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  1. Abstract

    Recent advances in shale gas development have largely outpaced efforts to manage associated waste streams that pose significant environmental risks. Wastewater management presents significant challenges in the Marcellus shale, where increasing fluid volumes concomitant with expanding development will threaten to overwhelm existing infrastructure over the next decade. In this work, we forecast growth in drilling, flowback, and produced fluid volumes through 2025 based on historic data and consider conventional and alternative disposal options to meet future demands. The results indicate that nearly 12 million m3(74 MMbbl) of wastewater will be generated annually by 2025. Even assuming wastewater recycling rates in the region rebound, meeting increased demands for wastewater that cannot be reused due to poor quality or logistics would require significant capital investment to expand existing disposal pathways, namely treatment and discharge at centralized facilities or dedicated brine injection in Ohio. Here, we demonstrate the logistical and environmental advantages of an alternative strategy: repurposing depleted oil and gas wells for dedicated injection of wastewater that cannot otherwise be reused or recycled. Hubs of depleted wells could accommodate projected increases in wastewater volumes more efficiently than existing disposal options, primarily because the proximity of depleted wells to active production sites would substantially reduce wastewater transport distances and associated costs. This study highlights the need to reevaluate regional-scale shale wastewater management practices in the context of evolving wastewater qualities and quantities, as strategic planning will result in more socially and economically favorable options while avoiding adverse environmental impacts that have overshadowed the environmental benefits of natural gas expansion in the energy sector.

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  2. Abstract

    Target subsurface reservoirs for emerging low‐carbon energy technologies and geologic carbon sequestration typically have low permeability and thus rely heavily on fluid transport through natural and induced fracture networks. Sustainable development of these systems requires deeper understanding of how geochemically mediated deformation impacts fracture microstructure and permeability evolution, particularly with respect to geochemical reactions between pore fluids and the host rock. In this work, a series of triaxial direct shear experiments was designed to evaluate how fractures generated at subsurface conditions respond to penetration of reactive fluids with a focus on the role of mineral precipitation. Calcite‐rich shale cores were directly sheared under 3.5 MPa confining pressure using BaCl2‐rich solutions as a working fluid. Experiments were conducted within an X‐ray computed tomography (xCT) scanner to capture 4‐D evolution of fracture geometry and precipitate growth. Three shear tests evidenced nonuniform precipitation of barium carbonates (BaCO3) along through‐going fractures, where the extent of precipitation increased with increasing calcite content. Precipitates were strongly localized within fracture networks due to mineral, geochemical, and structural heterogeneities and generally concentrated in smaller apertures where rock:water ratios were highest. The combination of elevated fluid saturation and reactive surface area created in freshly activated fractures drove near‐immediate mineral precipitation that led to an 80% permeability reduction and significant flow obstruction in the most reactive core. While most previous studies have focused on mixing‐induced precipitation, this work demonstrates that fluid–rock interactions can trigger precipitation‐induced permeability alterations that can initiate or mitigate risks associated with subsurface energy systems.

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