Kinematical processes of inversion structure and its contribution to hydrocarbon accumulation in Xihu Depression of East China Sea Basin

Based on a large number of data from 2D reflection seismic and some wells,the kinematical processes of inversion structure in Xihu Depression were analyzed,and some parameters were calculated using the balanced cross-section technology.The results showed that two periods of tectonic inversion occurred respectively in the early Miocene Longjing Formation(from 23.3 Ma to 16.3 Ma before present) and in the late Miocene Liulang Formation(from 10.4Ma to 5.2 Ma before present).The tectonic inversions made the basin shortened by 0.61 km and 1.69 km in the northwest-southeast direction.The major reversion activities were concentrated in the late Miocene Liulang Formation,which resulted in the central inversion belt with all the Mesozoic strata involved and also resulted in about 911.6 m of erosion thickness and 1.46% of the crustal shortening rate in the north part of the basin,while resulted in erosion thickness of 226.7 m and the crustal shortening rate of 1.18% in the south part.The analysis on the relationship between sag inversion and hydrocarbon accumulation showed that some ideal traps were formed in the southern area of the central inversion belt.The inversion strengthened the formation of anticlines and provided good conditions for hydrocarbon accumulation.Xihu Depression is the important hydrocarbon accumulation zone of the East China Sea Basin.