Fan Deltaic Depositional Systems and Their Relationship to Oil and Gas Accumulation

Key words: 
• fan deltaic depositional system /
• oil and gas accumulation.

Abstract: Fan deltaic depositional systems are well developed in rift basins,and usually consist of fan delta plain as-sociation, fan delta-front association and prodelta association. Nine genetic facies can be distinguished in fandeltaic depositional systems. Controlled by sediment flux rate, available accommodation expansion rate andbasin-bounded fault,fan deltaic depositional system style can be generally divided into five types ,i. e. degrad-ing,aggrading,prograding,steep slope and slow slope fan deltas. The braided distributary channel sand-bodiesdeveloped in fan delta plains and their related subaqueous distributary mouth bar and flood gravity currentsand-bodies deposited in fan delta-front zones are high quality reservoirs. Oil exploration results have shownthat principal oil reservoirs are distributed dominantly in fan delta-front zones and interdistributary bays,andsome reservoirs are developed in fan delta plain areas. Influenced by burial-depth and diagenesis,principal oil-bearing beds in different areas and different horizons are different because of the various relationships betweenphysical properties and lithologies. Therefore,the relationship of depositional system distribution to oil and gasaccumulation can be applied to search for residual oil-bearing beds and to predict prospect areas.