Abstract
Up to now, different petrophysical methodologies have been developed to improve the success rate in selecting oil intervals in the Gulf of San Jorge Basin oilfields. These methodologies have been successful only in a limited number of cases and a solution that has field-wide applicability has been lacking. This project attempts to optimize previous results using an integrated petrophysical characterization workflow.
The geological complexity of the Estancia Cholita Field which is mostly due to limited lateral continuity and small reservoir bed thickness, particularly in the Castillo Formation, makes layer-by-layer correlation difficult. Several other factors add to the complexity of petrophysical evaluations, these include: alteration of petrophysical properties in certain zones near faults, variation of tuffaceous material content, formation damage, invasion of drilling fluids, zones with viscous oil, low and variable formation water salinity.
During this study, a two step petrophysical evaluation workflow was developed. The first step considers the application of quick-look log analysis techniques, specially the "Ratio" methodology, and the free fluid and permeability indexes (NMR), with the aim to evaluate those intervals of major potential in the well. The following step consists of a detailed analysis, in the zones where water production forecast has been identified, to calculate a formation water resistivity profile along the well.
Preliminary results of the study confirm that combining this methodology with local experience, layer-by-layer correlations, formation pressures data, log analysis, and supplementary information helps improve predictions of oil bearing zones in the Estancia Cholita Field.
