水平井随钻电磁波电阻率数值模拟

摘要

随钻电磁波电阻率随着钻井技术进步市场和份额逐渐增加,由于水平井测量环境与直井存在较大差别,仪器受到影响因素也与直井不同,明确水平井中随钻电磁波电阻率的测井响应规律有助于水平井测井资料解释.依据电磁波电阻率测量原理,根据Chew理论,推导了TI介质中电磁场的波场分解,进而建立三维空间电磁波电阻率数值模拟正演方法.模拟了不同工作频率、不同相对井斜角、不同围岩电阻率以及地层界面情况下电磁波电阻率的测井响应规律.结果表明:幅度比和相位差随着地层电阻率的增大而减小,表现出与地层电阻率呈单调递减的函数关系;相位差对地层电阻率的敏感程度明显优于幅度比,适用的地层范围更大;井斜角越大,地层界面上下地层电阻率对比度越高,越容易在层界面附近产生"极化角",有助于识别地层界面;相同工作频率,围岩对幅度衰减电阻率的影响要大于相位差电阻率的影响;相同测量方式,围岩对低频工作模式的影响要大于对高频工作模式的影响;随井斜角的增大,幅度衰减电阻率与相位电阻率出现分离;工作频率越高,不同源距的电阻率值分离程度大.%The market and share of LWD resistivity was gradually increased with the progress of drilling technology, due to the difference measurement environment between the vertical wells and the horizontal, the affected factors are also different from vertical wells, clear about the logging response law of the LWD resistivity will help to the horizontal well logging data interpretation.On the basis of electromagnetic wave resistivity measuring principle, according to Chew theory, the wave field decomposition of the electromagnetic field in TI medium was deduced, and then a three-dimensional numerical simulation forward modeling method was established.The response characteristics of the LWD resistivity in different work frequency and relative deviation angle and different surrounding rock resistivity and stratigraphic interface and so on were simulated.Results show that the amplitude ratio and phase difference decreases with the increase of formation resistivity, the sensitive degree of phase difference to the formation resistivity is better than the amplitude ratio.The higher relative deviation and greater formation resistivity contrast, the easier appear the polarization angle, this can help to identify the formation interface.the effect of surrounding rock resistivity on amplitude attenuation is greater than the phase difference resistivity in the same working frequency.In the same measurement methods, the influence of surrounding rock on low frequency working mode is greater than high frequency work mode.With the increase of deviation angle, amplitude attenuation resistivity and phase resistivity separated, the higher working frequency, the larger degree separation of different spacing.