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利用近代微震资料研究地震危险性 总被引：1，自引：0，他引：1
利用１９７０～１９９３年华北地区ＭＬ≥２．０的微震资料，根据其地震活动特点，从中挑选了一些有代表性的区域，做其Ｇ－Ｒ关系曲线，由该曲线可得到每个震级的年频次，同时，由该区域的历史地震（１３００－１９９３年）可得到较大震级的实际年频次，两者对比，发现具有很好的一致性。因此，当选取合适的区域时，利用近代微资料可以推测出该区域较大地震的活动情况，但同时有两点注意：（１）利用微震资料进行统计时，得到的得一 相似文献
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微震事件在震前预警、火山喷发监测、矿山安全监测、油气勘探和小当量核试验监测等方面发挥了重要的作用,而微震事件的自动识别工作是进行地震定位、震源属性判定和地震成像等一系列应用的基础.本文从单特征法、多特征法和综合分析法三个方面对已有的微震识别和震相拾取方法的原理、发展历程和特点进行了阐述.其中,单特征法具有算法简单,可操作性强和便于自动化处理的特点,但当信噪比较低时该类方法不适用;多特征法的抗噪能力较强,识别精度高,但计算速度慢;综合分析法在多种情况下都具有较好的识别效果,但往往需要人工参与.文章认为,三类方法各有利弊,单一方法无法适用于所有情形,需要根据具体的研究对象和区域,合理选择微震识别和震相拾取方法. 相似文献
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在深圳地区设置微震台网,于1985—1986年进行了两期监测。以台网记录结果并结合历年地震资料,研究分析了区内现代地震活动与现今构造应力场。得出:深圳市附近的现代地震活动均属微震范畴,频度不高,震源深度较浅,为5—10Km;研究区内现今构造应力场以水平作用为主,主压应力的优势方位为北西—南东向。 相似文献
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通过对北京遥测地震台网近年来记录到的北京及邻区地震的震中分布,地震活动频度及能量释放强度的分析,得到本区地震活动在时间分布上具有“聚堆性”。在年发震频度,地震强度和能释放方面均具有双峰值特征,并且具有较好的一致性和同步性,在空间分布上具有条带特征,且形成北东～南西和北西～南东的两条相互交汇的条带。又通过统计分析得到本区发震概率最大的时间段是每年的１０月前后,而地震主要发生在北西～南东带上。 相似文献
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利用美国国家地震信息中心的地震早期警报系统，通过对数字化地震记录的分析，针对各种可能出现的情况，对微震的自动识别和计算机实时处理进行了讨论。有关结论对地震的自动识别和震源参数的计算测定精度的提高，有重要的参考意义。 相似文献
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通过对太原盆地近１０ａ来,遥测台网记录到的地震做震中分布,地震活动频度及能量释放等分析,得出太原盆地地震活动时间分布上人有“丛集性”,盆地小震活动频繁,应变能释放常以小震群形式释放的结论。指出今后２ａ,太原盆地将出现地震活动频度高,应变能释放逐渐回升的现象。 相似文献
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Cluster analysis of low-frequency microseismic noise 总被引：1，自引：0，他引：1
A. A. Lyubushin 《Izvestiya Physics of the Solid Earth》2011,47(6):488-495
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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
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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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In unconventional reservoirs, small faults allow the flow of oil and gas as well as act as obstacles to exploration; for, (1) fracturing facilitates fluid migration, (2) reservoir flooding, and (3) triggering of small earthquakes. These small faults are not generally detected because of the low seismic resolution. However, such small faults are very active and release sufficient energy to initiate a large number of microseismic events (MEs) during hydraulic fracturing. In this study, we identified microfractures (MF) from hydraulic fracturing and natural small faults based on microseismicity characteristics, such as the time–space distribution, source mechanism, magnitude, amplitude, and frequency. First, I identified the mechanism of small faults and MF by reservoir stress analysis and calibrated the ME based on the microseismic magnitude. The dynamic characteristics (frequency and amplitude) of MEs triggered by natural faults and MF were analyzed; moreover, the geometry and activity types of natural fault and MF were grouped according to the source mechanism. Finally, the differences among time–space distribution, magnitude, source mechanism, amplitude, and frequency were used to differentiate natural faults and manmade fractures. 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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Mr. Markus Bath 《Pure and Applied Geophysics》1948,12(3-4):121-126
Summary The microseisms recorded at Uppsala have been studied for the time 1907–1947 with regard to long period variations. There
is clear evidence of an 11 year variation and slight indications of a 28 month variation. The 11 year variation is from 1923
negatively correlated to the sunspot frequency and is explained by corresponding meridional displacements of the dominant
cyclonic tracks.
