Contribution of organic and mineral compounds to the formation of solid deposits inside petroleum wells

Deposit samples collected from three Mexican wells, their asphaltene and residue fractions as well as the sediment and asphaltene fractions separated from the corresponding crude oils were characterized. An appreciable amount of minerals such as CaCO3, BaSO4, NaCl, quartz and iron compounds were detected in the deposit compositions. Additionally, aromatic factors and structural parameters such as interlayer distance and crystallite diameters were calculated from the (gamma) and (002) characteristic bands from the X-ray diffractograms of the deposits, deposit-asphaltene, oil-asphaltenes as well as oil-sediments. FTIR, elemental analysis and thermal techniques were also used to elucidate the sample compositions. The stages of the deposit formation inside petroleum wells include steel surface corrosion products formed in situ by the presence of brine and sulfur bearing compounds and adsorption or chemisorption of organic compounds on the modified tubing steel surface and mineral pores. Moreover, the high amount of vanadium and nickel indicates a time-dependent process of accumulation of some organometallic compounds independent of the oil-asphaltene amount. (C) 2001 Elsevier Science Ltd. All rights reserved.