Dependence of electrical conduction on pore structure in reservoir rocks from the Beibuwan and Pearl River Mouth Basins: A theoretical and experimental study

Abstract

The electrical conduction of reservoir rocks is crucial for estimating hydrocarbon and water saturation. The dependence of the electrical formation factor as a key parameter of electrical conduction on pore structure is analyzed through theoretical development, petrophysical experiments, error analysis, core-scale displacement experiments, and pore-scale numerical simulations. Through the tortuous fractal capillary bundle pore model, the electric formation factor is theoretically a function of three pore structure parameters: porosity, tortuosity fractal dimension, and pore fractal dimension. Through rock-electrical experiments from 46 reservoir rocks from the Beibuwan and Pearl River Mouth Basins, Thanh’s model can give a satisfactory performance with a suitable value for the ratio of minimum to maximum pore radius. Porosity-based formation factor models, including classical Archie’s law, have an unacceptable error at high formation factor. Our formation factor model provides better predictions with an error factor of ±10. The Archie’s cementation exponent can be expressed as the average tortuous degree of electrical conduction paths. The dependences of hydraulic and electrical conductions on pore structure are distinctly different. Hydraulic conductance has obvious pore-size dependence, the dominant flow channel, and threshold pressure, which are affected by displacement order. However, the case of electrical conduction is the opposite, in which electrical conduction has no dominant channel, and does not reflect the pore-size information under the same porosity.