Lower Tertiary Sequence Stratigraphy Study and the Forecast of Subtle Reservoir in Dongying Depression

On the basis of comprehensive study of seismic data, well logging and other data, applying the sequence stratigraphy theory, one supersequence set, four supersequences and ten sequences are distinguished in Dongying depression. We identify system tracts for each sequence and build up isochronous sequence framework in Dongying depression. The structural slope break zone, resulting in the abrupt change of the depositional slope, is initiated by the long term activity of syndepositional structure. Structural slope break zone in the fault subsidence lacustrine basin constrained the change in the accommodation space of the basins, controlling the development of the depositional sequence and the distribution of the depositional system tracts and the sand bodies. By means of establishing lower Tertiary equence stratigraphic framework and sequence system tract model of Dongying depression, this paper puts forward that lowstand sand bodies controlled by structural slope break zones are favorable for forming subtle reservoirs.