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1.
Burying receivers for improved time‐lapse seismic repeatability: CO2CRC Otway field experiment 
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下载免费PDF全文 Valeriya Shulakova Roman Pevzner J. Christian Dupuis Milovan Urosevic Konstantin Tertyshnikov David E. Lumley Boris Gurevich 《Geophysical Prospecting》2015,63(1):55-69
4D seismic is widely used to remotely monitor fluid movement in subsurface reservoirs. This technique is especially effective offshore where high survey repeatability can be achieved. It comes as no surprise that the first 4D seismic that successfully monitored the CO2 sequestration process was recorded offshore in the Sleipner field, North Sea. In the case of land projects, poor repeatability of the land seismic data due to low S/N ratio often obscures the time‐lapse seismic signal. Hence for a successful on shore monitoring program improving seismic repeatability is essential. Stage 2 of the CO2CRC Otway project involves an injection of a small amount (around 15,000 tonnes) of CO2/CH4 gas mixture into a saline aquifer at a depth of approximately 1.5 km. Previous studies at this site showed that seismic repeatability is relatively low due to variations in weather conditions, near surface geology and farming activities. In order to improve time‐lapse seismic monitoring capabilities, a permanent receiver array can be utilised to improve signal to noise ratio and hence repeatability. A small‐scale trial of such an array was conducted at the Otway site in June 2012. A set of 25 geophones was installed in 3 m deep boreholes in parallel to the same number of surface geophones. In addition, four geophones were placed into boreholes of 1–12 m depth. In order to assess the gain in the signal‐to‐noise ratio and repeatability, both active and passive seismic surveys were carried out. The surveys were conducted in relatively poor weather conditions, with rain, strong wind and thunderstorms. With such an amplified background noise level, we found that the noise level for buried geophones is on average 20 dB lower compared to the surface geophones. The levels of repeatability for borehole geophones estimated around direct wave, reflected wave and ground roll are twice as high as for the surface geophones. Both borehole and surface geophones produce the best repeatability in the 30–90 Hz frequency range. The influence of burying depth on S/N ratio and repeatability shows that significant improvement in repeatability can be reached at a depth of 3 m. The level of repeatability remains relatively constant between 3 and 12 m depths. 相似文献
2.
J. J. Galiana-Merino A. K. Mahajan C. Lindholm J. Rosa-Herranz A. K. Mundepi Nitesh Rai 《Bulletin of Earthquake Engineering》2011,9(5):1309-1325
In recent years, seismic noise array measurements have emerged as a promising way for estimating Vs profiles and characterizing
the corresponding soil structure. Although methods based on analysis of seismic noise are simpler, cheaper and faster than
conventional soil penetrating techniques, array deployment requires the use of several stations which are not always available
for all the research groups. Broadband stations are expensive, but even short-period sensors can require a significant economical
effort as it is necessary to use several. In this paper, the results from broadband stations and vertical geophones using
the f-k method have been compared. Circular arrays with both types of instruments were installed north and south of the Himalayan
Frontal Thrust (HFT) also known as Mohand Thrust, with different soil characteristics. The comparison carried out in terms
of dispersion curves shows an excellent agreement between broadband stations and geophones recordings in the frequency range
of applicability of the arrays used. These results indicate the possibility of using seismic refraction equipments for the
f-k analysis in the frequency band of geotechnical engineering interest. This has potentially great importance since the same
equipment is indicated to be applicable for both seismic noise measurements as well as for active reflection seismic surveys. 相似文献
3.
I. O. Kitov S. G. Volosov S. B. Kishkina N. L. Konstantinovskaya K. S. Nepeina M. A. Nesterkina I. A. Sanina 《Seismic Instruments》2016,52(1):19-31
A small-aperture seismic array consisting of seven three-component seismometers carried out continuous measurements of regional seismicity in a selected area of the Nizhni Novgorod nuclear power plant during four months of 2013. Automatic signal detection using beamforming was applied separately for each motion component. Two horizontal components were transformed into radial and transverse components for the given values of the velocity and azimuth of the plane wave front. We have investigated the dependence of the coherence of microseismic noise on frequency, azimuth, and slowness, as well as determining the level of cross-correlation between signals on separate channels in order to estimate expected improvement in the signal-to-noise ratio, which is crucial for signal detection. Most signals detected by the seismic array from regional sources are associated with quarry blasts. Using repetitive explosions at seven quarries, we have quantitatively estimated and compared the increase in detection efficiency of regional seismic phases using a three-component small aperture seismic array and a subarray of vertical sensors. Horizontal sensors showed a higher efficiency in the detection of transverse waves, while the subarray of vertical sensors missed S-waves from certain events. For one of the nearby quarries, the vertical subarray missed up to 25% of events (5 of 20). The results of the investigation point to the need for the use of three-component seismic arrays for the study of regional seismicity. 相似文献
4.
