Three-dimensional constrained gravity inversion of Moho depth and crustal structural characteristics at Mozambique continental margin

Mozambique's continental margin in East Africa was formed during the break-off stage of the east and west Gondwana lands. Studying the geological structure and division of continent-ocean boundary(COB) in Mozambique's continental margin is considered of great significance to rebuild Gondwana land and understand its movement mode. Along these lines, in this work, the initial Moho was fit using the known Moho depth from reflection seismic profiles, and a 3D multi-point constrained gravity inversion was carried out. Thus, highaccuracy Moho depth and crustal thickness in the study area were acquired. According to the crustal structure distribution based on the inversion results, the continental crust at the narrowest position of the Mozambique Channel was detected. According to the analysis of the crustal thickness, the Mozambique ridge is generally oceanic crust and the COB of the whole Mozambique continental margin is divided.

Constrained geometry analysis to resolve 3-D deformations from three ground-based radars

When multiple ground-based radars(GB-rads)are utilized together to resolve three-dimensional(3-D)deformations,the resolving accuracy is related with the measurement geometry constructed by these radars.This paper focuses on constrained geometry analysis to resolve 3-D deformations from three GB-rads.The geometric dilution of precision(GDOP)is utilized to evaluate 3-D deformation accuracy of a single target,and its theoretical equation is derived by building a simplified 3-D coordinate system.Then for a 3-D scene,its optimal accuracy problem is converted into determining the minimum value of an objective function with a boundary constraint.The genetic algorithm is utilized to solve this constrained optimization problem.Numerical simulations are made to validate the correctness of the theoretical analysis results.

3-D velocity structure in the central-eastern part of Qilianshan

The 3-D velocity tomography image of the central-eastern part of Qilianshan is obtained by the joint inversion of 3-D velocity structure and focal parameters based on the S-P data of micro-earthquakes recorded by the digital seismic network set up for a Sino-French cooperation program since 1996. The inversed velocity structure does primarily reflect some important features of the deep structure in the region and provide the scientific background for the further study of active tectonic structure and the calculation of earthquake parameters.

Earthquake relocation and 3-dimensional crustal structure of P-wave velocity in central-western China

A simultaneous inversion of earthquake relocation and three-dimensional crustal structure of P-wave velocity in central-western China (21癗~36癗, 98癊~112癊) were performed in this paper. The crustal P-wave velocity model and earthquake relocation for this region are obtained using Pg and Sg phase readings of 9 988 earthquakes from 1992 to 1999 recorded at 193 seismic stations within central-western China by SPHYPIT90 and SPHREL3D90 programs. A lateral inhomogeneous structure of P-wave velocity in this region was obtained. Ob-vious contrast of P-wave velocities was revealed on both sides of active fault zones. Relocated epicenters of 6 459 events show clear lineation along active faults, which indicated a close correlation between seismicity and the active faults in this region. Focal depths of 82% relocated events ranged from 0 to 20 km, which is in good agreement with that from double-difference earthquake location algorithm.

FAST APPROXIMATE INVERSION OF MAGNETOTELLURIC(FAIMT) DATA FOR A HORIZONTALLY LAYERED EARTH WITH NEAR-SURFACE INHOMOGENEITIES

This paper discusses use of approximations and the Integral Mean Value Theorem to show that 6 coefficients approximately describe the distortions of near surface inhomogeneities on the MT field of a horizontally layered earth model. When these 6 coefficients are considered together with those of the magnetic field of a horizontally layered earth model,the analytic and approximate wave impedance equations can be derived for the MT response of a horizontally layered earth model with near-surface 2-D and 3-D inhomogeneities. These approximate wave impedance equations are used with inverted MT data for 2-D and 3-D forward modelling. Although these 6 coefficients cannot be determined before inversion,initial estimates can be used. The 6 coefficients and the asistivity and thickness of each layer of a horizontally layered earth can be obtained by using published inversion methods. The 6 coefficients give important informaion (depths and resistivities) on the near-surface inhomogenelties.The authors inverted 2-D and 3-D theoretical models for Fast Approximate Inversion of Magnetotelluric (FAIMT) data for a horizontally layered earth with near-surface inhomogeneities compares favorably with traditional invrsion methods, especially for inverting regional or basin structures. This method simplifies computation and gives a reasonable 1 -D geological model with fewer nonuniquenas problems.

