Diagenesis and diagenetic facies studies for Yanchang Formation of the Triassic in Ordos basin.

The reservoirs of Yanchang Formation of the Upper Triassic in Ordos basin are low and super permeability reservoirs, which were formed by vigorous diagenesis. Generally, different sedimentary microfacies developed different types of cementation that controlled distribution of secondary pore dissolved by acid water solution. Through studying sedimentary microfacies of Chang 6 reservoir and analyzing about 500 thin sections, diagenetic facies of Chang 6 reservoir are classified as eight types. For the above mentioned study and analysis, the authors discuss the relation of sedimentary facies and cementation types. Finally, the authors predict the distribution of diagenetic facies for Chang 6 2 1 Chang 6 1 2 reservoirs and obtain a result that the favorable sedimentary facies tract and favorable diagenetic facies of Zhijing and Ansai delta may extend towards lake area.