不同极化模式的二维大地电磁非线性共轭梯度反演及应用研究

Study and application on the nonlinear conjugate gradient inversion method for 2D Magnetotelluric with different polarization modes

同时满足大地电磁反演精度与计算效率的反演方法中,非线性共轭梯度法具有明显优势。首先,利用该方法对块体低阻模型及隐伏构造模型进行TE、TM以及TE与TM联合(TE+TM)的视电阻率和相位反演研究,并完成了不同极化模式条件下,该方法对地下复杂构造的适用性与有效性测试,发现在二维构造条件下,TE+TM极化模式对异常体边界的刻画与反演精度均优于TE、TM极化模式。其次,采用该反演方法,对朝克乌拉凹陷大地电磁(MT)实测资料进行反演,对比不同极化模式反演曲线与测井电阻率曲线,发现基于TE+TM的反演电阻率吻合度最高。最后,对TE+TM极化模式的反演电阻率剖面进行了地质解释。解释剖面清晰地刻画了表层玄武岩分布及地层结构,为厘清研究区凹陷基底构造形态及储层提供了有效依据,表明大地电磁非线性共轭梯度反演方法在凹陷构造定量刻画方面优势明显。

The nonlinear conjugate gradient method has obvious advantages among inversion methods that can achieve both accuracy and calculation efficiency.First,this method was used to invert the apparent resistivity and phase data of TE,TM,and TE combined with TM for the block low resistivity model and concealed tectonic model.The applicability and effectiveness of this method for complex structures under different polarization conditions were tested.The results showed that the TE combined with TM polarization mode is better than the TE or TM polarization mode in describing and inverting the boundary of the anomalous body in a two-dimensional structure.Magnetotelluric(MT)data inversion was performed using this inversion method.By comparing the inversion curves of different polarization modes with the logging resistivity curves,it was found that the inversion resistivity of TE combined with TM polarization mode had the highest consistency.Finally,a geological interpretation of the inversion resistivity profile based on this polarization model was performed.The interpretation profile clearly depicted the distribution of surface basalt and stratigraphic structure,which provided an effective basis for clarifying the basement structure and reservoir of the depression.The results showed that the MT nonlinear conjugate gradient inversion method has the advantage of quantitatively describing depression structures.