Determinative marks and distribution characteristics of braided river deposits in 1st section of Quantou Formation of Lower Cretaceous in Xiaochengzi area, southern Songliao Basin

The Ⅲ-Ⅴ sedimentary sand bodies in the lower part of the 1st section of the Quantou Formation in the southern Songliao Basin were deposited at the beginning of depression sedimentation, and they were important for the Nongan oil reservoirs. Complicated characteristics and unclear origin had delayed the study of reservoir distribution. A case study was carried out in the Xiaochengzi area of the southern Songliao Basin. Through analyzing the multiple perspectives of characteristics about cores, well logging data, seismic interpretation, grain size analysis and so on, the results showed that the Ⅲ-Ⅴ sand bodies in the lower part of the 1st section of the Quantou Formation were proximal and small braided river deposits under special background. 2 sedimentary subfacies (river and flood plain) and 4 sedimentary microfacies were further divided. 6 determinative markers such as rock type combination, rock texture and sand body distribution on profile were concluded for the determination of braided river. According to the relationship between seismic and sedimentary facies, the distribution and variation of braided river deposits in the Ⅲ-Ⅴ sand bodies in the lower part of the 1st section of the Quantou Formation were made clear.