大地电磁偏移成像技术的研究进展及其解决复杂地质问题的能力

总结和分析了大地电磁场成像技术的研究现状 ,在Zhdanov等对偏移电磁场的研究和成像技术基础上 ,提出了改进的有限差分法大地电磁场偏移成像技术 ,使差分方程精度和成像分辨率有了明显的提高 ,将前人大地电磁场偏移成像的模型试验研究推进到适用于复杂地电模型和实际资料处理解释的阶段 ,并通过松辽盆地大地电磁测深资料的偏移成像处理和解释展示了该方法的有效性和实用性     

大地电磁场偏移成像方法的改进与应用

本文在对电磁场成像技术进行系统研究和总结的基础上,分析综述了大地电磁场成像技术的研究现状与存在问题,进而提出了改进的有限差分法大地电磁场偏移成像技术,使差分方程精度和成像分辨率得到了提高,并对客观选取背景电导率、两种极化模式联合成像以及多参数和再次成像进行了创新研究,最后利用模型试验和实际大地电磁场资料的实例展示了该方法偏移成像的成果及其实用性.     

大地电磁场成像方法综述与新进展

对电磁场成像技术进行了系统总结，分析阐述了大地电磁场成像技术的研究现状与存在问题，并对各种方法的特点进行了比较和归纳，进而在Zhdanov等对偏移电磁场的研究和成像技术基础上提出了改进的有限差分法大地电磁场偏移成像技术，该方法提高了差分方程的精度和成像分辨率，并对客观选取背景电导率、两种极化模式联合成像、多参数和再次成像以及全频段成像和成像结合反演技术进行了研究。     

有限差分法大地电磁多参数偏移成像

提出一种改进的有限差分法进行大地电磁场偏移成像,通过保留波数对水平方向的一阶导数项,使差分方程精度和成像分辨率得到了提高,并采用快速近似反演结果作为对背景电导率的客观估计,对两种极化模式联合成像以及多参数和再次成像进行了研究,通过模型试验和实例说明有限差分法大地电磁多参数成像技术解决复杂问题的能力,证明了该方法的有效性和实用性.     

叠前时间偏移技术在淮北某煤矿采区三维地震勘探中的应用与效果

淮北某煤矿采区三维地震勘探地质条件极为复杂,区内褶皱、断层构造发育,常规叠后时间偏移处理很难准确成像,给后期资料解释工作带来不利影响.针对这一问题,采用叠前时间偏移技术,结合煤田地震勘探特点,对影响叠前偏移处理质量的关键步骤（预处理、静校正、叠前去噪、时间域速度模型建立）进行了研究,取得了显著效果.利用叠前偏移数据体解释,最终圆满完成了地质任务.本文通过应用实例,说明了煤田地震勘探资料处理利用叠前时间偏移技术对复杂构造成像效果较好,信噪比提高,断点解释更可靠.     

大地电磁资料偏移成像

在研究Zhdanov的二维电磁场偏移成像的基础上, 针对它在某些方面的不足, 研究并提出了改进算法. 首先, 用一维反演结果确定初始背景电阻率, 然后在延拓计算过程中, 利用迭代算法进行逐层修正、 延拓计算, 从而获得较准确的电阻率; 第二, 研究了有限差分方程的改进算法, 根据大地电磁场变化的特点, 设计了纵向以等比级数变网格的迭代算法. 通过以上两方面技术的改进, 经理论模型和实际资料试算验证, 取得了较好的结果.      

南堡凹陷潜山面精细成像目标攻关处理研究

南堡凹陷勘探开发程度的不断提高使潜山逐渐成为油田重要的勘探新领域,为提高潜山面和内幕成像质量,开展叠前深度偏移技术的应用研究.在以往处理的基础上,充分认识潜山面地震反射特征,讨论叠前深度偏移的针对性技术和措施.在整个过程中,地质认识贯穿处理的每个环节.结果表明,在地质认识指导下的潜山面精细成像目标攻关处理,改善了潜山面和内幕的成像质量,为构造解释、储层反演和裂缝预测提供可靠的基础资料.     

