Observations from an enhanced gas recovery field trial for coal mine gas management

This article describes the implementation of and results arising from an enhanced gas recovery trial conducted at an Australian coal mine. The objective of the trial was to determine whether pre-drainage of methane from a coal seam can be accelerated and the residual gas content reduced to negligible levels through the use of nitrogen as an enhanced recovery agent. The trial was conducted in a partially depleted reservoir (having been pre-drained using medium radius drilling techniques) and used the existing mine gas drainage facilities and goaf inertisation facilities. Over a period of 4 months in 2010 1.9 kilo-tonnes of nitrogen was injected into the reservoir. During this time the flow rate, well operating pressures and composition of the gases produced were monitored. Additionally reservoir pressure was monitored at two locations between the injection and production wells using two vibrating wire piezometers. The effect of the nitrogen injection was to increase the gas production rates at the production wells in a manner consistent with the reservoir model predictions. The anticipated enhanced diffusion effects were however not proven by subsequent gas content testing. (C) 2012 Elsevier B.V. All rights reserved.