While designing a subsea separator retention time and slug size are two important parameters that need to be considered. By using high speed control valves, the separator can be made smaller. A typical case will be discussed where the separator size could be reduced significantly (by approximately 50 to 90%) if high speed control valves and algorithms are used instead of a more conventional design. This consequently results in significant reduction in weight, size, cost of the separator. Also for deeper waters and higher design pressures, large separator vessels become increasingly difficult (or even impossible) to build, so this technique can be an enabling factor for deep / high pressure subsea separation system.
This paper discusses 5 different control schemes that are considered to achieve the necessary control objectives of a subsea separator. All the control schemes discussed in this paper can handle process upsets, both liquid slugs and gas bursts. However, the ability to handle such transients varies depending on which control scheme is implemented. This paper also discusses two extreme cases and explains how well the 5 control schemes cope with them. This shows that the control loops can be configured in several ways with increasing performance and complexity. In general, performance is increased at the cost of complexity. Also there is a trade-off between separator size and control system performance: a better control system arrangement can reduce the size of the separator.
Paper also touches upon the concept of subsea closed loop control system where SEM acts as a standalone processing unit which provides a fast response time.
Subsea Separation, Boosting, Compression
Results from FEED study performed for an operator located in GoM are discussed in this paper. The study showed a significant reduction in separator size (50% to 90%) and cost. It also improves the reliability and performance of the subsea separator control system.
Qualified subsea closed loop control system, fast acting valves has helped to implement subsea separation technology in North Sea fields.
This experience can be extended to GoM and unlock the potential of the subsea processing and boosting equipments.