3-D seismic tomography for velocity and interface structure of the crust and upper mantle(theoreticalpart)

A method of three dimensional (3-D) model parameterization is presented that makes forward and inverse problems become easy. The velocity and interface structure of crust and upper mantle are described by a set of highly smoothed functions. Shooting ray tracing method is chosen to calculate the ray paths for both forward and inverse problems. The partial derivatives of traveltime with respect to parameters of the model grids are calculated analytically while rays are being traced. Because velocity and interface functions have second-order continuous partial derivatives, the geometrical shadow zones at the surface caused by scattering and focusing of ray paths can be prevented. After ray tracing, an equation consisting of matrix and vectors for inverse problem is obtained. We use singular value decomposition method with damped factor to solve the equation. A synthetic data set which consists of several in-line profiles is used to test the methods. The results show that the methods are robust. Compared with the two dimensional method, the 3-D inversion method can give the right position of interfaces and the velocity structure when the crustal model is complicated.

Inversion of gravity gradient data based on spatial gradient weighting

Compared with traditional gravity measurement data,gravity gradient tensor data contain more high frequency information,which can be used to understand the earth's interior structure,mineral resources distribution etc. In this study,the authors present an algorithm for inverting gravity gradiometer data to recover the three-dimensional( 3-D) distributions of density. Spatial gradient weighting was used to constrain the extent of the body horizontally and vertically. A more accurate inversion result can be obtained by combining the prior information into the weighting function and applying it in inversion. This method was tested on synthetic models and the inverted results showed that the resolution was significantly improved. Moreover,the algorithm was applied to the inversion of empirical data from a salt dome located in Texas,USA,which demonstrated the validity of the proposed method.

Reconstruction of Temperature Field in 3-D, Absorbing, Emitting, and Anisotropically Scattering Medium

The soft measurement technology of flame temperature field is an efficient method to learn the combustion status in furnace. Generally, it reconstructs the temperature field in furnace through the image of flame, which is a process to solve radiative inverse problem. In this paper, the flame of pulverized coal is considered as 3-D, absorbing, emitting, and anisotropically scattering non-gray medium. Through the study on inverse problem of radiative heat transfer, the temperature field in this kind of medium has been reconstructed. The mechanism of 3-D radiative heat transfer in a rectangular media, which is 2 m×3 m× 5 m and full of CO2, N2 and carbon particles, is studied with Monte Carlo method. The 3-D temperature field in this rectangular space is reconstructed and the influence of particles density profile is discussed.

Advanced Computational Methods of Rapid and Rigorous 3-D Inversion of Airborne Electromagnetic Data

We develop a new computational method for modeling and inverting frequency domain airborne electromagnetic(EM)data.Our method is based on the contraction integral equation method for forward EM modeling and on inversion using the localized quasi-linear(LQL)approximation followed by the rigorous inversion,if necessary.The LQL inversion serves to provide a fast image of the target.These results are checked by a rigorous update of the domain electric field,allowing a more accurate calculation of the predicted data.If the accuracy is poorer than desired,rigorous inversion follows,using the resulting conductivity distribution and electric field from LQL as a starting model.The rigorous inversion iteratively solves the field and domain equations,converting the non-linear inversion into a series of linear inversions.We test this method on synthetic and field data.The results of the inversion are very encouraging with respect to both the speed and the accuracy of the algorithm,showing this is a useful tool for airborne EM interpretation.

A Two-Streamfunction-Coordinate Method for the Numerical Solution of 3-D Aero-Thermodynamics Direct and Inverse Problems

This paper describes a new method which has been developed for the solution of direct and inverse problems of 3-D compressible flows in turbomachinery.Two types of streamfunctions are proposed in the paper and the streamfunction-coordinate system is applied in numerical computations.The algorithm is applied to stator blades and the results are compared with experimental data,It is shown that the comparisons are very satis- factory.

