基于稀疏反演三维表面多次波压制方法

三维表面多次波压制是海洋地震资料预处理中的重要研究课题,基于波动理论的三维表面多次波压制方法(3D SRME)是数据驱动的方法,理论上来说,可有效压制复杂构造地震数据表面多次波.但该方法因对原始地震数据采集要求高而很难在实际资料处理中广泛应用.本文基于贡献道集的概念,将稀疏反演方法引入到表面多次波压制中,应用稀疏反演代替横测线积分求和,无需对横测线进行大规模重建,进而完成三维表面多次波预测,这样可有效解决实际三维地震数据横测线方向稀疏的问题.基于纵测线多次波积分道集为抛物线的假设,为保证预测后三维表面多次波和全三维数据预测的多次波在运动学和动力学特征上基本一致,文中对预测数据实施基于稳相原理的相位校正.理论模型和实际数据的测试结果表明,本文基于稀疏反演三维表面多次波压制方法可在横测线稀疏的情况下,有效压制三维复杂介质地震资料中的表面多次波,从而更好地提高海洋地震资料的信噪比,为高分辨率地震成像提供可靠的预处理数据保障.     

3D LBFGS inversion of controlled source extremely low frequency electromagnetic data

The controlled source extremely low frequency (CSELF) electromagnetic method is characterized by extremely long and powerful sources and a huge measurement range. Its electromagnetic field can therefore be affected by the ionosphere and displacement current. Research on 3D forward modeling and inversion of CSELF electromagnetic data is currently in its infancy. This paper makes exploratory attempts to firstly calculate the 1D extremely low frequency electromagnetic field under ionosphere-air-earth coupling circumstances, and secondly analyze the propagation characteristics of the background electromagnetic field. The 3D staggered-grid finite difference scheme for solving for the secondary electric field is adopted and incorporated with the 1D modeling algorithm to complete 3D forward modeling. Considering that surveys can be carried out in the near field and transition zone for lower frequencies, the 3D Limited-memory Broyden-Fletcher-Goldfarb-Shanno (LBFGS) inversion of CSELF electromagnetic data is presented (in which the sources, or primary fields, are included), with the aim of directly inverting the impedance data, regardless of where it is acquired. Derivation of the objective functional gradient is the core component in the inversion. Synthetic tests indicate that the well-chosen approximation to the Hessian can significantly speed up the inversion. The model responses corresponding to the coexistence of conductive and resistive blocks show that the off-diagonal components of tensor impedance are much more sensitive to the resistivity variation than the diagonal components. In comparison with conventional scalar inversion, tensor inversion is superior in the recoveries of electric anomalies and background resistivity.     

多道瞬变电磁法共中心点道集数据联合反演

多道瞬变电磁法是目前地面资源勘查领域的研究热点,开展该方法观测数据的一维反演对完成装备研发及技术推广具有积极的推动作用.针对多道瞬变电磁法特殊的源波形和数据采集方式,本文对多道瞬变电磁数据的响应提取和一维反演进行了研究.首先,采用反卷积方法从伪随机二进制序列全波形响应数据中提取大地脉冲响应.为了避免脉冲响应中空气波的干扰,提出采用反向积分算法,把脉冲响应转换成下降沿阶跃响应,并将其整理成共中点道集.最后,为充分利用各个偏移距下的响应数据对不同深度范围目标体的分辨能力,采用基于OCCAM算法的联合反演方法对共中心点道集数据进行联合反演.结果表明在不同目标体深度以及有噪声干扰的情况下,共中心点道集数据联合反演计算均可获得较好的结果.     

随钻方位电磁波测井多参数快速反演

大斜度井/水平井随钻测井技术已被广泛的应用于各种复杂油气藏中,但传统随钻电磁波测井仅提供仪器轴向磁场分量,井斜和各向异性对测井响应影响耦合在一起,难以剥离,无法基于反演同时获取多个参数,进行相应的地层评价,且不能提供方位信息,难以实现地质导向功能.随钻方位电磁波测井在提供仪器轴向磁场分量的基础上,还提供了仪器横向磁场分量,其提取的地质导向信号,对地层界面非常敏感,受井斜、地层电阻率对比度和各向异性影响弱,可以反演得到准确的界面位置.此外,额外的磁场分量信息,有效降低了井斜与各向异性的耦合程度,可基于反演算法实现多参数联合反演,满足电阻率测井精细解释评价需求.

