The coast effect in terms of deviated electric currents: a numerical study

A numerical thin-sheet model is used to study the coast effect and to determine the magnitude of the near-surface part of the anomalous field. Theoretical induction arrows are computed for Australia, California, Japan and the British Isles and compared with the observed arrows. This comparison shows that the main part of the coast effect, and in some cases the whole coast effect, is due to the deviation of currents flowing in the ocean by the upper part of the resistive continents. It is suggested that the term ‘coast effect’ should refer to the anomalous field whose source is near-surface. The coast effect so defined behaves like a regional anomaly superimposed on other anomalous features of the transient geomagnetic field. A numerical determination of the geometrical features of the coast effect allows consideration of its elimination. This elimination is performed for California and Japan. A correlation between the resulting residual and heat-flow data is apparent in both cases.     

时移地震监测水驱前沿的方法和应用研究

油藏开发过程的有效监测是合理开采油藏和提高采收率的关键之一.本文根据水驱油藏流体变化的基本规律以及其他实验和统计结果,讨论了长期注水开采油藏储层物性变化及其引起的弹性参数变化和地震响应变化特征,明确了水驱前沿的概念,提出了基于差异振幅和奇异值分析的时移地震监测水驱前沿方法.理论模型研究表明该方法是可行的.通过对东部地区某油田的两次三维地震数据处理、分析,确定了水驱前沿的位置,后钻的两口井证实了预测结果的准确性和方法的有效性.研究结果还表明,通过水驱前沿的监测并结合初期油藏描述的结果,时移地震可以很好地预测长期水驱油藏剩余油的分布.     

福建东南沿海重力场演变特征及其与地震的关系

分析研究了福建地区2001～2008年的流动重力测量资料,探讨了福建东南沿海地区重力场变化与永春ML4．6和长泰ML=4．7级地震的关系。结果表明：这2次地震前,靠近震中测点的重力值有明显的变化。     

DB气田非均质储层级别划分及常规测井识别方法

DB气田以裂缝-孔隙型、孔隙型岩屑砂岩储层为主,非均质性强,裂缝发育程度是决定产能高低的关键因素之一.立足于储层的录井、岩心分析和测井资料,开发了储层级别划分和常规测井识别储层级别的方法.首先,定义了每米产能指数作为标准化的产能参数;其次,基于产能参数与储层物性参数关系的考察,筛选综合物性参数(孔隙度和总渗透率的乘积)作为储层级别划分的评价指标,将DB气田储层分成了2个级别,给出了分级的物性标准;最后,应用主成分分析法计算了综合主成分,基于综合主成分与每米产能指数交会图给出了应用常规测井资料识别储层级别的标准.2口井的应用效果表明,依据上述方法划分及识别的储层级别与生产情况吻合得较好.     

Field Measurements and Numerical Simulations of the 2004 Tsunami Impact on the East Coast of Sri Lanka

This paper employs a numerical model of tsunami propagation together with documented observations and field measurements of the evidence left behind by the tsunami in December 2004, to identify and interpret the factors that have contributed to the significant spatial variability of the level of tsunami impact along the coastal belt of the eastern province of Sri Lanka. The model results considered in the present analysis include the distribution of the amplitude of the tsunami and the pattern of wave propagation over the continental shelf off the east coast, while the field data examined comprise the maximum water levels measured at or near the shoreline, the horizontal inundation distances and the number of housing and other buildings damaged. The computed maximum amplitude of the tsunami at water points nearest the shoreline along the east coast shows considerable variation ranging from 2.2 m to 11.4 m with a mean value of 5.7 m; moreover, the computed amplitudes agree well with the available field measurements. We also show that the shelf bathymetry off the east coast, particularly the submarine canyons at several locations, significantly influences the near-shore transformation of tsunami waves, and consequently, the spatial variation of the maximum water levels along the coastline. The measured values of inundation also show significant variation along the east coast and range from 70 m to 4560 m with a median value of 700 m. Our analyses of field data also show the dominant influence of the coastal topography and geomorphology on the extent of tsunami inundation. Furthermore, the measured inundation distances indicate no apparent correlation with the computed tsunami heights at the respective locations. We also show that both the computed tsunami heights and the measured inundation distances for the east coast closely follow the log-normal statistical distribution.     

