A two-layer structure for stabilization and optimization of an oil gathering network

Abstract

In this work, we present the control and optimization of a network consisting of two gas-lifted oil wells, a common pipeline-riser system and a separator. The gas-lifted oil wells may be open-loop unstable. The regulatory layer stabilizes the system by cascade control of wellhead pressure measurements without needing bottom hole sensing devices. An economic Nonlinear Model Predictive Control (NMPC) based on the Multiple Shooting (MS) formulation is applied for optimization of the network operations. The optimization layer thus provides optimal settings for the regulatory controllers. The control structure has been validated by using the realistic OLGA simulator as the process, and using simplified models for Kalman filtering and the NMPC design. The simplified models are implemented in Modelica and fit to the Olga model to represent the main dynamics of the system. The proposed two-layer controller was able to stabilize the system and increase the economical outcome.