The production experience from Emilio sub-sea gas field is reported. This field produces both gas and condensate from the gas cap, under which a heavy oil layer is present. Since the early production tests of well Emilio 3 heavy hydrocarbon slugs reached the gas processing centre and induced massive fouling at heat exchange units. Such problems hindered production from reaching the target allowed by well performance; furthermore, operating costs were increased by clean-up operations. Lab tests were performed on produced fluids and deposits recovered in the plant in order to identify the nature of the slugs, that turned out to be asphaltene-rich emulsions of formation water, oil and gasoline. Further tests demonstrated incompatibility between oil (15°API) and hydrocarbon condensate (50 °API), suggesting that asphaltene instability occurs upon mixing, inducing the formation of a stable, viscous emulsion. The range of asphaltene instability ratios was also determined. A method was devised to identify oil in the condensate stream coming along with gas, and this allowed to verify on the field that mixing is taking place during production at the wellhead level in the range were asphaltene instability was measured. Two kinds of solutions were devised: removal of deposits by means of solvent clean-up operations, and prevention by means of demulsifier injection at the inlet of the processing plant. Both methods were successfully applied: the emulsion breaker injection significantly reduced the volume of the slugs, so that the production target was reached; removal procedures were optimised for the minimum time and maximum removal efficiency. The results of both methods are reported.

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