二氧化碳驱波及控制智能响应流体特征及作用机理

Characteristics and mechanism of smart fluid for sweeping control during CO_(2)flooding

针对低渗透油藏—致密油CO_(2)驱面临的气体窜流控制难题,以叔胺基为响应单元,设计合成具有双子表面活性剂自组装属性的CO_(2)驱波及控制智能响应流体,研究了该流体遇CO_(2)/遇原油智能响应特征及作用机理、遇CO_(2)自增稠聚集体的剪切特征,评价了该流体与增稠聚集体耐温抗盐特性,验证了实现CO_(2)驱均衡波及控制的可行性与有效性。研究表明:(1)智能流体遇CO_(2)响应组装为高黏聚集体,流体质量分数为0.05%~2.50%时,增稠倍数9~246,黏度13~3100 mPa·s,实验条件下低渗透岩心波及体积大幅提高;(2)智能流体遇模拟油,流体质量分数为0.5%~1.0%时界面张力降至1×10^(-2)mN/m数量级,模拟油饱和度大于10%时,囊泡状胶束增溶油相全部转化为球状胶束,流体具有遇原油响应不增稠、降低界面张力特征;(3)智能流体遇CO_(2)自增稠聚集体可剪切变稀、静止增稠,经剪切—静止多次循环后仍保持初始结构状态,具备自修复特性,可实现储集层深部放置;(4)智能流体与增稠聚集体耐温抗盐性能长期稳定。

A smart response fluid was designed and developed to overcome the challenges of gas channeling during CO_(2)flooding in low-permeability tight oil reservoirs.The fluid is based on Gemini surfactant with self-assembly capabilities,and the tertiary amine group serves as the response component.The responsive characteristics and corresponding mechanism of the smart fluid during the interaction with CO_(2)/oil were studied,followed by the shear characteristics of the thickened aggregates obtained by the smart fluid responding to CO_(2).The temperature and salt resistance of the smart fluid and the aggregates were evaluated,and their feasibility and effectiveness in sweep control during CO_(2)flooding were confirmed.This research reveals:(1)Thickened aggregates could be assembled since the smart fluid interacted with CO_(2).When the mass fraction of the smart fluid ranged from 0.05%to 2.50%,the thickening ratio changed from 9 to 246,with viscosity reaching 13 to 3100 mPa×s.As a result,the sweep efficiency in low-permeability core models could be increased in our experiments.(2)When the smart fluid(0.5%to 1.0%)was exposed to simulated oil,the oil/fluid interfacial tension decreased to the level of 1×10^(-2)mN/m.Furthermore,the vesicle-like micelles in the smart fluid completely transformed into spherical micelles when the fluid was exposed to simulated oil with the saturation greater than 10%.As a result,the smart fluid could maintain low oil/fluid interfacial tension,and would not be thickened after oil exposure.(3)When the smart fluid interacted with CO_(2),the aggregates showed self-healing properties in terms of shear-thinning,static-thickening,and structural integrity after several shear-static cycles.Therefore,this fluid is safe to be placed in deep reservoirs.(4)The long-term temperature and salt resistance of the smart fluid and thickened aggregates have been confirmed.