In a repository for radioactive waste hosted in a clay formation, hydrogen and other gases may be generated due to the corrosion of metallic materials under anoxic conditions, the radioactive decay of waste and the radiolysis of water. If the gas production rate exceeds the gas diffusion rate within the pores of the clay, a discrete gas phase will form and accumulate until its pressure becomes large enough to exceed the entry pressure of the surrounding material, at which point dilatant, advective flow of gas is expected to occur.

The purpose of Task An under DECOVALEX-2019 is to better represent the processes governing the advective movement of gas in both low-permeability argillaceous repository host rocks and clay-based engineered barriers within numerical codes. In this paper special attention is given to the mechanisms controlling gas entry, flow and pathway sealing and their impact on the performance of the engineered clay barrier. Previous work suggests gas flow is accompanied by the creation of dilatant pathways whose properties change temporally and spatially within the medium. Thus, four new types of approaches have been developed: (i) standard two-phase flow models (continuous techniques) incorporating a range of different mechanical deformation behaviours, (ii) enhanced two-phase flow models in which fractures are embedded within a plastic material (continuous techniques) or incorporated into the model using a rigid-body-spring network (discrete approaches), (iii) a single-phase model incorporating a creep damage function in which only gas flow is considered, and (iv) a conceptual approach used to examine the chaotic nature of gas flow. The outputs from these different approaches are compared. This is an essential step as the choice of modelling approach strongly impacts the representation and prediction of gas flow in a future repository. In addition, experience gained through this task is of direct relevance to other clay-based engineering issues where immiscible gas flow is a consideration including hydrocarbon migration, carbon capture and storage, shale gas and landfill design.

This paper summarises the outcomes of work in Task A conducted between May 2016 and May 2019 and provides a brief overview of the experimental data and a synthesis of the work of the participating modelling teams.

在以粘土形式存在的放射性废物的储存库中，由于缺氧条件下金属材料的腐蚀，废物的放射性衰变和水的辐射分解，可能产生氢气和其他气体。如果气体产生速率超过粘土孔隙中的气体扩散速率，则将形成并累积离散的气相，直到其压力变得足够大以超过周围材料的入口压力为止，此时，气体的对流膨胀预计会发生。

DECOVALEX-2019中任务A的目的是更好地表示在数字范围内控制低渗透性泥质油藏主体岩石和基于粘土的工程屏障中气体对流运动的过程。在本文中，应特别注意控制气体进入，流动和通道密封的机制及其对工程粘土屏障性能的影响。先前的工作表明，气流伴随着膨胀路径的产生，其性质在介质中随时间和空间变化。因此，已经开发出四种新型方法：（i）结合了一系列不同的机械变形行为的标准两相流模型（连续技术），（ii）增强的两相流模型，其中将裂缝嵌入塑料材料中（连续技术），或者使用刚体-弹簧网络（离散方法）将其合并到模型中；（iii）包含蠕变损伤函数，其中仅考虑气流，并且（iv）用于检查气流的混沌性质的概念方法。比较了这些不同方法的输出。这是必不可少的步骤，因为建模方法的选择会严重影响未来存储库中气流的表示和预测。此外，通过此任务获得的经验与其他基于粘土的工程问题直接相关，在这些问题中，不溶性气体流动被考虑在内，包括碳氢化合物迁移，碳捕获和储存，页岩气和垃圾填埋场设计。

本文总结了2016年5月至2019年5月进行的任务A的工作成果，并对实验数据进行了简要概述，并对参与的建模团队的工作进行了综合。