On the potential of offshore sensors and array processing for improving seismic event detection and locations in the North Sea
On the potential of offshore sensors and array processing for improving seismic event detection and locations in the North Sea
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海上传感器和阵列处理在改善北海地震事件探测和定位方面的潜力
DOI：
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发表时间：
2022
影响因子：
2.8
通讯作者：
V. Oye
中科院分区：
文献类型：
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作者：
A. Jerkins;A. Köhler;V. Oye
探测和定位北海地震活动的能力对于确保未来二氧化碳储存作业的安全是必要的。目前，事件定位能力受到单侧网络配置的阻碍，因为只有部署在挪威大陆上的传感器才能提供良好的信噪比。然而，将阵列处理技术应用于部署在油气储层的海上传感器组可以提高这些地点的信噪比，这些地点通常遭受来自平台或地震射击的高噪声污染。在这项研究中，我们测试阵列处理的可行性，以传感器部署在格拉内油田，以提高地震事件的位置。在安装的3400个节点中，我们可以访问两个数据子集：i）来自遍布整个领域的10个传感器的连续数据，以及ii）来自30个传感器的短数据段，目的是应用阵列方法。由于10个传感器之间的平均站间距离为6 km，记录的波场不相干，传统的阵列处理方法不适用。为了优化使用的10个传感器的海上数据的事件定位的目的，我们开发了一种新的非相干阵列处理方法。我们计算一个特征函数的基础上的峰度的地震道之前的频率波数分析。该方法成功地确定了几乎所有评价地震的慢度和后方位角。使用共同的相干阵列处理，30个传感器显示出比10个传感器更优越的探测能力，因此，如果有连续数据，将大大降低该区域地震事件的探测阈值。我们的结论是，海上传感器在格拉纳可以包括作为一个系统的一部分，在北海被动地震监测。为此，我们建议使用30个传感器的数据。然而，由于我们在这项研究中只能获得来自10个传感器的连续数据，我们发现当30个传感器数据不可用时，它们是一个很好的替代品。
The capability to detect and locate seismicity in the North Sea is necessary to ensure the safety of future CO2 storage operations. Currently, the event location capabilities are hampered by a one-sided network configuration, as only sensors deployed on the Norwegian mainland are providing good signal-to-noise ratios. However, applying array processing techniques to groups of offshore sensors deployed at oil and gas reservoirs can improve the signal-to-noise ratio at such sites, which generally suffer from high noise contamination originating from platforms or seismic shooting. In this study we test the feasibility of array processing to sensors deployed at the Grane oil field to improve earthquake event locations. Out of the 3400 nodes installed, we have access to two data subsets: i) continuous data from 10 sensors spread out over the whole field, and ii) short segments of data from 30 sensors selected with the purpose to apply array methods. As the average interstation distance between the 10 sensors is 6 km, the recorded wavefield is not coherent and traditional array processing methods are not applicable. To optimize the usage of the 10-sensor offshore data for event location purposes, we develop a new method for incoherent array processing. We compute a characteristic function based on the kurtosis of the seismic traces prior to a frequency-wavenumber analysis. This method successfully determines slowness and back azimuth for almost all the evaluated earthquakes in this study. Using common coherent array processing, the 30 sensors show superior detection capabilities over the 10 sensors and will therefore decrease the detection threshold for seismic events in the region significantly if continuous data are available. We conclude that offshore sensors at Grane can be included as a part of a system for passive seismic monitoring in the North Sea. We recommend using the 30-sensors data for this purpose. However, as we only have access to continuous data from the 10 sensors in this study, we found that they are a good substitute when the 30-sensor data are not available.