The decollement structures in Jiyang Depression, Bohai Bay Basin, China

The study with seismic,drilling,and exploitation data on the strata,structural deformation and the physical properties of the rocks shows the existence of decollement structures in the Jiyang Depression. The decollement structures occurred mainly along the unconformity surface between the Cambrian and Archean,and the disconformity surface between the Carboniferous and Ordovician. The decollement structure also developed within Paleozoic and Cenozoic. The decollement structure surface was a fault zone with cataclastic rocks and folds in the seismic profile. Near the decollement structure surface,at the bottom of the Cambrian and the top of the Archean,developed an interjacent fractured zone which shows high porosity and high permeability. The bottom of the Cambrian might be missed or overlapped,and the latter occurred in the seismic profile as double reflection time corresponding to decollement folds and stacking anticline. Because of the synchronisms of oil-gas formation and decollement structure occurrence,the decollement structure afforded the effective shortage space and channel to accumulation of oil-gas,which were the key elements to the buried hill oil-gas pool.