Attributes and behaviours of crude oils that naturally inhibit hydrate plug formation

Abstract

The severe operating pressures and distances of deepwater tiebacks increase the risk of hydrate blockage during transient operations such as shut-in and restart. In many cases, complete hydrate avoidance through chemical management may be cost prohibitive, particularly late in a field’s life. For a unique subclass of crude oils, however that have not been observed to form a hydrate blockage during restart, active hydrate prevention may be unnecessary. In the past 20 years, limited information has been reported about the chemical or physical mechanisms that enable this particular non-plugging behaviour. This extended abstract demonstrates a systematic method of characterising this oil, including: physical property analysis that includes and builds upon ASTM standards; water-in-oil emulsion behaviour; and, the effect of oil on hydrate blockage formation mechanics. This last set of experiments uses a sapphire autoclave to allow direct observation of hydrate aggregation and deposition, combined with resistance-to-flow measurements. The effect of shut-ins and restarts on the oil’s plugging tendency is also studied in these experiments. The method was tested with several Australian crude oils, some of which exhibited non-plugging behaviour. In general, these particular crude oils do not form stable water-in-oil emulsions but do form stable non-agglomerating hydrate-in-oil dispersions. The oils suppress hydrate formation rates and their resistance-to-flow does not increase significantly when the amount of hydrate present would normally form a plug.