Polymers are being applied increasingly in the field as more environmentally acceptable alternatives to phosphonates for inhibition of common mineral scales. However, the systematic design and optimization of these compounds by traditional experimental methodologies can be complicated by several factors. The intrinsically random nature of polymerization reactions means that final products are heterogeneous, containing molecules of various weights and functionalities. This can create problems when determining the concentration, adsorption, desorption, and inhibition characteristics of active constituents. Additionally, reservoir rock can further complicate the issue by chromatographically fractionating these species in the field following squeeze application, leading to errors when quantifying returning inhibitor concentrations by reference to laboratory prepared analytical calibration curves. Accordingly, the determination of polymeric scale inhibitors needs to be carried out with care and the results carefully interpreted to reach valid conclusions. Ideally, an assay method should be applied which efficiently isolates and quantifies only the active species from solutions. If a reliable protocol could be used to investigate structure-activity relationships during the development of new inhibitors, this would represent an additional advantage with potential commercial implications.
In this paper, a wide range of analyses are described that were used to fully characterize a commercialized phosphorus-functionalized co-polymeric scale inhibitor currently being applied in the field. Dialysis and solid phase extraction were employed to split the inhibitor into six defined fractions based on specific properties. These components, as well as starting materials and the commercial material, were then analyzed by various techniques with the results used to quantify the ratio of polymeric/nonpolymeric compounds. The unique characteristics of species in each isolated fraction were subsequently related to the observed ability to inhibit sulfate scaling in static jar tests and the potential to interfere with polymer quantification during flowback.
Comparing the masses and activities of each fraction under controlled conditions proved, as expected, that high molecular weight compounds in the commercial product were most active in terms of barite inhibition efficiency. However these components were diluted to an extent by side-products persisting from the polymerization process. Importantly, it was shown definitively for the first time that this polymer operates by a dual-mechanism of scale inhibition to effectively prevent both nucleation and growth of barite crystals. The results confirmed which isolation/identification methodology was best suited to determining the level of scale protection in a reservoir in the time period between squeeze applications, whilst also explaining previous analytical anomalies. Finally, the identities of certain impurities were suggested, proposing modifications to the polymerization which would lead to more active products with a higher degree of homogeneity.
These analyses will contribute to a significant improvement in understanding mechanisms of scale inhibition and form a logical basis for proposing future generations of scale inhibitors with reduced levels of analytical interference, allowing for detection in produced waters to a higher degree of accuracy and precision. Isolating the active components from novel polymer chemistries will allow more appropriate comparison of inhibition potential without the influence of impurities, ensuring chemicals are ranked appropriately.