联合高压压汞和恒速压汞实验表征致密砂岩孔喉特征

The combination of high-pressure mercury injection and rate-controlled mercury injection to characterize the pore-throat structure in tight sandstone reservoirs

文中利用铸体薄片、扫描电镜、高压压汞和恒速压汞技术,定量研究了四川盆地下志留统小河坝组致密砂岩储层的孔喉结构特征。通过联合高压压汞和恒速压汞实验,有效表征了小河坝组砂岩的总孔喉大小,其中孔隙半径为50~260μm,喉道半径为0.004~50.000μm。总体而言,致密砂岩渗透率(K)主要受控于小部分(小于40%)较粗的孔喉。对于渗透率良好的致密砂岩(K>0.1×10^-3μm^2),较大的微孔和中孔是渗透率贡献的主体;反之,渗透率则主要受控于较大的纳米孔。此外,尽管大量小孔喉(半径小于0.1μm)对储层孔隙度和渗透率都有一定贡献,但对前者贡献远大于对后者贡献。

In this paper,the pore-throat structure in tight sandstone reservoirs in Lower Silurian Xiaoheba Formation in Sichuan Basin are studied by means of casting thin slices,scanning electron microscope,high-pressure mercury injection(HPMI)and rate-controlled mercury injection(RCMI).The combination of the HPMI and RCMI experiment effectively reveals the total pore-throat size in the Xiaoheba Formation sandstones,and the pore radius ranges from 50μm to 260μm and the throat radius ranges from 0.004μm to 50.000μm.Overall,the permeability(K)of the tight sandstones is mostly affected by the small fraction(<40%)of relatively wide pore-throats.For the tight sandstones with good permeability(K>0.1×10^-3μm^2),the larger micropores and mesopores exert a great influence on the permeability.In contrast,the permeability is mainly influenced by the larger nanopores.Furthermore,although the large number of narrow pore-throats(radius<0.1μm)make a certain contribution to both reservoir porosity and permeability,their contribution to the former is far more than to the latter.