Perpustakaan Digital ITB

The exploration for unconventional reservoirs is growing rapidly in recent years, especially in Indonesia. One of these reservoirs is Coal Bed Methane (CBM). However, only a few publications on physical properties of CBM is found. Rock physics model for CBM is discussed in this paper using dry coal data taken from Morcote’s laboratory measurement. The elastic modulus of fluid is calculated based on Batzle-Wang equation, while the elastic modulus of mineral is estimated from the modulus of dry coal. Fluid substitution is performed by gradually replacing methane into water from 60 to 100 percents. Results, that has been validated with data from Yao and Han's laboratory measurement, show the dependencies of water saturation to VP, VS, VPVS ratio, and Thomsen anisotropy factor and 𝛾. Pore stiffness experiment based on Morcote's data is 𝜀 also analyzed in this paper.Results of this experiment show that with the increase of water saturation,VP significantly increases,VS slightly decreases, VPVS ratio significantly increases, and anisotropy factor εsignificantly decreases. This result agrees well with Yao and Han's experiment. VPVS ratio is found to be the most sensitive parameter to water saturation. This parameter can therefore be used to help estimate methane saturation in CBM reservoir exploration.