Отправлено: 06.04.13 08:40. Заголовок: Corrections for downhole NMR logging

Corrections for downhole NMR logging
Pet.Sci.(2012)94-52

Hu Haitao, Xiao Lizhi and Wu Xiling
State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing 102249, China
© China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg 2012

Abstract: Nuclear magnetic resonance logging (NMR) is an open well logging method. Drilling mud
resistivity, formation resistivity and sodium ions influence its radio frequency (RF) field strength and
NMR logging signals. Research on these effects can provide an important basis for NMR logging data
acquisition and interpretation. Three models, water-based drilling mud—water bearing formation, waterbased drilling mud—oil bearing formation, oil-based drilling mud—water bearing formation, were
studied by finite element method numerical simulation. The influences of drilling mud resistivity and
formation resistivity on the NMR logging tool RF ¿eld and the inÀuences of sodium ions on the NMR
logging signals were simulated numerically. On the basis of analysis, RF ¿eld correction and sodium ion
correction formulae were proposed and their application range was also discussed. The results indicate
that when drilling mud resistivity and formation resistivity are 0.02 ȍÂm and 0.2 ȍÂm respectively,
the attenuation index of centric NMR logging tool is 8.9% and 9.47% respectively. The RF ¿eld of an
eccentric NMR logging tool is affected mainly by formation resistivity. When formation resistivity is 0.1
ȍÂm, the attenuation index is 17.5%. For centric NMR logging tools, the signals coming from sodium ions
can be up to 31.8% of total signal. Suggestions are proposed for further research into NMR logging tool
correction method and response characteristics.
Key words: NMR logging, ¿nite element method, RF ¿eld, NMR signal, formation resistivity, sodium
ions