Depositional features and properties analysis of Yanchang Formation in Fuxian area,Ordos Basin

Physical properties characteristics and controlling factors of Triassic Yanchang Formation reservoir are studied by depositional facies and diagenesis.The authors have considered that the main depositional microfacies of the Yanchang Formation include subaqueous distributary channel,mouth bar,sheet sand and interdistributary bay.Subaqueous distributary channel of delta front is the best reservoir with average porosity 10.85% and permeability 0.613×10-3 μm2.Among all the diagenesis reservoir experienced,compaction has greater effect to sandstone physical properties.After the sands of subaqueous distributary channel compacted,the original porosity reduced 13.6%.Cementation has certain destructive action to reservoir physical properties,but the remaining primary intergranular pores can be preserved by early cement and the soluble components also provided material base to secondary intergranular pores.Dissolution can improve the reservoir physical properties greatly;structural microcracks only play path function locally.The reservoir is low in porosity and low in permeability on the whole,and the main pore types are dissolved pores between grains and dissolved pores in grains.Sedimentary facies control the sandbody type,size,original physical properties and spatial distribution in macro-level,diagenesis impact the evolution of reservoir pore and the change of reservoir physical properties in micro-level.The structural cracks can improve reservoir physical properties in partial.