A Critical Review of the Physicochemical Impacts of Water Chemistry on Shale in Hydraulic Fracturing Systems

• Published in: Environmental science & technology Vol. 55; no. 3
• Main Authors: Khan, Hasan Javed, Spielman-Sun, Eleanor, Jew, Adam D., Bargar, John, Kovscek, Anthony, Druhan, Jennifer L.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 11-01-2021
• Subjects: Clay; Deformation; ENVIRONMENTAL SCIENCES; Fluids; geochemistry, hydrofracturing, shales; Minerals; Shale
• ISSN: 0013-936X; 1520-5851

Hydraulic fracturing of unconventional hydrocarbon resources involves the sequential injection of a high-pressure, particle-laden fluid with varying pH's to make commercial production viable in low permeability rocks. This process both requires and produces extraordinary volumes of water. The water used for hydraulic fracturing is typically fresh, whereas 'flowback' water is typically saline with a variety of additives which complicate safe disposal. As production operations continue to expand, there is an increasing interest in treating and reusing this high-salinity produced water for further fracturing. Here we review the relevant transport and geochemical properties of shales, and critically analyze the impact of water chemistry (including produced water) on these properties. We discuss five major geo-chemical mechanisms that are prominently involved in the temporal and spatial evolution of fractures during the stimulation and production phase: shale softening, mineral dissolution, mineral precipitation, fines migration, and wettability alteration. A higher salinity fluid creates both benefits and complications in controlling these mechanisms. For example, higher salinity fluid inhibits clay dispersion, but simultaneously requires more additives to achieve appropriate viscosity for proppant emplacement. In total this review hiighlights the nuances of enhanced hydrogeochemical shale stimulation in relation to the choice of fracturing fluid chemistry.