**Sveinung Johan Ohrem 1,\*,†, Håvard Slettahjell Skjefstad 2, Milan Stanko <sup>2</sup> and Christian Holden <sup>1</sup>**


Received: 8 March 2019; Accepted: 28 March 2019; Published: 2 April 2019

**Abstract:** To enable more efficient production of hydrocarbons on the seabed in waters where traditional separator equipment is infeasible, the offshore oil and gas industry is leaning towards more compact separation equipment. A novel multi-pipe separator concept, designed to meet the challenges of subsea separation, has been developed at the Department of Geoscience and Petroleum at the Norwegian University of Science and Technology. In this initial study, a control structure analysis for the novel separator concept, based on step-response experiments, is presented. Proportional-integral controllers and model reference adaptive controllers are designed for the different control loops. The proportional-integral controllers are tuned based on the well-established simple internal model control tuning rules. Both control methods are implemented and tested on a prototype of the separator concept. Different measurements are controlled, and results show that the performance of the separator under varying inlet conditions can be improved with proper selection of control inputs and measurements.

**Keywords:** process control; separation; oil and gas
