鄂尔多斯盆地姬塬-元城地区构造裂缝特征与形成期次的划分

通过分析鄂尔多斯盆地姬塬-元城地区野外地质露头与井下裂缝特征，结合构造应力场背景分析，获得以下认识：1)该区构造裂缝以斜交于最大主应力的单条裂缝为主，尤其以SWW-NEE或近EW向裂缝和NNE-SSW或近S-N向裂缝较为发育，并发育少量对应的NW-SE和NE-SW向共轭裂缝。2）根据露头区裂缝系统的切割关系，NE向和近S-N向延伸的裂缝为后期发育， NW向和NEE向延伸的裂缝为早期发育；3)燕山期北西-南东向压应力场背景下，早白垩世末构造抬升造成的主应力差是早期共轭裂缝形成的主要原因；喜山期区域北东-南西应力挤压是后一期延伸裂缝的主要原因。

The Characteristics and Formation Phase of Structural Fracture of the Jiyuan-Yuancheng Area in the Ordos Basin

The development of structural fractures changes the mechanical properties of the reservoir rock, directly affecting the efficiency of dense reservoir exploration and development. Therefore, the development characteristics of the fractures is of very important theoretical significance and practical value. We analyze the characteristics of the fracture from geological outcrop and the underground in the Jiyuan-Yuancheng area of the Ordos basin, and combine the tectonic stress field background getting the following results in this paper: (1) the structural fracture is given priority oblique to the maximum principal stress of a single fracture, with the trend of SWW-NEE or nearly E-W and NNE-SSW or nearly S-N, and a small amount of the corresponding conjugate fracture NW-SE and NE-SW fracture develops; (2) according to the cutting relationship between the fracture system in the outcrop area, the trends of NE-SW and nearly S-N latter develop, and SWW-NEE or nearly E-W fracture develop early; (3) in the background of pressure stress field in the north west and south east of Yanshan period, the principal stress difference caused by the early cretaceous tectonic uplift is the main reason for the formation of early conjugate fractures. The stress extrusion of north east-south west in the Himalaya period is the main reason for the fracture.