Hydrocarbon preservation conditions in the Dangyang synclinore were studied on the basis of its tectonic evolution with paleo-fluid. Infillings of multi-stage paleo-fluid of multiple stages occurred in Lower Permian-Lower Triassic strata in the Dangyang synclinore. 87Sr/86Sr of part of fluids changes from 0.710 0 to 0.710 4, suggesting its allochthonous origin, probably came from the mud carbonate rocks or mud gypsum rock of Middle Cambrian and Upper Cambrian. 87Sr/86Sr of other fluids is between 0.707 5 and 0.708 1, similar to that of host rock and contemporary seawater, suggesting an endogenous fluid origin. No organic inclusions were found in above mentioned fluids. In early-middle Yanshanian period, multi-stage thrusting along Middle Cambrian gypsum rock took place,fluids rich in 87Sr/86Sr from the Middle and Upper Cambrian migrated upwards along fault and filled in different overlying marine strata, and the paleo-gas reservoir under the detachment plane was not destroyed.
