Estimating magnetic dike parameters using a non‐linear constrained inversion technique: an example from the Särna area,west central Sweden     

Majid Beiki  Laust B. Pedersen 《Geophysical Prospecting》2012,60(3):526-538

In this paper, we describe a non‐linear constrained inversion technique for 2D interpretation of high resolution magnetic field data along flight lines using a simple dike model. We first estimate the strike direction of a quasi 2D structure based on the eigenvector corresponding to the minimum eigenvalue of the pseudogravity gradient tensor derived from gridded, low‐pass filtered magnetic field anomalies, assuming that the magnetization direction is known. Then the measured magnetic field can be transformed into the strike coordinate system and all magnetic dike parameters – horizontal position, depth to the top, dip angle, width and susceptibility contrast – can be estimated by non‐linear least squares inversion of the high resolution magnetic field data along the flight lines. We use the Levenberg‐Marquardt algorithm together with the trust‐region‐reflective method enabling users to define inequality constraints on model parameters such that the estimated parameters are always in a trust region. Assuming that the maximum of the calculated g_zz (vertical gradient of the pseudogravity field) is approximately located above the causative body, data points enclosed by a window, along the profile, centred at the maximum of g_zz are used in the inversion scheme for estimating the dike parameters. The size of the window is increased until it exceeds a predefined limit. Then the solution corresponding to the minimum data fit error is chosen as the most reliable one. Using synthetic data we study the effect of random noise and interfering sources on the estimated models and we apply our method to a new aeromagnetic data set from the Särna area, west central Sweden including constraints from laboratory measurements on rock samples from the area.  相似文献   

火－沉粘土岩的成因标志及研究方法   总被引：2，自引：0，他引：2  

冯宝华 《煤田地质与勘探》1994,22(2):6-10

论述了火－沉粘土岩的概念、产状、岩石特征、矿物成分、化学成分和自然伽马测井曲线等成因标志以及研究方法,对其命名问题也提出了意见。   相似文献   

青海省都兰县巴隆岩金矿床地质特征及找矿标志          下载免费PDF全文

管祥波  李军 《山东国土资源》2016,32(12)

对巴隆岩金矿成矿地质背景、矿体特征、矿石特征及其控矿因素等进行分析研究。认为区内矿体与NWW向断裂关系密切,NWW向昆中主断裂为矿床的导矿构造,NWW向F1断裂为矿床的配矿构造,矿区内F2,F3,F4,F5等NWW向次级断裂为矿床的容矿构造;尤其是在拐弯或膨胀处;强烈的印支期岩浆活动,剧烈的构造运动为金元素的活化、迁移、富集、沉淀提供了通道和成矿空间;矿石类型主要为构造蚀变岩型;重砂矿物标志、地貌标志、颜色标志、气味标志、化探异常标志等是该区的主要找矿标志。结合区域上成矿背景分析认为该矿区有着良好的找矿前景,并建议对矿床深部及外围做进一步工作。  相似文献   

Marine transient electromagnetic sounding of deep buried hydrocarbon reservoirs: principles,methodologies and limitations          下载免费PDF全文

Pavel O. Barsukov  Edward B. Fainberg 《Geophysical Prospecting》2017,65(3):840-858

The possibility of a time‐domain electromagnetic sounding method using excitation and measurement of vertical electric fields to search for and identify deeply buried reservoirs of hydrocarbons offshore is investigated. The method operates on source–receiver offsets, which are several times less than the depth of the reservoir. Geoelectric information is obtained from the transient responses recorded in the pauses between the pulses of electric current in the absence of the source field. The basics of the method, as well as its sensitivity, resolution, and the highest accessible depth of soundings for various geological conditions in a wide range of sea depths, are analyzed. For the analysis, 1D and 3D geoelectric models of hydrocarbon reservoirs are used. It is shown that under existing technologies of excitation and measurement of vertical electric fields, the highest accessible depth of soundings can be up to 4 km. Technology for the inversion and interpretation of transient responses is demonstrated on experimental data.  相似文献   

A rock physics model to map gross lithology using compaction     

Jeremy Gallop  Olena Babak  Kun Liu 《Geophysical Prospecting》2020,68(2):615-630

Differential compaction has long been used by seismic interpreters to infer subsurface geology using knowledge of the relative compaction of different types of sediments. We outline a method to infer the gross fraction of shale in an interval between two seismic horizons using sandstone and shale compaction laws. A key component of the method involves reconstruction of a smooth depositional horizon by interpolating decompacted thicknesses from well control. We derive analytic formulae for decompaction calculations using known porosity–stress relations and do not employ discrete layer iterative methods; these formulae were found to depend not only upon the gross fraction of shale but also on the clay content of the shales and the thickness of the interval. The relative merits of several interpolation options were explored, and found to depend upon the structural setting. The method was successfully applied to an oil sands project in Alberta, Canada.  相似文献   

A comparison of seismic saltbody interpretation via neural networks at sample and pattern levels     

