Thomas Brichart

The Use of Fluorescent Tracers for Inhibitor Concentration Monitoring Useful for Scale Inhibitor Squeeze Evaluation

A common problem, in oilfield reservoirs is mineral scale deposition. The build-up of scale inside well bores and the surrounding reservoir causes millions of dollar in damage every year. The most common remedy is to treat the formation of such minerals with scale inhibitor chemicals in a “squeeze” treatment; which is performed periodically. One of the big challenges remains the real-time and on-site control of inhibitor concentration during production. A simple and accurate method to determine the concentration of inhibitors has been developed; this method is based on the use of luminescent tracers. The multiple lifetimes as well as the differences shown in the emission and excitation spectra of the tracers appear to be suitable for the luminescence detection. The increased signal to noise ration due to the suppression of the background resulting from the organic oil residues is used to measure the concentration of residual inhibitors in production waters. Furthermore, the use of a technique as versatile and simple as luminescence spectroscopy allows the online and/or on-site monitoring with very limited drawbacks. This paper describes the use of novel real-time scale inhibitor monitoring; this new technique will help to optimize the treatment rates of the scale inhibitor squeeze treatment.

How to Monitor Scale Inhibitor Squeeze Using Simple TRF Tracers

Mineral scale deposition in oilfield reservoirs has caused millions of dollars in damage every year. The most common remedy to the build-up of scale inside well bores and the surrounding reservoir is the periodical “squeeze” treatment by inhibitor additives. The real-time and on-site control of inhibitor concentration during production remains one of the big challenges. Indeed, current techniques of inhibitor monitoring that use elemental analysis appear too complex for an efficient long-term industrial solution. With this in mind, we have developed a simple and accurate method for scale inhibitor quantification in production waters based on the use of time-resolved fluorescence (TRF) tracers. The characteristic luminescence signature (lifetime value, emission and excitation spectra) of TRF tracers allows the reliable tracking of inhibitors additives. Moreover, their long-lifetime luminescence signal can significantly increase the signal to noise ratio thanks to the suppression of organic oil residual background emission. Our experimental tests on produced water collected from different sites confirm the detection of a larger variety of inhibitors i.e. for carboxylates, phosphonates and sulphonates by simple post-chelation with TRF tracers at low concentration. Indeed, the non-fluorescent inhibitor species have been switched to fluorescent compound by the addition of few amounts of tracer in order to be detectable and quantified at sub-ppm concentrations. The coupling between TRF tracers and specific TRF spectrofluorometer apparatus then open new and accurate ways for the online and/or on-site monitoring of scale inhibitors for better risk management of flow assurance during production.