论文标题：High density oilfield wastewater disposal causes deeper, stronger, and more persistent earthquakes

期刊：Nature Communications

作者：Ryan M. Pollyea, Martin C. Chapman, Richard S. Jayne, Hao Wu

发表时间：2019/07/16

数字识别码： 10.1038/s41467-019-11029-8

微信链接：https://mp.weixin.qq.com/s/YTsX_bllq_tn_BOgVz8LSA

在陆上油气开采所产生的废水泵回地下的速度下降多年后，有震感的地震仍有可能继续发生。本周《自然-通讯》发表的一项模型研究High density oilfield wastewater disposal causes deeper, stronger, and more persistent earthquakes表明，在美国俄克拉荷马州和堪萨斯州的油田废水注入速度下降后，高震级地震发生频率的降速可能低于整体地震率。

图1 研究区域地震和废水数据汇总 图源：Pollyea等

油田产生的废水一般通过盐水处置井，泵入深层地层。这个过程会导致基地岩石承压不断上升，直至达到一定阈值后通过地震活动释放压力。在美国中部，尤其是俄克拉荷马州和堪萨斯州，这会导致所谓的注入诱导型地震——一般发生在地下4-8千米。

美国弗吉尼亚理工学院暨州立大学的Ryan Pollyea及同事利用数值模型表明，油田废水密度可能大于基底岩石中的流体，因此它们渗入岩石的深度超出此前预期。模型预测显示，这会显著推迟压力恢复过程，可能导致在废水注入速度下降很长时间后，基底岩石中的流体压力仍会上升。作者认为减少或停止废水注入并不一定会减少或停止地震活动，而且在废水注入速度减缓十年后，地震活动仍可能继续。作者总结表示，上述发现可能对油气开采活动活跃地区的未来规划和地震灾害评估具有一定意义。

摘要：Oilfield wastewater disposal causes fluid pressure transients that induce earthquakes. Here we show that, in addition to pressure transients related to pumping, there are pressure transients caused by density differences between the wastewater and host rock fluids. In northern Oklahoma, this effect caused earthquakes to migrate downward at ~0.5 km per year during a period of high-rate injections. Following substantial injection rate reductions, the downward earthquake migration rate slowed to ~0.1 km per year. Our model of this scenario shows that the density-driven pressure front migrates downward at comparable rates. This effect may locally increase fluid pressure below injection wells for 10+ years after substantial injection rate reductions. We also show that in north-central Oklahoma the relative proportion of high-magnitude earthquakes increases at 8+ km depth. Thus, our study implies that, following injection rate reductions, the frequency of high-magnitude earthquakes may decay more slowly than the overall earthquake rate.

（来源：科学网）