Microseismic monitoring using a fibre-optic Distributed Acoustic Sensor (DAS) array
Microseismic monitoring using a fibre-optic Distributed Acoustic Sensor (DAS) array
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DOI：
10.1190/geo2019-0752.1
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发表时间：
2020-03
期刊：
影响因子：
3.3
通讯作者：
J. Verdon;S. Horne;A. Clarke;A. Stork;A. Baird;J. Kendall
中科院分区：
文献类型：
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作者：
J. Verdon;S. Horne;A. Clarke;A. Stork;A. Baird;J. Kendall
我们提出了一个案例研究，演示了使用“L”形的井下光纤阵列监测微震活动。我们使用一个相对简单的方法来检测事件从连续的波形数据，并开发了一个工作流程手动事件定位。位置用圆柱坐标系定义，DAS电缆的水平轴为对称轴。事件定位使用三个手动“挑”，约束（1）零偏移“宽边”通道的事件（2）在宽边通道的P-S波到达时间差，和（3）的角度，？从数组中提取事件的。由于单分量DAS阵列无法记录舷侧通道上的P波能量，因此通过确保模拟的P波和S波时差曲线与观测数据匹配来间接进行P波拾取。的？角度要求在阵列的垂直部分上观察到信号，在我们的情况下，这是可能的，因为工程光纤而不是标准电信光纤提供了噪声水平的显著降低。由于只需要进行三次拾取，因此我们的手动方法比井下检波器数据的等效手动处理要有效得多，其中必须为每个接收器进行P波和S波的拾取。我们发现，所定位的事件定义一个紧密的集群周围的注入间隔，表明这种方法提供了相对精确和准确的事件位置。在该场地还使用了地面微震阵列，其检测到的事件明显较少，其位置的散射明显大于DAS阵列位置。最后，我们通过检查DAS微震数据的一些其他方面，包括在非常短的时间窗口内存在多个事件，以及转换后的相位的存在，这些相位似乎代表了水力压裂本身的能量散射。
We present a case study demonstrating the use of an “L”-shaped downhole fibre-optic array to monitor microseismicity. We use a relatively simple method to detect events from continuous waveform data, and develop a workflow for manual event location. Locations are defined with a cylindrical coordinate system, with the horizontal axis of the DAS cable being the axis of symmetry. Events are located using three manual “picks”, constraining (1) the zero-offset “broadside” channel to the event (2) the P-S wave arrival time difference at the broadside channel, and (3) the angle, ? of the event from the array. Because the one-component DAS array is unable to record P-wave energy on the broadside channel, the P-wave pick is made indirectly by ensuring that the modeled P- and S-wave moveout curves match the observed data. The ? angle requires that signal is observed on the vertical part of the array, in our case this is possible because an engineered fiber, rather than standard telecommunications fiber, provided a significant reduction in the noise level. Because only three picks need to be made, our manual approach is significantly more efficient than equivalent manual processing of downhole geophone data, where picks for P- and S-waves must be made for each receiver. We find that the located events define a tight cluster around the injection interval, indicating that this approach provides relatively precise and accurate event locations. A surface microseismic array was also used at this site, which detected significantly fewer events, the locations of which had significantly greater scatter than the DAS array locations. We conclude by examining some other aspects of the DAS microseismic data, including the presence of multiple events within very short time windows, and the presence of converted phases that appear to represent scattering of energy from the hydraulic fractures themselves.