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1.
Break through the limits of vibroseis data quality 总被引：1，自引：0，他引：1
The vibroseis method has become the principal data acquisition method in land seismic exploration. It seems that this method has been extended to its limits as the search for energy resources continues. Many practical issues arising from field operations have remained theoretically unexplained, for example, variations in wavelet arrival time, inaccurate wavelet estimation and harmonics in the wavelet itself. The focus of this paper is the proposal of a new model, which is referred to as the vibrator‐coupled ground model, to simulate the filtering effects of a complex coupling system consisting of the coupling between the baseplate and the ground as well as the coupling between the captured ground mass near the vibrator baseplate and the surrounding earth. With this vibrator‐coupled ground model many of the practical issues mentioned above were reasonably addressed. Furthermore, it was demonstrated from experimental tests that both the pilot sweep and the weighted‐sum groundforce, when filtered by the vibrator‐coupled ground model, are proportional to the far‐field particle velocity whereas the unfiltered signals are not. The harmonics on the filtered weighted‐sum groundforce successfully maintain a proportional relationship with the harmonics seen in the far‐field signal. 相似文献
2.
Modelling and modal analysis of seismic vibrator baseplate 总被引：1，自引：0，他引：1
Zhouhong Wei 《Geophysical Prospecting》2010,58(1):19-32
The vibroseis method must be extended to its limits as the search for oil and gas continues on land. To successfully improve vibroseis data quality, it is crucial to evaluate each element in the vibroseis data acquisition system and ensure that the contribution from each element is successful. Vibroseis systems depend greatly upon the ability of vibrators to generate synchronous, repeatable ground-force sweeps over a broad frequency range. This requires that the reaction mass and the baseplate of the vibrator move as rigid bodies. However, rigid-body motion is not completely true for high- frequency vibrations, especially for the vibrator baseplate. In order to accurately understand the motion of the vibrator baseplate, a finite element analysis model of the vibrator baseplate and the coupled ground has been developed. This model is useful for simulating the vibrator baseplate dynamics, evaluating the impact of the baseplate on the coupled ground and vibrator baseplate design. Model data demonstrate that the vibrator baseplate and its stilt structure are subject to six significant resonant frequencies in the range of 10–80 Hz. Due to the low rigidity of the baseplate, the baseplate stilt structure experiences severe rocking motions at lower frequencies and the baseplate pad experiences severe flexing motions at higher frequencies. Flexing motions cause partial decoupling, which gives rise to increased levels of harmonic distortion and less useable signal energy. In general, the baseplate pad suffers more bending and flexing motions at high frequencies than low frequencies, leading less efficiency in transmitting the useable energy into the ground. 相似文献
3.
The wavefield in, and at the surface of, a homogeneous, isotropic, perfectly elastic half-space, excited by a traction distribution at the surface of the medium is investigated. The emitted wavefield is a spatial convolution of the surface tractions and the spatial impulse response. The properties of the wavefield in the far-field of the medium are derived and it is shown that the far-field particle velocity is essentially equal to a weighted sum of the time derivative of the integrated surface tractions, that is, of the components of the ‘ground force’. The theory is valid for an arbitrary geometry and orientation of the surface tractions, and is independent of the boundary conditions at the surface of the medium. The surface tractions are related to a source that consists of a mass distribution with an arbitrary force distribution imposed upon it. A boundary condition is introduced that accounts for the mass load and the forces applied to it but neglects vibrations within the mass. The boundary condition follows from the equation of motion of the surface mass load. The theory is applied to the Vibroseis configuration, using a P-wave vibrator model with a uniformly distributed force imposed on top of the baseplate, and assuming that horizontal surface traction components are absent. The distribution of displacement and stress directly underneath the baseplate of a single vibrator and an array of vibrators is investigated. Three different boundary conditions are used: (1) assuming uniform pressure, (2) assuming uniform displacement, (3) using the equation of motion of the baseplate as a boundary condition. The calculations of the distribution of stress and displacement over the plate for different elastic media and several frequencies of operation show that only the results obtained with the mixed boundary condition agree with measurements made in the field. The accuracy of three different phase-feedback signals is compared using synthetic data. Baseplate velocity phase-feedback leads to huge deviations in the determination of the far-field wavelet; reaction mass acceleration phase-feedback looks stable but neglects the differentiating earth filter; and phase-feedback to a weighted sum of baseplate and reaction mass accelerations becomes unstable with increasing frequency. The instability can be overcome using measurements over the whole baseplate. The model can be extended to a lossy layered earth. 相似文献
4.
