Abstract: The Cambrian Qiongzhusi Formation is one of the earliest series of strata for shale gas exploration and research in China. In the early stage, due to unclear understandings of the overall geological cognition and limited technological conditions, a number of wells were only deployed in the Weiyuan anticline and Changning anticline with a burial depth less than 3 500 m and a relatively gentle structure. The production rate of the wells is low, indicating a failure in the large-scale commercial development. Recently, major exploration breakthroughs have been made in Well Zi201 and Well Weiye1H, marking significant progress in geological cognition of the deep shale gas in Qiongzhusi Formation of the Deyang-Anyue aulacogen. The sedimentary environment of Qiongzhusi Formation is controlled by the aulacogen. The deep-water siliceous argillaceous shelf facies in the trough and deep-water silty argillaceous shelf facies on the slope of the trough edge are the dominant sedimentary facies zones, which are conducive to the enrichment and accumulation of shale gas. Vertically, Qiongzhusi Formation has developed multiple sets of shale reservoirs, mainly consisting of the 1st, 3rd, 5th, and 7th substrata. In particular, the 5th substratum is a key breakthrough layer with the total organic carbon content of 2.7% to 3.1%, porosity of 4.2% to 4.9%, brittle mineral content of 69.5% to 76.5%, gas content of 7.8 m³/t to 9.5 m³/t, and moderate maturity of 3.0% to 3.5%. The 3rd substratum is a potential exploration stratum. Qiongzhusi Formation is expected to realize multi-interval three-dimensional development. The bottom margin of the Cambrian System has a simple structure in the middle section of the aulacogen, lacking of obvious major faults. The pressure coefficient of Qiongzhusi Formation is generally above 1.8, and the preservation conditions are favorable. The aulacogen provides sufficient sedimentary space and material basis, as a result of which the shale in Qiongzhusi Formation is rich in hydrocarbon sources and has achieved a high volume of gas production; the existence of Leshan-Longnüsi paleo-uplift prevents the shale in Qiongzhusi Formation from excessive thermal evolution. A "aulacogen-paleouplift" shale gas enrichment model has been established, and it has been determined that the favorable exploration area of Qiongzhusi Formation is 4 400 km² and the resources amounts to 2×10¹²m³. The exploration breakthrough of shale gas in Qiongzhusi Formation has opened up another new field for achieving a trillion of cubic meters of reserves and a billion of cubic meters of production. Next, the geological-engineering integrated high-yield model of Well Zi201 will be promoted and applied to the exploration and development fields of marine deep and ultra-deep shale gas in the entire Upper Yangtze area of southern China.

Key words: Sichuan Basin, aulacogen, Qiongzhusi Formation, deep shale gas, reservoir formation conditions, exploration breakthrough

摘要： 寒武系筇竹寺组是中国最早进行页岩气勘探和研究的层系之一,早期由于整体地质认识不清,加之受工程技术条件限制,仅在埋深小于3 500 m、构造相对平缓的威远背斜和长宁背斜实施勘探评价工作,但生产情况不佳,未实现大规模的商业开发。近期,资201井和威页1H井取得重大勘探突破,标志着"德阳—安岳"裂陷槽筇竹寺组深层页岩气在地质认识上取得了重大进展。"德阳—安岳"裂陷槽控制了筇竹寺组的沉积环境,槽内深水硅质泥棚相和槽缘斜坡深水含粉砂质泥棚相为优势沉积相带,有利于页岩气富集成藏。筇竹寺组在纵向上发育多套页岩储层,以1小层、3小层、5小层和7小层为主。其中,5小层为主力突破层,其总有机碳含量为2.7% ~3.1%, 孔隙度为4.2% ~4.9%, 脆性矿物含量为69.5% ~76.5%, 含气量为7.8~9.5 m³/t,成熟度适中,为3.0% ~3.5%; 3小层为潜力勘探层。筇竹寺组有望实现多层段立体开发。裂陷槽 中段寒武系底界构造简单,无明显大断层,筇竹寺组的地层压力系数主体在1.8以上,保存条件良好。裂陷槽的存在提供了充足的沉积空间和物质基础,使得筇竹寺组页岩的烃源丰富,生气量高;乐山—龙女寺古隆起的存在避免了筇竹寺组页岩过高热演化。建立了"槽-隆"页岩气富集模式,明确了筇竹寺组有利勘探面积为4 400 km²,资源量为2×10¹²m³。筇竹寺组页岩气的勘探突破开辟了又一个万亿立方米储量、百亿立方米产量的页岩气增储上产新阵地。下一步将复制资201井地质—工程一体化高产模式,将其推广应用到整个南方上扬子地区海相深层—超深层页岩气勘探开发领域。

关键词: 四川盆地, 裂陷槽, 筇竹寺组, 深层页岩气, 成藏条件, 勘探突破