A continuum-scale two-parameter model for non-Darcian flow in low-permeability porous media

Numerous studies have demonstrated that Darcy velocity exhibits nonlinear dependence on the pressure gradient in lower-permeability porous media such as clays and shales when the pressure gradient is low. Non-Darcian flow has important implications to geologic disposal of high-level nuclear waste, because shale has been proposed as a disposal medium, with compacted bentonite clay as a buffer material. Consideration of the impact of temperature on non-Darcian flow in an engineered clay barrier is necessary, because the clay barrier is subjected to significant temperature changes resulting from the heat-releasing nuclear waste package. In this study, a continuum-scale, two-parameter predictive model is developed to facilitate experimental data interpretation and to provide mechanistic insights into the role of temperature on non-Darcian flow in saturated low-permeability porous media. This model has several advantages when it is applied at the continuum scale. First, this model is consistent with the current theory about the role of temperature and provides more flexibility in fitting experimental data associated with varying temperatures. Second, the values of the two independent parameters in the model can be easily determined and the solution is unique. This leads to practical convenience when the model is used to interpret continuum-scale laboratory data. Third, although the two-parameter model is simple, its performance in fitting existing experimental data is satisfactory. This suggests that the model achieves a balance between simplicity and effectiveness.