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微地震事件初至拾取是井下微地震监测数据处理的关键步骤之一.初至误差的存在会使微地震震源定位结果产生较大偏差,进而影响后续的压裂裂缝解释.通常初至拾取过程对所有的微地震事件选择相同的特征函数并采用一致的拾取参数进行统一处理,然而当事件的能量、震源机制、传播路径以及背景噪声等存在明显差异时,所得初至拾取结果差别显著.为了提高微地震事件初至拾取标准一致性,本文提出基于波形相似特征的初至拾取及全局校正方法.该方法首先利用互相关函数对每个事件内的各道记录进行时差校正,得到初始初至信息并形成叠加道,再对所有事件的叠加道进行全局互相关得到事件间初至相对校正量,最终初至结果可以通过各个事件的初始初至信息与其相对校正量相加得到.方法将所有微地震事件初至结果作为一个整体处理,从而能够克服常规方法初至拾取标准一致性差的缺陷.实际资料处理结果表明,相比于常规方法,该方法可以有效提高事件初至拾取和定位结果的一致性. 相似文献
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地层速度模型精度对水力压裂微地震事件的定位结果起着关键的作用,常规的速度建模方法是根据声波测井资料建立初始层状速度模型,根据拾取的射孔信号初至通过反演进行速度模型优化,结果受射孔信号信噪比及初至拾取误差的影响较大,不适用于地面微地震监测.为了提高地面微地震速度模型的精度,提出了将多道射孔信号的叠加能量作为目标函数,基于粒子群优化算法的地面微地震速度模型优化方法,并通过模型数据和实际数据的处理进行了验证,结果表明该方法避免了无法拾取初至或初至拾取不准对速度模型优化结果的影响,有效实现了速度模型的优化,明显提高了地面微地震监测的定位精度. 相似文献
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随着非常规致密砂岩气、页岩气藏的开采开发,压裂技术在储层改造中起着举足轻重的作用,而微地震监测技术是评价压裂施工效果的关键且即时的技术之一.根据微地震监测处理高精度地反演微震位置,从而预测压裂裂缝的发展趋势及区域,对压裂施工效果进行跟踪及评判,同时也为后期油气藏的开采和开发提供技术指导.定位精度直接影响地下裂缝的分布特征,错误或精度不高的定位结果,必将导致对裂缝趋势的误判.文章结合理论和数值模拟方法,对初至拾取精度的影响因素进行了分析,讨论初至误差对定位精度的影响.同时结合地层岩石物理特性、射孔资料对速度模型的校正、速度各向异性、地层倾角、多段压裂等因素,分析了这些因素对精细速度模型及定位精度的影响.最后结合定位方法本身所存在的局限,探讨反演方法及方位角对定位精度的影响.通过理论及数值模拟分析表明,初至误差、速度模型精度及定位方法对定位精度有着紧密关系,并将其归类为可控误差及系统误差,通过区别对待可控误差和系统误差,可最终为高精度微地震监测定位技术的研究及应用提供指导. 相似文献
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震源定位是微地震监测关键技术之一。本文提出用于微地震定位的弹性波和加权弹性波(WEW)干涉成像方法。该方法在保证定位精度的同时,还可避免震源假象。通过各向同性水平层介质状模型的数值试验,初步表明该方法可适应低信噪比微震信号、速度随机扰动、较稀疏的检波器分布等情况,并在速度模型存在一定的系统误差时也仍保持较高的定位精度。由于干涉成像方法不需要进行初至拾取,定位效率相对传统走时方法也得到了提高。采用二维断层模型试算Nnumerical results of using a two-dimensional fault model,表明方法还能实现多震源定位,且比逆时成像有更高的定位精度。 相似文献
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水力压裂是页岩气开发过程中的核心增产技术,微地震则广泛用于压裂分析、水驱前缘监测和储层描述.微地震反演过程中,用于反演的速度模型往往基于测井、地震或标定炮资料构建,忽略了压裂过程中裂缝及孔隙流体压力变化对地层速度的影响.本文首先基于物质守恒、渗流理论和断裂力学模拟三维水力压裂过程,得到地下裂缝发育特征和孔隙压力分布.继而根据Coates-Schoenberg方法和裂缝柔量参数计算裂缝和孔隙压力对速度场的影响,得到压裂过程中的实时速度模型.最后利用三维射线追踪方法正演微地震走时和方位信息,并采用常规微地震定位方法反演震源位置及进行误差分析.数值模拟结果表明,检波器空间分布影响定位精度,常规方法的定位误差随射线路径在压裂带中传播距离增加而变大,且不同压裂阶段的多点反演法与单点极化法精度相当. 相似文献
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《地球物理学进展》2017,(5)
本文采用CAP方法反演了2011年两次岷县中等地震的震源机制解,首先讨论了方位角对反演结果的影响,通过对不同方位角组合的比较,得到的结果比较稳定,进一步得出两次地震的震源机制解.然后,采用自助抽样(bootstrap)方法,基于CAP方法进行多次重复反演,得到岷县两次中等地震事件的大样本量震源机制解数据.基于这些大样本数据,以Kagan角为目标函数,利用粒子群非线性优化方法搜索震源机制解的优化解,并估计了震源机制解的误差范围,M_S4.0、M_S4.5的误差分别为6.0°和18.3°.结果分析表明,CAP结果与得到的优化解基本接近,其误差在可接受的误差范围内. 相似文献
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常规的地震定位方法通常需要拾取地震记录的初至,当初至不明显或被较高水平的噪声淹没时精度较低.本文采用基于三维高斯射线束的偏移成像方法对震源进行定位,较好地解决了该问题.通过三维高斯射线束对台站记录进行偏移归位,并将各台站成像结果的交点作为地震能量释放的中心位置;当各台站成像结果不能交于一点时,采用三维空间高斯滤波方法可实现震源位置的自动获取.提出的变网格计算方案极大地减少了计算量,显著地提高了成像精度和计算效率.利用首都圈地震台网数据,对涿鹿、滦县以及房山三个地震事件进行试算,结果表明:基于变网格三维高斯束偏移成像的地震定位方法自动化程度很高,而且具有较好的抗噪能力,特别适合处理低信噪比资料的地震定位问题. 相似文献
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微震源反演数学模型、反演算法等对象是微震源定位误差的重要来源。针对P波速度易衰减、首波到时数据拾取误差较大的情况,基于到时差模型(ATD)和P波到时方程组,建立到时差比值法反演数学模型(ATDRM),从目标函数中消除了P波速度和发震时刻等参数;同时,引入范数概念,得到改进的L1、L2、L3、L4范数模型,设计一系列反演模型对比实验和反演算法对比实验综合分析研究这些模型的优越性。工程数据显示：ATDRM模型的定位效果整体比经典ATD模型更好,ATDRM-L1模型震源误差可减少13.437 0 m;反演模型的定位误差受反演算法影响较大,单形替换法相比遗传算法(GA)、非线性最小二乘法(NLSM)、模拟退火算法(SA)等方法定位精度更高,稳定性更好;在应用单形替换法求解模型时,反演误差会随着范数参数N的增加(L1→L4)呈现先下降再上升的现象;ATDRM模型及其范式形式对提高微震源定位精度有一定价值。 相似文献
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针对煤矿上覆岩层层状赋存和离层带的特点,构建矿井尺度的微震监测系统异向波速模型,模型中波速向量由地面探头速度与井下探头速度组成.研究了在只有强矿震信号和混有爆破信号两种条件下,以到时残差最小为目标和震源定位误差最小为目标的两种求解模型,模型求解选用具有全局寻优特性的遗传算法与CMEAS算法结合的混合算法.现场实际应用得出,只使用爆破信号的到时残差法最优,混有强矿震信号的到时残差法其次;与爆破信号定位所用的统一简化波速模型相比,震源定位误差大幅度降低.在此基础上进一步减低定位误差,还需从微震台网的优化布设方面解决. 相似文献
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Locating microseismic events using borehole data 总被引：1，自引：0，他引：1
