苏丹Muglad盆地Aradeiba组低阻油层的地质成因

Geological Origin of Low Resistivity Oil Layer in Aradeiba Formation of Muglad Basin,Sudan

根据岩心、粒度分析、铸体薄片、扫描电镜、压汞曲线、试油及矿化度分析等资料,分析研究Muglad盆地Aradeiba组低阻油层的地质成因。其形成受沉积、成岩、成藏等多种作用的综合影响。泥质沉积背景下,黏土矿物附加导电性、复杂的孔隙结构是形成Aradeiba组低阻油层的岩石物理成因。Aradeiba组主要砂体类型为三角洲前缘砂体,水下分流河道砂体横向相变快,油气规模小、高度低,而远砂坝、席状砂砂体厚度薄,砂泥互层沉积,整体泥质含量高,均易于形成低阻油层。Aradeiba组砂岩属于早成岩阶段B期,溶蚀作用、石英次生加大等,使得孔隙结构复杂,并且所含黏土矿物以蒙脱石等附加导电型的黏土矿物等为主,低阻油层发育。反向断块构造幅度低、成藏高度小,岩性或成岩圈闭范围局限,成藏复杂,多套油水层发育,形成低阻油层。

Based on data of core,grain size analysis,cast slice,SEM,mercury injection curves,oil testing and formation water salinity,geological mechanism of low resistivity oil layers of Aradeiba Formation in Muglad Basin,Sudan has Been analyzed. The result showed that it was influenced by the sedimentation,diagenesis and reservoir forming process. The petrophysical origin of low resistivity oil layers is the existence of additive conductivity of clay minerals and the complicated pore structure under the shale-rich background. The delta front sands which mainly are subaquatic distributary channels,distal bar and sheet sand led to low resistivity oil layers,because subaquatic distributary channels reservoirs are small and poor and distal bar and sheet sand are thin sand-shale interbedding and high-content shale. The diagenesis in the B period of early diagenetic stage resulted in the development of low resistivity oil layers for the complicated pore structure which is resulted from dissolution and quartz overgrowth and additive conductivity of clay minerals which are the main type of clay minerals such as smectite. The low structure amplitude and hydrocarbon height of the reverse fault blocks,the limited range of lithological or diagenetic traps,the complex reservoir forming process and multiple sets of oil and water layers result in the low resistivity oil layers.