New developments on the analysis of scale inhibitors

Scale inhibitors (SI) are used to control oilfield scale formation and the ability to analyse these species is very important such that SI concentrations as low as 0.5ppm active need to be measured accurately. If phosphorus is present in the SI molecule, then ICP based methods may be used for analysis. However, the oil industry’s increasing requirement to be environmentally friendly means that polymeric ‘green’ scale inhibitors are now increasingly being used, which raises issues over detection techniques i.e. ICP vs. wet chemical techniques. ICP detection for scale inhibitors is generally easier but, if it cannot be used, then at least time-saving improvements to wet chemical techniques are extremely beneficial.

In this paper, we describe a range of analytical approaches which we have been using recently to improve chemical SI assay, especially at low near threshold levels (a few ppm active of SI). Progress is reported in 5 areas of SI analysis as follows: (1) Assay of sulphonated copolymer (VS-Co) was not possible by straightforward analysis without extensive dialysis and sample preparation. However, calibrations and repeats of a similar accuracy to the C18 were found for VS-Co using amino-propyl (NH2) cartridges and the Hyamine method (the Rhodia Method). (2) The Oasis® 2x4 method has been applied to SI analysis and this is able in principle to assay all types of polymeric scale inhibitors. This method has been used to detect a VS-Co scale inhibitor (SI) in a wide variety of different brine salinities from distilled water (DW) to high salinity formation waters (e.g. a Heron type FW). Although achievable under these different conditions, there was a significant decrease in the absorbance signals recorded with increasing salinity which was not significantly improved by a higher capacity sorbent cartridge. (3) Various elements have been assayed in the oil phase using ICP. Calibrations and accurate repeats within 5-10% error were achieved. After solving compatibility issues, the concentration of an oil-tolerant SI was determined successfully using calibrations and accurate repeats over a range of 0-10 ppm and 0-2500ppm active SI. (4) A matrix-matching Hyamine technique has been developed which allows any chloride ion effects on the chelating process between the Hyamine and SI to be negated, allowing accurate analysis of low polymeric SI concentrations. (5) ICP and wet chemical techniques have been able to accurately detect a P-tagged co-polymer type SI. The ability to apply 2 independent analytical methods to a given species offers some important advantages when more than one SI is deployed in a field system. In this work, we show excellent correlation between the wet chemical and ICP assay methods for this P-tagged SI.

This study updates and adds to the set of analytical methods and procedures reported for scale inhibitor analysis by this group almost 20 years ago (Graham et al, 1993, 1994, 1995, 1996; Sorbie et al, 1992) and described in our FAST (Flow Assurance and Scale Team) Laboratory Procedures Manual (Sorbie and Boak, 2006).