Post-stack high-resolution deconvolution using Cauchy norm regularization with FX filter weighting

High-resolution deconvolution can mathematically be viewed as a regularized inverse problem. Besides, the result of the high-resolution deconvolution is generally accepted as reflectivity series of the layered media. On the other hand, lateral continuity is frequently poorer than vertical resolution on post-stack seismic section after application of any high-resolution deconvolution. However, because of the ill-posed inherent of the deconvolution problem, the Cauchy norm regularization term, a non-quadratic prior-information is widely used to provide the stability and uniqueness of the problem. But, it does not provide adequate quality of deconvolution if the noise in the data is strong. In this study, a stable and high-resolution deconvolution of post-stack seismic data was accomplished by an iterative inversion algorithm incorporating the Cauchy norm regularization with FX filter weighting. Cauchy norm regularization was utilized to force the solution to a spikiness structure, while the effective random noise reduction was performed by using the FX filter. Applications to synthetic and real post-stack data showed that the resolution in the vertical direction and continuity in the lateral direction are better improved. Thus, we think that this process makes seismic sections obtained especially from thin layered sedimentary basins more interpretable.     

History matching time-lapse seismic data using the ensemble Kalman filter with multiple data assimilations

The ensemble Kalman filter (EnKF) has become a popular method for history matching production and seismic data in petroleum reservoir models. However, it is known that EnKF may fail to give acceptable data matches especially for highly nonlinear problems. In this paper, we introduce a procedure to improve EnKF data matches based on assimilating the same data multiple times with the covariance matrix of the measurement errors multiplied by the number of data assimilations. We prove the equivalence between single and multiple data assimilations for the linear-Gaussian case and present computational evidence that multiple data assimilations can improve EnKF estimates for the nonlinear case. The proposed procedure was tested by assimilating time-lapse seismic data in two synthetic reservoir problems, and the results show significant improvements compared to the standard EnKF. In addition, we review the inversion schemes used in the EnKF analysis and present a rescaling procedure to avoid loss of information during the truncation of small singular values.     

Restoration of seismic data using the two-dimensional DMO equation

This paper presents a method for restoring missing seismic traces by using the two-dimensional dip moveout (DMO) equation. A fundamentally new formulation of the initial-boundary-value problem based on the Goursat problem is proposed. A modified finite element method is used for numerical solution. The method is tested on model examples and actual seismic data.     

Modeling of seismic hazard for Turkey using the recent neotectonic data

Recent developments in the neotectonic framework of Turkey introduced new tectonic elements necessitating the reconstruction of Turkey's seismic hazard map. In this regard, 14 seismic source zones were delineated. Maximum earthquake magnitudes for each seismic zones were determined using the fault rupture length approximation. Regression coefficients of the earthquake magnitude–frequency relationships for the seismic zones were compiled mostly from earlier works. Along with these data, a strong ground motion attenuation relationship developed by Joyner and Boore [Joyner, W.B., Boore, D.M., 1988. Measurement, characterization, and prediction of strong ground motion. Earthquake Engineering and Soil Dynamics, 2. Recent Advances Ground Motion Evaluation, pp. 43–102.] was utilized to model the seismic hazard for Turkey using the probabilistic approach. For the modeling, the “earthquake location uncertainty” concept was employed. A grid of 5106 points with 0.2° intervals was constituted for the area encompassed by the 25–46°E longitudes and 35–43°N latitudes. For the return periods of 100 and 475 years, the peak horizontal ground acceleration (pga) in bedrock was computed for each grid point. Isoacceleration maps for the return periods of 100 and 475 years were constructed by contouring the pga values at each node.     

Random seismic noise attenuation data using the discrete and the continuous wavelet transforms

In this paper, we propose a technique of random noise attenuation from seismic data using discrete and continuous wavelet transforms. Firstly, the discrete wavelet transform (DWT) is applied to denoise seismic data using the threshold method. After, we calculate the continuous wavelet transform of the denoised seismic seismogram, the final denoised seismic seismogram is the continuous wavelet transform coefficients at the lower scale. Application to a synthetic seismogram shows the robustness of the proposed tool for random noise attenuation. Application to real vertical seismic profile recorded in Algeria clearly shows the efficiency of the proposed tool for random noise attenuation.     

