(189j) Optimal Use of Water for Hydraulic Fracking of Gas Shale Production

The development of the gas shale industry by the continuous discovery of new shale reserves around the world, the improvement of extraction technologies, and the design of the new logistic process operations have produced the global interest in exploiting this resource to satisfy the current increasing energy demand based on the dependence on fossil energy sources. Although, shale gas is surrounded by several controversies, mainly environmental issues, due to the large amounts of water required for the extraction processes (hydraulic fracturing), as well as the large volumes of polluting effluents that are discharged to the environment (flowback fluid). In these sense, this work proposes an optimization approach to the design of a water network for gas shale production considering the recycle and reuse of water to reduce the fresh water consumption and the decrease the discharge of polluting effluents where it is included a storage system and a sophisticated treatment system.

The discharge of effluents produced by the shale gas extraction processes are composed by several substances that cause major problems, mainly high ecosystem damage and human health problems. The identified pollutants that cause major affectation and are presented in greater concentration are the TDS (Total Dissolved Solids), the treatment system is composed of specific separation units to obtain certain concentration of TDS according to the limits to be discharged to the final disposal or according to the specification to be recirculated in the water network. It is proposed the implementation of the eco-indicator 99 methodology to evaluate the efficiency for the treatment system, and quantify the total environmental impact of the water network operations. The model defines the number and type of treatment units in the water network according with the environment impact and cost. The multi-objective optimization model is defined by the economic objective function that aims to minimize the total annual cost for the water network that includes the storage system and the treatment system, and operations and capital costs. The environment objective is specified by the minimization of the environmental impact by the discharged concentration of TDS and the consumption of fresh water.

Finally, a case study for the northwest of Mexico is implemented to evaluate the proposed methodology, it should be noticed that there is a severe water scarcity problem in this region.