Three-dimensional images of sandstones containing residual nonwetting phase were obtained using synchrotron x-ray tomography with a resolution of approximately 9 μm. We determined the size distribution of disconnected nonwetting phase clusters (ganglia); the number of ganglia of size s is N(s)~s(-τ) with τ=2.05 . The vast majority of the residual phase was contained in large clusters, spanning many pores. This result implies that we have clusters of all sizes providing a huge surface area for geochemical reactions and dissolution while allowing mobilization of the residual phase during improved oil recovery in hydrocarbon reservoirs and carbon dioxide storage in aquifers.

[1] We performed a series of X-ray tomographic experiments and lattice Boltzmann permeability simulations on pyroclastic products from explosive activity at Stromboli between December 2004 and May 2006. We reconstructed the 3-D textures of vesicles to investigate the relationship between the nature of vesiculation in the erupted products and the dynamics of gas transport in the shallow conduit in order to derive implications for the eruptive behavior of basaltic volcanoes. Scoriae from normal Strombolian explosions display remarkably consistent vesicle volume distributions fit by power laws with an exponent of 1 (±0.2). We ascribe the origin of such distributions to the combined effect of coalescence and continuous nucleation events in the steady state, shallow magma system that supplies normal Strombolian activity. Volume distributions and textures of vesicles in pumice clasts from the 5 April 2003 and 15 March 2007 paroxysmal activity are markedly different from those in the scoriae. Besides a power law function with a higher exponent, portions of these distributions can be also fit by an exponential function, suggesting the attempt of the system to reach near-equilibrium conditions. The investigated pumice clasts also lack the large, connecting vesicles responsible for the development of degassing pathways in the Stromboli magma that erupts the scoriae. This testifies to a decreased degassing efficiency of the magma associated with paroxysmal explosions and potential overpressure buildup at depth. By comparison with degassing experiments on basaltic melts, we derive a time constraint on the order of minutes to hours for the incubation of paroxysms at Stromboli.

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The development and application of a strategy are presented, for estimating the full tensor of hydraulic permeability of porous media, without any a priori assumption on the principal directions. A comprehensive description of the X-ray tomographic and image analysis techniques is drawn for the quantitative morphological characterization of the pore space. Pore-scale Direct Numerical Simulation is used to compute the velocity and pressure fields in the digital pore space, reconstructed from high-resolution X-ray tomography. A commercial Finite Volume fluid dynamic solver is used, which operates on voxel-based computational meshes. The proposed methodology is validated by reproducing literature results on monodisperse periodic arrays of spheres. The hydraulic permeability of real-life porous media, characterized by highly complex morphology, is compared with laboratory experimental measurements.

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