Subsecond pore‐scale displacement processes and relaxation dynamics in multiphase flow

Abstract

With recent advances at X-ray microcomputed tomography (μCT) synchrotron beam lines, it is now possible to study pore-scale flow in porous rock under dynamic flow conditions. The collection of four-dimensional data allows for the direct 3-D visualization of fluid-fluid displacement in porous rock as a function of time. However, even state-of-the-art fast-μCT scans require between one and a few seconds to complete and the much faster fluid movement occurring during that time interval is manifested as imaging artifacts in the reconstructed 3-D volume. We present an approach to analyze the 2-D radiograph data collected during fast-μCT to study the pore-scale displacement dynamics on the time scale of 40 ms which is near the intrinsic time scale of individual Haines jumps. We present a methodology to identify the time intervals at which pore-scale displacement events in the observed field of view occur and hence, how reconstruction intervals can be chosen to avoid fluid-movement-induced reconstruction artifacts. We further quantify the size, order, frequency, and location of fluid-fluid displacement at the millisecond time scale. We observe that after a displacement event, the pore-scale fluid distribution relaxes to (quasi-) equilibrium in cascades of pore-scale fluid rearrangements with an average relaxation time for the whole cascade between 0.5 and 2.0 s. These findings help to identify the flow regimes and intrinsic time and length scales relevant to fractional flow. While the focus of the work is in the context of multiphase flow, the approach could be applied to many different μCT applications where morphological changes occur at a time scale less than that required for collecting a μCT scan.

Real‐time visualization of Haines jumps in sandstone with laboratory‐based microcomputed tomography

“…The development and implementation of more sophisticated 4‐D noise filtering methods, which preserve both the spatial and the temporal structure of the original 4‐D image, could prove important to the further development of real‐time pore‐scale imaging with laboratory‐based micro‐CT [e.g., Eklund et al ., ; Mendrik et al ., ]. Another way to reduce motion artifacts is to select appropriate starting angles for the consecutive tomographic reconstructions [ Armstrong et al ., ].…”

The Impact of Pore‐Scale Flow Regimes on Upscaling of Immiscible Two‐Phase Flow in Porous Media

“…Concurrent improvements of X‐ray microtomography combined with its nondestructive features have allowed direct visualization of pore‐scale structures and distribution of phases as inputs to computational models. A number of authors have investigated pore‐scale phases distribution using X‐ray microtomography and demonstrated the complexity of the nonwetting and wetting phase interface geometry (e.g., Armstrong et al, ; Blunt et al, ; X. Chen & DiCarlo, ; X. Chen et al, ; Gao et al, ; Garing et al, ; Moghadasi et al, ; Prodanovic et al, , ; Reynolds et al, ).…”

Fast laboratory-based micro-computed tomography for pore-scale research: Illustrative experiments and perspectives on the future

“…During drainage, the displacement process happens by fast, irreversible events (Haines jumps) alternated by smooth, reversible displacement related to fluid storage in pinned interfaces [76,77]. Such a Haines jump corresponds to the filling of a single geometrical pore body.…”

“…The rate of non-wetting fluid injection does not influence the duration of individual Haines jumps, but it does influence their frequency. Single pore events have been found to transpire on the millisecond time scale [76], and [77] states that cascades of pore filling events take place on a time scale of typically 0.5-2 s. Clearly, to investigate dynamic effects related to the irreversible displacement, it is crucial not to interrupt the non-wetting fluid injection during the imaging. In their groundbreaking work on real-time visualization of two-phase flow in natural stone, executed at the TOMCAT beamline of the Swiss Light Source synchrotron facility, Berg et al [6] were able to perform such an experiment for the first time.…”

“…In this study, they suggest that dynamic effects cause pore filling events to be non-local. Since then, this topic has been investigated further [77,78], yet many aspects of the occurring dynamic effects and particularly of their influence on larger-scale petrophysical properties remain unclear. Further imaging experiments may thus prove extremely valuable in understanding these processes.…”