Detailed Fracture System of the Soultz-sous-Forêts HDR Field Evaluated Using Microseismic Multiplet Analysis

—?The reservoir structure of the Soultz HDR field has been investigated by examining induced microearthquake multiplets. Microseismic events with similar waveforms have been selected from microseismic data obtained during a 1993 hydraulic fracturing experiment. Precise relative arrival times and source locations have been determined by cross-spectrum analysis. The cross-spectrum analysis decreased the residual from 0.75?ms to 0.1?ms. The estimated orientations of the multiplet planes are consistent with fracture orientations detected in Soultz boreholes. A comparison between the stress field and the orientation of structural planes suggests that the structural planes were under a critical condition of frictional slip.     

水库库容变化对蓟县地震台DSQ型水管倾斜仪观测的影响

对比于桥水库库容变化与蓟县地震台DSQ型水管仪观测数据表明,水库容量对水管仪长周期趋势性变化影响不大,蓄水和泄水过程中库容量变化与水管仪观测数据不存在相关关系。根据近场三维不规则形状荷载模型,对于于桥水库3次蓄水和3次泄水过程,定量计算库容变化对蓟县地震台DSQ型水管倾斜仪观测影响的理论值,结果表明,库容变化引起的水管仪倾斜值与实际观测数据变化幅度相比小得多,库容改变不足以对水管仪倾斜观测造成显著干扰。该分析结果可在观测资料异常判定中提供参考。     

Crustal movement and deformation in Taiwan and its coastal area

Introduction Both Taiwan Island and Chinese mainland belong to Eurasian plate in geological structure. And the nearest distance between Taiwan Island and Fujian Province, which is located on the opposite coast, is only 130 km. Although there are high-precision GPS networks in both Taiwan and Fujian Province, joint GPS measurement cannot be made directly because of the inconvenient contact due to the strait between them. However, the GPS networks arranged on b…     

频谱成像技术研究进展

频谱成像技术是近年来发展起来的一项基于频率谱分解的储层特色解释技术,是地震属性分析中重要组成部分.频谱成像技术具有在空间横向上分辨率高的特点,是一种利用三维地震资料的多尺度信息对储层进行高分辨率成像、检测储层时间厚度变化的工具.地震数据振幅谱可以识别地层的时间厚度变化,相位谱可以检测地质体横向不连续性,在确定油藏边界、计算地层厚度方面比传统地震属性研究方法具有更大的优势.频谱成像技术的核心模块是信号的时频分析,本文回顾了频谱成像技术的基本概念和目前在频谱成像中广泛应用的时频分析方法,简单介绍了几种新的时频分析方法:广义S变换和改进的匹配追踪算法.     

Surface current patterns observed by HF radar: methodology and analysis of currents to the north of the Yaeyama Islands,East China Sea

A new method was developed to compare the classifications of different kind of data maps based on the self-organizing map (SOM) analysis. The surface current maps of the northern coast of Ishigaki and Iriomote Islands, East China Sea, observed by high-frequency (HF) radar were classified by SOM. Winds, sea surface temperatures (SST), and reanalysis data were also classified by SOM. The optimum area for classification was determined objectively by the new method, which relates these patterns to HF radar current patterns. We found two typical surface patterns: the first was that northeastward flows are dominant in the observation area and the second was that a clockwise eddy was also dominant in this area. The southwestward wind pattern was strongly related to the dominant clockwise eddy pattern of the HF radar current field.     

Vertical and horizontal components of the lake Baikal electrotelluric field and their relation to the electric conductivity

Synchronous observations of the electrotelluric field were performed on the lake ice and the coast. The ice-based vertical/horizontal field ratio at periods of a few seconds to a few minutes ranges from a few hundredths to a few thousandths, which is comparable to the noise level. The results of these observations favor a plane wave model. At the coastal station, the vertical and horizontal fields are similar, which is related to geoelectric heterogeneity of the medium. An electric tipper is used to control the behavior of heterogeneity in the spectral-time domain. Anomalous changes associated with earthquakes of K ≥ 12 are revealed from data of the tipper monitoring at epicentral distances of up to 300 km. A longitudinal MTS curve free from the effect of local geoelectric heterogeneities is obtained from ice-based data. Deep conducting layers are recognized as minimums in this curve.     

