川南下古生界高演化页岩成熟度指标

Research on thermal maturity indicators of lower Palaeozoic over-mature shale in southern Sichuan Area

川南下古生界下寒武统筇竹寺组及下志留统龙马溪组2套页岩,具有时代老、热演化程度高、缺乏镜质体等特点,因此,如何准确定量化评价有机质成熟度,一直是学术界争论的焦点。为此,文中总结了过成熟页岩各项成熟度实验过程及数据应用时的注意事项:1)热解实验需要人工识别真实的热解烃峰值温度,排除钻井液污染产生"假峰"的影响,获取真实的热解峰温;2)分析每个样品所有测点沥青质反射率及笔石反射率的分布特征,剔除不可靠测值的影响;3)伊利石结晶度可应用于伊蒙混层比小于15%的过成熟页岩,当无测点或测点少时,作为过成熟度的可靠指标。最终采用了岩石热解峰温-沥青质反射率-笔石反射率-伊利石结晶度综合评价方法,明确了永川、威远地区龙马溪组镜质体反射率(Ro)为2.05%~2.35%;井研地区筇竹寺组Ro为2.57%~2.74%。

With the characteristics of old age, high thermal maturity, lack of vitrinite in the Qiongzhushi Formation and Longmaxi Formation shales of the lower Palaeozoic in the southern Sichuan Area, the quantitative evaluation of the maturity of organic matter has been the focus of academic debate. To overcome the uncertainty of various maturity index, the considerations of the maturity experimental process and data application for over-mature shale are summed up: pyrolysis experiment requires to identify real S2 peak temperature, eliminate "false peak" caused by drilling fluid pollution, in order to obtain the real pyrolysis peak temperature;analyze all the measuring point distribution features of each bituminous reflectance and graptolite reflectivity sample, eliminate the influence of unreliable observation; illite crystallinity can be used to get layer ratio which is less than 15% of the mature shale, when there is less or no measuring point as a reliable indicator of maturity. Finally, the rock pyrolysis peak temperature-bitumen reflectance-graptolite reflectance-illite crystallinity evaluation method is adopted. The Rovalue of Yongchuan and Weiyuan areas is from 2.05% to 2.35% and the Rovalue of Jingyan Area is from 2.57% to 2.74%.