A Novel Method for Accurate Measurement of Fluid Saturation in Shaly Sandstone During CO2 Sequestration

Accurate monitoring of fluid saturation is crucial for preventing fingering or leakage during CO2 sequestration. Due to the difficulty in testing the cementation factor of shaly sandstone, the evaluation of fluid saturation in such reservoirs by the Archie equation may be significantly biased. This study presents modifications to the Rhoades capillary bundle model and the Waxman-Smits parallel model for the clay conductivity phase and cementation exponent, based on the principle of the best conduction pathway. we use two different conductivity models and fluid transport coefficients in rock pores to modified the cementation coefficient. We compare different conductivity models and refine them by fitting them to on-site CO2 storage monitoring data. We analyze the impact of parameter variations on conductivity and saturation, and verify the accuracy of the equation. It is found that the relative error of the modified model is 10.76% compared with the conductivity of the dual-water model. Shaly sandstone reservoirs are characterized by clay-water expansion phenomena, with clay conductivity comprising the predominant fraction of total conductivity. The variation in water phase transmission and conductivity can be divided into two phases. In the first phase, conductivity experiences a rapid increase, while in the second phase, it rises gradually in a linear fashion. In shaly sandstone reservoirs, the relative error of the modified model is 5.44%. The enhanced accuracy in saturation calculations serves as a safeguard against measurement errors by on-site engineers.