Hydrocarbon accumulation history of the Cambrian Longwangmiao Formation in the Anyue structure of the central Sichuan basin
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    Abstract:

    This paper analyzes the cementation/filling sequences and hydrocarbon accumulation history of the Cambrian Longwangmiao Formation reservoir in the Anyue structure of the central Sichuan Basin by means of core and thin section observations, together with the cathodoluminescence analysis, fluid inclusion analysis, laser Raman analysis, stable isotope analysis on fillings, and apatite fission track dating. Seven stages of cementation/filling sequences are identified, i. e. , fibrous dolomite cementation in the submarine environment→granular dolomite cementation in the shallow- burial environment→vadose silty dolomite filling in the epidiagenesis environment→dolomite filling in the shallow- re- burial- moderate- burial environment→dolomite filling in the deep- burial environment→calcite filling in the deep- burial environment→quartz filling in the uplifting burial environment. The characteristics of fluid inclusions in the cements and fillings and their relationships with bitumen reveal at least 5 stages of hydrocarbon accumulation in the Longwangmiao Formation. The fluid inclusions captured in the Stage Ⅳ dolomite to the Stage Ⅶ quartz demonstrate the phases from liquid hydrocarbon inclusion to gas- liquid two- phase hydrocarbon inclusion and then to gas hydrocarbon inclusion, indicating that the Longwangmiao Formation has experienced the formation of paleo- oil reservoir, destruction of paleo- oil reservoir, re- formation of paleo- oil reservoir, cracking of oil into gas, formation of paleo- gas reservoir, and reworking and finalization of gas reservoir along with the structural uplifting in the Himalayan. The analysis on apatite fission track indicates that the Anyue structure was uplifted by 1865~2030 m in the Himalaya, contributing to the reworking and finalization of the Longwangmiao Formation gas reservoir, which is recorded by the Stage Ⅶ quartz. The 87Sr/86Sr, δ13C and δ 18O of the Stage IV dolomite fillings in the Longwangmiao Formation reservoir reflect that the Stage Ⅳ dolomite is related to the re- dissolution and precipitation of the surrounding rock matrix, which occurred during burial at a relatively high temperature. The 87Sr/ 86Sr, δ 30Si and δ18O of the later quartz fillings in the pores, vugs and fractures indicate that the quartz was mainly derived from the silica- bearing diagenetic fluid and is independent of the activity of the mantle- derived hydrothermal fluid in the deep strata. The contribution of foreign destructive fluids to the hydrocarbon accumulation process is not found.

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LIN Xuemei, YUAN Haifeng, ZHU Lianqiang, ZENG Wei, XU Yunqiang.2020. Hydrocarbon accumulation history of the Cambrian Longwangmiao Formation in the Anyue structure of the central Sichuan basin[J]. Acta Geologica Sinica,94(3):916-930

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History
  • Received:September 29,2019
  • Revised:January 21,2020
  • Adopted:January 21,2020
  • Online: February 05,2020
  • Published: