绿泥石包壳对碎屑岩储层物性的影响及其形成环境--以鄂尔多斯盆地大牛地气田上古生界为例

以大牛地气田含绿泥石胶结物样品为研究对象,结合国内外研究现状,研究绿泥石包壳的成因及其对储层物性的影响,并探讨其环境指示意义.大牛地气田的绿泥石包壳形成于成岩作用早期,厚10~20 μm,由原生粒间孔的边缘向中心晶形渐好,颗粒渐大.据铁质来源绿泥石包壳可分为原地和异地成因,原地成因由先体黏土矿物和岩屑溶解未排出的富铁流体生成,一般以混层黏土和晶体较小的包壳形式存在;异地成因是富铁矿物及岩屑溶蚀、溶解形成的富铁流体通过河流异地絮凝沉淀生成,结晶充分、晶形好.绿泥石包壳的储层保护机理为:①抑制石英次生加大;②增加矿物颗粒间抗压实强度,抑制压溶作用;③抑制碳酸盐胶结,促进溶蚀作用.大牛地气田的绿泥石包壳主要发育于盒一段(63%)和山二段,当其含量在15%以下时,孔隙度随绿泥石含量的增高呈线性递增.绿泥石包壳可作为三角洲(辫状河三角洲)前缘水下分流河道(水下辫状河道)等强水动力条件的微观相标志.

The Influence and Formation Environment of Chlorite Coatings in the Clastic Rock

Unifying the domestic and international research information and using chlorite cement as the research object in the Daniudi Gas Field, we have discussed the cause of chlorite coatings and its influence on reservoir physical property, moreover studies on its environment designating signification. The chlorite cement of Daniudi Gas Field which thickness is 10~20 μm formed in early stage of diagenesis, and the crystal becomes better, the particlebecomes bigger gradually from the edge of primary intergranular pores to the center. Chlorite coatings can be divided into in autochthonous genesis and allochthonous genesis according to the source of ferruginous. The autochthonous chlorite coatings existing as mixed layer clay and the smaller crystal coatings was generated from the undischarged Fe-rich fluid which was produced by precursory clay mineral and the dissolution of rock fragment. The allochthonous chlorite coatings crystallizing fully and well was generated from the Fe-rich fluid which was produced by Fe-rich minerals and cuttings dissolution flocculating offsite through rivers. Mechanism of reservoir protection of chlorite coatings: ①inhibition of secondary quartz increases; ②increased mineral particle compaction strength and restrain pressure solution; ③inhibition of carbonate cementation and promote corrosion. The chlorite coatings of Daniudi Gas Field mainly developed in H1(63%) and S2. Porosity rises linearly with the increase of content of chlorite when chlorite content below 15%. Chlorite coatings can be used as delta (braided river delta) front of underwater distributary channel (underwater braided rivers) and other microfacies marker of strong hydrodynamic conditions.