GEOMAR Helmholtz Centre for Ocean Research Kiel , 24148 Kiel, Germany.
Department of Earth System Science, Stanford University , Stanford, California 94305, United States.
Environ Sci Technol. 2017 Sep 5;51(17):10262-10268. doi: 10.1021/acs.est.7b02732. Epub 2017 Aug 16.
Shallow gas migration along hydrocarbon wells constitutes a potential methane emission pathway that currently is not recognized in any regulatory framework or greenhouse gas inventory. Recently, the first methane emission measurements at three abandoned offshore wells in the Central North Sea (CNS) were conducted showing that considerable amounts of biogenic methane originating from shallow gas accumulations in the overburden of deep reservoirs were released by the boreholes. Here, we identify numerous wells poking through shallow gas pockets in 3-D seismic data of the CNS indicating that about one-third of the wells may leak, potentially releasing a total of 3-17 kt of methane per year into the North Sea. This poses a significant contribution to the North Sea methane budget. A large fraction of this gas (∼42%) may reach the atmosphere via direct bubble transport (0-2 kt yr) and via diffusive exchange of methane dissolving in the surface mixed layer (1-5 kt yr), as indicated by numerical modeling. In the North Sea and in other hydrocarbon-prolific provinces of the world shallow gas pockets are frequently observed in the sedimentary overburden and aggregate leakages along the numerous wells drilled in those areas may be significant.
浅地层气沿烃井运移构成了一种潜在的甲烷排放途径，目前在任何监管框架或温室气体清单中都没有得到承认。最近，在北海中部（CNS）的三口废弃海上油井中进行了首次甲烷排放测量，结果表明，大量源自深部储层覆盖层浅层气藏的生物成因甲烷通过井筒释放。在这里，我们在 CNS 的三维地震数据中识别出许多穿透浅层气藏的油井，这表明大约三分之一的油井可能会发生泄漏，每年可能向北海释放总共 3-17 千吨的甲烷。这对北海的甲烷预算构成了重大贡献。大量的这种气体（约 42%）可能通过直接气泡输送（0-2 千吨/年）和溶解在表层混合层中的甲烷的扩散交换（1-5 千吨/年）到达大气中，这是数值模拟所表明的。在北海和世界上其他石油资源丰富的地区，经常在沉积覆盖层中观察到浅层气藏，在这些地区钻探的众多油井可能会发生大量泄漏。
