摘要
本文提出了一种井间低频电磁波测量方法 ,用于重建地下介质电阻率分布。首先选择一个位于井轴上的垂直磁偶极子作为场源 ,并假设参与计算的介质相对于偶极子轴是轴向对称的 ,这样可将模型作为二维问题处理。文中每次进行迭代涉及的正演模拟把总场分为背景场和散射场两部分 ,背景场使用解析法计算 ,而散射场使用 FFM数值近似方法计算 ;在反演计算时使用正则化最小二乘拟合反演技术 ,从跨井电磁波测量资料中重现地下介质的电阻率剖面 ,使用互换原理来处理格林函数的计算以得到电磁响应对电阻率的偏数 ,从而改善了计算精度和工作效率。模型重现的结果表明 ,这种电磁成像方法同时适用于高电阻率对比度模型。像的垂直分辨率随频率的提高而改善 ,而水平分辨率则与频率、收发间距和异常体到钻孔的距离等因素有关。数值模拟的结果表明 。
The paper studied a method that inverted resistivity distribution in crosshole section song crosshole low frequency electromagnetic surveying data. First,a vertical magnetic dipole on bole axis is selected as a field source and assuming calculated medium is axis symmetry in respect of dipole axis,so,the model can be treated as a 2 D problem. Total field is divided into two parts:background field and scattering field in forward modeling concerning with each iteration in the article,the background field is calculated by FFM numerical approximation;using normalized least square fitting inversion technique in inverted calculation,resistivity section of subsruface medium can be reappeared from crosshole electromagnetic surveying data,us ing reciprocity principle for calculating Green function and getting partial derivative of electromagnetic response with respect to resistivity,the computing accuracy and efficiency can be improved. Results of model reappearance show that the electromagnetic imaging method is suitable both for high resistivity contrast model and for low resistivity contrast model. Vertical resolution of image improves with increasing frequency and improvement of lateral resolution relates to the factors such as frequency,interval between source and receriver and distance from anomaly body to borehole.numeric modeling results demonstrate that best working frequency must be selected according to adjacent bed resistivity.
出处
《石油地球物理勘探》
EI
CSCD
北大核心
2000年第6期741-750,共10页
Oil Geophysical Prospecting
基金
国家科学基金委员会资助
关键词
跨井电磁成像
测量资料
电阻率
油气勘探
crosshole electromagnetic imaging,resistivity,finite element calculation,normalized inversion
