Joint inversion of gravity and seismic data along a profile across the seismogenic fault of 2010 Yushu Ms7. 1 earthquake

Yushu Ms7.1 earthquake occurred on the Ganzi-Yushu fault zone, across which we carried out a joint relative-gravity and seismic-reflection survey, and then performed a gravity inversion constrained by the seismic-reflection result. Based on the data of complete Bouguer gravity anomaly and seismic reflection, we obtained a layered interface structure in deep crust down to Moho. Our study showed that the inversion could reveal the interfaces of strata along the survey profile and the directions of regional faults in two-dimension. From the characteristics of the observed topography of the Moho basement, we tentatively confirmed that the uplift of eastern edge of Qinghai-Tibet plateau was caused by the subduetion of the Indian plate.

Joint inversion of gravity and magnetic data for a two-layer model

Based on the synchronous joint gravity and magnetic inversion of single interface by Pilkington and the need of revealing Cenozoic and crystalline basement thickness in the new round of oil-gas exploration, we propose a joint gravity and magnetic inversion methodfor two-layer models by concentrating on the relationship between the change of thicknessI and position of the middle layer and anomaly and discuss the effects of the key parameters. Model tests and application to field data show the validity of this method.

3D inversion modeling of joint gravity and magnetic data based on a sinusoidal correlation constraint

Joint inversion based on a correlation constraint utilizes a linear correlation function as a structural constraint.The linear correlation function contains a denominator,which may result in a singularity as the objective function is optimized,leading to an unstable inversion calculation.To improve the robustness of this calculation,this paper proposes a new method in which a sinusoidal correlation function is employed as the structural constraint for joint inversion instead of the conventional linear correlation function.This structural constraint does not contain a denominator,thereby preventing a singularity.Compared with the joint inversion method based on a cross-gradient constraint,the joint inversion method based on a sinusoidal correlation constraint exhibits good performance.An application to actual data demonstrates that this method can process real data.

3D Joint inversion of gravity and gravity tensor data

The processing and interpretation of gravity and gradient data plays an important role in geophysics.The cross gradient joint inversion is usually used for achieving structure coupling of multiple geophysical models. In order to realize the coupling of gravity and gravity tensor data,the authors analyzed each component.The results show that different types of data contain different direction information,and derived the joint inversion based on cross gradient function and applied it to model data. The theoretical model results show that the cross gradient method can reduce the multi solution and significantly improve the resolution of the inversion.The method was also applied to inverse the gravity tensor data in Vinton salt dome,showing that this method can get higher resolution results than the separate linear inversion,and be closer to the real density from drilling data.

Fast 3D joint inversion of gravity and magnetic data based on cross gradient constraint

The gravity and magnetic data can be adopted to interpret the internal structure of the Earth.To improve the calculation efficiency during the inversion process and the accuracy and reliability of the reconstructed physical property models,the triple strategy is adopted in this paper to develop a fast cross-gradient joint inversion for gravity and magnetic data.The cross-gradient constraint contains solving the gradients of the physical property models and performing the cross-product calculation of their gradients.The sparse matrices are first obtained by calculating the gradients of the physical property models derived from the first-order finite difference.Then,the triple method is applied to optimize the storages and the calculations related to the gradients of the physical property models.Therefore,the storage compression amount of the calculations related to the gradients of the physical property models and the cross-gradient constraint are reduced to one-fold of the number of grid cells at least,and the compression ratio increases with the increase of the number of grid cells.The test results from the synthetic data and field data prove that the structural coupling is achieved by using the fast cross-gradient joint inversion method to effectively reduce the multiplicity of solutions and improve the computing efficiency.

Joint inversion of gravity and vertical gradient data based on modified structural similarity index for the structural and petrophysical consistency constraint

Joint inversion is one of the most effective methods for reducing non-uniqueness for geophysical inversion.The current joint inversion methods can be divided into the structural consistency constraint and petrophysical consistency constraint methods,which are mutually independent.Currently,there is a need for joint inversion methods that can comprehensively consider the structural consistency constraints and petrophysical consistency constraints.This paper develops the structural similarity index(SSIM)as a new structural and petrophysical consistency constraint for the joint inversion of gravity and vertical gradient data.The SSIM constraint is in the form of a fraction,which may have analytical singularities.Therefore,converting the fractional form to the subtractive form can solve the problem of analytic singularity and finally form a modified structural consistency index of the joint inversion,which enhances the stability of the SSIM constraint applied to the joint inversion.Compared to the reconstructed results from the cross-gradient inversion,the proposed method presents good performance and stability.The SSIM algorithm is a new joint inversion method for petrophysical and structural constraints.It can promote the consistency of the recovered models from the distribution and the structure of the physical property values.Then,applications to synthetic data illustrate that the algorithm proposed in this paper can well process the synthetic data and acquire good reconstructed results.

