陇东地区延长组层序格架内储层质量差异及其控制因素

Differences and controlling factors of reservoir quality within sequence stratigraphic framework of Yanchang Formation in Longdong Area, Ordos Basin

基于岩心分析和测井资料,对鄂尔多斯盆地陇东地区延长组层序格架内沉积微相、砂体叠置规模、砂岩粒径和储层质量特征进行研究,探讨长期基准面旋回内储层质量差异性及其控制因素。研究结果表明:延长组长81—长63长期基准面旋回内,A/S值变化控制层序格架内沉积微相分布、同类沉积微相砂体叠置样式及规模和岩石颗粒大小的变化,从而影响储层质量。长81(上升半旋回下部)发育切叠式三角洲分流河道砂体,厚度较大、粒度较粗,在后期的成岩作用过程中经历较弱的压实作用,保存的粒间孔隙为酸性流体运移提供通道,从而在整体低孔低渗的背景下形成以中—小粒间孔和细—微细喉为主,物性较好的相对优质储层。

Based on the core analysis and logging data, the characteristics of sedimentary microfacies, sand body stacked scales, grain size and reservoir quality were analyzed to understand the reservoir quality differences and its controlling factors in the long-term base level cycles of the Yanchang Formation in Longdong Area, Ordos Basin. The results show that the changes of sedimentary microfacies, sand body stacked patterns, scales and grain size of the similar sedimentary microfacies are controlled by A/S within the sequence stratigraphic framework, thus affecting the reservoir quality. The cut stacked, thick and coarse grain size distributary channel sand bodies of Chang8~ at the lower part of the long-term base level rising hemicycle has experienced weaker compaction and saved more intergranular pores. This will provide channels for acidic fluid migration to dissolve. Eventually, it forms relative high quality reservoir with mid-small pore and fine-micro throat in the overall context of the low permeability reservoir.