扩散作用对低渗透油藏CO_2驱相渗特征的影响

Effects of Diffusion on Relative Permeability Curves of CO_2 Flooding in Low Permeability Reservoirs

目前,对于CO_2驱多相渗流理论的研究大多没有考虑CO_2的扩散作用,使得其在预测见气时间等方面存在问题。应用压力降落法测定了气体在原油中的扩散系数,采用非稳态相渗实验方法进行了油气相对渗透率测定实验,分别研究了N_2和CO_2气体相渗曲线的差异以及不同压力下扩散作用对CO_2驱相渗的影响。研究结果表明,低渗透油藏CO_2驱过程中的扩散作用对油气相渗存在较大影响,CO_2的扩散作用对油相相对渗透率影响较大,对气相相对渗透率影响甚微,CO_2扩散作用的影响有利于增强油相渗流,进而降低残余油饱和度,提高原油采收率。

At present,most of the studies on multiphase seepage theory of CO2 flooding do not consider the diffusion of CO2,which makes it difficult to accurately predict gas breakthrough time. The diffusion coefficients of N2 and CO2 in crude oil were measured by pressure drop method,and the relative permeability of oil and gas was measured by unsteady relative permeability experiments. The difference of relative permeability curves between N2 and CO2 and the effect of diffusion on relative permeability of CO2 flooding under different pressures were studied. The results show that the diffusion of CO2 gas during CO2 flooding of low permeability reservoirs has great influence on relative permeability of oil phase,but little effect on relative permeability of gas phase,which is conducive to enhancing oil phase percolation,thereby reducing residual oil saturation and improving oil recovery.