Simultaneous Structure-Coupled Joint Inversion of Gravity and Magnetic Data Based on a Damped Least-Squares Technique

The structure-coupled joint inversion method of gravity and magnetic data is a powerful tool for?developing improved physical property models with high resolution and compatible features;?however, the conventional procedure is inefficient due to the truncated singular values decomposition?(SVD) process at each iteration. To improve the algorithm, a technique using damped leastsquares?is adopted to calculate the structural term of model updates, instead of the truncated SVD. This?produces structural coupled density and magnetization images with high efficiency. A so-called?coupling factor is introduced to regulate the tuning of the desired final structural similarity level.?Synthetic examples show that the joint inversion results are internally consistent and achieve?higher?resolution than separated. The acceptable runtime performance of the damped least squares?technique used in joint inversion indicates that it is more suitable for practical use than the truncated SVD method.

A MATLAB-Based Numerical and GUI Implementation of Cross-Gradients Joint Inversion of Gravity and Magnetic Data

The cross-gradients joint inversion technique has been applied to multiple geophysical data with a significant improvement on compatibility, but its numerical implementation for practical use is rarely discussed in the literature. We present a MATLAB-based three-dimensional cross-gradients joint inversion program with application to gravity and magnetic data. The input and output information was examined with care to create a rational, independent design of a graphical user interface (GUI) and computing kernel. For 3D visualization and data file operations, UBC-GIF tools are invoked using a series of I/O functions. Some key issues regarding the iterative joint inversion algorithm are also discussed: for instance, the forward difference of cross gradients, and matrix pseudo inverse computation. A synthetic example is employed to illustrate the whole process. Joint and separate inversions can be performed flexibly by switching the inversion mode. The resulting density model and susceptibility model demonstrate the correctness of the proposed program.

Crustal thickness beneath Atlas region from gravity,topographic,sediment and seismic data

The Atlas region in northwest Africa is characterized by the Quaternary volcanism and elevated topography with past complex tectonic mitigation between the African and European plates.Geodynamics of this atypical region has left indubitably imprints in crustal architectonics,mainly regarding the crustal thickness as well as the crustal density structure.The knowledge of crustal thickness variations is of a significant interest,since it provides a crucial constraint to geodynamic and geophysical modelling of this region.In this study,we use gravity,topographic,bathymetric and sediment data together with results of seismic surveys to image the Moho topography beneath the Atlas region.The Bouguer gravity anomalies used for a gravimetric Moho recovery are obtained from the free-air gravity anomalies after subtracting the gravitational contributions of topography,bathymetry and sediments.The regional gravimetric Moho inversion constrained on seismic data is carried out by applying a regularized inversion technique based on Gauss-Newton’s formulation of improved Bott’s method,while adopting Earth’s spherical approximation.The numerical result reveals relatively significant Moho depth variations in the Moroccan Atlas,with minima of approximately 24 km along continental margins of the Mediterranean Sea and maxima exceeding 51 km beneath the Rif Cordillera.The Moho depth beneath the West African Craton varies from 32 km in its southern margin to 45 km beneath the Middle Atlas.The Tell Atlas is characterized by the shallow Moho depth of approximately 22 km and further deepening to 42 km towards the northern edge of the Aures Mountains.Our findings indicate a limited tectonic shortening of the High Atlas with the crustal thickness mostly within 36-42 km.Topographic discrepancies between the Rif Cordillera and the Atlas Mountains suggest that the hypothesis of isostatic compensation cannot be fully established.

Deep structural research of the South China Sea: Progresses and directions

The South China Sea(SCS)is the hotspot of geological scientific research and nature resource exploration and development due to the potential for enormous hydrocarbon resource development and a complex formation and evolution process.The SCS has experienced complex geological processes including continental lithospheric breakup,seafloor spreading and oceanic crust subduction,which leads debates for decades.However,there are still no clear answers regarding to the following aspects:the crustal and Moho structure,the structure of the continent-ocean transition zone,the formation and evolution process and geodynamic mechanism,and deep processes and their coupling relationships with the petroliferous basins in the SCS.Under the guidance of the“Deep-Earth”science and technology innovation strategy of the Ministry of Natural Resources,deep structural and comprehensive geological research are carried out in the SCS.Geophysical investigations such as long array-large volume deep reflection seismic,gravity,magnetism and ocean bottom seismometer are carried out.The authors proposed that joint gravitymagnetic-seismic inversion should be used to obtain deep crustal information in the SCS and construct high resolution deep structural sections in different regions of the SCS.This paper systematically interpreted the formation and evolution of the SCS and explored the coupling relationship between deep structure and evolution of Mesozoic-Cenozoic basins in the SCS.It is of great significance for promoting the geosystem scientific research and resource exploration of the SCS.

