随钻电阻率测井的固定探测深度合成方法

针对随钻电磁波电阻率测井仪原始曲线探测深度不确定的问题，开展了将原始测井结果合成为具有固定探测深度曲线的研究。研究中首先采用了一种简单快速的迭代反演算法进行曲线的围岩校正处理，之后利用高斯牛顿梯度下降反演算法对每层地层进行三参数反演，获得地层的侵入带电阻率、侵入半径和地层真电阻率，再根据提出的伪源距概念，利用获得的三参数绘制探测深度与源距、源距与视电阻率的关系图版，最终通过插值获得具有固定探测深度的测量曲线。通过一系列数值模拟发现，合成后的不同探测深度曲线在有侵地层中出现有规律的分离现象，该现象与地质特征吻合很好，相比原始曲线能更直接地反映地层侵入特性，说明本方法能够提升该类仪器的应用效果，可以与阵列感应曲线进行对比，方便地质解释人员做出更准确的地层评价。

The Synthetic Approach of Fixed Depth of Investigation for Resistivity Logging While Drilling

To solve the problem of uncertain investigation depth of the original logging curves electromagnetic LWD Resistivityinstrument，this paper studied on synthesizing the original logs into curves with fixed depth of investigation. We firstlyused a simple and fast iterative inversion algorithm for shoulder-bed correction，followed by Gauss Newton-gradient descentalgorithms to inverse invaded formation resistivity，true formation resistivity and invasion radius for each layer. Then accordingto the concept of the pseudo spacing，we drew the chart of investigation depth and source spacing，source spacing and apparentresistivity by using the three parameters obtained before. Finally we obtained curves with fixed depth of investigation byinterpolation. Through a series of numerical simulation，we found that the different curves which were synthesized showed theseparation phenomenon with regularity in the invaded formation，which coincided with the geological characteristics well，andcan reflect invasion characteristics more directly compared to the original curves. So this method could improve the applicationeffect of this kind of instrument，and can be compared with the array induction curves，which makes geological interpretationon formation evaluation more accurately.