| Badaowan Formation in the hinterland of Junggar Basin is a potential exploration replacement field of
Jurassic. By analyzing the formation conditions and sedimentary characteristics of the lowstand system tract(LST) sand
body of Badaowan Formation in Western Well Pen-1 Sag, combined with the study of reservoir forming conditions, this
paper proposes that LST sand bodies are developed below the slope break of depressional lake basin, and the reservoir
forming conditions of LST sand body are superior. The results show that: (1) A complete third-order sequence is
developed in the Badaowan Formation of the Western Well Pen-1 Sag in the Junggar Basin, and during the Badaowan
sedimentation period, slope breaks are developed around the Western Well Pen-1 Sag. Braided river delta from the
eastern provenance system prograde towards the sag, and unload sediment in the sag area below the slope breaks, creating
conditions for the development of LST sand body in the sag area. (2) LST sand bodies of braided river delta are developed
in Badaowan Formation of Western Well Pen-1 Sag, which is formed through the continuous unloading of sediment
below the slope break after long distance transportation. The LST sand body is sand-shale interbeded, and laterally
contacts with the flood plain mudstone of the delta plain, so the roof and floor and shielding conditions are good.
Therefore, the lithologic trap conditions are superior, and the LST sand bodies have the conditions to form a large-scale
lithologic trap group. (3) The low porosity and ultra-low permeability reservoir of LST sandstone is developed in the
Western Well Pen-1 Sag, and the local microfractures improve the physical properties of the reservoir. Two sets of source
rocks of the Permian Fengcheng Formation and Lower Wuerhe Formation are developed in the sag, so the source
conditions are good. (4) In addition, two groups of deep and shallow faults are developed around the Western Well Pen-1
Sag, vertically connecting the LST sand bodies of Badaowan Formation with Permian source rocks, which is conducive to
the accumulation oil and gas, so the LST sand bodies have great exploration potential and are favorable exploration fields
for the next step of oil and gas discovery in the Junggar Basin. This understanding provides a geological basis for the next
step of oil and gas exploration in Junggar Basin, and also provides a reference for oil and gas exploration in depressional
lake basins with similar geological backgrounds at home and abroad. |