Geophysical benefits from an improved seismic vibrator 总被引：1，自引：0，他引：1
The seismic vibrator has become a very important source for land data acquisition and there have been dramatic improvements in recent times in the application of the vibroseis technique. These improvements have led to much increased productivity and in many cases much denser source sampling. At the same time, the vibrator itself has seen little improvement over the last couple of decades. There are needs in a few areas where an improvement in the vibrator itself can bring benefits to the quality of the seismic data acquired. This paper describes progress in four such areas, low‐frequency performance, high‐frequency performance, an improved estimate of the vibrator groundforce and source signature consistency over variable ground conditions. Each of these vibrator characteristics will be discussed in turn. Meanwhile, two field test results in which the performance of two different vibrators in these four areas are compared. 相似文献
5.
For a linear elastic Earth the time derivative of the ground force is considered proportional to the far-field wavelet. Under the assumption that the baseplate is stiff and the bending forces of the baseplate are negligible, the ground force is also approximated by the sum of the accelerations of the baseplate and the reaction mass weighted by the respective masses. Combining these two assumptions, the time derivative of the weighted sum is considered proportional to the far-field wavelet. This result, often referred to as the far-field wavelet assumption, although convenient and most often employed is not always valid. We explore its validity using the spectral harmonic ratios of recorded data, which are used extensively in data filtering and analysis of vibratory data. We show that the far-field wavelet assumption fails particularly for harmonic components of even order. More compact soil after repeated shots further invalidates this assumption. Non-linear modelling of the ground under the vibrator point may provide a direction towards solving this discrepancy. Finally, we describe a method for the estimation of the harmonic spectral ratios. 相似文献
6.
The output from the hydraulic vibrators typically used for land seismic surveys is controlled by monitoring the acceleration measured by accelerometers mounted on the reaction mass and baseplate. The considerable energy output by such vibrators, which are coupled with the sensitivity of the accelerometers used, results in crosstalk if more than one vibrator is being used. In this paper, we present the results of a field experiment in which we measured the crosstalk between two adjacent vibrators. We found that the level of crosstalk was approximately ‐20 dB when the vibrators were adjacent but decreased with increasing frequency and separation. This result has implications for measurements of vibrator performance, source‐signature deconvolution, and in particular, estimates of the total energy output by a fleet of vibrators. 相似文献
7.
DENNIS K. REUST 《Geophysical Prospecting》1993,41(1):43-60
The Pelton DRTM Servovalve Enhancement causes the natural output of a vibrator to resemble the desired output more closely. This simplifies the control problem and reduces harmonic distortion. The traditional type of servovalve used on seismic vibrators is a flow-control servovalve. Flow is proportional to a vibrator's baseplate velocity, with respect to its reaction mass. The new servovalve control parameter is pressure rather than flow. The differential pressure applied to a vibrator's actuator piston, multiplied by the area of the piston, equals the force applied to the vibrator's baseplate structure. This may be defined as actuator force. There is a simpler and more linear relationship between actuator force and ground force than between actuator velocity and ground force. Thus, it is better for the servovalve to control pressure into the actuator rather than flow. A flow-control servovalve can be made to control pressure by sensing the differential pressure across a vibrator's actuator piston and applying it as a negative feedback around the servovalve main stage. This has been carried out and tested. The result is more accurate vibrator control and reduced harmonic distortion. 相似文献
8.
J. E. MARTIN 《Geophysical Prospecting》1993,41(8):943-967
An experiment was undertaken at BP's Fulbeck Geophysical test site to compare the viability of various simultaneous vibroseis recording techniques, which are often recommended as a means of improving data acquisition production rates for 3D seismic surveys. Of particular interest were: (a) the ability to separate the signals from each source during processing, (b) the generation and suppression of harmonics and (c) the effects of any source interaction. Two vibrators were deployed with a baseplate separation of 10 m, about a borehole containing a vertical array of geophones. Our analysis concentrated on the groundforce signals measured at each vibrator and the far-field signatures measured using a vertical geo-phone at a depth of 204 m. By comparing single vibrator records with similar but separated records from a simultaneous recording sequence, signal separability, harmonic suppression and vibrator interaction could be fully studied. Separated far-field signatures from simultaneous vibroseis methods using combinations of up and downsweeps exhibited unsuppressed harmonics and substantial energy from the undesired source which leaked through the correlation process. The ‘up/down’ method was capable of separating the signal from each source by only 12.7 dB, and is therefore unsuitable as a field technique. The variphase simultaneous vibroseis methods studied afforded some harmonic suppression and gave signal separations of about 30.0 dB. Use of variphase simultaneous vibroseis methods will compromise the quality of the data recorded, when compared with single-source acquisition methods. None of the simultaneous vibroseis methods tested provided adequate signal separation and, therefore, cannot be recommended as data acquisition techniques. The ‘alternate sweeping’ method coupled with multispread recording will give the desired improvement in data acquisition rates, while preserving the necessary quality of our seismic data. 相似文献
9.
