高含水油藏CO_2驱油机理

CO_2 flooding mechanism in high water cut reservoirs

CO_2驱油能够有效提高原油采收率,但在高含水油藏中,水能够溶解CO_2,并影响CO_2与原油接触,从而影响驱油效果。针对这一问题,开展了CO_2在油、水中的浓度分配实验,通过建立CO_2在油、水中扩散的数学模型,使用核磁共振研究CO_2驱替实验,探索了CO_2在高含水油藏中的溶解扩散机理以及对综合驱油效果的影响。结果表明,在高含水油藏中,CO_2在水中溶解损失的比例不高,同时CO_2能够快速渗透水膜,与被水屏蔽的剩余油接触,波及水驱未波及区域内的剩余油。由于水膜阻隔了原油与CO_2的直接接触,在CO_2驱替过程中会首先驱出水膜,使油、气直接接触,再驱出剩余油。其宏观表现为注气早期含水率较高、采油速度较低,当CO_2突破后,含水率急剧下降,采油速度升高。研究明确了高含水油藏CO_2驱油机理,解释了其见效特征,并为改善高含水油藏CO_2驱油效果提供了参考。

CO2flooding is able to effectively increase crude oil recovery rate.However,in high water cut oil reservoirs,water can dissolve CO2 and hamper contact between CO2 and crude oil,thereby influencing flooding effect.To address this issue,this study conducts a concentration partitioning test of CO2 in oil and water,builds a mathematical model for diffusion of CO2 in oil and water,and performs analyses on CO2 flooding test by NMR,so as to the explore dissolution and diffusion mechanism of CO2 in high water cut oil reservoir and its influences on overall flooding effect.The results indicate that in a high water cut oil reservoir,the percentage of CO2 dissolution loss in water is not high,and CO2 can penetrate water film quickly to contact the remaining oil shielded by water and affect the remaining oil in the area unaffected by water flooding.Since water film blocks direct contact between crude oil and CO2,water film will be displaced first during CO2 flooding so that oil comes in direct contact with gas,then the remaining oil will be displaced.This is macroscopically represented by high water cut and low oil recovery speed during the early gas injection,and sharply decreased water cut and increasing oil recovery speed after CO2 broke through,.This study defines a CO2 flooding mechanism for high water cut oil reservoirs,explains its effectiveness characteristics,and offers reference for improving the CO2 flooding effect of high water cut oil reservoirs.