(94d) Attributes and Behaviours of Crude Oils That Naturally Inhibit Hydrate Plug Formation

The severe operating pressures and distances of deepwater tiebacks increase the risk of hydrate blockage during transient operations. In many cases, complete hydrate avoidance through chemical management may become cost prohibitive, particularly later in the field’s life. However, for a unique subclass of crude oils that have not been observed to form a hydrate blockage during restart, active hydrate prevention may be unnecessary. Over the last 20 years, limited information has been reported about the chemical or physical mechanisms that enable this “magic” non-plugging behaviour. This paper demonstrates a systematic method of characterising whether an oil is “magic”, including (i) physical property analysis that includes, and builds upon, ASTM standards; (ii) water-in-oil emulsion behaviour; and (iii) the effect of oil on hydrate blockage formation mechanics. This last set of experiments utilises a sapphire autoclave to allow direct observation of hydrate aggregation and deposition, combined with resistance-to-flow measurements. The effect of shut-in and restart 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 “magic” 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. These results suggest that magic oils contain specialised, active chemistries that discriminate between hydrate-oil and water-oil interfaces.