Abstract:
A pore-scale study was conducted to determine model reservoir systems most amenable to oil recovery by investigating the behavior of three fractions of crude oil distribution and morphology in three types of porous media with increasing heterogeneity (in grain size distribution) during sequential surfactant flooding episodes. Multiple columns, packed with three types of sand, were established with residual saturations of light, heavy, and extra-heavy crude oil fractions, respectively. These columns were then flooded with anionic surfactant solution in various episodes. Synchrotron X-ray microtomography (SXM) was used to obtain high-resolution 3-D images before and after each surfactant flooding event. Results show homogeneous distributions of light and heavy oil fractions, as residual saturation conditions, within the homogeneous sand. Heterogeneous oil blob distributions were observed within the two higher heterogeneous porous media types. Oil blob distributions became more heterogeneous after surfactant flooding for all porous-media systems. Oil recovery was most effective from the homogenous sand (100% recovery) after 5 pore volumes (PVs) of flooding. Mildly-heterogeneous sand yielded a limited but consistent recovery after each flooding episode (23% and 43% recovery for light and heavy after 5-PV flood). The highly-heterogeneous sand showed greater recovery (42% and 16% for light and heavy) only after 5-PVs of flushing. SXM images effectively demonstrate trapping mechanism and mobilization of extra-heavy oil controlled by wettability of porous media. Homogeneous sand showed limited recovery (6%), whereas highly-heterogeneous sand showed consistent 20% recovery of extra-heavy oil after each flooding episode. Although spontaneous in-situ-stable-emulsion was formed in the mildly-heterogeneous sand, no recovery was attained due to the "jamin" effect after the 2-PV flood and 7% recovery after the 5-PV flood. In general, oil blobs within the homogeneous and mildly- heterogeneous sands showed an increase in total surface area, but a gradual reduction of total surface area within the highly-heterogeneous sand after each surfactant flood. This innovative and cutting-edge research, for the first time, implemented SXM technology to understand the pore scale processes affecting enhanced oil recovery techniques. The results of this study can be extremely beneficial to establish 3-D model for pore-scale displacement efficiency for various reservoir media systems.
