Experimental Investigation of Osmosis as a Mechanism for Low-Salinity EOR
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The topic of this thesis is an experimental investigation of osmosis as a mechanism for low-salinity enhanced oil recovery by evaluation of the effect of surface-to-volume ratio on oil recovery. Increased oil recovery due to osmosis is expected to have a stronger correlation to the surface-to-volume ratio than other low-salinity EOR mechanisms. Low-salinity spontaneous imbibition tests were performed on oil-wet Bentheimer sandstone samples with varying surface-to-volume ratios. Fluids and core samples were chosen to promote osmosis-induced connate water expansion while impeding the effects of other proposed low-salinity mechanisms. The experiment was performed twice, the first at elevated temperatures and second at ambient temperature. The experiment at elevated temperature resulted in low values of increased oil production by low-salinity spontaneous imbibition. The low response is believed to be caused by thermal effects from repeated heating and cooling of the samples. The experiment at ambient temperature resulted in increased oil production values of 8-22% of pore volume. No clear correlation was found between increased oil recovery and the surface-to-volume ratio. A correlation was, however, seen between increased oil production and pore volume. The results of the experiment were unsuccessful in determining the relative importance of osmosis in either small scale low-salinity experimental results or larger scale low-salinity EOR. The results of the experiment do not reject osmosis as a mechanism for low-salinity EOR. Two possible explanations of how increased oil production relates to the pore volume are presented.