ANOMOLOUS TWO-PHASE FLOW BEHAVIOR IN FRACTURED SANDSTONE EXPLAINED USING X-RAY COMPUTED TOMOGRAPHY

Understanding fracture morphology in terms of a porous media is necessary for accurate simulation of multiphase transport in fractured rocks. Although ambient- stress methods for obtaining fracture morphology exist, previous research lacks the ability to map fracture closure as a function of stress or the distribution of immiscible phases in the fracture. A twenty-five-millimeter cylindrical sandstone sample was artificially fractured in tension and placed under confining stress in an x-ray transparent vessel. The fracture morphology was characterized under dry conditions using high-resolution x- ray computed tomography. Multi-phase fluid distributions in the fracture were mapped between limits of the mobile saturation range using controlled fractional flows. These distributions were correlated with flow rate and pressure drop measurements. We observed order of magnitude differences in effective permeabilities under conditions of nearly constant overall fracture saturations. These differences in permeability are associated with re-arrangement of the physical distribution of the phases. Distributions associated with low permeability are unstable on a time frame of several hours, much longer of the time frame associated with snap-off phenomena. This phenomenon may be responsible for similar field observations reported in the literature.