基于协同克里金方法的重力梯度全张量三维约束反演

随着重力梯度全张量测量技术的日趋成熟,重力梯度全张量数据的三维反演技术日益受到重视与关注.全张量数据反演与重力数据反演一样仍然面临着严重的多解性问题.本文将基于地质统计学的协同克里金方法应用于重力梯度全张量数据三维反演,建立了密度约束下的多变量协同克里金联合反演方程,以降低反演的多解性.模型试验表明密度信息的加入能够有效降低反演的多解性,提高反演结果的分辨率,尤其是纵向分辨率能够得到显著提高.最后对美国德克萨斯州一个岩丘区所获得实际资料的应用表明了本文方法的实用性.

地震反演中的三维复杂约束模型

地震反演中约束信息模型的建立,特别是多井、断裂发育区的三维复杂约束模型的建立,是地震波阻抗约束反演中的关键技术环节,对反演质量有着重要影响。运用地震、地质综合分析方法,系统地研究了测井资料垂向井孔轨迹约束、地质层位横向控制约束、断块约束、地层沉积模式和接触关系约束等三维约束模型的关键要素。在三维复杂构造和沉积框架关系建立、约束信息三维空间内插外推以及二次修正方法研究的基础上,建立了包括逆断层在内的复杂断裂约束模型以及河道、盐丘(或礁体)和地层缺失等地层沉积模型。通过对胜利油田牛庄地区三维复杂区块实际约束模型的建立和反演,证明了该方法行之有效,大大提高了反演结果的精度,取得了良好的应用效果。

基于Extrapolation Tikhonov正则化算法的重力数据三维约束反演

通过研究重力数据三维反演解的病态性,利用基于拉格朗日插值方法的Extrapolation Tikhonov正则化方法来解决反演中解的不唯一性和不稳定性问题,该方法最大限度的减少了因正则化参数的引入而在反演结果中介入的误差,同时详细讨论了基于三种选择原则的正则化双参数的具体选择方法,模型试算结果表明,与原Tikhonov方法相比,该方法提高了反演的拟合精度.其次,为了消除核函数随深度增加而快速衰减对反演结果的影响,本文改进了前人的重力数据三维反演深度加权函数,改进后的加权函数与原函数相比能更好的识别异常体底部密度分布特征,对于埋深较深的异常体具有较好的识别效果,更好的解决了由近地面趋肤效应作用引起的密度分布不均的问题.同时,利用上下限约束函数限制每一个立方体的密度差范围,并应用于多组人工合成模型.结果表明:该反演方法能准确地获得正演模型的预设参数范围和位置.

东营凹陷典型剖面重磁电震综合解释方法研究

潜山内幕、砂砾岩和深层地质体是东营凹陷地震勘探相对困难的目标。为此,选择总长度约100 km的SL616测线进行了重磁电震综合解释方法的研究,该测线依次经过广饶凸起、东营凹陷和陈家庄凸起3个二级构造单元。阐述了航磁资料的三维欧拉反褶积、电法资料的快速松弛反演(RRI)和重力资料的约束正反演等处理方法。地震勘探中存在屏蔽效应的潜山、砂砾岩体等隐蔽地质目标在重磁电资料上有明显的异常特征。通过重磁电震资料的综合对比分析,重新认识了潜山内幕、砂砾岩体、边界断裂和深部地层,发现了新的地质体。认为陈家庄凸起并非是单一的太古界地层,其内部存在断裂和低阻、低密度体;根据地震资料解释的东营凹陷古生界顶面最深点应向北偏移。

