53rd U.S. Rock Mechanics/Geomechanics Symposium,
New York City, New York
2019. American Rock Mechanics Association
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22 since 2007
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ABSTRACT: Several gas injection tests were performed in-situ through packed off sections of two boreholes in order to study the migration of gas phase in an indurated clay rock: the Callovo-Oxfordian (COx) claystone of the Paris basin, France. Different gas injection tests (nitrogen) have been performed at various flow rates from ∼1 mLn/min to ∼500 mLn/min. The data analysis and a two-phase flow modelling revealed that gas percolates first in the borehole damaged zone but that a small quantity of gas migrates through the intact host rock. This in-situ test confirmed that gas entry pressure in COx claystone is over 4 MPa.
It was possible to fracture the rock at various gas pressure values that depend very strongly on gas injection flow rate, and that are below or above the far field minimum principal stress magnitude.
The French national radioactive waste management agency (Andra) has developed, through the last twenty years, an underground research laboratory (URL) to study a possible radioactive waste repository in a claystone formation. It is located in the Callovo-Oxfordian claystone encountered at a depth between 420 to 550 m near the village of Bure, in the eastern Paris Basin (Fig. 1). The first objective of this URL is to characterize the confining properties of the clay through in situ hydrogeological tests, chemical measurements, diffusion experiments and the effect of excavation work on surrounding rock mass. The goal is to demonstrate that the construction and operation of a geological repository would not introduce pathways for radionuclides migration. The program turn out for demonstration issue and optimization of the concept of different elements (tunnel, waste cells, seal,…) of the repository. In this framework, understanding the migration of gas produced by corrosion of metals, microbial degradation and radiolysis of water within a deep geological repository for radioactive waste is of great importance for assessing the performance and long-term evolution of the repository. If the rate of gas production exceeds the rate of diffusion of dissolved gas in the pore-water of the host rock and the engineered barriers, a gas phase will form and accumulate until the associated pressure buildup is large enough to overcome the hydraulic pressure and the capillary resistance of the surrounding confining rock. Consequently, these processes may damage the rock mass around and could affect the safety function of the host rock.
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