This paper describes a number of different evaporative processes which can cause flow assurance issues within oilfield production systems including chemical application via gas lift systems, halite deposition and gunking in injection lines. Similarities and differences are described and laboratory test methods are presented for each case.
While the challenges all involve evaporative processes, each system is different and requires suitable approaches to evaluate and mitigate the risks. These attempt to mimic the field system in the laboratory and allow observation under controlled conditions. Laboratory test methods vary from basic static bottle tests, through glass capillaries in autoclaves to dynamic tests using brine and a partially saturated gas phase, or neat chemical and dry gas lift media. In particular, the challenges when applying a chemical via a gas lift system will be described including field case studies.
Static tests with unlimited volume to evaporate produce a worst case for any evaporative process. However, it is frequently too severe to produce any useful results. Instead a test regime should be designed to mimic the field conditions. For example, evaporation within a pressure vessel can mimic the self-limiting process within a downhole injection line. Application of a chemical via a gas lift system requires a dynamic test where hot pressurised dry gas and neat chemical are co-injected with continual monitoring of gunking as indicated by flow path restrictions. Halites require a similar dynamic test method but with extensive modelling of the in situ saturation ratio to fully understand the system.
This paper will present case studies, summarise our understanding of the different evaporative processes, and give best practice guidelines for laboratory evaluation of the risks and mitigation strategies.