Parametric analysis of EoS

This work presents a parametric analysis and practical comparison of four cubic equations of state (EoS): Soave – Redlich – Kwong (SRK), Soave – Redlich – Kwong – Peneloux (SRKP), Peng – Robinson (PR), and Peng – Robinson – Peneloux (PRP) using a QA/QC-verified PVT dataset from the Volve field provided by the technical literature. The aim is to compare the results of four EoS-based PVT simulations with experimental data, and to correlate the deviations to the physical meaning of the EOS parameters. The first step in the workflow was the validation of the bottom hole sample reliability through a material balance assessment. Furthermore, an equilibrium consistency check was performed using Hoffman and Buckley plots to verify the validity of the phase behaviour predictions. The four models with default parameters were run on 23 component compositions to perform the EoS parametric analysis. PR underestimated Psat by approximately 9% compared to experimental data, while SRK overestimated Psat by about 5%. PR and PRP showed a better match for the Constant Composition Expansion (CCE). However, SRK and SRKP predicted Differential Liberation parameters better compared to PR and PRP. Overall, the study showed a systematic offset between PR and SRK consistent with the different formulations of the attractive and repulsive terms. Following this, plus-fluid regression was applied on 23-component mixture to improve heavy end characterisation. The composition was then lumped to 8 components and tuned within acceptable tolerances. The study demonstrates that each EoS has its own strengths and limitations. Furthermore, a workflow for fit- for- purpose EoS methodology is presented. In this study we focused on a single composition, however in practice, field wide EoS is tuned using multiple samples to obtain a representative EoS model.