西湖凹陷反转构造定量运动学过程及对油气的控制作用

基于较密集分布的2D地震资料和少量钻井资料,利用平衡剖面模拟方法对发育在西湖凹陷的反转构造进行了定量运动学过程和参数的模拟与分析。结果表明,西湖凹陷自中生代以来主要经历了2次挤压反转构造作用,分别发生在早中新世的龙井组沉积时期(距今23.3~16.3Ma)和晚中新世的柳浪组沉积时期(距今10.4~5.2Ma),造成了盆地北西—南东方向分别缩短0.61km和1.69km。其中主要的反转作用发育在柳浪组沉积时期,不但使中生代以来的地层全部卷入其中,形成了中央反转构造带,而且还造成了盆地北部和南部平均约911.6m和226.7m厚的地层剥蚀、以及1.46%和1.18%的盆地缩短率,北部反转强度明显大于南部。在中央反转构造带的南部区域,由于反转作用强化了部分背斜,形成了较理想的圈闭构造,为油气的聚集提供了有利条件,成为盆地重要的油气聚集带。

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 23.3Ma to 16.3Ma 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 0.61km and 1.69km 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 911.6m of erosion thickness and 1.46％ of the crustal shortening rate in the north part of the basin, while resulted in erosion thickness of 226.7m 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.