CO2 Subsea Separation: Concept & Control Strategies

Abstract

The high CO2 content found in Pre-Salt offshore oil fields has led to cost-energetically processes for CO2 removal and destination. In this paper, an innovative and promising alternative subsea separation process (SSP), proposed by Petrobras, was analyzed. Since a CO2 rich phase is expected at reservoir conditions, subsea gravity separators can be employed avoiding large volumes of CO2 from being sent to the topside, lowering gas processing plant complexity. A differential-algebraic system of equations (DAE) was developed for the SSP modeling. Design and steady-state simulations were carried out within EMSO simulator. To ensure the process variables remain at their desirable values two control strategies, PID and Linear Model Predictive Control (MPC), were compared. The proposed process showed technical feasibility with up to 62% GOR reduction. The control strategies presented reasonable performance. MPC had for most of the controlled variables a better performance.