Adsorption and precipitation of scale inhibitors on shale formations

Abstract

Abstract Scale inhibitor is one of the most important ingredients in hydraulic fracturing fluids for shale gas production. However, the adsorption and precipitation behaviors of scale inhibitors on shale formations have never been reported. The objective of this study is to develop mechanistic understanding of interactions between common scale inhibitors and shale formations so that we can predict the fate and transport of scale inhibitors in shale formations. The adsorption and precipitation of DTPMP and PPCA on Eagle Ford and Marcellus shales were studied in batch reactors at oil field temperature of 70 °C. The adsorption kinetics shows a fast adsorption process of inhibitors on shales, and inhibitor concentrations reach equilibrium between 4 and 8 h. In batch adsorption isotherm experiments, initial concentrations of scale inhibitors in aqueous phase varied from 5 ppm to 44,000 ppm. At low DTPMP concentration ranges, surface adsorption occurs on both Eagle Ford and Marcellus. Above certain concentrations, DTPMP and calcium forms precipitate on Eagle Ford, which increases the attachment, and slightly acidic pH and high calcium concentrations enhance the precipitation. The adsorption of PPCA on Eagle Ford was more significant at slightly acidic conditions, and PPCA adsorption onto Marcellus did not exhibit a notable difference between different pH conditions. Due to the strong chelating effect of DTPMP and PPCA, iron was extracted from Marcellus under high inhibitor concentrations.