Surfactant inhibition mechanisms of carbonate mineral dissolution in shale

Surfactants are common additives to hydraulic fracturing and enhanced oil recovery (EOR) fluids, under consideration for amendment supercritical carbon dioxide geological sequestration (GCS). The effect of a anionic surfactant, internal olefin sulfonate (IOS), on mineral dissolution from shale into brine was evaluated. When added at concentrations exceeding the critical micelle concentration (94 mg/L), IOS inhibited carbonate in an Eagle Ford shale, as well optical quality calcite (the dominant shale). Laser profilometry images provide spatial resolution across > 3 orders magnitude, indicate that addition both enhances formation new etch pits calcite, impedes their further growth. Time-of-flight secondary ion mass spectrometry surface profiles show first time preferentially adsorbs pit edges versus flat surfaces (i.e., terraces). Surface pressure calculations, sulfur K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy results, density functional theory (DFT) calculations support this observation; DFT results head group molecule binds strongly step site compared terrace site. S NEXAFS adsorbed more etched smooth surfaces. Overall, weak adsorption terraces) disrupts water transfer dissolution, while strong displaces inhibits This work provides direct evidence preferential links it macroscopic kinetics. has implications surfactant-containing fluids used fracturing, EOR potentially GCS subsurface injection rich reservoirs.