A Theoretical Study on the Governing Laws for Fluid Transport in Rough Fractures

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9804789GeNatural rock fractures exist at all scales in the earth's upper crust. They play a major role in groundwater movement, solute transport, and waste isolation in geologic media. Characterizing fluid flow and mass transport in fractured rocks depends on our knowledge of how fluid transports through individual fractures. Yet fluid flow in fractures bounded by two rough surfaces is complex. Important questions on the validity of the cubic law and the Reynolds equation for rough fractures have been studied by many. The general conclusions are that the cubic law can only provide a qualitative description of flow rate, the Reynolds equation is not valid for rough fractures and effects of aperture and tortuosity need to be included in better governing flow laws. The primary goals of this research are (1) to systematically explore and quantify the effects of fracture roughness, tortuosity, and the formation of flow channeling on governing flow laws, and (2) to develop a better governing flow law for rough fractures by understanding the fluid transport mechanisms. Specifically, I will attempt to achieve the following objectives: (1) develop a rational method to characterize fracture geometry of natural rocks, (2) investigate the formation of channelized flow paths in generated and profiled fractures, (3) examine the conditions under which the modified Reynolds equation is valid, (4) identify the transitional flow regime from Darcian to non-Darcian flow, and (5) construct a better governing law that captures the dominant features of fluid transport in rough fractures. I will employ an array of theoretical approaches and utilize the existing lab experimental data to achieve these objectives. The Reynolds equation, the modified Reynolds equation including geometric variables of local aperture and tortuosity, and the Navier-Stokes equations will be solved numerically to simulate fluid flow in rough fractures. The Lattice Boltzmann method will be used for simulating both linear and non-linear fluid transport in fractures with complex geometries. The proposed research represents a comprehensive theoretical attempt to examine the governing laws for fluid transport in rough rock fractures.