Structure Interpretation And Reservoirs Prediction In Triassic Jiucaiyuanzi Formation In Bei80 Well Region, East Of The Junggar Basin

The study area is located in the high position of Xiquan structural nose in the west of Beisantai periclinal uplift in the eastern Junggar Basin. The whole structure was arcual around Beisantai uplift, faults developed in the axis of nose-uplift. Strata from Carboniferous to Quaternary developed in the region. The strata bellow Cretaceous gradually thinning and pinch out in the uplift. The oil and gas of Jiucaiyuanzi formation (T1j) was generated by the source rocks of Triassic Pingdiquan formation in Fukang Depression and Jimsar Depression.The reservoirs of T1j in the region of Bei80 well in the east of Junggar Basin are characterized by thin sandstones and large variation of petrophysics. Based on systematic observation of the cores on lithology, grain size, bedding and fabric components, fine structural interpretation using three-dimension seismic data, seismic attribute analysis and acoustic impedance inversion, this research predicted favorable regions for reservoir sandstones development and petroleum accumulation.Observations of the cores revealed that T1j is alluvial fan, river, and flood plain depositional systems developed in arid climate condition. The frame sandbodies are mainly abandoned channel sediments which are composed of thick bedded red mudstone with imbedded thin sandstone and glutenite, showing‘Mud Sand’structure with more mudstone than sandstone.Fine structure interpretation using three dimension seismic data revealed the faults and strata distributions which supported seismic attribute analysis and acoustic impedance inversion. The strata bellow Cretaceous is dipped to the southwest with steep angle. A series of block traps developed in the slope. Drilling showed the reverse blocks controlled by reverse faults are more favorable for the oil and gas accumulation. Sandstone showed high electric resistance, high acoustic impedance, and low natural potential. The natural gamma can not identify sandstone effectively. So prediction of sandstone reservoirs was carried out by the acoustic impedance inversion.The shape of traps and sand distribution revealed that the T1j traps in Bei80 well region are mainly controlled by both structure form and sandbodies distribution. The main channel sandbodies with higher porosity and permeability in fault blocks are favorable regions for petroleum accumulation. The drilling targets should be selected both in the main oil production layers and other oil layers for reducing drilling risk as the reservoirs have multi-oil layers.