In recent years a number of significant advances in the molecular monitoring of residual corrosion inhibitors in oilfield fluids have been reported. The techniques used, chromatography and mass spectroscopy, provide molecular specificity with high sensitivity, and allow individual molecules to be tracked at low levels (sub ppm) throughout oil production systems, These analyses have demonstrated for the first time how individual corrosion inhibitor molecules behave in real systems, and the results obtained have shown some interesting phenomena. For
example, for a series of quaternary ammonium compounds, the
concentrations of residual inhibitor molecules remaining in the fluid is dependant not only on the length of the alkyl chain, but also the degree of methyl branching. In an attempt to explain these field observations, a number of laboratory partition and surface adsorption experiments have been performed on pure synthetic and industrial grade quaternary
ammonium corrosion inhibitor compounds. By relating the results of these laboratory studies with data obtained from the field, a more complete understanding of oilfield corrosion inhibitor behaviour has begun to evolve.
Keywords: corrosion inhibitors, residuals, quats, chromatography, mass spectrometry, partitioning, surface adsorption, performance