High Fidelity Vibratory Seismic (HFVS) acquisition and separation can play an important role in today's land acquisition schemes. The method – in which multiple vibrators are swept simultaneously using sweeps with known phase encoding and then the data are inverted and separated into individual records – can improve productivity in the field and at the same time improve signal characteristics in the data. It relies on the measured weighted sum of accelerations (base plate and reaction mass) to invert the acquired data and separate the individual vibrator responses. Separation can be sub-optimal if the measured motions vary from the 'true source' input into the ground. Differences in true source and measured source can arise due to poor coupling between vibrators and ground, soil compaction or other factors. Using both a synthetic model and real data, we show that if the true source changes between sweeps but is not measured, vibrator responses can leak into adjacent vibrator responses upon separation. In a recent survey with HFVS acquisition, we observed a 25–30 dB separation between adjacent vibrators, which could be improved with greater reliability of the source measurement. The vibrator leakage can reduce the data quality considerably. We discuss the results of this survey and show that separation is affected by source measurement error. Further, we conclude that it is necessary either 1) to use source measurements that can capture the variability of the true source between sweeps or 2) to compensate for the source measurement variations in processing or in acquisition. 相似文献
10.
The quality of Vibroseis survey data can be improved by continuously monitoring the vibrator's baseplate and reaction mass accelerations. Equipment failures can be detected as they occur, rather than relying on similarity trials at the beginning and end of the day's production. Equipment faults can then be corrected as they happen and thus would not have a detrimental effect on the quality of the survey data. Source efficiency can be optimized by monitoring the amount of harmonic distortion generated by the vibrator at different drive levels on the different surfaces which may be encountered during a survey. Phase problems introduced by poor coupling of the baseplate to the ground can also be identified and addressed in the field. Rapid analysis of vibrator signals is required if continuous monitoring is to be useful. Frequency-time (f-t) analyses of vibrator signals are often used in processing centres, but are slow and require a large storage capacity which makes the technique unsuitable for a field analysis system. The two methods proposed to analyse vibrator signals entail the use of hodograms and time-varying notch filters. Hodograms provide a qualitative analysis of harmonic distortion and vibrator performance. A fast, time-varying notch filter gives quantitative and qualitative information about the harmonic distortion present in the signal and can be used to identify problems with vibrator behaviour. Both the hodogram and fast, time-varying notch filter methods can analyse the vibrator's reaction mass and baseplate accelerations as it progresses through its sweep and can present automatically interpreted results to the operator before moving to the next vibrator point. 相似文献
11.
Zhouhong Wei 《Geophysical Prospecting》2009,57(1):151-161
Several mechanical and hydraulic limitations hinder the ground-force energy output of a seismic vibrator at low frequencies. The hydraulic pump flow, pump response time, reaction mass stroke, servo valve stroke, engine horsepower, accumulator size, harmonic distortion and vehicle chassis isolation each play a role in limiting the ground-force energy output of vibrators. In addition, the peak-decoupling force – which is defined as the smaller value of either the maximum peak force or the hold-down weight – also plays a role in limiting ground-force energy production. A model useful for simulating seismic vibrator dynamics is developed to evaluate the impact of these parameters on the vibrator fundamental force envelope at low frequencies. Model data show that among these factors the reaction mass stroke and the peak-decoupling force are key parameters for setting the target fundamental force that can be achieved at low frequencies. Formulas are derived to estimate fundamental force, peak force and the reaction mass displacement. These formulas can serve as guidelines for sweep designers who plan to design low frequency sweeps with considerable dwell time in the lower frequency ranges. Test data show that formulas can be used to profile the vibrator envelope at low frequencies. 相似文献
12.
W.E. Lerwill 《Geophysical Prospecting》1981,29(4):503-528
The amplitude and phase response of a simple model is compared with the performance of a real vibrator working in the field. The field results show a characteristic phase response which confirms that the real drive force applied to the baseplate and its load impedance is faithfully represented by the acceleration of the reaction mass. It follows that all the parameters necessary to calculate the load impedance and the true power dissipated in the earth can be measured at the output of the vibrator. It also follows that the current method of baseplate phase compensation should be reconsidered. 相似文献
13.
