A State-of-the-Art Review To Develop Injection-Water-Chemistry Requirement Guidelines for IOR/EOR Projects

Abstract

Summary 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.