油基钻井液多频随钻方位侧向电阻率成像测井响应研究

Study on Logging Response of Multi-Frequency Azimuthal Laterolog Resistivity Imaging While Drilling in Oil-Based Mud

  • 摘要: 针对油基钻井液环境下随钻电阻率成像仪器探测深度不足、方位识别能力有限的问题,提出一种极板式接收的多频随钻方位侧向电阻率成像测井结构。结合仪器工作原理,建立等效电路模型与三维有限元模型,对均匀地层进行模型验证,并进一步构建四方位地层、高低阻异常体地层及倾斜层状地层,分析不同频率下阻抗实部、虚部的响应规律及地层电阻率敏感范围。等效电路结果与均匀地层有限元正演结果吻合较好;在四方位地层中,低频段实部和虚部对高、低阻层变化响应更明显,高频可辅助区分不同电阻层;异常体模型表明,方位张开角增大时响应幅度增强,且实部与虚部具有互补性;倾斜层状地层中,多频联合分析可增强层界面识别能力,并提高倾角计算的稳定性。该多频方位侧向电阻率成像方案能够较好表征复杂地层的方位电性差异,为油基钻井液条件下的成像测井研究提供了模型基础与方法参考。

     

    Abstract: Aiming to address the limited investigation depth and inadequate azimuthal identification capability of logging-while-drilling (LWD) resistivity imaging tools in oil-based drilling fluid environments, a multi-frequency azimuthal lateral resistivity imaging logging structure with plate-type receivers is proposed. Based on the operating principle of the tool, an equivalent circuit model and a three-dimensional finite-element model are established. The models are validated using a homogeneous formation, and further simulations are carried out for a formation with four azimuthal sectors, a formation containing high- and low-resistivity anomalies, and an inclined layered formation. The response characteristics of the real and imaginary parts of the impedance under different frequencies, as well as the sensitive range of formation resistivity, are analyzed. In the homogeneous formation, the equivalent-circuit results agree well with the finite-element forward simulation results. In the azimuthally partitioned formation, the real and imaginary parts at low frequencies are more sensitive to variations in high- and low-resistivity layers, while high frequencies can assist in distinguishing layers with different resistivities. The anomaly-body model shows that the response amplitude increases with the azimuthal opening angle, and the real and imaginary parts are complementary. In the inclined layered formation, multi-frequency joint analysis can enhance the identification of layer interfaces and improve the stability of dip-angle calculation. The proposed multi-frequency azimuthal lateral resistivity imaging method can effectively characterize azimuthal electrical differences in complex formations, providing a model basis and methodological reference for imaging logging research under oil-based mud conditions.

     

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