DESIGN OF PIPELINE FLUSH OPERATIONS 

Pipeline flushing are routine scheduled operations in onshore, offshore oil and gas and refinery industries for various purposes, which involves liquid-liquid or gas-liquid displacement in pipelines. Some common examples are dead oil displacement of live oil in subsea pipelines, displacement of one crude by another crude in refinery transfer lines during batching process, pre-commissioning and commissioning of subsea/onshore pipelines etc. For all such operations, it is critical to accurately estimate the displacement time, circulation rate, volume of displacing fluid required, mixing length, sweeping efficiency or acceptable percentage of contamination. Industries use different approaches (correlations, analytical solutions, generic rule of thumb, CFD, commercial transient simulator, pilot scale testing/experiments etc.) to arrive at these key predictions to help in their respective flushing operations. This paper will briefly address the various approaches used in the industries. As part of this work, a few case studies were performed with a 1-D transient simulator, OLGA (licensed by Schlumberger) for illustration. Effects of flowrates and crude properties on flushing efficiency were also investigated. This paper will also identify areas for improvement in the methodologies for studying flushing.