Abstract:

Petrology and pore characteristics of the tight oil reservoir in the Lucaogou Formation, Jimusar Sag, were carefully
studied by core observation, thin section identification, and EMPA analyses, with reference to outcrop profiles, and logging and
seismic data. It was found that the reservoir section was heterogeneous and mainly consisted of rhythmically interbedded dolomite/
siltstone and mudstone, with 3~5 rhythms in one section. Rock types identified include dolomitic siltstone, silty dolomite, dolarenite,
and dolomicrite, of which the former two were most widely distributed and served as the main reservoir rocks of the upper
and lower reservoir segments ‘( sweet points’) of the Lucaogou Formation; while dol-arenite was distributed only in the upper
segment and dolomicrite occurred as thin interlayers in both segments. Observations of EMPA showed that dissolved pores, which
could be subdivided into intragranular pores, intergranular pores and cracks, were the main pore type, and their diameter ranges
from several μm to 30μm. The minerals dissolved were mainly albite, followed by dolomite. As to the composition of the rocks,
dolomitic siltstone and silty dolomite mainly consisted of albite, dolomite, and some potassium feldspar. Dol-arenite was composed
of microcrystalline dolomite and some albite, and dolomicrite mainly consisted of microcrystalline dolomite and some quartz,
albite and other minerals.

Key words: Jimusar sag, Lucaogou Formation, tight oil reservoir, lithology characteristic, porosity characteristic