How Real-Time Evaluation of Slugging Severity Can Help Maximize Production

Abstract

In recent years, Aker BP has explored and developed a number of digital improvements to optimize production. The underlying business drivers are meant to improve efficiency, increase production and reserves, decrease costs, and reduce the carbon footprint from operations. The example described in this article has innovative elements of digitalization and automation of workflows which provide a new approach for better handling of slugging in subsea developments with long tiebacks. The new solution has a potential for optimizing production and limiting the amount of flaring. Flow Instabilities in the Vilje Field The Aker BP-operated Vilje field in the Norwegian Continental Shelf has occasionally experienced production-flow instabilities in the production pipelines and risers due to slugging. The company worked with Turbulent Flux to develop a software solution, the FLUX Stability Adviser, to continuously and precisely monitor production in real time. Field Description and Outline of Problem The Vilje field is a subsea development with three horizontal producers tied back to the Alvheim floating production, storage, and offloading (FPSO) facility through a production line longer than 20 km. The inlet separator at Alvheim is shared with other third-party developments. After an initial period of dry-oil production at the field, which started production in 2008, the oil rate has gradually decreased as a result of increased water cuts (WC) over time. Gas lift has been used to sustain production. The occasional slugging at the inlet separator had been controlled by increasing the backpressure to the production line and/or shutting in one of the producers. However, this practice affects production potential and may lead to production losses or deferral. Explanation of the Solution The two companies developed a Stability Adviser application to advise operators of the settings to optimize production in real time while lowering the risks related to slugging at any point in time. The developed solution runs on a cloud infrastructure with an interactive web-user interface. The main user interface contains a 3D heat map which is based on output from a series of pre-run transient simulations and a statistical analysis of the associated slugging severity. The model quality of the pre-run simulations was benchmarked with field data, and a similarity index was introduced to evaluate the degree of matching. Transient multiphase flow simulations represent the state of the art in the prediction and analysis of slugging behavior in multiphase transport pipelines (both terrain-induced and hydrodynamic slugging). These simulators capture and follow slugs as they are forming along the pipeline. That said, these simulations are time consuming, which limits their usefulness in a real-time operational context.