致密油藏非等径毛细管微观渗吸影响因素

Influencing factors of non-equal-radius capillary microscopic imbibition in tight reservoir

非等径毛细管模型是目前研究微观渗吸的主流模型,目前大多数对非等径毛细管模型自发渗吸研究主要基于气-液系统,液-液系统下非等径毛细管的渗吸过程缺乏相关研究。而液-液系统下的渗吸作用对致密油藏的注水开发具有重要的影响,因此基于泊肃叶定律和渗吸理论,推导出液-液系统下非等径毛细管自发渗吸理论公式,建立了考虑毛细管结构和黏度比影响的新型渗吸理论模型,明确了多段式扩径-缩径毛细管中液-液系统下的微观渗流行为。结果表明:毛细管几何尺寸是影响非等径段渗流行为的主要因素,液-液渗吸结束时间远大于气-液渗吸的时间,随着非等径段的增加,渗吸曲线呈现一条曲线;黏度比对液-液系统下渗吸结束时间的影响较大,气相黏度的增加对渗吸结束时间影响较小,在此基础上建立了多段式扩径-缩径等效毛细管模型,与传统LW (Lucas和Washburn)渗吸模型相比,预测偏差更小,符合率更高。利用该模型可以快速、准确地预测在非等径毛细管中的渗吸过程,为致密油微观渗吸研究提供了新的思路。

Non-equal-radius capillary model is a mainstream model for studying microscopic imbibition. At present most micro-imbibition study of non-equal-radius capillary models are mainly based on gas-liquid system, and there is a lack of relevant research on imbibition process of non-equal-radius capillary in liquid-liquid system. Imbibition in liquid-liquid system has much influence on water injection development of tight reservoirs. Therefore, based on Poiseuille’s law and imbibition theory, theoretical formula of spontaneous imbibition with non-equal-radius capillary in liquid-liquid system is derived, a new theoretical model of imbibition considering influence of capillary structure and viscosity ratio is established, and microscopic flow behavior in liquid-liquid system in multi-segment radius expanding-shrinking capillary is clarified. The results show that capillary geometry size is the main factor affecting the flow behavior of non-equal-radius section. The end time of liquid-liquid imbibition is much longer than that of gas-liquid imbibition. With the increase of non-equal-radius section, the imbibition curve shows a convex curve. Viscosity ratio has much influence on end time of imbibition in liquid-liquid system, and the increase of gas viscosity has less influence on end time of imbibition. On this basis, multi-segment radius expanding-shrinking equivalent capillary model is established, with lower prediction deviation and higher coincidence rate than traditional LW(Lucas and Washburn) model. This model can quickly and accurately predict imbibition process in nonequal-radius capillary, providing new idea for study on microscopic imbibition of tight oil.