Constraining microseismic hypocentres in and around hydrocarbon reservoirs and their overburdens is essential for the monitoring of deformation related to hydraulic fracturing, production and injection and the assessment of reservoir security for CO2 and wastewater storage. Microseismic monitoring in hydrocarbon reservoirs can be achieved via a variety of surface and subsurface acquisition geometries. In this study we use data from a single, subsurface, vertical array of sensors. We test an existing technique that uses a 1D velocity model to constrain locations by minimizing differential S‐to‐P arrival times for individual sensors. We show that small errors in either arrival time picks or the velocity model can lead to large errors in depth, especially near velocity model discontinuities where events tend to cluster. To address this issue we develop two methods that use all available arrival times simultaneously in the inversion, thus maximizing the number of potential constraints from to N, where N is the number of phase picks. The first approach minimizes all available arrival time pairs whilst the second approach, the equal distance time (EDT) method defines the hypocentre as the point where the maximum number of arrival time surfaces intersect. We test and compare the new location procedures with locations using differential S‐to‐P times at each individual sensor on a microseismic data set recorded by a vertical array of sensors at the Ekofisk reservoir in the North Sea. Specifically, we test each procedure's sensitivity to perturbations in measured arrival times and the velocity model using Monte Carlo analysis. In general, location uncertainties increase with increasing raypath length. We show that errors in velocity model estimates are the most significant source of uncertainty in source location with these experiments. Our tests show that hypocentres determined by the new procedures are less sensitive to erroneous measurements and velocity model uncertainties thus reducing the potential for misinterpretation of the results. 相似文献
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For years, severe rockburst problems at the Lucky Friday mine in northern Idaho have been a persistent safety hazard and an impediment to production. An MP250 based microseismic monitoring system, which uses simple voltage threshold picking of first arrivals, has been used in this mine since 1973 to provide source locations and energy estimates of seismic events. Recently, interest has been expressed in developing a whole waveform microseismic monitoring system for the mine to provide more accurate source locations and information about source characteristics. For this study, we have developed a prototype whole-waveform microseismic monitoring system based on a 80386 computer equipped with a 50 kHz analog-digital convertor board. The software developed includes a data collection program, a data analysis program, and an event detection program. Whole-waveform data collected and analyzed using this system during a three-day test have been employed to investigate sources of error in the hypocenter location process and to develop an automatic phase picker appropriate for microseismic events.Comparison of hypocenter estimates produced by the MP250 system to those produced by the whole-waveform system shows that significant timing errors are common in the MP250 system and that these errors caused a large part of the scatter evident in the daily activity plots produced at the mine. Simulations and analysis of blast data show that analytical control over the solutions is strongly influenced by the array geometry. Within the geophone array, large errors in the velocity model or moderate timing errors may result in small changes in the solution, but outside the array, the solution is very sensitive to small changes in the data.Our whole-waveform detection program picks event onset times and determines event durations by analysis of a segmented envelope function (SEF) derived from the microseismic signal. The detection program has been tested by comparing its arrival time picks to those generated by human analysis of the data set. The program picked 87% of the channels that were picked by hand with a standard error of 0.75 milliseconds. Source locations calculated using times provided by our entire waveform detection program were similar to those calculated using hand-picked arrival times. In particular, they show far less scatter than source locations calculated using arrival times based on simple voltage threshold picking of first arrivals. 相似文献
