黄骅坳陷乌马营潜山天然气地球化学特征及差异聚集

黄骅坳陷乌马营潜山发育复式油气藏，不同层段天然气的地球化学特征差异明显，造成这种差异的地质原因尚不明确，制约着乌马营潜山天然气进一步勘探。利用天然气组分、岩石热解模拟实验和碳、氢同位素分析等测试手段，通过地球化学特征分析，探讨乌马营地区不同层段天然气地球化学特征差异性的成因，剖析油气充注过程，建立油气成藏模式，以期为天然气勘探提供理论指导。乌马营地区天然气具有碳、氢同位素较重，干燥系数较大，轻烃中环烷烃、芳烃丰度高等特点；垂向上，随着埋藏深度变小天然气甲烷碳同位素变重、干燥系数变大、C₆轻烃相对丰度降低。岩石热解气碳同位素、岩石热解轻烃的地球化学特征指示乌马营地区天然气属于成熟—高成熟煤型气，其烃源岩为研究区石炭系—二叠系煤系地层。不同成藏模式造成了乌马营地区不同层段天然气地球化学特征差异明显。乌马营地区发育近源连续聚集和远源阶段聚集两种天然气成藏模式，近源的奥陶系和二叠系主要发育近源连续聚集型油气藏，聚集了不同成熟阶段的天然气，属于全天候聚集型，天然气资源丰富，是下一步天然气勘探的主力方向；远源的二叠系上部、中生界和古近系油气藏属于阶段性、幕式型聚集，主要聚集高成熟天然气，天然气富集程度受控于断层开启时间的早晚、开启时间的长短、储层物性和保存条件等，是乌马营地区重要的天然气勘探领域。

Geochemical characteristics and differential accumulation of natural gas in Wumaying buried-hill,Huanghua depression

Complex reservoirs are developed in Wumaying buried-hill in the Huanghua depression. The geochemical characteristics of natural gas in various intervals are obviously different. The geological reason for this difference is still not clear, which restricts the further exploration of Wumaying buried-hill. Using gas composition, simulation experiment of rock pyrolysis as well as carbon and hydrogen isotope analysis, this paper explores the causes of the differences in natural gas geochemical characteristics in various intervals in the Wumaying area by analyzing geochemical characteristics, conducts a detailed analysis on the process of oil and gas charging, and establishes a model of oil and gas accumulation, aiming to provide theoretical instructions for gas exploration. The natural gas in the Wumaying area is characterized by heavy carbon and hydrogen isotopes, large drying coefficient, as well as high abundance of naphthenic and aromatic hydrocarbons in light hydrocarbons. In the vertical direction, as the burial depth decreases, the methane carbon isotope of natural gas becomes heavier and the drying coefficient becomes larger. The relative abundance of C₆ light hydrocarbons is reduced. The carbon isotope of rock pyrolysis gas and the geochemical characteristics of rock pyrolysis light hydrocarbon indicate that the mature and high-mature coal-type gas exists in the Wumaying area, and its source rock is the Carboniferous to Permian coal-measure strata in the study area. Different accumulation modes have caused obvious differences in the geochemical characteristics of natural gas in different intervals in the Wumaying area. In this area, there are two accumulation modes of natural gas:near-source continuous accumulation and far-source staged accumulation. The near-source continuous accumulation-type oil and gas reservoirs were mainly developed in the Ordovician and Permian periods, accumulating gas in different mature stages, classified as the weatherproof type, and rich in gas resources; this is the main direction of gas exploration in the next step. The Upper Permian, Mesozoic and Paleogene far-source oil and gas reservoirs were formed by staged and episodic accumulations, mainly accumulating high-mature natural gas. The enrichment degree of natural gas is controlled by the opening time of the fault, the length of the opening time, the physical properties of the reservoirs and the preservation conditions. These reservoirs are an important field of natural gas exploration in the Wumaying area.