Abstract
Many studies focus on the flow of multiple phases in smooth fractures yet most real fractures are rough thus flow regime maps and results for multiphase flow in smooth fractures are not completely applicable to flow in rough fractures. The effect of wall roughness is difficult to understand in multiphase flow in fractures since it leads to heterogeneities of the fracture aperture and potentially alters the roles of capillary and viscous forces in the flow. Here, the effects of wall roughness, fracture orientation, and fluids flow direction within a fracture, modeled as narrow gap in a Hele-Shaw cell, on co-current flow of oil and water were examined. The results are presented in the form of oil and water relative permeability curves. The results demonstrate that roughness impacts phase distribution, flow regimes, and phase relative permeability (a measure of phase interference); roughness increases oil–water phase interference and hysteresis of the flow resistance when scanning up and down in water saturation. Fractal analysis of images of the phase arrangement in the fracture reveals that the fractal dimension (reflects geometry and complexity), lacunarity (gappiness and complexity), and tortuosity relate the complexity of flow and the change in relative permeability behavior. The experimentally derived relative permeability data were fitted to the saturation exponent model and to an equivalent homogenous single-phase model.
Highlights
One of the most commonly used definitions for a natural fracture within a rock is given by Aguilera (1995) as follows ‘‘a discontinuity that results from stresses that exceed the rupture strength of the rock’’
Fractal analysis of images of the phase arrangement in the fracture reveals that the fractal dimension, lacunarity, and tortuosity relate the complexity of flow and the change in relative permeability behavior
The up-dip DWIR curves for Cases 4–7 shown in Fig. 7 exhibit similar behavior to the IWIR ones but they are shifted to higher water saturation, higher end-point water saturations, and higher irreducible water saturations with increasing inclination angles
Summary
One of the most commonly used definitions for a natural fracture within a rock is given by Aguilera (1995) as follows ‘‘a discontinuity that results from stresses that exceed the rupture strength of the rock’’. A rock fracture is a planar-shaped void filled with oil, water, gas, and/or rock fines. Those fractures may span from micron-scale microfractures to large-scale faults that span tens to hundreds of meters (Aguilera 1995). Outcrop studies show that factures are often rough with variable aperture the application of multiphase flow results obtained from smooth-walled model fractures are approximations to flow in real fractures. We focus on oil and water flow in a roughened-wall Hele-Shaw cell to examine the effect of roughness on phase distributions, flow regime, and phase interference.
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