Application Of Magnetic Resonance Logging In San Jorge Basin (Argentina)

Magnetic Resonance Imaging Log (MRIL) data are providing formation evaluation information heretofore not available in the Golfo San Jorge basin. Argentina, and are contributing to increased well productivity. This paper deals with log interpretation problems associated with conventional tools, and the solutions provided by the MRIL service. We briefly explain the geology of the basin and the principal problems encountered in the evaluation of the conventional logs. We then describe an empirical MRIL interpretation methodology and compare the predictions with production results. In the San Jorge basin, the sandstone reservoirs contain a high percentage of diagenetic clays, volcanic lithic fragments in a tuffaceous and argillaceous matrix. This complex lithology influences conventional porosity and resistivity tools, so despite extensive analysis with conventional logs, completion strategies remain costly and uncertain. Conventional porosity and resistivity tools are heavily influenced by the complex lithology. The MRIL service, based on the principle of nuclear magnetic resonance and relaxation, provides critical petrophysical formation evaluation data. Without relying on radioactive sources, it offers a mineralogy independent, effective porosity. It provides a measure of free fluid, irreducible water saturation, and pore-size distribution. From these data, permeability is derived. The MRIL permeabilities are compared with core and production data. Finally, the MRIL data have permitted us to identify sands suitable for fracture stimulation. The predicted results compared well with actual production data. The MRIL service has improved the accuracy of productivity predictions and increased hydrocarbon production.