Abstract

This study covers a methodology applied by PDVSA-INTEVEP in collaboration with Paradigm Geophysical to evaluate a carbonate gas and condensate reservoir, located offshore in West Venezuela. The main goal of this study is to effectively account for the high heterogeneity of the rock fabric and associated high variability in permeability encounter on the reservoir, despite of showing porosity values uniformly distributed.

This carbonate reservoir is clearly subdivided in two different sections: a Lower Section, comprise of mostly rudstone and floatstone, preserving micro-porosities in some bioclasts and carbonate mud, defining a unimodal pore distribution and size, with a small pore throat radius. The Upper Section presents primarily coarse-grained limestones(rudstone) preserving primary and secondary porosities, causing a variable distribution of pores and a heterogeneous pore throat radius associated with the particle micro-fracturing contribution (Criollo and Marin, 2015).

For this study, a reference well with a comprehensive dataset was selected, that included Core data (Sedimentological facies, Porosity and Permeability), Micro-resistivity Images and NMR data. The images were used to quantify with high resolution the rock fabric changes seen on the formation. Similarly, the whole NMR T2 distribution was used to account for changes in the pore system. This information was then combined with standard petrophysical logs and core facies using the Multi Resolution Graph-Based clustering method, to produce detailed electrofacies models, focusing on honouring the rock fabric and pore distribution in the reservoir.

These detailed electrofacies models constructed were then calibrated with core data, allowing to predict permeabilities on sections of the well not covered by the original core, as well as on neighbouring wells, where no core data was available.

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