Jurassic sequence stratigraphic frames in the Middle Junggar Basin

The identification signs of the Jurassic sequence boundary are determined and two kinds of sequence boundaries, unconformity and shift surface of deposition, are identified according to drilling, logging and seismic data in the middle Junggar Basin. Five Jurassic sequence boundaries are developed as four long-term base level cycles further in the middle basin. Stratigraphic frames are built on the basis of well and seismic-data calibration. It is confirmed that the Sangonghe Formation is the key target series for exploration in the middle basin where reservoir sands are the river mouth bar and distributary channel sandstones of delta front. The distribution of advantaged reservoir facies is closely related to their position in the sequence and mainly developed at the half cycle of increasing A/S conditions.