Fluid Substitution Analysis Using Gassmann’s Equation Modification on Carbonate Environment

Abstract

Gassmann’s equation can be used to determine the velocity of compressional waves that pass through rocks with various pore fluid contents, using fluid substitution concept, but is generally applied to certain conditions only (physical rock properties). Carbonate rock has properties in contrary of Gassmann’s assumption; is a heterogenic, anisotropic rock and does not have a well-interconnected pores. In this research, secondary data from laboratory measurements are used, consisting of carbonate rocks (limestone and dolomite) to test modified Gassmann’s equation on carbonate rocks. Two approaches of Gassmann’s equation are used by using k-dry and k-1 components, which are the value of compressional modulus bulk of saturated rocks. The result of both approaches shows that the usage of k-1 component is more optimal to be applied to carbonate rocks because it does not use k-dry component, which should only be used on field measurements, as there is a difference in the environment condition (air, temperature, and pressure) on reservoir and laboratory.