THE LOWER CRETACEOUS PETROLEUM SYSTEM IN NE CHINA

Abstract

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.