Improved Scale Inhibitor Assay for Sulphonated Polymers in Oilfield Brines

Abstract

Abstract Residual scale inhibitor analysis in produced waters, particularly for the sulphonated co-polymers is recognised as an ongoing challenge for many offshore production environments. Although methods have been well documented (e.g. dialysis / hyamine based techniques), there are a number of known difficulties when assaying residual ppm and sub ppm levels of sulphonated polymers where separation of the inhibitor from the brine phase can be a time consuming, labour intensive and often difficult operation. This paper describes a number of recent developments made to enable rapid, accurate, reliable and robust analysis of sulphonated polymers in oilfield brines. The work focuses primarily on those inhibitors which are not readily separated by conventional C18 techniques. This includes more appropriate solid phase extraction, SPE, techniques which demonstrate near 100% retention of sulphonated polymers from brines of different salinities and therefore negate the requirement for dialysis. The work couples these newly developed separation techniques to different assay methods including conventional post separation Hyamine derivitisation as well as direct analysis using appropriate HPLC detection systems. The paper will describe the challenges faced with residual scale inhibitor analysis in oilfield produced waters. Present advances made in the separation and assay of these and other polymeric species include the ability to obtain reliable separation and when required concentration using SPE methods as well as the utility of a variety of different detection systems. Extensive validation tests in a range of high salinity brines demonstrating the limits of detection and repeatability at ppm and sub ppm level for a variety of different polymers including PVS, VS-Co and more conventional polyacrylate as well as phosphorus containing polymers. In short, the results will demonstrate the ability to accurately assay a range of different polymers in different brine systems and mark a significant advancement over previously employed dialysis / Hyamine approaches. The paper will also illustrate the potential application of the techniques for separation and individual assay of different polymers from mixtures, which still represents a significant challenge for produced water analysis in many situations.