Research On Microscopic Mechanisms And Numerical Simulation Of Induced Polarization In Water Bearing Argillaceous Sandstone

Induced polarization (IP) method is an important electrochemical prospecting method. The microscopic mechanism of IP effect in argillaceous sandstone is mainly from the hypothesis of the electric double-layer deformation and the concentration difference polarization. There is no mathematical model to describe this up to now. In this paper, firstly, the macroscopic characteristics of induced polarization are described by a series capillary model. We obtained the relationship between the cation exchange capacity and the electric double-layer potential- Zeta potential by deriving the relationship between the macroscopic parameter of structure in argillaceous sandstone and the microscopic parameter of capillary model. According to the theory of the electromigration and ion diffusion in porous medium, we formulated the mathematical expression of the ion flux and the electric current intensity in the stable state of IP effect. Meanwhile, we derived an analytical expression of ion concentration distribution and the mathematical model of the induced polarization potential and the spontaneous potential for water bearing argillaceous sandstone based on the conservation law of charge and the conservation law of matter. And we get the influences of porosity, permeability, concentration of saturated solution, cation exchange capacity and the microscopic parameter of pore structure on the stable state of induced polarization effect by numerical simulation. Secondly, according to the conservation law of charge and the conservation law of matter in the dynamic state of induced polarization effect, the dynamic procedure of ion migration is studied by a series capillary model, and the governing equations, initial condition and boundary condition are obtained. The forming process of the concentration difference polarization is simulated by finite difference method, and the process of electric double-layer deformation with the variation of the concentration of solution is simulated mathematically. The result shows that the induced polarization effect is caused by ion concentration difference polarization potential and the potential of electric double-layer deformation. We also get the influences of all kinds parameters on the dynamic state of induced polarization effect by numerical simulation. Finally, the decay curve of induced polarization is inversed from the multi-exponential inversion by Levenberg?Marquardt. The influences of porosity, cation exchange capacity, concentration of solution, temperature, and discharging time on the induced polarization relaxation time spectrum are analyzed. The results show that the relaxation time spectrum is not only the expression of the microscopic pore structure in rock, but also the diffusion process of ion repristination.