Qatar Carbonates and Carbon Storage Research Centre, Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, London, UK.
Carl Zeiss X-ray Microscopy Inc., Pleasanton, CA, USA.
Sci Rep. 2017 Jul 12;7(1):5192. doi: 10.1038/s41598-017-05204-4.
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 CO. 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.
理解可渗透介质中两相间流体流动的细观动力学对于许多过程非常重要，例如水在土壤中的渗透、采油以及二氧化碳的地质封存。在非润湿相被润湿相驱替的过程中，竞争最激烈的两个过程是孔隙填充或活塞状驱替和 snapped-off（突断）；后一过程会导致非润湿相的捕获。我们使用快速同步加速器 X 射线微断层扫描进行了一项三维动态可视化研究，通过对局部曲率和毛细压力进行逐孔时变分析，提供了对这些过程的新见解。我们表明，导致 snapped-off 的界面移动和盐水层膨胀的时间尺度为数分钟，比排水过程中的 Haines 跳跃观察到的要慢几个数量级。突断后，由于捕获相找到一个新的局部能量最低点，局部毛细压力迅速增加。然而，压力变化不如排水过程中观察到的那么剧烈。我们还表明，在吸入过程中，盐水-油界面会在大约恒定的局部毛细压力下逐孔跳跃，事件大小约为平均孔径，再次远小于排水过程中出现的大脉冲。
