Extended two-phase flow model with mechanical capability to simulate gas migration in bentonite

Abstract

Long-term gas migration through clays cannot be simulated by conventional two-phase flow models alone owing to the presence of material deformation. In this article, an extended twophase flow model that incorporates mechanical effects is proposed. The model allows the formation of preferential pathway and considers the relation between pore moisture and pore deformation. It was carried out with the intention of avoiding the complexity of a fully coupled thermal, hydraulic and mechanical modelling. In the new model, porosity, permeability, swelling pressure and pathways formation threshold depend on the water saturation. The model is validated on different gas injection experiments with controlled flow rate and controlled pressure. Some experiments are well known in the literature; some are new. In each case, an inverse approach is used to identify the model parameters. The results confirm that, depending on the type of bentonite (MX80, Avonlea, KunigelV1), modelling the gas migration could require the existence of a pressureinduced saturation-depending preferential pathway. In laboratory-scale experiments, the model leads to an accurate evaluation of the long-term gas migration trends, including not just the gas migration stage but also the water re-saturation level. In a field-scale experiment, the behaviour of the model in a realistic context is revealed.

Coseismic Groundwater Drawdown Along Crustal Ruptures During the 2016 Mw 7.0 Kumamoto Earthquake

“…An integral finite difference method is employed for spatial discretization to ensure local mass balance, and a fully implicit time discretization is employed to achieve stable computation. This simulator has been verified by many analytical solutions, controlled laboratory data, and more than 500 field data in Japan and overseas to ensure its accuracy and applicability (e.g., Kitamura et al, 2016;Mori et al, 2015;Sakuma et al, 2017;Tawara et al, 2014).…”

Gas migration in pre-compacted bentonite under elevated pore-water pressure conditions

“…In such cases, gas migration at in situ conditions is not 76 thought to occur unless the applied gas pressure, P g , exceeds the total stress, σ, experienced 77 by the clay (resulting from the sum of the applied water pressure and the swelling pressure, 78 Π) Harrington and Horseman, 2003). Above this critical value, a 79 mechanical interaction between the gas and clay will begin Tawara et al, 2014), leading to the generation of pathways which allow gas transport. 82 In order to assess the dominant form of advective gas flow in bentonite, it is therefore 83 necessary to conduct laboratory experiments on the selected clay under the relevant 84 boundary conditions for a given repository concept.…”

Gas diffusion property of compacted GMZ bentonite with consideration of saturation and gas pressure

“…How to safely dispose these wastes has been becoming an international critical issue. Previous studies proved that deep geological repositories with multi-barriers including natural barrier (surrounding rocks) and arti cial barriers (engineering-barriers and canisters) can effectively isolate nuclides from the human environments (Horseman et al 1999;Tawara et al 2012). Due to its ultra-low permeability, high adsorption and good swelling capacities, compacted bentonite is commonly recognized as the most preferred buffer/back ll material for constructing engineering-barriers in the geological repository (Ohazuruike and Lee 2023; Ye et al 2009).…”