Description of a CO2 Enhanced Coal Bed Methane Field Trial Using a Multi-Lateral Horizontal Well

Abstract

Enhanced recovery of coal bed methane by CO2 injection (CO2-ECBM) offers the potential of increasing recovery of the gas in place over primary recovery methods and at the same time storing CO2. This paper describes a CO2-ECBM field trial using a multi-lateral horizontal well for injection. The trial, preforemed in China's Ordos basin, involved transport of liquid CO2 to the injection site and pumping of this directly into the injection well. A u-tube sampling system was installed in a monitoring well approximately 20m from the main horizontal branch close to the vertical section of the injection well. This u-tube system comprised three intervals separated by inflatable packers from which gas and water samples were automatically collected and recovered to an on-site field laboratory for gas analysis. The middle interval of this packer assembly sampled the target coal seam. At the start of injection a pulse of a non- adsorbing tracer gas was added to the CO2. There was clear breakthrough of the tracer in the middle packer interval of the monitoring well demonstrating the good connection between injection and monitoring wells. The CO2 composition of the gas sample from the coal seam gradually increased over time as injected CO2 migrated to the monitoring well. Some significant aspects of this trial are the use of a multi-lateral horizontal well for ECBM, tracer gas in coal bed methane, the monitoring of gas displacement during ECBM and the u-tube sampling system.