The Effect of Microporosity and Wettability on Initial and Residual Oil Saturations of a Bimodal Carbonate

Abstract

Summary The water flooding performance of carbonates is more complex than sandstones because of their multiple pore systems and intermediate wettability. The oil distribution in complex pore systems of carbonates with different wettability is not well studied. This study attempts to examine the pore size distribution and wettability contributions by monitoring oil distributions in pore and core scales during oil/water (deuterium oxide) floods and centrifuge drainage/imbibition utilizing low-field NMR techniques. The oil saturation after water flood appears to vary from 30 to 40% or higher. It is less affected by micro/macro pore ratio. The initial oil saturations after centrifuge drainage have positive correlations with macro pore ratio and oil wetness. The oil/water distributions in micro and macro pores are affected by both pore size distribution and wettability. Residual dodecane may not be present or only partially present in micro pores depending on the micro pore size. There is significant residual model oil (dodecane with 2%wt carboxylic acid) in micro pores. Dodecane is slightly affected by the rock surface, while model oil may replace water on some rock surfaces in the macro pores.