Diagenesis and its influence on the reservoir quality of Member 6 of the Upper Triassic Yanchang Formation oil reservoirs in Ordos Basin,China

Through analyzing and synthesising the litho-thin sections,cast thin sections,cathode light and stereoscanning,this paper systematically researches the characters of Member 6 of the Upper Triassic Yanchang Formation(Chang-6) reservoirs in Ordos Basin.The rock type includes feldspathic sandstone,debris-feldspathic sandstone,and feldspar-debris sandstone.The maturaty of components is generally low and that of the texture is medium-fine.The main pore type is divided into intergranular pore,intragranular dissolved pore,intercrystal pore and microfissure,etc..The most proportion of the pores is the residual intergranular pore.The reservoir rocks are very compactive.The pore structure is the micropore throat.The anisotropism is very strong.The physical property of the reservoir is relatively bad,most of the reservoirs are low porous and low permeable,but there are some low-medium permeable reservoirs in the wide low porous-low permeable reserviors.The diagenetic types to influence the reservoir include compaction,cementation and dissolution.Dissolution and chlorite cementation circle rims are favorable to form fine reservoirs.