Laboratory Evaluation of Sodium Hydroxide, Sodium Orthosilicate, and Sodium Metasilicate as Alkaline Flooding Agents for a Western Canada Reservoir

Abstract

ABSTRACT The performance of sodium hydroxide, sodium orthosilicate, and sodium metasilicate solutions in oil recovery was evaluated in displacement tests using core samples and fluids from a Western Canada sandstone oil reservoir. Each core plug was first waterflooded with the formation (produced) brine and then resaturated with the reservoir oil before being treated with a given alkaline solution. The latter was injected either continuously or as a slug. Up to 2 pore volumes injected (PVI) of alkaline solution, 0.3 weight percent sodium hydroxide and 1.0 weight percent sodium metasilicate recovered the largest amount of additional oil. At higher PVI, 0.3 and 1.0 weight percent sodium hydroxide solutions recovered more additional oil than all other solutions. The oil recovery from the alkaline slugs (0.5 to 0.66 PV) was poorer, possibly because most of the alkali injected was consumed through reactions with the rock and reservoir fluids. Emulsification and interfacial tension measurements as well as alkali consumption data suggest that all of the alkaline solutions used in the displacement tests should have had similar performance. The differences observed in the oil recoveries could be explained in terms of mineral and/or structural heterogeneity of the reservoir rock. In addition, the effects of freezing part of the sample in liquid nitrogen may have played a role in the observed performance of the alkaline solutions.