Surfactants assist oilin-water monitoring by fluorescence

Surfactants have been facilitating oil-in-water measurements by fluorescence in California steamfloods for more than 10 years. Two main benefits have been realized. First, the selective amplification of dispersed oil fluorescence has made it possible to reliably monitor sub-ppm concentrations of dispersed oil in the presence of highly fluorescent Water-Soluble Organics (WSOs). Second, the cleaning action provided by continuous surfactant injection makes it practical to use flow-cell instruments in place of falling-stream instruments. The reduced water flow required by a flow cell reduces surfactant cost significantly. Recent field studies suggest that a surfactant modulation technique could allow one online fluorometer to monitor both dispersed oil and WSOs. This article proposes such a technique. Aromatic fractions of dispersed oil and WSOs in produced water can be stimulated to emit fluorescent light. Fluorescence is an extremely sensitive analytical technique, capable of monitoring most oils in produced water at concentrations less than 1 mg/L.