输水管网模糊地震可靠性的 Monte Carlo 法分析程序

本文详细介绍了笔者所建议的运用模糊图理论和方法进行城市输水管网的地震可靠性分析途径和计算程序。对于输水管网中每段管道的震害预测,建立了相应的专家系统。在此基础上,定义了管网系统的模糊可靠性,更好地反映了人们对于管道损坏状态估计的模糊性和对可靠性要求上的模糊性。以模糊矩阵来描述输水管网的状态是十分方便的。通过计算模糊矩阵的传递闭包,极易找出最短路、关键段等。由于地震作用和管道抗震能力都是随机的,因此整个管网系统的可靠性分析是藉助Monle Carlo法进行的。以Monle Carlo法对模糊图进行分析,从而得到管网的地震可靠性,这还是首次。用PASCAL和PROLOG编制了在微机上实用的计算机程序,特别是以智能语言PROLOG编制的程序,更有许多特色。由于采用了一些技巧,使在微机上可以分析相当大的系统,为城市抗震防灾工作提供了一个有力的工具。     

三探测器密度测井的Monte Carlo模拟

为了改善传统岩性密度测井仪的缺陷,本文基于传统的双 源距探测器密度测井仪,提出在负源距范围内增加一个反散射探测器,构成新的三探测器密 度测井仪器. 利用Monte Carlo方法通用程序MCNP(3B),从光子与地层相互作用的机理出发 ,计算得到了反散射探测器、长源距探测器和短源距探测器的光子通量的能谱分布、光子通 量与源距的关系、光子通量与地层密度的关系、源距与探测深度的关系以及计数能窗等. 从 结果看,三探测器密度测井仪的长、短源距探测器对地层的响应关系与双源距密度测井仪的 长、短源距探测器一致,而反散射探测器对地层具有明确的响应关系,其响应关系与长、短 源距探测器近似相反,且其计数率很高. 因此,在负源距范围内增加第三个探测器是可行的 ,这将有利于提高密度测井的测量精度和垂向分辨率. 同时表明了Monte Carlo方法在核测 井仪器早期研制中的有效性,对仪器设计具有指导作用.     

A PREDICTION OF SEDIMENTARY ENVIRONMENT FROM MARINE SEISMIC DATA *

Stratigraphic models are usually oversimplified by petroleum geologists, and the result is that the principles which we use for interpreting geophysical data are also over-simplified or even incorrect. Based on the marine seismic data from the Adriatic Sea, an example of prediction of a rather complex sedimentation model of detrital sediments is shown. On the basis of the stratigraphic interpretation using seismic techniques only for this some very important characteristics are discussed: — paleotopography of the valley and conditions which have given opportunity to map accurately the pre-depositional surface, — seismic signatures of the sedimentary section of the ancient valley in which we have recognized aluvial sequence and marine one. The conclusion is that there is a real opportunity for exploration of stratigraphic traps in this part of the Mediterranean Basin.     

碳氧比能谱测井的蒙特卡罗模拟

介绍碳氧比能谱测井蒙特卡罗模拟方法及软件,内容包括输运计算与探测器响应计算,其中中子诱发y使用了期望值技巧,γ散射采用指向概率法.计算结果可分别给出次级γ线光和连续光,还可给出被探测物或元素的非弹性谱和俘获谱,新方法基本解决了碳氧比能谱测井深穿透、低计数率的难题.     

THE CORRELATION OF SEISMIC VELOCITIES WITH FORMATIONS IN THE SOUTH-WEST OF SCOTLAND *

In seismic studies being carried out to elucidate the structure at depth of the Midland Valley rift and the Tertiary igneous province in the West of Scotland, a lack of deep boreholes makes the collection of velocity data imperative for identification of seismic events and for determinations of depth. Three methods are used to investigate the correlation of seismic velocities and geological formations. The results show as strong a dependence of velocity on method of measurement as on lithology and the wide spread of values within a given formation makes the attribution of discrete velocity ranges to specific formations impossible. Changes of velocity are more significant than absolute values. The variations in both are discussed.     

CALCULATION OF VELOCITY FROM SEISMIC REFLECTION AMPLITUDE *

It is not possible to determine accurate geological velocities from seismic velocity analysis for thin layers or complex structural features, especially under an unconformity. Instead, we can approach the problem of interval velocity with seismic amplitudes analysis and compute the reflection coefficient along the unconformity surface. An error estimation has been made on a model to test the possibility of such a method and to choose the best parameters to be used. The method has been applied on an actual case: the computed interval velocities show good correlation with the values obtained by a sonic log.     

