微震震源定位新方法——混合差定位法

当微地震事件个数较多时,传统双差定位算法的数据存储量和计算量巨大,难以适应微震震源的定位。提出一种新的微震震源定位算法——混合差定位法。这种算法综合了双差定位算法和Geiger定位法的优点,不仅数据的存储量和计算量大大减小,且与双差定位相比,其定位结果不受初始震源丛的质心位置的影响。模型数据和实际微地震数据测试结果验证了该方法的有效性和实用性。      

基于差分进化算法的微震定位

针对传统基于走时微震定位方法存在的定位精度依赖于走时精度问题,提出了改进定位目标函数的差分进化微震定位方法。基于传统微震P波走时定位方法,在定位目标函数中加入了误差加权系数,通过降低初至拾取精度低的微震信号道对定位误差的影响,减弱了初至拾取精度对微震定位的影响;利用差分进化算法,通过种群初始化、变异、交叉和选择等操作,求解改进的微震定位目标函数,实现微震定位;对模型数据和实测数据进行试处理,结果表明:改进的目标函数能明显降低误差较大分量对总误差的贡献;提出的改进定位目标函数的差分进化微震定位方法,在部分微震信号道走时拾取误差较大甚至错误的情况下,能很大程度减弱拾取误差对定位精度的影响,可以获得较好的定位结果。      

微地震技术在农安油页岩靶区的应用

微地震初至时间拾取是微地震资料处理过程中的一个重要步骤,也是地层速度模型建立的重要依据。为提高拾取精度,本文提出一种新的自动拾取初至时间的方法,计算三分量地震数据的小时窗协方差矩阵特征值,将其作为特征函数引入到STA/LTA能量比法当中,从而实现自动拾取初至时间,并结合P波时差法完成震源定位。理论模型及农安浅井油页岩水力压裂试验的微地震资料处理结果表明,该方法可以有效地拾取微地震初至时间并实现震源定位。     

微地震震源定位方法综述

微地震震源定位方法是微地震监测领域的一项核心技术,而考量微地震技术应用效果好坏的准则在于震源定位方法的精确程度。针对非常规油气开发过程中微地震震源定位方法的应用,本文对微地震震源定位方法进行阐述。其中：几何作图法具有稳健、效率高的优势,但震源位置较深时定位精度较低;线性定位法无需速度模型精度,但对初至拾取的精度有较大影响;非线性定位法对初至拾取较为敏感,对速度模型的精度要求较高,但计算量较小;混合优化定位法在一定程度上提高了定位的精度和效率,但在低信噪比、速度模型精度较低时优势不明显;基于波形偏移的定位方法无需考虑初至拾取的精度,但计算量较大;基于神经网络的定位方法采用训练网络进行训练,定位精度高,误差小。同时,本文还介绍了多方法多参数信息融合技术在油气藏微震震源定位中的应用。     

月震重定位

由于前人的月震定位结果主要是基于20世纪70、80年代的月球速度模型, 定位结果误差较大, 无法为月震层析成像等研究提供精确的月震参数.随着对月球内部结构研究的不断深入, 月球速度模型及分层结构的精细程度已经有了很大提高.通过对Apollo月震数据解码及分析, 重新拾取了月震初至数据, 在总结前人震源定位的基础上, 利用月球新近速度模型, 采用Geiger震源定位方法进行了月震震源定位, 给出了较为全面的月震参数目录, 并对月震和地震的分布及形成机制进行了对比, 可为以后月震及月球内部结构的深入研究提供更多的依据.      

Pn-Pg震相组合测定震源深度方法的应用研究——以广东和河北地区为例

在直达波射线走时算法改良的基础上,利用天然地震初至震相Pn、Pg进行组合的方法,对区域地震震源深度进行重新定位,结果显示,广东台网观测报告里震源深度和这里新方法定位深度总体上吻合较好。河北台网观测报告里震源深度普遍偏浅3km~6km,新定位结果显示唐山老震区还存在下地壳地震。Pn-Pg震相组合法对唐山老震区的震源深度定位效果一般更深些,同时也进一步反映了断层构造信息。     

一种基于时差的地震救助生命定位方法

参照经典的地震定位方法Geiger法,提出了一种在地震救助中很实用的基于振动直达波到达时差的定位方法,通过模拟实验和计算,验证了该方法的可行性。     

基于快速行进迎风线性插值的微震定位算法研究

准确的微震定位方法是微震监测技术进行岩体稳定性分析的基础,而初至波走时计算方法是决定微震定位精度重要因素之一。引入一种由快速行进法(fast marching methods, FMM)与线性插值射线追踪法(LTI ray tracing)改进而来的线性插值算法,实现了在复杂岩体中相对准确的微震初至走时计算,并在均一速度模型和Marmousi模型中得到了验证。在此基础上,采用常微分方程数值算法中的单步高精度Runge-Kutta法,得到了震源点和传感器之间的射线路径,并在分层和带空洞的岩体模型中验证了其合理性。选取最小二乘法为目标函数,通过寻找目标函数值最小的方式来获得最优节点实现微震定位。在所建立的加入地下硐室的Marmousi岩体模型中,对于预设震源点的定位结果误差分别为1.41、1.00、2.83、1.41、1.41m,验证了所提方法在复杂岩体速度模型中能够实现较准确的微震定位,为进一步提高工程岩体的微震定位精度提供了新思路。     

