Abstract: Liupanshan Basin, a Cretaceous fault basin, shares similar hydrocarbon accumulation conditions with Jiuquan Basin and Hetao Basin, which have already seen breakthroughs in oil and gas exploration. It is considered one of the important basins with exploration breakthrough potential in the periphery of Ordos Basin and Hexi Corridor structural belt. This study systematically evaluates the Cretaceous hydrocarbon accumulation conditions in the basin by integrating field outcrops observations, drilling data, analytical testing results, as well as the latest geophysical data including seismic framework profiles, time-frequency electromagnetic data, and two-dimensional seismic reprocessing data. The research results show as follows. (1)The Lower Cretaceous Madongshan Formation develops high-quality source rocks of semi-deep lake to deep lake facies, with thickness ranging from 100 m to 600 m, total organic carbon (TOC) content of 0.08 % to 6.46 % (with an average of 1.57 % ), and vitrinite reflectance (R_o) between 0.56 % and 1.12 % (with an average of 0.88 % ). The organic matter is primarily of Type Ⅰ to Type Ⅱ₁, exhibiting rich oil and gas reserves and significant oil generation potential. (2)The reservoirs can be divided into two types, i.e., sandstone from Liwaxia Formation and Sikouzi Formation, and shale-mudstone from Madongshan Formation. The regional cap rocks include thick mudstone interbedded with gypsum from Qingshuiying Formation and evaporites from Naijiahe Formation. These strata form two types of accumulation assemblage models. One is the self-generating, self-reserving and self-sealing model, the other is the generation in lower part and reservoir in upper part model. The structural, structural-lithological, and lithological traps are mainly developed in the study area. (3)Madongshan Formation in the four major hydrocarbon-generation sags of Liupanshan Basin, i.e., Haiyuan sag, Guyuan sag, Shagou fault terrace, and Longde sag, covering a total area of 5 800 km², has an in-situ petroleum resource of approximately 1.7×10⁸ t. (4)An innovative exploration approach of "hydrocarbon accumulation under the control of source rocks with matching between fault and cap rock" was proposed to identify structural trap groups near the hydrocarbon generation center, focusing on areas with well-developed faults and cap rocks. The primary target is to achieve a breakthrough in the exploration of medium- to high-quality reservoirs in the upper strata of source rocks. Four favorable target zones were identified, including Lijun, Zhangyi, Yanglangnan, and Chengmengou areas, with a total area of 1 700 km², which provides crucial geological evidence for achieving breakthroughs in the next phase of oil and gas exploration in the basin.

Key words: Shagou fault terrace, Longde sag, hydrocarbon generation center, structural oil-gas group, Madongshan Formation, Liupanshan Basin, periphery of Ordos Basin

摘要： 六盘山盆地作为白垩纪断陷盆地,与已获油气勘探突破的酒泉盆地和河套盆地具有相似的成藏条件,是鄂尔多斯盆地周缘及河西走廊构造带具有勘探突破潜力的重要盆地之一。通过整合野外露头、钻井、分析测试和最新物探资料(地震格架大剖面、时频电磁和二维地震重处理),系统评价了盆地白垩系油气成藏条件。研究结果表明:①下白垩统马东山组发育半深湖—深湖亚相优质烃源岩,其厚度为100~600 m,总有机碳(TOC)含量为0.08%~6.46%(平均为1.57%),镜质体反射率(R_o)为0.56%~1.12%(平均为0.88%),有机质类型以Ⅰ型—Ⅱ₁型为主,油气显示丰富,生油潜力大;②储层包括李洼峡组—寺口子组砂岩和马东山组页岩-泥灰岩2类,以清水营组厚层泥岩夹膏岩和乃家河组蒸发岩为区域盖层,形成自生自储自盖型与下生上储型2种成藏组合,发育构造、构造-岩性和岩性3类圈闭;③在六盘山盆地的4大生烃凹陷区(海原凹陷、固原凹陷、沙沟断阶和隆德凹陷,总面积为5 800 km²),马东山组的石油原地资源量约为1.7×10⁸t;④创新提出"烃源岩控藏、断裂-盖层匹配"的勘探思路,寻找靠近生烃中心的断裂、盖层发育区的构造圈闭群,重点突破烃源岩上部层位的中等—优质储层,优选出李俊地区、张易地区、杨郎南地区和城门沟地区4个有利目标区(总面积为1 700 km²),为下一步盆地油气勘探突破提供了重要地质依据。

关键词: 沙沟断阶, 隆德凹陷, 生烃中心区, 构造油气群, 马东山组, 六盘山盆地, 鄂尔多斯盆地周缘