随钻电磁波测井响应函数理论及探测特性

为研究随钻电磁波测井响应探测特性,基于Born几何因子近似方法,推导各向异性介质中随钻电磁波测井响应函数,用于刻画各向异性地层中信号空间分布特征,以有效分析幅度比和相位差信号的敏感性。在此基础上定义径向及纵向积分几何因子,分析信号频率、地层电阻率及线圈距对探测能力的影响。结果表明幅度比和相位差信号空间分布规律相似,幅度比信号分布相对发散,具有更大的探测范围,而相位差信号分布更为聚焦,纵向分层能力更强;井斜角的加大导致响应函数的旋转对称性消失,对各向异性的敏感性增高;随着各向异性系数的加大,响应函数空间分布受水平电阻率的影响逐渐增强;径向及纵向积分几何因子能够表征仪器的探测能力,随着信号频率的增加,仪器的径向探测深度减小,纵向分辨能力增强;仪器径向探测深度及纵向分辨率,随着线圈距均匀改变而出现规律性的变化;在电阻率逐渐减小的过程中,随钻电磁波测井空间响应会出现负贡献区域。

Theory of response function and analysis of detecting characteristic of electromagnetic logging while drilling

Based on the Born geometric factor approximation method,a response function of electromagnetic logging while drilling in anisotropic medium is constructed to characterize the spatial distribution of the response function in electromagnetic wave logging while drilling.This response function can be effectively used to analyze the sensitivity of amplitude ratio,phase shift signals,and to study the detection characteristics of electromagnetic wave logging while drilling.On this basis,the radial and vertical integral geometric factors are defined to analyze the radial detection range and vertical resolution.In addition,the influences of signal frequency,formation resistivity and spacing on detection ability are analyzed.The research indicates that the spatial distribution of amplitude ratio and phase shift is similar.The distribution of amplitude ratio signal is relatively less focused,which has a larger detection range.The distribution of phase difference signal is more focused,and the vertical stratification is stronger.With increasing dipping angle of the well,the rotational symmetry in response function's spatial distribution disappears and the response function is more sensitive to the coefficients.With increasing anisotropy coefficient,the spatial distribution of response function is gradually influenced by horizontal resistivity.Radial and vertical integral geometric factors can be quantitatively used to characterize the detection capability of the instrument.With increasing signal frequency,the detection range of the instrument decreases but the vertical resolution increases.The detection range and vertical resolution of the instrument vary periodically with uniform variations in spacing.In the process of decreasing resistivity,the spatial response of electromagnetic logging while drilling will have a negative contribution area.