Economics of CO2 Sequestration in Coalbed Methane Reservoirs

Abstract Enhanced Coalbed Methane Recovery (ECBM) is presently not commercial due to the high cost of compression and capture of the injection gas either carbon dioxide (CO2) or nitrogen (N2). Recently, the necessity to reduce greenhouse gas emissions has provided a dual role for coalbeds – as a source of natural gas and as a repository for CO2. The second role arises because of the storage mechanism for gas in coal. Unlike CO2-enhanced oil recovery processes, CO2 injected during ECBM recovery is strongly adsorbed onto the coal, and in a relatively homogeneous reservoir is not expected to break through to the production wells until the bulk of the coalbed methane (CBM) reservoir is swept of methane. This provides a huge CO2 storage potential in coalbeds throughout the world. However, based on current economic factors, it makes more sense to partially deplete the coal reservoir of methane before injecting CO2. The exact strategy depends on two economic factors, the costs and credits for sequestration of CO2 and the natural gas sales price. CO2 credits would have a major effect on the production strategy used for CBM, and would favor early use of ECBM. An example is used later in this paper to illustrate this point that takes into account the differences between "gross CO2" sequestered (CO2 captured), and "CO2 avoided" (net CO2 sequestered).