Characteristics of Ordovician Fracture-Vuggy Carbonate Reservoir in Mazatage Structure Belt,Tarim Basin

The Ordovician weathering carbonate reservoirs with low matrix porosity,permeability and intensive anisotropy are composed mainly by the secondary dissolution pores and holes and fractures.It is important for marine carbonate reservoir to evaluate the fracture-vuggy distribution in the Mazatage structure belt of Tarim basin.We use the cores and logging date to identity the multi-stages kartification and fracturing.The kartification of the Ordovician carbonate is well developed in the area,which affects the depth up to 400m and the dissolution pore-hole layers about 3-5 layers with individual thickness about 10-50m in the wells.The karst is developed in the vadose zone rather than the phreatic zone.The karst intensity is weak,associated with the straggling distribution of pore-vuggy.The cave scale is small and filled seriously.The karst model is proposed based on structure and palaeogeomorphology recovery.The Hetianhe gas field is located in the karst gentle slope and bottomland,so the caverns filled by argillo arenaceous with ineffective exist is observed.The area of southern crust which was superimposed by three stage karstificaition lies in the favorable karst slope.Therefore,the large area of southern crust as a potential exploration is favorable for the development and preservation of fracture-vuggy reservoir.