Pore-scale images of trapped immiscible fluid structures in oil-wet and water-wet bead packs


Publications

  1. Pore-scale images of trapped immiscible fluid structures in oil-wet and water-wet bead packs>
    . Pore-scale analysis of trapped immiscible fluid structures in oil-wet and water-wet bead packs. Geofluids. .
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    Abstract — The objective of this study is to obtain quantitative evidence of pore-scale immiscible fluid distribution in oil-wet and water-wet porous media using X-ray computed microtomography. Temporal and spatial saturation profiles, as well as surface and interfacial areas, are thoroughly analyzed through cycles of drainage and imbibition using samples with different wetting characteristics but similar pore structures. The population of individual immiscible fluid structures (‘blobs’) was also evaluated. The specific nonwetting phase surface areas of both porous media are found to be in close correlation with the specific solid surface area. On the other hand, the differing wetting strengths of the two porous media affect the curvature of the fluid–fluid interface and thus the specific meniscus interfacial area of the two porous media. Although the magnitude of the specific meniscus interfacial areas is different, they both trend toward a maximum at wetting phase saturations of 0.35–0.55. The differences in wetting characteristics are also apparent in the blob populations. The number of blobs in the oil-wet porous media is three times greater than that of the water-wet porous media at similar saturations; the increase in population is a result of the increase in the amount of smaller blobs inhabiting the smaller pore spaces. The surface areas of individual blobs as a function of the individual blob volumes are found to closely agree with the specific surface area of a sphere at blob volumes below the minimum individual grain volume and with the specific pore space surface area above this volume. These results show how wettability and saturation history influence the distribution of immiscible fluids within the pore space.

  2. Pore-scale images of trapped immiscible fluid structures in oil-wet and water-wet bead packs>
    . Experimental investigation of trapped oil clusters in a water-wet bead pack using X-ray microtomography. Water Resources Research. .
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    Abstract — Uncertainties in the quantification of transport properties associated with multiphase flow in porous systems often make the prediction of fluid residence and migration a difficult task. Movement and trapping of immiscible fluids in permeable formations depends upon a complex combination of fluid properties, rock properties, fluid-solid interactions, and forcing conditions. This work consists of using X-rays and visualization techniques to map the distribution of immiscible fluids, particularly trapped oil clusters, residing in a glass bead pack subject to different flow conditions. We analyze the effect of flowing conditions on the evolution of fluid microstructures using X-ray microtomography. Spherical glass beads (0.425–0.600 mm in diameter), a water-wet porous medium, were packed inside a specially designed core holder. High-resolution imaging provides detailed mapping of pore structures resulting from bead packing, and characterization of fluid microstructures formed during sequential water and oil injections. We present spatial distribution of trapped oil clusters for the entire bead pack, as well as mechanistic explanations leading to the fluid configurations observed. We also present simple statistical analyses of blob size, shape, and surface area at the end of different fluid injection cycles. Trapped oil clusters appear in sizes that range from 5.923 x 10^-5 mm^3 to 3.119 x 10^3 mm^3, where 0.01–0.50 mm^3 clusters are most common. About 98% of the total trapped oil at the end of drainage and imbibition cycles corresponds to blobs that are smaller than 1 mm^3. It is also shown that most blobs are larger than the mean pore size (0.03 mm^3). The mean oil blob size is about 5 times larger than the average pore. A typical blob extends through various interconnected pores, exhibiting elongated of ramified shapes that include multiple voids and constrictions at the same time. The mean aspect ratio of these clusters is less than 2, and the surface area to volume ratio is constant for those larger than 0.1 mm^3. Experimental methods and findings presented in this paper are expected to lead to powerful calibration mechanisms for multiphase flow models.