Yannick Anguy

On the ability of a class of random models to portray the structural features of real, observed, porous media in relation to fluid flow

Abstract The description of transport processes is practically accomplished at the macroscopic scale compatible with our ability to observe, and measure processes. The macroscopic description requires to faithfully account for the effects of the detailed inter-phase boundaries on the microscopic level (the micro-structure) in the expression for macroscopic transport coefficients such as permeability. Herein, the porous descriptors held to express macroscopic coefficients are the porosity and the autocorrelation function (ACF) measured directly on a 2-D finite digital image of the porous material. The flow-relevance of the selected porous descriptors will be eventually demonstrated if synthetic porous media generated through a random model from measured porosity and ACF yield the same transport properties than the actual media. Towards that goal, synthetic 2-D numerical porous micro-structures are generated from measured porosity and ACF on two types of natural mechanical aggregates: an Upper Shoreface and a Tidal Channel Sandstone. The achieved synthetic porous media are shown to include all the geometrical features of the real, observed, natural aggregates. Such agreement between synthetic and actual media is demonstrated to be the consequence of: (1) the richness of the structural information carried out by the ACF and, (2) a structural noise produced by the “practical use” of the random model. The requirement to account for the impact on macroscopic physics of this structural noise is emphasized. Extension of the approach to artificial aggregates such as cement, mortars or concrete is shown to be a promising avenue.

A Study of the Behavior of Implicit Pressure Explicit Saturation (IMPES) Schedules for Two-phase Flow in Dynamic Pore Network Models

We focus on the numerical difficulties that typify implicit pressure explicit saturation (IMPES) schedules in dynamic “ball-and-stick” pore network models for two-phase flow. We show that a time stepping procedure based on a prescribed maximum variation of the local capillary pressure rather than on a (usual) maximum variation of the local saturation along with the addition in the solution algorithm of suitable “flow constraints” (in Koplik and Lasseter, Soc. Pet. Eng. J. 25(1):89–100, 1985) provide more stability and a significant run time speed up. In particular, the slow convergence and the oscillatory behavior that typify IMPES schemes at low Ca values due to capillary pinning are efficiently suppressed.

French Bread Baking

Bread has been a basic foodstuff for thousands of years. This product requires energy, time, and a very precise dexterity. Only a few simple ingredients are used. The bread maker seems to be a kind of magician. In this chapter, we describe briefly its current state of the art and then present the materials used and the methods of measurement. We highlight the links between the kinetics of mass loss from a French loaf of bread, the variation in the relative humidity of the air as it comes out of the oven, and the thickness of the product, which is linked with the internal pressure. Stress is put on use of image analysis for quantifying properties such as the distribution of the bread 3D air cells or the impact of steam on the porosity and the microstructure (e.g., size of starch grains).