EVALUATION OF LOW-SALINITY WATERFLOODING FOR 51 FIELDS IN WYOMING

This report evaluates the effectiveness of low-salinity flooding in the Minnelusa Formation in the Powder River Basin of Wyoming. The Minnelusa sandstone play constitutes a resource of several hundred fields with cumulative production of more than 600,000,000 barrels of oil. Currently there are 130 Minnelusa fields that are in active waterflood. Fifty-five are flooded with low-salinity water, 52 with mixed salinity water and 23 with formation brine. Recovery factors for 51 fields were compiled and used as the primary metric to evaluate the effectiveness of low-salinity waterflooding. A second metric used was normalized production versus % oil cut, which is independent of recovery factor. Neither metrics showed any increased production for the fields that used low-salinity injection compared to fields flooded with reservoir brine or mixed water. In the field cases studied, the low-salinity injection water was derived from wells in the shallow Lance and Fox Hills Formations, which have an average salinity of 2100 ppm, while the Minnelusa fields had initial formation water salinity ranging from 1134 to 261,000 ppm. Some fields studied did not have sufficient salinity reduction because injected salinity was very similar to formation water salinity. In other cases where there was sufficient dilution there was still no increase in oil production. Dilution factor was expressed as salinity ratio to allow direct comparison of all fields. Regardless of dilution, there was no apparent trend of increasing recovery with lower salinity injection.