Widespread application of water injection for reservoir flooding invariably leads to increasing water cuts of Russian oilfields. High water cuts account for a substantial fraction of overall operating costs associated with bringing crude oil to export quality by dehydration and desalting. Treating produced fluids using gravity separation combined with chemical demulsification is the industry standard for crude oil processing. Understanding demulsifier structure-activity relationship is important for optimum performance and design of treatment facilities. Composition analysis is not part of the current testing protocols in oil companies for this category of production chemicals, necessitating massive and laborious performance evaluations during contracting procedures. Knowledge of the chemical nature of active bases together with field application history would allow to narrow down the list of potential candidates by excluding inherently incompatible and identical products. Numerous researchers have pointed out that hydrophilic-lipophilic balance (HLB) of polymeric non-ionic surfactants comprising the active base is key to understanding demulsifier activity. HLB value is proportional to the percentage of hydrophilic units in the polymer. The study describes application of infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy for determining the composition of a representative set of 25 oilfield demulsifier samples from domestic suppliers. Methanol, water, toluene, and o-xylene are used to formulate solvents ensuring the required stability of the commercial products. Active base of nearly every sample consists of ethylene oxide – propylene oxide block copolymers, in some cases supplemented with 1-10% Neonol (alkyl phenol ethoxylates) and/or esters. Deconvolution of the 3000-2800 cm-1 C–H IR stretching vibration region and interpretation of 13C NMR spectra have led to ethylene oxide content in 24 active bases varying from 6 to 46 % with an average of 23 % which for most of the samples translates to HLB of 3-7 on a number scale introduced by Griffin. This corresponds to hydrophobic surfactants, with plausible benefits for demulsification process offered by preferential distribution into the oil phase of high water cut emulsions found in most oilfields.
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