Visualizing and Quantifying the Residual Phase Distribution in Core Material

At the conclusion of flooding in an oilor gas-bearing reservoir, a significant fraction of the original hydrocarbon in place remains in the swept region as trapped residual phase. In addition to the amount of trapped phase, its microscopic distribution within the pore space of a reservoir rock is important to gain a better understanding of recovery mechanisms and for the design and implementation of tertiary recovery processes. Despite the importance of the pore scale structure and distribution of residual oil, little quantitative information is currently available. We utilize a technique for imaging the pore-scale distribution of fluids in reservoir cores. The method allows the same core to be imaged after flooding under different wettability conditions, saturation states and flooding rates. Secondary and tertiary floods can be considered. Recovery mechanisms can be directly tested and the differences in the habitat of the residual fluids under different conditions can be directly quantified. We present results for imbibition experiments on a number of sandstone and reservoir carbonate samples of varying complexity. The role of rate, wettability and initial water saturation on residual phase saturations are given. The detailed structure of the residual trapped phase is described; the size distributions of residual oil blobs, features of blob shape and dimensions are enumerated and compared under variable flooding conditions. These results provide an important platform for both the understanding of pore scale displacement mechanisms and for the testing and calibration of image and networkbased models of multiphase flow. INTRODUCTION Unlike drainage, the physics and displacement mechanisms of waterflooding are nontrivial. A variety of conditions and mechanisms can affect waterflooding; these include variable wettability, displacement rates, brine compositions, the existence of films, the time dependent swelling of wetting films, the fluctuations in film pressure and thickness, and snap-off initiated cluster growth. Models that are currently developed to describe waterflooding processes rely on macroscopic observations of the displacement phenomenon, often observed on 2D glass micromodels of capillary ducts (Lenormand et al, 1983) with idealized fluids. Aside from these simple systems, there are very few other experimental processes that allow the observation of multiphase flow phenomenon. In this paper we undertake a number of waterflooding experiments of core samples and visualize the distribution of residual phase at the pore scale in three dimensions. We focus on the study of the trapped residual hydrocarbon saturation on