Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, USA.
Ground Water. 2013 Jul-Aug;51(4):525-38. doi: 10.1111/gwat.12071. Epub 2013 Jun 7.
A series of Mb 3.8-5.5 induced seismic events in the midcontinent region, United States, resulted from injection of fluid either into a basal sedimentary reservoir with no underlying confining unit or directly into the underlying crystalline basement complex. The earthquakes probably occurred along faults that were likely critically stressed within the crystalline basement. These faults were located at a considerable distance (up to 10 km) from the injection wells and head increases at the hypocenters were likely relatively small (∼70-150 m). We present a suite of simulations that use a simple hydrogeologic-geomechanical model to assess what hydrogeologic conditions promote or deter induced seismic events within the crystalline basement across the midcontinent. The presence of a confining unit beneath the injection reservoir horizon had the single largest effect in preventing induced seismicity within the underlying crystalline basement. For a crystalline basement having a permeability of 2 × 10(-17) m(2) and specific storage coefficient of 10(-7) /m, injection at a rate of 5455 m(3) /d into the basal aquifer with no underlying basal seal over 10 years resulted in probable brittle failure to depths of about 0.6 km below the injection reservoir. Including a permeable (kz = 10(-13) m(2) ) Precambrian normal fault, located 20 m from the injection well, increased the depth of the failure region below the reservoir to 3 km. For a large permeability contrast between a Precambrian thrust fault (10(-12) m(2) ) and the surrounding crystalline basement (10(-18) m(2) ), the failure region can extend laterally 10 km away from the injection well.
一系列在美国中西部地区由流体注入引起的 Mb3.8-5.5 级地震事件，是由于将流体注入没有下部隔水层的基底沉积储层或直接注入下部结晶基底杂岩引起的。这些地震可能发生在沿基底杂岩中可能处于临界受力状态的断层上。这些断层距注入井的距离相当远（可达 10km），震源处的水头升高可能相对较小（约 70-150m）。我们提出了一套模拟，使用简单的水文地质-地质力学模型来评估在整个中西部地区的结晶基底中，促进或阻止诱发地震事件的水文地质条件。注入储层以下存在隔水层是阻止基底结晶岩中诱发地震活动的单一最大因素。对于渗透率为 2×10(-17) m(2) 和特定储层系数为 10(-7) /m 的结晶基底，以 5455 m(3) /d 的速率向无下部基底封隔层的基底含水层注入 10 年，导致储层以下约 0.6 km 深处可能发生脆性破坏。包括一个位于注入井 20m 处的渗透性（kz = 10(-13) m(2) ）前寒武纪正断层，将储层下方的破坏区域深度增加到 3 km。对于前寒武纪逆冲断层（10(-12) m(2) ）与周围结晶基底（10(-18) m(2) ）之间的大渗透率对比，破坏区域可以从注入井向两侧延伸 10km。
