地面一井孔电磁系统成像方法研究

IMAGING METHOD IN SURFACE-TO-BOREHOLE ELECTROMAGNETIC SYSTEM

在地面一井孔（ＳＴＢ）电磁成像系统中，将发射器放置在地面距裸眼井一定距离和方位处，将接收器置人裸眼井的目的层段。使用这种电磁系统，只需一口裸眼井，现场测量灵活方便。在成像过程中，应用基于逐次逼近解法的迭代反演算法对目的层段的二维电导率剖面进行成像。该方法用一阶Ｂｏｍ近似将积分方程线性化，在选代反演中应用高阶Ｂｏｍ近似。为了提高成像效果，采用多种发射频率并扩大接收器的垂向接收范围和接收密度，但是由于发射源固定在地面，成像效果低于跨井孔电磁成像效果。数值计算结果表明，ＳＴＢ电磁成像系统能较准确地确定出电导率异常体的垂向位置，但水平方向分辨能力差，精确地描述地层中电军率异常体的分布还需要其它测量信息。

In the surface-to-borehole (STB) electromagnetic imaging system, the transmitter is placed on the ground with certain distance and horizontal direction from the naked hole, and the receiver is placed in the target area of the borehole the system only needs one naked hole, and the measurement is flexible. An iterative inversion method based on successive approximation method is developed to image the two-dimensional conductivity profile of the target area . The method employs the first Born approximation to linearize the integral equation, and a high Born approximation is applied to the iterative inversion. In order to improve the imaging effects, many kinds of frequency are used, and the vertical space and vertical density of the receiver increased. But the imaging effects are not as as good as that of the crosshole electromagnetic imaging system because of the unmovable place of the. transmiter. Numerical calculation results indicate that the STB system can precisely determine the vertical place the abnormal conductivity, while the distinguishability is much worse in the horizontal direction Other measuring information should be needed to precisely estimate the conductivity structure.