ISOTOPIC CHARACTERISTICS OF OIL FILED WATERS FROM ORDOVICIAN OIL ACCUMULATIONS IN TAHE OILFIELD AND ITS GEOLOGICAL SIGNIFICANCES

Hydrogen isotope values(δD) of oil field waters from the Ordovician oil accumulations in Tahe oilfield cover -44.7‰～-61.0‰(SMOW),from which one can conclude that the oilfield waters are mostly paleo-atmospheric waters mixed with original sediment seawater.Based on the transverse change trends of the parameters in these oilfield waters,such as high pressure physical parameter,carbon isotope of CO₃^- electronegative ion and ⁸⁷Sr/⁸⁶Sr ratio of strontium isotope,one can roughly deduce that the predominant flow direction of paleo-atmospheric water is from the northeastern tectonic high position to the southwestern plunge end of the Arkekule nose salient.In this process,the current flowed from axis to two wings of the tectonic,which would cut through weakness belt of faults or cracks and enlarge the space by carbonates corrosion,finally formed complicated karst fracture-cavity system of the Ordovician carbonates in Tahe Oilfield.Therefore,the flow direction of paleo-atmospheric water controled the distribution of fracture-cavity system and connectivity of fracture-cavity cells.