Title : Experimental investigation of low salinity polymer from pore to core scale in heavy oil sandstone reservoirs
Recently, the synergic combination of low salinity water flooding (LSWF) with polymer flooding (PF) has been a subject of paramount interest for the oil industry. Numerous studies have investigated the efficiency of enhanced oil recovery using low salinity polymer flooding (LSPF). However, there is no clear conclusion that can explain the incremental oil recovery, determine the main factors controlling the oil recovery process, and define the relative contribution of rock/fluids or fluid/fluid interactions to extra oil recovery. Therefore, this study aims to perform a systematic investigation of the interactions between oil, polymer, low salinity and sandstone rock surface from pore to core scale during LSP. Partially hydrolyzed polyacrylamide (HPAM) polymer, Boise outcrop, a crude oil sample and reservoir cores from an Omani oil field, and two level of brine salinities were used in the study. A multidimensional experimental approach including static bulk measurements of polymer solutions prepared with brines of high and low salinities, single phase displacement experiments, along with rheological, pH, conductivity, total organic carbon (TOC) and ion chromatography (IC) measurements to analysis ion exchange reactions, polymer adsorption, and viscosity loss and, and finally two-phase experiments to demonstrate the oil recovery efficiency of LSP. The results obtained from this study show that the incremental oil recovery from LSP flooding related to the combination of the reduction in the water-oil mobility ratio, an increase in the repulsion forces between COBR interfaces and an increase in the pH of the aqueous solution. Moreover, lowering the salinity of the make-up brine resulted in a larger conformation (expansion) of the polymer molecules, which in turn resulted in less adsorption and a greater in-situ viscosity without any negative impact on injectivity. This plays a positive role in the oil displacement process. In addition, LSPF resulted in higher oil recovery with more acidic oil with a viscosity of 480 cP compared with that of 170 cP. However, there was loss of viscosity in the effluents of LSP that related to an increase in cations concentration which is mainly controlled by the mineralogical compositions of the rock surface.