Genesis relationship between faults and karst reservoirs in the Yingshan formation,Medieval No.8 wellblock

There are abundant oil and gas resources in the Ordovician carbonate formation of the Tarim basin.The superposition and transformation in many episodes of different types of karst development are the main driving force of Tazhong ancient karst reservoirs.Faults are an important factor affecting karst reservoirs.The Medieval No.8 wellblock is situated in a northwest-southeast trending thrust fault zone of the Caledonian period and a northeast-southwest trending strike-slip fault zone of the Hercynian period,which form a network system.The karst reservoirs developed in the subsurface from the top of Yingshan formation to 120 km depth,which are of hole type,cavity type,fissure type and fissure-hole type.Of these,the fissure-hole type and hole-type are dominant.The multi-episode faults and associated fissure network system of the Caledonian to Hercynian period serve as good migration channels for fluids,which promote the development of the fissure-hole system,burial dissolution and dolomitization,improving the performance of reservoirs to become a complex combination of carbonate holes,cavities and cracks.