起伏地表地震资料成像方法分析

西部地区地表起伏剧烈,往往伴随着地下构造复杂,给地震偏移处理工作带来了极大的困难,导致后续的解释结果与实际构造存在一定的差异.因此,复杂地区的地震资料成像问题显得尤为重要.文章通过对复杂地表模型的正演模拟以及山区实际地震资料的应用两方面的分析,获得了适合复杂地表的成像方法.结果表明:针对复杂地区,叠加技术成像比偏移技术成像更能真实地反映地下构造形态,是一种提高复杂地区构造成像精度的有效方法;同时,将叠加剖面和偏移剖面两者有机结合,对复杂地表资料进行解释分析,更能体现地下构造的真实形态,为煤矿工作的安全开采提供了有利依据.     

地震叠前深度偏移方法流程及应用

针对复杂介质的成像问题，提出了一套地震资料叠前深度偏移方法流程，主要包括三部分：（１）地震资料精细预处理；（２）速度－深度模型建立；（３）叠前深度偏移成像．以Ｋｉｒｃｈｈｏｆｆ偏移理论为基础，强调地质与地球物理的综合以及地震处理与解释的一体化．在ＺＸ地区成功地实现了二维地震资料叠前深度偏移，所获得的ＮＥ２０６叠前深度偏移剖面揭示了复杂的ＺＸ古潜山及其内部构造，并清楚地展示了逆掩断层的存在．     

克希霍夫叠前时间偏移技术在复杂构造带地震资料处理中的应用

在辽河盆地东部凹陷中部的A区块地下构造复杂,以往的资料虽然反应了该区的整体面貌,但断裂带的成像效果不是很好,为此,开展了叠前时间偏移处理技术研究.详细介绍了保福克希霍夫叠前时间偏移的原理和数据的预处理,讨论了主要的偏移参数的测试和选取方法,通过Deregowski循环法和百分比偏移扫描速度建立和优化速度模型.处理结果表明,该区三维叠前偏移剖面较常规三维叠后偏移剖面有明显改善.     

误差对大地电磁测深反演的影响

本文讨论了几种不同分布的误差对大地电磁测深反演的影响.首先基于给定的正演模型计算得到相应的理论合成数据,然后在合成数据中分别加入满足不同均值和方差的高斯分布、均匀分布和Gamma分布的误差,最后使用非线性共轭梯度法进行反演.反演结果表明, 较简单的模型在考虑的几种误差分布下可以较好地给出模型的基本信息;但复杂的模型随着误差方差的增大,与已知模型的偏差越明显; 在均值和方差相同时,上述三种不同分布的误差的反演结果相差很小.     

一种反演不均匀介质大地电磁测深资料的方法

通过反演受近地表不均匀介质影响的大地电磁测深资料的新方法,可获得较准确的一维地电断面参数、不均匀体埋藏深度及其电性特征。本方法计算速度快,单测ρxy,ρyx可独立反演并相互验证结果的准确性     

APPLYING 3D INVERSION OF SINGLE-PROFILE MAGNETOTELLURIC DATA TO IDENTIFY THE SHADE AND YUNONGXI FAULTS

Many synthetic model studies suggested that the best way to obtain good 3D interpretation results is to distribute the MT sites at a 2D grid array with regular site spacing over the target area. However, MT 3D inversion was very difficult about 10 years ago. A lot of MT data were collected along one profile and then interpreted with 2D inversion. How to apply the state-of-the-art 3D inversion technique to interpret the accumulated mass MT profiles data is an important topic. Some studies on 3D inversion of measured MT profile data suggested that 2D inversions usually had higher resolution for the subsurface than 3D inversions. Meanwhile, they often made their interpretation based on 2D inversion results, and 3D inversion results were only used to evaluate whether the overall resistivity structures were correct. Some researchers thought that 3D inversions could not resolute the local structure well, while 2D inversion results could agree with the surface geologic features much well and interpret the geologic structures easily. But in the present paper, we find that the result of 3D inversion is better than that of 2D inversion in identifying the location of the two local faults, the Shade Fault(SDF)and the Yunongxi Fault(YNXF), and the deep structures. In this paper, we first studied the electrical structure of SDF and YNXF based on a measured magnetotelluric(MT) profile data. Besides, from the point of identifying active faults, we compared the capacity of identifying deep existing faults between 2D inversion models and 3D models with different inversion parameters. The results show that both 2D and 3D inversion of the single-profile data could obtain reasonable and reliable electrical structures on a regional scale. Combining 2D and 3D models, and according to our present data, we find that both SDF and YNXF probably have cut completely the high resistivity layer in the upper crust and extended to the high conductivity layer in the middle crust. In terms of the deep geometry of the faults, at the profile's location, the SDF dips nearly vertically or dips southeast with high dip angle, and the YNXF dips southeast at depth. In addition, according to the results from our measured MT profile, we find that the 3D inversion of single-profile MT data has the capacity of identifying the location and deep geometry of local faults under present computing ability. Finally, this research suggests that appropriate cell size and reasonable smoothing parameters are important factors for the 3D inversion of single-profile MT data, more specifically, too coarse meshes or too large smoothing parameters on horizontal direction of 3D inversion may result in low resolution of 3D inversions that cannot identify the structure of faults. While, for vertical mesh size and data error thresholds, they have limited effect on identifying shallow tectonics as long as their changes are within a reasonable range. 3D inversion results also indicate that, to some extent, adding tippers to the 3D inversion of a MT profile can improve the model's constraint on the deep geometry of the outcropped faults.     

