Petrophysical model for bulk density of complex lithologies

Abstract

The workflow for an integrated well log analysis must incorporate physically-consistent models for rock properties prediction. Therefore, the selection
of the conceptual model is a crucial step in deriving the petrophysical model under investigation. In this paper, we apply the parallel layers conceptual model to derive
a petrophysical model for bulk density of complex lithologies. This conceptual model assumes the natural rock as a set of parallel layers with individual densities,
incorporating the main factors affecting bulk density of sedimentary formations (i.e., the solid matrix, porosity and fluid content). The resulting petrophysical model
shows the volumetric fractions of individual rock constituents as the key parameters for bulk density description. Further parameters of the dependence can be easily
selected from petrophysical tables. In this way, evaluation of predefined volumetric fractions of rock constituents is a mandatory procedure for applying the investigated
petrophysical model. We present results of calibration and estimation of bulk density well log measurements through turbiditic sediments forming the Namorado reservoir,
Campos basin. In evaluating the facies-described volumetric fractions of main constituents of rocks at well surroundings, fundamental well log measurements represented
the inputs for mineral volume analysis using the non-negative least-squares inversion method. The outcomes of both experiments exhibited the good performance of
the petrophysical model in estimating bulk density with negligible absolute errors and high correlation coefficient. As a conclusion, the parallel layers conceptual model
revealed enough robustness for construction of petrophysical models of other well log measurements.