Analysis and validation of two mathematical models of acoustic impedance in well logs: An example in Namorado oilfield, Campos basin, Brazil

This paper is concerned with the reliability of two different models to compute acoustic impedances in the Namorado oilfield, Campos Basin, Brazil. The acoustic impedance is a physical property related to the interaction of a seismic pulse and the components of the rock. This interaction is useful to understand lithological aspects of the studied area. Numerous models have been proposed in the literature with undesirable results. Particularly for Namorado oilfield, there is few models to estimate acoustic impedances in a reliable framework, specially for lack of log data. To achieve this purpose, we use a petrophysical expression that directly estimates acoustic impedances without the need of density logs. In addition, we also discuss empirical expressions to compute compressional velocities using other log data. To validate both models, we calculate the observed acoustic impedance directly from the elastic theory and also present 2-D maps of impedances for the whole Namorado oilfield. The results show that both models are good for low values of impedance, despite of the overall sub-estimation of the acoustic impedance by the petrophysical model. The empirical model presents more dispersive estimations of acoustic impedance when faced with the observed impedance. With this paper, we are intended to present more possibilities for the poor data coverage of Namorado oilfield.