Van Stempvoort Dale, Maathuis Harm, Jaworski Ed, Mayer Bernhard, Rich Kathleen
National Water Research Institute, Burlington, Ontario, Canada L7R 4A6.
Ground Water. 2005 Mar-Apr;43(2):187-99. doi: 10.1111/j.1745-6584.2005.0005.x.
When fugitive methane migrates upward along boreholes of oil and gas wells, it may migrate into shallow ground water or pass through overlying soil to the atmosphere. Prior to this study, there was little information on the fate of fugitive methane that migrates into ground water. In a field study near Lloydminster, Alberta, Canada, we found hydrogeochemical evidence that fugitive methane from an oil well migrated into a shallow aquifer but has been attenuated by dissimilatory bacterial sulfate reduction at low temperature ( approximately 5 degrees C) under anaerobic conditions. Evidence includes spatial and temporal trends in concentrations of methane and sulfate in ground water and associated trends in concentrations of bicarbonate and sulfide. Within 10 m of the oil well, sulfate concentrations were low, and sulfate was enriched in both 34S and 18O. Sulfate concentrations had a strong positive correlation with delta13C values of bicarbonate, and sulfide was depleted in 34S compared to sulfate. These data indicate that bacterial sulfate reduction occurred near the production well. Near the oil well, elevated concentrations of bicarbonate were observed, and the bicarbonate was depleted in 13C. Modeling indicates that the main source of this excess 13C-depleted bicarbonate is oxidized methane. In concert with the sulfate concentration and isotope data, these results support an interpretation that in situ bacterial oxidation of methane has occurred, linked to bacterial sulfate reduction. Bacterial sulfate reduction may play a major role in bioattenuation of fugitive natural gas in ground water in western Canada.
当逸散的甲烷沿油气井钻孔向上迁移时，它可能会迁移到浅层地下水中，或穿过上覆土壤进入大气。在本研究之前，关于逸散到地下水中的甲烷的归宿几乎没有相关信息。在加拿大艾伯塔省劳埃德明斯特附近进行的一项实地研究中，我们发现了水文地球化学证据，表明一口油井逸散出的甲烷迁移到了浅层含水层中，但在厌氧条件下（约5摄氏度），通过异化细菌硫酸盐还原作用已被衰减。证据包括地下水中甲烷和硫酸盐浓度的时空趋势以及相关的碳酸氢盐和硫化物浓度趋势。在油井10米范围内，硫酸盐浓度较低，且硫酸盐在34S和18O中均有富集。硫酸盐浓度与碳酸氢盐的δ13C值呈强正相关，与硫酸盐相比，硫化物的34S含量有所降低。这些数据表明在生产井附近发生了细菌硫酸盐还原作用。在油井附近，观察到碳酸氢盐浓度升高，且碳酸氢盐的13C含量有所降低。模型表明，这种过量的13C贫化碳酸氢盐的主要来源是氧化的甲烷。与硫酸盐浓度和同位素数据一致，这些结果支持了一种解释，即发生了甲烷的原位细菌氧化作用，这与细菌硫酸盐还原作用相关。细菌硫酸盐还原作用可能在加拿大西部地下水中逸散天然气的生物衰减过程中起主要作用。
