1. School of Resource Engineering， Longyan University， Longyan, Fujian 364012；
2. State Key Laboratory of Lithospheric Evolution， Institute of Geology and Geophysics， Chinese Academy of Sciences， Beijing 100029
Ordos Basin is an important hydrocarbon basin in China，yet the majority of hydrocarbon reservoirs were affected by the natural fracture. Based on the systematic field observation and indoor statistical analysis，we descript the natural fracture characteristics and major controlling factors in Mesozoic strata in basin. Six trends of fracture sets（E—W trending， ENE—WSW trending，NNE—SW trending，N—S trending，NNW—SSE trending and NNE—SSW trending）are found in Mesozoic strata within Ordos Basin. Among them， E—W trending，ENE—WSW trending and NE—SW trending sets are systematic fractures， other three sets are nonsystematic fractures. As for the fracture assemblage， there are two main groups of orthogonal fracture system（E—W trending and N—S trending，ENE—WSW trending and NNW—SSE trending）， the orthogonal fracture system consisted of E—W trending and N—S trending is only outcropped in the Triassic and Jurassic strata. Meanwhile， there are two main groups of conjugate fractures（ENE—WSW trending and NNE—SSW trending， ENE—WSW trending and ESE—WNW trending）， the conjugate fracture consisted of ENE—WSW trending and NNE—SSW trending is outcropped in entire Mesozoic strata，yet the other set is only outcropped in the Yanchang Formation. In addition，fracture spacing analysis indicates that：1）Layer thickness has a low effect on the fracture spacing.2）Fracture intensity of systematic fracture（E—W trending and ENE WSW trending）is more than nonsystematic fracture（N—S trending）. 3）The thinner the layer thickness， the greater the fracture intensity. 4）In addition to the layer thickness， regional stress field has important effects on the fracture formation. The fractures in the study area are mainly formed in the two phases regional stress fields. The first is Late Jurassic E—W trending compressional stress field caused by the subduction and collision of paleo—Pacific plate and Eurasia plate. The second is Cenozoic NE—SW trending compressional stress field caused by the subduction and collision of India plate and Eurasia plate.
Jiang Lin,Wang Qingchen,Guo Yusen et al. The natural fracture characteristics of Mesozoic strata in Ordos Basin and evolution of the tectonic stress field
[J]. Chinese Journal of Geology, 2016, 51(3): 706-731.