Wastewater management strategies for sustained shale gas production

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 m 3 (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.

Assessment of groundwater well vulnerability to contamination through physics-informed machine learning

“…Surface spills of drilling fluids, hydraulic fracturing fluids, flowback and produced waters are of particular concern [30][31][32], especially because these fluids contain chemicals that are detrimental to human health [33]. Produced water is continuously generated throughout the operational lifespan of a UD well, and risks of spills are exacerbated by limited options for proper treatment and disposal [34].…”

Water Adsorption and Its Pore Structure Dependence in Shale Gas Reservoirs

“…With the excessive consumption of conventional oil and gas, the role of unconventional energy such as shale gas has become increasingly significant. , The United States, Canada, China, and several other countries have already realized commercial development of shale gas, whereas the majority of shale gas reservoirs are still in the exploration phase due to the complex accumulation and production mechanism. , The occurrence of water is a crucial influencing factor on gas content and production. , The water content of in situ shale gas reservoirs ranges roughly from 10 to 60%, with certain reservoirs in some areas of southern China reaching even 90%. − Water occurs mainly as irreducible water, which refers to the non-flowing water on the pore surface and throat existing in the forms of a water film, a water cluster, and condensation water through adsorption. ,, In general, the water content of reservoirs is much lower than that of irreducible water saturation. , Moreover, shale gas reservoirs are generally characterized by low porosity and permeability; therefore, reservoir stimulation is required to improve and stabilize production. , Hydraulic fracturing is extensively employed to stimulate reservoirs, and horizontal drilling and multi-stage hydraulic fracturing technologies greatly promote the commercial development of shale gas. , However, the flowback rates of water-based fracturing fluids are mostly less than 50%; hence, the majority of the fracturing fluids remain in the shale gas reservoirs. , Therefore, besides in situ water, the fracturing water is the main proportion of the reservoir in the exploitation process. , This influences the recovery of shale gas and triggers reservoir damage, waste of fresh water resources, pollution of surface water and ground water, and increases costs. The adsorption capacity of shale to water is clearly higher than that of CH 4 , which will desorb the pre-adsorbed CH 4 with water occurrence.…”

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

“…Reusing this “cleaned” produced water for field operations could be of vital importance as the produced volumes can overwhelm the local disposal facilities. , However, the cleaning necessary to make these fluids suitable for reinjection is nontrivial. − While conventional oxidation techniques can readily be used to remove organics and some inorganics (e.g., iron) from produced water, monovalent and other divalent inorganic ions can be more difficult and economically burdensome to remove. , Additionally, such large variation in the produced volumes and salinity add to the complexity of dealing with this fluid from an operational standpoint (e.g., facility size and transport cost). , These engineered fluids often contain a range of additives designed to control viscosity, friction, microbial growth, and corrosion, resulting in a wide variety of chemical compositions ,− and contaminants such as oils, soluble organic compounds native to the fractured formation, and degraded products of the injected organic compounds. , Therefore, injection of this produced water reintroduces the alkali earth metals to the rock and ultimately exacerbates blocking of fractures due to secondary mineral precipitation . Constricted flow can potentially mobilize precipitated mineral scale by matrix dissolution leading to further fracture occlusion.…”

“…36,37 Additionally, such large variation in the produced volumes and salinity add to the complexity of dealing with this fluid from an operational standpoint (e.g., facility size and transport cost). 33,38 These engineered fluids often contain a range of additives designed to control viscosity, friction, microbial growth, and corrosion, resulting in a wide variety of chemical compositions 26,38−41 and contaminants such as oils, soluble organic compounds native to the fractured formation, 42 and degraded products of the injected organic compounds. 43,44 Therefore, injection of this produced water reintroduces the alkali earth metals to the rock and ultimately exacerbates blocking of fractures due to secondary mineral precipitation.…”