Near-critical reservoirs such as gas condensate exhibit complex phase behavior due to the existence of a two-fluid system, comprising reservoir gas and liquid condensate. It will be more challenging when the fluid composition has complex mixture components such as naphthenic complexes, aromatic complexes, and contaminants. This paper presents a characterization of complex fluid mixtures of the gas condensate reservoir at an offshore field with very high CO2 and other contaminants content.

Extensive PVT fluid experiments started from preliminary quality checks on the fluid samples, have been carried out. Complex fluid composition analyses were measured with 25 components including complex mixtures. The equilibrium gas composition was analyzed using the natural gas analyzer (NGA). Meanwhile, the equilibrium condensate was analyzed using high-temperature gas chromatography (HTGC), which gives detailed hydrocarbon compositions. Standard PVT experiments such as constant composition expansion (CCE), constant volume depletion (CVD), and fluid properties were measured and validated through the thermodynamic modeling equation of states (EOS).

The EOS has been utilized to study the near-critical phase behavior of complex mixtures, emphasizing the complexity and wide-ranging volatility of gas condensates and reservoir crudes. A thermodynamical model EOS was developed using PVT software and achieved an acceptable match against all PVT experiments, including dew point pressure. An an improved analysis on gas flow assurance can be done by conducting thermodynamic modeling of solid precipitation. The predicted solid precipitation where only observed at very extremely low temperature and pressure that unlikely to occur in operating condition of this field. In conclusion, proper characterization of complex fluid mixture near-critical gas condensate reservoir fluid will strengthen the quality, assist engineers in gaining a better phase behavior understanding of complex fluid mixtures, and prepare field development plans with better depleting strategies, reservoir management, and flow assurance mitigation.

This paper contributes to the broader understanding of phase behavior of gas condensate reservoir with high CO2 content and complex fluid mixtures and offers practical using thermodynamic modeling for improved understanding of fluid phase behavior and flow assurance issue. The results presented herein will establish a foundation for further research and development in this field, eventually underpinning the development of more efficient and sustainable extraction technologies.

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