Sustainable Reuse of Hypersaline Oil-Produced Water for Green Energy Production
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abstract
Crude oil and natural gas extraction and exploration in Qatar are associated with the co-production of significant volumes of wastewater, called â produced water (PW)â . For every barrel of oil extracted, three to ten barrels of PW are generated, making it the largest waste stream flow at oil production facilities. PW from oil production (hereafter, oil-PW) in Qatar is characterized by its very high salinity, being more than five times as saline as seawater, and this makes its reuse prohibitively costly. Thus, oil-PW is typically reinjected into the formation to maintain reservoir pressure and/or it is disposed via deep-well injection. In both cases, pretreatment is required to maintain injectability and minimize operational costs. Although the hypersalinity of oil-PW hinders its availability for reuse, this hypersalinity is a type of stored energy that can be converted into usable mechanical energy. Pressure-retarded Osmosis (PRO) is a process that can convert osmotic energy into electrical energy using a hydro-turbine and generator in a way that is similar to conventional hydropower plants. However, there are only very few rigorous studies of the capabilities and limitations of PRO when applied to hypersaline water with such complex composition as found in oil-PW. Harnessing osmotic energy effectively from oil-PW will require innovative process design and development, including a new generation of membranes. The high salinity and complex composition of oil-PW pose several challenges. The first challenge caused by the high osmotic pressure of oil-PW is the high operating hydraulic pressure that will be required to obtain peak power density. This requires the development of PRO membranes with high mechanical strength that can withstand high operating pressures. Another major challenge for PRO is the low power density and energy efficiency that is practically achievable compared to theoretical values. This limitation is the result of concentration polarization and membrane fouling. However, it will be challenging to fabricate PRO membranes that can withstand high pressures with a thin support layer that is necessary to minimize concentration polarization. Nevertheless, any gains in achieving higher hydraulic pressures will improve the efficiency of energy extraction, especially if an optimized PRO system is employed. Therefore, the overarching goal of this project is to define the fundamental behavior of the PRO system with novel design and components that uses high-performance membranes in order to develop a robust and highly efficient system for green energy generation utilizing oil-PW..........
