Advantages, Utility, and Efficiency of Geophysical Well Log Cross-Plots to Evaluate the Petrophysical Properties of Oil Reservoirs

Abstract

Core sample measurements and well logs were integrated to evaluate reservoir petrophysical properties and develop more precise models for oil production. These logs are frequently used to generate cross-plots that reveal underlying patterns and assist in reservoir classification. In this study, cross-plots helped characterize the petrophysics of Namorado sandstone and Enchova limestone reservoirs in the Campos Basin, southeastern Brazil. Hingle, Pickett, Buckles, Neutron-Density, and M-N cross-plots were created from basic logs obtained from a single borehole in each oilfield. The estimated sonic porosity aligns with laboratory measurements of effective porosity and is more suitable for reservoir calculations, offering nearly continuous, full-interval estimates. Results show that transit time in the Enchova reservoir is slightly higher than in Namorado, while formation water resistivity, matrix density, and irreducible water saturation are similar. The limestone reservoir holds more water, and a higher formation water resistivity suggests it contains more oil in its pores. This study underscores the usefulness and efficiency of cross-plots for petrophysical assessment, highlighting their role as vital tools for quickly visualizing data and understanding relationships among multiple properties.