High-pressure PVT properties of synthetic oil/gas systems for EOR: The effect of CH4 and a CO2-rich gas on a heptane/toluene mixture

Resumo

Understanding the flow and phase behavior properties of reservoir fluid–injected gas systems is essential for optimizing oil production strategies and designing gas injection-based Enhanced Oil Recovery (EOR) techniques. In the absence of live oil data, synthetic model mixtures with similar characteristics can provide reliable input for reservoir simulation. This study investigates the bubble point pressures (BPP) and the volumetric behavior of two synthetic systems: (n-heptane + toluene + methane) and (n-heptane + toluene + carbon dioxide + methane). BPP values were measured for mixtures with varying CH₄ or (CO₂ + CH₄) content over the (304.7–363.2) K range. The two experimental techniques used, a stepwise and a visual method, showed excellent agreement with each other (RMSD = 0.01 MPa). Liquid phase densities were determined across wide temperature (293.2–363.2) K and pressure (5–90) MPa ranges.

The Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR) equations of state (EoS) were applied to model the saturation pressures, achieving average relative deviations (ARDs) of 5.8% and 6.0%, respectively. The experimental density data were correlated using the Tammann-Tait equation, yielding low ARDs of 0.09% (ternary system) and 0.03% (quaternary system). Isothermal compressibility and the isobaric thermal expansivity were subsequently derived from the fitted Tammann-Tait equation parameters. Finally, liquid densities were predicted using the original and volume-translated (VT) forms of the SRK and PR EoS. The volume-translated correction significantly improved predictive accuracy, reducing the global ARD from 11.2% (SRK) to 2.1% (SRK-VT) and from 2.0% (PR) to 1.4% (PR-VT).

Autores

Sérgio M. Vilas-Boas, Fernanda P. Pelaquim, Ivanei F. Pinheiro, Vanessa C.B. Guersoni, Mariana C. da Costa, Paulo T.V. Rosa.

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