Asphaltene deposit formation is a severe problem frequently faced during crude oil production and transportation, that affects the reservoir, production tubing and surface facilities, depending on the stage where this critical point is reached. This point corresponds to the pressure at which asphaltene particles start to form. This value is directly related to the oil physical chemical stability. When flocculation pressure is reached into the reservoir, severe formation damages occur due to asphaltene precipitation in the porous media, evidenced as wettability and/or relative permeability alterations. When asphaltenes precipitate in the production tubing, refractory plugs reduce or even stop crude oil production until chemical/mechanical removal is performed. The stability of several crude oils produced in a North Monagas oil field (Carito) from Venezuela, in terms of asphaltene deposition, was evaluated to predict their behavior and prevent future plugging. "Spot Test" and n-heptane titration (asphaltene flocculation onset determination under atmospheric conditions) were used as crude oil stability criteria. Solid deposits, from these wells production tubing and surface facilities, were characterized in order to establish if their origin was organic (asphaltenes or paraffins) or inorganic (scales or sand), and to confirm the stability results assessed in the first set of experiments. Once the asphaltene problem was identified, several commercial asphaltene inhibitors were evaluated, considering their efficiency when a fixed dosage of these products was added to the studied crude oils. Dead oil n-heptane titration of treated crude oils allowed identifying the products that induced higher flocculation onsets when compared with untreated sample results. A second condition that was evaluated for inhibitor selection, was the product thermal stability, considering that downhole treatments would require to face temperatures as high as 150°C. Results of some practical applications derived from this evaluation are presented in this work.

Keywords:
inhibitor, concentration, paraffin remediation, remediation of hydrates, procedure, correspond, flocculation onset, fraction, asphaltene deposition, wax inhibition
Subjects:
Production Chemistry, Metallurgy and Biology, Flow Assurance, Fluid Characterization, Improved and Enhanced Recovery, Inhibition and remediation of hydrates, scale, paraffin / wax and asphaltene, Precipitates (paraffin, asphaltenes, etc.), Completion Installation and Operations
Copyright 2003, Society of Petroleum Engineers
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