The combination of thermal analysis and supercritical extraction as a tool for the characterization of mixed deposits and sludges

The deposition of solids in oil production may bring serious operational consequences. The comprehension of compositional aspects of the solid material formed is essential in order to avoid precipitation or to plan the removal procedures. In some cases, however, the presence of mixed deposits is a challenge to the characterization approaches because of the difficulties for the exact determination of the contents of the components of each class. Normally, three classes are considered in oil production: paraffinic, asphaltenic and inorganic materials. The situation is even more complex with the possible presence of water that is normally associated to the deposits. Therefore, novel procedures have been developed, validated and added to the characterization routine for deposits. An analytical step by differential scanning calorimetry (DSC) by which sharp peaks are yielded was developed for the positive identification of the presence of water by the melting transition at 0 degreesC or around that temperature, depending on the salinity of water. A quantitative procedure for the determination of paraffin and asphaltene contents in mixed deposits was developed with the use of supercritical fluid extraction with pure carbon dioxide. The best known aspect of supercritical extraction is the possibility to tune the selectivity and solvation capacity. Both concepts were explored and a general procedure by which even long-chained alkanes are selectively extracted was developed. Extracts are collected onto glass beads at room pressure and weighed for a very accurate gravimetric determination of the contents of the components of both classes. (C) 2001 Published by Elsevier Science B.V.