Development and accurate assay techniques for poly vinyl sulphonate (PVS) and sulphonated co-polymer (VS-Co) oilfield scale inhibitor

In the application of chemical inhibitors in field squeeze treatments for the prevention of sulphate and carbonate mineral scale formation, it is very important that the chemical species involved can be accurately assayed. When the inhibitor concentration drops below a predetermined threshold for scale inhibition (Ct) then the well may need to be re-squeezed. The importance of an accurate assay is primarily related to the determination of the end of squeeze lifetime. However, it is also necessary in order to carry out reliable modelling work which can lead to the optimisation of future squeeze treatments.

This paper examines the problems associated with the accurate detection of sulphonated polymers at the ppm level using the conventional pinacyanol cholride anayltical technique. The major problems associated with the use of this techniques are identified and modified procedures are presented in order to improve the assay, and allow the use of synthetic brines as calibration standards for assay in produced waters. Pre-treatment techniques are introduced which allow the inhibitor chemical to be separated from the brine salts thus allowing analysis using a variety of colorimetric techniques. An approach based upon the turbidimetric Hyamine 1622 detection method (commonly used for polyacrylate based species) is introduced and shown to provide very accurate detection and assay in both synthetic and produced water samples. This method suffers from less of the interferences and sensitivities associated with with the pinacyanol chloride method and has been adopted by a number of service companies currently operating in the North Sea. However, it should be noted that, due to the nature (shape) of the turbidimetric calibration curve, poor sensitivity is achieved at very low inhibitor concentrations (<2 ppm). However, at concentrations higher than these, this would be the method of choice in a wide variety of field produced waters.