Zusammenfassung Die in Uppsala registrierte Bodenunruhe ist für die Zeit 1907–1947 betreffs langperiodischen Schwankungen untersucht worden. Eine 11-j?hrige Variation wird festgestellt und es gibt weiter Anzeichnungen einer Variation von 28 Monaten. Die 11-j?hrige Variation ist seit 1923 zur Sonnenflecken-frequenz negativ korreliert und ist durch entsprechende meridionale Verschiebungen der am meisten betretenen Zyklonenbahnen, erkl?rt.
Riassunto L'agitazione microsismica registrata a Uppsala nel quarantennio 1907–1947 venne esaminata in vista di determinare le oscillazioni di lungo periodo. Si è accertata una oscillazione undecennale, trovandosi altresi indizi per una oscillazione di 28 mesi. Dal 1923 l'oscillazione undecennale manifesta una correlazione negativa con la frequenza delle macchie solari e viene spiegata con i corrispondenti spostamenti meridionali delle rotte cicloniche dominanti.相似文献
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Fractures are pervasive features within the Earth’s crust and have a significant influence on the multi-physical response of the subsurface. The presence of coherent fracture sets often leads to observable seismic scattering enabling seismic techniques to remotely locate and characterise fracture systems. In this study, we confirm the general scale-dependence of seismic scattering and provide new results specific to shear-wave propagation. We do this by generating full waveform synthetics using finite-difference wave simulation within an isotropic background model containing explicit fractures. By considering a suite of fracture models having variable fracture density and fracture size, we examine the widening effect of wavelets due to scattering within a fractured medium by using several different approaches, such as root-mean-square envelope analysis, shear-wave polarisation distortion, differential attenuation analysis and peak frequency shifting. The analysis allows us to assess the scattering behavior of parametrised models in which the propagation direction is either normal or parallel to the fracture surfaces. The quantitative measures show strong observable deviations for fractures size on the order of or greater than the dominant seismic wavelength within the Mie and geometric scattering regime for both propagation normal and parallel to fracture strike. The results suggest that strong scattering is symptomatic of fractures having size on the same order of the probing seismic wave. 相似文献
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In downhole microseismic monitoring, accurate event location relies on the accuracy of the velocity model. The model can be estimated along with event locations. Anisotropic models are important to get accurate event locations. Taking anisotropy into account makes it possible to use additional data – two S-wave arrivals generated due to shear-wave splitting. However, anisotropic ray tracing requires iterative procedures for computing group velocities, which may become unstable around caustics. As a result, anisotropic kinematic inversion may become time consuming. In this paper, we explore the idea of using simplified ray tracing to locate events and estimate medium parameters. In the simplified ray-tracing algorithm, the group velocity is assumed to be equal to phase velocity in both magnitude and direction. This assumption makes the ray-tracing algorithm five times faster compared to ray tracing based on exact equations. We present a set of tests showing that given perforation-shot data, one can use inversion based on simplified ray-tracing even for moderate-to-strong anisotropic models. When there are no perforation shots, event-location errors may become too large for moderately anisotropic media. 相似文献
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T. B. Yanovskaya 《Izvestiya Physics of the Solid Earth》2017,53(6):819-824
Based on the theory of surface waves in a media with weak lateral heterogeneities, an explanation is given for the peculiarities that are considered as prospecting indicators in the microseismic sounding method (MSM). According to this theory, during the propagation of surface waves in such media, their local characteristics are the same as in the case of propagation in a horizontally homogeneous medium characterized by the same vertical velocity section as underlying a given point. Since the wave energy flux through a semiinfinite vertical strip is conserved, the amplitude of the wave is redistributed along the vertical. Based on this principle and simple physical considerations, it is shown that above a low-velocity domain, the amplitudes of microseisms should increase at wavelengths approximately exceeding the depth of the anomaly by a factor of three and decrease at small wavelengths. The model calculations show that variation of spectral amplitudes only allows a depth to the anomaly to be estimated rather than its average extent. Practically identical spectra characterize the anomalies in which the product of the vertical extent of the anomaly and the velocity contrast is approximately similar. 相似文献
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非常规油气开采中实施的储层改造,通常是利用水力压裂技术向储层注入高压流体,改变储层原有的孔缝连通结构,实现油气开采.水力压裂会改变储层应力并使岩石破裂,从而产生微地震事件.微地震研究的重要内容之一是其震源破裂的机制.通过对微地震震源机制的研究,可揭示微地震的产生机理和地下储层的应力变化规律,有效地优化水力压裂和储层改造... 相似文献