复杂断块砂砾岩油藏地震解释

地震构造层位的解释精度对砂砾岩油藏的预测起关键性作用.本文以夏子街油田夏18-36区块砂砾岩扇体油藏的构造和层位解释为例,研究砂砾岩油藏地震精细解释技术.研究中采用快速地震扫描、相干体分析、精细层位标定、构造样式及断裂组合分析相结合的工作思路,在地震资料品质中偏差先天不足条件下,实现了全工区200余口井的井震统一.运用多种解释方法综合印证来提高砂砾岩油藏的解释精度,为油藏参数的反演和储层预测及注水生产奠定了坚实的基础.     

A seasonal effect in diurnal variation of the atmospheric electric field on the Pacific coast of Japan

The measurement of the atmospheric electric field was carried out with a field mill at a small island in a bay on the Pacific coast of Japan. The data obtained during 80 months from 1971 to 1977 were analysed. It was found that characteristically the diurnal variation regularly alters with the seasons. Whereas the electric field in winter has the same diurnal pattern as that observed at globally representative stations, it exhibits in summer a pattern depending on the variation of the local electric conductivity. The alteration is inferred to be associated with regional atmospheric conditions surrounding the observation site.     

Shoreline management plan for a protected but eroding coast along the southwest coast of India

Coastal erosion is a serious problem of concern along the southwest(SW) coast of India. Various coastal protection measures have been applied for the recovery of the coast, but the devastating effect of erosion still continues. The present study focuses on a coastal stretch situated on the southern sector of the SW coast of India, where Sundar and Sannasiraj(2006) proposed a groyne field along with an existing seawall to control severe erosion. In order to confirm the net littoral drift of this region and for a preliminary assessment of the performance of the groynes prior to construction of the proposed groyne field, two groynes were initially constructed as a pilot program in 2008-09. Periodic monitoring of shoreline position with the two groynes in place was carried out during 2009-14. A shoreline evolution model for the study region was setup, calibrated,and validated using field observations during 2010-11. In addition to traditional shoreline evolution modelling procedures, a profile simulation model was applied for simulating the shoreline behaviour during extreme monsoon seasons. The validated LITPACK model has been used to evaluate the performance of the proposed groyne field in controlling erosion, and the study also considered testing a modified transitional groyne field proposed as an alternative solution to the existing problem, and the modified transitional groyne field was found to be more effective than the prior design. A beach is expected to develop about 30-50 m within the groyne cells during the fair season which enhances the possibility of retaining a minimum beach width of 10 m during monsoon periods.     

Anomalies of the natural electric field on Lake Baikal

The paper presents results of observations of the electromagnetic field conducted on the ice and coast of Lake Baikal. The horizontal and vertical components of the electric field contain anomalous disturbances coinciding in time with earthquakes and with the origination of a crevice in the ice cover of the lake. A possible origin of the anomalous disturbances is considered.     

Multi‐dimensional analyses of the SEAM controlled source electromagnetic data—the story of a blind test of interpretation workflows

Using a subset of the SEG Advanced Modeling Program Phase I controlled‐source electromagnetic data, we apply our standard controlled‐source electromagnetic interpretation workflows to delineate a simulated hydrocarbon reservoir. Experience learned from characterizing such a complicated model offers us an opportunity to refine our workflows to achieve better interpretation quality. The exercise proceeded in a blind test style, where the interpreting geophysicists did not know the true resistivity model until the end of the project. Rather, the interpreters were provided a traditional controlled‐source electromagnetic data package, including electric field measurements, interpreted seismic horizons, and well log data. Based on petrophysical analysis, a background resistivity model was established first. Then, the interpreters started with feasibility studies to establish the recoverability of the prospect and carefully stepped through 1D, 2.5D, and 3D inversions with seismic and well log data integrated at each stage. A high‐resistivity zone is identified with 1D analysis and further characterized with 2.5D inversions. Its lateral distribution is confirmed with a 3D anisotropic inversion. The importance of integrating all available geophysical and petrophysical data to derive more accurate interpretation is demonstrated.     

