In recent years,many researchers reported that water flooding recovery factor increased by injecting lowsalinity(LS)water into sandstone reservoirs,but the mechanism of improved recovery using LS water isstill a topic of debate.Recently we studied the role of clays and their impact on oil recovery during LS waterflooding into sandstone.This paper qualifies the calcite role and the vital role of pH in the water floodingof LS water in sandstone with and without calcite as a function of temperature.Four chromatography columns composed dissimilar amount of quartz and calcite(100% quartz;100%calcite;10% calcite + 90% sand;20% calcite + 80% sand)were water flooded with high salinity(HS)waterfollowed with LS water at two different temperatures 25 and 90°C and measuring the effluent Ca2+ andCH3COO-and pH.The columns with the minerals inside were then aged for a week at 70°C with 0.01 molar(M)sodium acetate to mimic the bonding of oil-bound carboxylic acids with the reservoir.To qualify thecalcite impact,a 100% calcite and calcite-free samples were investigated;the detected acetate and Ca2+ inthe effluent were,approximately,in the same range of other columns.Characteristically,a higher calcite content saw a considerable upsurge in pH.Still,the calcite-freesamples also saw an increase in pH,as high as that of the calcite-containing cores.There was a generaldecrease in calcite dissolution,ion exchange,and pH increment when the test temperature increased for allexperiments.The positively charged-COOCa+ group released from SiO-when LS water injected into sandonly column,and as the calcite concentration increases,the calcite dissolution increases,and the carboxylicacid releasement increases too.The approach of this work is that it allows us to isolate the interplay between ion exchange,pH,andcarboxylate release,which should allow us to better decode the chemical mechanisms that control LS waterflooding.
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