Seismites and their geological significances of the Triassic Yanchang Formation in Fuxian exploration area, Ordos Basin
Tian Yuan1, Zhong Jianhua1, Wang Shubao2, Tao Hongsheng2, Liu Shaoguang2, Li Yong1, Sun Ningliang1, Shao Zhufu3, Ni Liangtian1, Mao Cui1, Ge Yuzhu1, Chen Bin1, Qu Junli1, Wang Guilin1
1 School of Geosciences,China University of Petroleum(East China),Qingdao 266580,Shandong
2 Research Institute of Yanchang Petroleum(Group)Co.,Ltd.,Xi'an 710075,Shaanxi
3 College of Geosciences, Northeast Petroleum University, Daqing 163318,Heilongjiang
Combined with regional tectonic setting,this study identifies typical seismites of the Upper Triassic Yanchang Formation in Fuxian exploration area of Ordos Basin through observation of cores from 26 drillholes. In the study area,representative sedimentary structures include liquefied sand-veins,liquefied curled deformation structures,loop beddings,load structures,ball-and-pillows,pillows,micro-faults,micro-fissures,and shatter breccias. Among these,liquefied sand-veins and liquefied curled deformation structures are the major earthquake-induced soft sediment deformation structures. The vertical successions of seismites are classified into two types:One is dominated by brittle deformations underlying and overlying unshocked layers,and consists of disturbed bedding layer,layer of step micro-fault,micro-fissure and seismic breccias,liquefied curled deformation layer,layer of shatter breccias,and liquefied sand-veins layer,respectively,from bottom to top;the other is dominated by soft-sediment deformations,which also underlies and overlies unshocked layers,and is divided into loop bedding layer,disturbed bedding layer,layer of ball-and-pillow and load structure,liquefied sand-veins and liquefied curled deformation layer,and pillow layer,respectively,from bottom to top. The seismites in the Yanchang Formation of Fuxian exploration area prove that there existed a competent structure and active periods of palaeotectonic movement;the presence of micro-faults,micro-fissures,shatter breccias and liquefied sand-veins is conductive to the improvement of reservoir physical property;furthermore,the seismic breccias and reticulate sand-veins are both good reservoirs.
Tian Yuan,Zhong Jianhua,Wang Shubao et al. Seismites and their geological significances of the Triassic Yanchang Formation in Fuxian exploration area, Ordos Basin[J]. JOPC, 2015, 17(4): 541-552.
