Nanoindentation-enhanced screening of hydraulic fracturing fluid additives

Abstract

This paper describes a viable nanoindentation-enhanced technique for screening hydraulic fracturing fluid additives via quantifying the effects of rock-fluid interactions on the mechanical properties of a clay-rich shale. Big data nanoindentation testing was conducted on both the intact shale and counterparts hydrothermally treated by four fracturing fluids, including water, KCl solution, and two surfactants, to extract simultaneously the statistical, cross-scale mechanical properties of both the bulk rock and individual constituent phases (e.g., clay matrix, carbonate, and quartz), accompanied by scanning electron microscopy for surface imaging and elemental mapping. Results show that pure water and KCl solution significantly degrade the clay matrix's Young's modulus and hardness by up to 39.4–42.5% and 42.9–57.1%, respectively, which can be mitigated or prevented by appropriate surfactant additives. The physicochemical rock-fluid interactions, such as dissolution of carbonate, are mainly responsible for the property degradation, as evidenced by the hydrothermal treatment-induced large cavities and secondary pores on the surface that tend to impair microstructural integrity of the shale. The big data nanoindentation technique can be implemented as an adaptive toolkit for screening, tailoring, and optimizing the chemical additives in fracturing fluids used for a specific shale formation to prevent shale softening, protect reservoir stability, and maximize well production.