湿润性对孔隙介质两相渗流驱替效率的影响

EFFECTS OF WETTABILITY ON DISPLACEMENT EFFICIENCY OF TWO-PHASE FLOW IN POROUS MEDIA

孔隙介质中多相渗流的驱替效率对二氧化碳封存效率和石油采收率具有决定性影响,是实际工程调控中的一个关键指标.湿润性是影响多相渗流驱替模式及其效率的一个重要因素.本文通过微流体模型−显微镜−高速相机可视化实验平台,对基于真实砂岩孔隙结构的微流体模型进行湿润性修饰,开展了5种流量和2种湿润性的两相驱替可视化实验,研究了湿润性对砂岩孔隙结构中两相渗流驱替模式及其效率的重要影响.实验结果表明:随着流速的增大,两相渗流驱替模式由毛细指流向稳定流发生转变;在低流速条件下,由于毛细力的主导效应,亲水性介质中指进的宽度和被驱替流体团簇的数目均小于疏水性介质,而被驱替流体团簇的最大半径、平均半径和方差均大于疏水性介质.实验结果还证实了亲水性介质中由于单支优势通道和“绕流”现象的发生,驱替效率显著小于疏水性介质.最后,通过考虑接触角效应对毛细管数进行修正,建立了考虑湿润性影响的驱替效率和毛细管数之间的统一关系式,为不同湿润性条件下驱替效率的预测提供了一种潜在方法.

Displacement efficiency and displacement pattern of multiphase flow in porous media have a profound influence on many geo-energy applications such as geologic CO2 sequestration and enhanced oil recovery.Wettability is one of the most important factors affecting the displacement pattern and displacement efficiency of multiphase flow in porous media.Here,we combined the glass microfluidics,inverted microscope and high speed CMOS camera to set up a visualization experimental system and modified the surface wettability of the glass microfluidics by using the silanization treatment and piranha solution.Pore-scale visualization displacement experiments were conducted on five flow rates and two wetting conditions(hydrophilic and hydrophobic conditions)in glass microfluidics which are fabricated from the pore structure of natural sandstone.Experimental results show that the displacement pattern shifts from capillary fingering to compact displacement pattern both in the hydrophilic and hydrophobic media as the flow rate increases.Under lower flow rates,the capillary force plays the dominant role in the fluid invasion processes.The invasion finger width and the number of air clusters in hydrophilic media are both smaller than those in the hydrophobic media,but the maximum air cluster radius,the average cluster radius and the standard deviation of cluster radius are all greater under hydrophilic conditions.The results also demonstrate that the displacement efficiency under hydrophilic condition is significantly lower than that of hydrophobic conditions due to single-channel flow and“by pass”flow phenomena which both only occur in hydrophilic media.Finally,a modified capillary number was introduced in order to consider the role of wettability(contact angle)under favourable displacement.Then,a relationship between the displacement efficiency and the modified capillary number was proposed,which provides a potential and useful method for the prediction of displacement efficiency under different wetting conditions during favourable displacement.