Diagenesis and Its Influencing Factors of the Chang 8 Interval in Ordos Basin Yanding Area

The reservoir of Chang8 interval in Ordos basin,controlled by diagenesis,is characterized by low porosity and extraordinary low permeability. Comprehensive analyses have been made on the sedimentary characteristic,property characteristics,rock thin sections,casting thin sections and so on. The results reflect that arkose and lithic arkose is well developed and secondly feldspathic litharenite in the Chang 8 interval of the study area. The reservoir spaces are mainly protogenetic intergranular pore and dissolution pore. The diagenetic types include compaction,pressure solution,cementation,dissolution,metasomatism and recrystallization; in which the chlorite cementation. feldspar dissolution and laumontite dissolution are favorable to improve porosity and reservoir,while the compaction and carbonate cementation are the main contributors to decreasing the intergranular pore and reservoir compaction. Above all,diagenesis is affected by original components of sediments,sedimentary environment,fluid property of stucture and pore,burial metamorphism and so on,which are connected with tectonic background.