X-ray MCT based numerical analysis of residual oil pore-scale characteristics under various displacing systems

Taking a water-wet sand pack, for example, the X-ray micro-computed tomography (MCT) displacement system is utilized to acquire the high-resolution MCT images of water-flooding, polymer flooding and preformed particle gel (PPG) flooding at specific displacement stages, which are transformed to the three-dimensional data volume of grains and multiple phases by image processing technology. On this basis, information of residual oil clusters at single pore-throats is extracted and such characteristic parameters such as quantity, average volume, contact area ratio, and shape factor are further developed to represent the flexible microstructure. Finally, numerical analysis of residual oil pore-scale characteristics including population, mobilization and morphology under various displacing systems are extensively addressed. Results show that, for single displacing system, increasing pore volume of displacing fluid results in a larger quantity, a lower average volume and a smaller contact area ratio. The majority of residual oil clusters is approximately 20 times larger than the average pore size. Moreover, morphology of residual oil clusters is changed gradually from meshwork to other types. It also indicates that, as to PPG displacing system, the synergistic interaction between profile control of PPG and improvement of sweep efficiency by polymer injection has great influence on pore-scale characteristics of oil clusters, and there still exists one third of residual oil clusters with various morphologies remained at microscale. During the end of water or polymer flooding, meshwork types of residual oil clusters with complicated microstructure are overwhelming, however, the counter-dominant oil clusters' morphology of PPG flooding has converted to meshwork and cellular type, which provides insight into the direction of potentially tapping remaining oil during the later stage of chemical flooding recovery.