Modelling a CO2 meter for a petroleum multiphase mixture at subsea conditions

Measuring high levels of carbon dioxide (CO2) in Brazilian pre-salt production flows remains a considerable technological challenge. The complexity of the three-phase flow and the variable CO2 solubility within each phase poses difficulties in accurately measuring CO2 in this scenario. Moreover, existing CO2 measurement techniques designed for single-phase fluids prove insufficient under mixed-phase conditions. This study proposes a methodology for a simple CO2 meter capable of determining the CO2 content in an oil and gas production stream. The proposed meter operates by analyzing the pressure change during a heating assay of an imprisoned sample. A computational model was developed in the ASPEN HYSYS (R) process simulator with the Peng-Robinson Equation of State to calculate the mixture properties emulating the isochoric process in the meter under different CO2 levels and initial conditions. The modelling results indicate that the pressure-temperature (P-T) behavior exhibits linearity with a slope that increases with higher CO2 content, which is characteristic of many pre-salt production fields. The model successfully reproduced published experimental data for an isochoric process.