A Critical Review of Alternative Desalination Technologies for Smart Waterflooding
Authors: Ayirala Subhash C. , Yousef Ali A. 
Published: October 2016

Summary
The importance of tuning injection-water chemistry for upstream is moving beyond formation-damage control/water incompatibility to increasing oil recovery from waterflooding and different improved-oil-recovery (IOR)/enhanced-oil-recovery (EOR) processes. Smart waterflooding through tuning of injection-water salinity and ionic composition has gained good attention in the industry during recent years for IOR in carbonate reservoirs. The water-chemistry requirements for IOR/EOR have been relatively addressed in the recent literature, but the key challenge for field implementation is to find an easy, practical, and optimum technology to tune water chemistry. The currently available technologies for tuning water chemistry are limited, and most of the existing ones are adopted from the desalination industry, which relies on membrane-based separation. Even though these technologies yield an achievable solution, they are not the optimum choice for altering injection-water chemistry in terms of incorporating selective ions and providing effective water management for large-scale applications. In this study, several of the current, emerging, and future desalination technologies are reviewed with the objective to develop potential water-treatment solutions by use of both seawater and produced water that can most efficiently alter injection-water chemistry for smart waterflooding in carbonate reservoirs.
Standard chemical-precipitation technologies, such as lime/soda ash, alkali, and lime/aluminum-based reagent, are only applicable for removing certain ions from seawater. The lime/aluminum-based reagent process looks interesting because it can remove both sulfates and hardness ions to provide some tuning flexibility for key ions included in the smart water. There are some new technologies under development that use chemical solvents to extract salt ions from seawater, but their capabilities to selectively remove specific ions need further investigation.
Forward osmosis (FO) and membrane distillation (MD) are the two emerging technologies, and they can provide good alternatives to reverse-osmosis (RO) seawater desalination for the near-term. These technologies can offer a more cost-effective solution in which there is availability of low-grade waste heat or steam. The two new desalination technologies, based on dynamic vapor recompression and carrier-gas extraction (CGE), are well-suited to treat high-salinity produced water for zero liquid discharge (ZLD), but they may not be able to provide an economical solution for seawater desalination. Carbon nanotube-based desalination, graphene sheet-based desalination, and capacitive deionization are the three potential future seawater-desalination technologies identified for the long term. Among these, carbon nanotube-based desalination is more attractive, although the technology is still largely under research and development.
The results of this review study show that there is no commercial technology yet available to selectively remove specific ions from seawater in one step and optimally meet the desired water-chemistry requirements of smart waterflooding. As a result, different conceptual process configurations involving selected combinations of chemical precipitation, conventional/emerging desalination, and produced-water-treatment technologies are proposed. These configurations represent both approximate and improved soutions to incorporate specific key ions into the smart water selectively, besides presenting the key opportunities to treat produced-water/membrane reject water and provide ZLD capabilities in smart-waterflooding applications. The developed configurations can provide an attractive solution to capitalize on existing huge produced-water resources available in carbonate reservoirs to generate smart water and minimize wastewater disposal during fieldwide implementation of smart waterflood.