Geoenvironmental Research Centre
Canolfan Ymchwil Ddaearamgylcheddol

Fate of repository gases: A large scale experiment (PhD)

Work is ongoing at Cardiff University undertaking an analysis of the dataset arising from the Large Scale Gas Injection Test (Lasgit). Lasgit is a field scale experiment run by the British Geological Survey (BGS) and is located approximately 420m underground at the Aspo Hard Rock Laboratory (HRL) in Sweden. It has been designed to study the impact on safety of gas build up within a KBS-3V concept high level radioactive waste repository.

A novel Exploratory Data Analysis (EDA) is being performed on the Lasgit dataset. This is being achieved through the development of a computational toolkit.
The toolkit seeks to provide a generic applicability to large-scale long-term datasets while specifically catering to the Lasgit dataset. Notably, an ability to apply the computational procedures to non-uniform datasets is provided. A number of computational techniques have been utilised such as: parameterisation of time series enabling automated despiking and event detection through specific visualisations; frequency domain analysis; and trend/component determination in a non-parametric manner.

The Lasgit EDA is expected to produce both descriptive statistics of the behaviour of the system and provide quantitative measurement regarding observable phenomenon. The EDA is intended to look at the dataset at a finer scale than an assessment of the experiment as a whole would i.e. investigating the dataset in an event by event manner rather than observing the system evolution as a whole.
This is termed a ‘second order analysis’ and is being undertaken in order to attempt to gain a metaphorical ‘value for money’ from the dataset.

Initial application of the developed toolkit has provided confirmation and quantification of observable phenomenon (such as the amplitude and phase of the annual temperature cycles with depth). This process provides rigour to the information scientific inferences are made from by turning observations into measurements. Other preliminary descriptive information about the system have also been exposed, such as an indication of the experiments sensitivity to external influences, and the presence of mathematical singularities in the dataset indicating a significant change in system behaviour that coincide with known changes to the experimental setup.

It is hoped that information exposed by the EDA will lead to an improvement in the understanding of the Lasgit experiment. To that end an in depth interpretation of the information exposed by the EDA will be performed at Cardiff in close conjunction with the BGS, who are conducting the overview analysis of the experiment. As Lasgit is an ongoing experiment new data will become available for Confirmatory Data Analysis (CDA) processes should they be required.