Geological Sequestration of CO2 in Deep, Unmineable Coalbeds: An Integrated Research and Commerical-Scale Field Demonstration Project

Abstract

Abstract Coalseams represent an attractive opportunity for near-term sequestration of large volumes of anthropogenic CO2 at low net costs. There are several reasons for this:Coals have the ability to physically adsorb large volumes of CO2 in a highly concentrated state.Coals are frequently located near large point sources of CO2 emissions, specifically power generation plants.The injection of CO2 into coalseams actually enhances the commercial methane recovery process.The recovery of coalbed methane is enhanced when the injected gas contains nitrogen, a major constituent of power plant flue gas. A joint U.S. Department of Energy and industry project to study the reservoir mechanisms and field performance of CO2 sequestration in coalseams has recently been initiated. The project involves laboratory and field-testing to define critical reservoir mechanisms, including multi-component (CO2-CH4-N2 ternary) sorption behavior. Two existing fields in the San Juan Basin, the most prolific coalbed methane basin in the world, are currently under CO2 and/or N2 injection. These two fields, the Tiffany Unit (operated by BP) – now under N2 injection (but with mixed CO2/N2 injection being studied), and the Allison Unit (operated by Burlington Resources) – under CO2 injection since 1995 will be thoroughly studied via reservoir simulation to understand CO2 sequestration and enhanced coalbed methane recovery performance, using both pure CO2 and N2, as well as CO2/N2 mixtures. This paper presents the fundamental reservoir mechanisms of CO2 sequestration and enhanced recovery of methane from coalseams, and the field performances to date of the Tiffany and Allison Units. Introduction and Background The concentration of carbon dioxide (CO2) in the atmosphere is rising and, due to growing concern about its effects, the U.S. and over 160 other countries ratified the Rio Mandate in 1992, which calls for"...stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system". Since under virtually any stabilization or market scenario fossil fuels will remain the mainstay of energy production for the foreseeable future even modest stabilization will require enormous reductions in greenhouse gas (GHG) emissions resulting from fossil fuel use; energy-related CO2 emissions resulting from fossil-fuel combustion account for 82% of all U.S. GHG emissions1. Further, in addition to emissions reductions via fuel-switching, conservation, and efficiency improvements, achieving atmospheric stabilization that is deemed acceptable will require large-scale, low-cost sequestration of carbon, a need for which no cost-effective technology exists today. As a result, the U.S. Department of Energy (DOE) developed its carbon sequestration R&D program, which addresses the entire carbon sequestration ‘life cycle’ of capture, separation, transport, and storage or reuse.