羌塘盆地波尔藏陇巴背斜构造特征及其油气地质意义

波尔藏陇巴背斜作为羌塘盆地东部典型构造之一,是一个已经被后期构造破坏的圈闭构造,油气包裹体研究结果表明曾经历过多期次的油气运移。其构造演化是羌塘东部区域构造演化史的缩影,构造变形始于印支晚期,燕山期为构造定型时期,喜马拉雅早期表现为叠加变形等构造调整作用,喜马拉雅晚期以快速抬升和构造破坏为特征。构造解析及碳氧同位素研究表明,羌塘盆地东部构造挤压应力早期以NNE-SSW向为主,晚期以NE-SW向为主;间有NW-SE向和近EW向。早期构造变形与油气运移具有很好的配套性,晚期则以构造破坏为主。从构造变形程度看,羌塘东部以及中央隆起带等受喜山运动的构造破坏较强烈,但羌塘坳陷中部应该存在保存条件较好的构造圈闭。综合分析认为,羌塘坳陷上三叠统含油气系统可能较之侏罗系含油气系统更加良好,它受到喜山期的构造改造程度应该是非常有限的。

Structural Characteristics and its Petroleum Geological Significance of the Boerzanglongba Anticline in the Qiangtang Basin,Northern Tibetan Plateau, China

Qiangtang basin, the largest marine sedimentary basin of China, is located in the northern Tibetan Plateau. Hydrocarbon source rocks are well developed and very thick in the basin. The structural deformation controls the trap, migration and preservation of oil and gas in the Qiangtang basin. The structural deformation periods include Indosinian, Yanshanian and Himalayan periods. Structural deformation of the Boerzanglongba anticline in the eastern Qiangtang basin can be divided into three stages: the early NNE-SSW compression stage, the middle NW-SE compression-shear stage and the late NE-SW compression stage. The three deformation stages correspond to the closure of Jinshajiang river, the closure of Bangong-Nujiang river and the collision between India and Eurasian plates, respectively. The results of the fluid inclusions of crack-filling veins show that the Boerzanglongba aticline was an ancient structural trap and reservoir for some oil-gas at one time. The structural strain formed the migration channels and controlled the migration of oil and gas. The time of the structural deformations matches the time of the oil-gas migration and pooling. The upper Triassic petroleum system should be the main target of oil-gas exploration in the Qiangtang basin. The destruction resulted from the structural deformation of Himalayan period is very limited for the whole basin. Although the Himalayan movement caused the structural uplift in the eastern Qiangtang basin, the deformation is not very strong, and thus, the preservation conditions are still good in the central part of the Qiangtang basin.