Abstract:

Exploration of subtle reservoirs is a hot topic and one of the future directions in oil exploration.In this paper,research on sequence stratigraphy of the upper third member of the Shahejie Formation(Es³) in the Liuxi area of the Raoyang Sag,the Jizhong Depression is made based on basic principles of sequence stratigraphy and by using seismic,logging and lithofacies and other data.Sequence stratigraphic framework of the Liuxi area is established.According to the research,the upper Es³ is a complete third-order sequence which can be divided into lowstand,lake transgression and highstand system tract.Based on these results,the plane distribution features of sedimentary facies in each system tract are analyzed under the sequence stratigraphic framework.The upper Es³ is dominated by braided river delta facies,of which the delta front subfacies is the most extensive.The sandstone in the lowstand system tract and the source rock in the lake transgression system tract form an excellent source-reservoir-seal combination,which is favorable for the development of subtle reservoirs.Considering the regional structure features,it is suggested that the favorable exploration targets for subtle reservoirs should be the sand body in the braided river delta front of the lowstand system tract in the upper Es³ in the central and southern parts of the study area.

Key words: sequence stratigraphy, braided river delta, subtle reservoir, Liuxi area, Raoyang Sag, Jizhong depression