The dual laterolog response of fractured-vuggy reservoirs based on conductivity tensor and Maxwell–Garnett mixing rule

Dual laterologs measure reservoir resistivity at deep and shallow depths around a wellbore, a thorough understanding of the dual laterolog response of fractured-vuggy reservoirs is key for reservoir identification and saturation evaluation. The joint development of the fracture and vugs complicates the laterolog response of fractured-vuggy reservoirs. In this study, the conductivity model of the dipping anisotropic structure on the horizontal plane was analyzed according to the theory of the conductivity tensor. Then, based on the Maxwell–Garnett mixing rule, a conductivity model of the vuggy reservoirs was established. On this basis, the dual lateral conductivity model of fractured-vuggy reservoirs was established by equating the vuggy reservoir to the matrix and the dipping anisotropic structure plane to the fracture plane. Furthermore, based on the dual lateral conductivity model and physical experiments, the dual laterolog responses with respect to the fracture dip angle, fracture porosity, and vug porosity were systematically analyzed. The study revealed that (1) the fracture dip angle significantly affects the separation of the dual laterolog. In other words, at a low dip angle, the fracture shows a negative separation of the dual laterolog, whereas a positive separation at a high dip angle; (2) for vuggy reservoirs, the development of vugs decreases the deep and shallow laterologs, and the more the vugs developed, the greater the decrease; (3) for fractured-vuggy reservoirs, the dual laterolog response is mainly controlled by fractures. The development of vugs did not change the negative or positive separation of dual laterologs with different fracture dip angles.