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The transport problem in a three-layer channel consisting of a noticeable transition layer sandwiched by a free-fluid region and a homogeneous porous medium is investigated analytically. The heterogeneous transition layer is characterized by the continuous variation of porosity and permeability, which are specifically described by applying two sets of functions. The Brinkman model is employed in the transition layer, and the analytical velocity profile is obtained in terms of the Airy function. Consistency is found between the computation results and the PIV data measured by Goharzadeh et al. (Phys. Fluids 17:057102, ). After comparing the estimated permeability variations with the calculated variation, we find the former predicted permeability values are two orders of magnitude larger than the latter ones. The velocity discrepancy in the transition layer is ascribed to the effectiveness of the empirical permeability function: although the well-known Kozeny- Carman formula can precisely predict the permeability of the monodisperse spherical packing bed with constant porosity, it will overestimate the permeability in the transition layer. Then, the exact permeability variation is expressed by an exponential function, and a more general formula is needed to model the gradual change of permeability along the transition layer region. [ABSTRACT FROM AUTHOR]

The volumetric lattice Boltzmann method (VLBM) has been recently developed and validated for dealing with flows in complex geometries. To reveal the intricate and arbitrary porous media skeleton, VLBM categorizes the computational domain into fluid, solid, and boundary cells by introducing a volumetric parameter P ( x → ) , through which the lattice Boltzmann equations are self-regularized. As a result, the no-slip bounce-back boundary condition at the inter walls is integrated in the streaming term. Since its data structure is aligned and kernel pattern is clear, VLBM is ideally suited for GPU parallelization. Using the P ( x → ) in the streaming operation, branch diverse can be effectively decreased. In this paper, we use several optimization methods, such as memory arrangement and kernel design, to maximize the performance of parallelization for VLBM. As an application, we simulated petroleum flow in a digital sandstone with two resolutions, 256 3 and 256 2 × 512 , and evaluated its permeability. The best parallel performance reaches 808.7 MLUPS (Million Lattice Updates Per Second), which is 1421.3-times speedup compared with the serial computation with allocated memory. [ABSTRACT FROM AUTHOR]

Non-marine sandstones in the Upper Triassic Xujiahe Formation form an important reservoir unit in the Sichuan Basin, western China. Widespread authigenic chlorite cement is present in the second and fourth members of the formation, referred to as the Xu II and IV members. This study, based on data from 12 wells from three gasfields, focusses on chlorite development and evolution and attempts to evaluate its influence on reservoir quality. Data included results of X-ray diffraction (XRD) and electron microprobe analyses (EMPA), scanning electron microscopy (SEM), and stable carbon and oxygen isotope analyses. The results showed that chlorite coatings preserve primary pore spaces in the sandstones by inhibiting the nucleation of quartz cements on grain surfaces. Iron for chlorite growth came from the dissolution of Fe-rich magmatic rocks derived from the palaeo-Longmenshan fold-belt, from dissolved and colloidal iron which had been precipitated in the Xujiahe Formation in a fluvio-deltaic environment, and from compacting mudstones in other pars of the formation. The chlorite initially precipitated from pore waters during eodiagenesis (< 70 °C; < 2 km burial depth). During mesodiagenesis (>70 °C, > 2 km), the chlorite was modified due to exposure to Mg-rich fluids derived from the underlying carbonate-dominated Leikoupo Formation. Thus the Mg content of chlorite in the Xu II member increases with depth. However this phenomenon was not observed in the Xu IV member. The effects of authigenic chlorite on the sandstones' petrophysical properties were evaluated from correlations between chlorite content and porosity. Optimum thicknesses for chlorite coatings range from 5 to 10 microns. Thicker or thinner coatings appear to be less capable of preserving primary porosity and permeability. [ABSTRACT FROM AUTHOR]

The stress-dependent flow and transport behaviors of porous media are ubiquitous in various scientific and engineering applications. It has been shown that the change of effective stress has important effects on the permeability and porosity of porous media. In this paper, a new stress sensitivity model for porous media is developed based on the fractal theory and the elasto-plastic thick-walled cylinder model. The proposed model is able to predict the elasto-plastic deformation of the fractal porous media under loading–unloading stress cycles, which plays a crucial role on the permanent variations of the permeability and porosity. It is found that the permeability of stress-sensitivity porous media is related to the capillary fractal dimension, capillary fractal tortuosity dimension, minimum and maximum capillary diameters, Young's modulus and Poisson's ratio of capillary. Each parameter has a clear physical meaning. The validity of the developed fractal model is verified by comparing the model predictions with the available experimental data. [ABSTRACT FROM AUTHOR]