Diagenetic Sequence Stratigraphy Characteristics of Lower Cretaceous Bashijiqike Formation in Kuqa Depression

Key words: 
• diagenetic sequence stratigraphy /
• sequence boundary /
• systems tract /
• diageneisi /
• ECS /
• Bashijiqike Formation /
• Keshen gas field

Abstract: On the basis of thin section, casting thin sections, X-diffration and scanning electron microscope data, this article discusses reservoir properties including lithology, physical property and reservoir space of the Cretaceous Bashijiqike Formation in Dabei area of the Kuqa Depression. Combining with Elemental Capture Spectroscopy (ECS) logging, diagenesis and characteristics of diagenetic mineral assembladges were studied. The difference of diagenesis between Ba 2 (the second member of Bashijiqike Formation) transgressive system tract and Ba 1 highstand system tract is also analyzed. The results show that corrosion phenomena are widely observed in the thin sections, with the decrease of feldspathic litharenite content near the boundary and improvement of physical property near sequence boundary. The clay content is higher both at the maximum flooding surfaces due to deposition, and under the sequence boundaries due to kaolinization after corrosion. On the whole, the controls of sequence boundaries and system tracts on carbonate cementation are not obvious. Different contents of carbonate cement could be seen in every part of sequence, which are related to alkaline diagenetic environment of the study area. Study results are beneficial for the track and comparison of reservoirs; Moreover, these would direct the exploration of gas and promote the development of the sequence stratigraphy theory.