大斜度井/水平井随钻方位电磁波测井资料实时反演方法

Real-time inversion of logging-while-drilling azimuthal electromagnetic measurements acquired in high-angle and horizontal wells

水平井钻进过程中,地层边界的准确预测对地质导向决策至关重要.但水平井测井环境复杂,随钻方位电磁波测井响应不直观,储层性质、地层界面等信息的精确、定量评价困难.本文提出了一种适用于大斜度井/水平井随钻方位电磁波测井资料的电阻率及地层界面信息的实时提取方法.该方法主要基于以下几个技术:(1)引入滑动开窗策略将高维随钻方位电磁波测井资料的反演问题转化为多个连续窗口的一维反演问题;(2)对反演参数进行多初值初始化,结合正则化Levenberg-Marquardt算法保证解的全局最优性;(3)充分利用随钻方位电磁波测井多种探测深度信息,采用分级反演策略提高反演速度.数值和实测资料反演结果表明:降维反演方法可实现对地层界面的实时、准确提取,且适用于多数复杂地层结构和任意井眼轨迹;利用浅探测地质信号可实现随钻方位电磁波测井资料的分级反演,最终反演速度可提升10倍以上.

During the drilling process,accurate determination of the approaching bed boundary is critical to real-time geosteering decision making.However,due to the complex logging environment,the responses of azimuthal electromagnetic measurements(AEM)are usually not straightforward.As a consequence,it is difficult to quantitatively assess the formation properties and bed boundaries.In this paper,we present an inversion scheme to extract the bed boundary and formation resistivities from AEM data acquired in high angle and horizontal wells.The inversion is featuredby the following techniques:(1)sliding window approach,which is capable of converting the high dimensional inversion problem into a set of stitched 1D ones;(2)regularized LevenbergMarquardt algorithm associated with multiple initial guesses strategy to guarantee the derivation of the global solution;and(3)hierarchical inversion approach which takes advantages of the curves with different depths of investigations to improve the inversion efficiency.Numerical experiments performed over synthetic examples show that the equivalent inversion method is capable of providing accurate bed positions in real-time,and is suitable for most of the 3D complex scenarios and arbitrary well path.Moreover,by using the shallow geosignals and deep ones separately,hierarchical inversion of AEM is at least 10 times faster than the conventional inversion method.