Multistage dolomitization and formation of ultra-deep Lower Cambrian Longwangmiao Formation reservoir in central Sichuan Basin, China
Multistage dolomitization and formation of ultra-deep Lower Cambrian Longwangmiao Formation reservoir in central Sichuan Basin, China
复制标题
川中下寒武统超深层龙王庙组储层多期白云石化作用及形成
DOI：
10.1016/j.marpetgeo.2020.104752
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发表时间：
2021
影响因子：
4.2
通讯作者：
Lei Jiang
中科院分区：
文献类型：
--
作者：
Dawei Liu;Chunfang Cai;Yongjie Hu;Yanyan Peng;Lei Jiang
The deeply buried dolostones in the Lower Cambrian Longwangmiao Formation at Central Sichuan Basin of.China are a crucial hydrocarbon exploration target. However, the origin of various types of dolomite for these.carbonate reservoirs has not been well understood. In this study, petrological studies, geochemical analyses.including C, O and Sr isotopes, in-situ trace elements and rare earth elements, and fluid inclusions analyses are.performed in order to uncover the dolomitization mechanisms. The results show that an initial pervasive.replacive dolomitization phase (Md, D1 and D2) was followed by volumetrically less important cement phases.(D3, D4, D5, D6 and calcite). The δ18O values and element concentrations (e.g., Na and Sr) appear to suggest that.this early dolomitization was caused by reflux of slightly modified seawater. In the shallow burial realm, influx of.meteoric water led to a decrease in Fe content (from 1000 ppm down to 70 ppm) and ΣREE content (from 34.22.ppm down to 9.56 ppm) in early diagenetic D3 dolomite with more negative δ18OSMOW values. This early.meteoric water flux may have created considerable dissolution porosities. The D3 and D6 dolomite cements were.interpreted as the result of dolomite dissolution and reprecipitation due to burial compaction. The D4, D5 dolomites.and late calcite cements display markedly positive Eu anomalies suggesting the presence of hydrothermal.fluid. Some late diagenetic calcites with negative δ13C values as low as 5‰ V-PDB and relatively higher Y/Ho.ratio of ca. 36.9 were interpreted to be derived from thermochemical sulfate reduction (TSR). The effects of.hydrothermal fluid and TSR on reservoir qualities seem to be minor in this case. Hence, this study emphasizes the.role of late diagenetic preservation of primary and early diagenetic porosity in the formation of economically.important, ultra-deep dolostone reservoirs in sedimentary basins.
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