Date of Graduation
Eberly College of Arts and Sciences
Geology and Geography
Production of oil and gas from organic-rich shale formations has become viable through advancements in multi-stage hydraulic fracturing. The decline of shale gas production after the initial days of fracturing operations coupled with falling oil and gas prices, has pushed industry operators to use new chemical additives as an attempt to increase hydrocarbon production. The implementation of highly reactive fracturing fluids that include strong oxidizing agents, pose as a potential solution to increase well productivity. Strong oxidizing chemicals commonly known in fracturing operations as breakers, are used to improve the viscosity of gel-based fluids after the proppant is transported into fracture zones of the target formation. These oxidizing agents have been observed to degrade the organic matter and unstable constituents of shale formations. However, fluid-rock interactions during this process have not been extensively investigated. The goal of this study was to investigate the fluid-rock interactions between Marcellus Shale and three solutions of oxidizing hydraulic fracturing fluid (HFF) at formation temperature. Three synthetic HFF solutions containing common oxidative breakers, ammonium persulfate, sodium bromate, and sodium hypochlorite were reacted for a 14-day period to mimic the shut-in period when fluid remains in contact with the reservoir rock during a fracturing operation. The chemical analysis focused on observing organic contaminant release, critical mineral mobility, mineralogy, and significant changes in ionic species. Results showed that individual oxidizing breakers controlled the type and amount of volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) present in the control and shale reacted effluents. An abundance of halogenated organic compounds was observed in effluents with sodium bromate and sodium hypochlorite, and negligible amounts were associated with ammonium persulfate. Additionally, the transformation of VOCs was observed to occur between control and shale reacted effluents. Organic acids were present in variable amounts in all effluent samples. Results show an enhanced but variable dissolution of shale organic matter and other unstable constituents such as pyrite by each oxidative fluid. This oxidation of shale organic matter and constituents, stimulated the release of critical minerals such as metals and metalloids into solution. Additionally, shifts in major ions and XRD results indicated that carbonate mineral dissolution and barite precipitation occurred in all shale reacted effluents. Similarly, the precipitation of gypsum was observed to occur in samples where sulfate ions were abundant due to enhanced dissolution of pyrite. Halite precipitation occurred in one effluent sample containing sodium hypochlorite breaker. These results suggest that oxidizing agents in HFF may provide a means for enhanced hydrocarbon production through oxidative dissolution. However, the generation and transformation of VOCs, critical mineral release, and secondary mineral dissolution and precipitation should be considered.
Donmoyer, Shaun, "Effect of oxidative breakers on organic matter degradation, contaminant mobility and critical mineral release during shale-fracturing fluid interactions in the Marcellus Shale" (2021). Graduate Theses, Dissertations, and Problem Reports. 8100.