The Impact of Integrating Reservoir and Surface Facilities with Liquid-Liquid Subsea Separation Systems on Decision-Making in a Post-Salt Deepwater Heavy Oil Reservoir

Abstract The objective of this paper is to investigate the effects of integrating heavy oil sandstone reservoir and surface facility models with liquid-liquid subsea separation (LLSS) systems on the forecasting, deliverability, and decision analysis within closed-loop field development and management (CLFDM) workflow. From a production management perspective, the study aims to answer how different surface facility layouts and various boundary conditions will impact the performance of the integrated models. In the first part, we considered six integration scenarios over an optimized standalone production model, which included three surface facility layouts: (1) without separation unit (NOSEP), (2) with a LLSS unit (WSEP), and (3) a LLSS system with recycled water injection unit (WINJ) and two boundary conditions for each layout to ensure the required pressure for production in surface facilities is sufficient. In the second part, we conducted sensitivity analysis, selecting one of the cases (WINJ-WHP) and changing the number of wells to investigate different production strategies in the observed simulations. When the boundary condition was fixed at the bottom hole, the type of surface facility did not impact the oil production. Differences in observed performance were primarily related to separate water at the surface facilities. The simulator attempted to impose the BHP values accordingly. When the boundary conditions were set at the wellhead, the effects of different surface facility layouts impacted the BHPs, which were not constant in this case. The oscillation of BHP values resulted in chaining average reservoir pressure and the oil and water production rates changed as a consequence. Also, when the boundary condition was set to the bottom hole condition of the wells, one producer in all surface facilities became inactive due to slug flow pattern condition. Adjusting the well boundary condition to wellhead can resolve this issue, but this solution is case sensitive. After integration was completed, the second part of the study revealed differences in production and NPV and the need for strategy re-optimization. Removing less productive wells highlighted the limitations of relying solely on a standalone simulation result, as the standalone simulation fails to consider the influence of surface facility models, which can significantly impact the behavior of the integrated model. From a reservoir management standpoint and for accurate decision-making, re-optimization is an essential step that must be performed after integration. The results of this study, using LLSS facilities as an example, can help field operators in decision-making and reservoir management. Operators can determine whether integrating the surface facilities is beneficial by comparing a post-integration optimization against a full integration from the very start of the simulation, which is more time-consuming. However, this decision is case-sensitive, depending on the field's operational conditions.