THE APPLICATION OF STRONTIUM ISOTOPES IN DIVISION OF PALEOKARST STAGES IN TAHE OIL FIELD

Tahe oilfield is an Ordovician carbonate rock fissure vug oil pool which is mainly related to unconformity.Its reservoir rock is reformed by superimposition of multistages karstification,so it is very important to identify paleo-karstification stages and confirm distribution of different stage of karstfication reservoir for further exploration.Through recent years exploration,it is thought that the ratio of ⁸⁷Sr/⁸⁶Sr is an effective indicator distingishing middle Caledonian stage of karstification reservoir from early Hercynian stage of karstification reservoir.Its theory is that strontium isotope composition in the global ocean water at any one time in geologic history is homogeneous,that is,⁸⁷Sr/⁸⁶Sr value in ocean water changes timely.Combined with the geological setting that ⁸⁷Sr/⁸⁶Sr value in Caledonian stage of karstification reservoir is different from ⁸⁷Sr/⁸⁶Sr value in Hercynian stage of karstification reservoir and the experimental data,Pa-leokarstification reservoir stages is identified and predicted,and distribution pattern in Tahe oilfield is discussed in the paper,which provides geological evidence for further petroleum exploration in Tahe oilfield.