Injection of carbon dioxide into unmineable coal seams is a promising technology for reducing anthropogenic gas emissions and increasing ultimate recovery of coalbed methane. The combination of incremental methane produced and possible tax incentives might compensate for the costs associated with CO2 injection.

Currently the U.S. Department of Energy (DOE) is co-funding a pilot CO2 sequestration and enhanced coalbed methane (ECBM) project in the Appalachian Basin, in a thin coal seam. Horizontal wells have been drilled in the seam to increase CO2 injectivity and methane production rate. Previously, the reservoir simulations we performed for the planned pilot pattern indicated an optimum length for the horizontal injectors to maximize methane recovery and CO2 storage. By varying operational parameters such as time of primary production, injector length, injection pressure, injection timing, and production well pressure, we can evaluate different production alternatives to determine possible tradeoffs between optimum recovery of methane and CO2 sequestration, as defined by the amounts of the gases injected or produced.

The economics of an ECMB/sequestration project using horizontal wells are sensitive to the design parameters. In commercial practice it is necessary to select a design that maximizes the economic return. In the work presented here, net present value (NPV) was used to optimize the economics of the project. The evaluation used actual design parameters, current costs to equip the field for CO2 injection, and operating costs in the actual price range of ongoing projects: coalbed methane (CBM) and CO2 enhanced oil recovery. Methane recovery and CO2 injection data were obtained from our reservoir simulations. The economic impact of tax incentives was also considered in the analysis.

The analysis demonstrates the significance of reservoir size, proper design and implementation, and tax incentives for economic viability of projects for enhanced coalbed methane production and coalseam sequestration.

You can access this article if you purchase or spend a download.