Gas injection test in the Callovo-Oxfordian claystone: data analysis and numerical modelling

This paper describes a field-scale experiment on gas transport mechanisms performed
at Andra’s Underground Research Laboratory (URL) in a clay rock. The experimental layout
consists of two parallel boreholes that are equipped with multiple packer completions isolating
three intervals each, which have been continuously monitoring the pore pressure evolution of
the clay rock. Nitrogen gas was injected in the middle test interval of one of the boreholes at
increasing rates. The entire gas test comprised six periods of controlled gas injections, each fol-lowed by a shut-in pressure recovery phase. The experimental data are presented along with their interpretation by means of numerical modelling of two-phase flow of gas and water using different numerical codes and different geometrical approaches that include axisymmetric, half-space and full 3D models. An iterative modelling process was used to show step-by-step how an accu-rate description of each component of the experiment system produced a satisfactory reproduc-tion of the experimental data and an improved understanding of the relevant phenomena. For instance, the initial volume of remaining water in the test interval, and the presence of a damaged zone around the boreholes, was important for the models to obtain good agreement with the field data.