The andesite in north Alsen was formed by at least 12 magmatic eruptionsand 3 volcanic explosions. The lava beds of each eruption can be dividedinto 2-3 belts

and the reservoirs are mainly distributed in 1-2 belts of theupper part. Pores are developed at the main flow line of eruptive subfacies

the eruptive minor facies zone near the crater and structural topes

composedfour kinds of reservoir rocks: lava-flow autoclastic rocks

andesite conglome-rate

vesicular-amygdaloidal andesite and compact massive andesite

andconstituted seven kinds of pores and three pore assemblages. These reservoirsare characterized by low porosity-permeability

poor porous texture

highanisotropy. Original aqueous satuation is up to 89% and aqueous exploitaionstarted at the very beginning.