电磁波传播测井地层介电常数测量应用分析

      Application analysis of electromagnetic wave propagation logging in formation dielectric constant measurement

      • 摘要: 受地层水矿化度的影响,复杂油气储层电性特征复杂,采用电阻率测量方法难以对复杂储层流体进行准确评价与识别;但介电常数受地层水矿化度影响小,并且水的介电常数远大于油气介电常数,通过电磁波传播测井仪测量地层介电常数可有效准确区分油气储层与水层,且其地层响应转换图版的精准性对复杂储层流体的准确评价至关重要。本文基于等效磁偶极子模型推导了层状介质中1 GHz电磁波传播计算公式,提出了将测量探头几何工程参数融入有限元的精确仿真方法,采用COMSOL Multiphysics建立1∶1有限元仿真模型,分析了探头几何工程参数对地层转换图版的影响。搭建实验系统验证了理论仿真的准确性,测量结果显示基于精确仿真方法得到介电常数与真实值的相对误差约为1%。研制出电磁波传播测井仪,并在某油田开展了非常规页岩油气测井应用,为油田复杂油气储层的评价提供了一种有效的测量方法。

         

        Abstract: Complex oil and gas reservoirs have complex electrical characteristics owing to the influence of formation water salinity. It is difficult to accurately evaluate and identify the fluid in such complex reservoirs by using the conventional resistivity method. However, the water salinity of the formation has a reduced effect on its dielectric constant, and the dielectric constant of water is far greater than that of oil and gas. Therefore, formation dielectric constant measured by electromagnetic wave propagation logging tool can be used to effectively distinguish oil and gas reservoirs and water layers. The accuracy of the formation response inversion charts of dielectric logging instruments is important for accurately evaluating fluids in complex reservoirs when these instruments are used. Based on the equivalent magnetic dipole model, this study deduces the calculation formula of 1 GHz electromagnetic wave propagation in layered media, proposes to integrate the geometric engineering parameters of the measuring probe into the finite element accurate simulation method, and establishes a 1∶1 finite element simulation model using COMSOL-multiphysics. Then, the influence of the probe geometric engineering parameters on the formation conversion chart is analyzed. Meanwhile, the experimental system is established to measure the accuracy of theoretical simulation. The results show the relative error between the dielectric constant obtained using the precise simulation and the real value is about 1%. The electromagnetic wave propagation logging tool is developed and it is applied to unconventional shale oil and gas logging in an oilfield, providing an effective measurement method for the evaluation of complex oil and gas reservoirs in oil fields.

         

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