Impact of Antiscalants on the Fate of Barite in the Unconventional Gas Wells

Abstract

Abstract

Formation of barite (BaSO₄) scale is a potential problem for unconventional (shale) gas extraction, as the excessive scale can reduce well productivity by plugging the proppant pack. This study was designed to evaluate the impact of antiscalants on the formation and transport of barite particles through proppant sand under well-controlled laboratory conditions using batch and column experiments. Extensive attachment of BaSO₄ particles to proppant sand was observed at typical background salinity and in the absence of antiscalants due to relatively large barite particle size and screened electrostatic interaction. Presence of polymeric antiscalants can enhance the mobility of BaSO₄ particles by decreasing their size and providing electrosteric repulsion. Ethylene glycol that may be added to hydraulic fracturing fluid to prevent scale deposition can reduce the size of BaSO₄ precipitates but has no impact on the deposition of BaSO₄ particles during transport through proppant sand. Polymaleic acid and sulfonated poly-phosphino-carboxylic acid that are generally considered when the goal is to inhibit formation of mineral scales are unlikely to prevent barite formation at high supersaturation conditions that are typical for unconventional gas industry. However, they can reduce the size and alter the morphology of barite particles as well as inhibit the deposition of bulk precipitates onto proppant sand surface by inducing stronger repulsive interactions.