微纳尺度油水界面离子调控机制及其微观渗流规律研究

Low salinity waterflooding is considered as a potential EOR technique yet the underlying mechanism remains controversial. Majority of the research revolves around the interactions among crude oil brine and reservoir rocks however the interplay between crude oil and brine has been paid much less attention to. Therefore, droplet-based microfluidics is employed to explore the influence of brine composition on the basic fluid flow behaviors inside the single pore-throat geometry. Subsequently, microfluidic chips with pore-throat network is applied to investigate the effect of brine composition on the pore-level flow pattern as well as the generation and distribution of residual oil saturation. A mechanism interpreting the influence of brine composition on the crude oil brine interfacial activity and fluid flow behaviors is expected by combining the molecular dynamics simulation on the crude oil-brine interfacial phenomena. Finally, low salinity waterflooding is simulated inside a real rock sample to elucidate the role of crude oil-brine interfacial activities on the two phase flow through porous media. The systematic and in-depth investigation of the crude oil brine interfacial phenomena can be beneficial to the understanding on the mechanism of the ion-mediated interfacial activity and its specific influence on the fluid flow behavior, which will ultimately aid in unravelling the mechanism of low salinity waterflooding and providing an insight on the future application of combining low salinity waterflooding with other chemical flooding approaches.

低矿化度水驱在当前低油价和高环保要求的背景下具有巨大的应用潜力，然而对于其提高采收率的机理还缺乏统一认识，目前开展的研究主要围绕油水与岩石的反应却忽略了油水间的相互作用。因此，本项目拟利用液滴微流控芯片，探索水相离子对单孔喉内单分散油滴基本流体行为的影响机制，随后扩展至具有孔隙网络结构的微模型以考察水相离子对油水两相微观渗流现象以及驱替后剩余油形成和分布的作用机理，结合分子模拟深入分析水相离子对油水界面活动的调控规律，提出离子对油水界面性质及油水两相渗流的微观影响机理。最后基于真实岩心模型，明确油水界面性质在油水岩三相系统中对微观两相渗流现象的具体影响。通过对油水界面现象系统、深入的机理研究，弥补对离子与油水界面性质之间关系认识的不足，阐明油水界面性质对微观两相渗流的具体影响机制，完善低矿化度水驱机理，为低矿化度水驱的高效利用以及与其他驱替方式的结合应用奠定理论基础。

低矿化度水驱在当前低油价和高环保要求的背景下具有巨大的应用潜力，然而对于其提高采收率机理还缺乏统一认识。本项目利用微流控芯片探索水相离子组成与矿化度对微观尺度油相流体行为的影响机制。利用均质孔隙网络结构芯片模拟不同水驱过程，实验发现在低矿化度下驱替过程中形成的乳状液更易聚并从而保持油相连续性，而Na+的存在相比Ca2+更有助于油水界面融合或乳状液聚并生成更大的乳状液从而提高水驱效率。结合前期研究发现低矿化度水驱提高采收率是被阻碍的油相卡断和被促进的乳状液聚并协同作用的结果。利用具有高低渗区域的非均质芯片模拟含有不同水相离子组成和含量的水驱过程。结果表明MgCl2水驱效率相对较低，和常规地层水驱效率相当，且矿化度对采收率的影响较小，低矿化度NaCl和KCl驱油效率相对较高，实验表明低矿化度条件下芯片亲水性较好且形成较多乳状液。随后研究不同驱油剂组成对驱替过程中油水两相微观渗流现象以及驱后剩余油形成和分布的作用机理，实验发现单一低浓度表面活性剂驱与低矿化度水驱采收率相当，较高浓度表面活性剂驱则优于低矿化度水驱。相比于低矿化度水驱，阴离子与两性离子型表面活性剂复合驱油能够显著降低界面张力，油相更易卡断形成小油滴，对油相动用能力更强，尤其在低渗区域优于低矿化度水驱。水相化学组成对原油采收率的影响具有多面性，同时受多种化学反应和多重因素的共同影响，而最终采收率则是油水界面行为、油-水-岩石三相间作用综合影响的结果。对于非均质性多孔介质进一步提高采收效率，实验发现注入纳米聚合物微球能够封堵高渗介质从而提高采收效率，而影响其封堵效率的因素依次为颗粒粒径、浓度和渗透率，以上研究为低矿化度水驱与其他驱替方式的结合从而进一步提高采收率奠定理论基础。