昭通页岩气示范区旧司组页岩发育的古环境特征及勘探潜力

Paleoenvironmental characteristics of the Jiusi Formation and potential for shale gas exploration in Zhaotong shale gas demonstration zone

为实现昭通页岩气示范区可持续发展,寻找新的潜在页岩气目的层系,针对石炭系旧司组页岩气部署实施了A井,以期探索旧司组页岩含气性。基于A井样品有机碳、主量、微量及稀土元素的系统测试,结合岩石学、生物遗迹化石特征和色谱质谱测试,分析了A井旧司组元素地球化学特征,判别了旧司沉积期的氧化还原条件,揭示了黑色页岩发育的古环境。研究结果表明:昭通页岩气示范区A井旧司组岩石学特征和主量、微量及稀土元素特征,与五峰组—龙马溪组差异较大。A井钻揭的旧司组有机碳含量相对较高,平均值为1.13%,TOC含量与深度相关性不强。旧司组主量元素中Al2O3含量较高,以钙质页岩和黏土质页岩为主。微量元素及稀土元素等氧化还原指标揭示旧司组沉积期为相对富氧环境,且与TOC含量相互印证。旧司组灰质泥岩中的Chondrites遗迹组合化石、页岩色谱质谱特征也同时揭示了旧司组发育于海陆过渡相的古沉积环境,其古生产力相对五峰组—龙马溪组沉积期较低,故旧司组页岩有机质丰度相对较低。

In order to realize the sustainable development of Zhaotong shale gas demonstration area and search for new potential target strata of shale gas,Well A targeted at the carboniferous Jiusi Formation shale gas exploration was deployed and implemented to explore the gas content of Jiusi Formation shale gas.Based on the systematic test of organic carbon,major content,trace amount and rare earth elements in Well A,combined with petrology,biological relic fossil characteristics and chromatography-mass spectrometry,the geochemical characteristics of elements in Jiusi Formation in Well A were analyzed,and the REDOX conditions in Jiusi sedimentary stage were identified,revealing the sedimentary environment for the development of black shale.The research results show that the petrological characteristics,major,trace and rare earth elements of Jiusi formation in Well A of Zhaotong shale gas demonstration area are quite different from those of Wufeng formation and Longmaxi formation.The organic carbon content of Jiusi group in Well A drilling is relatively high,with an average value of 1.13%,and the TOC content is not strongly correlated with depth.The content of Al2O3 in the main elements of Jiusi formation is high,mainly calcareous shale and clayey shale.The REDOX indexes such as trace elements and rare earth elements indicate that the depositional stage of the Jiusi formation was a relatively oxygen-rich environment,which was mutually verified with the content of TOC.Chondrites combination fossil and shale chromatogram mass spectrum characteristics in the gray mudstone of the Jiusi formation also reveal that the Jiusi formation was developed in the paleosedimentary environment of the transition facies of sea and land,and its paleoproductivity was lower than that of the Wufeng formation and Longmaxi formation,and the abundance of organic matter in the Jiusi formation was relatively low.