摘要
成岩作用过程中骨架颗粒长石的溶蚀淋滤是碎屑岩储层形成次生孔隙的重要作用。长石在溶蚀反应中Al元素的活动性最低,只有在流体动力较强的条件下Al才发生迁移作用,长石溶蚀反应中高岭石的形成与分布受控于Al的迁移富集能力。因此研究成岩元素Al在流体中迁移富集特征对于储层评价具有重要意义。运用铸体薄片、扫描电镜以及粉晶衍射等分析测试技术,对东营凹陷碎屑岩储层的成岩特征进行了研究,结果在镜下可见研究区长石溶蚀以及Al的迁移富集特征明显。通过斜长石溶蚀形成高岭石的化学反应方程式,对比反应前后斜长石含量的变化,对河140井2 921.3~2 925.8 m深度段的砂岩进行了理论高岭石含量的计算。这种理论计算结果和实际形成高岭石含量曲线的差异,说明相对开放体系里长石溶蚀产物Al发生了微观的迁移富集作用。通过研究牛庄凹陷砂岩夹层中高岭石的含量分布特征,发现在砂泥岩界面靠近砂体一侧出现高岭石的富集,说明长石溶蚀产物Al在一定的流体动力条件下发生了迁移富集。研究区储层中长石溶解后形成高岭石,且其分布基本上受流体活动活跃的砂/泥岩界面位置和岩石物性控制。以钠长石和钾长石溶蚀形成高岭石和石英为例,对成岩反应前后岩石的体积变化进行了理论计算,结果表明如果长石溶解产物Al没有发生较大尺度的迁移,那么长石溶蚀后几乎相等体积的次生矿物将会沉淀充填孔隙。对于碎屑岩储层,次生孔隙发育的岩相学特征只能说明砂岩骨架颗粒发生了溶蚀作用、引起了孔隙重新分布、增加了砂体的非均质性,不足以说明砂岩孔隙度是否会真正提高。同时高岭石含量不能作为有效次生孔隙发育的标志,只有在Al发生迁移净输出之后,才能真正提高储集层的物性。
The leaching and corrosion of feldspar as framework grain of sandstone is an important role of the formation of secondary porosity in diagenesis. Because the mobility of Al is the lowest in the corrosion of feldspar,Al can be migrated under strong hydrodynamic conditions of fluid. The kaolinite distribution and feldspar corrosion are controlled by migration and enrichment ability of Al. So it has important significance to study the migration of Al. In this paper,the diagenetic characteristics of reservoir in Dongying depression are analyzed through quantity thin section analysis,core observation,scanning electron microscope and X-ray powder diffraction. The feldspar corrosion of sandstone reservoir is general and the characteristics of migration and enrichment of Al areobvious in Dongying depression. We calculate the kaolinite contents through chemical reaction equation of the formation of kaolinite by plagioclase dissolution on well He 140（ 2,921. 3 to 2,925. 8 m）. The difference between the theoretical calculation and the actual formation of kaolinite content shows that the migration and accumulation characteristics of Al in the relatively open system. Through the study of kaolinite distribution of the sandstone in the Niuzhuang sag,we find the enrichment of kaolinite occurs near the sand body at the interface of sandstone and mudstone. It shows that the Al as feldspar dissolution product has migrated and enriched under certain hydrodynamic conditions. The distribution of kaolinite from feldspar corrosion is controlled by the sandstone-mudstone boundary where the fluid activity is active and reservoir physical property in research area. Taking the formation of kaolinite and quartz from albite and potash feldspar as examples,we have calculated the volume changes before and after diagenesis. The results show that if the Al of the feldspar dissolution does not have a large scale migration,the nearly equal volume of secondary minerals after feldspar dissolution will precipitate and fill the pores. Petrographic criteria of secondary porosity alone are an insufficient measure that the rock has undergone leaching resulting in porosity enhancement. It only means redistributional secondary porosity,dissolution of framework grains and reservoir heterogeneity. The kaolinite content is not the mark of effective porosity on the sandstone reservoir. The reservoir physical property can be increased if the Al is moved out.
作者
张永旺
李峰
曲正阳
ZHANG Yongwang;LI Feng;QU Zhengyang(State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;College of Geosciences, China University of Petroleum, Beijing 102249, China;Fourth Oil Extraction Factory of Changqing Oilfield, Yulin, Shaanxi 718500, China)
出处
《现代地质》
CAS
CSCD
北大核心
2018年第2期357-363,共7页
Geoscience
基金
国家自然科学基金项目(41572113)
中国石油大学(北京)科研基金项目(KYJJ2012-01-25)
关键词
碎屑岩储层
长石溶蚀
Al迁移富集
次生孔隙
clastic reservoir
feldspar corrosion
migration and enrichment of Al
secondary pore
