尼日尔Termit盆地古近系Sokor1组储层特征及其主控因素

Reservoir characteristics and its controlling factors of the Paleogene Sokor1 Formation in Termit Basin,Niger

尼日尔Termit盆地目前已发现90%的储量位于古近系Sokor1组,但是对其主力产层的砂岩储层质量的影响因素仍然缺乏深入研究。本文基于55口井的71m岩心和568个井壁取心样品资料,开展普通薄片、铸体薄片、X衍射及扫描电镜分析,研究Sokor1组E5-E1各段的储层特征,并探讨其影响因素。研究表明,E5-E1段储层的岩石类型主要为石英砂岩与岩屑石英砂岩,成分成熟度高;结构成熟度低-中等,以细粒和不等粒结构为主,分选中等-差;磨圆差,一般为次棱角-次圆状。孔隙类型以原生孔隙为主,其次为粒间溶蚀孔;成岩作用弱-中等,主要处于中成岩A期阶段。E5-E1段储层孔渗正相关性好,其中E5和E2段储层质量最好,以中孔-中渗和高孔-高渗为主,E4、E3和E1段储层质量次之且非均质强。通过分析,揭示了沉积微相是影响储层质量的主要因素,成岩作用次之。分流河道和河口坝是优质储层发育的主要环境,砂岩中粘土杂基含量是影响储层非均质性的主要因素。

Almost 90%of reserves was discovered in the Paleogene Sokor1 Formation in Termit Basin,Niger.However,impacts on reservoir quality of these sandstones are still poorly studied.Petrographic of these sandstones of 71m conventional cores and 568 sidewall core samples from 55 wells was studied with thin sections,casting thin sections,X-ray diffraction and SEM investigations.Based on the results,the authors analyzed the lithological characteristics of the Sokor1 sandstones(E5,E4,E3,E2 and E1 members)and explore the related factors.The results show that the rock types are quartz sandstones and lithic quartz sandstones which are characterized by high component maturity,low-medium texture maturity and poor-fair rounding.Fine grained and inequigranular textures are dominated types with poor-medium sorting and subangular-subrounded grains.Poor-medium diagenesis and middle diagenetic A stage of E5-E1 sandstones lead to well-developed primitive intergranular and intergranular dissolution pores.Porosity and permeability data based on cores show a good positive relationship in E5-E1 sandstones.E5 and E2 reservoirs are of the highest qualities,and they are characterized by medium porosity and medium permeability,and some with high porosity and high permeability.However,the reservoir quality of E4,E3 and E1 sandstones are characterized by strong heterogeneity.Microfacies of sandstones is the key controlling factor for the reservoir quality,while diagenesis is the second controlling factor.Distributary channel and mouth bar are the best sedimentary environments for high quality reservoirs in the study area.Clay matrix content in the sandstones plays an important role for reservoir heterogeneity.