利用井孔斯通利波及其诱导震电波场联合反演地层渗透率和电阻率

To develop new exploration methods and joint inversion from multi-methods, multi-physical-fields and multi-components is a hot research topic in oil-gas exploration field at present. Great expectation has been placed on the seismoelectric logging method, which is based on the coupling between elastic and electromagnetic wavefields in porous rocks and has a potential application to permeability detection. This project studies the numerical simulations and the experimental measurements in small-scaled model borehole of the Stoneley wave and its induced seismoelectric wavefields, and the joint inversion of formation permeability and resistivity from the amplitudes and phases of the two physical fields. It will lay a foundation for the interpretation of the in-situ borehole seismoelectric signals and inverting formation parameters from the in-situ signals, and will boost the practical research on seismoelectric logging method. It focuses on the following aspects. First of all, to establish the joint inversion method according to the analysis in theory and experiment of the relationships between borehole seismoelectric wavefields and porous formation parameters. Secondly, to invert permeability and resistivity from the theoretically simulated and experimentally measured borehole seismoelectric wavefields. Thirdly, to study the three-dimensional finite-difference algorithm for calculating the poroelastic waves and the seismoelectric wavefields across all frequencies. Fourthly, to simulate the borehole seismoelectric wavefields when the porous fluid salinity varies nearby the borehole wall and the formation horizontal interfaces. Finally, to measure seismoelectric signals in small-scaled model borehole and investigate the relations of the Stoneley wave and its induced seismoelectric field with porosity, permeability, tortuosity, resistivity, etc.

发展新的勘探方法，进行多方法、多物理场、多分量的联合勘探是目前油气勘探开发研究的热点。基于岩石中弹性波和电磁场耦合特性的震电测井方法被人们寄予厚望，在地层渗透率的探测等方面具有潜在应用价值。在前期工作基础上，本项目研究斯通利波及其诱导震电波场的数值模拟和小模型井实验测量，以及利用这两种物理场的幅度比和相位差联合反演地层渗透率和电阻率，为解释现场井孔震电信号以及利用现场信号反演地层参数奠定基础，促进震电测井的实用化研究。主要内容有：基于井孔震电波场与地层参数相关性的理论和实验分析，建立联合反演方法，利用理论模拟和实验测量的井孔震电波场反演渗透率和电阻率；研究全频率范围适用的孔隙介质弹性波、震电波的三维有限差分模拟算法，计算流体矿化度在井壁侵入带中和地层水平分层界面附近渐变时的井孔震电波场；实验测量不同小模型井的震电信号，分析斯通利波及其诱导电场与孔隙度、渗透率、弯曲度、电阻率等参数的相关性。

渗透率是油气储层评价和油田开发等方面的重要参数，然而现有勘探方法尚不能对其进行准确地井下连续性探测。鉴于含流体孔隙岩石中弹性波与电磁场耦合效应（震电效应）与渗透率的密切相关性，以及电阻率与渗透率的关联性，本项目提出基于震电效应联合反演渗透率和电阻率的想法，并在理论分析、数值模拟和实验测量三个方面开展了基础研究工作。截止目前，针对本项目的主要研究内容，我们已发表了9篇SCI和3篇EI论文，包括在勘探地球物理领域公认的高水平期刊GJI上发表的3篇SCI论文。另有2篇英文SCI的修改稿正在审稿中。主要研究内容和取得的重要结果简述如下：.1.理论方面：分析了含流体孔隙地层的四种弹性体波势对井孔震电波场的贡献，证明了采用似稳法计算震电电场和磁场的可行性，并给出了似稳法的适用条件；推导出了任意孔隙尺寸均适用的动电耦合系数表达式，并对比分析了薄双电层假设近似对井孔震电波场的影响；提出了修正的复电阻率模型以及渗透率反演的经验公式，并进行了实验验证；提出了一种高分辨率的模式波提取方法，可用于从复杂的实验室和现场测量信号中提取斯通利波。.2.数值模拟方面：在国际上最先实现了井孔震电波场的有限差分模拟算法，计算发现了界面附近的幅度显著的电磁首波，有望用于探测井外地层界面；实现了正交各向异性介质中弹性波模拟的三维时域有限差分算法，以随钻声波测井的复杂柱面分层模型为例，验证了算法的正确性，并深入分析了钻铤波的传播特性，阐明了震电测井全波中存在钻铤波的原因。.3.实验方面：改进了自建实验测量系统的夹持器，显著提高了渗透率反演精度；测量了23个砂岩样品的流动电势系数、电渗压力系数和电导率，并反演出了与气测渗透率一致的结果;分析了随钻环境下的钻铤波信号传播特性，实验证实了震电测井时仍然存在显著的钻铤波。