Three sorts of diagenetic fractures and five stages of structural fractures developed in Ordovician carbonate rocks in Hetian River Gasfield.Their characters of development time

attitude

scale

packing degree and so on are different each other.The fractures are characterized by high angle and small micro fractures

most of them are filled by mud and calcite.The suture and 2～5 stage structural fractures contain spaces for hydrocarbon preservation and migration.Fractures are the principal contributors of permeability(supplying 99.4% of total permeability)

and it is the main cause for carbonate rocks to be efficient reservoirs.development degree of fractures was controlled by lithology and tectonic movement.