估计辐射参数的井间电磁波层析成像技术

Cross-well electromagnetic imaging method with radiation parameter estimation

为了避免使用不合理初始辐射场强和方向性因子带来的误差,研究了估计辐射参数的井间电磁波层析成像技术.通过时域有限差分法模拟表明,天线长度与波长的比值、钻孔充填情况、钻孔周围介质的物性均会影响偶极天线的初始辐射场强或方向性因子;为此结合已知的分层资料,将它们设为未知参数,并设定初始辐射场强与发射点位置相关,方向性因子随射线角度而变化;采用正则化反演方法,由钻孔资料建立了模型方差目标函数,使得反演结果与钻遇的地质特征保持一致.通过理论模型试验和实例应用分析表明,相对于传统射线层析成像方法,估计辐射参数的正则化层析成像技术有助于提高反演的准确性.

We present a ray-based amplitude tomography with radiation parameters estimation for cross-well radio-frequency electromagnetic data,which permits to avoid distortions from utilizing incorrect source strength and radiation pattern.Numerical simulations using the finite difference time domain method indicate that the source strength and radiation pattern are seriously affected by the ratio of antenna length to wavelength,the filling of borehole and properties of the surrounding materials.To solve these problems,combining with the existing stratified data,the source strength and radiation pattern are treated as unknown parameters with the assumption that the source strength varies with the position of the transmitter and radiation pattern changes with the ray angle.The regularization inversion method is adopted,and constraints are applied to the model according to the geological features of the boreholes revealed to make inversion results in accordance with geological characteristics from drilling.Tests on theoretical models and field data show that this regularized tomography technique with radiation parameters estimation can help improve the accuracy of inversion compared with traditional ray-based tomography.