NON-LINEAR ESTIMATION OF REFLECTION COEFFICIENTS FROM SEISMIC DATA*

For years, reflection coefficients have been the main aim of traditional deconvolution methods for their significant informational content. A method to estimate seismic reflection coefficients has been derived by searching for their amplitude and their time positions without any other limitating assumption. The input data have to satisfy certain quality constraints like amplitude and almost zero phase noise—ghosts, reverberations, long period multiples, and diffracted waves should be rejected by traditional processing. The proposed algorithm minimizes a functional of the difference between the spectra of trace and reflectivity in the frequency domain. The estimation of reflection coefficients together with the consistent “wavelet’ is reached iteratively with a multidimensional Newton-Raphson technique. The residual error trace shows the behavior of the process. Several advantages are then obtainable from these reflection coefficients, like conversion to interval velocities with an optimum calibration either to the well logs or to the velocity analysis curves. The procedure can be applied for detailed stratigraphic interpretations or to improve the resolution of a conventional velocity analysis.     

POROSITY PREDICTION FROM SEISMIC DATA*

The inversion of seismic traces allows the estimation of reservoir porosity from an analysis of transit times derived from the pseudo-velocity logs. A four-step computational procedure is illustrated consisting of (i) inversion of seismic traces and calculation of interval velocities; (ii) accurate stratigraphic interpretation; (iii) determination of the petrophysical parameters for the porosity evaluation; (iv) analysis of the reliability of the results and final corrections. Both the possibilities and the limits of the method are discussed. One of the causes of error is the fact that impedances—and not velocities—are readily obtainable from seismic data. Moreover, the porosity due to fracturation contributes only slightly to velocity, while it often contributes most importantly to the permeability. Results are shown for two of the most significant reservoir types, i.e. carbonatic and clastic. Two cases belonging to the latter type will be examined. In the first case the primary porosity is dominant. The second case is very complex and both primary and secondary porosity are present.     

A FIELD EXAMPLE OF THE USE OF ANISOTROPY PARAMETERS DERIVED FROM RESISTIVITY SOUNDINGS*

In areas where steep dips are encountered conventional practice in resistivity work has involved orienting arrays favourably in relation to the geological strike. In concealed conditions, however, the geological strike may not be known; moreover, strike may change with depth. Considerable advantage is to be gained, in such circumstances, by the use of crossed square arrays in that these yield orientationally insensitive resistivity measurements and also allow strike determinations and measurements of the effective vertical anisotropy. Two traverses of crossed square array observations are presented, together with one deeper sounding. The results show that, in favourable circumstances, reliable data on concealed strike directions can be obtained, and that the anisotropy findings greatly assist the subsequent interpretation. Model results pertinent to the field material are presented and discussed.     

MEASUREMENTS OF EARTH ATTENUATION FROM DOWNHOLE AND SURFACE SEISMIC RECORDINGS*

Frequency-dependent attenuation of compressional waves within the earth has been estimated in the vicinity of wells from

• 1 spectral power ratios of the coherent events in separate time gates on the seismic section
• 2 matching a broadband synthetic trace with seismic data at the well, and
• 3 determining the operator that transforms one down(up) going pulse recorded in the well into another recorded at a deeper (shallower) level.

The accuracy of estimation of all three methods was insufficient to estimate attenuation over small depth intervals, and it was not possible to distinguish between the contribution due to internal multiples and that of genuine absorption with much confidence. Spectral ratios from (1) showed a smoother variation with frequency—and one more consistent with other estimates—when they were compensated for the spectra of the reflectivities over the time gates employed, but they did not provide more than a broad indication of attenuation over a substantial depth interval. Approach (2) was hampered by the restricted durations over which synthetic trace and seismic data can be reliably matched; approach (3) gave the best results. Here matching is a much more powerful tool than the spectral-ratio techniques that are commonly applied since it can yield the form of the attenuation operator, i.e., both its amplitude and phase response, together with properly defined measures of its accuracy, while at the same time it minimizes the influence of noise and local interference effects at each recording level. For seismic target depths where internal multiple activity was low the logarithms of the amplitude responses of the estimated attenuation operators decreased approximately linearly with frequency and the phase responses showed no significant dispersion. Application of approach (3) to downgoing and upgoing waves estimated from a vertical seismic profile revealed the importance of changes in frequency-dependent geophone coupling and their effect on values of Q determined from downgoing pulses only.     

