Geochemical characteristics and origins of fracture- and vug-fillings of the Ordovician in Tahe oilfield, Tarim basin

Chun Fang Cai, Kai Kai Li, Bin Li, Liu Lu Cai, Lei Jiang

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    23 Citations (Scopus)

    Abstract

    Fracture-filling calcite and huge crystalline calcite from Ordovician carbonate reservoirs of Tahe Oilfield were measured to have 87Sr/ 86Sr mainly higher than bulk limestone and contemporaneous seawater, indicative of a significant contribution from external 87Sr-rich fluid in this area. 87Sr-rich fluid may have derived from paleo-freshwater flowing through detrital strata during Hercynian Orogeny or from deep hydrothermal fluid. Paleo-freshwater is indicated by low Sr concentrations and the relationship between λD and λ 18O. Infiltration of paleo-freshwater resulted in biodegradation of early emplaced oil and generation of organic acids and anions (OAAs) and pyrite with λ34 down to -25‰. Hydrothermal fluid is indicated by relatively high Sr concentrations and significantly higher homogenization temperatures of fluid inclusions (up to 150 ̃ 190°C ) than what ambient limestone experienced, suggesting that radiogenic Sr may have derived from deeper pre-Cambrian detrital strata. Mixing of hydrothermal, basinal and likely fresh fluids led to dissolution of calcite, thus improvement of porosity in local areas.

    Original languageEnglish
    Pages (from-to)2399-2404
    Number of pages6
    JournalActa Petrologica Sinica
    Volume25
    Issue number10
    Publication statusPublished - 2009

    Keywords

    • Hydrothermal fluid
    • Porosity
    • Strontium isotopes
    • Sulphur isotopes
    • Tarim basin

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