A three-dimensional site-scale numerical model has been developed to simulate water and gas flow, heat transfer, and radionuclide transport in the unsaturated zone of Yucca Mountain, Nevada, the American underground repository site for high level radioactive waste. The modeling approach is based on a mathematical formulation of coupled multiphase fluid and heat flow and tracer transport through porous and fractured rock. This model is intended for use in predicting current and future conditions in the unsaturated zone, so as to aid in assessing the system performance of the repository. In particular, an integrated modeling methodology is discussed for integrating a wide variety of moisture, pneumatic, thermal, and isotopic geochemical data into comprehensive modeling analyses. The reliability and accuracy of the model predictions were the subject of a comprehensive model calibration study, in which the model was calibrated against measured data, including liquid saturation, water potential, and temperature. This study indicates that the model is able to reproduce the overall system behavior at Yucca Mountain with respect to moisture profiles, pneumatic pressure and chloride concentration variations in different geological units, and ambient geothermal conditions.

This paper presents a theoretical study of non-Darcy fluid flow through porous and fractured reservoirs using a numerical modeling approach. In the numerical model, the non-Darcy flow is described by the Forchheimer equation, implemented in a three-dimensional, multiphase flow reservoir simulator. The non-Darcy flow through fractured reservoir is handled using a general dual continuum approach, covering commonly used conceptual models, such as double porosity, dual permeability, explicit fracture, etc. The objectives of this study are (1) to obtain insights into the effect of non-Darcy flow on transient pressure behavior through porous and fractured reservoirs and (2) to provide type curves for well test analyses of non-Darcy flow wells. The type curves generated include various types of drawdown, injection, and buildup tests with non-Darcy flow occurring in porous and fractured reservoirs. In addition, non-Darcy flow into partially penetrating wells is also considered. The transient pressure type curves for flow in fractured reservoirs are based on the double-porosity model. Furthermore, a simple graphic approach for determining formation non-Darcy flow coefficients by well testing is presented. The type curves provided in this work for non-Darcy flow in porous and fractured reservoirs will find their applications in well test interpretation using the type-curve matching technique. In particular, these curves may be directly used for analyzing non-Darcy flow behavior of production and injection wells in oil and gas reservoirs.