利用大地电磁资料对玄武岩成像的可行性

The magnetotelluric （MT） method has been among the favorite supporting tools for seismic imaging of sub-salt and sub-basalt targets. In this paper we present an example from Kachchh, India （where basaltic rocks overlie Mesozoic sedimentary rocks）, and discuss the feasibility of using MT method as an exploration tool in this geological setting. Our results highlight the difference in magnetotelluric response caused by the thin intrabasalt layering. The key issue addressed in this paper is what MT can and cannot provide in such geological settings. First, we compute apparent resistivity and phase response curves using representative resistivity-depth models and borehole data from the study area. Later, we compare these results to assess the plausibility of using MT to image the sub-volcanic sediments at Kachchh. Finally, we substantiate our discussion through one-dimensional inversion of the field observed MT data from this region that exhibits poor sensitivity of MT for thin basalt layers.     

大地电磁有限差分数值解对比

基于网格精度、形成系统方程的方式、边界条件以及预条件线性算子等,文中对大地电磁（MT）有限差分数值解作了对比.对不同网格剖分方式下的三个均匀半空间模型的一维MT响应对比显示,在降低首层厚度的同时保持层间厚度变化在合理范围可以同时提高主场和辅助场的精度.在利用正常中心网格法（主场和辅助场都定义在单元顶面的中心）计算二维（2-D）TM模式响应时,应该从Maxwell一次差分方程开始组建二次差分方程,这样可以更充分考虑模型电阻率的变化.在对边界值如何影响数值解的测试表明,仅仅提高一维（1-D）边界值的精度对提高2-D MT有限差分数值解的精度是有限的.线性算子对提高MT解的效率十分重要,简单的对比进一步表明合适的预条件再配合好的线性算子（如文中求解2-D MT时所采用的DILU-BICGSTAB方法）不仅可以加速收敛,而且可以降低迭代次数.     

自适应非结构有限元MT二维起伏地形正反演研究

在山区进行MT勘探时,用规则网格有限元方法模拟起伏地形会受到限制.本文采用非结构三角网格可以有效地模拟任意二维地质结构,如起伏地形、倾斜岩层和多尺度构造等.正演引入自适应有限元方法,其在网格剖分过程中能根据单元误差自动细化网格,保证了正演结果的精度.将自适应有限元与Occam算法结合,且引用并行处理技术提高正反演计算速度.通过对比两个理论模型,讨论了地形对MT正演响应的影响;其次进行了不同地电模型带地形反演展示了本文算法的正确性和适用性;最后将该方法应用于实测MT数据处理,证明了自适应非结构有限元方法是复杂地形下处理MT数据的有力工具.     

Joint three-dimensional inversion of magnetotelluric and magnetovariational data

The problem of quantitative three-dimensional interpretation of the magnetotelluric (MT) data ranks among the most difficult problems in electromagnetic (EM) geophysics. Our paper presents a new rigorous numerical method for MT inversion, based on the integral equations technique. An important feature of the proposed method is the calculation of the Frechet derivative with the aid of a quasi-analytical approximation with an inhomogeneous background. This approach simplifies the algorithm of inversion and requires only a single forward modeling on each iteration. We have also developed a method for a joint inversion of MT and magnetovariational (MV) data. We show in the present paper that the joint inversion of MT impedances and the Wiese-Parkinson vectors can automatically allow for the static shift in the observed data, which is caused by the geoelectric inhomogeneities contained in the near-surface layer.