Two-phase flow visualization and relative permeability measurement in natural rough-walled rock fractures

Understanding and quantifying multi-phase flow in frac-tures is important for mathematical and numerical simu-lation of geothermal reservoirs, nuclear waste reposi-tories, and petroleum reservoirs. While the cubic law for single-phase flow has been well established for parallel-plate fractures theoretically and experimentally, no reliable measurements of multi-phase flow in frac-tures have been reported. This work reports the design and fabrication of an apparatus for visualization of two-phase flow and for measurement of gas-liquid relative permeability in realistic rough-walled rock fractures. A transparent replica of a natural rock fracture from a core specimen is fabricated by molding and casting in clear epoxy. Simultaneous flow of gas and liquid with control of capillary pressure at inlet and outlet is achieved with the Hassler “sandwich ” design: liquid is injected to the fracture through a porous block, while gas is injected directly to the edge of the fracture through channels in the porous block. A similar arrangement maintains capillary separation of the two phases at the outlet. Pressure drops in each pha::e across the fracture, and capillary pressures at the inlet and outlet, are controlled by means of pumps and needle valves, and are measured by differential and absolute pressure transducers. The clear epoxy cast of the natural fracture preserves the geometry of the fracture and pennits visual observation of phase distributions. The fracture aperture distribution can be estimated by filling the fracture with a dyed liquid, and making pointwise measurements of the inten-sity of transmitted light. A st:t of two-phase flow experi-ments has been performed which has proven the viabil-ity of the basic experimental design, while also suggest-ing further improvements in the apparatus. Preliminary measurements are presented for single-phase permeabil-ity to liquid, and for relative nermeabilities in simultane-ous flow of liquid and gas