Resistivity Change Mechanism in the Carbon Dioxide Sequestration Process

Abstract

This study explores the variation law, influencing factors, and mechanisms of resistivity in the interaction between CO₂ and saltwater. This study used a hollow PEEK conductor to simulate core pores. With excellent thermal stability, mechanical strength, and electrical insulation, its homogeneous, nonporous nature eliminates interference from rock properties, providing an ideal medium for studying pure fluid changes. The resistivity at different temperatures and pressures, and that of different fluids during the displacement process was experimentally measured. The results show that mineralization is the main factor affecting the resistivity, and the resistivity of formation water is reduced by 98.83–99.41% compared with that of deionized water under the same conditions. With the increase of temperature, the ion hydration effect weakens and increases the ion mobility rate, and the resistivity of various fluids decreases by 55.13–66.87%. The effect of pressure on resistivity is relatively weak, and the resistivity is reduced by approximately 2.29–11.08% by reducing the distance between ions and increasing the collision frequency between ions. However, in CO₂-containing systems, increased pressure promotes CO₂ dissolution and ionization of more ions, which results in a larger decrease of 17.72–9.31%. It is particularly noteworthy that CO₂ dissolved in pure water reduces the resistivity by 91.50–94.50%, but when dissolved in formation water, the resistivity increases by 276.63–430.94%. Based on the ideal pore characteristics of the PEEK model, we fix the parameters (a, b, m, n) in the Archie formula to 1, and derive a simplified saturation model: Sw = Rw/(φRt). This achieves the quantitative representation of resistivity monitoring data into saturation distribution, improves the accuracy of calculating CO₂ saturation using resistivity data, and has important guiding significance for interpreting field monitoring data and evaluating CO₂ sequestration. Future research aims to translate these findings into practice using real rock cores.