页岩地球化学特征及沉积环境分析
——以川南长宁地区五峰组—龙马溪组为例

Geochemical characteristics and sedimentary environment of shale reservoir: a case study of the Wufeng?鄄Longmaxi Formation in the Changning area, Southern Sichuan Basin

卢畅,陈雷,杨扬,周昊,谭秀成,李雪松

西南石油大学地球科学与技术学院，四川 成都 610500 中国石油天然气集团有限公司碳酸盐岩储层重点实验室西南石油大学研究分室，四川 成都 610500 天然气地质四川省重点实验室，四川 成都 610500 四川长宁天然气开发有限责任公司，四川 成都 610051

School of Earth Science and Technology, Southwest Petroleum University, Chengdu 610500, China Southwest Petroleum University, Division of Key Laboratory of Carbonate Reservoirs, CNPC, Chengdu 610500, China Sichuan Provincial Key Laboratory of Gas Geology, Chengdu 610500, China Sichuan Changning Gas Development Co., Ltd., Chengdu 610051, China

长宁地区是五峰组—龙马溪组海相页岩气勘探开发的重要区块，前人对其沉积特征、储层特征及油气成藏等方面开展了大量研究，但是地球化学特征及沉积环境的相关研究较少。文中通过主量元素和微量元素分析，对长宁地区五峰组—龙马溪组页岩的地球化学特征及沉积环境进行了研究。结果表明：五峰组—龙马溪组页岩均处于缺氧环境，五峰组页岩处于贫氧—厌氧环境，龙马溪组页岩垂向上从极度缺氧的厌氧环境向贫氧环境演变；盆地水体滞留程度也发生了变化，五峰组页岩沉积时期，盆地环境封闭，水体与外界交换少，属于强滞留环境，而龙马溪组页岩沉积时期为半滞留环境。五峰组—龙马溪组沉积时期，长宁地区古气候总体为温暖湿润，随着龙马溪组化学风化指数（CIA）由底部至顶部逐渐增大，古气候也逐渐向温度更高、湿度更大的方向演变。

Changning area is an important area for marine shale gas exploration and development of the Wufeng-Longmaxi Formation. A large number of researches related to shale deposition, shale gas reservoir and shale gas accumulation in this area have been carried out. However, there are few studies related to geochemical characteristics and sedimentary environment. Therefore, the geochemical characteristics and sedimentary environment of the Wufeng-Longmaxi shale has been studied though major and trace elements analysis in Changning area. The results show that shales are in anoxic environment during Wufeng-Longmaxi Formation sedimentary period and in poor oxygen and anaerobic environment during Wufeng Formation sedimentary period. The shales evolved in vertical from extreme anoxic environment to poor oxygen environment during Longmaxi Formation sedimentary period. At the same time, something about watermass restriction has also changed. The basin was closed as little water exchange with the outside, which was in a strong watermass restriction during Wufeng Formation deposition period, but change to moderately restricted basin during the Longmaxi Formation deposition period. During the Wufeng-Longmaxi Formation deposition period, the paleoclimate was generally warm and humid in the Changning area. The chemical index of alteration (CIA) of Longmaxi Formation gradually increased from bottom to top, indicating that the climate was changing to higher temperature and greater humidity.

10.6056/dkyqt202106001