Abstract: A significant breakthrough has been achieved in the hydrocarbon exploration of the lower assemblage in Dongwan structural belt along the southern margin of Junggar Basin. During formation testing, Well QB1 obtained a high industrial oil and gas flow from the Cretaceous Qingshuihe Formation, with the gas output of 50.7×10⁴m³/d and oil production of 288 t/d. This demonstrates favorable hydrocarbon accumulation conditions and significant exploration potential in this belt. The result of research shows as follows. (1)Multiple sets of large-scale source rocks are developed in Dongwan structural belt, dominated by the Jurassic humic-type source rocks, while oil reservoirs are contributed by the mixture of Permian sapropelic-type and Cretaceous mixed-source rocks. (2)The Qingshuihe Formation features a dual reservoir system comprising basal sandstone and fracture networks, exhibits low matrix porosity but achieve high and stable hydrocarbon production through pore-fracture dual media under overpressure conditions. (3)The lower assemblage has favorable geological conditions such as high-quality reservoir-cap combinations and wide and gentle structural trap groups. (4)The favorable temporal matching between trap formation and hydrocarbon generation-expulsion peaks has laid the foundation for hydrocarbon accumulation in large gas fields. The exploration breakthrough of Well QB1 demonstrates that the natural gas resource potential of Dongwan structural belt is estimated to be 100 billion cubic meters, providing important practical evidence for deep to ultra-deep exploration in the northern Tianshan piedmont. The current exploration of lower assemblage in the southern margin of Junggar Basin mainly focuses on increasing reserves and enhancing productivity in the Hutubi, Dongwan, and Wuchang structural belts, while simultaneously accelerating exploration breakthroughs in replacement zones and reserve areas.

Key words: southern margin of Junggar Basin, Dongwan structural belt, lower assemblage, hydrocarbon accumulation condition, exploration prospect

摘要： 准噶尔盆地南缘东湾构造带下组合油气勘探取得重大突破,QB1井在白垩系清水河组试油,获得产气量为50.7×10⁴m³/d、 产油量为288 t/d的高产工业油气流,证实东湾构造带具备形成 大型油气田的优越成藏条件和显著勘探潜力。研究结果表明:①东湾构造带发育多套规模烃源岩,以侏罗系腐殖型烃源岩为主力气源,而油藏则存在二叠系腐泥型烃源岩与白垩系烃源岩的混源贡献;②清水河组发育底部砂岩与裂隙体双重储集体,基质的孔隙度虽低,但超压条件下,孔-缝双重介质储层可实现高产稳产;③下组合具备优质储-盖组合与宽缓构造目标圈闭群等有利地质条件;④圈闭形成期与烃源岩生/排烃高峰期良好匹配,奠定了大型气田成藏基础。QB1井勘探突破证实东湾构造带具备千亿立方米级天然气资源潜力,为天山北麓深层—超深层勘探提供了重要实践依据。当前,准噶尔盆地南缘下组合勘探重点围绕呼图壁构造带、东湾构造带和乌昌构造带3大构造带推进增储建产,同时加快接替区和储备区的勘探突破。

关键词: 准噶尔盆地南缘, 东湾构造带, 下组合, 成藏条件, 勘探前景