Gas Breakthrough of Compacted Bentonite/Sand-Argillite Interfaces

Abstract

This paper focuses on gas breakthrough tests through bentonite-argillite interface. The main contribution of our study is to provide insights into the swelling kinetics, gas breakthrough pressure of these materials. During the tests, bentonite/sand plugs and bentonite-argillite plugs are used to perform swelling tests and gas breakthrough tests. Experimental results show that continuous gas passage through fully saturated bentonite/sand is not obtained until 10.5 MPa gas pressure. When a bentonite/sand plug swells inside a smooth metal tube, gas passage occurs at 7–8 MPa, which is similar to the effective swelling pressure of bentonite, as measured by independent swelling experiments. For argillite alone, saturated with water until sealing (water permeability on the order of 10⁻²⁰–10⁻²¹ m²), gas breakthrough may occur at as low a pressure as 0.2 MPa and up to 6 MPa for undisturbed argillite. Finally, also after full water saturation, continuous gas breakthrough through the bentonite-argillite interface is detected at between 7 to 8 MPa gas pressure. It is interpreted that the argillite rock or the bentonite-argillite interface are both preferential pathways for gas migration when all materials become fully saturated.