低渗砂岩储层孔喉的分布特征及其差异性成因

应用筛析粒度、铸体薄片、图像孔隙、扫描电镜与高压压汞等方法,对苏北盆地沙埝地区E1f3和三塘湖盆地牛圈湖地区J2x两类不同低渗储层的孔喉类型和分布特征进行了分析对比,对其差异性成因进行了探讨。研究表明,E1f3储层孔隙类型主要为碳酸盐胶结物和长石溶孔,J2x储层主要为凝灰质和长石溶孔,前者溶蚀成因的粗大孔隙较多,而后者细小的晶间孔较多。E1f3储层喉道分布为溶蚀成因的粗单峰分布、压实或压实胶结混合成因的细单峰分布、管束状喉道的无峰分布,以及溶蚀成因与压实或压实胶结混合成因组成的双峰分布四类;J2x储层喉道为溶蚀成因的粗单峰分布、管束状喉道的细单峰分布,及管束状喉道与压实或压实胶结成因组成的双峰分布三类,未见溶蚀成因喉道与其他成因喉道组成的双峰分布。两区孔隙半径、喉道半径均随粒级变细呈减小趋势,平均孔隙半径也总是小于碎屑颗粒半径;在粒度相近的情况下,J2x储层孔隙、喉道半径均小于E1f3储层。E1f3储层较高的成分成熟度与结构成熟度和早期碳酸盐胶结作用使其在压实过程中保存了较大的原始粒间孔隙空间,且为后期溶蚀作用所扩大,牛圈湖地区J2x储层较高的塑性岩屑含量和同沉积期形成的凝灰质,使储层原始孔隙空间在压实过程中大量减少,后期溶蚀作用较弱。杂基对原始孔隙空间的充填程度及其与塑性岩屑共同造成的压实与溶蚀强度的差异,是造成两区目前孔隙结构差异的主要原因。

Pore and Pore-throat Sizes Distributions in Low Permeability Sandstone Reservoir and Its Origin

By the comprehensive analyse grain size analysis, thin slices, pore image, SEM, mercury-injection data, the pore and pore-throat sizes distributions in two low permeability sandstone reservoirs with different origins, E1f3 in Shanian area, Subei basin, and J2x in Niujuanhu area, Santanghu basin, are analysed. The different origins of them is studied. The research shows, the pore types is mainly carbonate cement and feldspar dissolved pores in E1f3, tuffaceous and feldspar dissolved pores in J2x. There are more and greater dissolved pores, less intercrystal pores in E1f3 than in J2x. The pore-throat size distributions in E1f3 are gross single-peaked curve with dissolution origin pore-throats, fine single-peaked curve with compaction or compaction- cementation origins pore-throats, double-peaked curve with dissolution origin pore-throats and compaction or compaction- cementation origins pore-throats, and peakless curve with tube bundle pore-throats. The pore-throat size distributions in J2x are are gross single-peaked curve with dissolution origin pore-throats, small single-peaked curve with tube bundle pore-throats, and double-peaked curve with tube bundle pore-throats and compaction or compaction- cementation origins pore-throats. The pore and pore-throat sizes decrease with the grain size being smaller, and the pore radius is always smaller than size. The higher maturity and early phase carbonatite cementation make the E1f3 keeping larger primary origin intergranular pore-space, which are enlarged by dissolution. The higher plastic detritus content and consedimental tuffaceous make origin intergranular pore-space of J2x decreasing greatly, and the latter dissolution is feeble. They are the main orgins of the pore structures difference of two sandstone reservoirs.