Gas migration in fractured rock : results and modelling of a helium gas injection experiment at the Reskajeage Farm Test Site, SW England, United Kingdom

Abstract It is anticipated that the U.K. radioactive waste repository will be sited in a saturated low-permeability fractured geology. The repository will contain material that will give rise to the generation of significant quantities of gas over an extended period of time. It is important to understand the mechanisms whereby these gases are released from the repository and migrate away. If the gases were to be localised at surface they could potentially pose radiological, toxicological or flammability risks to man. This paper discusses experimental and modelling studies of gas migration in water-saturated fractured rock. A field-scale helium gas injection experiment has been undertaken at a test site in a disused quarry. The aims of the experiment were to establish whether gas injected at depth was localised on release at the land surface, and to contribute to building confidence in the models being developed to describe gas migration processes. Gas was injected for nine days and throughout this period and the subsequent twelve months soil-gas surveying was used to establish release locations. Data from the experiment have been modelled using a number of approaches ranging from analytical scoping calculations to numerical simulations of two-phase flow in a porous medium. These approaches have proved useful in modelling gas injection experiments.