Geoffrey Thyne, SPE
Pubudu Gamage, SPE
Enhanced Oil Recovery Institute
Abstract
This report evaluates the effectiveness of low-salinity waterflooding in the Minnelusa Formation in the Powder River Basin of Wyoming. The Minnelusa sandstone play constitutes a resource of over one-hundred fields with cumulative production of more than 600,000,000 barrels of oil. We conducted initial laboratory screening using Minnelusa oil and rock with synthetic brine, supplemented with geochemical models of low-salinity injection, to evaluate the potential for low-salinity waterflooding in this formation. The laboratory experiments showed little or no incremental recovery from low-salinity injection. Calculation and comparison of recovery factors for 51 Minnelusa reservoirs were used to further evaluate the effectiveness of low-salinity waterfloods at the field scale. There was no increase in recovery for fields that used low salinity injection (26) compared to fields with mixed or formation water injection (25). Since some Minnelusa fields have relatively fresh formation water, the amount of dilution was quantified using the salinity ratio (SR), defined as the ratio of salinity of injected water to salinity of formation water. This analysis showed that while some fields actually had little or any salinity reduction (13), the remaining fields with significant dilution (38) still showed no correlation between dilution and recovery factor. Since some postulated mechanisms involve change in wettability, injection of low-salinity water may produce later water breakthrough. Analysis of water breakthrough timing and watercut evolution for 23 fields found no significant difference between fields with low-salinity injection and mixed-water or saline injection.
