THE LOWER CRETACEOUS PETROLEUM SYSTEM IN NE CHINA

NE China is situated on the pre-Mesozoic folded belt between the Siberian and Sino-Korean Cratons. Beginning in the Late Jurassic, the oceanic Izanagi Plate was subducted NW wards beneath the Eurasian Plate, resulting in a change in the structural setting from north-south compression to NW-SE extension leading to intracontinental rifting. The Early Cretaceous marked a peak in the development of syn-rift lacustrine basins, and there are about 200 rift depressions in the study area. Left-lateral strike-slip activity on the NE-SW oriented Tan-Lu Fault, and a change in the rate and direction of subduction of the Izanagi Plate, ended the syn-rift stage. Thick, post-rift lacustrine sequences only developed in the Songliao Basin, and today form source and reservoir rocks at the “giant” Daqing oilfield. Gas-source rock correlations in the Lower Cretaceous strata of the Songliao Basin, and oil-source rock correlations in the Erlian and other basins have indicated that all the hydrocarbons were generated in, and have migrated from, Lower Cretaceous source rocks. The Lower Cretaceous syn-rift sequence has been proved to be a known petroleum system. Twenty-two oil- and gasfields have been found in six basins. Each rift depression constitutes an independent petroleum system, and plays can be divided into four types (boundary fault; deep-sag; central flexural; and flexural margin), of which the central flexural play is the most prospective. It is anticipated that these small rift basins will become targets for future exploration.