钻井过程中钻头对井底的冲击振动为钻头前方地层的探测提供了震源,可用来消除钻井过程中的地质不确定性和降低钻井风险.本研究在分析井下钻头振动信号特点的基础上,根据现代地震观测技术的新发展,将多道勘探地震仪和流动数字地震仪的性能进行了对比分析,将天然地震的观测设备和分析方法应用到随钻地震检测中,提出了一套新的随钻地震检测方案,利用高灵敏度流动数字地震仪连续检测钻井过程中的钻头振动信号,初步现场试验表明该技术方案可行,获得的信号信噪比高,易于钻井工程师掌握,为随钻地震技术提供了新的技术路线. 相似文献
5.
地震台阵是为了监测核爆而发展起来的一种地震观测系统。近年来,地震台阵被推广到地球内部速度间断面的研究中并极大地推动了地震学的发展。本文主要介绍处理台阵资料的技术方法,如聚束、倾斜叠加、N次根叠加、频率波数法以及相位加权叠加等,并讨论各种方法的优缺点。在提取微弱但相关信号方面,重点讨论相位加权叠加方法及现有的研究成果。结果表明,这些方法都在不同程度上提高了记录的信噪比,高质量的台阵数据使得地球内部速度结构的成像研究更加精细。 相似文献
6.
地球深部结构探测是地球物理学的核心领域,而地震体波可以深入地球内部且分辨率较高,是研究地球内部结构不可或缺的技术手段。基于背景噪声提取高信噪比体波信号技术的迅速发展,极大地促进了地震学的发展和应用范围,使其在地球深部结构成像、城市浅层空间探测等领域日益发挥出重要作用。本文详细综述了如何利用地震干涉法及台阵处理技术提取出用于研究不同探测尺度（局部、区域、全球）的各类体波信号。其中,地震干涉法通过对地震台站记录到的波形信号进行互相关,抵消掉重合的射线路径,最后得到台站对之间的地震记录;而台阵处理方法是基于接收器台阵发展起来的数据处理手段,该技术不仅能够进一步提高信噪比（SNR）,而且能够获得方位信息。一般来讲,背景噪声中包含的体波信号能量远低于面波信号能量,提取难度大。本文着重介绍了Bin-叠加法、双波束方法（DBF）以及相位加权叠加法（PWS）,并对3种方法的适用条件进行了总结。 相似文献
7.
M. H. SAFAR 《Geophysical Prospecting》1978,26(3):538-549
It is well known that the application of the “bright spot’ technique has been more successful in marine prospecting than in land prospecting. This is due partly to the problem of distortion of the seismic signal caused by the geophone-ground coupling, especially when carrying out high resolution, shallow seismic surveys in swampy terrain. The effect of geophone-ground coupling on the response of a single geophone to the incident compressional waves has been treated by several authors. However, they have always neglected the influence of mutual interaction between an array of geophones on the response of each geophone forming the array. We show that mutual interaction, which results from the re-radiation of the incident compressional waves by the geophones forming the array, can have considerable effect on the response of each geophone. The effect of the geophone-ground coupling on the response of a seismic channel is considered in the absence and presence of mutual interaction between a group of geophones for the case when the shear wave velocity of the soil varies by a factor of three. 相似文献
8.
根据汶川地震序列,选出距离合适、波形相关性较好的事件作为震源阵,联合永久台阵(那曲、和田台阵),进行震源阵与固定台阵组合研究,计算其台阵响应.结果表明,地震序列可以形成震源阵,按照地震台阵的特殊方法进行研究,可以提高信噪比,为揭示地下精细结构提供条件. 相似文献
9.
