Determination of the velocity of sound in reservoir fluids using an equation of state
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Production of oil and gas from hydrocarbon reservoirs results in reduction in reservoir pressure and changes in the fluid composition and saturations. Enhanced oil recovery methods such as Gas Injection, Water Flooding, CO2 Injection, in-situ Combustion, Water Alternative Gas injection (WAG) and so on have similar effects. Variation of these properties can lead to changes in the velocity of sound in subsurface layers. On the other hand, any change in temperature, pressure, composition and density of pore fluids has strong influence on the seismic elastic properties. Elastic properties of fluids are usually simplified in geophysics. All existing software employs empirical relations to calculate seismic wave velocities in reservoir fluids. In this study, thermodynamic properties have been considered as first and second order derivative properties of the thermodynamic potentials. For this purpose, a statistical thermodynamic approach, with the Statistical Associated Fluid Theory – Boublik - Alder – Chen – Kreglewski has been used and developed further for mixtures and real oils by proposing new mixing rules, tuning binary interaction parameters, and utilizing the properties of single carbon numbers. In addition, a large number of experimental data on pure, binary and multi-component systems have been generated in this work. The predictions of the model developed in this work have been validated against the experimental data generated in this work and those reported in the literature. The predictions were found to be in very good agreement with independent experimental data.