الملخص الإنجليزي
Recently, there has been a growing interest regarding the synergistic combination of
low salinity water with polymer flooding as a technique for enhanced oil recovery. Numerous
studies have been conducted to investigate the efficiency of low salinity polymer (LSP)
flooding in sandstone oil reservoirs; yet, there is no clear conclusion on the driving
mechanism. Research lacks detailed explanation on the influence of brine chemistry, polymer
characteristics, and rock mineralogy on the various aspects of crude oil/brine/rock (COBR)
interactions. Consequently, the relative contribution of rock/fluid or fluid/fluid interactions to
enhance oil recovery by LSP flooding is not well-understood. This study aims to scrutinize
the main factors controlling the oil recovery during LSP flooding by performing a systematic
experimental investigation of the interactions between crude oil, fluids and rock surface. Static
and dynamic experimental measurements were conducted using artificial and native reservoirs
systems (fluids and rocks) using brines of different chemistries. Rheological and fluid
properties of the injected and produced fluids were measured to establish a baseline and
quantify the main factors affecting the LSP flooding process. The impact of low salinity and
polymer flood on oil recovery was assessed using synthetic brines and native reservoir core
samples. The results revealed that the concentration of divalent cations and brine salinity
significantly influenced the electro-kinetic properties of the crude oil/brine and rock/brine
interfaces in the presence of polymer. The rock/brine interface became less negatively charged
with decreasing concentrations of divalent cations and brine salinity, while the oil/brine
interface became more negatively charged under the same conditions. Furthermore, reducing
the concentration of divalent cations or the salinity of the make-up brine showed a significant
impact on the viscoelasticity of polymer solutions but did not affect pH or the interfacial
tension (IFT). In addition, the presence of polymer in the brine was found to affect ion
exchange reactions, equilibration processes, and extending the stabilization time during
flooding experiments. Polymer molecules led to an increased concentration of divalent cations
in the effluent, which was more pronounced with decreasing brine salinity. Additionally, it
highlighted the greater influence of anion exchange reactions on pH of the effluent compared
to cation exchange. Moreover, LSP flooding showed better viscosity recovery, which can be
attributed to the relative change in cation and anion exchange reactions. LSP led to high
presence of sulfate ions in the effluent. The sulfate ions act as bridges between divalent
cations, preventing strong interactions with the polymer chains and maintaining viscosity
stability. The ratio of monovalent to divalent cations was identified as a major factor
influencing oil recovery by LSP flooding, regardless of rock mineralogy and injection
sequence mode, while pH and mineral dissolution had a minor effect. The viscoelasticity of
the crude oil/brine interface, influenced by factors such as oil viscosity and total acid number
(TAN), was found to be a crucial determinant of the success of LSP flooding. These results
have broad application and significance in LSP flooding for heavy oils to design LSP injection
strategies that yield improved oil recovery from sandstones reservoirs.
