Modeling gas-water processes in fractures with fracture flow properties obtained through upscaling

Abstract

Many environmental systems are driven by complex gas-water processes in fractured aquifers. One example is degassing processes occurring in fractures in the vicinity of radioactive waste disposal sites. These fractures can represent a potential fast track for radioactive substances to reach the surface: due to buoyancy effects, the created gas phase can move relatively quickly to the surface. The aim of this paper is to investigate and model the involved processes. First, a model for a single fracture is developed. Based on statistical properties of real fractures, an aperture distribution (raster element model) is created. A percolation-renormalization model yields effective properties, such as relative permeabilities and capillary pressure, and provides the size of a representative elementary volume. These effective relationships represent the basis for modeling the migration of the created gas phase through the fractured aquifer of the subsurface. An example modeling degassing and flow in a single fracture is shown and compared to experimental data. The presented model represents a conceptual method for degassing processes and the subsequent migration of the gas phase in fracture-matrix systems, improving predictions on the fate of radioactive substances. Copyright 2010 by the American Geophysical Union.