Abstract

Presently, low salinity waterflooding is considered one of the most promising and cost-effective EOR methods. Although the recovery mechanisms are still uncertain, decrease of residual oil saturation and alternation of rock wettability are considered to be main mechanisms of the incremental oil recovery. In addition, laboratory and mathematical studies conducted over recent years suggested that mobility control is also a possible mechanism for enhanced oil recovery during low salinity water injection. The mobility control effect is due to induced fines migration and consequent permeability reduction in water invaded areas. The laboratory studies show that the incremental recovery gained from low salinity fines-assisted water flooding strongly depends on end point relative phase permeability for formation and injection waters. Permeability reduction due to fines migration decreases injected water mobility and increases the reservoir sweep. In this study, 24 years of production data from Zichebashskoe field (Russia) including 7 years of low salinity waterflooding are used to study the effect of water relative permeability reduction during low salinity waterflooding on improved oil recovery. The results of 3D reservoir simulations show low incremental oil recovery by low salinity water injection mainly due to two reasons: first a significant amount of water produced before the water injection, that is, a significant mixture between formation and injected waters that decrease the effect of low salinity; and second already high sweep efficiency as a result of water injection into water zone. The sensitivity study shows that the incremental recovery increases for greater relative permeability reduction by low salinity water injection .However, with 20 times decrease of Krwor from formation water to injected water, the incremental oil recovery is still negligible (4%).

Key words: Low salinity waterflood, fines-assisted waterflooding, field case, sensitivity study, fines migration.