Flow Behavior and Electrical Conductivity Characteristics of Carbonate Rocks Based on Pore-Scale Glass-Etched Experiments

Deep complex carbonate reservoirs contain different types of pore space, including vugs and fractures. Their gas–water distributions and flow characteristics are complex. The effect of pore structure and gas–water flow on resistivity in deep complex carbonate reservoirs remains unclear. This uncertainty creates challenges for natural gas exploration and development. A gas–water displacement and impedance synchronous measurement platform was established. Three types of glass-etched micromodels were fabricated from CT images of real carbonate cores. These models included a fracture–vuggy type with large aperture, a fracture–vuggy type with small aperture, and a vuggy type. After the micromodels were saturated with dyed formation water, gas–water displacement and water–gas displacement were conducted sequentially. Microscopic images of gas–water distribution, water saturation, resistivity, and resistivity index were obtained. The results showed that gas preferentially entered connected fractures and large pore throats, forming preferential channels. Residual water was mainly retained in vug corners, narrow throats, and weakly connected zones. During gas–water displacement, resistivity increased as water saturation decreased. The resistivity response showed a three-stage pattern of slow increase, rapid increase, and subsequent slow increase. During water–gas displacement, resistivity decreased as water saturation increased. The resistivity response showed a three-stage pattern of slow decrease, rapid decrease, and subsequent slow decrease. All three models exhibited non-Archie behavior. The stage-specific saturation exponent n ranged from 2.62 to 13.10, 4.36 to 7.24, and 5.37 to 9.84 for the fracture–vuggy type with large aperture, fracture–vuggy type with small aperture, and vuggy type, respectively. Their overall n values were 7.26, 6.36, and 5.39, showing that the fracture–vuggy type with large aperture had the most abrupt electrical response. This study clarified the relationship between gas–water flow characteristics and conductive response in carbonate rocks with different pore structures. The results provide pore-scale experimental evidence for water-invasion identification, remaining gas evaluation, and calibration of rock electrical parameters in complex carbonate reservoirs.