Asphaltene plugging is one of the most frequent causes of production depletion in medium and light crude oil reservoirs, specially when the pressure declines due to its exploitation, and asphaltene solubility reaches a minimum. Other physico-chemical phenomena, like intrinsic unstability of the produced crude oil, incompatibility between "commingled" produced oils, drilling fluids and produced oil, or between streams entering flow stations, as well as inadequate stimulation procedures, can be responsible for asphaltene deposition during crude oil production and transportation, going from the reservoir to surface facilities. Prevention methods oriented to asphaltene deposition control include the injection of chemical additives. These products have the particularity of disperse or inhibit asphaltene aggregation, avoiding the formation of precipitates that eventually deposit on metal or mineral surfaces, causing a severe flow reduction, and even formation or tube plugging. The main purpose of this work is to show the application of a systematic technique for chemical treatment evaluation, oriented towards the production restarting of asphaltene plugged oil wells in a Lake Maracaibo reservoir. Dead oils and deposits from neighbor oil wells of the same reservoir were characterized, along with the evaluation of some commercial additives, in terms of their performance as asphaltene deposition inhibitors, under atmospheric conditions. The results allowed selecting the best product to be evaluated under reservoir conditions. Its addition to live oil samples, at reservoir pressure and temperature, showed a clear reduction of the asphaltene precipitation pressure onsets. A complete chemical treatment, including the selected product, was used for production restarting of the plugged oil wells. Field operation procedures used in these cases are described. Also, production history data of the actual oil wells, comparing their productivity before and after the treatment, are shown in order to demonstrate the efficiency of the methodology.

Keywords:
oilfield chemistry, inhibitor, oil production, crude oil, scale remediation, production chemistry, remediation of hydrates, oil well, paraffin remediation, depletion
Subjects:
Production Chemistry, Metallurgy and Biology, Flow Assurance, Inhibition and remediation of hydrates, scale, paraffin / wax and asphaltene, Precipitates (paraffin, asphaltenes, etc.)
Copyright 2001, Society of Petroleum Engineers
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