Effect of brine composition on recovery of Moutray crude oil by waterflooding

The effect of brine composition on oil recovery by waterflooding is under investigation. Wettability states of cores used in this study were achieved by aging with Moutray crude oil. Two brine compositions were tested, 4% NaCl + 0.5% CaCl2 and 2% CaCl2; they are referred to as Brine 1 and Brine 2, respectively. Tests in which the same brine was used throughout are referred to as standard waterfloods and standard imbibition tests. Those in which the brine composition is changed one or more times during the test are referred to as mixed-brine tests. In standard waterfloods, Brine 2 gave 5.5% higher waterflood recovery than Brine 1. Imbibition rate tests showed that Brine 2 gave less water-wet conditions than Brine 1. For mixed-brine waterfloods, Berea Sandstone gave waterflood recoveries of Moutray crude oil ranging from 59-72% of original oil-in-place (OOIP), according to the choice of initial and injected brine compositions and initial water saturation. Changes in brine composition can be favorable to recovery as compared to standard waterfloods. For Moutray/brine/Berea systems, waterflood recoveries were improved significantly if the core was initially equilibrated with Brine 2 and subsequently flooded first with Brine 1 and then with Brine 2. The effects of brine composition are highly specific to the crude oil and aging conditions. Standard waterfloods with Brine 1 and Brine 2 gave a difference of 15% OOIP for an Alaskan crude oil, but with Brine 1 giving the higher recovery and less water-wet conditions than Brine 2.