An industrial ecology based systems approach for optimization of wastewater management from shale gas production

The rapidly developing unconventional shale gas industry offers economic benefits but also poses several outstanding environmental challenges. One such critical challenge is reducing the consumptive use of water in hydraulic... [ view full abstract ]

The rapidly developing unconventional shale gas industry offers economic benefits but also poses several outstanding environmental challenges. One such critical challenge is reducing the consumptive use of water in hydraulic fracturing and sustainable management of high salinity wastewater. Roughly 10-25% of the water injected during hydraulic fracturing returns to the surface as contaminated water with high salinity and potential detrimental impacts on human health and surrounding ecosystems. The current dominant strategies for shale gas wastewater management is disposal into underground injection wells and recycling for future fracking operations. Underground injection has come under increased scrutiny because of concerns over seismic activity in regions close to underground injection wells. Furthermore, underground injection and recycling may become impractical as the wastewater supply from production wells surpasses water demand for future fracking suggesting an urgent need for developing alternative management strategies. This has prompted research into developing more economical and environmentally sustainable management strategies centered on advanced desalination technologies. Moreover, a holistic systems approach is required for integrated water management as opposed to optimizing and investigating each solution in isolation. Shale gas water management using optimization techniques has gained traction to inform decision-making for shale gas supply chain management. However, the majority of existing work is focused on short term planning where shale gas wastewater could be recycled for future hydraulic fracturing requirements with little emphasis on long term planning for produced water management. This work presents a scalable optimization-based decision-making framework for guiding environmentally and economically conscious management of high salinity wastewater in Marcellus shale play. A mixed-integer linear programming (MILP) model will be presented that optimizes the shale gas produced water management while explicitly accounting for economic and environmental impacts. The model investigates optimal management strategies for produced water by incorporating detailed treatment cost data obtained from techno-economic assessment of treatment technologies as well as detailed transportation cost data from shale gas sites to treatment or disposal facilities. We evaluate water management alternatives ranging from direct disposal in Class II injection wells to advanced centralized, decentralized, and onsite treatment, recycle, and reuse options. Specifically, we focus on Membrane Distillation (MD) technology which holds great promise for desalination of shale gas wastewater. MD is a thermally driven membrane-based process with relatively high thermal energy requirements compared to conventional desalination techniques. However, there are industrial ecology opportunities for coupling MD with available waste heat from natural gas (NG) compressor stations to offset its energy requirements and enhance sustainability of shale gas wastewater management. Preliminary results from our optimization model reveal that only 56% of the available waste heat at NG compressor stations in Pennsylvania is sufficient for desalination of shale gas wastewater. These results are compelling as they show that synergistic integration of shale gas wastewater treatment process with waste heat sources could provide economic and environmental benefits over direct disposal of wastewater into injection wells. The results of scenario analysis investigating how changes in regulatory environments and production scenarios may affect the choice of wastewater management alternatives will be described in detail.