The time-honoured method of attenuating coherent noise in the seismic record is by the use of source and geophone arrays. In theory, and using methods familiar in the synthesis of digital frequency filters, arrays can be designed having virtually any desired response in the wavenumber spectrum. In practice, arrays cannot be implemented with the same precision that is applied in design. The response actually achieved must be compromized by a number of factors. These include inaccuracies in the effectiveness or positioning of individual array elements, variations in ground coupling, and the effect of local heterogenities in the environment of the array. We have no reliable way of knowing how well a particular array will perform from one location to the next. Statistical modelling methods have been applied to examine the effects of implementation errors. Experimental results, supported by statistical theory, show that errors are expected to impose a limit upon the rejection capabilities of an array. The expected limiting value of attenuation due to errors in element weights is inversely proportional to the standard deviation of errors and directly proportional to the square root of the number of array elements. Position errors exert a limiting influence which is wavenumber dependent such that attenuation decreases with increasing wavenumber. For arrays of common dimensions, Gaussian random errors of 10% standard deviation in element weights and positions result in an expected attenuation limit of about 30 dB. It follows that the more ambitious array designs are less tolerant of errors, and must be implemented with greater care and precision in the field. The present work enables us to specify tolerances for any particular array design. Ultimately, the degree of pattern refinement which may be effectively employed in any area is determined by errors which are associated with the array environment. Complex arrays are expensive to operate. In order to avoid over-design it would be useful to establish the magnitude of errors to be expected under different terrain conditions. 相似文献
10.
A new broadband electromagnetic induction (EMI) array sensor, GEM-5, for detecting and characterizing Unexploded Ordnance (UXO) has been developed in order to provide high production rates for EMI surveys. The sensor consists of a single rectangular loop transmitter around a linear array of seven pairs of coaxial receiver coils, with each coil in a pair located at the same vertical distance above and below the loop transmitter. The coil pairs are wired in an inverted series so that the signal consists of the difference between the voltage induced in the upper and lower coils. This particular configuration provides a high degree of primary field cancellation, dense spatial sampling rate due to simultaneous and continuous operation of all sensors, suppression of motion-induced and environmental noise, and strong source fields at typical UXO burial depths providing deep detection range. Our prototype tests indicate that the array yields a lower static and motion-induced noise over the critical low frequencies than that of existing sensors, and in particular, the signal-to-noise ratio at 90 Hz is 32 dB higher. Environmental noise can be largely removed from the difference measurements. The field test results from UXO test sites show that the prototype sensor has smoother background and appears to detect more seeded targets than the GEM-3 concentric sensor, however some of that gain can be attributed to higher power transmitter electronics. 相似文献
11.
For seismic observations in mines or wells, instead of three-component geophones, four-component ones with sensors located along the tetrahedral axes are sometimes used. When a geophone is placed in a hard-to-reach area for a long time, the requirements on its reliability increase, so it is necessary to monitor its operation. From this viewpoint, a four-component geophone has certain advantages over the conventional three-component geophone, the three ones being suppression of instrument noise for the recalculation of a four-component record into a three-component one, saving of the polarization analysis data in case one geophone component fails, and sensitivity control of individual geophone components. To suppress instrument noise in records from a four-component geophone, the following processing should be performed: first, calculation of the covariance matrix of recording components, second calculation of the eigenvalues and eigenvectors of the covariance matrix, and third, the parameter used to assess the ratio of instrument noise to the useful signal is calculated. After that, the operator projecting a four-component displacement vector onto a three-dimensional subspace is constructed. Application of this operator to data suppresses interference or noise (which do not correspond to motion in three-dimensional space). The output of the processing is data partially cleaned of instrument noise. In this paper, using model examples, we analyze the features of processing data from four-component geophones. The possibility of suppressing instrument noise and controlling the sensitivities of individual geophone components is demonstrated, and the effect on polarization analysis results is shown. 相似文献
12.
Distributed acoustic sensing is a growing technology that enables affordable downhole recording of strain wavefields from microseismic events with spatial sampling down to ∼1 m. Exploiting this high spatial information density motivates different detection approaches than typically used for downhole geophones. A new machine learning method using convolutional neural networks is described that operates on the full strain wavefield. The method is tested using data recorded in a horizontal observation well during hydraulic fracturing in the Eagle Ford Shale, Texas, and the results are compared to a surface geophone array that simultaneously recorded microseismic activity. The neural network was trained using synthetic microseismic events injected into real ambient noise, and it was applied to detect events in the remaining data. There were 535 detections found and no false positives. In general, the signal-to-noise ratio of events recorded by distributed acoustic sensing was lower than the surface array and 368 of 933 surface array events were found. Despite this, 167 new events were found in distributed acoustic sensing data that had no detected counterpart in the surface array. These differences can be attributed to the different detection threshold that depends on both magnitude and distance to the optical fibre. As distributed acoustic sensing data quality continues to improve, neural networks offer many advantages for automated, real-time microseismic event detection, including low computational cost, minimal data pre-processing, low false trigger rates and continuous performance improvement as more training data are acquired. 相似文献
13.
