高盐油藏耐油泡沫驱体系的构建及泡沫稳定机制研究

Due to the instability of traditional foam under high salinity and oil-bearing conditions, foam flooding is usually unable to function well in high-salinity reservoirs. Recently, we found a new type of foam whose stability could increase with increased salinity. However, the relevant mechanisms are unclear, and the foam stability in the presence of oil is unknown. Therefore, we will investigate the foam stability mechanisms of this special foam in the absence and in the presence of crude oil in this work, and eventually formulate an oil-tolerant foam flooding system by utilizing the high concentration salts. Firstly, the bulk/surface properties of the foam system as well as the foam film structure and stratification will be measured to reveal the mechanisms of the salt synergism. Then, the responses of pseudoemulsion film stability and thin film stratification on salinity changes will be thoroughly examined to understand the effect of crude oil on the salt synergism. The relationship between pseudoemulsion film stability and bulk/surface properties of the evaluated system, as well as that between thin film stability and swollen micelle properties will be presented, and thus develop effective methods to improve the oil tolerance of the system. Furthermore, oil displacement tests of foams with various oil tolerances will be conducted to compare their flow behaviors and further optimize the system. It is expected that these findings can provide a stable foam flooding system for high-salinity reservoirs, add insight into the formulation of foam flooding systems, and offer technical support to enhance the oil recovery of high-salinity reservoirs.

传统泡沫在高盐、含油条件下的欠稳定问题是制约泡沫驱效果的技术难点。申请人前期研究发现了稳定性可因高盐而加强的盐增效泡沫，但其作用机理不清、含油环境中的表现不明。本项目拟探究高盐增效泡沫稳定性的机制及原油对其影响规律，进而有效利用高盐构筑一种耐油泡沫驱体系。通过表征高盐条件下泡沫体系的体相性质、表面性质、液膜结构与薄液膜分层薄化行为，揭示泡沫盐增效机理；分析假乳液膜稳定性、含油薄液膜分层薄化行为等对矿化度变化的响应，阐明原油影响泡沫盐增效的机制，探寻假乳液膜稳定性与表面活性剂表/界面性质、含油薄液膜稳定性与含油胶束性质的联系，建立改善高盐泡沫耐油性的方法；对比不同耐油性泡沫在多孔介质中的流动行为，明确泡沫耐油性与其提高采收率能力的关系，提出高盐泡沫驱体系优化思路。研究成果可望为高盐油藏泡沫驱提供一种稳定体系，为体系构建提供理论依据，为高盐油藏提高采收率提供技术支持。

我国高盐油藏储量丰富，泡沫驱在其有效开发上极具潜力，但矿场实施效果受泡沫欠稳定问题严重制约。开发满足高盐油藏需求的耐油泡沫驱体系，阐明泡沫在高盐、含油环境下的稳定机制，是目前高盐油藏泡沫驱技术与理论研究中亟待解决的关键问题。本项目研究显示，C12~15短链甜菜碱和C16~21长链甜菜碱的泡沫稳定性均表现出高盐增效性，NaCl浓度从2.3%增至21.1%，泡沫半衰期最高可延长13倍。结合泡沫体系的表面性质、体相性质以及薄液膜薄化行为发现，盐度增加，甜菜碱饱和吸附量增大、扩散吸附速率减小，导致扩张模量增大、液膜弹性增强。随盐度增强的扩张粘弹性与超分子振荡结构力是控制短链甜菜碱泡沫高盐增效性的主导因素，而高盐诱导蠕虫状胶束形成协同表面扩张粘弹性提升是导致长链甜菜碱泡沫高盐增效性的关键机制。C21长链甜菜碱浓度增加，虽表面扩张黏弹性降低，但蠕虫状胶束形成、生长并逐渐紧密纠缠，促使体相黏弹性增强，液膜薄化特征转变、速度下降。基于甜菜碱构建了弱耐油泡沫体系RC与强耐油泡沫体系RCS，60%含油（原油黏度650mPa·s）下，0.2%RCS的泡沫半衰期较0.2%RC延长237倍。两种泡沫耐油性存在差异的原因在于，RC体系的进入系数为正值且形成的假乳液膜不稳定，造成油滴易进入液膜表面并以低粘弹性油水界面取代高粘弹性气水表面。RCS体系的进入系数为负值且假乳液膜稳定，其泡沫半衰期取决于气水表面扩张粘弹性。随含油量增加，RCS液膜水相中表面活性剂浓度降低，引起气水表面扩张粘弹性增强，泡沫半衰期随之延长。RC与RCS均可在稀油（原油黏度10.8 mPa·s）存在条件下于岩心中生成泡沫，但后者的流度控制能力明显更强。通过将原油乳化为稳定O/W乳化液RCS含油泡沫可在临界泡沫质量与低泡沫质量下（泡沫质量≤50%）表现出较无油泡沫更高的有效粘度。可见，采用恰当的泡沫体系与注入参数，泡沫与乳化液可产生协同流度控制作用。本项目研究成果可为高盐油藏泡沫驱矿场方案设计和技术应用奠定关键理论基础。