Suppression of liquid slugs and phase separation through pipeline bends

Abstract

This study examines the suppression of liquid slugs in the transport and separation of multiphase flows in pipelines. Two well-known slug control approaches are evaluated in this paper. The methods are employed to control and stabilize an undesired and unstable flow regime, optimize flow production, reduce operating costs, and in general, improve overall safety requirements of oil and gas pipelines. Unlike designs with an additional flowline to separate gas upstream, this study shows that active topside choking can suppress slugs and stabilize the system flowrates and pressures without the requirement of separation upstream of the topside valve. Careful choking is required to minimize production losses that can result from excess back pressure. A riser-based, gas-lift method reduces system instability and increases production. This study also reveals that negligible improvement in stability is achieved when large volumes of gas are injected. The system shifts into an annular flow regime when the injection is further increased. A large separator may be required to accommodate high gas volumes. This study shows that gas-lift not coordinated with choking is not effective for slug mitigation through pipeline bends. This paper also presents and discusses new non-dimensional correlations, including slug control inputs in the pipelines such as choke openings, based on new experimental data.