下扬子地区上二叠统页岩红外光谱特征及其对油气勘探的指示意义

INFRARED SPECTROSCOPIC CHARACTERISTICS OF UPPER PERMIAN SHALE IN LOWER YANGTZE REGION AND ITS IMPLICATIONS FOR OIL AND GAS EXPLORATION,CHINA

红外反射光谱技术在烃源岩评价、盆地热演化史研究等油气资源勘探方面具有广泛的应用前景。下扬子地区上二叠统暗色页岩具有厚度大、有机碳含量高、有机质成熟度高等特点,是中国南方页岩气勘探开发的主要潜力层位之一,也是检验红外光谱技术在油气资源勘探领域应用潜力的良好场地。本次研究以扬子地区JY1井为研究对象,分析了上二叠统龙潭组和大隆组暗色页岩的空间分布特征,并结合QEMSCAN矿物定量分析技术对红外反射光谱的分析精度进行验证。结果表明:红外反射光谱技术对石英、碳酸盐、高岭石3种矿物的识别具有较高的精度,相关系数R~2均达到0.88以上,其中碳酸盐和高岭石的检出限分别可以达到3%和4%。大隆组页岩伊利石的结晶度主要位于0.3~0.5之间,而龙潭组页岩伊利石的结晶度主要位于0.6~2.6之间,反映龙潭组页岩具有更高的热成熟度演化,这与随着地温梯度增加,蒙脱石经过伊蒙混层矿物逐渐向伊利石发生转变的程度趋于增加规律一致。大隆组页岩光谱反射率平均值为0.13,而龙潭组页岩光谱反射率平均值为0.12,反映大隆组和龙潭组页岩整体具有相似的有机质丰度,龙潭组的有机质丰度略微高于大隆组。光谱平均反射率与TOC含量具有较好的负相关性,表明光谱平均反射率可以用于评价页岩的有机质丰度。

Infrared reflectance spectroscopy has a wide application prospect in hydrocarbon resources exploration,such as source rock evaluation and basin thermal evolution history research.The Upper Permian dark shale in the Lower Yangtze region has the characteristics of large thickness,high organic carbon content and high maturity of organic matter.It is one of the main potential formations for shale gas exploration and development in southern China,and it is also a good site for testing the application potential of infrared spectroscopy technology in oil and gas exploration.In this paper,the spatial distribution characteristics of Upper Permian Longtan Formation and Dalong Formation dark shale are analyzed based on well Jingye 1 in the Sichuan area,and the analytic accuracy of infrared reflectance spectrum is verified by QEMSCAN mineral quantitative analysis technology.The results show that infrared reflectance spectroscopy has high accuracy in the identification of quartz,carbonate and kaolinite,and the obtained correlation coefficients R~2 are all above 0.88,with the detection limits of carbonate and kaolinite reaching up to 3%and 4%,respectively.The crystallinity of illite in the Dalong Formation(mainly 0.3 to 0.5)and that of illite in the Longtan Formation(mainly 0.6 to 2.6)reflect that the Longtan Formation shale has a higher thermal maturity evolution.It is consistent with the increasing rule of the degree of montmorillonite,gradually transforming into illite through the mixed layer minerals of illite&montmorillonite with the increase of geothermal gradient.The average spectral reflectance of the Dalong Formation shale is 0.13,while that of the Longtan Formation shale is 0.12,indicating that the Dalong Formation and Longtan Formation shale have similar organic matter abundance as a whole,and the organic matter abundance of Longtan Formation is slightly higher than that of Dalong Formation.Since the spectral mean reflectance has a good negative correlation with TOC content,it can be used to evaluate the abundance of organic matter in shale.