Abstract:In this work, we present a novel laboratory-based micro-computed tomography (micro-CT) experiment designed to investigate the pore scale drainage behavior of natural sandstone under dynamic conditions. The fluid distribution in a Bentheimer sandstone was visualized every 4 seconds with a 12 second measurement time, allowing the investigation of single- and few-pore filling events. To our knowledge, this is the first time that such measurements were performed outside of synchrotron facilities, illustrating the … Show more
“…The procedure for obtaining the pore-filling events is explained in Figure S8 (also refer to the Material and Methods section). The distribution shows that the volume of a pore-filling event in imbibition is of the order of the average pore volume, which is about 2–3 orders of magnitude smaller than can occur in drainage 5, 20 . However, the distribution of event sizes follows an approximate power law with an exponent of −1.27, which is slightly lower than for a percolation-theory-type analysis where filling occurs in a disordered system in order of size 35 .Figure 6Pore-filling events.…”
Understanding the pore-scale dynamics of two-phase fluid flow in permeable media is important in many processes such as water infiltration in soils, oil recovery, and geo-sequestration of CO2. The two most important processes that compete during the displacement of a non-wetting fluid by a wetting fluid are pore-filling or piston-like displacement and snap-off; this latter process can lead to trapping of the non-wetting phase. We present a three-dimensional dynamic visualization study using fast synchrotron X-ray micro-tomography to provide new insights into these processes by conducting a time-resolved pore-by-pore analysis of the local curvature and capillary pressure. We show that the time-scales of interface movement and brine layer swelling leading to snap-off are several minutes, orders of magnitude slower than observed for Haines jumps in drainage. The local capillary pressure increases rapidly after snap-off as the trapped phase finds a position that is a new local energy minimum. However, the pressure change is less dramatic than that observed during drainage. We also show that the brine-oil interface jumps from pore-to-pore during imbibition at an approximately constant local capillary pressure, with an event size of the order of an average pore size, again much smaller than the large bursts seen during drainage.
“…The procedure for obtaining the pore-filling events is explained in Figure S8 (also refer to the Material and Methods section). The distribution shows that the volume of a pore-filling event in imbibition is of the order of the average pore volume, which is about 2–3 orders of magnitude smaller than can occur in drainage 5, 20 . However, the distribution of event sizes follows an approximate power law with an exponent of −1.27, which is slightly lower than for a percolation-theory-type analysis where filling occurs in a disordered system in order of size 35 .Figure 6Pore-filling events.…”
Understanding the pore-scale dynamics of two-phase fluid flow in permeable media is important in many processes such as water infiltration in soils, oil recovery, and geo-sequestration of CO2. The two most important processes that compete during the displacement of a non-wetting fluid by a wetting fluid are pore-filling or piston-like displacement and snap-off; this latter process can lead to trapping of the non-wetting phase. We present a three-dimensional dynamic visualization study using fast synchrotron X-ray micro-tomography to provide new insights into these processes by conducting a time-resolved pore-by-pore analysis of the local curvature and capillary pressure. We show that the time-scales of interface movement and brine layer swelling leading to snap-off are several minutes, orders of magnitude slower than observed for Haines jumps in drainage. The local capillary pressure increases rapidly after snap-off as the trapped phase finds a position that is a new local energy minimum. However, the pressure change is less dramatic than that observed during drainage. We also show that the brine-oil interface jumps from pore-to-pore during imbibition at an approximately constant local capillary pressure, with an event size of the order of an average pore size, again much smaller than the large bursts seen during drainage.
“…To this end, recent advances in pore-scale imaging-based characterization methods (see review [26]) that enable the fast visualization of two-phase flow at pore-scale resolution, most notably microscopy imaging of thin micromodels [18,[27][28][29], X-ray computed tomography [30][31][32][33][34], and confocal microscopy [35,36], have provided valuable insights into 2 Geofluids the interplay of viscous, capillary, gravitational, and inertial forces constituting the complexity of interface dynamics at the pore-scale. For instance, free-energy driven Haines jumps have been confirmed as dominant displacement mechanism for flow at small capillary numbers [29,32].…”
We perform pore-scale resolved direct numerical simulations of immiscible two-phase flow in porous media to study the evolution of fluid interfaces. Using a Smoothed-Particle Hydrodynamics approach, we simulate saturation-controlled primary drainage in heterogeneous, partially wettable 2D porous microstructures. While imaging the evolution of fluid interfaces near capillary equilibrium becomes more feasible as fast X-ray tomography techniques mature, imaging methods with suitable temporal resolution for viscous-dominated flow have only recently emerged. In this work, we study viscous fingering and stable displacement processes. During viscous fingering, pore-scale flow fields are reminiscent of Bretherton annular flow, that is, the less viscous phase percolates through the core of a pore-throat forming a hydrodynamic wetting film. Even in simple microstructures wetting films have major impact on the evolution of fluid interfacial area and are observed to give rise to nonnegligible interfacial viscous coupling. Although macroscopically appearing flat, saturation fronts during stable displacement extend over the length of the capillary dispersion zone. While far from the dispersion zone fluid permeation obeys Darcy's law, the interplay of viscous and capillary forces is found to render fluid flow within complex. Here we show that the characteristic length scale of the capillary dispersion zone increases with the heterogeneity of the microstructure.
“…By comparison with results shown in [6], this figure is likely to show an individual Haines jump (note that the apparently gradual filling of the pore is due to remaining motion artifacts in the reconstruction). Further analysis of the experiment is presented in [81]. It can be concluded that it is becoming possible to visualize the fundamental pore-scale processes which govern drainage in geological porous media with laboratory-based micro-CT scanners, despite remaining challenges related to spatial and time resolution.…”
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