Subsea Compact Separation: Control System Design

Abstract

Abstract This paper summarizes key results of the development and verification for a subsea compact separation control system based upon a literature review, control system design, dynamic simulations, and an integrated system test. The compact separation system being considered is designed for applications in water depths up to 3,000m. The control system is a key technology element of the compact separation system, and its satisfactory performance is critical to ensure stable operation of the overall system. A thorough literature review was conducted to evaluate the control system designs for comparable subsea separation systems in industry, to understand the technical challenges, and to incorporate the key learnings into the development of this control system design. From this work, best practices were identified and were used as guidelines. A preliminary control system was developed, and the robustness of its design was assessed through dynamic simulations. Later, an integrated system test was performed with real crude and methane at realistic operating conditions to evaluate the performance of the compact separation equipment and to validate the model of the control system. The dynamic simulations and integrated system test results demonstrated the control system response following transient events, such as slugging, and provided insight into the system dynamics that then led to further modifications of the control system design and enhanced the overall system performance. This paper also delineates challenges associated with the design of a control system for a subsea compact separation system consisting of multiple, closely integrated gas-liquid and oil-water separation units. For example, the relatively small control volumes in compact separation equipment and the interaction between the different components can both add complexity to the control system design. Lessons learned from the modeling and implementation of such a sophisticated control system are discussed with the intent to serve as a reference for future subsea separation projects in the oil and gas industry.