STRUCTURAL-DEPOSITIONAL FRAMEWORK AND HYDROCARBON EXPLORATION PROSPECTS IN THE CHAGAN DEPRESSION, THE YINGEN-EJINAQI BASIN

Developed on the the Xing Meng Hercynian Folded Belt, the Yingen-Ejinaqi Basin is a Cretaceous strike slip one with coexisting of rags and highs in the structure. Each sag is characteristic of multiple and near provenance fillings with delta and coastal depositional systems extremely developed, and the latter surely played an important role in the formation of oil and gas reservoirs in this basin. The results illustrated that the Chagan Depression is a most important sedimentary unit lying in the northeast of the basin, and the features of the basin are strong volcano activity, high geothermal gradient (4.8℃/100m) and large sedimentary thickness during the period of rift faulting (K₁b-K₁s). The diageneses in the target reservoirs (K₁b-K₁s) occurred early and strongly, which resulted in the low porosity and permeability of reservoir properties (type Ⅳ/Ⅴ). Moreover, due to subjected to reformation and uneven erosion in the forth episode of the Yanshanian event (in the end of K₁s), the structural and stratigraphic framework of the primary basin had been changed obviously. Therefore, to resume the proto basin and its distribution and then to seek the syngenetic successive structures principally controlled by paleo-highs should be one of the solutions to looking for the rather good reservoirs and potential petroleum accumulation zones. This favorable reservoir zones are believed to be the controlled by the development of both paleo-highs and depositional systems, while the structural stratigraphic traps will be the main targets for the further exploration.