Fluid substitution in carbonates based on Gassmann equation and Eshelby-Walsh theory

Abstract

Fluid substitution of carbonates is more difficult than it is in clastics for two reasons. First, there are much more uncertainties in rock physics modeling, especially in how to acquire the moduli of carbonate rocks’ solid matrix, because most of laboratory measurement data came from sand reservoirs and much less attention has been paid to its study. Second, it is difficult for us to model pore geometry of carbonates due to their complex pore systems, and hence to evaluate their influence on the results of fluid substitution. In order to solve these problems, we firstly present a new fluid substitution method of carbonate rocks using Gassmann equation and Eshelby-Waslsh theory (GEW) in this paper. Then, we discuss how to calculate the moduli of carbonate rocks’ solid matrix and the effect of pore geometry on fluid substitution with rock samples. Finally, we make a fluid substitution and a comparison with the conventional Gassmann fluid substitution. The results show that our new method is accurate and reliable in the fluid substitution of complex carbonates.