Integrated Asset Modeling of a Deep-Offshore Subsea Development Using 2 Complementary Reservoir-Surface Coupling Workflows
Authors: Darche Gilles , Marmier Rémy , Samier Pierre , Bursaux Romain , Guillonneau Nicolas , Long Jérôme , Kalunga Hernani , Zaydullin Rustem , Cao Hui 
Published: March 2019

Abstract
We present a global simulation strategy of coupling reservoir and surface network models to manage production profiles of a deep-offshore field (West Africa) operated with a subsea development. This strategy allows a better consolidation of both short-term and long-term production profiles as compared to stacked standalone reservoir profiles.
The simulation study consists of 4 independent reservoir models, connected to surface facilities through a common subsea network. The first method uses loose external coupling between a new-generation commercial reservoir simulator and a commercial subsea network modeling package. It will be used to derive an optimal management of the network (network design, surface controls). This first coupling approach can also generate input data (pressure drops in network described by VLP tables) necessary for the second coupling approach, consisting in a fully coupled reservoir-surface simulator developed in-house, used to evaluate infill scenarios and to compute long-term production profiles.
These two coupling approaches bring their own value to the evaluation of the potential of the field.
The loose external reservoir-network coupling better manages surface constraints. It enables to design and to optimize the subsea network, accounting for the surface capacities. It also manages transient effects in the network, therefore enabling short-term optimization of the production. It will also highlight critical features (like pipe erosion, managed through the C-factor parameter) for the network.
However due to high TCPU and numerical instability, it is unsuitable for extensive sensitivity studies. For that, we use our in-house fully coupled reservoir-network simulator, with network description provided through the external coupling approach. These fully-coupled simulations, though using simpler network descriptions, are much faster and more robust, enabling to perform sensitivities on reservoir management, on infill well scenarios, in order to maximize long-term production profiles. We also developed new options in our in-house simulator to model the critical network features identified by the external coupling approach (like C-factor, fluid mixing, gas-lift optimization on risers).
Therefore, the use of these two workflows has enabled a full optimization of the field development, both The study has shown that these two technical coupling approaches are complementary, and bring better value to a field development when performed together. Furthermore, the external coupling approach identified the critical network features to be also managed in a fully-coupled reservoir-surface simulator, leading to new developments into this simulator (management of C-factor, fluid mixing, gas-lift optimization on risers).
The paper proposes a novel framework for the reservoir and surface facilities modeling. Our new approach benefits from the advantages of the two previous approaches: numerical stability/efficiency of the fully coupled approach and the workflow/accuracy of the separated approach.