Abstract: The Mianyang-Guang’an shallow-water shelf is another key area for Permian-Triassic natural gas exploration in Sichuan Basin, following the Kaijiang-Liangping trough. Currently, existing efforts mainly focus on hydrocarbon exploration in bioclastic bank development zones at the margin of Suining and Guang’an platforms on both sides of the study area, while insufficient attention has been paid to the clustered biological reefs within the shelf. In 2003, the gas testing of Permian Changxing Formation at Well Pengshen10 deployed within the shelf demonstrates a high-yield industrial gas flow of 206.36×10⁴m³/d, exhibiting the promising exploration prospects of biological reefs. Through petrographic and geochemical analyses based on core samples, solid bitumen samples as well as seismic and logging data, this study systematically investigates the stratigraphic and sedimentary characteristics, hydrocarbon accumulation conditions, periods and patterns of Changxing Formation at Well Pengshen10. The research results show as follows. (1)The Changxing Formation at Well Pengshen10 is composed of the pinnacle reef subfacies of shallow-water shelf. The reef reservoir is charaterized with abundant dissolution pores and structural fractures, forming a good reservoir-cap combination with the overlying Feixianguan Formation mudstone. (2)The geochemical characteristics of solid bitumen in natural gas reservoir demonstrate the contributions of source rocks from Longtan Formation and Qiongzhusi Formation. The Pengshen10 well area has developed a deep-seated strike-slip fault that runs through the Sinian Dengying Formation and the Permian Changxing Formation, serving as a key channel for vertical oil and gas migration. The lithologic traps are primarily developed in Changxing Formation at Well Pengshen10. (3)The homogenization temperature of inclusions and the burial-thermal history of reservoirs jointly reveal that hydrocarbon charging mainly occurred in the Early Triassic and Middle to Late Jurassic. Based on this, combined with the development of faults and traps during the oil and gas charging period, a hydrocarbon accumulation model was ultimately established, involving multi-source hydrocarbon supply, fault-mediated migration, as well as oil-gas accumulation and adjustment in the lithological and structural traps. The exploration breakthrough at Well Pengshen10 reveals that it is a representative area for the large-scale hydrocarbon accumulation in biological reefs over the shallow-water shelves, which points out a new direction for the exploration and deployment of natural gas in the Permian-Triassic reef shoal reservoirs of Sichuan Basin.

Key words: Sichuan Basin, Permian Changxing Formation, Mianyang-Guang’an shallow-water shelf, Well Pengshen10, biological reefs, accumulation condition, accumulation model

摘要： 绵阳—广安浅水陆棚是继开江—梁平海槽后,四川盆地在二叠系—三叠系开展天然气勘探的又一个重点区域,目前的勘探主要聚焦于其两侧的遂宁—广安生屑滩发育区,而对陆棚内部集群发育的生物礁未给予足够关注。部署于陆棚内的蓬深10井于2023年在二叠系长兴组试气,取得了206.36×10⁴m³/d的高产工业气流,展示了绵阳—广安浅水陆棚生物礁领域具有巨大的油气勘探前景。基于岩心样品、固体沥青样品以及地震-测井资料,通过岩石学和地球化学分析,对蓬深10井长兴组的地层和沉积特征、油气成藏条件、油气成藏期次和成藏模式进行了系统研究。研究成果表明:1蓬深10井长兴组发育浅水陆棚相塔礁亚相沉积,礁体储层发育大量溶孔和裂缝,与上覆的飞仙关组泥岩形成了良好的储-盖组合。②储层内固体沥青的地球化学特征表明天然气具有来自二叠系龙潭组和寒武系筇竹寺组烃源岩的贡献,蓬深10井区发育了贯穿震旦系灯影组与二叠系长兴组的深大走滑断裂,是油气垂向输导的关键通道;蓬深10井长兴组圈闭主要为岩性封闭,构造运动对圈闭有效性的影响较小。③包裹体均一温度与储层埋藏史-热演化史揭示,油气充注主要发生在早三叠世、中侏罗世和晚侏罗世,结合油气充注时期的断裂及圈闭发育情况,最终建立了多源供烃、断裂沟通、构造-岩性圈闭内聚集调整的油气成藏模式。蓬深10井的勘探突破揭示该井为浅水陆棚生物礁领域有效规模成藏的代表,为四川盆地二叠系—三叠系礁滩领域天然气的勘探部署指明了新方向。

关键词: 四川盆地, 二叠系长兴组, 绵阳—广安浅水陆棚, 蓬深10井, 生物礁, 成藏条件, 成藏模式