Abstract :
Low salinity waterflooding is an emerging EOR technique in which chemistry play major role in improved oil recovery. Numerous laboratory tests from many research groups and some field applications confirmed its effectiveness in enhanced oil recovery. Various mechanisms have been suggested since its appearance to explain the mechanism of the process. Nevertheless, none of them could explain and predict all aspects of the process and possibility of enhanced oil recovery and yet, its mechanism is matter of debate. This paper provides a comprehensive review of low salinity waterflooding. Attempt is made to cover all aspects and features of low salinity waterflooding to shed light on critical and challengeable features and clear the gaps and deficiencies of conducted studies. The proposed mechanisms are discussed and their success and failure are explained. Analytical and numerical modelling of low salinity waterflooding is presented. Both approaches via conventional simulators and geochemical modelling are reviewed. The pore-scale investigation trend is also addressed as a new approach to unveil fundamental phenomena behind the process. Secondary and tertiary low salinity waterflooding are compared in the term of additional oil recovered. Surface forces and rock/fluid/brine interaction and its relationship to wettability are discussed. Results of study of combined low salinity and EOR methods are described which includes simultaneous use of low salinity with polymer flooding, surfactant flooding, CO2 flooding and also hot water injection. Field applications are demonstrated and necessary conditions to achieve low salinity oil recovery enhancement are discussed. Based on this review, it seems that multi ion exchange and double layer expansion both can contribute in oil recovery enhancement due to low salinity water injection. In fact both proposed mechanisms can reduce oil film thickness which in turn releases more oil. In fundamental point of view, any mechanism that alters surface forces (DLVO theory is starting point) can lead to oil detachment. The process not only is low cost in operation but also can reduce the amount of EOR agents (surfactant, polymer, etc..) and their effectiveness when it combine with other EOR techniques. Accordingly low salinity waterflooding-EOR methods have great potential for enhanced oil recovery in future.
