Laboratory Investigation of Low Salinity Waterflooding as a Tertiary Recovery Process: Effect of Crude Oil Composition
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Low salinity water flooding has been established in relevant literature as a promising method for enhanced oil recovery. The presence of polar components within the oil has been established as a necessity for any effect of low salinity waterflooding (Tang and Morrow, 1999a). The objective of this study was to investigate the effects of different components of crude oil on recovery during flooding with low saline water. This was done by extracting the polar components from the oil resulting in 4 oils; one normal, one without basic components, one without acidic components and one without asphaltenes. Berea cores with 6,5% kaolinite and one core with 1,5% were saturated with the 4 different oils and flooded with tree brines. First a brine with 3,5% NaCl, similar to seawater, were injected followed by diluted brine so that the Na+ concentration was 1500 and 350 ppm, respectively. The result showed almost no additional recovery, the maximum were seen for the high clay content cores saturated with normal crude oil (3,75%OOIP), and acid free oil (3,39%OOIP), the core with asphaltene free oil had about half the additional recovery of the previous cores, 1,86%OOIP. While the additional recovery for the core saturated with acid free oil and the core with low clay content was negligible. The additional recovery with the low salinity floods were so low that no clear conclusions on the effect of oil composition can be drawn. An interesting effect of removing polar components was seen on the recoveries after the seawater flooding. The recovery for the base free oil was significantly higher than any of the others, while the acid free oil clearly had the lowest recovery. This is believed to be due to a combination of lowered IFT by dissolution of acids on the oil-water interface, and stronger absorption of the basic components.