基于各向异性和极化介质的多参数三维可控源电磁法三维正反演研究

The complex geological situation urgently needs the high precision three-dimensional forward and inversion as an important tool for the interpretation of electromagnetic data. Based on the scientific problem of multiple parameter three dimensional (3D) controlled source electromagnetic method of forward and inversion which involved anisotropy and polarization model, the integrated geophysical reservoir exploration theory will be derived and established. The purpose is to create a comprehensive geophysical detection technology for fine imaging and fluid identification of reservoir. Three dimensional forward algorithm of electromagnetic method, including the algorithm for induced polarization effect and anisotropic model, based on various simulation and observation configuration as well as complex terrain will be deeply carried out. Through the algorithm utilizing structure information obtained from seismic data and logging data to obtain the high accuracy of reservoir resistivity and chargeability parameters as the constraint, large scale and multi-parameter joint inversion including complex topography will be fulfilled to further improve the resolution of resistivity and chargeability imaging. Using established petrophysical relationship of complex pore structure of reservoir, as well as the relationship among resistivity, porosity and fluid saturation, the multiple geophysical information constraint inversion theory and method will be studied and completed. The key of the research is to improve resistivity imaging resolution and accuracy of reservoir based on the anisotropic and polarized model to enhance the utilization of controlled source electromagnetic method for quantitative evaluation for oil and gas reservoir, dynamic monitoring and fluid identification ability. Finally the scientific purpose of acquisition of three-dimensional anisotropic information, reservoir fine description, as well as dessert predication of shale gas by 3D controlled electromagnetic method will be achieved.

地下复杂的地质情况迫切需要高精度三维正反演作为电磁资料解释的重要工具。围绕基于各向异性和极化介质的多参数三维可控源电磁法正反演这一科学问题，以建立油气藏地球物理探测理论、催生精细成像和流体识别为核心的综合地球物理探测技术为目标，深入开展多种观测条件下的包括极化效应和各向异性的三维复杂模型的电磁响应的正演算法研究，利用包含由地震资料获得的构造信息与测井资料获得的储层信息给电阻率与极化率参数作为约束，利用建立的储层复杂孔隙结构、油气储层的电阻率—孔隙度—流体饱和度的物性与电性关系模型，实现包含地形模型的大尺度和多参数的多元地球物理信息的约束联合反演，进一步提高各向异性储层电阻率与极化率成像的分辨率和精度，提升利用可控源电磁法进行油气储层定量评价、动态监测和流体识别的能力，达到获取地层三维各向异性分布、提高对储层进行定量描述和页岩气甜点预测的科学目的。

各向异性和IP效应的存在是导致各向同性可控源电磁法解释不准确的重要原因。围绕各向异性和极化介质的三维可控源电磁法三维正反演研究问题，开展了地表和地层条件下岩石物性变化对弹性及电性特性的影响及变温压条件对岩石弹性及电性参数的影响研究，采用双科尔模型反演并获得了频谱参数。研究了温压共同变化时对岩石复电阻率及频谱参数的影响。根据理想模型制作了人工砂岩样品，获得了地层条件下含导电矿物的频散特征与复电阻率模型。通过对地层水饱和致密砂岩和灰岩的测量，发现砂岩复电阻率与孔隙度及渗透率存在着幂指数关系，灰岩复电阻率与渗透率则存在着指数关系。推导了用电阻率求取渗透率的表达式，得到了公式中致密砂岩胶结指数的最佳取值范围。.从有源麦克斯韦方程出发，推导了任意各向异性介质中三维可控源电磁法基于电场双旋度方程的边值问题，采用基于虚功原理的Galerkin非结构网格的节点有限元法进行了方程的推导并按行压缩方式存储系数矩阵，选用了ILU分解将预处理后的方程用稳定双共轭梯度法进行迭代求解，计算中使用了变节点数网格以及无限元法将边界拓展到数值的无限远处，采用任意四边形单元网格改变地形网格节点高程实现了对地形的加载。利用电流密度无散的特性对变分问题进行了散度校正，利用基于Krylov子空间的迭代技术求解线性方程组并计算出了视电阻率和阻抗相位。研究发现，视电阻率和相位均对地层各向异性特征表现敏感，IP效应对大地电磁场同样存在着不可忽视的影响，该效应会导致张量阻抗及视电阻率的减小，幅值和视电阻率的减小与激电效应的强度呈正相关关系，极化率对视电阻率的影响较时间常数和频率相关系数更大，相位的变化规律较视电阻率更为复杂。分别研究了标量源、倾斜源和张量源激发下的视电阻率响应，发现采用张量源数据获得的视电阻率在不同方向上均能较清晰地刻画出异常体的边界，表明了采用张量源激发和多分量采集方式可有效地刻画地层介质的各向异性特征。