New type of pore-snap-off and displacement correlations in imbibition

Kamaljit Singh; Tom Bultreys; Ali Q Raeini; Mosayeb Shams; Martin J Blunt

doi:10.1016/j.jcis.2021.11.109

New type of pore-snap-off and displacement correlations in imbibition

J Colloid Interface Sci. 2022 Mar:609:384-392. doi: 10.1016/j.jcis.2021.11.109. Epub 2021 Nov 27.

Authors

Kamaljit Singh¹, Tom Bultreys², Ali Q Raeini³, Mosayeb Shams³, Martin J Blunt⁴

Affiliations

¹ Institute of GeoEnergy Engineering, Heriot-Watt University, EH14 4AS Edinburgh, UK; Qatar Carbonates and Carbon Storage Research Centre, Department of Earth Science and Engineering, Imperial College London, SW7 2AZ London, UK. Electronic address: k.singh@hw.ac.uk.
² Department of Geology, Pore-Scale Processes in Geomaterials Research (PProGRess), Ghent University, Krijgslaan 281/S8, B-9000 Ghent, Belgium; Centre for X-ray Tomography (UGCT), Ghent University, Proeftuinstraat 86, B-9000 Ghent, Belgium.
³ Department of Earth Science and Engineering, Imperial College London, SW7 2AZ London, UK.
⁴ Qatar Carbonates and Carbon Storage Research Centre, Department of Earth Science and Engineering, Imperial College London, SW7 2AZ London, UK.

PMID: 34902675
DOI: 10.1016/j.jcis.2021.11.109

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.

Keywords: 4D X-ray imaging; Imbibition; multiphase flow; pore-filling; porous media; snap-off.