铜川野外露头区延长组裂缝发育特征及形成机理

Crack Development Characteristics and Formation Mechanism of Yanchang Formation in Tongchuan Outcrop Area

延长组是鄂尔多斯盆地最重要的油气勘探开发目的层系,铜川延长组野外地质露头区裂缝极为发育。在对延长组野外地质露头观测的基础上,结合区域地质背景分析成果,对该区裂缝活动的期次、性质及其形成演化过程进行分析。结果显示,铜川地区延长组内发育NEE向、NWW向与近NS向三组裂缝,其中NEE向裂缝形成于印支期末期SW-NE向挤压兼左旋剪切动力学环境,受基底断裂左旋滑动造成的走滑剪切作用控制;NWW向与NS向两组裂缝形成于燕山期早期SE-NW向的构造挤压;燕山期晚期与喜山期构造运动对裂缝改造程度较弱,未见明显变化。印支期末期形成的NEE向裂缝规模大,为沟源断裂,其对油气运移具有重要控制作用;燕山期早期的NWW向和近NS向裂缝多分布于低幅度背斜区,其对裂缝型背斜圈闭发育及油气富集成藏具有重要控制作用。燕山期晚期与喜山期的改造,NWW和NEE向裂缝剪切改造相对强烈,其对油气运聚和后期调整有一定影响。

Yanchang Formation is one of the most important oil and gas exploration targets in Ordos Basin,and the outcrop cracks of Yanchang Formation in Tongchuan area are extremely developed.In this paper,on the basis of remote sensing of geological outcrops in the field,combined with the analysis of geological background,the activity stages,charactiristices and formation and evolution process of cracks are analyzed using UAV photography and 3D geological modeling technology.The results show that three groups of cracks in the direction of NEE,NWW and NS are developed in the Yanchang Formation of Tongchuan area.The NEE cracks were formed in the environment of SW-NE compression and late Indosinian sinistral shear structure.The NWW and NS cracks were formed in the early Yanshanian SW-NE compression.The tectonic movement in the late Yanshanian and Himalayan periods had a weak effect on the reconstruction of cracks,and they had no significant change.The NEE trending cracks formed in the late Indosinian period have a large scale and are gully source fractures,which play an important role in controlling oil and gas migration.In the early Yanshanian period,NWW trending and near NS trending cracks were mostly distributed in low amplitude anticlinal areas,which played an important role in controlling the development of fractured anticlinal traps and the accumulation of oil and gas.The shear action on NWW and NEE trending cracksduring the late Yanshanian and Himalayan periods was relatively strong,which had a certain impact on oil and gas migration and accumulation and late adjustment.