Double-difference seismic attenuation tomography method and its application to The Geysers geothermal field, California
Double-difference seismic attenuation tomography method and its application to The Geysers geothermal field, California
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DOI：
10.1093/gji/ggab017
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发表时间：
2021-02-16
影响因子：
2.8
通讯作者：
Thurber, Clifford
中科院分区：
文献类型：
--
作者：
Guo, Hao;Thurber, Clifford
衰减结构的知识对于了解地下材料性质非常重要。提出了一种双差地震衰减层析成像方法，用于三维衰减构造的高分辨率成像。我们的方法包括两个主要部分，事件对差分e（de）数据的反演和三维衰减层析成像与de数据。我们开发了一种新的谱比方法，该方法联合反演在一组公共台站观测到的成对事件的谱比数据，以确定de数据。光谱比方法消除了仪器和现场响应项，与使用单个光谱的传统方法的绝对t* 相比，得到更准确的de数据。合成试验表明，用我们的谱比方法反演dt* 数据是强大的源模型的选择和适度的噪音。我们修改了现有的速度层析成像代码，使它可以反演dt* 数据的三维衰减结构。我们将新方法应用于间歇泉地热田，加州，其中蒸汽为主的水库和注水的历史悠久。一个新的Qp模型在间歇泉确定使用P波数据的地震在2011年，使用我们更新的地震位置和Vp模型。通过利用更准确的dt* 数据和消除模型的不确定性沿着共同路径的源区域外，DDQ层析成像方法实现了更高的分辨率，特别是在地震震源区，相比使用e数据的标准层析成像方法。通过真实的数据和合成数据的检验，验证了这一点。我们的Qp和Vp模型显示了常温储层中的一致变化，这可以通过压裂、渗透率和流体饱和度和/或蒸汽压力的变化来解释。一个突出的低Qp和Vp区非常活跃的地震活动成像内的高温水库在深度低于2公里。该异常带可能被注入流体部分饱和。
Knowledge of attenuation structure is important for understanding subsurface material properties. We have developed a double-difference seismic attenuation (DDQ) tomography method for high-resolution imaging of 3-D attenuation structure. Our method includes two main elements, the inversion of event-pair differential e (de) data and 3-D attenuation tomography with the de data. We developed a new spectral ratio method that jointly inverts spectral ratio data from pairs of events observed at a common set of stations to determine the de data. The spectral ratio method cancels out instrument and site response terms, resulting in more accurate de data compared to absolute t* from traditional methods using individual spectra. Synthetic tests show that the inversion of dt* data using our spectral ratio method is robust to the choice of source model and a moderate degree of noise. We modified an existing velocity tomography code so that it can invert dt* data for 3-D attenuation structure. We applied the new method to The Geyser geothermal field, California, which has vapour-dominated reservoirs and a long history of water injection. A new Qp model at The Geysers is determined using P-wave data of earthquakes in 2011, using our updated earthquake locations and Vp model. By taking advantage of more accurate dt* data and the cancellation of model uncertainties along the common paths outside of the source region, the DDQ tomography method achieves higher resolution, especially in the earthquake source regions, compared to the standard tomography method using e data. This is validated by both the real and synthetic data tests. Our Qp and Vp models show consistent variations in a normal temperature reservoir that can be explained by variations in fracturing, permeability and fluid saturation and/or steam pressure. A prominent low-Qp and Vp zone associated with very active seismicity is imaged within a high temperature reservoir at depths below 2 km. This anomalous zone is likely partially saturated with injected fluids.