三维井间电磁场的联合反演方法

考虑到井间电磁测量信息量的局限性,基于积分方程在发射接收剖面对三维电导率异常体进行近似成像。成像过程中将沿垂直于发射接收剖面方向的成像区域限制在一定范围并假设电导率在该方向不变。成像实例显示,这种剖面成像的精度取决于垂直于发射接收剖面方向的成像范围与异常体在该方向实际范围的接近程度。考虑到实际情况下背景层电导率值往往是未知的或虽已知但并不准确,还提出了联合反演方法,以一维反演结果作为初始值,既反演一维背景地层的电导率,也反演三维异常体在发射接收剖面的电导率,两个过程交替进行。反演实例显示,经过几轮迭代后,背景层电导率分布及异常体在发射接收剖面的电导率分布均大大改善,说明了联合反演的有效性和必要性。

Combined inversion algorithm of three-dimensional cross-hole electromagnetic fields

An approximate imaging algorithm based on integral equations for three-dimensional anomalous conductivities on the transmitter-receiver profile was developed in consideration of the limited information from the cross-hole electromagnetic measurements so far available. The imaging domain in the direction perpendicular to the transmitter-receiver profile is restricted to a certain range and the conductivities are supposed to be constant in the direction during the imaging. Examples indicate that the precision of the approximate imaging-on-profile algorithm depends on how close between the imaging domain and the domain of the anomalous conductivities in the direction perpendicular to the profile. A combined inversion algorithm was also proposed considering the fact that the background conductivities are generally unknown or not accurately known. Taking the one-dimensional inversion results as the initial conductivities, the one-dimensional background conductivities and the three-dimensional anomalous conductivities on the transmitter-receiver profile are inverted alternatively in the algorithm. Inversion examples indicate that the distributions of both the background conductivities and the three-dimensional anomalous conductivities on the transmitter-receiver profile are greatly improved after several iterations. These examples demonstrate the effectiveness and the necessity of the combined inversion algorithm clearly.