Retrograde gas condensate systems are complex systems as a result of the unique compositional changes that when the reservoir pressure is decreased. Correct selection of Equation of State (EOS) is necessary for proper fluid characterization so that the PVT behavior in the simulation model is a good representation of the reservoir fluid. High quality and accurate PVT data can reduce uncertainty in reservoir fluid properties and set the stage for reservoir engineering modeling whilst improving the technical work on which investment decisions are made.

In order to obtain reliable PVT data for effective reservoir modeling, the following steps are essential:

  • Acquisition of sufficient volumes of representative reservoir fluid samples.

  • Proper examination and supervision of all field and laboratory experiments to ensure accuracy, consistency and validity of the resulting PVT analysis results.

  • Results from the PVT experiments are imported into PVT software for validation in order to ascertain a good match between the simulated and experimental data.

This process generates the Equation of State model required for material balance and other simulation studies for gas condensate reservoirs.

The mass balance test is one of the methods that can be used to validate laboratory PVT data. It is a rigorous test for the evaluation of compositional consistency between feed composition, separator vapor and liquid compositions. Other laboratory PVT data validation means include Mass balance plot, Hoffman plot CVD/CCE comparison plots and Campbell diagrams. These plots serve as data quality assessment methods prior to their use for EOS characterization. PVT validation checks helps to confirm the true content of the fluid as either a rich or lean gas condensate and also confirm the Gas oil ratio of the system.

Inaccurate PVT data can give misleading information that could cause a wrong evaluation of hydrocarbon in place. However, when these methods are properly applied it could lead to huge savings for the company as accurate results are obtained from reservoir simulation models which could aid optimization efforts and achieve incremental recovery.

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