面向深部矿产资源勘探的井中重磁三维交叉梯度联合反演

单一井中重磁方法解决问题有限,其三维反演具有严重的多解性。开展面向深部矿产资源勘探的井中重磁三维交叉梯度联合反演,采用交叉梯度函数对密度和磁化率进行耦合,综合井中重磁多参数信息进行联合反演,减少反解的多解性,提高深部矿体识别的准确性。通过理论模型和实际资料进行反演分析。结果表明:井中重磁交叉梯度联合反演具有较高的纵向分辨能力,可以显著提高深部矿体识别的准确性,特别是能有效识别深部隐伏矿体。

基于地震和InSAR联合反演2018年M_(L)5.7兴文地震破裂过程

2018年12月16日发生的M_(L)5.7兴文地震很可能是由页岩气水力压裂所诱发,确定此类震级较大的诱发地震的震源破裂过程具有重要意义。文中利用近震数据和InSAR数据联合反演,获得了兴文地震的破裂过程。与单独使用地震数据或InSAR数据进行反演相比,联合反演得到的地震破裂过程可同时拟合2种类型数据,因此具有更高的时空分辨率。联合反演结果显示该地震为典型的单侧破裂,破裂方向近N向。破裂过程的持续时间为6s,能量释放主要集中在前5s,呈分段式破裂。主震破裂过程分为2个阶段:沿着断裂的走向,紧挨着震中的0~5km范围内为破裂的第1阶段(1~3s);距震中6~8km处为破裂的第2阶段(3~5s)。同震滑移主要集中在5km以浅的区域,峰值滑移约为0.27m,这可以解释为何M_(L)5.7兴文地震造成了较为严重的破坏。结合前震和余震分布可以看出,前震主要集中在滑移区的东部,说明该区域在主震发生之前就已发生破裂,意味着该区域可能存在注入的流体。余震主要分布在滑移区周围,是由主震破裂后的余滑引起的。对比单独反演结果,联合反演克服了台站分布不均匀的影响,提高了破裂分布的分辨率,所得结果更加符合真实物理过程。文中联合反演得到的破裂模型为进一步研究诱发地震机理、地震灾害评估和震后防灾减灾奠定了基础。

临河坳陷高效油气勘探综合物探技术及应用

针对临河坳陷主力生烃凹陷不清、构造及地层难以落实、成藏目标不清、突破井位难以落实等长期以来制约勘探的难点问题,提出了适用勘探新区高效勘探的技术路线及关键技术。以基于多种灵活约束机制的中浅层重力多密度界面反演及归一式重力正演剥层为核心,利用深层目标重力异常提取技术重新认识了临河坳陷地质结构。淖西深洼槽是临河坳陷的主力生烃区,临河坳陷南斜坡受黄河断陷槽控制,发育了中央断垒式潜山披覆构造带,具备两侧双源供烃的有利成藏条件,具有巨大的油气勘探潜力;提出并应用基于井、震资料控制的时频电磁模拟退火电阻率约束反演及基于精细地电结构模型的极化率约束反演等时频电磁目标储层油气检测技术,提高了深层目标的电性分辨率及目标储层的油气预测精度,快速锁定JH2x、LH1x及XH1井等靶区目标,为临河坳陷油气勘探的突破发挥了关键先导性作用,为低勘探程度新区、特别是盆地深层油气勘探提供了有效的方法与技术思路。

速度—密度双参数重震联合反演方法

速度和密度参数在地震资料处理和储层预测中发挥着重要作用,然而多参数间的相互耦合使密度在全波形反演中难以重构。为获得更准确的密度信息,将重力梯度数据纳入全波形反演过程,优化密度更新算法,并制定了一种重震联合反演策略。首先,通过重力梯度数据反演,获得反映地下介质整体密度信息的初始模型,再进行速度—密度参数同步联合反演目标函数的构建及求解。本文方法避免了先验速度—密度关系的限制,降低了对初始模型的依赖程度,模型试算结果表明,重力梯度数据的加入改善了波形反演密度结果的质量,验证了该方法的有效性和准确性,具有较大的应用潜力。

