FRACTURES OF THE ORDOVICIAN LIMESTONE AND THEIR RELATIONSHIP WITH HYDROCARBON ACCUMULATION IN THE SANGTAMU FAULT BELT OF THE TARIM BASIN

Sangtamu fault belt was located at Tabei uplift in Tarim basin. A lot of oil and gas resource was discovered in the Ordovician limestone of buried hill. Reservoirs are pore-fracture type. Many fractures were developed in the reservoirs. Average fractures density in cored inteval is 3.3 strap per meter. The fractures are characterized by small, oblique and half-filled ones. Two belt of fractures were vertically developed with the first one located under uncomformity surface. Its thickness is 20～50m. The second one is located below 100m of the first belt. Its thickness is 50～80m. In different position of fault belt, development level of fractures is different, and fracture is more developed inside the fault belt than the outside. Unconformity surface and lithology infleunced the vertical distribution of fractures. There is close relationship between hydrocarbon accumulation and fractures. The location with little fractures is poor for oil and gas production. Fractures are principal contributor of permeability and porosity of ressrvoirs. They supplied for 99.4% of total permeability and 12% of total porosity.