Sedimentary characteristics and mechanism analysis of a large-scale fan delta system in the Paleocene Kongdian Formation, Southwestern Bohai Sea, China

Abstract

Exploration of the deep buried sandstones and glutenites of the Paleocene Kongdian Formation of the Bozhong 19-6 structure was a significant success. An integrated analysis of 3D seismic data, logging curves, core observation, thin sections, and casting thin sections was applied to characterize the sequences, petrology, sedimentary facies, and reservoir properties of the glutenite of the Kongdian Formation. The results indicated that the Kongdian Formation mainly consisted of tuffaceous glutenites at the lower section and glutenites in the upper section. The porosities ranged from 0.3% to 17.7%, whereas the permeability ranged from 0.0175 to [Formula: see text], indicating ultralow porosity and ultralow permeability reservoir characteristics. The northern source area, the Chengbei Low Uplift in the west, and the Bonan Low Uplift in the southeast surrounded the Bozhong 19-6 structure and provided abundant proximal coarse-grained sediments for a large-scale fan delta system. The paleogeography, slope type, parent rock type, and lake-level changes were the key factors controlling the glutenite reservoirs. The paleogeography reconstructed by prototype basin analysis controlled the southward-thickening sedimentation pattern of the glutenite. The slope type controlled the multistage development of the glutenite. The parent rock controlled the reservoir quality. The lake-level cycle controlled the stacking pattern of the glutenite. The successful gas discovery in the Bozhong 19-6 structure suggests that the deep buried fan delta system of the Kongdian Formation could have great petroleum potential for future exploration of the Bohai Bay Basin.