海安凹陷阜三段特低渗储层的成岩作用与孔隙演化史

Diagensis of extra-low permeability and porosity in third member of Funing formation in Haian depression and analysis of its pore evolution

针对苏北盆地海安凹陷阜宁组阜三段储层低孔特低渗及孔隙度演化的复杂问题,分析阜三段低孔特低渗储层的成因及主控因素,综合应用扫描电镜、铸体薄片、全岩衍射、粒度分析等方法,依据铸体薄片镜下资料计点统计法定量反演研究区阜三段孔隙演化史。结果表明:阜三段储层岩屑长石砂岩为主,成分成熟度低,成岩阶段处于中成岩A期;砂岩未固结时平均孔隙度35. 3%,经强烈压实作用后孔隙度降至12. 7%,由于胶结、交代作用使孔隙度降至4. 7%,后期溶蚀作用发育,改善了储层条件,使得孔隙度最终保持在10. 8%;成岩缝和微裂隙造影响与实测孔隙度存在误差,但误差率仅在0. 4%,在合理范围之内,可以证明研究方法可行。

This paper is an attempt to address low porosity and ultra-low permeability and complex porosity evolution in the third member of the Funing formation in the Haian depression of the Subei basin.The study is focused on the analysis of the cause of the extra-low permeability reservoir and the main controlling factors and subsequent quantitative inversion of the evolution history of the third member of the study area by applying the methods,including the scanning electron microscope,cast thin slice,whole rock diffraction,and particle size analysis,and employing the point counting method featuring SEM analysis of the cast thin slice.The analysis shows that the reservoir in the third member of Fu is composed mainly of lithic feldspar sandstones with low component maturity and diagenetic stage in the middle diagenetic A stage.When unconsolidated,the sandstones have the average porosity of 35.3%,and after strong compaction,show the porosity reduced to 12.7%.The cementation and metasomatism cause the porosity to be reduced to 4.7%,leading to the development of the later dissolution,greatly improving the reservoir conditions and allowing the porosity to be kept at 10.8%.The errors occur between simulated and measured porosity due to the action of diagenetic fractures and micro-fractures,but the error rate is only 0.4,within a reasonable range,validating the feasibility of the method.