绿泥石环边的再研究——来自镇泾地区延长组砂岩的证据

Further study of chlorite rim in sandstone:evidences from Yanchang Formation in Zhenjing area,Ordos Basin,China

绿泥石环边是砂岩中自生绿泥石的常见赋存状态,因其常与储集性较好的砂岩相伴生而备受关注。针对已有研究中存在的争论问题,作者以鄂尔多斯盆地镇泾地区三叠系长9油层组砂岩为主要研究对象,通过详细研究铸体薄片、扫描电镜和物性资料,对绿泥石环边的形成阶段、环边对成岩作用的影响、环边与砂岩的储集性之间的关系进行了再次研究,获得一些不同于前人的认识,并得出如下结论:绿泥石环边出现在早成岩阶段的A—B期;环边的存在并不能增强砂岩的抗压能力;绿泥石环边对石英次生加大的抑制主要是由于两者形成的介质条件不同,而与自生石英的形成没有明显关系;绿泥石环边并不能明显保护和改善砂岩的储集性,但绿泥石环边的存在指示了砂岩具有发育的原生粒间孔。

Chlorite rim is the most important occurrence of authigenic chlorite as a common kind of clay cements in sandstone, and it is attracted by peoples＇ special attention because it always accompanies with the high quality sandstone reservoirs. Aiming at some debates about chlorite rim in the previous researches, this paper studies the sandstone of Chang 9 oil-bearing segment of Triassic Yanchang Formation in the Zhenjing area of Ordos Basin. Through researching casting thin section, scanning electron microscope and porosity-permeability data, this paper discusses such questions again, that is, the forming stage of chlorite rim, the effect of chlorite rim on diagenesis, and the relationship of chlorite rim with the reservoir quality of sandstone. On the basis of the research results, some opinions different from the previous research are acquired and the following conclusions are obtained. 1） The chlorite rim forms at the A-B phase of earlier diagenesis stage. 2） The chlorite rim can not enhanced the mechanical strength of rocks and the ability of resisting compaction. 3） The reason of the ability of the chlorite rim preventing the secondary enlargement of quartz is that the pore-water forming the chlorite rim has different pH value and Sr concentration from the pore-water suitable for quartz growing. However, the chlorite rim bears no relationship with the forming of authigenic quartz. 4） The chlorite rim can not enhance the reservoir quality of sandstone obviously. However, the appearance of the chlorite rim indicates the abundance of the primary intergranular pore in sandstone.