Large scale gas injection test (Lasgit) : results from two gas injection tests

This paper describes the initial results from a large scale gas injection test (Lasgit) performed at the Äspö Hard Rock Laboratory, Sweden. Lasgit is a full-scale field-scale experiment based on the Swedish KBS-3V repository concept, examining the processes controlling gas and water flow in compact buffer bentonite. The first 2 years of the test focused on the artificial hydration of the bentonite buffer. This was followed by a programme of hydraulic and gas injection tests which ran from day 843 to 1110. A further period of artificial hydration occurred from day 1110 to 1385, followed by a more complex programme of gas injection testing which remains on going (day 1385+). After 2 years of hydration, hydraulic conductivity and specific storage values in the lower filter array were found to range from 9 × 10−14 to 1.6 × 10−13 m/s and 5.5 × 10−5 to 4.4 × 10−4 m−1 respectively, with the injection filter FL903 yielding values of 7.5 × 10−14 m/s and 2.5 × 10−5 m−1. A second set of hydraulic measurements were performed over 1 year and a half later yielding similar values, in the range 7.8 × 10−14 m/s and 1.3 × 10-13 m/s. The hydraulic conductivity of FL903 had reduced slightly to 5.3 × 10−14 m/s while specific storage had increased to 4.0 × 10−5 m−1. Both datasets agree with laboratory values performed on small-scale saturated samples.