Abstract: Based on a systematic compilation of seismic, drilling, mud logging, well testing, and geochemical analytical data from Shawan sag, this paper systematically investigates the hydrocarbon distribution patterns and accumulation and enrichment mechanisms. The results indicate that multiple sets of source rocks, including the Middle Permian and Lower Permian Fengcheng Formation, are developed in Shawan sag. These source rocks have undergone a complete hydrocarbon generation sequence from oil to gas, providing a material foundation for integrated oil-gas exploration in the sag. Hydrocarbons distributed along the basal unconformity of the Upper Permian exhibit a vertical pattern of oil-over-gas and a lateral pattern of oil in distal areas and gas in proximal source areas (outer-oil and inner-gas). The differential distribution is controlled by the multiple effects of the unconformity. The Upper Permian basal unconformity structurally separates two vertically stacked overpressure oil-gas sealing systems and establishes lateral pathways for long-distance, rapid hydrocarbon migration. The oil-over-gas pattern results from the dynamic coupling of two-stage formation pressure system evolution and two-stage hydrocarbon charging, whereas the outer-oil and inner-gas pattern is attributed to large-scale migration of early oil along the unconformity toward the source margin, followed by late gas accumulation in proximal and intra-source areas as the reservoirs became increasingly tight. Spatially, four types of Permian hydrocarbon reservoirs have been identified in Shawan sag:source-reservoir separated conventional glutenite oil reservoirs, source-reservoir separated discontinuous tight gas reservoirs, source-reservoir adjacent quasi-continuous tight sandstone gas reservoirs, and source-reservoir integrated self-sourced and self-reservoired shale gas reservoirs. This differentiation is governed by the source-reservoir coupling relationship, which controls hydrocarbon accumulation dynamics and fluid seepage patterns. Based on these findings, a hydrocarbon accumulation model is established, characterized by overpressure sealing, oil-over-gas pattern, source-reservoir coupling, as well as outer-oil and inner-gas pattern. The Middle-Lower Permian in Shawan sag is identified as the primary target interval for large-scale natural gas exploration. Considering burial depth and trap types, three key exploration directions are proposed:source-reservoir separated stratigraphic reservoirs in the northern onlap-truncation zone, source-reservoir adjacent tight gas reservoirs in the central uplift zone of plunging fold, and source-reservoir integrated shale gas reservoirs in the southern deep sag zone. These findings demonstrate the broad exploration potential of deep natural gas in Shawan sag.

Key words: hydrocarbon distribution patterns, unconformity, abnormal pressure, source-reservoir coupling, unconventional oil and gas, accumulation mechanism, Shawan sag, Junggar Basin

摘要： 基于沙湾凹陷地震、钻井、录井、试油和分析化验资料的系统整理，对其油气分布规律与成藏富集机理进行了深入探讨。研究结果表明，沙湾凹陷发育中二叠统和下二叠统风城组等多套烃源岩，经历了生油—生气的完整生烃序列，为沙湾凹陷的油气兼探奠定了物质基础。油气沿上二叠统底界不整合面呈现纵向上“上油下气”、横向上“远源油、近源气”（外油内气）的分布规律，其差异分布机理在于不整合面的多重控制作用：上二叠统底界不整合面在结构上塑造了纵向上的2套油气超压封存系统以及横向上的油气长距离快速运移通道；“上油下气”是两期地层压力系统演化与两期油气动态耦合的结果，“外油内气”则源于早期油沿不整合面规模运移至源边，晚期气受储层致密化影响而聚集于近源及源内。在空间上，沙湾凹陷的二叠系形成了源-储分离型常规砂砾岩油藏、源-储分离型非连续分布致密气藏、源-储邻近型准连续分布致密砂岩气藏和源-储一体型自生自储页岩气藏，其机理在于源-储耦合关系控制了成藏动力与流体渗流方式。基于上述认识，建立了“超压封存、上油下气、源-储耦合、外油内气”的成藏模式，明确了沙湾凹陷中—下二叠统为天然气规模勘探的主攻层系，并结合埋深与圈闭类型提出了3大勘探方向[北部上超削蚀带（超削带）源-储分离型地层油气藏、中部鼻状隆起带（鼻隆带）源-储紧邻型致密天然气藏、南部深凹带源-储一体型页岩气藏]，展现了沙湾凹陷深层天然气广阔的勘探前景。

关键词: 油气分布规律, 不整合面, 异常压力, 源-储耦合, 非常规油气, 成藏机理, 沙湾凹陷, 准噶尔盆地