三维井间电磁响应的灵敏度分析和成像方法

Sensitivity Analysis and Imaging Technique of the 3D Crosswell Electromagnetic Measurements

三维井间电磁测量能给出井间储层的电阻率分布。由于三维井间电磁响应的复杂性 ,大多数研究都基于二维或2 5维模型 ,这些简化模型只能在某些特定条件下近似实际储集体 ,在实际生产应用中受到较大限制。利用灵敏度方程的方法 ,导出了三维介质中电场和磁场对电阻率的灵敏度计算公式 ,分析了磁场垂直分量和水平分量灵敏度的空间分布。给出了三维井间电磁数据的正则化最小二乘反演及反演参数约束的实现方法。由数值模拟结果知道 ,磁场垂直分量和水平分量纵横向上表现出不同的灵敏度分布 ,在靠近源和接收器的区域具有高灵敏度 ,而在两井的中间区域为低灵敏区 ,稳定的三维成像结果显示了三维反演成像方法的正确性和有效性。

Resistivity is one of the most important parameters in evaluating the water saturation among many petrophysical parameters. Because 3D crosswell electromagnetic measurement can provide the interwell resistivity between two boreholes, its importance in evaluating formation hydrocarbon was regarded more and more highly. However, because of complexity of the 3D crosswell electromagnetic responses, up to now, the study has been mainly focused on the two dimensional or 2.5D model which can only simulate formation approximately in some special cases and their applicability in practice has been largely limitted. In this paper, the method of the sensitivity equation was adopted to derive the sensitivity of the magnetic and electric fields to the conductivity. Analysis of spatial distribution of the sensitivity was carried out in 3D space. The regularized least square iterative inversion was carried out to produce 3D resistivity image. In the inversion process, the implementation of constraints of the model parameters was addressed. Through numerical simulation, it is indicated that the horizontal and vertical components of the magnetic field present different sensitivity distributions both in vertical and radial directions, the higher sensitivity occurs on the area nearby the transmitter and receiver, whereas the low sensitivity exists on the middle part between the two wells?The validity of the imaging technique was checked by the stable imaging result of the 3D numerical data.