基于Hyposat和HypoDD的山东地区地震波一维速度模型

本文收集了2009—2016年山东地区M≥0.1的1 554次地震事件及其走时数据,对该地区地震波一维速度模型进行了研究。首先,使用走时曲线拟合、折合走时曲线分析等方法给出了山东地区地震波一维速度结构模型的初始模型以及参考变化范围;然后,精选55次震相较为丰富的地震事件,用Hyposat方法进行批量重定位,根据残差以及地球物理背景给出P波参考模型,之后对理论波速比加入合理的扰动,对所有P波和S波速度模型组合进行批量地震重定位,根据残差结果极小值获得了最优的P波和S波速度模型;最后,利用多重检验方法对最优模型进行检验,包括天然及非天然地震事件检验、3种定位水平差异检验、4种定位深度差异检验以及乳山和长岛震群的双差定位检验,最终获得了较为可靠的山东地区地震波一维速度模型:vP1=6.13km/s,vP2=6.88km/s,vP3=7.93km/s,H1=22km,H2=33km,vS1=3.54km/s,vS2=3.95km/s,vS3=4.46km/s。另外,本文发现,单纯型等非线性算法的定位结果对于速度模型依赖性较低,反之Geiger类型的线性迭代定位方法则较为依赖速度模型。     

振幅叠加的井地联合微地震监测技术研究

微地震地面监测主要缺陷在于垂向定位分辨率不足,而井下监测则存在横向定位分辨率较低问题。针对这些问题,通过井中-地面联合监测的方法提高微地震定位可信度,并结合振幅叠加方法对地面噪声进行压制。模拟三维地震数据的反演实验证明该方法的可行性,反演得到的震源位置与模拟震源点位置一致。以山西宁武盆地一次水力压裂监测为例,证明笔者所提出的方法在实际应用中具有可行性。     

Downhole Microseismic Source Location Based on a Multi-Dimensional DIRECT Algorithm for Unconventional Oil and Gas Reservoir Exploration

Downhole microseismic data has the significant advantages of high signal-to-noise ratio and well-developed P and S waves and the core component of microseismic monitoring is microseismic event location associated with hydraulic fracturing in a relatively high confidence level and accuracy. In this study, we present a multidimensional DIRECT inversion method for microseismic locations and applicability tests over modeling data based on a downhole microseismic monitoring system. Synthetic tests inidcate that the objective function of locations can be defined as a multi-dimensional matrix space by employing the global optimization DIRECT algorithm, because it can be run without the initial value and objective function derivation, and the discretely scattered objective points lead to an expeditious contraction of objective functions in each dimension. This study shows that the DIRECT algorithm can be extensively applied in real downhole microseismic monitoring data from hydraulic fracturing completions. Therefore, the methodology, based on a multidimensional DIRECT algorithm, can provide significant high accuracy and convergent efficiency as well as robust computation for interpretable spatiotemporal microseismic evolution, which is more suitable for real-time processing of a large amount of downhole microseismic monitoring data.     

基于稳健模拟退火-单纯形混合算法的微震定位研究

为提高矿井微震的定位精度,通过模拟试验对比分析常规定位及新方法在定位求解中的适用范围及优缺点,研究反演未知变量数目、检波器的密度、波速等对各自定位方法的影响。基于单纯形法的优点,并结合模拟退火法的全局收敛性,提出采用稳健的模拟退火-单纯形法进行微震定位。研究发现,该方法不必直接搜索发震时刻,只需通过稳健方法预先估算,利用较少的检波器就可进行微震定位,且基本不受初始波速影响,从而大大减少搜索步数,有效地提高定位精度及收敛速度。以柿竹园矿人工爆破定位测试试验为例,重点分析比较模拟退火-单纯形法、稳健模拟退火-单纯形法及其他定位方法的空间绝对距离及目标函数误差,认为检波器数量较多且可获得理想的P波信息时,应用非线性最小二乘法能求出可信的结果;其余定位方法的三维定位误差及目标函数误差相差不大,但稳健模拟退火-单纯形法目标函数误差最小,稳定性最高,可在矿井微震定位中推广使用。     

A nonlinear microseismic source location method based on Simplex method and its residual analysis

