Sedimentary facies and evolution of the third member of Shahejie Formation in West Depression of Liaohe basin

The lacustrine sandbodies in the 3~(rd) member of Shahejie Formation in West Depression are most important reservoirs for petroleum accumulation in the deeply buried sequences in Liaohe basin. The sedimentary environments of the 3~(rd) member of Shahejie Formation are dominantly deeper water lakes on the basis of organic geochemical marks and sedimentary features including fossils and trace fossils. Fandelta systems are recognized based on studies of sedimentary sequences and sandbody geometries. The overall finding upward sequence is characteristic of fandeltas that build out to the slope of a basin. The slope fandelta facies can be divided into proximal fan, middle fan and distal fan. Types, characteristic, areal distributions and vertical evolution of sedimentary facies of the fandelta systems in the 3~(rd) member of Shahejie Formation are described. The sedimentary supply from the western provinance produced the thick fandelta clastic wedges in the 3~(rd) member of Shahejie Formation. The sandbodies adjacent to the oil source area, and integrating with the structure and trapping conditions are important targets to find out oil and gas fields.