基于页岩X射线μ-CT三维成像的微观弹性波传输数字岩心仿真研究

This research will focus on the fundamental research of transport properties of elastic wave in gas-bearing shale to study the anisotropic dispersion of velocity of saturated rock caused by microfactors in a wide range of frequency. The image of minerals distribution and pore structure in the rock at micrometer scale can be obtained with the pantoscopic X-Ray μ-CT instrument with a high resolution. A new algorithm for image segmentation using the weighted filter is developed to effectively recognize the mineral and pore space of rock from the images, hence, the digital core of anisotropic rock can be constructed. On this basis, the Lattice Gas Automata (LGA) method can be improved by using a new rule of particle evolution to simulate the more complex mode of wave transporting in rock. Therefore, the law and mechanism for the effects of minerals distribution, pore structure, saturation and flow capacity on the velocity of wave changing with different frequencies can be investigated from the micro scale with the new LGA and digital core of rock. Furthermore, we can analyze, through the simulated results, how the velocity of elastic wave, the compressional-to-shear velocity ratio and elastic anisotropy of rock, will change with the frequency spanning from well logging to seismic domain in saturated rock. At last, by the way of doing research from micro scale to macro scale, we try to construct the quantitive relationship between the anisotropic dispersion of wave velocity and the micro factors such as saturation, pore structure and so on, and try to develop a new model of matching velocity in different frequency which can be applied in both well logging and seismic domain. Generally, the purpose of this research is to explore a new theory and technology to match the velocity between well logging and seismic measurements, and to research a new theory and method for exact description of reservoir structure, fine seismic exploration and quantitive interpretation in complex reservoir.

本研究针对含气页岩弹性波传输特性基础问题，开展全频段岩石微观多因素波传输特性研究，利用高分辨率广角X射线μ-CT装置扫描岩石获得其内部微米成像，开发基于加权滤波岩石成像成分分割新算法，以实现矿物成分和孔隙空间的有效识别，建立弹性各向异性数字岩心模型。在此基础上，通过引入新的演化规则改进传统格子气自动机方法，使其可以模拟更加复杂的波动模式，进而从微观角度研究矿物成分、微孔隙结构、流体饱和度和流动特性等对不同频域各向异性波传输特性的影响规律和作用机理，分析弹性波速、纵横波速比、弹性各向异性等岩石特性随波动频率的变化特征。以从微观到宏观的方式，最终建立流体分布、孔隙结构等微观参数与岩石各向异性波速频散间的定量关系，开发可在测井、物探等频域范围适用的全频段波速匹配新模型，探索复杂储层测井、地震波速匹配的新理论和实用技术，为非均质储层结构准确描述、精细勘探、定量分析解释提供新理论和方法。

微观因素对弹性波频散特性的影响规律也是勘探开发中的重要问题，由于岩石的微观结构无法直接观测更无法控制，因而很难通过岩心实验来准确地研究其主要的微观影响因素。本项目从我国西部获取岩心样本8块，利用高分辨率广角 X-CT 扫描获得微米成像，开发基于加权滤波岩石成像成分分割算法，通过在过渡带优化处理使误差最小，实现对不同成分的识别和分割，分析矿物成分和流体分布，得到数字岩石模型。采用分形算法对岩石孔隙结构连通特性进行定量分析，发现岩心的孔隙空间连通具有明显的各向异性。通过引入新的演化规则改进传统模拟方法，从微观角度研究矿物成分、微孔隙结构、流体饱和度等对不同频域波传输特性的影响规律和作用机理，分析弹性波速随频率的变化特征。利用颗粒堆积算法重构孔隙介质模型，利用已开发的算法模拟研究波传输速度，结果表明随着孔隙度增大，波速逐渐减小，其减小规律呈现明显的非线性，而且模拟结果均分布在理论模型预测的范围内。采用H-S、V-R和Hill等作为参考理论模型，模拟结果显示在高孔隙度区间及颗粒松散接触情况下，力学参数的绝对值与H-S、V-R模型符合，与Hill模型具有较大差别；而当孔隙度减小，颗粒呈现紧密压实情况下，模拟结果与Hill模型比较一致，而与H-S、V-R模型存在较大差异。这些情况与物理实验结果一致。针对建立的饱和流体的数字岩心模型，模拟结果显示声波速度随着频率的增加而增大。频率低于60Hz或高于1000Hz时，速度随频率变化不明显。在60-100Hz范围内，波速测量出现共振。100-1000Hz间，随频率增加，波速快速增大。根据研究结果，开发了新模型预测岩心在不同频率情况下的波速，该模型与模拟结果吻合良好。当岩心内部存在微裂缝时，裂缝周围存在连续的串珠状振幅能量异常。研究成果已用于指导宏观实际资料的处理，改进了声波探测的方式和方法。研究成果有助于开发复杂储层测井、地震波速匹配的新理论和实用技术，为非均质储层结构准确描述、精细勘探、定量分析解释提供新理论和方法。