Sedimentary microfacies of the eighth member of the lower Shihezi Formation in northern Sulige Gas Field,Ordos Basin

The eighth member of the Shihezi Formation consists of braided stream deposits including the channel and flooding plain subfacies on the basis of petrography,palaeontology,sedimentary structures,sectional architectures and well logs of more than twenty wells in northern Sulige Gas Field.The channel subfacies may be subdivided into two sedimentary microfacies: river-bed lag deposits and channel bar.These sedimentary microfacies generally display fining-upward depositional sequences,and moderate-to high-amplitude box-shaped or bell-shaped well logs.The flood plain subfacies comprises the alternating beds of sandstone and mudstone,and exhibits zigzag well logs.The sedimentary microfacies analysis has led to the construction of the sedimentary facies plans and model for the eighth member of the Shihezi Formation.