Data-driven shear wave velocity prediction model for siliciclastic rocks

Abstract

Theoretical and experimental investigations of elastic wave propagation in sedimentary rocks have shown that shear-wave velocity is strongly correlated to compressional-wave velocity. This is because most of the factors that affect the shear-wave velocity also affect the compressional-wave velocity. In areas where shear-wave velocity logs are not available, empirical relationships based on regression analyses are often used to estimate the shear-wave velocity from the compressional-wave velocity. However, most of the available empirical relationships in the open literature were developed primarily for consolidated rocks and their applications to unconsolidated formations may produce inaccurate estimates. Moreover, in siliciclastic environments, empirical relationships that work well for clean sandstone formations may perform poorly in shale formations and vice versa. In this paper, an attempt is made to develop a new shear-wave prediction model that can be applied to a wide range of lithologies and formation strengths in siliciclastic environments. The model is tested using actual field data from the Niger Delta basin and the Norwegian North Sea. The new model is developed based on establishing a relationship among shear-wave velocity, compressional-wave velocity, and formation bulk density. In general, an excellent agreement is observed between the predicted and measured shear-wave velocity. The statistical analysis shows that the accuracy of the shear-wave velocity prediction can be improved by incorporating the formation bulk density term.