Abstract

The Uinta Basin is an unconventional oil play that has, since 2017, annually increased hydrocarbon extraction through modern drilling and fracing techniques with increased frac loading. The primary production target is the Uteland Butte Member of the Green River Formation, which consists of interbedded limestones, dolostones, and thick, organic-rich mudstones. Along with increased hydrocarbon production, volumes of produced water from the Uteland Butte Member have also risen. Water is co-produced with hydrocarbons and is an undesirable byproduct of hydrocarbon extraction. Large frac operations now consistently have highly variable percentages of recovered water volume relative to oil. This increase in water production has increased water disposal costs and creates economic challenges for operators in the Uinta Basin. Isotopic and elemental analyses effectively track produced water evolution over time. Time-series sampling from wells landed in the Uteland Butte Member provides discrete datasets demonstrating that these compositional changes occur in unconventional reservoirs in a manner similar to conventional systems. We use δ¹⁸O, δD, and elemental geochemistry to characterize produced water sources, subsurface mixing processes, and geochemical end members. These data are used to allocate produced water production from the Uteland Butte Member and other sources to constrain subsurface connectivity. This approach relies on comparisons between produced water samples and defined end member prototype compositions, where each prototype represents water derived from member and formations outside the target Uteland Butte interval. End member prototypes include meteoric water, supply water, water from the stratigraphically overlying Douglas Creek Member, Carbonate Marker Member, Castle Peak Member, and underlying Wasatch Formation. Time-series sampling was conducted on seven newly completed Uteland Butte and one Castle Peak hydrocarbon well. Samples were collected from initial frac fluid flowback through stabilized formation water production. These samples were collected across all wells from November 25, 2024 to February 3, 2026. Stabilization is defined by the production of statistically similar geochemical compositions over time and is assessed through comparison with established prototype water compositions. Time-series data migrate toward these stable prototype compositions as injected frac fluid is progressively displaced by in-situ formation water. Quantitative comparison of produced water compositions with multiple end member prototypes enables identification of the source(s) contributing to increased amounts of produced water and higher water-cuts seen in the Uteland Butte Member based on distinct isotopic and elemental fingerprints found in each source. These results can then be used to develop a subsurface connectivity framework that can be integrated into existing models to improve predictions of hydrocarbon-to-water ratios in the Uinta Basin.

Degree

College and Department

Geological Sciences; Computational, Mathematical, and Physical Sciences

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