鄂尔多斯盆地东缘A区块上古生界致密砂岩储层微观孔喉结构表征

Micro pore throat structural characterization of Upper Paleozoic tight sandstone reservoir of block A in the eastern margin of Ordos Basin

致密砂岩储层非均质性强,微观孔喉结构复杂,宏观上控制了储层物性差异、储层内气水分布及含气量。运用铸体薄片、扫描电镜、纳米CT、高压压汞、恒速压汞及核磁共振等高精度实验技术开展储层微观孔喉结构表征研究。结果表明:(1)孔隙组合划分为粒间孔型、粒间孔+溶蚀孔+晶间孔型、粒间孔+晶间孔型、溶蚀孔+晶间孔型以及晶间孔型5种类型;(2)粒间孔型对应最佳的进汞曲线形态,启动压力小于1 MPa,进汞饱和度大于80%,核磁共振右峰比例大,孔喉半径大,大孔含量多,孔隙度最高,一般大于10%。随晶间孔含量增多,启动压力明显增加,总进汞饱和度降低,核磁共振逐渐过渡为左峰型,孔喉分布逐渐减小,整体孔隙度小于6%;(3)粒间孔型大孔含量多,可动饱和度最高,可达60%。以晶间孔为主的组合类型主要为小孔组成,流体可动性差,可动部分一般小于30%,多为束缚流体。研究认识对鄂尔多斯盆地东缘上古生界致密砂岩气藏的增储上产及下一步滚动勘探具有理论指导作用。

The tight sandstone reservoir has strong heterogeneity and complex microscopic pore-throat structure characteristics,which controls the physical property difference,gas and water distribution,and gas content in the reservoir macroscopically.High-precision experimental techniques such as cast thin section,scanning electron microscopy,nano CT,high-pressure mercury injection,constant velocity mercury injection and NMR are used to characterize microscopic pore-throat structure.The results show that:(1)Pore combinations can be divided into five types:intergranular pore,intergranular pore+secondary dissolution pore+intercrystal pore,intergranular pore+intercrystal pore,secondary dissolution pore+intercrystal pore and intercrystal pore;(2)Intergranular pore type corresponds to the best mercury intake curve shape,with starting pressure of less than 1 MPa and mercury intake saturation of greater than 80%.In the meantime,NMR shows large right peak ratio,large pore throat radius,large proportion of macropores and therefore the highest porosity,generally greater than 10%.With the increase of intergranular pore content,the starting pressure increases noticeably,the total mercury saturation decreases,and the NMR gradually transitions to left peak.The pore throat distribution decreases gradually,and the overall porosity is less than 6%.(3)Intergranular pore type has more macropores,with highest mobility saturation,up to 60%.The combination type dominated by intercrystal pores is mainly composed of mircopores,and its fluid mobility is poor,showing that most of the pore fluid is irreducible,and mobile fluid is basically less than 30%of the total.The research provides a certain theoretical guidance for increasing reserves and production of the Upper Paleozoic tight sandstone gas reservoir in the eastern margin of Ordos Basin and for the next step of rolling exploration.