Deep-injection and closely monitored induced seismicity at Paradox Valley, Colorado
Deep-injection and closely monitored induced seismicity at Paradox Valley, Colorado
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DOI：
10.1785/0120040072
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发表时间：
2005-04-01
影响因子：
3
通讯作者：
Block, L
中科院分区：
文献类型：
--
作者：
Ake, J;Mahrer, K;Block, L
美国垦务局的ParkingValley单位（PVU）从科罗拉多西南部ParkingValley的Dolores河沿岸的9口沿着威尔斯井中提取含水层盐水，处理后，高压将盐水注入地表以下4.3-4.8 km处。PVU注入速率在800至1300 L/min之间。自1991年以来，PVU已注入超过4 X 10（6）m（3）的流体，并诱发了4000多个地表记录的地震事件。这些事件被当地15个台站的Paradox Valley地震网络记录下来。在Parkland诱发的地震活动分为两个不同的震源区：一个主要区域（> 95%的事件）不对称地围绕注入井，最大径向距离约为3 km，另一个次要的椭圆形区域，长约2.5 km，中心位于注入井西北8 km处。自1999年年中以来，即在开始连续注入约三年后，这些区域的扩展已趋于稳定。在主区内，震源以不同的线性模式排列，显示出深层地层和当地的Wray梅萨断裂和断层系统。Wray梅萨系统的主要故障是asependently，罢工的推断最大主应力方向平行，一个或多个故障，可能，作为流体管道的次级地震带。在这两个区域中，单个地震事件与短期注入参数没有明显的相关性;然而，注入井西北方0.5 km（2）的区域对注入速率的长期、大规模变化和超过阈值注入压力做出了响应。震源机制的诱发事件是一致的简单双力偶，走滑矩和近水平向北东延伸。此外，断层面与钻孔崩落确定的主应力方向一致。超过99.9%的PVU地震活动低于人类检测（类似于M2.5）。然而，当地已经感受到了大约15次事件，其中最大的是M4.3级。由于M4.3和两个较早感觉到的类似于3.5的M事件以及注入经济性，PVU自1996年以来三次改变注入策略。这些变化使地震活动从每年1100次减少到每年60次。
The U.S. Bureau of Reclamation's Paradox Valley Unit (PVU) extracts aquifer brine from nine shallow wells along the Dolores River, Paradox Valley, in southwestern Colorado and, after treating, high pressure injects the brine 4.3-4.8 km below the surface. PVU injects at rates between similar to 800 and similar to 1300 L/min. Since 1991, PVU has emplaced over 4 X 10(6) m(3) of fluid and induced more than 4000 surface-recorded seismic events. The events are recorded on the local 15-station Paradox Valley Seismic Network. The induced seismicity at Paradox separates into two distinct source zones: a principle zone (> 95% of the events) asymmetrically surrounding the injection well to a maximum radial distance of similar to 3 km, and a secondary, ellipsoidal zone, similar to 2.5 km long and centered similar to 8 km northwest of the injection well. The expansion of these zones has stabilized since mid-1999, about three years after the onset of continuous injection. Within the principal zone, hypocenters align in distinct linear patterns, showing at-depth stratigraphy and the local Wray Mesa fracture and fault system. The primary faults of the Wray Mesa system are aseismic, striking subparallel to the inferred maximum principal stress direction, with one or more faults, probably, acting as fluid conduits to the secondary seismic zone. Individual seismic events, in both zones, do not discernibly correlate with short-term injection parameters; however, a 0.5 km(2) region immediately northwest of the injection well responds to long-term, large-scale changes in injection rate and the surpassing of a threshold injection pressure. Focal mechanisms of the induced events are consistent with simple double-couple, strike-slip moments and subhorizontal extension to the northeast. In addition, the fault planes are consistent with principal stress directions determined from borehole breakouts. More than 99.9% of the PVU seismicity is below human detection (similar to M 2.5). However, approximately 15 events have been felt locally, with the largest being a magnitude M 4.3. Because of the M 4.3 and two earlier-felt M similar to 3.5 events and injection economics, PVU changed injection strategies three times since 1996. These changes reduced seismicity from similar to 1100 events/year to as low as similar to 60 events/year.