摘要
目前流行的岩石薄片染色方法识别砂岩中方解石和白云石胶结物经常出现混乱,究其根源主要是由于方解石或白云石胶结物中MnO质量分数偏高导致的。鄂尔多斯盆地延长组砂岩中方解石胶结物的有效识别结果表明,岩石薄片染色方法将MnO质量分数偏高的浸染状铁Ⅰ方解石错误地识别为含铁白云石或铁白云石,将MnO质量分数偏高的斑块状无铁方解石错误地识别为铁Ⅲ方解石或含铁白云石。鉴于此,把方解石和白云石胶结物的识别方法厘定为"岩心观察大致推断碳酸盐胶结物的类型及岩石体积分数→岩石薄片染色观察碳酸盐胶结物的颜色变化及赋存状态→电子探针原位测试定量识别不同赋存状态碳酸盐胶结物",从而有效地识别方解石和白云石胶结物,为砂岩储层研究提供更加可信的地质依据。
Confusion often occurs inidentifying calcite and dolomite cements in sandstone using thin section dyeing,whose main reason is high mass fraction of MnO in calcite or dolomite cement.The effective identification results of calcite cements in Yanchang Formation sandstones in Ordos Basin show that by thin section dyeing method,the disseminated iron I calcite with high MnO content is misidentified as iron-bearing dolomite or iron dolomite,and the plaquelike iron-free calcite with high MnO content is misidentified as iron Ⅲ calcite or iron dolomite.In view of this,the recognition of calcite and dolomite cements in sandstone is divided into three steps.Firstly,the type and volume fraction of carbonate cements are roughly inferred from core observation,then,the color change and occurrence state of carbonate cements are observed by rock slice dyeing,and finally,the carbonate cements in different occurrence states are quantitatively identified using in-situ test of electron probe to effectively identify the calcite and dolomite cements and provide more credible geological basis for research of sandstone reservoirs.
引文
[1] 罗晓容,王忠楠,雷裕红,等.特超低渗砂岩油藏储层非均质性特征与成藏模式:以鄂尔多斯盆地西部延长组下组合为例[J].石油学报,2016,37(增刊1):87-98.LUO Xiaorong,WANG Zhongnan,LEI Yuhong,et al.Heterogeneity characteristics and accumulation model of ultra-low permeability sandstone reservoirs:a case study of the lower part of Yanchang Formation in the western Ordos Basin,China[J].Acta Petrolei Sinica,2016,37(s1):87-98.
[2] 周晓峰,李书恒,宋鹏,等.鄂尔多斯盆地西南部长8砂岩中方解石胶结物表面绿泥石膜的形成机制[J].西安石油大学学报(自然科学版),2017,32(3):34-43.ZHOU Xiaofeng,LI Shuheng,SONG Peng,et al.Forming mechanism of chlorite film on calcite cement in Chang 8 sandstone,Southwest Ordos Basin[J].Journal of Xi'an Shiyou University(Natural Science Edition),2017,32(3):34-43.
[3] PETTIJOHN F J,POTTER P E,SIEVER R.Sand and sandstone[M].New York,Heidelberg,Berlin:Springerverlag,1973:383-437.
[4] LINDHOLM R C,FINKELMAN R B.Calcite staining:semiquantitative determination of ferrous iron[J].Journal of Sedimentary Research,1972,42(1):239-242.
[5] EVAMY B D.The precipitational environment and correlation of some calcite cements deduced from artificial staining[J].Journal of Sedimentary Petrology,1969,39(2):787-821.
[6] 郭宏莉,张荫本,胡迁勇,等.岩石薄片鉴定:SY/T5368—2000[S].北京:中国石油和化学工业局,2000.
[7] DICKSON J A D.Carbonate identification and genesis as revealed by staining[J].Journal of Sedimentary Petrology,1966,36(2):491-505.
[8] 强子同,兰光志.铁氰化钾和茜素红S混合染色剂及其在碳酸盐岩研究中的应用[J].西南石油学院学报,1981,3(1):31-38.QIANG Zitong,LAN Guangzhi.Stain of alizarin red-S and potassium ferricyanide and its application to carbonate[J].Journal of Southwest Petroleum College,1981,3(1):31-38.