Abstract：
The second member of the Kongdian formation (Ek
2
) in the Cangdong Sag of the Bohai Bay Basin is a closed con
tinental lacustrine basin deposit with extensive horizontal distribution and stable vertical distribution, good source rock quality,
and rich shale oil resources. The Ek
2
shale oil reservoir has diverse lithology, which has obvious features of thin inter layering with
fine grained sediments. It has developed very well, and has complex mineral compositions so it is difficult to use conventional
logging data to carry out qualitative lithologic identification and mineral content calculation. In this paper, the main rock types
of shale oil reservoirs in the target block are felsic shale, calcareous shale, mixed shale, and clay stone. These were determined
by comprehensive analysis of geological and core data. By combining core analysis and logging data analysis, the response
characteristics of different rock types on micro resistivity imaging logging and conventional logging data are defined. Optimizing
the deep resistivity, compensation density and compensated sonic logging curves, and proposing a qualitative identification method
for rock types of “
φDT
-
φDEN
&
R
t
/
R
sh
” cross plot, effectively improved the accuracy of shale oil reservoir lithology identification,
and realized continuous automatic discrimination of rock type classifications. In view of the complicated shale lithology and diverse
mineral composition in the target block, as well as the large difference between the conventional mineral content calculation method
and the actual situation, according to the X-ray diffraction analysis data of rock samples from the target block, it is determined that
the main minerals of the shale oil reservoir are felsic minerals (quartz and feldspar), carbonate minerals (calcite and dolomite), and
clay. From this, the corresponding mineral volume model is established, using compensated acoustic wave logging, compensation
density, normalized difference between compensation density and compensated neutron logging, deep resistivity, natural gamma and
other sensitive curves. The calculation of the content of carbonate rock and clay minerals is carried out using the method of multiple
stepwise regression, and the calculation accuracy of the content of carbonate rock and clay minerals is significantly improved
through three multiple regressions. On this basis, a logging interpretation model which is suitable for quantitative calculation of
shale oil reservoir mineral content in research blocks is derived. The mineral content calculated by this interpretation model is highly
consistent with the core analysis results. The developed method effectively solves the difficult problem of lithology evaluation of
shale oil reservoirs and improves the accuracy of lithology evaluation using conventional logging data.
Key words：shale oil; logging evaluation; rock types; lithology evaluation; qualitative identification; multiple stepwise regression; mineral content calculation
Corresponding Authors： changjc@cnpc.com.cn
Cite this article：LIU Jundong, PU Xiugang, CHANG Jingchun, HAO Liping, XU Ming, YUAN Xuehua, LI Jin. Logging of a shale oil reservoir in a closed lake basin: A comprehensive lithology evaluation technique. Petroleum Science Bulletin, 2021, 01: 58-66.
