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In the 2008 report narrative, I commented on the graduation of the PhD student assigned to this research project, and the two recent peer-reviewed paper submissions that derived from his work. The status of these two publications is still under review. The first of the two describes the implementation of a percolation-based model to simulate immiscible flow in a rough fracture, whose structure had been mapped through X-ray microtomography scanning (MCT). We determine capillary pressure curves and discuss simulation results as they compare to experimental MCT images of oil-water distribution. The second manuscript describes a spatial analysis of various fracture aperture realizations and demonstrating their impact on two-phase, capillary flow through fractures. We simulate both the fracture aperture realizations and two-phase displacements through these aperture realizations to identify the relationship between statistical parameters of the aperture field (mean aperture, variance, and correlation distance) and the corresponding fracture transport properties (irreducible water saturation and entry capillary pressure) that are relevant to numerical modeling of fluid flow through fractured rocks.

In addition to the described modeling effort in the area of fracture transport properties, I performed core flood experiments in the summer of 2008, which lead to two additional publications and promising results for continued research in the area of multiphase flow in complex structures and pore-scale transport mechanisms. These experiments were the results of a request to expand the scope of the original PRF# 45799-G9 grant (approved by Ronald E. Siatkowski in Nov 2007) to study the effect of wettability on the distribution and transmissibility of fluids in porous media, in collaboration with the University of Wyoming. The experiments consisted of conducting consecutive drainage-imbibition cycles at different flow rates into artificial porous media of varying wetting characteristics (oil-wet, water-wet, mixed-wet). Throughout the experiment, we monitored fluid distributions inside the porous medium, characterizing the pore structure of the sample, and recording pressure and saturation history. High-resolution X-ray CT scanning was used to accomplish a detailed characterization of the medium, as a function of space and time, during the core flood experiments. The most relevant findings are discussed below:

(1) "Experimental investigation of trapped oil clusters in a water-wet bead pack using x-ray microtomography"

This work consists of mapping the distribution of immiscible fluids, particularly trapped oil clusters, residing in a glass-bead pack (0.425-0.600 mm diameter beads) subject to different flow conditions. We analyze the effect of flowing conditions on the evolution of fluid micro-structures using x-ray microtomography. 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 x10-5 mm3 to 3.119x103 mm3, where 0.01-0.50 mm3 clusters are most common and about 98% of the total trapped oil at the end of drainage and imbibition cycles corresponds to blobs that are smaller than 1 mm3. It is also shown that most blobs are larger than the mean pore size (0.03 mm3). 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 mm3.

(2) "Experimental pore-scale analysis of fluid interfacial areas in oil-wet and water-wet bead packs" Temporal and spatial saturation profiles, as well as interfacial areas were thoroughly analyzed through cycles of drainage and imbibition using samples with different wettability but similar pore structures. This is the first paper in its field that reports interfacial areas for the total sample volume. The entire bead pack is scanned to assess the extent of inlet/outlet boundary effects. The wetting-phase saturation profiles along the vertical axis of the bead packs show distinct fluid distribution zones. These zones are shown to strongly depend on gravitational effects and initial saturation conditions. Total specific interfacial area of the fluids correlates linearly with non-wetting phase saturation, independent of fluid distribution zone, cycle of flooding, saturation history and wettability, while meniscus specific interfacial area tends to a maximum around 0.25-0.40 non-wetting phase saturation. This behavior is in good agreement with previously reported observations. The fluid-normalized specific interfacial areas are shown to be nearly constant with respect to saturation, saturation history and wettability. For strongly wetting bead packs, fluid interfacial areas seem to be mainly a function pore space morphology.

As a final note, I once again thank the support of the American Chemical Society through their PRF program, which brought positive momentum to my research efforts and provided support for a foundation of high-impact research in the area of multiphase flow through porous media, with special focus on petroleum engineering applications.