High GR Glutinite Feature and Micro-Sedimentary Facies in Wuerhe Oil-field, Junggar Basin——Taking the Baikouquan Group in Wu 36 Area as an example

Key words: 
• natural gamma anomaly glutinite /
• micro-sedimentary facies /
• Wuerhe Oilfield /
• Junggar Basin

Abstract: Based on rock core documentation, well logging analysis and the rock fragment  data, we carried out  the sedimentology research on the Triassic Baikouquan Group in Wu 36 area of Junggar Basin. This  study   revealed that the Baikouquan Group developped in  alluvial fan  system. The glutenite is characterized by unusually high natural gamma and the mudstone is characterized by low inside the alluvial fan. This feature is mainly controlled by the high radioactive substance in the original rock, for example the tuff. The spatial variation in high natural gamma anomaly was influenced by sediment grain size, transport distance and facies distribution. According to the spatial variation characteristics of Gamma anomaly, we established a clay content formula and put forward a new method on the division of sedimentary facies. Our study area mainly develops mid-fan braided stream line microfacies, mid-fan braided stream sand island microfacies, mid-fan sheetflood microfacies and cross flow microfacies in marginal subfacies. We also carefully portrayed the distribution and vertical evolution of these sedimentary microfacies of different stages. The results show that the 3^rd member in Baikouquan Group developed four fan bodies. There is a sedimentary evolutionary sequence in the vertical profile controlled by fast dereliction and slow retrograding. The 2^nd member in Baikouquan Group developed three fan bodies and presented a retrograding evolutionary sequence in the vertical. The 1^st member in Baikouquan Group performed the alluvial fan marginal sedimentary. Compared with the actual production, this study better explained the production status of the regional producing well and verified the feasibility and practicality of using natural gamma characteristics of high natural gamma glutinite to make research on sedimentary microfacies.