Based on dolomite structure analysis，the formation mechanism of Ordovician Ma55 dolomite was discussed with geochemistry test data of carbon isotopes，oxygen isotopes，strontium isotopes，and order degree.The study showed that reservoir-effective lithology is mud-powder crystal dolomite and powder crystal dolomite.The mud-powder crystal dolomite is non-cathode luminescence with 0.71 order degree，0.1‰ , δ13C，and -6.3‰ δ18O，while the powder crystal dolomite is mainly dark-red cathode luminescence with 0.85 order degree，-0.68‰ δ13C，-6.58‰ δ18O.The carbon and oxygen isotopes of mud-powder crystal dolomite and powder crystal dolomite are roughly equivalent to the value of seawater in the Middle Ordovician.It reflected that dolomitization fluid is related to the same period seawater，with characteristics of reflux-seepage dolomitization.Combined with palaeogeographic background，the reflux-seepage dolomitization model was established.The dry and hot paleoclimate，which had the ability to form Mg-rich brine in Ma55 deposition period，is the key to form Ma55 dolomite.Syngenetic dolomitization prepared the ground for the spread of dolomite，provided effective seepage channel for supergene dolomitization，and was conducive to the preservation of pores in burial period.Near the paleouplift area，the whole segment is dominanated by dolomite.Influenced by southern slope of the Yimeng paleocontinent，the middle and upper segment is dominanated by dolomite in Yulin-Shenmu area，and the middle segment is dominated by dolomite in Jingbian-Ansai area.The whole dolomite segment and the middle dolomite segment are favorable exploration targets.
Zhang Dao-feng, Yao Jing-li, Gao Xing, Xi Ming-li, Zhao Hui-tao, Yan Xiao-xiong, Fu Xun-xun
. Formation mechanism and distribution regularity of Ordovician Ma55 dolomite reservoir in Ordos Basin[J]. Natural Gas Geoscience, 2019
, 30(1)
: 74
-82
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DOI: 10.11764/j.issn.1672-1926.2018.11.007
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