Determination of the acoustic properties of hydrocarbon rich gases using PVT relations

Published approaches for determining the seismic properties of pore fluids are investigated to examine the effect of gas quality at constant pressure and temperature. For this purpose, a range of fluids from natural gas to rich gas condensate is prepared and tested to determine pertinent acoustic properties of the fluid at single-phase conditions. The results show that the ratio of heat capacities of fluids in currently used models do not vary with the change in gas quality, consequently the calculated gas bulk modulus may not appropriately reflect the fluid composition dependency. Therefore a new approach is suggested in this work to calculate the ratio of heat capacities of gases where the effect of gas quality is taken into consideration. This leads to an increase in accuracy of predicted seismic property changes for gas condensate and other gas reservoirs.