This work presents a mathematical model for the simultaneous optimisation of water and energy usage in hydraulic fracturing using a continuous time scheduling formulation. The recycling/reuse of fracturing water is achieved through the purification of flowback wastewater using thermally driven membrane distillation (MD). A detailed design model for this technology is incorporated within the water network superstructure in order to allow for the simultaneous optimisation of water, operation, capital cost, and energy used. The study also examines the feasibility of utilising the co-produced gas that is traditionally flared as a potential source of energy for MD. The application of the model results in a 22.42% reduction in freshwater consumption and 23.24% savings in the total cost of freshwater. The membrane thermal energy consumption is in the order of 244 × 10 3 kJ/m 3 of water, which is found to be less than the range of thermal consumption values reported for membrane distillation in the literature. Although the obtained results are not generally applicable to all shale gas plays, the proposed framework and supporting models aid in understanding the potential impact of using scheduling and optimisation techniques to address flowback wastewater management.
As global exploration of shale gas reserves increases, there is a need for an accurate and efficient approach to proper water management, which is one of the vital problems related to shale gas production. This study looks at the effect of using multiple or hybrid treatment technologies in maximizing hydraulic fracturing wastewater reuse while ensuring the sustainability of the process in terms of energy and associated cost. The study considers ultrafiltration and membrane distillation processes as possible pretreatment and desalination technologies for flowback water management. It also considers the possibility of supplying the electrical and thermal energy requirements of these regenerators using flared gas. Two different scenarios are considered based on the flowback water composition in hydraulic fracturing in terms of salinity. Application of the proposed model to a case study leads to a 24.13% reduction in the quantity of water needed for fracturing. In terms of energy requirements, the approach yields a 31.6% reduction in the required thermal energy in membrane distillation and 8.62% in energy requirement for ultrafiltration. For flowback water with moderate total dissolved solid concentration, 93.6% of wastewater reuse comes from pretreated water by ultrafiltration and 6.4% from membrane distillation. However, as the flowback water salinity becomes higher, the percentage of pretreated reusable water reduces to 81.1% and the percentage supply through membrane distillation increases to 18.9%. In all cases, the results indicate that the decision to allow the pretreated water to pass through desalination technology strictly depends on the quantity of water required by a wellpad and the salinity of the wastewater.
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