Quantifying Trapped Residual Oil in Reservoir Core Material at the Pore Scale: Exploring the Role of Displacement Rate, Saturation History and Wettability

摘要

At the conclusion of flooding into an oil- or gas-bearing reservoir, a significant fraction of the original hydrocarbon in place remains in the swept region as trapped residual phase. In addition to detemining the amount of trapped phase, the microscopic distribution within the pore space of the reservoir rock is important to gain a better understanding of recovery mechanisms, and for the design and implementation of improved or enhanced recovery processes. Despite the importance of the pore scale structure and distribution of residual oil, little quantitative information is currently available. This study presents a method to obtain this critical information. We utilize a new technique for imaging the pore-scale distribution of fluids in reservoir cores in three dimensions. The method allows reservoir core material to be imaged after flooding under different wettability conditions, saturation states and flooding rates. Oil recovery mechanisms are directly tested and the differences in the habitat of the residual fluids under different conditions are quantified. This paper describes the results of a range of flooding experiments performed on elastic and carbonate core material of varying complexity. Variations in the remaining hydrocarbon saturation are enumerated in-situ within the pore structure as flow rates, wettability and saturation history is varied. Detailed pore scale information of the residual oil saturation is reported.