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微地震事件的空间分布可以用来监测水力压裂过程中裂缝的发育情况。因此,震源定位是微震监测中重要的环节。震源定位依赖准确的速度模型,而震源位置和速度模型的耦合易导致线性迭代的同时反演方法陷入局部极小值。邻近算法作为一种非线性全局优化算法,能够最大程度地避免陷入局部最优解。本文将邻近算法应用于单井监测的微震定位和一维速度模型同时反演,首先利用邻近算法搜索一维速度模型,再使用网格搜索方法进行震源定位,并根据定位的走时残差产生新的速度模型,最后通过若干次迭代使其收敛到最优解。理论和实际数据结果均表明该方法能够避免局部最优解,得到较为可靠的震源位置和一维速度模型。 相似文献
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微地震监测被广泛应用于非常规油气资源的水力压裂作业、油藏描绘和水驱前缘监测工程中.微地震定位采用的初始速度模型一般是基于地震测井记录和射孔数据建立,该速度模型的不准确性易引起定位误差.为降低这种定位误差,本文发展了一种微地震定位和各向异性速度结构同时反演的方法.研究对象为1-D的层状TI介质,其中对称轴方向任意.利用改进的分区多步最短路径算法计算qP、qSV和qSH波的到达时间和射线路径,结合共轭梯度法求解带约束的阻尼最小二乘问题.数值模拟结果表明,该算法能同时进行各向异性速度结构模型(每层的Thomsen参数和界面深度)和微震震源参数(空间坐标和发震时刻)的反演,并且对随机噪声不敏感,有利于实际工程应用. 相似文献
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P. L. Swanson L. H. Estey F. M. Boler S. Billington 《Pure and Applied Geophysics》1992,139(3-4):375-404
The accuracy and precision of microseismic event locations were measured, analyzed, and compared for two types of location systems: anolog and digital. In the first system, relative times of first arrival were estimated from analog signals using automated hardware circuitry; station positions were estimated from mine map coordinates; and event locations were determined using the BLD (Blake, Leighton, and Duvall) direct solution method. In the second system, arrival times were manually measured during interactive displays of digital waveforms; station coordinates were surveyed; and the SW-GBM (Salamon and Wiebols; Godson, Bridges, and McKavanagh) direct basis function was used to solve for locations. Both systems assume constant isotropic seismic velocity of slightly different signals data sets, calibration blast signals with known source site and origin time, and microseismic event signals, were recorded by each location system employing the same array of high-frequency (5 kHz) accelerometers with 150 m maximum dimension. The calibration blast tests indicated a location precision of ±2 m and accuracy of ±10 m for the analog system. Location precision and accuracy for the digital system measured ±1 m and ±8 m, respectively. Numerical experiments were used to assess the contributions of errors in velocity, arrival times, and station positions on the location accuracy and precision for each system. Measured and estimated errors appropriate to each system for microseismic events were simulated in computing source locations for comparison with exact synthetic event locations. Discrepancy vectors between exact locations and locations calculated with known data errors averaged 7.7 and 1.4 m for the analog and digital systems, respectively. These averages are probably more representative of the location precision of microseismic events, since the calibration blast tests produce impulsive seismic arrivals resulting in smaller arrival-time pick errors in the analog system. For both systems, location accuracy is limited by inadequate modeling of the velocity structure. Consequently, when isotropic velocity models are used in the travel-time inversions, the increased effort expended with the digital location system does not, for the particular systems studied, result in increased accuracy. 相似文献