基于源体生长思想的全张量重力梯度数据联合反演

基于源体生长思想的三维反演是一种使用系统搜索的反演方法。和正则化反演相比,该方法计算量小,运算速度快。源体生长的判断准则是其核心,影响着结果质量。本文提出了一种全张量重力梯度数据源体生长反演方法,旨在提高纵向的反演效果。首先,在判断准则中引入深度加权函数,优化对不同深度上源体生长的判断;其次,根据单分量梯度数据反演结果,调整不同类型数据的权重,建立联合反演方法;最后,利用矩阵压缩减少内存占用,提高反演计算效率。通过模型数据与文顿盐丘地区实测数据试验,证明了提出的方法能够有效地引导源体生长,对深部目标具有更高的分辨能力,适用于较复杂形态目标的反演,且具有较高的计算效率和抗噪性。

重力与地震资料的模拟退火约束联合反演

联合反演是综合地球物理研究的重要定量解释手段.本文在总结和分析重力与地震资料联合反演的研究现状基础上,利用改进的全局寻优的快速模拟退火算法,实现了重力和地震资料的约束同步联合反演.针对性地设计了密度和速度界面不完全一致的模型,理论模型的试验说明了方法的效果和适用性.结合最近完成的广东徐闻地区实际资料的处理和解释,表明该方法可准确确定复杂构造物性界面的密度和速度结构,在该地区的油气勘探中发挥了作用.在先验信息约束下,该联合反演方法要明显优于单独的重力反演.

三维重力地震剥层联合反演

以地震资料解释的三维构造图作为模型,用重力三维正演剥离基底及基底以上界面所产生的重力效应,然后对分离后的基底岩性异常进行反演求取基底密度。在具体联合反演算法上,首次将广泛用于地震层析成像反演的DLSQR法引入位场反演,不仅增加了联合反演结果的稳定性,而且极大地提高了反演速度。理论模型的试算和实际资料的反演结果表明,两者反演的剩余密度等值线图形十分相似,剩余密度最小值和最大值相对误差小于4%。

准噶尔盆地北部基底结构与属性问题探讨

准噶尔盆地的基底结构与属性一直是地学界关注的焦点问题之一.横跨准噶尔盆地北部,走向近东西的克拉玛依—喀姆斯特地震剖面提供了该盆地北部详细的地壳与上地幔顶部的速度结构与构造,特别是基底顶界面的速度.沿剖面发现了数条走向近南北的"H"型超壳断裂,它们没有明显的断差,断裂处反射系数明显降低,介质的Q值减小,推测具"开裂"性质;利用盆地内1:20万重磁数据完成了重磁联合反演,获得了沿剖面的地壳与上地幔顶部的二维密度结构与二维磁性结构.根据在一定深度范围内介质的速度-密度-岩性之间的关系,确定了盆地北部基底岩性分布.结果表明,准噶尔盆地北部的基底多处为基性和超基性物质,推测为深部(上地幔)物质沿超壳断裂进入地壳内部并对地壳物质进行改造的结果.这一推断得到盆地内部高磁性、高重力异常的支持,也与盆地具有较高的地壳平均速度相一致.综合其他地球物理与地质资料综合分析,给出了综合地质解释剖面,建立了准噶尔盆地北部基底结构与属性的动力学模型.

密度和速度随机分布共网格模型的重力与地震联合反演

针对重力与地震联合反演存在的问题,结合已有的研究成果,本文研究实现了速度和密度随机分布共网格单元模型的建模技术,以适应密度和速度剧烈变化的复杂模型及联合反演的计算要求.重力正演利用了该网格的二度半体模型,并进一步改进了地震走时的二维射线追踪计算方法,以适用于速度随机分布的网格介质.结合改进的模拟退火算法,实现了这种共网格条件下的重力与地震资料的同步联合反演.模型试验证明了重力与地震联合反演可以准确确定复杂物性界面的密度和速度结构,适用于物性界面不完全一致和物性变化剧烈的复杂模型,并且联合反演结果要优于单独的重力反演.带先验信息约束下的实际资料的联合反演,进一步证明了该方法的适用性和效果,可提高反演精度并减少多解性.

密井网条件下随机地震反演及其在河道砂体预测中的应用

以大庆长垣油田萨尔图油层为例,研究了密井网条件下随机地震反演方法及其在河道砂体预测中的应用。研究表明：不同厚度砂体的随机地震反演结果符合率差异较大：厚度大于3m的砂体符合率为91%;厚度为2~3m的砂体符合率为83%;厚度小于1m的砂体符合率为70%。随着砂体厚度的减小,符合率降低,井网密度越大,预测精度下降幅度越小。利用＂地震反演引导,井点微相控制＂方法,根据测井曲线形态差异与反演剖面砂体发育状况的分析,能够较为准确地对河道砂体的单一河道边界、走向、井间砂体叠置关系及窄小河道砂体进行描述。利用随机地震反演结果在河道砂体沉积模式的控制下完成油田开发中后期各类河道砂体的精细描述是切实可行的,且效果显著。