致密油“近源成藏”关键地球化学证据——以鄂尔多斯盆地延长组近源组合为例

Key geochemical evidence of "near-source accumulation" of tight oil: a case study of near-source assemblage of Triassic Yanchang Formation in Ordos Basin

肖正录 李勇 喻健 张海 路俊刚 尹相东 韩玫梅

XIAO Zhenglu LI Yong YU Jian ZHANG Hai LU Jungang YIN Xiangdong HAN Meimei

西南石油大学 油气藏地质及开发工程国家重点实验室, 成都 610500 西南石油大学 天然气地质四川省重点实验室, 成都 610500 西南石油大学 地球科学与技术学院, 成都 610500 中国石油 长庆油田分公司, 西安 710018 延长油田股份有限公司, 陕西 延安 716000

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China Natural Gas Geology Key Laboratory of Sichuan Province, Southwest Petroleum University, Chengdu, Sichuan 610500, China School of Geosciences and Technology, Southwest Petroleum University, Chengdu, Sichuan 610500, China PertoChina Changqing Oilfield Company, Xi'an, Shaanxi 710018, China Yanchang Oilfield Company, PetroChina, Yan'an, Shaanxi 716000, China

致密油“近源成藏”的结论是依据石油在低渗储层中难以长距离侧向运移的储层特征推断得出的，一直以来缺乏地球化学方面的直接证据。基于对鄂尔多斯盆地三叠系延长组近源组合(长6段—长81亚段)中烃源岩特征和油源差异性的分析，探究了致密油近源成藏的地球化学依据，并解释了引起近源成藏的原因。研究区近源组合中的石油皆来自于原位长7烃源岩，即便是邻近区块的油源也存在差异，石油在致密储层中难以发生大规模的侧向运移。鄂尔多斯盆地长7段烃源岩的生物标志化合物在平面上具有显著差异，并沿沉积中心呈环带状分布。不同相带生物标志化合物组合差异导致的油源差异，是前期学者们发现致密油“近源成藏”的根本原因。致密油“近源成藏”改变了之前油源对比全盆地、同一层烃源岩一概而论的观点，对未来单一盆地中不同类型油气资源量的分区分带精细评价具有重要意义。

The conclusion of "near-source accumulation" of tight oil is inferred based on the reservoir characte-ristics that crude oil is difficult to migrate laterally for a long distance in low-permeability reservoirs, yet there has been no direct geochemical evidence for a long time. Based on the analysis of the characteristics of source rocks and the source differences of oil in the near-source assemblage (Chang 6 member to Chang 81 sub-member) of the Tirassic Yanchang Formation in the Ordos Basin, this paper explores the geochemical basis of tight oil near-source accumulation and explains its cause. The results show that the crude oil in the near-source assemblage comes from the in-situ Chang 7 source rocks, and even the oil sources in the adjacent blocks are different. It is difficult for crude oil to undergo large-scale lateral migration in a tight reservoir. The biomarker compounds of Chang 7 source rocks in the Ordos Basin have significant differences in the plane and are distributed in a circularbelt along the sedimentary center. The oil source difference caused by the combination difference ofbiomarker compounds in different facies zones is the fundamental reason for the predecessors' discovery of "near-source accumulation" of tight oil. The "near-source accumulation" of tight oil has changed the previous view that oilsource correlation is a generalization of the whole basin and the source rocks of the same layer, and has important significance for the zoning and fine evaluation of different types of oil and gas resources in a single basin in the future.

国家自然科学基金 42002176;国家自然科学基金 42072185;中国石油—西南石油大学创新联合体科技合作项目 2020CX050000

https://doi.org/10.11781/sysydz202303517