皖南地区下寒武统荷塘组页岩矿物组成及脆度分析

Analyses on Mineral Compositions and Brittleness of the Lower Cambrian Hetang Formation Shale in South Anhui Province

为了研究皖南地区下寒武统荷塘组页岩的矿物组成和页岩气储集层物性,本文对采自荷塘组的页岩样品进行了X射线衍射分析和有机地球化学实验。结果表明,皖南地区荷塘组页岩有机碳含量较高（多为1.0%-10.0%）,有机质类型为Ⅰ型,热演化程度处于过成熟阶段（Rom为4.2%-5.3%）;荷塘组页岩矿物组成复杂,以石英、黏土矿物和碳酸盐矿物为主,平均含量分别为68.2%、24.5%和3.3%,部分样品中含有少量的长石、菱铁矿、黄铁矿和石膏。与北美地区页岩相比,皖南地区荷塘组页岩的脆性矿物含量较高（平均73.9%）,脆性指数较大（平均71.7%）,表明该区荷塘组富有机质页岩具有良好的脆度,有利于页岩气储集层的可压裂性。

In order to study the mineral compositions of the lower Cambrian Hetang Formation shale and the physical properties of shale gas reservoirs in South Anhui,the X-ray diffraction（XRD） and organic geochemical analyses were conducted in this paper. The characteristics of organic matter,mineral contents and brittleness of the Hetang Formation shale in South Anhui were discussed. The results showed that the organic carbon content of the Hetang Formation shale in South Anhui is relatively high（mainly 1. 0% - 10. 0%）,the organic matter are mainly type I organic matter and had undergone an over-mature thermal evolution（Rom= 4. 2% - 5. 3%）. The Hetang Formation shale has a complicated mineral composition,the major components are quartz,clays and carbonate mineral whose average contents are 68. 2%,24. 5% and3. 3%,respectively,while small amount of feldspar,dolomite,siderite,pyrite and gypsum were also found in some samples. The Hetang Formation shale in South Anhui has a higher brittle mineral content（average 73. 9%）,and bigger brittleness index value（average 71. 7%） in compared with those of North American. It is suggested that the Hetang Formation shale in South Anhui has good brittleness and is favorable to forming fracturing formation for shale gas.