The Comprehensive Study of the Connate Water Chemical Composition Effect on Oil Recovery in Carbonate Rocks

Two natural cores from Middle East oilfield were used to perform core flooding experiments under reservoir conditions. Each core was run with different objectives. One core was to check salinity effect while another was to investigate the effect of potential determining ion composition (Mg2+, Ca2+, and SO42−) on oil recovery during secondary and tertiary recovery modes. Oil recovery, pressure drop and core-effluent were tracked and analyzed for each core flooding experiment. The experimental results were compared with our proposed geochemical studies which were done by introducing the reactions between rock, water, and oil, showing good consistency. Core effluent study shows the calcium concentration increased corresponding to a higher oil recovery. Supported by geochemical model studies, the lower calcium concentration in the connate water resulted in smaller oil bound on the rock surface because attraction force between rock and water became stronger. This work makes a further step towards the understanding of smart waterflooding in carbonate reservoirs.