Numerical Study On The Electrical Response Characteristics Under Nonuniform Distribution Conditions Of Two-phase Flows In Pipes And Porous Media

The sample drilling technology of natural gas hydrate is complex and costly,thus field samples are extremely limited.Laboratory physical simulation experiments are also costly and time consuming.The actual conditions that can be simulated are limited and the detection information is less in physical simulation experiments.The numerical simulation of petrophysics provides a feasible way to overcome the above difficulties.The non-uniform distribution of two-phase fluids in pipes and porous media and the corresponding electrical response characteristics were investigated based on the finite element numerical simulation method of fluid-electric field coupling,it provides a modeling methodology for numerical simulation experiments of petrophysics containing natural gas hydrate or oil-water,and provides a model and theoretical basis for the parameter optimization of electrical sensors,analysis of the electrical test data.To explore the numerical simulation method of flow-electric field coupling and verify the validity of the numerical simulation model,a numerical simulation model of gas-liquid two-phase flow field coupled with electric field of dual ring-shaped electrodes was established.The influence of typical flow pattern of gas-liquid two-phase flow on the electric field response characteristics between dual ring-shaped electrodes and the quantitative relationship between the mixed conductivity and liquid fraction were analyzed.It has been demonstrated that:(1)The electrical response characteristics between electrodes can be obtained by the numerical simulation of flow-electric field coupling under the conditions of typical flow patterns like stratified flow,wavy flow,slug flow,bubbly flow and annular flow.(2)The flow pattern and phase distribution of the gas-liquid two-phases flow in a pipe can be judged through an analysis of the spatial distribution of the axial current density between electrodes.(3)The average liquid fraction can be calculated by using the dimensionless mixed conductivity.To simulate the non-uniform distribution of gas hydrate in porous media,the non-uniform distribution of hydrate/water in porous media was simulated by using the oil/water distribution formed in the process of water flooding,considering the similarity of electrical properties and micro-distribution of oil and hydrate,and a numerical simulation model of flow-electric field coupling was established.Based on this,the influence of microscopic factors of porous media(the skeleton particle shape,skeleton heterogeneity,wall contact angle,interfacial tension,oil-water viscosity ratio and inlet velocities)on oil-water two-phases distribution in porous media was discussed.The influence of the spatial distribution of two-phase fluids,the shape and location of electrodes on the electric field response characteristics was studied.Finally,the calculation method of oil/hydrate saturation was investigated based on the numerical simulation data.It has been demonstrated that:(1)The heterogeneous phase distribution of fluids in porous media can be obtained through the flow field calculation by adjusting the microscopic factors of porous media in the numerical simulation model.(2)The shape and position of electrodes affect the spatial distribution uniformity of the electric field intensity and the sensitivity to the phase distribution of fluids.(3)The dimensionless impedance amplitude of the porous medium containing oil and water with the electric field frequency ranging from 0.001 to 1000Hz shows frequency dispersion characteristics.The relationship between the dispersion of impedance magnitude and oil saturation is approximately linear,a method for calculating oil/hydrate saturation can be established.