基于OC-RPIM的压裂电位监测法模拟特征分析

Analysis of Simulation Characteristics of Hydraulic Fracturing Potential Monitoring Method Based on OC-RPIM

  • 摘要: 水力压裂监测过程中,信号特征可以反映裂缝扩展状态,因此基于电位监测方法和正演模拟算法对垂直井压裂裂缝信号特征进行了模拟分析。为了提高正演模型的稳定性及准确性,首先,针对二维电场方程,采用了可自适应调节形状参数的全局形状参数径向基点插值法(OC-RPIM),这样可以避免因使用不合理形状参数而带来的误差;其次,采用法向良导体界面等效方法对压裂裂缝进行简化建模,以提高多尺度问题计算的稳定性。正演结果表明,井壁电位信号的变化率会随着裂缝半径的增大逐渐降低,在地层电导率变化不大的条件下,建议采用远点井壁电位监测方式来提高裂缝半径的识别范围;在地层与裂缝填充物电导率对比度较高条件下,井壁电位信号与裂缝半径有更强的关联性,且其他因素对井壁信号的影响得到有效削弱。研究结果为电位法压裂监测信号解释提供了理论支撑,并提供了针对电位法压裂监测信号的有效正演手段。

     

    Abstract: In the process of hydraulic fracturing monitoring, the signal characteristics can reflect the state of fracture propogation. Therefore, based on the potential monitoring method and the forward simulation algorithm, the signal characteristics of the vertical well’s hydraulic fracture were simulated and analyzed. In order to improve the stability and accuracy of the forward model, first, for the two-dimensional electric field equation, the overall shape parameter C radial base point interpolation method (OC-RPIM) that could adaptively adjust the shape parameter was adopted, avoiding errors caused by using an unreasonable shape parameter. Second, the normal ideal conductor interface equivalent method was used to simplify the hydraulic fracture modeling process and enhance the computational stability in this multi-scale problem. The forward modeling results show that the change rate of the potential signal on well bore gradually decreases as the fracture half-lenght increases. Under the condition that the conductivity of the formation does not change much, it is recommended to use remote well bore potential monitoring to expand the detection range of the fracture half-length. In addition, when the conductivity contrast between the formation and the fracture filler is high, the well bore potential signal has a stronger correlation with the fracture half-length. This phenomenon can effectively weaken the influence of other factors on the borehole signal. The research results provide theoretical support for the interpretation of the fracturing potential,monitoring signals and an effective forward simulation method is proposed for the signals of potential fracturing monitoring.

     

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