Factors Influencing Resistivity Inversion for CO₂ Geological Storage Zones: A Quantitative Study

This study establishes a homogeneous half-space and a horizontally layered two-layer background stratigraphy model using cross-borehole electrical resistivity tomography (ERT) based on an incomplete Gauss-Newton (IGN) method to investigate the resistivity inversion characteristics of CO₂ storage zones. The effects of storage zone volume (VCO2), storage zone resistivity (ρCO2), background formation resistivity (ρf), and CO₂ diffusion on inversion results were systematically analyzed, and the mechanisms underlying the influence of different parameters on inversion imaging were explored. The results indicate that an increase in the VCO2 significantly affects the inverted resistivity. The ρCO2 can be well inverted within a certain range, but inversion accuracy decreases once the resistivity exceeds a threshold. The ρf is a critical factor influencing inversion results; as the ρf increases, the inverted resistivity values rise markedly, although this effect exhibits an upper limit. The study also uncovers the exponential nature of CO₂ diffusion in the storage zone, where diffusion leads to exponential changes in resistivity and the delineation of the diffusion zone is enhanced by comparing pre- and post-injection resistivity differences. These findings offer valuable insights for CO₂ storage monitoring, contributing to both safety assessments and the evaluation of storage stability in geological sequestration.