中国西部燕山运动及其对油气成藏的控制

中国西部地区的燕山中期构造运动是一次重塑西部构造格局的构造运动。侏罗纪末期,隶属新特提斯洋的雅鲁藏布江大洋岩石圈向北俯冲,班公湖-怒江洋发生闭合,拉萨地块与羌塘地块碰撞拼合,北部的鄂霍茨克海此时也发生了闭合。区域性的远程构造挤压作用使中国西部古老缝合线及大型古老断裂复活,造山带快速隆升。在西部各盆地内则表现为部位各异、程度不同的白垩系与侏罗系之间的角度不整合,在盆地的边缘以及断裂发育部位形成新的构造,同时进一步改造已有的各类构造样式。从白垩纪(各地区时间稍有差异)开始,西部的盆一山格局进入了一个新的发展阶段。燕山期构造运动对油气藏形成、调整具有重要的意义:首先,对下伏多套源岩的成熟具有双重作用,在山前坳陷相对连续、快速的沉降区会加速成熟,而在多期隆升和低速沉降地区会延缓成熟,为喜马拉雅期油气藏的高效率形成提供了保障;其次,变形、隆升、风化、剥蚀及淋滤作用对不整合之下的多套储层的储集性能具有明显的改善,不整合之上的白垩系下部沉积了分布广泛的优质砂砾岩储层;第三,形成了大量的构造、岩性、地层不整合等多类型圈闭,加之古隆起和断裂带的背景,为多类型、多层系油气藏形成与富集奠定了基础。

The Yanshanian movement and its control over hydrocarbon accumulation in western China

The mid-Yanshan tectonic movement had rebuilt the tectonic framework in western China.At the end of Late Jurassic,the Yarlung-Tsangbo oceanic lithosphere of the Neo-Tethys subducted northward,Bangong CoNu Jiang ocean was closed,Lasha and Qiangtang blocks collided,and the Okhotsk sea in the north was also closed.The regional tectonic compression reactivated the ancient suture and large old faults and accelerated the uplifting of the Orogenic belt in western China.It also led to the formation of angular unconformities of various scopes and types between the Jurassic and Cretaceous in the western basins,the formation of new structures at the margins of the basin and along the faults,and further reconstruction of the existing structures.Accompanying with the movement,the basins in western China entered a new evolution stage since the Cretaceous (the timing might be a little bit different in different regions).The significances of Yanshan movement to hydrocarbon accumulation and reservoir readjustment include:(1)it exerted dual influences to the underlying source rocks through speeding up thermal evolution in the relatively continuous and rapid subsidence zones at piedmont and postponing the peak of hydrocarbon generation and expulsion in zones experienced multi-stage uplifting and slow subsidence,thus providing conditions for the highly effective hydrocarbon accumulation during the Himalayan period;(2)deformation,uplifting,weathering,erosion,and leaching greatly improved the poroperm characteristics of the reservoirs underlying the unconformities,and extensive glutenite reservoirs of high quality were deposited in the lower part of the Cretaceous above the unconformities;(3)the various types of traps in combination with the paleohighs and faulted zones laid down foundation for the formation of different types of hydrocarbon accumulations in various strata.