     

大地电磁与地震联合反演研究现状与展望

由于大地电磁探测和地震勘探各自存在优势和局限,因此联合反演比单独一种地球物理资料反演更优越.本文剖析了联合反演的两类分类方法,指出大地电磁与地震方法具备联合反演的基础-理论上相似,物性上有联系,并重点分析国内外大地电磁与地震数据联合反演的研究现状与存在问题,总结层状均匀和非均匀两种介质结构的电震联合反演算法.对于如何耦合不同类型的物性参数这一联合反演的核心问题,指出目前广泛使用的岩石物理法和结构法两类方法的适用范围.最后提出大地电磁与地震联合反演的发展方向:层状均匀介质结构要优化线性迭代技术;非均匀的复杂地质结构,需加紧非线性反演理论向非线性反演发展,其中结构法反演前景广阔,要加强实际资料的运用;此外,电震联合反演也需与岩石物性等先验地质信息相结合.     

井地电磁法三维正演模拟和Born近似反演

本文提出一种数值模拟井地电磁法的方法。用体积分方程法对层状介质中的垂直长导线源三维电磁响应做了三维模拟。模拟的结果与解析解对比误差很小,说明算法是正确的。开发了井地电磁法Born近似反演程序,理论模型合成的数据反演结果非常好。     

3D Modeling and Born approximation inversion for the borehole surface electromagnetic method

We present a 3D approach to numerical modeling of the borehole-surface electromagnetic （BSEM） method. The 3D electromagnetic response created by a vertical line current source in a layered medium is modeled using the 3D integral equation method. The modeling results are consistent with analytical solutions. 3D Born approximation inversion of BSEM data is also conducted for reservoir delineation. The inversion method is verified by a synthetic reservoir model.     

基于不等式约束的三维电阻率探测混合反演方法

三维电阻率探测的线性反演和非线性反演中均存在着多解性的固有难题.电阻率线性反演方法的效率较高,但反演结果对初始模型的依赖性较强,易陷入局部极小;而非线性反演方法不依赖初始模型,但搜索效率极低,尚未见到关于三维电阻率非线性反演的文献.针对上述问题,融合线性与非线性反演方法的互补优势,提出了最小二乘法（线性方法）与改进遗传算法（非线性方法）相结合的混合反演方法的概念和思想.首先,提出了将介质电阻率变化范围作为不等式约束引入反演方程的思路,以实现压制多解性、提高可靠性的目标.提出了宽松不等式约束和基于钻孔推断的局部严格不等式约束的获取及定义方法.在此基础上,分别提出了基于不等式约束的最小二乘线性反演方法和遗传算法非线性反演方法.其次,对于遗传算法在变异搜索方向控制、初始群体产生等方面进行了改进,优化了其搜索方向和初始群体多样性.然后,提出了混合反演方法及其实现方案,利用改进遗传算法进行第一阶段反演,发挥其对初始模型的依赖程度低的优势,搜索到最优解附近的空间,输出当前最优个体;利用最小二乘法进行第二阶段反演,将遗传算法得到的当前最优个体作为初始模型,在最优解附近空间执行高效率的局部线性搜索,最终实现地电结构的三维成像.最后,开展了合成数据与实际工程算例验证,与传统最小二乘方法进行了对比,发现混合反演方法在压制多解性、摆脱初始模型依赖和提高反演效果方面有较好效果.

     

基于Russell近似的纵横波联合反演方法研究

PP波和PS波联合反演方法作为有效的地震技术,比单纯纵波反演精度要高,能够提高地震储层识别的精度.以Russell近似理论为基础,推导了新的转换波AVO近似公式,双层模型界面的反射特征数值模拟显示,新公式具有较高的近似精度,且具备直接反演流体因子f、剪切模量μ和密度ρ等参数的优势,有效避免间接反演带来的误差.结合纵横波联合反演理论,提出了基于贝叶斯理论的新型联合反演算法.在实际应用中,对纵波和转换波角道集进行同相轴匹配处理,综合利用纵波和转换波资料携带的信息,实现基于Russell近似的多波联合反演.模型数据和实际资料测试结果表明,反演结果与真实值或测井结果匹配度较高,证实该方法真实有效.     

航空瞬变电磁数据光滑拟二维反演

航空瞬变电磁法适用于浅表地层的大面积探测,由于实测数据量巨大,一维反演作为一种快速高效的方法被广泛应用.在层状地电条件下,横向约束反演能有效的改善传统单点阻尼最小二乘反演结果中界面横向不连续的情况,但其存在反演过程依赖初始模型,且在复杂层状情况下迭代不稳定的问题.本文提出一种基于OCCAM反演并在正则化项中引入横向光滑约束的光滑拟二维反演方法,在保持OCCAM方法对初始模型依赖性小优势的同时,也使得相邻测点电性横向连续.在反演过程中采用令满足迭代误差的测点不再参与后续迭代的策略,以此减少不必要的正演和雅可比计算,提高反演效率.通过对三个不同地电情况的理论模拟数据进行光滑拟二维反演,并与其他传统反演方法对比,验证了该方法能有效的提高反演稳定性,得到与理论模型高度吻合的反演结果.     

