparison, the ultimate oil recovery rate by cyclic CO2 injection is the largest, then followed by the water injection converting to CO2 injection, and the minimum oil recovery rate is by CO2 flooding. This research can provide theoretical references for the effective development of tight oil reservoirs by CO2 flooding.