The Hailar Basin is one of the larger petroliferous basins currently explored by the  Daqing Oilfield Company. The  Beier Sag is the biggest sag in the basin and it is one of the structural units comprising the  Beierhu  Depression in Hailar Basin. The sag is also the most prospective prospecting area. The main reservoirs include the Lower Cretaceous Nantun Formation and Tongbomiao Formation and the rock types are sandstone， tuffaceous glutenite， tuff and base rock weathering  crusts. The main reservoirs consist of sandstone, tuffaceous gravelly sandstones, and tuffs in the Nantun and Tongbomiao Formations, and weathered crust of the basement. The main reservoir rock types in the Lower Cretaceous Nantun Formation include volcanic clastics, siliciclastics and subordinate volcanic rock. Its main porosity types are intergranular pore， intragranular pore， calking pore， fracture pore and dissolution pore. The pore texture is not favorable， throat distribution is not centralized，  throat sorting is not very good， and throat radius is small. Due to the influence of sedimentary facies， compaction and secondary porosity， the main reservoir petrophysics is  characterized by moderate to low porosity， and low permeability. The reservoirs are   distributed in West Beier Subsag， West Beier monocline belt， Huoduomoer faultd nose structure belt， Surennuoer and Sudeerte fracture belts.