沙特B区块SHEEH构造带古生界成藏条件分析

Paleozoic Reservoir-forming Conditions of SHEEH Structural Belt in B Block,Saudi ArabiaBy YANG Yun-feng

沙特B区块中央凹陷SHEEH构造带古生界烃源岩主要为志留系Qusaiba段底部的一套静海相富含有机质页岩(HotShale),气源条件较好;储层主要为奥陶系Sarah组砂岩,属冰川沉积,具有特低孔特低渗非均质性强的特征;其区域性盖层为Sarah组之上的志留系Qusaiba组浅—半深海环境沉积的巨厚泥岩夹薄层粉砂岩,封闭性好;烃源岩大量排烃期为三叠—白垩纪,而Sarah组圈闭成型于志留系初,定型于白垩纪,二者在时空上匹配较好,烃类向下通过岩石孔隙注入Sarah组储层,因其盖层条件好,后期又未受到构造活动破坏,因而成藏于三叠纪—白垩纪的Sarah组圈闭致密气藏得以保存。针对Sarah组储层特征,建议应用最新的地球物理技术方法对地震资料进行特殊处理,弄清储层展布规律,寻找"甜点"进行钻探。

In SHEEH structural belt of B block,Saudi Arabia,the Paleozoic source rock is mainly composed of euxinic Hot Shale at the bottom of Silurian Qusaiba Formation,with better gas source conditions;the reservoir is dominantly Ordovician Sarah Formation sandstone,belonging to a glacial deposition,which is featured by extra low permeability and porosity as well as strong heterogeneity;the regional caprock is Silurian Qusaiba Formation,a shallow-bathyl deposition,overlain by Sarah Formation,which is composed of huge shale interbedded with thin siltstone with a better sealing property.In addition,for the source rock,the hydrocarbon expulsion mainly started from Triassic to Cretaceous.Sarah Formation trap formed in initial Silurian and set in Cretaceous;and hydrocarbon migrated to Sarah Formation through pores.In general,this tight gas reservoir formed from Triassic to Cretaceous and kept in a good condition not only due to better caprock but also because it was not destructed by subsequent structural events.At last,some suggestions have been made,including:(1)new geophysical prospecting technologies should be applied to seismic-data processing;(2)reservoir distribution should be made clear;and (3)some sweet spots should be found out.