鄂尔多斯盆地延长组长9油层组三角洲砂岩沉积特征

通过钻井、录井、测井及岩心等资料的综合分析,识别出辫状河三角洲和曲流河三角洲是鄂尔多斯盆地上三叠统延长组长9油层组主要的三角洲沉积相类型。辫状河三角洲分布于盆地西部,辫状分流河道和辫状水下分流河道发育砂岩,砂岩中主要发育冲刷面、槽状交错层理、板状交错层理和平行层理等,以向上变细的正粒序为主,砂岩粒度概率曲线主要为两段式或三段式。曲流河三角洲分布于盆地东部,陆上分流河道、水下分流河道和河口坝发育砂岩,砂岩中主要发育冲刷面、槽状交错层理、板状交错层理、平行层理和砂纹层理等,以向上变细的正粒序为主,也可见向上变粗的逆粒序,砂岩粒度概率曲线主要为两段式或三段式,可见四段式。进一步的对比分析表明,盆地内长9油层组辫状分流河道、辫状水下分流河道和陆上分流河道中砂体最发育,水下分流河道和河口坝砂体次之。

Sedimentary characteristics of the delta sandstones from the Chang-9 oil reservoirs in the Yanchang Formation,Ordos Basin

The integration of well logs and core examination show that the braided delta and meandering delta are the major delta facies types in the Chang-9 oil reservoirs of the Upper Triassic Yanchang Formation,Ordos Basin. The braided delta sandstones in the western part of the Basin are built up of braided distributary channel and braided subaqueous distributary channel sandstones,and characterized by developed scour surface,trough cross-bedding,tabular cross-bedding and parallel bedding,fining-upward sequences,and two-step and/or three-step grain-size probability curves. The meandering delta sandstones in the eastern part of the Basin assembled by subaerial distributary channel,subaqueous distributary channel and channel-mouth bar sandstones display the sedimentary structures such as scour surface,trough cross-bedding,tabular cross-bedding,parallel bedding and ripple lamination,fining-upward (occassionally coarsening-upward)sequences,and two-step and/or three-step (occasionally four-step) garin-size probability curves. The braided distributary channel,braided subaqueous distributary channel and subaerial distributary channel sandstones are best developed,followed by subaqueous distributary channel and channel-mouth bar sandstones in the Chang-9 oil reservoirs of the Yanchang Formation in the Ordos Basin.