Liquid-Gas Two-Phase Flow In Fractures:Characteristics And The Surface Tension Model

The study of fractured liquid-gas two-phase flow is of great significance for coalbed methane extraction,oil and gas field development,groundwater pollution control,and underground nuclear waste treatment.Based on a combination of laboratory tests,theoretical analysis and numerical analysis,this paper comprehensively studies the flow characteristics of liquid-gas two-phase flow in a fracture.Based on the generalized Darcy’s law,a surface tension model is proposed.The simulation method was used to verify the surface tension model,and the effect of roughness on liquid-gas two-phase flow in fractures was studied.The main results are as follows:(1)A set of transparent fracture liquid-gas two-phase flow test equipment was developed.The instrument can observe the flow characteristics in the fracture under different liquid-gas flow conditions,and can realize multi-point pressure measurement,liquid-gas flow measurement and other functions,and provide a new kind for studying the flow of liquid-gas two-phase flow in fracture.experiment method.(2)The liquid-gas two-phase flow pattern is obtained through the fracture liquid-gas twophase flow test and simulation:bubble flow,slug flow,annular flow and droplet flow.As the gas phase flow rate increases,bubble flow,slug flow,annular flow,and droplet flow occur successively.And the characteristic relationship between relative permeability and saturation is obtained.The relative permeability of the gas phase decreases as the liquid phase saturation increases,and the relative permeability of the liquid phase increases as the liquid phase saturation increases,and the sum of the relative permeability of the gas and liquid phases is less than 1.(3)A surface tension model is proposed.The liquid-gas two-phase flow with smooth and rough fractures is taken as the research object,and the influence of surface tension between the phases is considered.Based on the generalized Darcy’s law,the surface tension correlation term is introduced on the pressure drop of the fracture inlet and outlet to construct the surface tension model,and the applicability analysis of the surface tension model is carried out by the fracture liquid-gas two-phase flow test and simulation,and finally the surface tension is determined.The model works better for predicting the relationship between fracture relative permeability and saturation.The relationship between the surface tension correction coefficient and the variation of liquid-gas flow rate and liquid saturation in the surface tension model is analyzed.(4)The effect of roughness on the flow of liquid-gas two-phase flow in fractures was studied.Due to the increase of the roughness,the number of annular flow of the rough fracture increases.The contact angle increases with the increase of liquid-gas flow rate,the surface tension decreases with the increase of gas phase flow rate,and the relative permeability of gas phase and liquid phase decreases.