R.M. Laws D. Halliday J.-F. Hopperstad D. Gerez M. Supawala A. Özbek T. Murray E. Kragh 《Geophysical Prospecting》2019,67(6):1443-1471
Marine seismic vibrators are generally considered to be less intrusive than airguns from an environmental perspective. This is because they emit their energy spread out in time, rather than in a single, high-intensity pulse. There are also significant geophysical benefits associated with marine vibrators, and they stem from the ability to specify in detail the output acoustic waveform. The phase can be specified independently at each frequency. Such detailed control cannot be achieved with conventional airgun sources, where the phase can only be modified using simple overall time delays. The vibrator phase can be employed in several different ways: it can be applied to the overall source phase in a sequence so that it varies from one source point to the next; it can be applied to the individual vibrators within the source array so the source directivity is changed; it can be applied to the overall source phase of each source in a simultaneous source acquisition. Carefully designed phase sequences can attenuate the residual source noise, and this in turn allows extra source points to be interleaved between the conventional ones. For these extra source points, the relative phase of the vibrators within the array can be chosen to create a transverse gradient source, which illuminates the earth predominantly in directions out of the plane of the sail line without left/right ambiguity. If seismic vibrator data are acquired using interleaved conventional and transverse gradient sweeps, more information is collected per kilometre of vessel travel than is the case in conventional acquisition. This richer data acquisition leads to the possibility of acquiring all the necessary seismic data in a shorter time. Three-dimensional reconstruction techniques are used to recover the same image quality that would have been obtained using the conventional, more time-consuming acquisition. For a marine vibrator to be suitable for these techniques it must, in general terms, have ‘high fidelity’. The precise device specifications are defined through realistic end-to-end simulations of the physical systems and the processing. The specifications are somewhat more onerous than for a conventional vibrator, but they are achievable. A prototype vibrator that satisfies these requirements has been built. In a simulated case study of a three-dimensional deep-water ocean bottom node survey, the seismic data could have been acquired using marine vibrators in one third of the time that it would have taken using airguns. 相似文献
14.
Developments in vibrator control 总被引：1，自引：0，他引：1
Hydraulic limitations, non-rigidity of the baseplate as well as variable characteristics of the ground constantly distort the downgoing energy output by vibrators. Therefore, a real time feedback control must be performed to continuously adjust the emitted force to the reference pilot signal. This ground force is represented by the weighted sum of the reaction mass and the baseplate accelerations. It was first controlled with an amplitude and phase locked loop system, poorly reactive and sensitive to noise. Later on, new vibrator electronics based on a digital model of the vibrator were introduced. This model is based on the physical equations of the vibrator and of the ground. During an 'identification' process, the model is adjusted to each particular vibrator. Completed by a Kalman adaptive filter to remove the noise, it computes ten estimated states via a linear quadratic estimator. These states are used by a linear quadratic control to compute the torque motor input and to compare the ground force estimated from the states with the pilot signal. Test results using downhole geophones demonstrate the benefit of filtered mode operation. 相似文献
15.
讨论了几种非线性扫描信号自相关函数的旁瓣特性.对可控震源非线性扫描的地震响应进行了数值模拟.当震源扫描持续时间是检波器接收时间的一半时，相关运算把反射扫描信号压缩成脉冲信号的效果是显著的.有限度地增加震源扫描持续时间以及与之相适应的接收时间可以使反射扫描信号得到进一步的压缩，但在固定扫描与接收时间的条件下，增加采样点个数对反射扫描信号的压缩并不起作用.采用具有低频相关子波特性的非线性扫描震源信号，将有利于相关噪声的消除.模拟结果还证实了二次扫描在某些特定条件下会出现鞍点效应这样一个事实. 相似文献
16.
Since its introduction in the late 1950s, hydraulic vibrators have become the dominant source for land seismic surveys. The hydraulic vibrators typically used for commercial land seismic acquisition, however, are large, costly to operate and expensive to purchase. This inhibits their use for small-scale and short-duration surveys as well as Vibroseis research. In this paper we describe, in detail, the construction of a portable vibrator from commercially available components for a cost of less than $US2,000. Data shows that the vibrator is able to successfully transmit sweeps from 15 to 180 Hz with different spectral contents. The vibrator produces a stronger signal than a sledgehammer and we estimate its output to be around 1 kN. The frequency content of the data was concentrated at lower frequencies (<100 Hz) and the ground-roll was far more energetic than that produced using a sledgehammer. 相似文献
17.
