Injection-water chemistry plays a significant role in the impact of several improved-oil-recovery (IOR) and enhanced-oil-recovery (EOR) processes. Recently, advanced waterfloods through the tailoring of injection-water salinity and composition have received good attention in the oil industry for both sandstone and carbonate reservoirs. However, the importance of injection-water chemistry has not received its due attention as a whole in the IOR/EOR business because published studies in this area are distributed sparsely in bits and pieces without much relation to establish the strong connection. Also, injection-water-chemistry effects in certain EOR areas remain largely unexplored, even though they look somewhat promising. Moreover, the existing literature lacks a clear definition of injection-water-chemistry requirement guidelines for all IOR/EOR processes, including some of the newer processes that currently either are being practiced or are in research. In this paper, we provide a comprehensive review of more than 100 papers published during the past several decades in this subject area. The objectives of this review study are to provide an overview of smart-waterflooding technology; to describe important roles played by injection-water chemistry in the IOR/EOR business, with supporting examples; to extend the applicability of the smart-water concept to different IOR/EOR processes; and to develop the desired injection-water-chemistry requirement guidelines for IOR/EOR. The review analyses presented in this paper indicate that injection-water chemistry is important everywhere in the IOR/EOR business and is applicable not only to advanced waterfloods, but also to most of the recovery processes among the three major EOR types. These EOR processes include polymer flooding, alkaline-surfactant-polymer flooding, low-salinity surfactant flooding for sandstones, dilute-surfactant flooding for carbonates, carbonated waterflooding, miscible carbon dioxide (CO2) water-alternating-gas (WAG) flooding, and steamflooding. Injection waters of optimized salinity and ionic composition can also combine synergistically with several other EOR processes to result in higher incremental oil recoveries. Lower-salinity waters have a beneficial effect in polymer, surfactant, dilute-surfactant, and carbonated waterfloods, to yield better oil recoveries when compared with high-salinity water. The use of smart water for tertiary miscible CO2 WAG floods and carbonated waterflooding appears promising; however, it requires additional research to clearly distinguish and determine smart-water effects in these processes. The review analyses are finally extended to develop the desired injection-water-chemistry requirements for all individual IOR/EOR processes currently known. The findings of this study also put forward two major recommendations for consideration by the industry: (1) there is a need for close collaboration between water and oil industries to develop fit-for-purpose water-treatment solutions for addressing IOR/EOR injection-water-chemistry requirements, and (2) some thought should be given to develop “water chemistry” as a specialty discipline within the oil industry, for better integration of this emerging focus area with other key surface- and subsurface-related disciplines to effectively improve upon the IOR/EOR upstream value chain.
Water chemistry with selective ionic content and composition in the injection water plays a critical role to impact on several oil recovery enhancement processes. Lower ionic strength waters with threshold salinities less than 5,000 ppm are desired for SmartWater flooding in sandstones. Low salinity water depleted in monovalents, but enriched in sulfates and divalents is suited for SmartWater flooding in carbonates. Polymer floods mandate different low salinity water lacking both monovalent and divalent ions to reduce polymer dosage and improve project economics. ASP floods require optimal salinity water without the hardness ions to enable utilization of alkali and certain temperature tolerant surfactants in the chemical formulation design. Lower salinity water is desired for carbonated water flooding to increase CO2 dissolved quantities for better incremental oil recovery. Lower salinity waters could turn out to be advantageous even for CO2 WAG where low salinity benefits outweigh the adverse CO2 solubility effects. Thermal floods require fresh and hardness free water to generate the steam using boilers.
Injection waters of optimized salinity, ionic content and composition not only work on their own, but can also synergistically combine with other EOR processes to result in higher incremental oil recoveries. Lower salinity waters have a beneficial effect in polymer, surfactant, dilute surfactant and carbonated water floods to yield better oil recoveries when compared to high salinity water. In this paper we first provide an overview on the benefits of tuning injection water salinity and composition in different IOR/EOR processes with selected examples and then propose a unique set of injection water chemistry requirement guidelines for IOR/EOR. The study findings also point out the need to develop “water chemistry” as a specialty discipline within EOR portfolio and advocate for better integration of this area with other key surface and subsurface related disciplines to effectively improve upon IOR/EOR upstream value chain.