The 3rd Member of Hetaoyuan Fm constituting the reservoir of the Shuanghe Oilfield in the Biyang depression is represented by coarse clastics from rapid deposition.Pore spaces developed here are mainly of intergranular and corrosive types

and porosity in matrix is rare.There are four grades of pore space

from good to bad

as defind in this paper.However

majority of these pore spaces is of the good ones.The pore structure of reservoir is clearly improved due to the extensive development of secondary corrosive pore spaces.The development of secondary porosity is related both to rapid accumulation

poor maturity and lower compaction caused by earlier calcareous infilling andsubsequent cementation

and to the generation of water and carbon dioxde insource rocks during formation of hydrocarbons

These source rocks being coex-isted and interfingered with reservoirs contain mainly transitional types of kero-gen within a depth favourable to oil and gas generation

so the water and carbon dioxide generated inevitably would react with the early infilled carbonates and other minerals in adjacent reservoir rocks resulting in greater amount of secondary porosity.The development of the secondary porosity might also related to the structure of coarse grained rocks of the reservoir proper.