鄂尔多斯盆地富县探区三叠系延长组震积岩及其地质意义

通过对26口井岩心观察,结合区域构造背景,在鄂尔多斯盆地富县探区三叠系延长组中识别出典型的震积岩。该区震积岩代表性沉积构造有液化砂脉、液化卷曲变形、环状层理、负载构造、球枕构造、微断层、微裂缝、震裂岩与震碎角砾岩,其中液化砂脉和液化卷曲变形是地震引起的主要软沉积变形构造。震积岩垂向序列划分为两类:一种以脆性变形为主,自下向上依次为下伏未震层,扰动层,微断层、微裂缝及震裂岩层段,液化卷曲变形层段,震碎角砾岩层段,液化砂脉层段及上覆未震层;另一种以软沉积变形为主,自下至上依次为下伏未震层,环状层段,扰动层,球枕构造及负载构造层段,液化砂脉及液化卷曲变形层,枕状层及上覆未震层。富县探区延长组中的震积岩说明在该盆地晚三叠世存在一个强地震事件活跃期;震积岩中的微裂缝、微断层、震裂岩及液化砂脉可改善储集层物性,同时震碎角砾岩和网状砂脉也是良好的储集层。

Seismites and their geological significances of the Triassic Yanchang Formation in Fuxian exploration area,Ordos Basin

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.