微地震逆时聚焦定位算法的模拟实验研究

Parametric optimization on locating microseismic events with reverse time imaging

微地震事件的位置可由波动方程逆时聚焦获得,然而在实际应用中稀疏或有缺陷的观测系统会对定位结果产生较大影响,导致定位结果可能存在偏差及假象。提出以峰值信噪比和定位椭球半轴长作为定量评价定位结果清晰度与精度的新标准。通过地面与井下监测的模拟算例综合考察波形加载方式、成像条件、接收器密度、覆盖范围及多震源对定位结果的影响,并以此指导实际的微地震数据采集方案。模拟实验结果表明,混合逆时聚焦可调整定位精度与计算量,是一种较为灵活的波形加载方式;多尺度互相关成像条件具有较高的精度与分辨率,可满足实际定位需求;逆时聚焦定位结果的分辨率与精度分别取决于接收器密度与覆盖范围;由于多震源的互相干涉,分辨多震源需要更苛刻的采集条件。

Microseismic events can be located using reverse time imaging method,which employs the full waveform data to back propagate to its real origin based on wave equation. However,the estimated locations are strongly dependent on various implementations of the method and the sparsity of sensor geometry,which may result in unreliable location estimations. In this paper,we introduce the peak signal to noise ratio and the semi-axis of the imaged ellipse as new standards to quantita-tively evaluate the accuracy and precision of the algorithm. Subsequently,we select one reliable implementation which satis-fies the requirement of real data processing based on the pros and cons of various image conditions and waveform input methods. We investigate the impact of density and coverage of receiver array as well as the multiple events on the locations results using synthetic examples and use the results to guide real microseismic data acquisition. The simulated analysis shows that hybrid reverse time imaging trades off between location accuracy and computational efficiency. Multi-scale reverse time imaging condition has better location accuracy and precision, which satisfies the requirement of real-time processing in microseismic field work. In addition, the location accuracy and precision are mainly dependent on the density and coverage of the receiver array, respectively. Finally,successful location of simultaneous multiple microseismic sources requires more rigorous acquisition plans due to the interferences between different events.