非饱和岩石动电耦合波理论及井孔震电波场模拟和实验研究

Elastic waves and electromagnetic fields are coupled in water-filled porous media due to the electric double layer with excess charges nearby the solid/water interface. This kind of electrokinetic effect has potential applications in reservoir-permeability inversion, fluid-flow monitoring, earthquake-induced electromagnetic-field and so on. This project studies the theory of the electrokinetic coupled wavefileds in unsaturated rocks, investigates the characteristics of the borehole seismoelectric wavefields and discusses the possible of using seismoelectric logs to identify the porous fluids and estimate their relative contents. It focuses on the following aspects. First of all, we investigate the electrokinetic coupling mechanisms nearby the oil/water and gas/water interfaces as well as that nearby the solid/water interface, derive the macroscopic governing equations for the electrokinetic coupling waves in unsaturated rocks by using the volume-averaging method, and then validate our theoretical derivation according to the electrokinetic coupling coefficient obtained from the streaming-potential coefficient and the electroosmotic-pressure coefficient measured in laboratory. Secondly, we derive the analytical solutions of the borehole seismoelectric wavefields and then calculate the full waveforms by using the real-axis integration method. Thirdly, we analyze the component waves in the borehole seismoelectric wavefields by using the complex-function method, including calculating the dispersion and excitation curves, and simulating all the component waveforms. Finally, we investigate the characteristics of the borehole seismoelectric wavefields and their variations with the water saturation according to the numerical and experimental results.

含水孔隙介质中与双电层有关的弹性波-电磁场耦合效应（动电效应），对于储层渗透率反演，孔隙流体渗流监测，地震电磁场等问题有着潜在应用价值和重要意义。在前期针对含水饱和岩石研究的基础上，本项目研究非饱和岩石中的动电耦合波理论以及井孔震电波场特性，探索利用震电测井方法识别孔隙流体、估计各种流体相对饱和度的可能性。主要内容有：在孔隙尺度上研究固相/水、油（气）/水界面附近的双电层动电耦合机制，采用体积平均法推导宏观的非饱和岩石动电耦合波控制方程组；实验测量不同含水饱和度岩样的流动电势系数和电渗压力系数，计算动电耦合系数和渗透率，验证动电耦合波理论推导的正确性；推导非饱和岩石井孔震电波场的解析解，采用实轴积分法计算全波波形；采用复变函数法分析非饱和岩石井孔震电波场的分波特性，计算各分波的频散曲线、激发曲线和波形；实验测量不同含水饱和度模型井的震电信号，分析井孔震电波场特性及其饱和度相关性。

含水孔隙介质中与双电层有关的弹性波-电磁场耦合效应（动电效应），对于储层渗透率反演，孔隙流体渗流监测，地震电磁场等问题有着潜在应用价值和重要意义。在前期针对含水饱和岩石研究的基础上，本项目研究非饱和岩石中的动电耦合波理论以及井孔震电波场特性，探索利用震电测井方法识别孔隙流体、估计各种流体相对饱和度的可能性。经过四年的努力，课题组针对经典Biot孔隙弹性波控制方程组的问题，考虑实际孔隙岩石中裂隙特性等对孔隙岩石弹性波频散和衰减的影响，修正了经典Biot孔隙弹性波理论模型，开展纵横波传播和频散特性等研究，为进一步研究弹性波诱导电磁场奠定了基础。针对储层开发过程中的气、水吸附问题，通过数值计算研究了由于气或水吸附引起的孔隙介质基质膨胀效应导致的孔隙闭合现象，分析了孔隙尺度对渗透率的影响，为计算非饱和孔隙介质中的渗流问题提供了仿真工具。从实际孔隙岩石特性出发，针对复电导率、动态渗透率、动电耦合系数等动电耦合波方程组中的重要参数，开展了理论研究工作，在此基础上修正经典Pride理论，提出了一种非饱和孔隙介质震电耦合波理论。研究随钻环境、双套管井时的井孔声波特性以及井孔波场频散曲线提取算法等问题，为进一步研究这些复杂工况下的井孔震电耦合波奠定了基础。研究利用井孔激发声波探测井外地层远处裂缝问题（单井成像，SWI）渐进解析解、方位识别和快速数值算法，为研究震电测井远探测问题奠定基础。实现了非饱和水平分层孔隙地层中的震电波场解析解、井孔震电波场数值模拟算法，研究了井内流体、井外孔隙流体矿化度对震电波场影响等问题。开展了随钻测井环境下的声波信号、震电信号的精细测量、分析，提出了基于随钻震电测井反演地层纵横波速度的方法。