Micro-CT study of the Impact of Low Salinity Waterflooding on the pore-scale fluid distribution during flow
Research output: Research - peer-review › Paper
Many studies indicate that the recovery of crude oil by waterflooding can be improved in both sandstone and carbonate rocks by lowering the salinity of injected water. This socalled low salinity effect is thought to be associated with the change of the wetting state of rock towards more water wet. However, it is not very well understood how wettability alteration on the pore level could lead to an increase in production at the Darcy scale. Therefore, this study aims at direct pore scale observation of the wettability-changedriven fluid reconfiguration related to a low salinity (LS) flood at the length scale between a single pore and the Darcy scale (i.e. pore network scale). We investigate the low salinity effect in real time and in 3D using synchrotron beamline-based fast X-ray computed tomography during flow experiments. Cylindrical outcrop rock samples of 20 mm length and 4 mm diameter were initialized by first saturating them with high salinity (HS) brine and then with crude oil. Subsequently, they were aged at 30 bars and 70°C for one week in order to establish wettability states assumed close to reservoir conditions. The synchrotron beamline-based fast tomography allowed us to image the pore scale fluid distribution at a spatial resolution of 3 μm and (under flowing conditions) at time intervals of 10 s for a full 3D image. The micro-CT flow experiments were conducted on both sandstone and carbonate rocks, all in tertiary mode, i.e. by first performing a HS water flood i.e. forced imbibition (as base-line) followed by a LS waterflood, both at identical field relevant flow rates. The real-time imaging shows a saturation change during the HS waterflood which approaches a stable equilibrium at its end. When switching to low salinity water, we observe achange in average saturation and pore scale distribution of both fluids, which is distinctly different from the stabilizing saturation during HS flooding. Compared to the end of the HS flood, during the LS flood in both sandstone and carbonate rock, the oil moves from pore throats to the center of pore bodies. This movement is indicative of a pore scale wettability transition from a mixed wet to a more water wet state. This process involves (re)connection and disconnection of the oil phase as it moves through narrow pore throats which is characteristic of ganglion dynamics.
|State||Published - 21 Aug 2016|
|Event||International Symposium of the Society of Core Analysts - Snowmass, Colorado, United States|
Duration: 21 Aug 2016 → 26 Aug 2016
|Conference||International Symposium of the Society of Core Analysts|
|Period||21/08/16 → 26/08/16|