A suite of three tests was performed to characterize the signal fidelity of OBC 4C acquisition systems. The test methodology was to evaluate individual sensor stations by acquiring source lines that were parallel to the in‐line and cross‐line horizontal sensors and source lines that were at 45° to the in‐line and cross‐line sensors. This technique provides constant azimuth gathers with a uniform offset range and removes issues associated with source array directivity. Characterization of the test data identified the frequency content of the geophone signals and the correlation between the vertical and cross‐line geophones as the most sensitive indicators of signal infidelity. In the former case, stations with questionable signal fidelity exhibited a very reverberatory signal. This signal was most evident on the cross‐line sensor. In the latter case, when normalized cross‐correlation coefficients are computed in a moving window, the cross‐line sensor and the vertical sensor are highly correlated, beginning several hundred milliseconds after the first arrivals. These characteristics can be exploited to allow stations with questionable signal fidelity to be programmatically identified. One means of identifying questionable stations is to compute the histogram of the instantaneous frequency. The frequency distributions from questionable stations are unambiguously distinguishable from stations that exhibit better signal fidelity. It was noted that signal fidelity appeared as a range, between acceptable and poor. To characterize the signal fidelity of an acquisition system adequately, the number of test samples must be statistically significant. 相似文献
14.
当野外噪声很强,即使使用组合震源地震也无法获得满意信噪比的地震数据时,本文提出了一种基于可控震源阵列的定向照明控制方法,采用该方法可形成定向地震波.通过仿真研究合成了8激震器可控震源阵列分别采用简单组合及定向照明技术得到的单炮地震记录,可以看出采用合适的延时参数,定向照明单炮地震记录的反射波信噪比高于组合地震情况.定量的计算结果表明,实验条件下采用0.89 ms延时参数,各反射波信噪比分别提高了10.19 dB,3.23 dB和1.02 dB.由此可见,可控震源定向照明地震技术是一种提高原始地震资料信噪比的有效方法. 相似文献
15.
Surface arrays became an important tool for monitoring the induced seismicity in hydraulic fracturing experiments and for assessing the impact of fluid injection on the fracturing process of microearthquakes. The layout of sensors plays a key role in this task because it controls the accuracy of event locations and retrieved seismic moment tensors. We simulate various configurations of grid sensor arrays characterized by a different number of sensors, array span, sensor spacing, depth of sources and various shear/tensile source mechanisms of events. The moment tensor inversion is carried out using synthetically calculated P-wave amplitudes with added random noise. A bias in the solutions is evaluated by errors in the double-couple percentage of inverted moment tensors because the double-couple errors inform us about the sensitivity of the network to detect the shear/tensile fracturing mode of induced microearthquakes. The results show that the accuracy of the double-couple percentage is mostly controlled by the offset-to-depth ratio R defined as the ratio of half of the network size to the event depth. The optimum value of R is in the range of 0.75–1.5 irrespective of the type of the focal mechanism. If 121 (11 × 11) sensors are distributed in a regular grid and recorded data are characterized by a 10% random noise, the double-couple error is less than 6%. This error increases, if R is not optimum or if the number of sensors is reduced. However, even sparse arrays with 49 (7 × 7) or 16 (4 × 4) sensors can yield a reasonable accuracy, provided the surface grid arrays are designed to have an optimum size. 相似文献
16.
2007年西昌和天祝地电场观测台阵建立, 随后两年西昌台阵地电场的TGF-A波形明显, 天祝台阵则以TGF-B波形出现. 台阵内各台站间地电场相关性高, 这受地电场潮汐机理的支持; 不同台站或同一台站的不同方向地电场潮汐波峰谷值差异明显, 地电场潮汐机理和场地水文地质资料表明, 这主要与岩石、 裂隙度、 裂隙优势走向、 含水度、 透水率、 水矿化度和裂隙水压力差等因素相关. 潮汐电信号形成于裂隙水或水中电荷周期性移动, 电荷被岩壁吸附或脱离产生噪声, 该信噪比在同一台阵内基本相同, 信噪比值与潮汐电信号产生过程和场地电磁背景关系密切. 应用地电场潮汐谐波振幅计算裂隙水主体渗流方向, 结果与应用潮汐波峰谷值法基本一致, 这消除了峰谷值法取值的偶然误差. 2008年汶川MS8.0地震前, 两台阵内都存在场地裂隙水主体渗流方向的短临变异现象, 西昌台阵这种变异更明显. 相似文献
17.
