Optimization of water management strategies for shale gas extraction considering uncertainty in water availability and flowback water

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This paper addresses the multi-objective optimization of water management used in the extraction of shale gas through the hydraulic fracturing process. The optimization aims to minimize the total annual cost and simultaneously minimize the total water requirements. Two uncertain factors are considered about the available fresh water and flowrate of wastewater (flowback water). Due to the complexity of the problem, a hybrid optimization method is proposed by combining deterministic and metaheuristic optimization approaches. The deterministic model is programmed in the General Algebraic Modeling System (GAMS) commercial software. The metaheuristic algorithm is implemented in Microsoft Excel®. The stochastic tool for uncertainty consideration is a code declared in the Visual Basic for Applications environment. The communication of the necessary programs in the methodology is achieved by the action of code sets also programmed in Visual Basic for Applications. To illustrate the merits of the proposed approach, a case study is solved to address water management for a shale gas field where a variable number of wells from 20 to 60 with different scheduling are considered. The results offer the optimal operation scheduling of the wells accounting for the minimum total annual cost and total freshwater consumption. Additionally, the maximum number of wells is obtained up to where it is possible to find feasible solutions. The best results were found with a maximum number of 51 wells prioritizing the economic objective and with 59 wells if the environmental objective is prioritized.