Petroleum solid adherence on tubing surface

Blocking of the crude oil flow is induced occasionally by the presence of a black layer of material adhered along the internal walls of petroleum wells. A piece of tubing with a significant amount of organic material, collected from a Mexican oil well, was analyzed by Mossbauer Spectroscopy (MS), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIRS). At room temperature, a fraction of the adherence detaches easily off from the tubing surface, but part of it remains firmly adhered. Non-stoichiometric iron oxides (oxidized magnetite or maghemite) and iron sulfides (pyrrhotite) and also small amounts of iron hydroxides and organic material were found on the tubing surface with adhered-material. This suggests a competitive adsorption of sulfur atoms and hydroxyl groups from petroleum, on the surface iron sites. Finally, the organic material, which contains alkyl chains and aromatic rings, is adsorbed non-dissociatively on the modified surface but only in the presence of non-stoichiometric iron sulfide. (C) 2001 Elsevier Science Ltd. All rights reserved.