Microtomography Imaging of Fluid Distribution and Interfacial Area in Bead Packs under Variable Axial Loading

Open Access
Author:
Konya, Samet
Graduate Program:
Petroleum and Natural Gas Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 13, 2015
Committee Members:
  • Zuleima T Karpyn, Thesis Advisor
Keywords:
  • compaction
  • porosity
  • permeability
  • relative permeability
  • residual saturation
  • surface area
  • interfacial area
Abstract:
Reservoir stress and compaction play an important role in understanding transport phenomena in porous media. It is known that changing stress conditions has an impact on distribution and interaction of immiscible phases in the subsurface. However, there is limited pore-scale experimental data to examine the effect of compaction on porous media transport properties, which in turn requires further validation. The purpose of this work is to investigate macro- and pore-scale properties of granular packs with changing axial stress conditions using a synthetic water-wet porous medium. In this study, we provide a general framework to explore the effect of compaction on the porosity, permeability, relative permeability, surface area and interfacial area in a simplified porous medium. A specially designed core holder was used to exert simultaneous axial and radial stress on a glass bead column. Immiscible fluids (water and soltrol) were injected through the packing to reach equilibrium residual wetting and non-wetting phase saturation conditions. Then, variation in porosity, permeability, relative permeability, residual distribution of phases and interfacial area were monitored in accordance with different axial loadings ranging from 50 to 350 psig. X-ray microtomography (microCT) was used to monitor three-dimensional changes in pore structure. It was observed that axial loading resulted in minor changes in pore structure and residual fluid distributions. Average porosity dropped from 44.83% to 42.66%, whereas absolute permeability dropped from 30.39 to 25.11 Darcy with increasing axial loading. Scattered meniscus interfacial area (a^wn) values were found at irreducible wetting-phase saturation while similar a^wn values were found at residual non-wetting phase saturation as axial load increased. Thus, a^wn is more sensitive to changes in pore structure at irreducible wetting-phase saturation. In dynamic conditions, contact angle hysteresis have an impact on the shape of curvature of the interface between immiscible phases and its affect is proven experimentally in the literature. In most of those experimental studies, meniscus interfacial areas (a^wn) at different saturation points on drainage curve were reported to be higher than that of imbibition which could be explained by contact angle hysteresis. In the present study, similarly, higher a^wn values were found at the end of drainage cycles than that of imbibition. However, this behavior cannot be attributed to contact angle hysteresis, alone. Our findings provide evidence that contact angle hysteresis affects pore-scale displacement mechanisms which consequently lead to changes in final saturation states. It should also be noted that the sensitivity of a^w to change in pore structure is higher than that of a^n at high wetting-phase saturations. However, a^w and a^n are in a good agreement at low wetting-phase saturations with linear approximations obtained from solid specific surface areas and saturations.