Multiphase Flow In Porous Media The Impact Of Capillarity And Wettability From Field Scale To Pore Scale PDF Download

Pore space deformation significantly affects multiphase flow behavior in porous media. It alters the distribution of fluids at the pore scale which in turn leads to changes in the effective permeability, relative permeability, capillary pressure, etc. However, due to the lack of fundamental studies on the mechanisms correlating the pore-level fluid displacements with the pore space deformation, no compelling conclusions have been reached to account for the observed effects. To explore this correlation, a series of carefully characterized unsteady- and steady-state two-phase core-flooding experiments were performed on miniature sandpack samples under varying stress conditions while the pore space was being imaged using high-resolution x-ray microtomography techniques to acquire three-dimensional pore fluid configuration maps. In these studies, the deformation of the sandpack samples was characterized at both macro and micro scales. The impact of deformation on the frequency of various pore-scale fluid displacement mechanisms as well as fluid saturations and volumes during different flow processes (drainage and imbibition) were also investigated. Changes in the multiphase flow behavior, such as fluid velocity and pressure, were evaluated through direct simulations, which used a finite volume method to solve Navier-Stoke equations. Moreover, the variations in the in-situ capillary pressure caused by the pore space deformation were explored through interfacial curvature analysis. The relationship between relative permeabilities and effective stress was probed. Finally, in connection to the geological storage of carbon dioxide in deep saline aquifers, the impact of pore space deformation on residual trapping and dissolution of supercritical CO2 in brine saturated sandpacks was carefully examined through micro-scale flow experiments conducted under varying stress conditions. It was observed that in a water-wet porous medium, unsteady-state drainage can be both strengthened due to the higher fluid velocity and weakened by the increase in the threshold capillary pressure after the pore space contraction. By contrast, unsteady imbibition was affected solely by variations in the threshold capillary pressure and, consequently, was facilitated as the pore sizes reduced. During the steady-state core-flooding tests, additional drainage and imbibition displacements were triggered by the pore space expansion and contraction, respectively. Furthermore, it was found that wettability was one of the key properties that governed the impact of pore space deformation on the multiphase flow behavior in porous media. The wetting phase hydraulic conductivity was more sensitive to the pore space deformation than that of the non-wetting phase, because of their topologically different distributions in the pore space. Consequently, the relative permeability of the wetting phase decreased with the increase in the effective stress, while that of the non-wetting phase increased. However, this behavior changed as the wettability of the porous medium was altered to a weakly oil-wet state through a dynamic aging process. These studies provided novel insights into the fluid flow behavior in unconsolidated porous media under varying stress conditions, which are of ever-increasing importance to many subsurface applications, including hydrocarbon recovery, water management, CO2 sequestration, and hydrogen storage.