Abstract

Natural gas production from coal seam reservoirs started in the early 1980s. More than twenty years later, many of these prolific reservoirs are maturing and field operators now try to garner incremental recoveries from these natural gas sources. One such method is through the use of carbon dioxide enhanced coalbed methane (CO₂-ECBM).

CO₂-ECBM is a process by which CO₂ is injected into a coal seam in order to improve methane recovery, analogous to EOR. Due to its higher adsorptivity (as compared to methane), CO₂ is preferentially adsorbed onto the coal, displacing methane from its sorption sites and allowing it to be produced. This very unique characteristic of a coal allows it to serve double-duty as both a storage reservoir and the seal. However, the combination of a larger molecule (CO₂ versus CH₄) and the increased adsorptivity result in a permeability loss and consequently a decrease in injectivity. Nonetheless, geologic sequestration of carbon dioxide in deep, un-mineable coal seams may hold tremendous promise for long-term, secure storage of the greenhouse gases as well as providing incremental methane recovery.

Several small-scale and large-scale injection projects have been conducted so far and others are currently under way. This presentation will focus on the lessons learned from those various injection sites. In addition, another method of ECBM through nitrogen injection will also be presented.