(60a) An Optimization Model for the Integration of the Hydraulic Fracturing with a Power Plant Considering CO2 As Fracture Fluid

The natural gas has progressively increased its use for the generation of electricity with the purpose of substituting other more polluting fuels such as fuel oil and diesel. The electric power generation industry is the largest responsible for high CO₂ emissions into the environment; subsequently, an average 0.35 TonCO₂/MWh are emitted in a combined cycle power plant that uses natural gas. In this regard, according to the Energy Information Administration (EIA) in 2020, 7,257 trillion cubic feet (Tcf) of total global proven reserves of natural gas have been estimated and during the year 2021 the production of shale gas was approximately 26.8 billion around the world. In this context, a major challenge for the shale gas extraction industry is the huge amount of fracture fluid required to successfully complete the unconventional wells in order to produce shale gas where an average of 15,000 m³ of fluid fracture per well are demanded, which typically corresponds to water. However, recent researches employ some non-aqueous fracturing fluids, for example: carbon dioxide in supercritical conditions (ScCO₂). The ScCO₂-based fracturing technology associated with enhanced shale gas recovery represents a great promise for reducing water consumption; besides, the use of ScCO2 has proven to have a higher rock erosion capacity and requires a lower threshold pressure in comparison with water to initiate the fracture, which generates that the volume of fractured rock is several times greater compared to water and as consequence the shale gas production is higher when ScCO₂ is used.

Therefore, in this paper a formal optimization formulation is proposed for the mass integration of the shale gas production industry and a power plant implementing all possible mass interactions considering water and CO₂ treatment units as well as storage units for water, CO₂ and natural gas using completely or partially ScCO₂ as a fracture fluid. The economic objective consists of the minimization of the total annual cost, while the environmental goal corresponds to the minimization of freshwater consumption in the hydraulic fracturing phase as well as the reduction of the CO₂ released into environment by power plants. Finally, the applicability of the proposed mathematical approach is shown through a case study.