The conglomerate reservoir of the Alshan Formation in Mongolin Oilfield is special in containing abundant volcanic debris. The reservoir could be divided into polygenic conglomerate

tuff conglomerate and volcanic breccia.The reservoir is characterized by low compositional maturity and low textural maturity.The conglomerate with coarse complex matrix is more favourable for oil reservation

and its main reservoiring spaces are intergranular matrix soluted pores. The polygenic conglomerate contains primarily intergranular soluted pores and has better permeability; the tuff conglomerate and volcanic briccia contain respectively intragranular pores and residual intergranular pores

and their permeability are poor.