CHEMICAL ENGINEERING TRANSACTIONS VOL. 43, 2015 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Chief Editors: Sauro Pierucci, Jiří J. Klemeš Copyright © 2015, AIDIC Servizi S.r.l., I SBN 978-88-95608-34-1; I SSN 2283-9216 MILFP Model and Algorithms for Network Design and Long- Term Planning of Water Management System for Shale Gas Production Jiyao Gao, Fengqi You * Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL 60208, USA you@northwestern.edu This paper addresses the optimal design and operations of water supply chain networks for shale gas production. We develop a mixed-integer linear fractional programming (MILFP) model with the objective to maximize profit per unit freshwater consumption, such that both economic performance and water-use efficiency are optimized. The model simultaneously accounts for the design and operational decisions for freshwater source selection, multiple transportation modes, and water management options. Water management options include underground injection, commercial centralized wastewater treatment (CWT), and different onsite treatment technologies. To globally optimize the resulting MILFP problem efficiently, we present three tailored solution algorithms: a parametric approach, a reformulation-linearization method, and a novel Branch-and-Bound & Charnes-Cooper transformation method. The proposed models and algorithms are illustrated through one case study based on Marcellus shale play, in which onsite treatment shows its superiority in improving freshwater conservancy, maintaining a stable water flow, and reducing transportation burden. 1. Introduction Natural gas is playing a significant role in meeting global energy demand, and is also serving as a transition fuel as the U.S. develops more sustainable fuel options. Shale gas is unconventional natural gas extracted from shale rock and has emerged as one of the most promising energy sources within the past decade. In 2012, 35% of the U.S. natural gas production was from shale gas (EIA, 2011). With increasing production of shale gas, the U.S. has changed from an importer to a net exporter of natural gas (EIA, 2013). The recent large-scale production of shale gas would not have been possible without the development of hydraulic fracturing and horizontal drilling technologies (Gregory et al., 2011). Despite the economic potential of using hydraulic fracturing and horizontal drilling technologies for shale gas production, there are increasing concerns about its environmental impacts (Kotek and Tabasb, 2013). In 2006, about 35,000 shale wells were drilled in the U.S., and each well required approximately 4-6 million gallons of injected water for shale gas production (Jiang et al., 2013). Meanwhile, in shale plays such as Marcellus, 10%- 25% of the injected water flows back to the surface as highly contaminated water. This water contains a high concentration of total dissolved solids (TDS) as well as other toxic and radioactive dissolved constituents (Karapataki, 2012), which is challenging and costly to treat. Economical production of shale gas requires effective wastewater management to minimize freshwater consumption while ensuring sufficient water supply to fracturing operations. Due to different water flow rates and water compositions in the shale wells, it is very important to determine the corresponding optimal strategies for water management. Water from freshwater sources is transported to shale sites by pipelines or trucks. At shale sites, fracturing fluid is prepared and pumped into the wellbore at a high pressure, meanwhile a certain amount of the injected fracturing fluid returns to the surface as flowback water. This flowback water can be classified by the DOI: 10.3303/CET1543238 Please cite this article as: Gao J., You F., 2015, Milfp model and algorithms for network design and long-term planning of water management system for shale gas production, Chemical Engineering Transactions, 43, 1423-1428 DOI: 10.3303/CET1543238 1423