Mapping hydraulic fractures from tiltmeter data using the ensemble Kalman filter

Hydraulic fracturing involves the initiation and propagation of fractures in rock formations by the injection of pressurized fluid. The largest use of hydraulic fracturing is in enhancing oil and gas production. Tiltmeters are sometimes used in the process to monitor the generated fracture geometry by measuring the fracture‐induced deformations. Fracture growth parameters obtained from tiltmeter mapping can be used to study the effectiveness of such stimulations. In this work, we present a novel scheme that uses the ensemble Kalman Filter (EnKF) to assimilate tiltmeter data using a simple process model to describe the evolution of fracture growth parameters, and an observation model that maps the fracture geometry with the observed tilt. The forward observation model is based on the analytical solution for computing the displacements and tilts due to a point source displacement discontinuity in an elastic half‐space developed by Okada 1 . The displacement and tilts for any given fracture geometry are then obtained by numerical integration of this solution, by considering multiple point sources to be located at the quadrature points. The proposed method is validated using synthetic data sets generated from polygon and elliptical shaped fracture geometries. Finally, real data from a field site, where asymmetry was measured from the intersections of the hydraulic fracture with offset boreholes, have been analyzed. Preliminary results show that, in addition to extracting the fracture dip, orientation, and volume, the procedure is able to satisfactorily predict fracture growth parameters when the fracture is relatively close to the tiltmeter array and provides some insight into the development of asymmetry when the measurements are relatively far from the fracture plane. Copyright © 2015 John Wiley & Sons, Ltd.     

利用地震P波确定煤层瓦斯富集带的分布

查明煤层瓦斯富集区域,对可能的瓦斯突出点进行预报,是当前煤矿生产中亟待解决的重要课题。利用地震P波对裂缝性地层所表现出的方位各向异性特征,根据地震属性随方位角变化可以预测裂隙发育方向和密度的基本原理,应用多种地震P波方位属性预测裂隙发育带。通过对淮南张集煤矿西三采区三维地震P波资料的处理,获得6个方位地震数据体,从中提取多种与煤层和围岩裂隙相关的地震属性,并计算出裂隙的发育方向和密度,为确定瓦斯富集带的分布提供了一种新的途径。     

Converted phases analysis of the Campi Flegrei caldera using active seismic data

We applied a type of depth migration for converted seismic phases to active and passive seismic data sets from the Campi Flegrei volcanic region in southern Italy. The migration method is based on the diffraction summation migration technique. Travel times to grid points in a volume were calculated in smooth P and S-velocity models and trace energy near the calculated converted phase time was stacked over multiple sources at one receiver. Weighting factors based on Snell's Law at an arbitrarily oriented local interface were applied to better focus trace energy. PP reflection images from the active data set provide increased detail to images of the caldera rim from other studies. The migrated images also show features near 2–3 km in depth beneath Pozzuoli City, which may be associated with an over-pressured gas volume, as suggested by other geophysical investigations. Possible deeper features near 4 km depth may be related to the presence of the carbonate basement or may image a previously undetected feature, such as a small body of strongly thermometamorphosed volcanic rock. The current passive earthquake data set from the 1984 ground uplift episode was not well suited to the converted phases analysis due to narrow P–S windows and high noise levels in the traces. However, two stations provide confirmation and extension of imaged features in the active data.     

Geostatistical integration of seismic velocity and resistivity data for probabilistic evaluation of rock quality

This study applied a geostatistical approach to integrate various geophysical results for the probabilistic evaluation of rock quality designation (RQD) in regions between boreholes. Two of the geophysical survey results, electrical resistivity and seismic velocity, were transformed into a probabilistic distribution with the directly observed RQD values at the boreholes using an indicator value method. The initial spatial distribution of RQD, inferred from indicator kriging of observations from the boreholes, was improved by support of the geophysical results based on the integration by a permanence ratio. The integration was good enough to produce results that compensated for the defection of each exploration method. Also, the probabilistic feature of the final product of the RQD distribution made it possible to assess a more quantitative rock quality evaluation and better decision making for safety design.     

Crustal studies of the Koyna region using explosion data from deep seismic soundings

This study is based on the seismic data collected as a result of explosions carried out during the 1976 and 1978 Deep Seismic Sounding (DSS) field operations in the Koyna region. These shots were exploded from twelve shot points by the National Geophysical Research Institute along the Guhagar-Chorochi and Kelsi-Loni profiles.Refraction studies of the records reveal a two-layered crust. The top layer consists 17 km of granite and the second layer 19 km of basalt, giving the average depth of the Moho as 36 km in the region. The velocities of the phases P_g, P* and P_n have been computed as 5.82 ± 0.01, 6.61 ± 0.05 and 8.23 ± 0.05 km/sec respectively and those of S_g, S* and S_n as 3.41 ± 0.00, 4.09 ± 0.07 and 4.60 ± 0.08 km/sec respectively. The shear wave velocity in the basement rock has been found to be lower in comparison with other regions of the peninsular India.In some cases reflections were recorded both from the Moho as well as from the intermediate layer. These reveal a crustal thickness of 39 km with 19 km of granitic and 20 km of basaltic layers.Coda signal durations from DSS explosions recorded by microearthquake seismographs indicate a lateral heterogeneity in the crust on either side of Karad in an east-west direction.     

