The 1998 Valhall microseismic data set: An integrated study of relocated sources, seismic multiplets, and S-wave splitting
The 1998 Valhall microseismic data set: An integrated study of relocated sources, seismic multiplets, and S-wave splitting
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DOI：
10.1190/1.3205028
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发表时间：
2009-09-01
期刊：
影响因子：
3.3
通讯作者：
van der Baan, M.
中科院分区：
文献类型：
--
作者：
De Meersman, K.;Kendall, J. -M.;van der Baan, M.
我们重新定位303微震事件记录在1998年的传感器在一个单一的钻孔在北海瓦尔霍尔油田。半自动阵列分析方法重新挑选P波和S波到达时间和P波极化，这是定位这些事件所需的。重新定位的放射源主要局限于水库上方50米厚的区域，位置不确定性是以前努力的一半。多重峰分析确定了40个多重峰组，其中包括303个事件中的208个。最大的组包含24个事件，五个组包含10个或更多事件。在每个多重峰组内，我们通过互相关进一步提高了到达时间拾取，这提高了重新定位事件的相对准确性，并揭示了超过99%的地震活动在空间上位于三个不同的集群中。事件的空间分布和波形相似性揭示了两个断层状结构，与从三维地面地震数据解释的北-西北-南-东南走向的断层面匹配良好。位于这些断层上的多重态组之间的波形差异大多可以归因于S波相位含量和极性或P/S振幅比。在P-到-S振幅比的范围内观察到的故障解释最好的变化源机制。我们还发现了多重态组和地震各向异性的时间变化之间的相关性，揭示了S波分裂分析。我们解释这些发现的背景下，循环补给和消散的盖岩应力生产驱动的压实下伏油藏。这种机制的周期性驱动了地震各向异性的短期变化和微震源机制随时间的重新激活。
We relocate 303 microseismic events recorded in 1998 by sensors in a single borehole in the North Sea Valhall oil field. A semi-automated array analysis method repicks the P-and S-wave arrival times and P-wave polarizations, which are needed to locate these events. The relocated sources are confined predominantly to a 50-m-thick zone just above the reservoir, and location uncertainties are half those of previous efforts. Multiplet analysis identifies 40 multiplet groups, which include 208 of the 303 events. The largest group contains 24 events, and five groups contain 10 or more events. Within each multiplet group, we further improve arrival-time picking through crosscorrelation, which enhances the relative accuracy of the relocated events and reveals that more than 99% of the seismic activity lies spatially in three distinct clusters. The spatial distribution of events and wave-form similarities reveal two faultlike structures that match well with north-northwest-south-southeast-trending fault planes interpreted from 3D surface seismic data. Most waveform differences between multiplet groups located on these faults can be attributed to S-wave phase content and polarity or P-to-S amplitude ratio. The range in P-to-S amplitude ratios observed on the faults is explained best in terms of varying source mechanisms. We also find a correlation between multiplet groups and temporal variations in seismic anisotropy, as revealed by S-wave splitting analysis. We explain these findings in the context of a cyclic recharge and dissipation of cap-rock stresses in response to production-driven compaction of the underlying oil reservoir. The cyclic nature of this mechanism drives the short-term variations in seismic anisotropy and the reactivation of microseismic source mechanisms over time.