An Innovative Workflow for the Petrophysical Characterization of Tight Gas Reservoirs in Argentina

Abstract

The formation evaluation of low-porosity tight gas reservoirs in Argentina presents several well-known challenges in the estimation of main petrophysical properties as porosity, clay fraction, permeability, and water saturation. The main goal is to accurately quantify these petrophysical properties with a consistent and reliable petrophysical model. The next task is to reveal the key petrophysical responses that represent the link between petrophysics and production. The present work describes the main petrophysical challenges faced and an innovative workflow used in the Lindero Atravesado field with clear examples to illustrate the effectiveness of this approach. The workflow involves measurements such as advanced elemental gamma ray spectroscopy, multifrequency dielectric dispersion, and nuclear magnetic resonance (NMR). The advanced elemental gamma ray spectroscopy has been key for the creation of a robust mineralogical model, and to derive the matrix properties used to obtain an accurate porosity free of matrix and gas effects with the combination of NMR porosity. The dielectric dispersion provides a direct estimation of water volume, which, in turn, helps to adjust the conventional method of water saturation from resistivity. The good correlation between the petrophysical properties estimated from the proposed workflow and the core analysis, demonstrates the benefits of using the advanced log measurements. The final step of the workflow consists in the definition of poro-fluid facies determined with a new methodology, called NMR factor analysis, that is based on the extraction of multimodal information from the NMR T2 distribution to determine the optimal number of dominant modes (factors) that allow describing the reservoir. Production logging results showed a good relationship between the poro-fluid facies and reservoir productivity.