Sequence stratigraphic framework and source-reservoir-caprock assemblage of Yanchang Formation in western Nanliang area, Ordos Basin

In order to study sequence stratigraphic framework and source-reservoir-caprock assemblage of Upper Triassic Yanchang Formation in western Nanliang area,this paper studied the sequence boundary types,the characteristics of sequence stratigraphic framework,and the relationship between long-term base-level cycle and source-reservoircaprock assemblage by the theory and approach of high resolution sequence stratigraphy.The result shows that five third-order sequence boundaries are identified,the Yanchang Formation consist of four long-tern and one super-long term base-level cycles.The source-reservoir-caprock assemblage has close relation to the long-term base-level cycle.The sand bodies of delta plain distributary channel and front underwater distributary channel developed in the earlymiddle stage of the uprising periods and middle-late stage of subsiding periods are high quality reservoir,the turbidite sand bodies developed in the middle-late stage of the uprising periods and early-middle stage of subsiding periods are potential reservoir,and the lacustrine shale and carbon mudstone developed in the surrounding of transforming interface of uprising to subsiding of the long-term base-level cycle.The Yanchang Formation developed three types of source-reservoir-caprock assemblage, including upper-sourcing and lower-reservoiring type and lower-sourcing and upperreservoiring type and self-sourcing and self-reservoiring type.