Estimation of methane emission from shallow gas-bearing sandstones

This paper presents exponential model created by the author to estimate gas flow/time relationships for shallow methane-bearing Donetsk sandstones in Donetsk (Ukraine). Such estimation is indispensable in case of passing subway tunnels through these sandstones. The proposed model involves not only time, but also a ratio between average widths of shallow fractures in sandstones and average horizontal distances between these fractures. It is revealed that an increase in this ratio leads to an increase in gas volumetric flow rate, acceleration of gas emission, and an increase in the volume of methane emitted from borehole. It is shown that gas flow vs. time curves obtained for 17 boreholes drilled from the ground surface through sandstones are similar to those estimated by the proposed model. Observations show that the volume of methane extracted from each borehole is between 161 m3 and 673 m3, and maximum value of volumetric flow rate is ranged from 0.00265 m3/min to 0.0455 m3/min.