Evaluation of consolidation parameter data trendings and comparison between prediction models for well-log velocities: A case study from the Namorado Oilfield (southern Brazil)

摘要

The compressional and shear-wave velocities (V-P and V-S) have been used in studies for hydrocarbon exploration over the last decades. Nevertheless, the absence of S-wave velocity records in geophysical surveys is common. In this work, we applied the iterative method proposed by Lee (2006), which allows evaluations of P- and S-wave velocities by estimates of the consolidation parameter alpha. We use well-log datasets from a turbiditic reservoir at Namorado Oilfield (Campos Basin, southeastern Brazil) to test this methodology. Results were further compared to a well-established empirical model (Greenberg and Castagna, 1992). We verified a good agreement for V-S results provided by both methods, and a consistent correspondence between the measured V-P and those calculated by the Lee (2006) method. It was also possible to assume the reliability of the alpha values, although the presence of denser lithologies may produce local artifacts, which affect V-P(alpha) and V-S(alpha) estimates. Furthermore, the results for alpha, V-P(alpha) and V-S(alpha) pointed to: (i) an upward trending for V-P/V-S ratio values, for profile NA-01, that indicate a possible hydrocarbon-filling zone; (ii) the presence of two distinctive alpha data groupings with respect to porosity, which are clearly influenced by the involved type of lithologies; and (iii) the absence of a straightforward relationship between alpha and porosity under pressure conditions.