Abstract: The reservoir in Tongbomiao-Nantun Formation in Beier depression is characterized by low to medium porosity and low permeability. There are two anomalously high porosity zones in Beier depression; one is in the depth of 1 300[CD*2]1 800 m, and the other is at 2 400-2 700 m. The controlling factors for these two zones are as follows:①pyroclastic materials can be dissolved and form secondary pores;②the coating of detrital grains is suitable for conservation of primary porosity;③leaching of meteoric water has led to the formation of secondary porosity;④corrosion of organic acid has resulted in the generation of secondary porosity.Among them, leaching of meteoric water has contributed less to the formation of anomalously high porosity zones compared to other factors. As pyroclastic rocks are the main objects dissolved by organic acid and the newly generated cations are the major components forming chlorite and illite, the major controlling factors for the formation of anomalously high porosity in Beier depression are the physical properties of those special reservoir rocks.

Key words: reservoir physical property, pyroclasitc rocks, corrosion, dissolution, coating, Halaer basin