EOS Modelling of Export Sales Products & Water of Condensation Bringing Value to a Mature Gas Condensate Subsea Asset in the North Sea

TotalEnergies operates four offshore fields in the West of Shetlands area. Traditionally, Black-oil based reservoir models linked to an integrated asset model (IAM) were used capture the reservoir-to-plant fluid dynamics in these mature, turbiditic, gas condensate fields produced through a long subsea tieback. The project incorporated EOS modeling into the operational framework to engender multifaceted advantages. Firstly, it empowered asset managers with accurate predictions of water of condensation behavior, enabling optimized flow assurance measures to mitigate issues like hydrate formation and pipeline plugging. Secondly, the refined modelling of hydrocarbon composition improved the capacity of tailoring production techniques to maximize yields of Export Sales products. Additionally, compositional simulation methods enabled prediction of the backout impact on both a volume and energy basis, allowing finer computation of the economic impact of third-party tie-ins. The EOS lumping was designed to replicate major sales products (LPG, Condensate etc.) and was further modified, introducing water as an EOS component in order to capture the water condensation phenomenon. Water vapor was introduced into the initialized reservoir Fluid Column without compromising earlier fluid properties matched to PVT lab observations, allowing wells to produce this water element as part of the liquid stream after condensation. A plant pseudo process was established from Process Flow Diagrams and historical plant pressure and temperature conditions were applied via periodic updates in the IAM. The compositional simulation results were positive with excellent match to historical export sales products and water cut. Increased confidence in ability to predict condensed water allowed significant volume and cost optimization in MEG injected for Subsea Network Hydrate prevention. The enhanced accuracy in forecasting energy basis backouts vastly improved the economic assessments of third-party tie-ins. In conclusion, this project underscored the value proposition of incorporating EOS modeling in a mature Gas Condensate subsea asset in the North Sea. By harnessing the power of EOS models, a mature asset could be managed with heightened precision, optimizing export sales products, ensuring flow assurance, and enhancing the modelling of economic returns. Such an enhanced physics approach modelling clearly contributes to extending the lifespan and economic viability of the aging offshore assets and also assists in making potential future investment decisions.