Abstract:

The formation of the fracture is a complex process, so it must through many data to comprehensively analysis and determine genetic mechanism and terms of the fracture. First, in order to research the fracture of western Mahuangshan block in Ordos basin, the field investigations aiming at the fracture of analogous outcrop zone were done，the results show that the fracture systems are unstable, and the fractures are controlled by the structural deformation intensity and shape, structural deformation is the stronger the density of crack growth is larger. According to the core’s observation and the description of 23 wells, it shows the fractures are mainly vertical fractures and large angle-extensional fractures. From the segmentation, limitation and combination relationship, it indicates that the fractures formation have two stages. At last, based on the characteristics, genetic mechanism and forming stages of the fractures, experiments of acoustic emission experiment of rocks and carbon and oxygen isotope analyses of fracture fillings, and the background analysis of structural evolution in this study area indicated that the fractures are divided into two stages which are corresponding to the second and the third episodes of Yanshanian Movements, respectively.

Key words: Ordos basin, western Mahuangshan block, Yanchang Formation, Yan’an Formation, genetic mechanism of fracture, development stage of fracture