CHARACTERISTICS AND SIGNIFICANCE OF THE CALEDONIAN KARST IN THE TAHE OIL FIELD, THE TARIM BASIN

The Tahe oil field is located in the Akekule uplift in the north of Tarim basin.It is the biggest carbonate hydrocarbon reservoir found in the Tarim basin up to now,and the biggest in China.According to exploration,the Ordovician reservoir,as the main reservoir bed in Tahe oil field,is mainly composed of hole,cave and aperture.Karst development consequentially controls the development of carbonate aperture-cave reservoir and reservoir formation.Kinds of data indicate that,there is Caledonian,besides Hercynian karst in the Tahe oil field.Study findings indicate that,native rock characteristics,development of rupture and fissure,ancient physiognomy,climate and water system control karst development,among which ancient physiognomy and development of rupture and fissure are the main factors.The Caledonian karst plays an important role in the development of rupture and fissure system of Ordovician carbonate rock,and is important to the exploration of middle Ordovician Yijianfang Formation,middle-low Ordovician Yinshan Formation and upper Ordovician Lianglitage Formation covered by the upper Ordovician Sangtamu Formation,consequentially enlarging the exploration foreground in this area.