研究地球深部电导率结构的Monte—Carlo反演法

介绍了Ｍｏｎｔｅ－Ｃａｒｌｏ反演法的一种特殊设计：固定各层厚度,让各层电导率及汉数随机取样。文中研究和讨论了波数随机取样带来的问题。     

MIGRATION OF SEISMIC INTERFACES*

Most interpretation work is still based on stacked and not on migrated sections. In the case of heavy faulting and considerable velocity contrasts between formations, migration of interpreted interfaces poses a problem. In more detail, the problem may be specified as follows: — a given interpretation of a number of interfaces along with a given heterogeneous velocity field may not always have a plausible solution in the form of migrated interfaces in depth; — fault planes, salt boundaries, etc., are, in most cases, not directly interpretable in a section and are plotted by intuition using interface terminations as a guide; — the velocity field in fault zones is, in most cases, hard to determine. The interpreter may arrive at a plausible solution by repeating the migration process with various possible interpretations and various velocity assumptions. The subject of this paper is an algorithm based on ray-theory which allows one: — to handle faults and velocity variations at faults properly; — to perform migration in steps, working a particular geological unit at a time and proceeding to the next unit once the foregoing one has been properly migrated; — to display ray-paths, where necessary, for investigation of interface distortions, e.g., below fault areas. The algorithm is designed and implemented for application in an interactive environment. Inspection of intermediate and final results, investigation of interface distortions and modifications are performed on a graphics screen. Thus, various possible interpretations and velocity assumptions may be investigated within a short time. Interfaces interpreted on migrated sections may be over-migrated because of neglection of the influence of refraction in most section migration programs. This over-migration may also be corrected using the above algorithm in the “image ray” mode.     

THREE-DIMENSIONAL INTERPRETATION OF GRAVITY DATA FROM SEDIMENTARY BASINS USING AN EXPONENTIAL DENSITY-DEPTH FUNCTION*

In mapping the topography of the basement of deep sedimentary basins by gravity modelling, the accuracy can be improved by incorporating an exponential increase in density with depth. For calculating the gravity effect of a three-dimensional (3D) structure with such an exponential density-depth relation a frequency-domain forward algorithm based on series expansion is presented, the numerical evaluation of which can be performed efficiently by fast Fourier transform. The algorithm can be applied in a recursive procedure to give the inverse solution in terms of basement relief. The inversion procedure is satisfactorily tested on a 2D synthetic example and a 3D field example of gravity data from the western margin of the Pannonian Basin in eastern Austria, where up to 2.2 km of Tertiary sediments overlie an igneous or metamorphic basement. The results are confirmed by basement intersections in several wells.     

SEISMIC STRATIGRAPHY IN HIGH RESOLUTION SHALLOW MARINE SEISMIC DATA OF THE GEMLIK GULF1

Seismic stratigraphy and sedimentological studies of the Gemlik Gulf in the Sea of Marmara, Turkey, have been carried out. For this purpose, 19 lines totalling 189 km of excellent quality, high-resolution seismic data were recorded. Four major acoustic units were identified in the seismic profiles. Three were sedimentary units: irregular layered, cross-layered and well-layered; and the fourth was an acoustic basement which is probably composed of crystalline volcanic rocks. Some local areas in the Neogene formation contain gas accumulations. The formation of faults in E–W and N–S directions can be explained by the existence of shear stresses in the Gulf. The bathymetric map shows good accommodation with the shore line as does the tectonic map.     

地层学的进展对盆地研究的意义

地层学是地质研究的基本问题.从传统地层学发展到地震地层学及层序地层学,地层学的研究发生了一个极大的飞跃.其重要意义可与板块学说的问世相比拟.地震记录仪器的更新换代,地震学和地震勘探技术的发展,是层序地层学得以诞生的基础之一.运用层序地层学理论和方法确切地识别沉积相、沉积环境,建立完整的沉积体系,预测油气的生储盖组合,更易追踪对比的目标层.因此,它对于盆地研究具有非常重要的意义.     

