Abstract: With the further exploration of Ordos Basin, the new areas in the periphery of the basin have gradually become the next key exploration targets. By studying the source and reservoir conditions of Yanchang Formation in the southern Tianhuan depression of Ordos Basin, and analyzing the correlation between crude oil and source rock, as well as hydrocarbon accumulation period and characteristics, this paper discusses the hydrocarbon enrichment characteristics and accumulation model of the study area. The research results show that the shale of the 7th oil layer of Yanchang Formation (Chang 7 oil layer)has a thickness of 5-20 m in Pingliang-Yanwu area, thinning to the northwest in Yinjiacheng-Xiaocha-Pengyang area. Shale in the study area has type Ⅱ₁ and Ⅱ₂ organic matter types, low maturity (average vitrinite reflectance of 0.65%), and the total organic carbon content (2.37%on average)and hydrocarbon generation capacity significantly lower than those of the corresponding strata in the central basin. The reservoirs in the study area are bounded by the mudstone of Chang 7 oil layer, which can be divided into two sets of accumulation assemblages, i.e., the assemblage of source in the upper and reservoir in the lower and vice versa. The main charging stages of reservoirs are in the Early Cretaceous period. The oil source in Pingliang-Yanwu area is mainly from the high-quality source rocks of Chang 7 oil layer in the central basin, and its reservoir types are mainly structural and structural-lithologic reservoirs, with the overall characteristics of multiple reservoirs distributed above and below the source, multiple channels transported by faults and sand bodies, and reservoir controlled by the combination of structure and lithology. Pingliang-Yanwu area has favorable conditions for hydrocarbon enrichment and accumulation. With the progress of 3D seismic and reservoir reconstruction technology, Pingliang-Yanwu area has great potential for oil and gas exploration, and is an important replacement area for increasing reserves and production in the western margin of Ordos Basin.

Key words: accumulation mode, exploration potential, Yanchang Formation, Tianhuan depression, Ordos Basin

摘要： 随着鄂尔多斯盆地勘探程度深入,盆地外围新区逐渐成为下一步重点勘探目标。通过研究鄂尔多斯盆地天环坳陷南段平凉—演武地区延长组的烃源和储集条件,以及开展油源对比、油气成藏期和成藏特征等分析,探讨了研究区的油气富集特征及成藏模式。研究结果表明:平凉—演武地区延长组7油层组(长7油层组)泥页岩的厚度为5~20 m,并向西北部殷家城—小岔—彭阳一带减薄,其有机质类型以Ⅱ₁型和Ⅱ₂型为主、成熟度总体偏低(镜质体反射率平均为0.65%)、总有机碳含量(平均为2.37%)与生烃能力明显低于盆地中部对应层系;研究区的油气藏以长7油层组泥岩为界,可划分出"上生下储"和"下生上储"两套成藏组合,油气藏的主要充注期在早白垩世;平凉—演武地区的油源主要来自盆地中部长7油层组的优质烃源岩,油藏类型以构造和构造-岩性油藏为主,整体表现为"源上、源下立体多层,断裂、砂体多元输导,构造-岩性复合控藏"的特征。平凉—演武地区具备油气富集成藏的有利条件,且随着三维地震和储层改造技术进步,油气勘探潜力大,是鄂尔多斯盆地西缘增储上产的重要接替区。

关键词: 成藏模式, 勘探潜力, 延长组, 天环坳陷, 鄂尔多斯盆地