The Research Of Micro-Dynamic Model Of Liquid Collar During Gas Bubble Snap-Off And Slug Injection Design Of Foam Flooding

Foam flooding is considered as one of the enhanced oil recovery(EOR)technologies that have vast development potential.As immiscible two-phase displacement,the flowing characteristics of foam system depend on the physical and chemical properties of both the injected and displaced fluids,the hydrodynamic forces,and the physical and chemical properties of the porous medium.Also,the multiscale nature of the transport mechanisms makes the modeling of multiphase flow in porous medium challenging.The theories and models of foam flooding technology at present include empirical and mechanism models.The empirical models usually simplify the block effect of foam system in porous medium as the reduction of fluid mobility,and the reduction coefficient is matched with experiment results(phenomena).The mechanism models introduce the propagation and decay processes of foam,however,the simulation theory considers these two processes as the reactants and products in chemical reactions,which do not represent the micro-mechanical actions between gas bubble and pore-throat.The present foam flooding models do not reveal the events that happening at pore-throat scale.Therefore,a deep understanding of the physics that govern foam system flowing in porous medium is of great importance for its future developments of theory and technology.By simulating the profile outline of liquid collar in pore-throat and deriving the distribution of capillary pressure on the curved gas/liquid interface,a liquid collar shape model is established,which is able to study the developing principle of liquid collar shape during gas bubble snap-off.By deriving the flow rate equation of wetting phase fluid in liquid film that flowing into liquid collar,and combining it with the liquid collar volume calculated by the liquid collar shape model,the time that liquid collar needs to reach a certain phase(volume)can be calculated,thus a liquid collar evolvement model is established,which can simulate the shape of liquid collar varying with time.A computer program module is made by the software MATLAB,to simulate the evolvement of liquid collar shape during snap-off.The simulation result of liquid collar evolvement model is compared with the video data recorded in a gas bubble snap-off experiment and the experiment data of a core foam flooding,and the reasonability and precision of this model are verified.In numerical simulation at reservoir scale,the liquid collar evolvement model indicates that the slugs of foaming liquid and gas,which are injected in turns,should not maintain a constant gas-liquid ratio or constant injection rates.The key point that matters is to form an advantageous zone of foam propagation in formation,where the size of gas bubbles matches the size of pore-throat,so the target zone of reservoir will be flooded effectively.The model of liquid collar shape provides an evolvement path of liquid collar shape,and indicates that the shape of liquid collar only depends on the geometric parameters of pore-throat and has no relationship with the fluid properties(interfacial tension,fluid viscosity,etc.).It theoretically explains the factors controlling the evolvement principle of liquid collar shape,which are the developing limit of capillary pressure and the thermodynamic tendency of interfacial tension,and the specificality of liquid collar evolvement and some corresponding phenomena observed in experiments.As a dynamic model at pore-throat scale,the model of liquid collar evolvement can simulate the liquid collar shape varying with time during snap-off,which reveals that(in dilute solution)the developing speed of liquid collar,also known as the snap-off time,depends on the interfacial tension of gas/liquid interface and the volume of liquid collar.And the size of gas bubble that generated by snap-off is determined by both snap-off time and local gas phase flow rate.Therefore,the model of liquid collar evolvement reveals the micro-mechanical effects between gas bubble and pore-throat.The numerical simulation results of liquid collar evolvement model have a good match with the video data of gas bubble snap-off experiment and the data of core foam flooding experiment,which verifies the reasonability and precision of this model.The distributions of advantageous foam propagation zone in reservoir,with multiple gas injection flow rates,are calculated by liquid collar evolvement model,and an increasing slug injection method of foaming liquid and gas are proposed.Foam will be generated in inner reservoir locally,so that the valid lifecycle of foam can be fully used for flooding,which realizes the precise displacement of reservoir and improves the working efficiency of foaming liquid.