3-D approximate inversion for transient electromagnetic soundings

IntroductionThe issues of forward and inverse interpretation for homogeneous half space models and layered models of the Earth have well been solved in trAnsient electromagnetic sounding (TEM), butinterpreting data from more complicated 2-D or 3-D models are difficult because their responsefunctions are complicated and expensive to calculate. For the sake of simplification, based on thetheories of smoke ring (Nabighian, 1979), we regard current lines in the Earth induced by transmitting sou…     

三维频率域可控源电磁反演研究

对于三维可控源电磁,反演计算效率、张量测量、旁侧效应以及阴影效应是目前研究的热点.本文正演采用基于库仑规范条件的耦合势有限体积算法,反演采用有限内存BFGS(L-BFGS)算法.合成数据反演结果表明:(1)有限内存BFGS法比非线性共轭梯度法,在反演计算效率上具有一定的优势,更适合求解大规模三维可控源电磁反演问题.(2)张量可控源电磁法相对于标量可控源电磁法,前者在模型分辨率上优于后者.(3)在某个区域无法布置测网的情况下,我们可利用旁侧效应在异常体周围布置测网进行三维反演,从而获得真实异常体的信息.同时,为避免阴影效应,我们应在测网外增加可控源电磁控制点,使得三维反演的数据更加完备.     

Fast approximate 1D modelling and inversion of transient electromagnetic data

A novel, fast, and approximate forward modelling routine for time‐domain electromagnetic responses is presented. It is based on the separation of the forward problem into a configuration‐independent part, mapping conductivity as a function of depth onto apparent conductivity as a function of time, and a configuration‐dependent part, i.e., the half‐space step response. The response of a layered model is then found as the half‐space response for a half‐space conductivity equal to the apparent conductivity. The mapping is ten times faster than traditional accurate forward modelling routines, and through stochastic modelling, it is found that the standard deviation of the modelling error is 0.7 %. The forward mapping lends itself to integration in a modern state‐of‐the‐art inversion formulation in exactly the same way as traditionally computed responses, and a field example is included where inversion results using the approximate forward response are compared with those of an accurate forward response for helicopterborne transient electromagnetic data. In addition to being used in its own right in inversion of transient data, the speed and accuracy of the approximate inversion mean that it is well suited for quality control and fast turnaround data delivery of survey results to a client. It can also be used in hybrid inversion formulations by supplying initial iterations and high‐quality derivatives in an inversion based on accurate forward modelling.     

2.5D forward modeling and inversion of frequency-domain airborne electromagnetic data

Frequency-domain airborne electromagnetics is a proven geophysical exploration method. Presently, the interpretation is mainly based on resistivity—depth imaging and one-dimensional layered inversion; nevertheless, it is difficult to obtain satisfactory results for two- or three-dimensional complex earth structures using 1D methods. 3D forward modeling and inversion can be used but are hampered by computational limitations because of the large number of data. Thus, we developed a 2.5D frequency-domain airborne electromagnetic forward modeling and inversion algorithm. To eliminate the source singularities in the numerical simulations, we split the fields into primary and secondary fields. The primary fields are calculated using homogeneous or layered models with analytical solutions, and the secondary (scattered) fields are solved by the finite-element method. The linear system of equations is solved by using the large-scale sparse matrix parallel direct solver, which greatly improves the computational efficiency. The inversion algorithm was based on damping least-squares and singular value decomposition and combined the pseudo forward modeling and reciprocity principle to compute the Jacobian matrix. Synthetic and field data were used to test the effectiveness of the proposed method.     

Constraints in 3D gravity inversion

A three-dimensional (3D) inversion program is developed to interpret gravity data using a selection of constraints. This selection includes minimum distance, flatness, smoothness and compactness constraints, which can be combined using a Lagrangian formulation. A multigrid technique is also implemented to resolve separately large and short gravity wavelengths. The subsurface in the survey area is divided into rectangular prismatic blocks and the problem is solved by calculating the model parameters, i.e. the densities of each block. Weights are given to each block depending on depth, a priori information on density and the density range allowed for the region under investigation. The present computer code is tested on modelled data for a dipping dike and multiple bodies. Results combining different constraints and a weight depending on depth are shown for the dipping dike. The advantages and behaviour of each method are compared in the 3D reconstruction. Recovery of geometry (depth, size) and density distribution of the original model is dependent on the set of constraints used. From experimentation, the best combination of constraints for multiple bodies seems to be flatness and a minimum volume for the multiple bodies. The inversion method is tested on real gravity data from the Rouyn-Noranda (Quebec) mining camp. The 3D inversion model for the first 10 km is in agreement with the known major lithological contacts at the surface; it enables the determination of the geometry of plutons and intrusive rocks at depth.     

