Waterflooding is by far the most widely applied method of improved oil recovery. Crude oil/water/rock interactions can lead to large variations in the displacement efficiency of wa- terfloods. Laboratory waterflood tests and single-well tracer tests in the field have shown that injection of low-salinity wa- ter can increase oil recovery, but work designed to test themethod on a multi-well field scale has not yet been under- taken. Historical waterflood records could unintentionally provide some evidence of improved recovery from water- flooding with lower salinity water. Numerous fields in the Powder River basin of Wyoming have been waterflooded us- ing low salinity water (about 1000 ppm) obtained from the Madison limestone or Fox Hills sandstone. Three Minnelusa formation fields in the basin were identified as candidates for waterflood comparisons based on the salinity of the formation and injection water and reservoir characteristics. Historical production and injection data for these fields were obtained from public records. Field waterflood data were manipulated to display oil recovery in the same format as laboratory core- flood results. Recovery from fields using lower salinity injec- tion water was greater than that using higher salinity injection water—matching recovery trends for laboratory and single- well tests.
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