Haibin Di  Ghassan AlRegib 《Geophysical Prospecting》2020,68(2):521-535

Saltbodies are important subsurface structures that have significant implications for hydrocarbon accumulation and sealing in petroleum reservoirs, and accurate saltbody imaging and delineation is now greatly facilitated with the availability of three-dimensional seismic surveying. However, with the growing demand for larger survey coverage and higher imaging resolution, the size of seismic data is increasing dramatically. Correspondingly, manual saltbody interpretation fails to offer an efficient solution, particularly in exploration areas of complicated salt intrusion history. Recently, artificial intelligence is attracting great attention from geoscientists who desire to utilize the popular machine learning technologies for evolving the interpretational tools capable of mimicking an experienced interpreter's intelligence. This study first implements two popular machine learning tools, the multi-layer perceptron and the convolutional neural network, for delineating seismic saltbodies at sample and pattern levels, respectively, then compares their performance through applications to the synthetic SEAM seismic volume, and moreover tentatively investigates what contributes to the better convolutional neural network delineation. Specifically, the multi-layer perceptron scheme is capable of efficiently utilizing an interpreter's knowledge by selecting, pre-conditioning and integrating a set of seismic attributes that best highlight the target saltbodies, whereas the convolutional neural network scheme makes it possible for saltbody delineation directly from seismic amplitude and thus significantly reduces the dependency on attribute selection from interpreters. It is concluded that the better performance from the convolutional neural network scheme results from two factors. First, the convolutional neural network builds the mapping relationship between the seismic signals and the saltbodies using the original seismic amplitude instead of manually selected seismic attributes, so that the negative impact of using less representative attributes is virtually eliminated. Second and more importantly, the convolutional neural network defines, learns and identifies the saltbodies by utilizing local seismic reflection patterns, so that the seismic noises and processing artefacts of distinct patterns are effectively identified and excluded.  相似文献   

Semi-automatic fault/fracture interpretation based on seismic geometry analysis     

Haibin Di  Ghassan AlRegib 《Geophysical Prospecting》2019,67(5):1379-1391

Fault and fracture interpretation is a fundamental but essential tool for subsurface structure mapping and modelling from 3D seismic data. The existing methods for semi-automatic/automatic fault picking are primarily based on seismic discontinuity analysis that evaluates the lateral changes in seismic waveform and/or amplitude, which is limited by its low resolution on subtle faults and fractures without apparent vertical displacements in seismic images. This study presents an innovative workflow for computer-aided fault/fracture interpretation based on seismic geometry analysis. First, the seismic curvature and flexure attributes are estimated for highlighting both the major faults and the subtle fractures in a seismic volume. Then, fault probability is estimated from the curvature and flexure volumes for differentiation between the potential faults and non-faulting features in the geometric attributes. Finally, the seeded fault picking is implemented for interpreting the target faults and fractures guided by the knowledge of interpreters to avoid misinterpretation and artefacts in the presence of faulting complexities as well as coherent seismic noises. Applications to two 3D seismic volumes from the Netherlands North Sea and the offshore New Zealand demonstrate the added values of the proposed method in imaging and picking the subtle faults and fractures that are often overlooked in the conventional seismic discontinuity analysis and the following fault-interpretation procedures.  相似文献   

Connectivity constrained segmentation of geologic features     

Zhining Liu  Chengyun Song  Bin She  Xingmiao Yao  Guangmin Hu 《Geophysical Prospecting》2019,67(5):1369-1378

Segmentation of geologic features plays a significant role in seismic interpretation. Based on the segmentation results, interpreters can readily recognize the shape and distribution of geologic features in three-dimensional space and conduct further quantitative analysis. Usually, there are mainly two steps for the segmentation of geologic features: the first step is to extract seismic attributes that can highlight the occurrence of geologic features, and the second step is to apply the segmentation algorithm on the seismic attribute volumes. However, the occurrence of geologic features is not always corresponding to the anomaly value on the seismic attribute volumes and vice versa because of several factors, such as noise in the seismic data, the limited resolution of seismic images and the limited effectiveness of the seismic attribute. Therefore, the segmentation results, which are generated solely based on seismic attributes, are not sufficient to give an accurate depiction of geologic features. Aiming at this problem, we introduce the connectivity constraint into the process of segmentation based the assumption that for one single geologic feature all of its components should be connected to each other. Benefiting from this global constraint, the segmentation results can precisely exclude the interference by false negatives on seismic attribute volumes. However, directly introducing the connectivity constraint into segmentation would face the risk that the segmentation results would deteriorate significantly because of false positives with relatively large area when the connectivity constraints are enforced. Therefore, based on the seismic attribute that highlights the boundary of geologic feature, we further propose a post-processing technique, called pruning, to refine the segmentation results. By taking the segmentation of the channel as an example, we demonstrate that the proposed method is able to preserve the connectivity in the process of segmentation and generate better segmentation results on the field data.  相似文献   

山东莱芜地区牛泉矽卡岩型铁矿成矿条件及找矿标志          下载免费PDF全文

王云燕 《山东国土资源》2021,37(10)

山东省10年找矿突破战略行动开展以来,先后在鲁西莱芜和齐河-禹城深覆盖区取得了高品位矽卡岩型铁矿重大找矿突破。莱芜地区矿山岩体周边覆盖区发育有明显的航磁异常,通过对牛泉覆盖区磁异常和地质特征综合研究,认为该区具备良好的矽卡岩型铁矿成矿地质条件。并通过异常查证和系统的钻探施工,在牛泉覆盖区探明了一处中型矽卡岩型铁矿床。本文在总结勘查成果的基础上,分析了矿床主要成矿条件,探讨了找矿标志,对成矿有利部位进行了简单预测,以期为莱芜地区矽卡岩型铁矿下一步勘查工作提供帮助。  相似文献   

遥感技术在松潘县第二次土地调查中的应用     

王芳  杨武年  邵怀勇  郑富强 《四川测绘》2010,33(1):7-10

本文以1：10000标准分幅数字正射影像图（DOM）为载体，结合松潘县的地形地貌特征、植被分布规律和经济状况等数据，1：50000更新调查成果图，1：100000地形图，包括省、市、县等各级境界与乡、村等土地权属界线，以及土地利用现状数字线画图（LUDLG）为参考，采用内业解译和外业核实、补充调查相结合的方法，探讨与分析了影像解译过程中出现问题及所采取的思路与解决办法。  相似文献