Operational Performance of Offshore De-oiling Hydrocyclone Systems

Maturing Oil & Gas reservoirs in the North Sea result in constant increases of water-cut, which correspondingly poses an increasing strain on the current offshore Produced Water Treatment (PWT) facilities. As one of the key elements of the PWT facilities, the hydrocyclone systems, are responsible for removing the remaining hydrocarbon content in the produced water before the treated water can be discharged, disposed, or reused as injection water. The hydrocyclone's performance heavily correlates with a number of system's and operational parameters, as well as dedicated control strategies. However, these correlations haven't yet been clearly explored from a control oriented point of view, due to the complex separation dynamics inside the cyclone systems. This work investigates and evaluates the hydrocyclone system's operational performance with respect to the most commonly used control paradigm, Pressure Drop Ratio (PDR) control, based on a lab-scaled pilot plant. It has been clearly observed that in many situations the PDR is not consistently related to the system efficiency or to the inlet flow-rates, however these are assumed consistent in almost all available studies and control designs. In addition, the dynamic responses of PDR and de-oiling efficiency (measured in terms of Oil-in-Water (OiW) concentration) of the deployed hydrocyclone systems are systematically and experimentally studied in this paper. This data can be used to derive control-oriented dynamic models of the considered system, so that a control solution that is better than the current PID-based PDR control, could be developed based on those models.