New Developments in the Analysis of Scale Inhibitors

Abstract

Summary Scale inhibitors (SIs) are used to control oilfield scale formation, and the ability to analyze these species is very important such that SI concentrations as low as 0.5-ppm active need to be measured accurately. If phosphorus is present in the SI molecule, then inductively-coupled-plasma (ICP) -based methods may be used for analysis. However, the oil industry's increasing requirement to be environmentally friendly means that polymeric "green" SIs are now being used more, which raises issues concerning detection techniques (i.e., ICP vs. wet-chemical techniques). ICP detection for SIs 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, analytical approaches are described that have been used recently to improve chemical SI assay, especially at low near-threshold levels (a few ppm active of SI). Progress is reported in five areas of SI analysis: Assay of sulfonated copolymer (VS-Co) was not possible by straightforward analysis without extensive dialysis and sample preparation. However, calibrations and repeats of accuracy similar to that of the C18 were found for VS-Co using amino-propyl (NH2) cartridges and the Hyamine method.The Oasis® 2×4 method has been applied to SI analysis, and this is able to assay all types of polymeric SIs in principle. This method has been used to detect a VS-Co SI in a wide variety of different brine salinities from distilled water (DW) to high-salinity formation waters (FW) (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 that was not significantly improved by a higher-capacity sorbent cartridge.Various elements have been assayed in the oil phase using the ICP method. Calibrations and accurate repeats within 5 to 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 to 10 ppm and 0 to 2,500 ppm active SI.A matrix-matching Hyamine technique has been developed that 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.ICP and wet-chemical techniques have been able to accurately detect a P-tagged (phosphorus-tagged) copolymer-type SI. The ability to apply two 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, excellent correlation is observed 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 SI analysis almost 20 years ago (Graham et al. 1993, 1995a, 1995b, 1996; Sorbie et al. 1992) and are described in our Flow Assurance and Scale Team (FAST) laboratory procedures manual (Sorbie and Boak 2006).