Oil-Water Two-Phase Dynamic Imbibition Mechanism And Mathematical Model In Tight Oil Reservoirs

Due to factors such as small pore size and complex pore structure in tight oil reservoirs,the fluid seepage law is different from conventional ones,and development faces severe challenges.The development of tight oil reservoirs requires large-scale fracturing,and the existence of natural fractures and artificial fractures after fracturing provides basic conditions for imbibition.However,the basic theory of imbibition in tight oil reservoirs is still incomplete,such as the influence of three-phase contact line friction,rock factors,fluid factors,rock-fluid interaction,etc.on imbibition,which needs further research.Based on molecular kinetic theory(MKT),using theoretical analysis,formula derivation and numerical simulation,the dynamic wetting mechanism of the solid-liquidliquid(SLL)system,the dynamic imbibition mechanism and the dynamic relative permeability variation law of tight oil reservoirs are studied.The key conclusions and understandings are as follows:(1)Based on MKT,considering the viscous effects of the two fluids(liquid-liquid interaction)and the solid-liquid interaction,a dynamic wetting mathematical model of the SLL system is established.The established model can accurately reveal the true contributions of viscous effects and solid-liquid interaction to dynamic wetting.(2)From a microscopic point of view,based on the LWR(Lucas-Washburn-Rideal)equation,starting from the micron scale,considering the dynamic wetting angle effect,a mathematical model of dynamic imbibition in tight oil reservoirs at the micron scale is derived and established;then starting from the nanoscale,considering the dynamic wetting angle,nanoconfinement(anomalous properties of fluids in the solid-liquid interface region under nanoscale conditions)and slippage effects,a mathematical model of dynamic imbibition in tight oil reservoirs at the nanoscale is derived and established.The simulation effect of the established model is better than that of the conventional static imbibition model,which can accurately reveal the effects of fluid viscosity,interfacial tension,rock wettability,and pore size on dynamic imbibition.(3)From a microscopic point of view,starting from the fluid flow in a single pore,considering the dynamic wetting angle,nanoconfinement and slippage effects,the fluid flow equation in a single pore is derived;then a mathematical model of dynamic relative permeability suitable for tight oil reservoirs is obtained by the log-normal distribution theory and capillary bundle model.The established model can accurately reveal the effects of the dynamic wetting angle,nanoconfinement and slippage on the relative permeability of tight oil reservoirs.(4)From a macroscopic point of view,based on the classical oil-water two-phase seepage equation,considering the dynamic wetting angle effect,a mathematical model of oil-water two-phase dynamic imbibition is established,and the numerical simulation method is used to study the application of the model in different imbibition systems.The established model can accurately describe the effects of fluid velocity,boundary conditions,three-phase contact line friction,fluid interfacial tension,viscosity,rock wettability,and permeability on dynamic imbibition.By studying the dynamic wetting mechanism of the SLL system,revealing the dynamic imbibition mechanism and dynamic relative permeability variation law of tight oil reservoirs,this paper improves the basic theory of imbibition development in tight oil reservoirs and further promotes the reasonable and effective development of tight oil reservoir resources.