On the depth to anomaly estimation using Karous and Hjelt filter in VLF-EM data

The Karous and Hjelt filter has been long time used as a qualitative interpretation of VLF-EM data. It is derived directly from the concept of magnetic fields associated with the current flow in the subsurface and resulted in a 2-D cross section showing the current density distribution at different depths. Practically, as the distance between measuring points increases, the total depth of the 2-D current density distribution section increases. Theoretically, the common guide to estimate the depth of penetration of an electromagnetic wave is the skin depth, which depends on the frequency of the electromagnetic wave and the conductivity of the host geological material, regardless of the distance interval between measuring points. Accordingly, the accuracy of the Karous and Hjelt filter regarding depth estimation of the anomaly is tested in this study. We proposed a conductive anomaly in a definite dimension and depth. The response of this conductive body is calculated as in-phase and out-of-phase synthetic VLF data via forward modeling. The synthetic VLF data is filtered by the Karous and Hjelt filter at 1, 5, and10 m of interval distance between measuring points. The present study showed that the Karous and Hjelt filter is characterized by a large degree of accuracy in depth estimation.     

基于多t-x域联合的多震源地震数据混叠噪声分离方法

随着多震源同时激发采集方法在地震油气勘探领域的应用逐年增加,许多学者对其关键技术多震源地震数据混叠噪声分离进行了研究,就目前为止,仍需开展保真度更高的方法研究。基于以下设想:对多震源地震数据做正常时差校正(NMO),可以加强反射信号的线性分布程度(尤其在共中心点CMP道集内),并扩大反射信号和混叠噪声的分布差异;单域分离混叠噪声,仅针对混叠噪声和反射信号的某一分布特性差异进行分离,多t-x域联合分离可综合利用各t-x域内混叠噪声和反射信号在各域内的分布差异,其分离效果更好。首先,通过对多震源数据CMP道集做NMO以强化反射信号的线性程度、扩大随机分布混叠噪声的离散程度,利用中值滤波分离大部分混叠噪声,再在其他t-x域内(如共炮点CSG道集、共检波点CRG道集和共偏移距COG道集等)根据残余混叠噪声分布特征利用随机噪声衰减等方法进一步分离,并在整个分离处理中使用保幅处理方法。提出的多t-x域联合分离混叠噪声方法,经理论数据验证,相较于单域分离方法可以有效且保真分离多震源数据中的混叠噪声,并对其他噪声和横波有一定的压制作用;实际数据应用效果表明,该方法比单域方法分离效果较好,叠后成像效果品质较高。多t-x域联合分离混叠噪声方法,能够稳定、可靠和保真地分离多震源地震数据中的混叠噪声。      

综合应用测井及地震资料建立复杂断块地质模型

针对滩海油田具有完钻井少,以地震资料为主的特点,采用井震结合的方法进行地质建模。复杂断块油藏具有许多内部断层,充分利用地震解释层位和断层成果建立合理的构造模型。采用“多步建模”的思路,选用序贯高斯同位协同模拟算法建立储层参数模型。以测井资料为硬数据,地震反演数据为软数据,先后建立自然伽玛模型、泥质含量模型和砂泥岩相模型,然后以砂泥岩相模型为约束,建立储层参数模型。经研究表明,综合使用地震解释成果和三维地震数据体,有助于建立准确、合理的构造模型;而采用“多步建模”的思路,利用序贯高斯同位协同模拟算法,并综合测井资料、地震资料建立储层参数模型,有助于从地质的角度对储层参数模拟进行约束,提高储层随机建模精度,保证储层参数模型的准确和可靠性。     

Low velocity layer characterization in the Niger Delta: Implications for seismic reflection data quality

The problems of poor data quality and statics in seismic surveys have been attributed to lack of proper understanding of the low velocity layer characteristics of the area from which such data was acquired. Downhole seismic refraction survey was therefore conducted at twenty (20) borehole locations within parts of Niger Delta, Nigeria to determine the low velocity layer characteristics of the area using the Geometrics Stratavisor NZ11 instrument. The data was processed using Udysys software with spatial representation of the results presented. Static corrections were carried out on reflection seismic data acquired from the study area using Geoscribe II software to determine the effects of the low velocity layer on reflection seismic data in the area. Results of the study revealed that the velocity of the low velocity layer ranged between 144 and 996m/s with a regional average of 407m/s. The thickness of the low velocity layer varied between 3.0 and 9.6m with a mean value of 5.0m. Similarly, the velocity of the consolidated layer ranged between 1449 and 1812m/s with a mean value of 1738m/s. Results of the static correction carried out on the seismic reflection data revealed a substantial improvement in the resolution of the data after static correction. Based on these findings, it is therefore, recommended that shots for reflection seismic survey should be located at a minimum depth of 9.6m in the area to eliminate the effects associated with the low velocity layer.     

