Abstract: A number of wells in Qiudong subsag of Taibei sag of Tuha Basin have obtained high-yield oil and gas flow in Sangonghe Formation of the Middle-Lower Jurassic Shuixigou Group, showing a good hydrocarbon exploration prospect of the deep intra-source tight sandstone in the subsag area. To make clear the petroleum geological conditions of tight sandstone from Shuixigou Group in Qiudong subsag and comprehensively evaluate the exploration prospects of Shuixigou Group in Tuha Basin, based on the drilling knowledge obtained from new boreholes, this paper systematically summarizes the favorable accumulation conditions of Qiudong subsag, and points out the next exploration direction. (1)Qiudong subsag suffered from multiple tectonic movements and developed three tectonic zones, namely southern slope, central subsag, and northern slope. Among them, the central subsag was tectonically stable, which was conducive to hydrocarbon preservation in the multi-stage superimposed basin. (2)Shuixigou Group in Qiudong subsag developed two sets of coal-measure source rocks in Badaowan Formation and Xishanyao Formation respectively, as well as lacustrine argillaceous source rocks in Sangonghe Formation. The dominant kerogen types were Ⅱ₂—Ⅲ and in mature evolution stage. (3)Shuixigou Group in Qiudong subsag developed bidirectional braided river delta sedimentary system to the south and north. The sand-bodies in the subsag area developed well and effective reservoirs developed even below 5 000 m under the control of such factors as favorable facies, dissolution, overpressure, and fractures. (4)By comprehensively analyzing the exploration potential of tight sandstone gas from Shuixigou Group in Taibei sag, it showed that the superposition of large coal-measure source rocks and braided river delta front sand-bodies were developed in all three subsags (Shengbei subsag, Qiudong subsag and Xiaocaohu subsag). Five main fan bodies, namely Pudong, Hongbei, Lingbei, Qiudong, and Gebei, can be selected from Sangonghe Formation with the favorable exploration area of 1 090 km², evaluated natural gas resource of 5.29×10¹²m³, and petroleum resource of 5.2×10⁸t. The great resource potential shows that the sag area in Tuha Basin has a good exploration prospect.

Key words: Taipei sag, Qiudong subsag, Shuixigou Group, coal-measure source rock, tight oil and gas, braided-river delta

摘要： 吐哈盆地台北凹陷丘东洼陷有多口井在中—下侏罗统水西沟群三工河组获得了高产油气流,展现了洼陷区深层的源内致密砂岩具有良好的油气勘探前景。为明确丘东洼陷水西沟群致密砂岩的油气地质条件,整体评价吐哈盆地水西沟群的勘探前景,基于新钻井取得的钻探认识,系统梳理和总结了丘东洼陷的有利成藏条件,指明了下一步的勘探方向。①丘东洼陷经历了多期构造运动,发育南部斜坡、中部洼陷、北部斜坡3个构造带,其中,中部洼陷区构造稳定,有利于多期叠合盆地的油气保存。②丘东洼陷水西沟群发育八道湾组、西山窑组2套煤系烃源岩和三工河组湖相泥质烃源岩,其干酪根类型以Ⅱ₂—Ⅲ型为主,处于成熟演化阶段。③丘东洼陷水西沟群发育南、北双向辫状河三角洲沉积体系,洼陷区砂体发育,且受有利相带、溶蚀作用、超压、裂缝等因素控制,在5 000 m以下仍发育有效储层。④整体分析台北凹陷水西沟群致密砂岩气的勘探潜力,其内3个洼陷(胜北洼陷、丘东洼陷、小草湖洼陷)均具备大面积煤系烃源岩与辫状河三角洲前缘砂体叠置发育的条件;可在三工河组优选出葡东、红北、陵北、丘东、疙北5个主力扇体,有利勘探面积为1090 km²,评价的天然气资源量为5.29×10¹²m³,石油资源量为5.2×10⁸t,资源潜力大,展现了吐哈盆地凹陷区具有良好的勘探前景。

关键词: 台北凹陷, 丘东洼陷, 水西沟群, 煤系烃源岩, 致密油气, 辫状河三角洲