岩样动电耦合机制及地层渗透率的动电测井实验研究

The permeability, reflected the hydro-transport capability of the porous medium, is one of the most basic parameters for evaluating formation property. Therefore, measuring permeability with electrokinetic method becomes an important research direction in geophysical exploitation. Based on electrokinetic experiments with small rock samples and borehole models, this project studies the electrokinetic coupling mechanism and the seismoelectric logging waveforms, so as to verify the feasibility for determining rock permeability with seismoelectric well logging method or joint methods with acoustic/electric/ seismoelectric well loggings. A key step is to improve the experimental set-up and the measuring system for weak electrokinetic signals. Then the electrokinetic measurements are conducted with different rock models. First of all, to perform the streaming potential experiments with small rock samples at low frequency, then calculate the electrokinetic coupling coefficients and investigate the relations between electrokinetic signals and the rock parameters, such as porosity, permeability, resistivity, etc. Secondly, to conduct seismoelectric well logging experiments in small boreholes, and record the seismoelectric signals that accompany compressional wave, shear wave and Stoneley wave, then analyze the sensitivity of wave amplitude and phase on permeability. Thirdly, to propose the seismoelectric logging method for evaluating rock permeability with experimental measurements. Finally, to simulate the borehole seismoelectric wavefield with finite-difference algorithm for the small scaled borehole models, then compare the theoretical results with experimental measurements.

渗透率能够反映孔隙流体的传输能力，是评价储层可开采性的重要参数。因此，围绕渗透率动电测量这一当前油气勘探的前沿研究，本项目拟通过小岩样和井孔模型的动电实验测量，研究动电效应的耦合机制，分析动电测井的波场特性，为渗透率的井外动电测量，或基于声/电/动电法的多物理场联合测量提供实验依据和可行性分析。主要工作包括：（1）改进现有实验装置和检测系统，提高动电测量的有效性。（2）进行岩样低频动电实验，计算不同条件下的动电耦合系数，揭示动电信号与岩石物理参数间的关系，重点分析动电信号随渗透率的变化规律。（3）进行井中瞬态动电实验，研究动电转换波场的传播规律和频散特性，分析动电测井全波的幅度、相位及电声比对渗透率等地层参数的敏感性，阐明动电测井与传统声法/电法测井之间的联系，进而提出渗透率的动电测井实验测量方法。（4）针对实验井孔模型，利用有限差分算法模拟动电测井波场响应，与实验结果进行对比。

孔隙介质动电耦合特性及其在油气勘探领域的应用是当前地球科学的重点研究方向。因此，本项目针对动电效应的耦合机制，以及渗透率的动电测井评价等问题，开展了低频动电实验和瞬态动电测井实验研究，分析了动电耦合信号与固液相参数间的关系，提出渗透率的预测公式，研究了动电测井波场的传播规律，并与理论模拟计算进行对比。相关研究成果在GJI，Geophysics，地球物理学报等地球物理领域重要期刊发表SCI论文18篇，获得2019年全国检测会议优秀论文奖1项，主要研究内容和重要结果如下：.1)改进了原有流动电势和电渗联合实验测量系统，建立了含有双向气缸激励的驱动源和免拆卸堵头的岩样夹持器，提高了低频动电实验的可靠性。 .2)基于低频岩样流动电势实验结果，计算了不同浓度饱和岩样的流动电势系数和动电耦合系数，指出流动电势系数随溶液浓度、岩样渗透率、孔隙度、泥质含量等参数的变化规律。结果表明:在低浓度饱和情况下，流动电势系数与岩样孔隙度/渗透率等参数成正比关系;但是在高浓度饱和情况下，流动电势系数与地层参数无关。 .3)利用流动电势系数、电渗压力系数和岩样电导率，计算岩样的动电渗透率，验证了Onsager互易关系的有效性，同时拓展了动电渗透率的测量范围，实验结果与气渗透率相关性很好。.4)基于Stern层极化理论，在考虑颗粒形状、表面粗糙度、颗粒间接触以及颗粒尺寸分布等因素对复电导影响的条件下，建立了新的复电导模型，并通过复电导实验数据的拟合对比，建立了基于复电导效应的渗透率预测公式。理论和实验对比表明渗透率公式对0.01毫达西到100达西渗透率范围内岩石渗透率预测的有效性。.5)针对随钻动电测井中钻铤波干扰地层波测量的问题，分析了钻铤波的传播规律，定量研究了内外钻铤波的幅度量级关系，证实了随钻动电测井理论模拟中钻铤波动电转换信号是由外钻铤波诱导产生。