The error properties of arrays of accelerometers were studied on the basis of systematic experiments and analysis of the differences in the recordings of collocated sensors. Four identical tri-axial force-balance accelerometers with common recordings and time stamping, were set at symmetrical positions on a prototype oscillator, a T-type inverted pendulum, and were subject to controlled excitations. Based on Finite Element Modeling (FEM) the response of the oscillator was modeled and there were identified time series of acceleration of different collocated sensors predicted to be identical (“comparable”). The differences of the corresponding “comparable” measurement time series, which are functions only of noise, were found important, indicating that the accelerometer arrays are characterized by significant dynamic noise and not by low-amplitude Gaussian noise, as is widely assumed.Further analysis of time series of accelerometer noise was based on spectral analysis techniques in the frequency and the time domain and on coherence, on filtering and on cross-correlation, as well as on examination of the impact of noise in the drift (errors computation of displacements using double numerical integration).The output of this study is that phase noise (jitter, or phase instability) characterizes accelerometers, as in the case with all other array sensors and sensor networks and this is a main source of dynamic noise. The latter becomes significant especially at the level of sampling interval (0.005 sec in our experiments), characterizes strong motions, is not constant and may be regarded as instrument-specific noise. Strategies to overcome this dynamic noise important for the modeling of structural response are discussed. 相似文献
18.
地震检波器受到地面横向运动激励时的输入输出关系定义为检波器的横向灵敏度特性.本文对检波器线圈受到横向激励时产生的轴向振动进行了分析.可以看到,当悬挂线圈的弹簧片悬丝发生动力失稳时,检波器的横向灵敏度突然增大;在线圈横向振幅很小的情况下,失稳频率接近悬丝的横向固有频率.利用谱分析技术可以准确地从检波器噪声中检测出检波器的横向灵敏度和失稳频率,即检波器假频. 相似文献
19.
Ambient noise as the new source for urban engineering seismology and earthquake engineering: a case study from Beijing metropolitan area 下载免费PDF全文
下载免费PDF全文 In highly populated urban centers, traditional seismic survey sources can no longer be properly applied due to restrictions in modern civilian life styles. The ambient vibration noise, including both microseisms and microtremor, though are generally weak but available anywhere and anytime, can be an ideal supplementary source for conducting seismic surveys for engineering seismology and earthquake engineering. This is fundamentally supported by advanced digital signal processing techniques for effectively extracting the useful information out from the noise. Thus, it can be essentially regarded as a passive seismic method. In this paper we first make a brief survey of the ambient vibration noise, followed by a quick summary of digital signal processing for passive seismic surveys. Then the applications of ambient noise in engineering seismology and earthquake engineering for urban settings are illustrated with examples from Beijing metropolitan area. For engineering seismology the example is the assessment of site effect in a large area via microtremor observations. For earthquake engineering the example is for structural characterization of a typical reinforced concrete high-rise building using background vibration noise. By showing these examples we argue that the ambient noise can be treated as a new source that is economical, practical, and particularly valuable to engineering seismology and earthquake engineering projects for seismic hazard mitigation in urban areas. 相似文献
20.
Denis Mougenot 《Geophysical Prospecting》2018,66(5):922-933
The broadband capabilities of marine, seabed, and land seismic equipment are reviewed with respect to both the source and the receiver sides. In marine acquisition, the main issue at both ends of the spectrum relates to ghosts occurring at the sea surface. Broadband deghosting requires towing at variable depth to introduce notch diversity or using new equipment like multi‐component and/or low‐noise streamers. As a result, a doubling of the bandwidth from about three to six octaves (2.5–200 Hz) has been achieved. Such improvement is not yet observed for seabed surveys in spite of deghosting being a standard process on the receiver side. One issue may be related to the coupling of the particle motion sensor, particularly at high frequencies. For land acquisition, progress came from the vibrators. New shakers and control electronics using broadband sweeps made it possible to add two more octaves to the low‐frequency signal (from 8 to 2 Hz). Whereas conventional 10 Hz geophones are still able to record such low frequencies, 5 Hz high gain geophones or digital accelerometers enhance them to keep the signal above the noise floor. On the high end of the bandwidth, progress is not limited by equipment specifications. Here, the issue is related to a low signal‐to‐noise ratio due to the strong absorption that occurs during signal propagation. To succeed in enlarging the bandwidth, these improved equipment and sweeps must be complemented by a denser spatial sampling of the wavefield by point–source and point–receiver acquisition. 相似文献