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 well s. A piece of tubing with a significant amount of organic material, collect ed 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 t he tubing surface, but part of it remains firmly adhered. Non-stoichiometri c iron oxides (oxidized magnetite or maghemite) and iron sulfides (pyrrhoti te) and also small amounts of iron hydroxides and organic material were fou nd on the tubing surface with adhered-material. This suggests a competitive adsorption of sulfur atoms and hydroxyl groups from petroleum, on the surf ace 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 Elsev ier Science Ltd. All rights reserved.