飞行高度同时反演的固定翼航空瞬变电磁-维反演

航空电磁测量记录中,不仅感生电动势测量数据有观测误差,而且高度计测量数据也有误差,直接进行常规反演往往导致反演结果不可靠,研究飞行高度数据有误差下的反演算法具有实际意义.本文以层状模型的固定翼时间域航空电磁多分量理论响应数据为例,提出了两种针对飞行高度计记录数据有误差时的正则化反演算法,一个是自适应正则化反演方法,另一...     

Simultaneous joint migration inversion for high-resolution imaging/inversion of time-lapse seismic datasets

The current time-lapse practice is to exactly repeat well-sampled acquisition geometries to mitigate acquisition effects on the time-lapse differences. In order to relax the rigid requirements on acquisition effects, we propose simultaneous joint migration inversion as an effective time-lapse tool for reservoir monitoring, which combines a joint time-lapse data processing strategy with the joint migration inversion method. Joint migration inversion is a full-wavefield inversion method that explains the measured reflection data using a parameterization in terms of reflectivity and propagation velocity. Both the inversion process inside the imaging/inversion scheme and the extra illumination provided by including multiples in joint migration inversion makes the obtained velocity and reflectivity operator largely independent of the utilized acquisition geometry and, thereby, relaxes the strong requirement of non-repeatability during the monitoring. Because simultaneous joint migration inversion inverts for all datasets simultaneously and utilizes various constraints on the estimated reflectivities and velocity, the obtained time-lapse differences have much higher accuracy compared to inverting each dataset separately. It allows the baseline and monitor parameters to communicate with each other dynamically during inversion via a user-defined spatial weighting operator. In order to get more localized time-lapse velocity differences, we further extend the regular simultaneous joint migration inversion to a robust high-resolution simultaneous joint migration inversion process using the time-lapse reflectivity difference as an extra constraint for the velocity estimation during inversion. This constraint makes a link between the reflectivity- and the velocity difference by exploiting the relationship between them. We demonstrate the feasibility of the proposed method with a highly realistic synthetic model based on the Grane field offshore Norway and a time-lapse field dataset from the Troll Field.     

Pitfalls of 1D inversion of small-loop electromagnetic data for detecting man-made objects

In order to interpret field data from small-loop electromagnetic (EM) instruments with fixed source–receiver separation, 1D inversion method is commonly used due to its efficiency with regard to computation costs. This application of 1D inversion is based on the assumption that small-offset broadband EM signals are insensitive to lateral resistivity variation. However, this assumption can be false when isolated conductive bodies such as man-made objects are embedded in the earth. Thus, we need to clarify the applicability of the 1D inversion method for small-loop EM data. In order to systematically analyze this conventional inversion approach, we developed a 2D EM inversion algorithm and verified this algorithm with a synthetic EM data set. 1D and 2D inversions were applied to synthetic and field EM data sets. The comparison of these inversion results shows that the resistivity distribution of the subsurface constructed by the 1D inversion approach can be distorted when the earth contains man-made objects, because they induce drastic variation of the resistivity distribution. By analyzing the integrated sensitivity of the small-loop EM method, we found that this pitfall of 1D inversion may be caused by the considerable sensitivity of the small-loop EM responses to lateral resistivity variation. However, the application of our 2D inversion algorithm to synthetic and field EM data sets demonstrate that the pitfall of 1D inversion due to man-made objects can be successfully alleviated. Thus, 2D EM inversion is strongly recommended for detecting conductive isolated bodies, such as man-made objects, whereas this approach may not always be essential for interpreting the EM field data.     

无人机频率域半航空电磁法三维反演

当前无人机频率域半航空电磁方法(SAEM)成为地球物理勘探中的新兴技术,该方法通过空中无人飞行器测量地面上单个或多个可控源的垂直磁场.本文为无人机频率域SAEM开发了三维反演程序,正演采用交错网格有限差分.由于无人机采集的数据量巨大,因此使用了有限内存拟牛顿法(LBFGS)实现快速的三维反演,以避免计算和存储巨大的灵敏...