Study On Micro-Interfacial Characteristics And Methods To Improve Imbibition Recovery Of Tight Oil

Spontaneous imbibition is an important mechanism for the development of tight oil and has become a significant way to achieve efficient drainage of tight oil.The properties of micro fluid-solid interface determine the effect of imbibition,but the correlation between the interface properties and imbibition drainage is not yet clear.Thus,for providing some theoretical guidance and basises on enhancing imbibition efficiiency,this paper studies the methods of improving the tight oil imbibition mainly from the micro-mechanism of the liquid-solid interface.In this paper,the molecular dynamics simulation method is first used to explore the change of mechanical behavior of fluid on different rock and mineral surfaces to reveal the microscopic interaction mechanism of the liquid-solid interface;then,based on that,the imbibition effect in the micro-nano channel is simulated,and the number of water molecules absorbed is used to evaluate the effect of the imbibition in different systems,thus,the correlation between microscopic interface characteristics and imbibition effect is clarified;finally,the experimental study of the oil film adsorption and desorption under different systems is developed with the dissipative quartz crystal microbalance（QCM-D）,combining the macroscopic experimental phenomena with the microscopic mechanism of action,we obtain an effective method to improve the tight oil imbibition.Studies have shown that 1)The hydrophilicity of the surface of calcite is weaker than that of sandstone,and because the surface of the calcite is positively charged,it is more likely to adsorb negatively charged petroleum acid,which causes the change of surface from water wet to oil wet;The larger the binding energy with the polar component on the rock surface,the more obvious the effect of the polar component competing with water molecules,weakening the imbibition effect;There are two main mechanisms for surfactants to change the wettability,one is the adsorption of hydrophobic tail chains on oily wet minerals causing wetting reversal,second,the water channel is formed by the disturbance of the hydrophobic tail chain on the oil film or the bridging effect of the hydrophilic head group and the inorganic salt ions,moreover,effective disturbance of oil film is the key to form water channels and promote the oil film stripping;For the Na⁺,Ca²⁺and Mg²⁺saline solution with the same amount of positive charge,the binding capacity with O atom is as follows:Mg²⁺>Ca²⁺>Na⁺,and Mg²⁺has a greater influence on weakening the sandstones water wet.2)During the imbibition process,the electrostatic interaction between the polar component and the rock surface has a greater influence on the imbibition effect than the hydrogen bond interaction,therefore,for the same kind of petroleum acid fluid,the imbibition effect on the calcite surface is worse relative to the quartz sandstone;the imbibition recovery is not only related to the wettability of the rock surface and the interfacial tension,the formation of the water channel is even more critical;the larger brine concentration will not only weaken the water wettability of the minerals surface,but also promote the aggregation of surfactants,which are not conducive to the final imbibition effect;the imbibition recovery of asphaltene on the rock surface is not only related to the interaction between polar functional groups and silanol hydroxyl groups,but also to its complex network structure.3)Appropriate solution concentration of surfactants can effectively disturb the oil film to promote imbibition;ionic surfactants have a better oil displacement effect than nonionic surfactants due to the stronger electrostatic interaction between the hydrophilic group and water molecules;Adding appropriate inorganic cations to the surfactant aqueous solution makes it easier to achieve the purpose of improving the imbibition effect.