Chapter 9 - Deterministic inversion based interpretation of multifrequency electromagnetic logs from wolfcamp and bakken shale formations

Abstract

Chapter 9 presents a method to jointly interpret eight dielectric permittivity and conductivity dispersion logs (10 MHz–1 GHz) and one laterolog resistivity (∼1 kHz) acquired in 520-feet depth interval of the clay- and carbonate-rich Upper Wolfcamp formation. The proposed joint interpretation technique also processed eight dielectric permittivity and conductivity dispersion logs (22 –960 MHz) and one induction resistivity (∼20 kHz) logs acquired in 350-feet depth interval of the Bakken Petroleum System (BPS). In doing so, a continuous estimation of water saturation, brine conductivity, cementation exponent (textural index), and saturation exponent with ranges of possible values were obtained for the upper Wolfcamp formation and BPS. The proposed log processing technique is robust compared to processing only the dielectric dispersion logs, especially in pyrite-rich, low-porosity, and hydrocarbon-bearing formations. These estimates have higher certainty and better convergence at lower water saturation, which is desired feature of the processing technique. Compared to the estimates for saturation exponent and brine conductivity, water saturation and cementation exponent estimates exhibit higher certainty. Estimates of cementation exponent obtained using the proposed inversion exhibit higher variation with the increase in depth indicating an increase in heterogeneity/layering with depth.