Sequence analysis and isochronous correlation of the short-term base-level cycles in the third oil reservoirs of the Yanchang Formation in the Huachi Oil Field,Ordos Basin

The short-term base-level cyclic sequences in the third oil reservoirs of the Yanchang Formation in the Huachi Oil Field,Ordos Basin are examined on the basis of well logs and high-resolution sequence stratigraphy.These cyclic sequences may be divided into three types:"deepening"-upward asymmetrical type,"shallowing"-upward asymmetrical type and symmetrical type.The isochronous correlation for the short-term base-level cyclic sequences results in the construction of isochronous stratigraphic framework and model for the distribution of the short-term base-level cyclic sequences.