Towards a Better Understanding of Multiphase Flow in Porous Media: 3d In-situ Fluid Distribution Imaging at the Pore Scale

In this paper we present a new experimental setup combining laboratory high resolution computed micro-tomography (MCT) with a flow microcell specially designed to reproduce in-situ multiphase flow experiments and monitor the fluid distribution at the pore scale. The objective is to describe the fluid saturations and distribution at different steps of the capillary pressure cycle (drainage and imbibition) while maintaining the sample under pressure in the cell to avoid fluid re-distribution. Experiments have been performed on monomodal sandstone where the total porosity is resolved by the MCT. We compared successfully the saturation profiles calculated from the mean grey level of the 2D cross sections and the saturation profiles calculated by 3-phase image segmentation. The two above mentioned methods can be combined in bimodal pore systems to evaluate the fluid saturations in both micro (unresolved) and macro (resolved) porosity. Finally, we describe the distribution of each fluid at the different steps of the cycle and the influence of the pore geometry and interfacial tension on the oil trapping. INTRODUCTION Predicting the detailed behaviour of multiphase flow in porous media still presents a challenging domain of increasing interest. Through the past years, many models of fluid displacement mechanisms including fluid/fluid and fluid/solid interface description have been proposed and integrated in numerical modelling schemes like pore network models. The validation of such models is usually done either at the macroscopic level (Bakke et al., 1997, Knackstedt et al., 2004, Laroche et al., 2005) or at the microscopic level using 2D glass micromodels (Lenormand et al., 1988). Detailed experimental data on the 3D flow behaviour at the microlevel have been studied in very few works. Among the pioneers Swanson (Swanson, 1979) combined SEM, Wood’s metal porosimetry and acidization to study the distribution of the nonwetting liquid in a variety of porous systems. In a same type of approach (Chatzis et al., 1983) polymerised the nonwetting phase and then studied the structure of residual blobs by SEM. With the advances of synchrotron MCT over the 3 past decades and more recently the maturity of the laboratory MCT equipments it is now more common to get 3D images of porous media. Since the late 1990s, the introduction of X-Ray absorbent dopants to provide contrast between fluids has enabled non-destructive MCT studies of the 3D distribution of fluids in porous media (Coles et al., 1998). Different systems with different saturation process were imaged. In (Coles et al., 1998, Seright, 2001) a rock is imaged at residual saturation. In (Prodanovic et al., 2006) a specific core holder adapted to synchrotron setup was used and images were taken at different sequences of drainage