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).
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
9 March 2010
- Meeting paper published:
27 May 2010
- Revised manuscript received:
23 June 2010
- Manuscript approved:
27 July 2010
- Published online:
28 October 2010
- Version of record:
17 November 2010
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