南堡凹陷高南地区东三段低渗储层敏感性特征的微观机制研究

A microscopic study of the formation mechanism of low permeability reservoir sensibility of Ed_3 in Gaonan area

南堡凹陷高南地区东三段(Ed3)储层中速敏性的产生主要是分布于孔隙中的高岭石微粒发生迁移的结果;在粘土含量较低的样品中速敏性较弱,由于高岭石晶粒的长度及直径均多数大于喉道直径,因此随粘土杂基含量的增加,速敏性会随之增加。由于方解石胶结物主要分布于粒间孔隙中,喉道中胶结物及粘土杂基均较少,盐酸酸化对改善储层渗透性意义不大,只有采用土酸酸化处理才能起到应有的效果。由于喉道中石英的加大现象常见,而其他填隙物较少见,强碱性钻井液的浸入有助于改善储层渗透性。但因碱敏性实验测得pH值的临界值为7.7,以及大量强碱性钻井液浸入储层会造成大量碱不稳定组分的溶解,具有形成大量二次沉淀的潜在因素,加上钻井液难于及时返排,在钻井过程中还是要特别注意钻井液碱度的选择。由于蒙托石及伊/蒙混层粘土在不同位置含量的差别,导致了研究区储层的盐敏性程度相差较大。

Velocity sensitivity in the Ed3 reservoir of Gaonan area results from the migration of kaolinite distributed in pores. As the length and diameter of kaolinite are dominantly larger than the throat diameter, the velocity sensitivity becomes increasingly lower in samples with the lowering clay matrix content and gets higher and higher with the increasing clay content. Calcite cement is mainly distributed in rock pores of the reservoir, and minor cement and clay mineral matrix are distributed in the throat, indicating that earth acid rather than hydrochloric acid is more effective in acidification. Due to the extensive existence of secondary enlarged quartz in throat, strong alkali drilling fluid may somewhat help to improve the reservoir permeability. However, as the critical value of pH is about 7.7 which results in the secondary precipitation, and the flowing back of the drilling fluid is difficult, the alkalinity of drilling fluid should be taken into account during the drilling process. Montmorillonite and illite/montmorillonite are different greatly in content in different positions, which determines the difference of salt sensitivity in the reservoir.