Effective monitoring of scale inhibitor residuals following a downhole squeeze can present challenges due a variety of reasons including contamination of the produced fluid with a topside scale inhibitor, and in the case of subsea wells, often the production is commingled as several wells flow through a single riser. The introduction of phosphorus-tagged scale inhibitors has partially solved the detection issue, but more tags are still needed for subsea developments in the North Sea and for use in commingled production. Detection limits and turnaround time of the sample analysis are also concerns. A new tagged scale inhibitor has been developed combining the proven performance of sulphonated co-polymers coupled with fluorescence technology, thus allowing the scale inhibitor to be detected using fluorescence spectroscopy.
This paper discusses the development of the technology for use in a North Sea field located 130 miles northeast of Aberdeen that has a downhole barium sulphate scaling risk. It is comprised of platform wells and subsea wells that tie back to the host platform via two shared risers. The operator was experiencing difficulties in detecting the subsea squeeze returns so this new tagged scale inhibitor was introduced in one of the wells to improve the monitoring of the squeeze returns. The scale inhibitor was detected successfully in the produced water samples by spectrofluorimetry and validated with gel permeation chromatography. The ultimate goal is to analyse residual squeeze inhibitors using a portable fluorimeter for onsite detection, enabling real-time monitoring of the squeeze returns.
The development of the chemistry and detection monitoring technique and the preliminary results from the field trial, and demonstrates the validity of the analysis method is discussed. This new chemistry, being detectable in mixed fluids, reduces the need for shutting in wells or well tests for sampling, thus minimising process instability due to re-routing wells and shut-in losses.