基于离散余弦变换的集合Kalman滤波方法对河流相油藏渗透率场的反演

针对河流相油藏参数场的非高斯性及油藏生产数据与地质模型之间的非线性关系,提出了耦合离散余弦变换的半迭代集合Kalman滤波方法对河流相油藏进行生产历史拟合及反演.将河流相油藏非高斯渗透率场利用离散余弦变换变为类似高斯分布的DCT(Discrete cosine transform)系数,利用能量压缩特性对DCT系数进行截断,使得反演渗透率场的分布变得光滑,较好地解决了河流相油藏的非高斯分布问题.半迭代集合Kalman滤波法很好地解决了油藏生产数据与地质模型之间的非线性问题.理论证明了半迭代集合Kalman滤波与EnRML方法的等效性.比较了标准EnKF、耦合DCT的EnKF及耦合DCT的半迭代EnKF法对河流相油藏渗透率场的反演.讨论了DCT系数保留模式及系数保留数量对耦合DCT的半迭代集合Kalman滤波方法反演结果的影响,结果表明三角形系数保留模式可以用更少的系数保留参数场的地质特征,当保留2.5%的DCT系数时,反演结果已经充分反映了河流相油藏的地质特征.     

A BME solution of the stochastic three-dimensional Laplace equation representing a geothermal field subject to site-specific information

This work develops a model of the geothermal field in the Nea Kessani region (Greece) by means of the Bayesian maximum entropy (BME) method, which describes the temperature variations across space in the underground geological formations. The geothermal field is formed by a thermal reservoir consisting of arcosic sandstones. The temperature distribution vs depth was first investigated by the Greek Institute of Geology and Mineral Exploration (IGME) using measurements in a set of vertical drill holes. These measurements showed that hot fluids rising from the deep enter the reservoir in a restricted area of the field and flow towards local thermal springs. The field modelling, which was based on the powerful BME concept, involves the solution of a stochastic partial differential equation that assimilates important site-specific information. The stochastic three-dimensional steady-state Laplace equation was considered as general knowledge and the drilling exploration data were used to construct the specificatory knowledge base in the BME terminology. The produced map is more informative and, in general, it gives higher temperature estimates compared to previous studies of the same region. This is also in agreement with the quartz geothermometry analysis carried out by IGME.     

Probabilistic Regularities in Setup Variations in the Level of a Large Inland Water Body: Case Study of the Caspian Sea

The results of probabilistic analysis of data on setup level variations collected during long-term observations at all gages along the Caspian Sea coast are discussed. A procedure for evaluating low-probability sea level extremes is proposed. Estimates are given for the probabilities of outstanding setups in the Caspian Sea and the Sea of Azov.     

VHF radar observations of surface currents off the northern Opal coast in the eastern English Channel

Two very high-frequency radars (VHFR) operating on the Opal coast of eastern English Channel provided a nearly continuous 35-day long dataset of surface currents over a 500 km² area at 0.6–1.8 km resolution. Argo drifter tracking and CTD soundings complemented the VHFR observations, which extended approximately 25 km offshore. The radar data resolve three basic modes of the surface velocity variation in the area, that are driven by tides, winds and freshwater fluxes associated with seasonal river discharge. The first mode, accounting for 90% of variability, is characterized by an along-shore flow pattern, whereas the second and third modes exhibit cross-shore, and eddy-like structures in the current velocity field. All the three modes show the dominant semi-diurnal variability and low-frequency modulation by the neap-spring tidal cycle. Although tidal forcing provides the major contribution to variability of local currents, baroclinicity plays an important role in shaping the 3D velocity field averaged over the tidal cycle and may strongly affect tracer dynamics on larger time scales. An empirical orthogonal function (EOF) decomposition and a spectral rotary analysis of the VHFR data reveal a discontinuity in the velocity field occurring approximately 10 km offshore which was caused by the reversal in the sign of rotation of the current vector. This feature of local circulation is responsible for surface current convergence on ebb, divergence on flood and strong oscillatory vertical motion. Spectral analysis of the observed currents and the results of the Agro drifter tracking indicate that the line of convergence approximately follows the 30-m isobath. The most pronounced feature of the radar-derived residual circulation is the along-coast intensification of surface currents with velocity magnitude of 0.25 m/s typical for the Regions of Freshwater Influence (ROFI). The analysis has provided a useful, exploratory examination of surface currents, suggesting that the circulation off the Opal coast is governed by ROFI dynamics on the hypertidal background.