下扬子地区上二叠统页岩气成藏条件分析

【研究目的】下扬子地区上二叠统广泛发育龙潭组-大隆组暗色页岩，是中国页岩气调查的重点层位。目前该区勘探程度低，导致对该区页岩气成藏条件认识不清。【研究方法】通过龙潭组和大隆组页岩地球化学特征、储集性能，以及保存条件等方面的研究，对该区页岩气资源潜力进行了评价，对有利区进行了优选。【研究结果】龙潭组和大隆组有机质丰度高，TOC含量普遍大于2.0%，热演化程度适中(介于1.3%～2.5%)，储集空间以墨水瓶和狭缝状中孔为主，脆性矿物含量普遍高于50%，具有较好的生烃物质基础和可压裂性。龙潭组页岩累计厚度较大，具有良好的自封闭能力，保存条件总体优于大隆组。二者均发育多种类型的裂缝，是页岩气逸散的主要通道，此外，后期岩浆活动较为频繁，对于页岩气有很强的破坏作用，保存条件是页岩气富集的关键。【结论】下扬子地区上二叠统页岩气选区评价应以沉积环境、生烃能力、储集性能等为基础，以页岩气保存条件为关键，采取“强中找弱”的原则进行，最终在下扬子地区大隆组和龙潭组分别划分了5个有利区。

Analysis of shale gas accumulation conditions of the Upper Permian in the Lower Yangtze Region

This paper is the result of oil and gas exploration engineering.Objective]The dark shale of the Longtan-Dalong Formation is widely developed in the Upper Permian of the Lower Yangtze region, which is the key formation for shale gas exploration in China. At present, the degree of exploration in this area is low, resulting in unclear understanding of shale gas accumulation conditions.Methods]The geochemical characteristics, reservoir properties, and preservation conditions of the Longtan Formation and Dalong Formation shales were studied to evaluate shale gas exploration potential and optimize favorable exploration areas.Results]The organic matter abundance of the Longtan Formation and Dalong Formation is high, TOC content is generally greater than 2.0%, the thermal evolution degree is moderate (between 1.3% and 2.5%), the reservoir space is mainly ink bottle and slit-like mesopores, the brittle mineral content is generally higher than 50%, with good hydrocarbon generation material basis and fracturability. The Longtan Formation shale is thick, with good self-sealing ability, and the preservation conditions are generally better than those of the Dalong Formation. Both of them develop various types of fractures, which are the main channels for shale gas escape. In addition, the late magmatic activity is frequent, which has a strong destructive effect on shale gas, and the preservation conditions are the key to shale gas enrichment.Conclusions]The evaluation of the Upper Permian shale gas in the Lower Yangtze area should be based on sedimentary environment, hydrocarbon generation capacity, and reservoir conditions, taking the shale gas preservation conditions as the key and adopting the principle of finding weak areas in the context of strong tectonic activity. Finally, five favorable areas were divided in the Dalong Formation and Longtan Formation in the Lower Yangtze area.Highlights: The Upper Permian shales in the Lower Yangtze region have the material basis for shale gas enrichment; The preservation conditions are the key to shale gas enrichment in the Upper Permian in the Lower Yangtze region.