页岩有机碳含量的扫描电镜估算方法

A method for estimating TOC of shale by SEM

页岩有机碳含量(TOC)是评价页岩可采性的重要指标之一。实验室TOC含量的测试方法一般采用燃烧法,该测试方法的优点是测试结果较为准确,但需要的仪器设备和试剂材料多,步骤繁琐耗时,经济成本也高。氩离子抛光扫描电镜方法是研究页岩孔隙结构一种最常用、最直观的方法。该方法一般选择背散射成像模式,其特点是扫描电镜图像亮度与观测物质的局部平均原子量大小(原子序数)相关,所以有机质和矿物质可以根据其在电镜照片中的特征亮度来区分。基于这一原理,可以由计算机算出有机质面积占比,再结合有机质及矿物质的密度,计算出有机碳的含量。这种方法准确性较高,作为扫描电镜对页岩孔隙结构观察的附带分析结果,也节约了经济成本和时间成本。

TOC is one of the most important standards to evaluate the exploitability of shale.The test method of TOC in laboratory generally adopts the combustion method.The advantage of this method is that the test result is more accurate,but it needs more equipment and reagent materials,the steps are tedious and time-consuming,and the economic cost is also high.Argon ion SEM method is the most popular way to study pores in shale,the principle is that the brightness of SEM image is related to the local average atomic weight of the observed material.The organic matter and mineral matter can be distinguished according to their characteristic brightness in the electron microscope picture,so the content of organic matter in the picture can be estimated.This TOC estimation is a subsidiary analysis result of SEM observation of shale samples,which is efficient and low cost.