岩溶储层小型缝洞体三轴感应测井响应数值/物理模拟研究

As the major pore space and seepage channel developed in karstic reservoir, the small fracture-cave is characterized by its relative low resistivity and multi-axial anisotropy, which leads to the complicated electrical logging response. The formation resistivity and anisotropy provided by tri-axial induction logging, could offer benefits for the identification and characterization of fracture-cave structure by electrical logging. According to the geologic features, small fracture-cave structures are abstracted and equated. The model of bead-like and stratiform fracture-cave structures is established and the tensor conductivity is derived. The multiscale subdivision of complex fracture-cave structures is carried out based on adaptive Delaunay algorithm. Employing parallel technology of CPU and GPU along with preconditioner of sparse matrix, the numerical simulation of the tri-axial induction logging is conducted efficiently. Scaled-down model of formation and prototype of tri-axial induction logging tool is designed. Based on the flume model, the fracture-cave model is made by metallic paint and cement mixed with graphite. Combining the physical measurement with the numerical simulation, the application scope of the tri-axial induction logging is researched systematically,response of the small fracture-cave structure is researched systematically，laying the foundation for the representation of the fracture-cave structure in karstic reservoir and offer help for the distribution research and reservoir evaluation of the fracture-cave structure in karstic reservoir. The sensibility of the tri-axial induction logging to the parameters, combination and distribution of the fracture-cave structure is analyzed. The numerical/physical simulation of tri-axial induction logging response of small fracture-cave structures is researched systematically, laying the foundation for the qualitative identification and evaluation of the fracture-cave structures in karstic reservoir and offering method for exploring development rules and building geologic model of the fracture-cave structures in karstic reservoir.

岩溶储层小型缝洞发育，缝洞段电阻率偏低且多轴各向异性明显，导致其电测井响应尤为复杂。三轴感应测井可准确获取地层各向异性信息，为缝洞结构电测井识别与表征提供有利条件。本课题拟根据塔河岩溶地区小型缝洞体的地质特征进行抽象、等效，建立串珠状和成层状缝洞体模型，推导其张量电导率；基于自适应Delaunay算法实现复杂缝洞体跨尺度剖分，采用CPU+GPU并行技术及稀疏矩阵预处理条件子，实现三轴感应测井高效数值模拟。同时，研制实验室缩比模型与三轴感应测井样机，并在水槽模型基础上，利用金属喷漆及石墨水泥混合体构建缝洞物理模型。将实验室物理测量与数值仿真结果对比刻度，系统研究三轴感应测井电阻率适用范围，分析其对小型缝洞体参数、组合模式及分布形态的敏感性。岩溶储层小型缝洞体三轴感应测井响应数值/物理模拟研究，可为岩溶区小型缝洞体电测井定性识别与评价奠定基础，进而为探索该类储层发育规律和地质模型建立提供方法。

三轴感应测井测量丰富的地层电阻率信息，是岩溶储层小型缝洞体识别与评价的重要手段和发展方向。基于岩溶储层缝洞形态和分布特征，系统推导了洞穴型、裂缝型和缝洞组合型储层等效电导率张量；针对等效为各向异性介质的小型缝洞体储层，提出了VTI和TTI介质中电磁场快速计算方法，实现三轴感应测井响应快速模拟；针对较大尺寸井旁异常体，采用3D有限元和3D有限差分方法，开展了岩溶地层三轴感应测井响应精细模拟；考虑地层的横向和纵向不连续性，提出了2.5D模拟方法；搭建了缩小比例三轴感应测井实验室物理模拟系统，研制了三轴感应测井仪器样机。研究表明，对于排列规则的洞穴、裂缝和缝洞组合体，可以等效为各向异性地层，其导电特性可用电导率张量表示；基于并矢格林函数和广义反射和透射矩阵方法可求解多层TTI介质中的电磁场；三轴感应测井对井旁洞穴的识别范围与洞穴尺寸、填充电阻率等密切相关，当洞穴半径大于0.2m，填充电阻率小于100Ω•m时，yy，xz分量的识别范围约为1.0m。