西南石油大学学报(自然科学版)

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

Duan Baoliang1, Song Dianguang1,2*, Wei Baojun3, Zhang Guibin2   

  1. 1. China Research Institute of Radiowave Propagation,Xinxiang,Henan 453003,China
    2. School of Geophysics and Information Technology,China University of Geosciences,Haidian,Beijing 100083,China
    3. College of Science,China University of Petroleum,Qingdao,Shandong 266580,China
  • Online:2015-08-01 Published:2015-08-01

Abstract:

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

Key words: resistivity logging while drilling, fixed depth of investigation, pseudo spacing, inversion of three parameters,
correction for both relative dip and shoulder-bed