Low-Salinity Waterflooding to Improve Oil Recovery-Historical Field Evidence

Abstract

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 waterfloods. Laboratory waterflood tests and single-well tracer tests in the field have shown that injection of low-salinity water can increase oil recovery, but work designed to test the method on a multi-well field scale has not yet been undertaken. Historical waterflood records could unintentionally provide some evidence of improved recovery from waterflooding with lower salinity water. Numerous fields in the Powder River basin of Wyoming have been waterflooded using 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 coreflood results. Recovery from fields using lower salinity injection water was greater than that using higher salinity injection water-matching recovery trends for laboratory and singlewell tests. IntroductionAlmost without exception, at the start of a waterflood, water from the cheapest source (usually different in composition than the initial formation water) is used as the injection water, provided injectivity is not adversely affected by formation damage. Historically, little consideration has been given in reservoir engineering practice to the effect of the composition of the salt in the injection water on waterflood displacement efficiency or to the possibility of increased oil recovery through manipulation of the injection water composition. Most laboratory relative permeability tests and displacement tests are done using synthetic formation water as both the for-

Impact of Electrical Surface Charges and Cation Exchange on Oil Recovery by Low Salinity Water

“…It was found that water chemistry has a significant impact on recovery factor (Morrow and Buckley 2011). Several field trials proved the efficiency of low salinity water in improving oil recovery (Webb et al 2004;Robertson et al 2007;Lager et al 2008). In addition, several experimental work showed the success of low salinity water in both secondary and tertiary recovery mode (Zhang et al 2007;Agbalaka et al 2009), but sometimes for only one or the other (Zhang and Morrow 2006).…”

 Brine-Dependent Recovery Processes (Smart-Water/Low-Salinity-Water) in Carbonate and Sandstone Petroleum Reservoirs: Review of Laboratory-Field Studies, Interfacial Mechanisms and Modeling Attempts

“…Similarly, from a large dataset of waterflooding in Wyoming fields available in public records, Thyne, et al [191] published a comprehensive evaluation of historical low saline brine injection in 26 fields and compared with laboratory corefloods. In contrast to Robertson [190], they found no correlation between dilution and oil recovery. It was concluded based on historical field and coreflood data that no benefit was associated with low saline brine injection.…”

“…Elsewhere, in the Powder River basin of Wyoming, Robertson [190] published the comparison of three Minnelusa field performances based on historical evidence of unintentional injection of low saline brine. It was reported that the oil recovery trend in historical data appeared to increase as the salinity ratios decreased, which corrobated laboratory corefloods using Berea outcrop material.…”

A Comprehensive EOR Study Using Low Salinity Water in Sandstone Reservoirs

“…Numerous sandstone fields were waterflooded using low salinity formation brine (1,000 ppm) (Robertson et al 2003;Robertson 2007). Crude oil and rock types, particularly the presence and distribution of kaolinite, both play a dominant role in the effect that brine composition has on waterflood oil recovery.…”