随钻方位电磁波测井响应快速正演方法与地质导向应用

An analytically fast forward method of LWD azimuthal electromagnetic measurement and its geo-steering application

随钻方位电磁波测井解析快速正演是实现仪器响应特征分析、结构优化设计以及地层参数精确反演的基础.本文基于赫兹势函数法求解水平层状各向异性介质中的电磁场,通过引入地层界面位置,改造解势函数中的指数增大项,提取溢出因子,消除了势函数系数递推法中的数值溢出,实现了频率-波数域电磁场收敛计算.将算法应用于新型随钻方位电磁波测井技术,分析自主研发的Directional Wave Propagation Resistivity(DWPR)仪器原始响应信号特征,提取地质信号、电阻率信号.结果表明:DWPR新型仪器结构对地层界面及电阻率敏感,可提供准确的实时地质导向信息;水槽实验和实际地质导向应用结果进一步验证了本文算法的实用性和高效性.

The analytically fast forward modeling of Logging-While-Drilling(LWD)azimuthal electromagnetic measurement is the base of the tool responses analysis,structure optimum design and the formation parameters accurate inversion.In this paper,the Electromagnetic(EM)fields in anisotropic layers are obtained based on the Hertz potential function.By introducing the formation interfaces to reform the exponential increasing terms in the potential function,and figuring the overflow factors out so that the numerical overflow in the coefficient recurrence of the potential functions,the electromagnetic fields are convergent computed.This convergent algorithm is verified with published work and then applied to LWD azimuthal electromagnetic measurement.The original responses of the Directional Wave Propagation Resistivity(DWPR)tool,which is a new independently-developed type of LWD equipment,are verified and analyzed using the algorithm,and then the resistivity and geo-signal are obtained from the original responses.The numerical and experimental results show that the new DWPR structure is sensitive to the formation boundaries and resistivity,which can provide dependable real-time geo-steering guidance.The physical validation in the water tank,and the real-time geo-steering results,demonstrate the high practicability and efficiency of the convergent algorithm.