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Two dimensional simulations of percolation are realized on square networks of pore throats with a random capillary pressure distribution. We analyse the influence of a destabilizing gravity field (g) and of the standard deviation of the distribution of the capillary pressure thresholds (Wt). The fragmentation process is not taken into account in this study. For an increase of g or/and when Wt decreases, two transitions are analyzed with three different regimes displacement patterns: Invasion percolation, invasion percolation in a gradient, and invasion in a pure gradient. The transitions are controlled both by the ratio g/Wt and by the sample size (L). A scaling law between the saturation at the percolation threshold and g/Wt allows delineating the three regimes in agreement with theoretical argument of the percolation in a gradient.

Accurate estimates of losses occurring during secondary petroleum migration are of vital importance for valid petroleum systems assessments. In this paper, we discuss the development of migration pathways and the corresponding hydrocarbon losses using data from laboratory experiments based on diphasic immiscible draining processes. These experiments permitted us to study the formation of migration pathways, the distribution of non-wetting oil along these pathways, and the re-utilization of existing pathways by later pulses of migrating oil. The configuration of a migration pathway can be characterized by a phase diagram whose coordinates are two dimensionless numbers: the capillary number and the Bond number (a measure of the buoyancy force). NMR imaging was used to measure the saturation of residual oil within the pathways. It was found that, after migration, the average residual oil saturation within a pathway was generally less than 40% at a resolution of 0.4mm. Hydrocarbon losses during migration were estimated as the product of the volumetric proportion of the migrating cluster structure, defined using this spatial resolution, multiplied by the average residual oil saturation in the pathway.

The stationary dense granular flow along an inclined plane has been studied in the present work. Several experimental results of the velocity profile published previously can not be described using conventional constitutive laws of continuum mechanics. Considering recent results revealing the diphasic behavior of granular medium under stress, we propose a new constitutive law relating the stress tensor to non-local functions of the velocity field and structural parameters of the material.

We study miscible fluid displacement in heterogeneous porous media, in the presence of gravity, where the heterogeneity consists of multiple layers. Miscible fluids of different density and viscosity contrasts are used, such that the displacement is hydrodynamically stable. Depending on the values of the control parameters, the overall fluid displacement exhibits either an enhancement of the effect of heterogeneity or a damping. For a sufficiently large viscosity and/or density contrast, the effect of heterogeneity is overcome and the multi-layer system behaves as a single homogeneous layer. We determine experimentally an associated phase diagram and compare our data to a theoretical model valid for systems of large aspect ratio.

We study the stability of the downdip displacement in a porous medium of a dense and viscous fluid by a lighter and less viscous fluid, and vice versa. Conventional predictions based on a Long-Wave (LW) theory lead to identical instability thresholds for the two flows. A Short-Wave (SW) analysis suggests that instability sets in earlier than the LW predictions and that the two thresholds are different in the two flows. Using an acoustic technique in 3D displacements, we have determined these thresholds and the instability diagram. Our data support the SW approach.

The onset of viscous instability and the subsequent fingering have been mostly studied under conditions of a sharp mobility contrast. In stable miscible flows in porous media, however, mobility gradients of variable extent can develop due to hydrodynamic dispersion. Graded mobility and density profiles will affect instabilities, either by mitigating (in the case of a monotonic variation) or by enhancing (nonmonotonic variation) the rates of growth. The mitigating effect was exploited by Claridge and Gorrel and Homsy for the optimal design of graded mobility banks. Hickernell and Yortsos showed that in the linear stability limit, the growth rate is controlled by the maximum of the logarithmic derivative of the mobility profile. We present an experimental study of miscible displacements in porous media to study effects of mobility gradients in viscous instability. We take advantage of molecular diffusion in miscible displacements to create a mobility gradient zone and subsequently initiate the instability b...

International audience; In a previous work [1], the flow velocity of a steady two-dimensional granular flow along an inclined wall was investigated. The scaling law for the velocity field was found in good agreement with recent experimental results. The purpose of the present paper is to reformulate in more systematic manner and in a somewhat more general context the equations of mass and momentum conservation for dense granular flow! and also to present some new results with particular emphasis on roughness influence and dynamic dilatancy. Theoretical results are found in good agreement with experiments.

The effect of cataclastic derformation bands on fluid flow in a non saturated zones is still unclear. To discuss interaction between fluid flow and cataclastic bands in the vadose zone, we examine the spatial distribution of oxidation fronts around bands in the Turonian porous sandstones of Urchaux (SE France). Our study shows new field evidences that cataclastic bands behave as permeability barrier but also as capillarity conduits for wetweak fluid.