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Instruments / Technical Area	Publication Details	Published	Actions
I13-2-Diamond Manchester Imaging	New type of pore-snap-off and displacement correlations in imbibition Kamaljit Singh , Tom Bultreys , Ali Q. Raeini , Mosayeb Shams , Martin J. Blunt Journal Of Colloid And Interface Science 40 DOI: 10.1016/j.jcis.2021.11.109 Diamond Proposal Number(s): [11587] Show Abstract ▼ Abstract: Hypothesis: Imbibition of a fluid into a porous material involves the invasion of a wetting fluid in the pore space through piston-like displacement, film and corner flow, snap-off and pore bypassing. These processes have been studied extensively in two-dimensional (2D) porous systems; however, their relevance to three-dimensional (3D) natural porous media is poorly understood. Here, we investigate these pore-scale processes in a natural rock sample using time-resolved 3D (i.e., four-dimensional or 4D) X-ray imaging. Experiments: We performed a capillary-controlled drainage-imbibition experiment on an initially brine-saturated carbonate rock sample. The sample was imaged continuously during imbibition using 4D X-ray imaging to visualize and analyze fluid displacement and snap-off processes at the pore-scale. Findings: We discover a new type of snap-off that occurs in pores, resulting in the entrapment of a small portion of the non-wetting phase in pore corners. This contrasts with previously-observed snap-off in throats which traps the non-wetting phase in pore centers. We relate the new type of pore-snap-off to the pinning of fluid-fluid interfaces at rough surfaces, creating contact angles close to 90°. Subsequently, we provide correlations for displacement events as a function of pore-throat geometry. Our findings indicate that having a small throat does not necessarily favor snap-off: the key criterion is the throat radius in relation to the pore radius involved in a displacement event, captured by the aspect ratio.	Nov 2021
I13-2-Diamond Manchester Imaging	Verifying pore network models of imbibition in rocks using time‐resolved synchrotron imaging Tom Bultreys , Kamaljit Singh , Ali Q. Raeini , Leonardo C. Ruspini , Pål‐eric Øren , Steffen Berg , Maja Rücker , Branko Bijeljic , Martin J. Blunt Water Resources Research 56 DOI: 10.1029/2019WR026587 Diamond Proposal Number(s): [11587] Open Access Show Abstract ▼ Abstract: At the pore scale, slow invasion of a wetting fluid in porous materials is often modeled with quasi‐static approximations which only consider capillary forces in the form of simple pore‐filling rules. The appropriateness of this approximation, often applied in pore network models, is contested in the literature, reflecting the difficulty of predicting imbibition relative permeability with these models. However, validation by sole comparison to continuum‐scale experiments is prone to induce model overfitting. It has therefore remained unclear whether difficulties generalizing the model performance are caused by errors in the predicted filling sequence or by subsequent calculations. Here, we address this by examining whether such a model can predict the pore‐scale fluid distributions underlying the behavior at the continuum scale. To this end, we compare the fluid arrangement evolution measured in fast synchrotron micro‐CT experiments on two rock types to quasi‐static simulations which implement capillary‐dominated pore filling and snap‐off, including a sophisticated model for cooperative pore filling. The results indicate that such pore network models can, in principle, predict fluid distributions accurately enough to estimate upscaled flow properties of strongly wetted rocks at low capillary numbers.	Jun 2020

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