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Seismic activity triggered by water wells in the Parana Basin, Brazil

机译：巴西巴拉那盆地水井引发的地震活动

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摘要

Triggered seismicity is commonly associated with deep water reservoirs or injection wells where water is injected at high pressure into the reservoir rock. However, earth tremors related solely to the opening of groundwater wells are extremely rare. Here we present a clear case of seismicity induced by pore-pressure changes following the drilling of water wells that exploit a confined aquifer in the intracratonic Parana Basin of southeastern Brazil. Since 2004, shallow seismic activity, with magnitudes up to 2.9 and intensities V MM, has been observed near deep wells (120-200 m) that were drilled in early 2003 near the town of Bebedouro. The wells were drilled for irrigation purposes, cross a sandstone layer about 60-80 m thick and extract water from a confined aquifer in fractured zones between basalt flow layers. Seismic activity, mainly event swarms, has occurred yearly since 2004, mostly during the rainy season when the wells are not pumped. During the dry season when the wells are pumped almost continuously, the activity is very low. A seismographic network, installed in March 2005, has located more than 2000 microearthquakes. The events are less than 1 km deep (mostly within the 0.5 km thick basalt layer) and cover an area roughly 1.5 km × 5 km across. The seismicity generally starts in a small area and expands to larger distances with an equivalent hydraulic diffusivity ranging from 0.06 to 0.6 m~2/s. Geophysical and geothermal logging of several wells in the area showed that water from the shallow sandstone aquifer enters the well at the top and usually forms waterfalls. The waterfalls flow down the sides of the wells and feed the confined, fractured aquifer in the basalt layer at the bottom. Two seismic areas are observed: the main area surrounds several wells that are pumped continuously during the dry season, and a second area near another well (about 10 km from the first area) that is not used for irrigation and not pumped regularly. The main area displays cyclic annual activity, but the second area does not. We explain the earthquake swarms as being triggered by pore pressure diffusion in the fractured basalt layer due to additional pressure from the newly connected surface aquifer. This reaches critically prestressed areas up to a few kilometers away from the wells. During periods of continuous pumping, the reduction of pore pressure in the confined aquifer stops the seismic activity. Our study suggests that this kind of activity may be more common than previously thought and implies that many other cases of small tremors associated with the drilling of water wells may have gone unnoticed.
机译：触发地震通常与深水储层或注入井有关，在深注入水或注入井中，高压将水注入储层岩石。但是，仅与地下水井开通有关的地震很少发生。在这里，我们介绍了一个明显的案例，该案例是在巴西东南部克拉通的巴拉那盆地克拉通内开凿的水井之后，由孔隙压力变化引起的地震活动引起的。自2004年以来，在2003年年初在贝贝杜罗镇附近钻的深井（120-200 m）附近，观测到的浅层地震活动的震级高达2.9，强度为V MM。这些井是为灌溉目的而钻的，跨过约60-80 m厚的砂岩层，并从玄武岩流层之间的裂缝带中的承压含水层中抽水。自2004年以来，地震活动（主要是事件群）每年发生一次，主要发生在雨季，井未抽水。在干旱季节，当井几乎连续被抽水时，活度非常低。 2005年3月安装了一个地震网络，已定位了2000多次微地震。这些事件的深度不足1公里（主要在0.5公里厚的玄武岩层内），覆盖范围约为1.5公里×5公里。地震活动性通常始于小区域，并以0.06-0.6 m〜2 / s的等效水力扩散率扩展到更大的距离。该地区几口井的地球物理和地热测井表明，浅层砂岩含水层中的水从顶部进入井中，通常形成瀑布。瀑布顺着井壁流下，并向底部玄武岩层中的狭窄裂缝性含水层供水。观察到两个地震区域：主要区域围绕在干旱季节连续抽水的几口井，而另一个区域（距第一区域约10公里）附近的第二个区域则不用于灌溉且不定期抽水。主要区域显示周期性的年度活动，但第二个区域不显示。我们解释了地震群是由于新连接的地表含水层产生的额外压力而由裂隙玄武岩层中的孔隙压力扩散触发的。它到达临界预应力区，距离井只有几公里。在连续抽水的过程中，承压含水层中孔隙压力的降​​低会停止地震活动。我们的研究表明，这种活动可能比以前认为的更为普遍，并且暗示与水井钻探相关的许多其他小震颤案例可能没有引起注意。

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  • 来源
    《Water resources research》 |2010年第7期|P.W07527.1-W07527.11|共11页
  • 作者

    Marcelo Assumpcao; rnTereza H. Yamabe; rnJose Roberto Barbosa; rnValiya Hamza; Afonso E. V. Lopes; rnLucas Balancin; rnMarcelo B. Bianchi;

  • 作者单位

    Institute of Astronomy, Geophysics and Atmospheric Sciences, University of Sao Paulo, Sao Paulo, SP, 05508-090 Brazil;

    rnInstitute of Astronomy, Geophysics and Atmospheric Sciences, University of Sao Paulo, Sao Paulo, SP, 05508-090 Brazil;

    rnInstitute of Astronomy, Geophysics and Atmospheric Sciences, University of Sao Paulo, Sao Paulo, SP, 05508-090 Brazil;

    rnObservatorio Nacional, MCT, Rua General Crislino 77, Rio de Janeiro, RJ, Brazil;

    rnInstitute of Astronomy, Geophysics and Atmospheric Sciences, University of Sao Paulo, Sao Paulo, SP, 05508-090 Brazil;

    rnInstitute of Astronomy, Geophysics and Atmospheric Sciences, University of Sao Paulo, Sao Paulo, SP, 05508-090 Brazil;

    rnInstitute of Astronomy, Geophysics and Atmospheric Sciences, University of Sao Paulo, Sao Paulo, SP, 05508-090 Brazil;

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