Abstract:

Thin sandstone and mudstone interbed, deposited in lacustrine river-deltaic enviroment, is the necessary geologic condition of lithologic pool formation in the large, shallow-middle seated depressions, Songliao basin. Since the sedimentary accommodation, caused by the changes of base level, has a great difference in geologic time, the types of sand body have vertically a certain difference. Because the buried depth of reservoir rocks and relative position of reservoir rocks with source rocks are various, the formation condition and distribution of lithologic pools have also a certain difference in different plays. Fault plays an important role in the formation of lithologic pools, which is not only the basic attribute in the formation of composite fault-lithologic trap but also the major migration path of oil and gas into lithologic pools. In the areal extent, types of lithologic pool are controlled by structure position and sand body development. The lithologic pools are mainly developed in the delta-frontal facies belt in the large depressions, whereas the subtle oil and gas pools are mainly distributed in the periphery of the depressions.

Key words: shallow-middle seated strata, lithologic oil pool, main control factor, distribution feature, Songliao basin