ASPECTS OF VERTICAL SEISMIC RESOLUTION*

It is proposed that the vertical resolving power of a seismic signal is controlled by three aspects: the width of the central lobe, the side lobe ratio, and the side-tail oscillations. A comparative study of zero-phase signals covering the same frequency range shows that improvement of any one of these aspects inevitably leads to deterioration of one of the other aspects. An analytical simulation model is proposed of zero-phase signals free from side-tail oscillations, in which both the width of the central lobe and the side lobe ratio are adjustable. Analysis of the spectra of this model shows that, while the high frequency content of the spectrum is essential for obtaining a small width of the central lobe, the low frequency content of the spectrum plays an essential part in causing a low value of the side lobe ratio.     

蒙特卡罗反演法的改进及其在大地电磁测深资料解释中的应用

本文将Jones的蒙特卡罗反演法,与修改后的马夸特反演法有机地结合在一起,从而获得了一种新的蒙特卡罗反演法.它实际上是定向求解与随机求解的结合,具有占用机时短及解的拟合度高的优点.作者利用该法处理了理论视电阻率曲线,及实测的视电阻率曲线,获得了大量具有高拟合度的模型,进而获得了可能解的范围.      

VELOCITY DISPERSION OF SEISMIC WAVES*

In well velocity surveys made to calibrate Sonic (CV) Logs the calibration survey uses frequencies around 50 Hz whereas the Sonic Logging tool uses frequencies around 20 kHz. There thus exists the possibility of making a direct measure of velocity dispersion. In any one survey the disturbing factors, both instrumental and operational, will often mask any dispersive effect that might exist. Consequently this paper reports on a statistical analysis of the velocity differences resulting from calibration surveys and Sonic logs. Only Borehole Compensated Sonic Logs were used. Four areas were investigated: the North Sea, Abu Dhabi, Libya and Alaska. After rejecting logs and calibration records which were obviously in error there remained 424000 feet (about 130 km) of usable log distributed throughout 66 wells. The four areas were analysed separately and in no case was the estimated dispersion significantly different from zero. However, the mean values did correlate with lithology from (? 0.17 ± 0.18)% for the essentially carbonate section in Abu Dhabi to (+ 0.45 ± 0.25)% for the sand-shale section in Alaska, a positive sign meaning that the higher frequencies travelled faster. Except for Alaska the calibration surveys were made with a wall-clamp geophone, and for these areas amplitude measurements were made. After suitable corrections estimates of the absorption parameter Q were obtained. These varied from 20 to 200 with mean values of 63 for Libya, 70 for Abu Dhabi and 88 for the North Sea (excluding the Tertiary). If, as is usually assumed, the absorption mechanism is linear and is described by a Q which is independent of frequency, then these values would necessarily imply dispersion of several percent. As instanced above no such dispersion was observed. It is possible that the expected dispersion was compensated for by invasion of the mud filtrate into the borehole walls, but it is more likely that the absorption mechanism was substantially non-linear.     

OFFSET CONTINUATION OF SEISMIC SECTIONS*

Geometrical acoustic and wave theory lead to a second-order partial differential equation that links seismic sections with different offsets. In this equation a time-shift term appears that corresponds to normal moveout; a second term, dependent on offset and time only, corrects the moveout of dipping events. The zero-offset stacked section can thus be obtained by continuing the section with maximum offset towards zero, and stacking along the way the other common-offset sections. Without the correction for dip moveout, the spatial resolution of the section is noticeably impaired, thus limiting the advantages that could be obtained with expensive migration procedures. Trade-offs exist between multiplicity of coverage, spatial resolution, and signal-to-noise; in some cases the spatial resolution on the surface can be doubled and the aliasing noise averaged out. Velocity analyses carried out on data continued to zero offset show a better resolution and improved discrimination against multiples. For instance, sea-floor multiples always appear at water velocity, so that their removal is simplified. This offset continuation can be carried out either in the time-space domain or in the time-wave number domain. The methods are applied both to synthetic and real data.     

ABOUT A METHOD OF REPRESENTATION OF IP-VALUES OBTAINED OVER SEDIMENTARY FORMATIONS (TWO LAYER CASES).*

An operative technique is described along with a method of representation of Induced Polarization values obtained over homogeneous rocks against the electrical power per unit volume. The results of similar experiments over two-layer ground, are shown according to the same operative technique and method of representation. With the method of representation suggested in this paper it is possible to distinguish discontinuities and to get information about the thickness of the upper medium.