河流相砂岩油藏综合地质评价建模

以冀东油田庙北地区馆陶组油藏地质模型、油藏定量评价模型的建立为例 ,较有针对性地阐述了在河流相沉积的复杂断块区 ,以三维测井约束反演为基础 ,以产能建设为目标 ,按照模式约束、钻井控制、地震导向外推的技术思路 ,应用地质统计学技术 ,充分结合地质、测井、测试等信息 ,定量地研究储层岩性、物性和含油性。同时 ,在三维空间内 ,把构造、储层和油气水特征进行了有效地叠合 ,对油藏位置和特征进行精细描述 ,并建立起定量反映油气田特征的三维可视化模型。经实践检验 ,可大大提高建模精度 ,从而为高速、高效地开发油田 ,动用其地质储量提供了可靠的地质依据 ,为油藏数值模拟和开发方案的编制提供了地质模型 ,并起预测作用。

测井约束反演技术在煤田三维地震岩性勘探中的应用

利用地震技术解决岩性问题在煤田勘探中一直是近年来人们研究的一个热门课题,与其他地震反演技术相比,测井约束反演技术不仅可提高原始地震资料的垂向分辨率,而且将地震波转换为层的信息,因此正在岩性勘探中得到广泛应用.本文介绍了测井约束反演技术的原理及影响因素,并以开滦集团荆各庄矿某采区岩性勘探为例,说明了测井约束反演技术在煤田三维地震岩性勘探中的具体方法和应用效果.

多井约束反演技术在东濮文东地区储层预测中的应用

多井约束反演技术Interwell—3D是一种基于三维模型的交互式地震地层反演,具有层位标定、构造解释、快速建模等功能。引入三维地质模型约束机制,以钻井、测井资料为约束,采用网格反演的算法,反演出高精度波阻抗数据体,为进一步研究储层的空间分布、物性特征等提供可靠基础资料。应用该枝术对文东地区目标区Es33—Es34:地层进行了储层预测,对砂体的空间分布、厚度变化、物性特征做了精确描述,与钻井符合较好,为圈定有利储层提供了可靠依据。

埕南地区砂砾岩扇体储层的预测及效果

埕南大断层下降盘发育了许多不同规模的砂砾岩体。本文应用三维可视化技术、地震属性技术、相干分析技术对砂砾岩扇体的时空展布进行了分析研究和预测 ,采用测井约束反演技术、时频分析技术对单个砂砾岩扇体进行了描述 ,确定出研究区古地貌的 6个古冲沟及其对应的埕 913等 10余个砂砾岩体的空间展布特征 ,初步形成了砂砾岩体储层预测及描述技术序列 ,实现埕南断裂带上砂砾岩扇体油藏的高效勘探开发 ,取得了显著的勘探效果。

大情字井地区高精度三维地震解释技术及应用效果

本文针对大情字井地区“三小多断”(小构造、小断块、小断鼻、多断层 )复杂构造、“薄、窄、多变”复杂储层等特殊地质条件 ,开展了高精度三维地震解释方法的研究工作。应用三维可视化、相干数据体、水平切片和图分析等手段进行三维构造精细解释 ,明显提高了地震勘探识别地下复杂地质构造及地震异常反射体的能力。应用精细地质预测、属性分析、多井约束反演技术对薄互层地质条件下的储层进行了综合岩性解释 ,定量预测和描述了单层砂岩空间分布及变化规律。本套技术充分发挥了三维勘探的优势 。

川南河包场区块茅口组缝洞系统定量描述

在河包场构造钻遇下二叠统茅口组的16口井均位于逆断层上,有11口井获工业气流,其中5口井测试产气20×10~4m^3/d以上。该区茅口组茅四茅二段储层为裂缝和溶洞组成的储集体,为了定量描述缝洞系统的空间分布和发育规模,对下二叠统逆断层和茅口组茅四—茅二段储层顶、底进行了精细对比追踪,对茅四—茅二段进行了高分辨率的逆断层约束速度反演,并结合叠前、叠后地震属性选取敏感属性进行缝洞系统的定量检测,最后利用三维可视化技术融合高分辨率逆断层速度反演结果和高精度相干属性数据体进行缝洞系统三维雕刻,定量刻画了该区茅口组有利的缝洞系统空间分布情况。