Adaptive prediction method for shear wave velocity based on a generalised-regular polygon shape pore rock physics model

Abstract

In rock physics research, conventional modelling approaches represent complex-shaped pores in rocks as 2D ellipses or 3D ellipsoids, and few studies have been conducted on other types of pore representation. Considering the problems associated with multiple pore shape factors as well as the numerous possible rock pore shapes and the cumbersome application process of the 2D regular polygon shape pore (RPSP) model, this study introduces a new pore shape factor p to replace the multiple shape factors and produce a generalised RPSP (G-RPSP) rock physics model. Compared with the RPSP model in which several pore types are considered, the new model can consider a greater number of pore shape possibilities mathematically by the addition of p to the theoretical definition domain. Then, based on the combination of G-RPSP model, Voigt-Reuss-Hill average equation and Gassmann equation, this study establishes an adaptive prediction procedure for shear wave velocity. In the prediction procedure, the pore shape factor p is adaptive, calculated under the constraint of P-wave velocity, and used to calculate the shear wave velocity. The proposed method was used to perform trial calculations based on laboratory measurements and well logging data. The results show that the predicted S-wave velocities match well with the measured ones. Furthermore, we compare the predicted S-wave velocities deduced from the proposed method, the original RPSP model and an existing adaptive elliptical pores method. The results demonstrate that the proposed method is superior and can be satisfactorily implemented for laboratory measurement and on logging data.