Palaeogene sequence stratigraphy and subtle hydrocarbon exploration in the Maxi region,Raoyang depression,Hebei

The Palaeogene sequence stratigraphy in the Maxi region,Raoyang depression may be classified,on the basis of seismic data,well logs and sedimentary facies,into 3 second-order sequences and 10 third-order sequences.The third-order sequences VIII,IX and X are assigned to the fluvial sequences including the base-level rising systems tract and base-level falling systems tract.The third-order sequences Ⅰ,Ⅱ,Ⅲ,Ⅳ,Ⅴ,Ⅵ and Ⅶ represent the lacustrine sequences,each of which consists of lowstand systems tract,transgressive systems tract and highstand systems tract.The syndepositional structural breaks in the Maxi region have exercised a major control on the distribution of sandstones,development of source rocks,migration of hydrocarbons,and accumulation of subtle hydrocarbons in this region.The model for the accumulation of subtle hydrocarbons shows that Sequences Ⅲ,Ⅳand V below the structural breaks may be regarded as the targets for the further exploration of hydrocarbons.