Underground » Ventilation, Gas Drainage and Monitoring
The primary objective of this project was to demonstrate an ability to predict concentration and composition of Gas In Place (GIP) from a deterministic analysis of geophysical logs and laboratory measurements on core samples. We have achieved this goal in respect to the determination of gas concentration (the total amount of gas present) but not composition (the relative amount of different gases present). This is still a significant advance, as with some further development it could directly lead to a method for measuring total gas content from borehole logs that is more robust and cost effective than the statistical approach described elsewhere. It is also a first step towards resolving the combined concentration/composition problem and provides a model for analysis of fluid content with seismic methods.
This report discusses how a simple physical model, widely used in the petroleum industry for calculating the effect on sonic/seismic response of pore fluids, can be adapted to the determination of total gas-content in coal. The predictions of the model are tested in the laboratory. It is also used to reconcile laboratory measurements on core samples, with borehole logs and insitu gas-content data. Its predictions are then compared with trends in gas-content as a function of sonic velocity obtained from sets of boreholes. The overall consistency of predictions of the model with the data provides a compelling case. Finally the issues that presently limit the effectiveness of this method, and therefore represent the subject of further work, are identified.