ISOTOPIC APPROACHES FOR MONITORING POTENTIAL CONTAMINATION OF SHALLOW AQUIFERS WITH PRODUCED FLUIDS OR GASES FROM COALBED METHANE OPERATIONS IN ALBERTA, CANADA

摘要

Production of coalbed methane (CBM) or natural gas from coal (NGC) from shallow coal seams is a relatively new industry in Alberta (Canada) and constitutes a vital new source of natural gas supply in Western Canada. There are, however, signifi cant environmental concerns, some of them are related to the potential negative impacts on shallow groundwater resources. Since 2004, we have analyzed the chemical and isotopic compositions of fl uids and dissolved gases from more than 70 production wells in Alberta. Simultaneously, our research group has begun to generate a database summarizing chemical and isotopic parameters for shallow groundwater and its dissolved gases in the vicinity of coalbed methane operations. Preliminary data indicate that carbon isotope ratios of coalbed-derived methane are often isotopically distinct from dissolved “background” methane in shallow groundwater. Therefore, carbon isotope measurements on dissolved or free methane in shallow aquifers may serve as a suitable tool for monitoring potential contamination of shallow groundwater resources with produced gases. As a consequence, the Alberta government has introduced mandatory baseline testing standards that include carbon isotope measurements for methane for water wells in the vicinity of NGC operations in Alberta.