A large-scale Ordovician carbonate weathering crust was developed on the north slope of Tazhong area in Tarim basin.Studies on the weathering crust reservoirs and its reservoiring conditions show that the reservoirs feature in low porosity and low permeability dominated by secondary solution pores and cavities.They are mostly developed on the top of the Lower Ordovician and have an excellent correspondence relationship with the morphology of the unconformity surface.Reformed by the development of faults and fractures

the weathering crust reservoirs were widely distributed along the karst slope vertical superimpositon and horizontal connection.The hydrocarbon carrier system which is composed of faults and unconformities controlled the migration and accumulation of hydrocarbons;and the development of reservoirs controlled the enrichment of oil and gas in the weathering crust.Multiphase charging and heterogeneity of the reservoirs caused the differences of oil and gas occurrence.