Source location is one of the most valuable features of the microseismic technique due to its ability to delineate the unstable areas. In this paper, the precise formulas of the station residual and event residual are derived for the L1 norm statistical standard and the L2 norm statistical standard based on the residual analysis. Then, the error space for microseismic source location is proposed and analyzed. Based on the above research, a nonlinear microseismic source location method using the Simplex method is developed. This new method can search the microseismic source directly in the error space through four deformations of the simplex figures, and it is able to make use of both P-wave and S-wave velocities. Finally, the performance of the Simplex microseismic source location method is tested and verified by laboratory experiments. Test results show that the Simplex microseismic source location method can improve the accuracy and stability of the source location greatly when P-wave and S-wave velocities are involved simultaneously and correctly. The results also demonstrate that the L1 norm statistical standard always provides more accurate and reliable solutions than the L2 norm statistical standard when there are some major but isolated errors in the input data. However, none of the optimization methods are able to function when the errors in the input data are systematic and extreme, which indicates that an early detection and correction of these errors is of primary importance for microseismic source location.     

微地震事件不同初至拾取方法的对比分析

微地震事件初至的精确拾取是微震时空定位的关键技术之一。简述了STA/LTA (Short–Term to Long–Term Average)、AIC (Akaike Information Criteria)、分形维数3种微地震初至拾取方法的基本原理;采用理论模型数据对不同初至拾取方法进行了方法测试效果分析;并选取不同信噪比的实际数据对初至拾取精度、算法效率两个方面进行了比较。结果显示:高信噪比时,3种方法初至拾取的精度都比较高;在信噪比降低时,分形维数法初至拾取的精度仍然较高,具有较好的抗噪性;但是,分形维数法的效率较低,且受算法原理限制,并且与AIC法很难单独拾取事件初至。因此,采用STA/LTA识别微地震事件,初步确定初至范围,然后再使用AIC方法精确拾取初至,是微地震事件初至拾取的较好方法。      

基于变步长加速搜索的微震源定位方法

微震定位方法是微震监测技术的重要组成部分,其关键是定位震源位置。利用空间网格划分并计算网格交点目标函数值,对微震定位目标函数二维及三维空间分布进行了分析,并据此获取了目标函数连续且极小值唯一、单轴收敛范围逐步减小、各轴收敛范围不一的规律。利用以上规律及模式搜索法、网格搜索法的优缺点,探索出了基于连续比较模块、变步长模块、加速模块的变步长加速搜索法。通过模拟算例与工程数据下收敛稳定性、结果精确度、计算速度以及参数初始值影响程度4个指标的效果对比,结果表明：模拟算例下,对比模拟退火算法、遗传算法,变步长加速搜索法的目标函数值标准差、定位误差标准差、波速误差标准差均为0;该算法的定位误差平均值分别为其余二者的0.7%、1.9%;该算法的计算时间平均值分别为其余二者的6.9%、33.2%。该算法单独更改各参数对定位误差的影响在0.005～0.025 m之间;减小搜索步长下限可有效提高结果精确度,并增加相应的计算时间。在规定初至到时与目标函数模型及检波器位置坐标下,搜索算法对定位精度无实质影响。     

The Dynamic Evaluation of Rock Slope Stability Considering the Effects of Microseismic Damage

A state-of-the-art microseismic monitoring system has been implemented at the left bank slope of the Jinping first stage hydropower station since June 2009. The main objectives are to ensure slope safety under continuous excavation at the left slope, and, very recently, the safety of the concrete arch dam. The safety of the excavated slope is investigated through the development of fast and accurate real-time event location techniques aimed at assessing the evolution and migration of the seismic activity, as well as through the development of prediction capabilities for rock slope instability. Myriads of seismic events at the slope have been recorded by the microseismic monitoring system. Regions of damaged rock mass have been identified and delineated on the basis of the tempo-spatial distribution analysis of microseismic activity during the periods of excavation and consolidation grouting. However, how to effectively utilize the abundant microseismic data in order to quantify the stability of the slope remains a challenge. In this paper, a rock mass damage evolutional model based on microseismic data is proposed, combined with a 3D finite element method (FEM) model for feedback analysis of the left bank slope stability. The model elements with microseismic damage are interrogated and the deteriorated mechanical parameters determined accordingly. The relationship between microseismic activities induced by rock mass damage during slope instability, strength degradation, and dynamic instability of the slope are explored, and the slope stability is quantitatively evaluated. The results indicate that a constitutive relation considering microseismic damage is concordant with the simulation results and the influence of rock mass damage can be allowed for its feedback analysis of 3D slope stability. In addition, the safety coefficient of the rock slope considering microseismic damage is reduced by a value of 0.11, in comparison to the virgin rock slope model. Our results demonstrate that microseismic activity induced by construction disturbance only slightly affects the stability of the slope. The proposed feedback analysis technique provides a novel method for dynamically assessing rock slope stability and can be used to assess the slope stability of other similar rock slopes.