Carbonate Rock Resistivity Index Measurement using Equivalent Rock Model

摘要

The applicability of Archie’s relation depends on the link between pore structure and resistivity of the rock, and because of this relationship, the rock maybe classified as Non-Archie. Keeping this factor in view, for carbonates, the intricate pore systems, the application of Archie’s law becomes invalid and any estimate of water saturation using Archie’s equation will most likely yield erroneous results. Many scholars and researchers have attempted to come up with models linking well logs and laboratory data to estimate water saturation in complex pore systems. To appropriately capture the conduction behavior of a rock is aimed at and the conduction mechanism is then related to not only the pore geometry but also other petrophysical factors including wettability and the existence of conductive exterior minerals. For complex lithologies, resistivity index curves cannot be accurately defined by Archie’s law, and investigations at lower water saturation values are required to describe the non-Archie behavior. The shape of the RI curves varies quite considerably and an attempt to describe the variation qualitatively as well as quantitatively requires the use of either dual or triple conductivity models. In these models, the pore systems are linked with each other electrically in series or parallel, in addition, a combination of the two is also possible. This enables the use of simply two of the three adjustable parameters to adequately model the experimental outcomes. This study, presents a saturation model for dual porosity systems. Having NMR data will enable the use of this model to determine water saturation by utilizing the volume fraction of each contributing pore system (Macro and Micro) derived from NMR logs. Furthermore, this work also examined the effects of various influences on the electrical constraints which included cementation factor, the shape factor for the lithology and saturation exponent.