Active tectonics of the Yizre'el valley, Israel, using high-resolution seismic reflection data

We present a series of high-resolution seismic reflection lines across the Yizre'el valley, which is the largest active depression in Israel, off the main trend of the Dead Sea rift. The new seismic reflection data is of excellent quality and shows that the valley is dissected into numerous small blocks, separated by active faults. The Yizre'el valley is found to consist of a series of half grabens, rather than a single half graben, or a symmetrical graben. The faults are generally vertical and appear to have a dominant strike-slip component, but some dip-slip is also evident. A marked zone of compression near Megido is associated with the intersection of the two largest faults in the valley, the Carmel fault and the Gideon fault. Variable trend of the faults reflects the complexity of the local geology along the boundary between the wide NW–SE trending Farah–Carmel fault zone and the E–W trending basins and ranges in the Lower Galilee. This tectonic complexity is likely to result from a highly variable stress pattern, modified by the structures inside it. Normal faulting in the valley occurred at an early stage of its development as a tectonic depression. However, strike-slip motion on the Carmel fault, and possibly also on some of the other faults, appears to have started together with the onset of normal faulting. Earthquake hazard in the area appears to be uniform as faults are distributed throughout the Yizre'el valley.     

多分量重力梯度数据联合欧拉反褶积与软件系统设计

和传统欧拉反褶积相比,重力梯度数据联合欧拉反褶积具有更高的计算精度和反演分辨率。为了消除计算产生的发散解,在应用中须使用不同的筛选方法,使得计算流程变得相对繁琐。可见提供有效的筛选方法与开发一个易用的可视化软件有利于提高该方法的准确性、便捷性和使用效果。因此,本文提出基于相关系数边界识别约束的重力梯度数据联合欧拉反褶积,并依据界面直观、功能实用、代码简洁的设计原则,针对算法流程与功能需求,利用Python语言及其函数库设计了一种支持数据/文件管理、二/三维可视化、边界识别、重力梯度数据联合欧拉反褶积等功能的软件系统。通过理论模型与实测数据试验,验证了计算的准确性和软件的实用性,设计的软件系统能够提高应用效果。     

Towards improving ambient noise tomography using simultaneously curvelet denoising filters and SEM simulations of seismic ambient noise

The aim of this article is to investigate a possible way to improve ambient noise tomography by expanding the data base of useful cross-correlation measurements. We show that the curvelet transform makes it possible to compute synthetic noise correlations by simulating directly seismic ambient noise using the spectral element method. These synthetic correlations can in turn be used to identify surface waves and overtones even on correlations having a signal to noise ratio much lower than one. We hope that the possibility to compute SEM synthetic correlations and to extract more information from correlations will be useful to improve ambient noise tomography and monitoring.     

基于小波变换的阈值降噪方法在地震资料处理中的应用

这里主要讨论了小波变换阈值降噪方法的基本原理,并且将广泛使用的通用阈值方法与Birge-Massart阈值方法进行了比较,展现了Birge-Massart阈值选取方法的优越性。通过对模拟数据和实际地震资料的处理结果表明,基于小波变换的Birge-Massart阈值降噪方法对地震信号降噪具有很好的效果。     

Model identification and parameter estimation of elastoplastic constitutive model by data assimilation using the particle filter

Data assimilation, using the particle filter and incorporating the soil‐water coupled finite element method, is applied to identify the yield function of the elastoplastic constitutive model and corresponding parameters based on the sequential measurements of hypothetical soil tests and an actual construction sequence. In the proposed framework of the inverse analysis, the unknowns are both the particular parameter within the exponential contractancy model, n_E, which parameterizes various shapes for the yield function of the competing constitutive models, including the original/the modified Cam‐Clay models and in‐between models and the parameters of the corresponding constitutive model. An appropriate set, consisting of the yield function of the constitutive model and the parameters of the constitutive model, can be simultaneously identified by the particle filter to describe the most suitable soil behavior. To examine the validity of the proposed procedure, hypothetical and actual measurements for the displacements of a soil specimen were obtained for consolidated and undrained tests through a synthetic FEM computation and for consolidated and drained tests, respectively. After examining the applicability of the proposed procedure to these test results, the present paper then focuses on the actual measured data, ie, the settlement behavior including the lateral deformation of the Kobe Airport Island constructed on reclaimed land.     

利用地震资料预测煤层古河道冲刷带

为预测沁水盆地西缘某矿区煤层古河道冲刷带,开展了地震波数值正演模拟,利用地震属性分析技术,结合波阻抗反演技术、三维可视化技术等手段,研究了煤层古河道冲刷带分布的特征。后期钻孔验证表明,利用地震资料预测煤层古河道冲刷带的方法是可行的。