oa 3D Visualisation of Trapped Hydrocarbons in Carbonates from the Pore Scale: Exploring the Residual Hydrocarbon Phase after Secondary and Tertiary Flooding

At the conclusion of flooding in an oil- or gas-bearing carbonate reservoir, a significant fraction of the<br>original hydrocarbon in place remains in the swept region as trapped residual phase. In addition to the<br>amount of trapped phase, its microscopic distribution within the pore space of a reservoir rock is<br>important to gain a better understanding of recovery mechanisms and for the design and<br>implementation of improved or enhanced recovery processes. Despite the importance of the pore scale<br>structure and distribution of residual oil, little quantitative information is currently available. This study<br>presents a robust method to obtain this critical information.<br>Residual saturation visualization is undertaken in core material at the pore scale via microtomographic<br>imaging. We utilize a new technique for imaging the pore-scale distribution of fluids in reservoir cores<br>in three dimensions. The method allows reservoir core material to be imaged after different stages of<br>flooding; e.g. after secondary and tertiary floods. Core flooding can also be performed under different<br>wettability conditions, saturation states and flooding rates.<br>Although considerable attention has been paid to the subject of residual oil structure, the amount of<br>quantitative experimental information on the structure of the residual oil phase in reservoir core<br>material is limited. The detailed structure of the residual trapped phase is described. This information is<br>correlated to pore structural information from the 3D image data (pore geometry, connectivity),<br>mineralogy and rock type. These results provide an important platform for the testing and calibration<br>of pore scale modelling efforts for multiphase flow.<br>This detailed pore scale information of the residual oil saturation is crucial to the design and<br>implementation of improved recovery processes and can be related to conditions required for<br>mobilization of residual oil. Oil recovery mechanisms are directly tested and the differences in the<br>habitat of the residual fluids under different conditions are directly quantified.