Sinem Yavuz Roman Pevzner Sofya Popik Konstantin Tertyshnikov Todd Wood Michelle C. Robertson Julia Correa Barry Freifeld 《Geophysical Prospecting》2022,70(1):108-120
Time-lapse seismic is one of the main methods for monitoring changes in reservoir conditions caused by production or injection of fluids. One approach to time-lapse seismic is through permanent reservoir monitoring, whereby seismic sources and/or receivers are permanently deployed. Permanent reservoir monitoring can offer a more cost-effective and environmentally friendly solution than traditional campaign-based surveys that rely on temporarily deployed equipment while facilitating more frequent measurements. At the CO2CRC Otway Project, surface orbital vibrators were coupled to a buried geophone array to form a permanent reservoir monitoring system. These are fixed position seismic sources that provide both P and S waves using induction motor-driven eccentric masses. After an initial injection of CO2 in February 2016, five months of continuous seismic data were acquired, and reflection imaging was used to assess the system performance. Analysis of the data showed the effects of weather variations on the near-surface conditions and the sweep signatures of surface orbital vibrators. Data processing flows of the continuous data was adapted from Vibroseis four-dimensional data processing flows. Ground roll proved a significant challenge to data processing. In addition, variations in the surface wave pattern were linked to major rainfall events. For the appraisal of surface orbital vibrators in imaging, a Vibroseis four-dimensional monitor survey data with similar geometry was also processed. Surface orbital vibrators are observed to be reliable sources with a potential to provide a repeatable signal, especially if the ground roll should fall outside the target window of interest. To guide future permanent reservoir monitoring applications, a repeatability analysis was performed for the various key data processing steps. 相似文献
18.
M. H. SAFAR 《Geophysical Prospecting》1984,32(3):392-405
It is well recognized that in order to realize the full potential of the Vibroseis technique, one needs to ensure accurate phase locking and a meaningful cross-correlation. To achieve these two important objectives we require an accurate estimate of the compressional stress wave radiated by the vibrator into the ground. In this paper a simple method (subject of a patent application) is developed for predicting the compressional stress waves radiated by a vertical vibrator. The main feature of the proposed method is that it involves the field measurement of the acceleration of the reaction mass and the baseplate, respectively. The method is illustrated by computing the compressional stress waves generated by a typical vertical vibrator radiating into ice, chalk, sand, and mud. It is shown that for a seismic vibrator radiating into hard ground the pressure of the downgoing P-wave is 180° out of phase with the baseplate velocity. It is also shown that when the driving force of the seismic vibrator has a flat amplitude spectrum, the amplitude spectrum of the downgoing P-wave falls off by 6 dB/octave towards low frequencies. 相似文献
19.
针对地震勘探资料湮没在随机噪声中的微弱同相轴问题提出基于混沌理论的混沌振子检测算法. 利用修正的Duffing_Holmes方程建立检测微弱同相轴的混沌振子系统,之后经过对同相轴的扫描处理,构成新子波等时间间隔序列W(t),与此同时对随机噪声也进行相同的截断. 截断的随机噪声在混沌振子系统中可以具有与周期信号相同的表现;经过大量仿真实验确定出满足通常地震勘探子波延续时间的使混沌振子检测子波不呈现周期相态的随机噪声截断时间范围. 选用与松辽盆地T1、T2反射层类似的子波函数并构成待检微弱周期信号,经过MATLAB仿真试验成功地检测出该弱信号,信噪比达到约-103dB. 相似文献
20.
电磁驱动式可控震源在城市浅层地震勘探中所面临的最突出的困难是微弱的反射信号常常淹没在很强的背景噪声之中.为了提高地震记录的信噪比，可以利用多台可控震源阵列实施相位控制形成定向地震波束以增强地震波的能量.本文讨论这种相控阵震源的波束形成机制.引入了地震波场的边际能量密度的概念，利用地震波场的时间切片技术，对模型空间各个方向上的能量强度进行了定量分析.用有限差分法对相控阵震源Chirp信号扫描的地震响应进行了数值模拟.当定向地震波束的汇聚带与观测排列的空间范围相一致时，相控阵震源合成地震记录的能量强度要显著高于单个可控震源情形的能量强度，波形振幅的均匀性要明显优于常规组合激发震源情形波形振幅的均匀性. 相似文献