Discussion on a sedimentary model of river-controlled shallow-water delta plain subfacies:Taking the Shanxi Formation of the S59 Block Gas Field in Ordos Basin as an example
The Shan-1 member of the S59 Block in Ordos Basin is characterized by a stable structure,flat terrain,shallow ancient water depth,frequent rising and falling lake plane,sufficient provenance,and the development of a triangular,shallow-water deposition.On the basis of previous studies,the sedimentary characteristics of this shallow-water delta were discussed in terms of core samples from the well and well-logging facies analysis.Based on these,a sedimentary model of shallow-water delta plain subfacies was established.The results showed that the Shanxi Formation,Shan-1 Formation,represents the sedimentation of a river-controlled shallow-water delta.The sedimentary processes in the terrestrial portion of this shallow-water delta are consistent with meandering river deposition.Various microfacies are developed,including floodplain,"abandoned-type"abandoned river channels,mouth bars,and alluvial plains.On the map view,the river channels continuously erode on the concave banks and deposit sediments on the convex banks,forming microfacies of floodplains.Additionally,abandoned river channels of a certain scale are developed on the concave banks.The channel sands are distributed in a north-south direction,with a minor amount of mouth bar deposition.Fine-grained floodplain subfacies develop between the river channels.By clarifying the sedimentary characteristics of the first member of the Shanxi Formation,the establishment of the sedimentary model for deltaic plain subfacies provides geological evidence for predicting the development location of high-quality sand bodies.
Ordos BasinShan-1 Formationriver-controlled shallow water deltasedimentary model of delta plain subfacies
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