A Laboratory Study Of Caustic Flooding For Two Alberta Crude Oils

Abstract

Abstract This experimental study was concerned with the recovery of the Wainright (408 mPa.s) and Horsefly (18 mPa.s) crude oils, using aqueous caustic solutions. The oil recoveries were compared with those by a waterflood. Effect of injection rate and loss of caustic to the porous medium were also examined. It was found that oil recovery was higher than that by a waterflood for the lower caustic concentrations (0.01% and 0.1% by weight), approaching a maximum of 75% of in-place oil, but not for the higher concentration (2%). Recovery was sensitive to injection rate. In the case of the Horsefly crude oil, the caustic floods were only marginally more efficient than a waterflood. In all cases, loss of the caustic to the rock and fluids was significant. Reasons for the recovery trends observed, and the prevailing flow mechanisms are discussed. Introduction Chemical flooding methods for enhanced oil recovery (EOR) have a long history, but in the last decade they have received an inordinate amount of attention from researchers and operators alike. Chemical floods have not made an impact as economical EOR methods, but they hold promise for the future. Caustic flooding is one such method, which has been tested and developed for conventional as well as heavy oil recovery. This research addresses the use of aqueous caustic solutions for the recovery of the Wainwright (a moderately viscous oil) and Horsefly (a light oil) crude oils. Apart from oil recovery, the effect of velocity was of particular interest. Selected Previous Laboratory Studies The use of chemical additives in flood water was proposed by Atkinson(l). The benefits of alkaline flood water additives were known even before this as shown by the works of Nutting(2), Uren and Fahmy(3), and Bekstrom and Van Tuyl(4). Johnson(5) performed a thorough review of the status of caustic flooding methods and classified the proposed mechanisms into the following four types. (I) emulsification and entrainment, (2) wettability reversal (oil-wet to water-wet), (3) wettability reversal (water-wet to oil-wer), and (4) emulsification and entrapment. De Zabala el al.(6) cite eight mechanisms for the alkaline flood process. The emulsification and entrainment mechanism was first proposed by Subkow(7) in relation to the recovery of bitumen. He stated that the formation of an emulsion was the essential first step in the recovery process, followed by the entrainment or this emulsion in the flowing alkali with the mixture subsequently produced. Reisberg and Doscher(8) studied the effect of pH on the oil-water interface using a Ventura, California, crude oil. They concluded that for the same interfacial tension to oil, a caustic solution will displace the oil, while an acid solution would not. They attributed this to the stability of the rigid films at the interface confirming the earlier work of Nutting(2). They concluded that caustic flooding was impractical because of adsorption on, and interaction with, the rock. Chan(9), working with Wainright crude oil, concluded emulsification of the oil to be vital for increased oil recovery. This conclusion was based on the insignificant recovery increase in tests where emulsification did not occur.