An alternative formulation for estimating seismic properties of hydrocarbon fluids with sensitivities to amplitude variation with offset, sonic log, and time-lapse seismic modeling

ABSTRACT We develop new equations and workflow for computing the seismic properties of hydrocarbon fluids. More specifically, we provide a complete formulation to compute acoustic velocity, bulk modulus, and density, with separate workflows for oil and gas. The formulation combines equations of state and machine-learning-assisted empirical correlations, which are functions of pressure, temperature, molecular weight for oil, and specific gravity for gas. An extensive set of published experimental data is used to test and validate our formulation. The traditional method from Batzle and Wang (BW) is discussed in detail and used for comparisons through theoretical and experimental perspectives. In general, whereas the results suggest that both models provide adequate modeling of seismic properties, several cases exist where our formulation provides a more accurate description of experimental data of acoustic velocity in gases and oils. To investigate the potential impact of our formulation on geophysical applications, we perform an amplitude-variation-with-offset (AVO) modeling analysis at a hypothetical siliciclastic reservoir considering alternative oil and gas saturation scenarios. For various saturation scenarios, there are significant differences between AVO responses at higher pressures when hydrocarbon properties are computed using our formulation and BW equations. We further assess the impact of our formulation on the modeling of acoustic velocity using well-log data from the Norne Field, showing the impact of different fluid formulations in routine fluid substitution steps. Finally, we develop a seismic modeling exercise inspired by a Brazilian presalt carbonate reservoir, revealing the importance of fluid properties in time-lapse data analysis.