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Since 1972, Weir-Jones Engineering Consultants (WJEC) has been involved in the development and installation of microseismic monitoring systems for the mining, heavy construction and oil/gas industries. To be of practical value in an industrial environment, microseismic monitoring systems must produce information which is both reliable and timely. The most critical parameters obtained from a microseismic monitoring system are the real-time location and magnitude of the seismic events. Location and magnitude are derived using source location algorithms that typically utilize forward modeling and iterative optimal estimation techniques to determine the location of the global minimum of a predefined cost function in a three-dimensional solution space. Generally, this cost function is defined as the RMS difference between measured seismic time series information and synthetic measurements generated by assuming a velocity structure for the area under investigation (forward modeling). The seismic data typically used in the source location algorithm includes P- and S-wave arrival times, and raypath angles of incidence obtained from P-wave hodogram analysis and P-wave first break identification. In order to obtain accurate and timely source location estimates it is of paramount importance that the extraction of accurate P-wave and S-wave information from the recorded time series be automated—in this way consistent data can be made available with minimal delay. WJEC has invested considerable resources in the development of real-time digital filters to optimize extraction, and this paper outlines some of the enhancements made to existing Kalman Filter designs to facilitate the automation of P-wave first break identification. 相似文献
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Improved microseismic event location by inclusion of a priori dip particle motion: a case study from Ekofisk 总被引：1，自引：0，他引：1
Microseismic monitoring in petroleum settings provides insights into induced and naturally occurring stress changes. Such data are commonly acquired using an array of sensors in a borehole, providing measures of arrival times and polarizations. Events are located using 1D velocity models, P‐ and S‐wave arrival times and the azimuths of P‐wave particle motions. However in the case of all the sensors being deployed in a vertical or near‐vertical borehole, such analysis leads to an inherent 180° ambiguity in the source location. Here we present a location procedure that removes this ambiguity by using the dip of the particle motion as an a priori information to constrain the initial source location. The new procedure is demonstrated with a dataset acquired during hydraulic fracture stimulation, where we know which side of the monitoring well the events are located. Using a 5‐step location procedure, we then reinvestigate a microseismic data set acquired in April 1997 at the Ekofisk oilfield in the North Sea. Traveltimes for 2683 candidate events are manually picked. A noise‐weighted analytic‐signal polarization analysis is used to estimate the dip and azimuth of P‐wave particle motions. A modified t‐test is used to statistically assess the reliability of event location. As a result, 1462 events are located but 627 are deemed to be statistically reliable. The application of a hierarchal cluster analysis highlights coherent structures that cluster around wells and inferred faults. Most events cluster at a depth of roughly 3km in the Ekofisk chalk formation but very little seismicity is observed from the underlying Tor chalk formation, which is separated from the Ekofisk formation by an impermeable layer. We see no evidence for seismicity in the overburden but such events may be too distant to detect. The resulting picture of microseismicity at Ekofisk is very different from those presented in previous studies. 相似文献
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基于偏移成像的微地震定位方法由于可避免走时拾取误差以及可实现自动化定位等优点被广泛应用.绕射叠加方法将能量沿走时曲线聚焦到空间网格点上,进行成像时需要搜索发震时刻.干涉成像方法利用互相关提取的走时差信息可避免搜索发震时刻,但定位结果受数据信噪比的影响较大.为了进一步提高干涉成像法的定位精度,本文提出一种同时使用互相关和自相关道集的全干涉成像方法,增加的自相关道集提取的S-P走时差可降低震源-检波器方向的定位误差,提高定位精度.单井监测的理论测试和实际数据的研究结果表明,全干涉成像的定位精度高于仅使用互相关道集的干涉成像方法,同时计算效率高于绕射叠加方法. 相似文献