Niu Zicheng, Wang Yongshi, Li Zheng, Wang Ru, Wang Xin, Wang Xiuhong
Key Laboratory for Unconventional Oil and Gas Exploration and Development of Shandong Province, Dongying 257022, Shandong, China.
Key Laboratory of Shale Oil and Gas Exploration & Production, SINOPEC, Dongying 257022, Shandong, China.
ACS Omega. 2023 Sep 12;8(38):35093-35106. doi: 10.1021/acsomega.3c04555. eCollection 2023 Sep 26.
The freezing point of crude oils is an important factor affecting the process of exploration, development, and transportation of crude oils. In the Dongying Sag, the freezing point of crude oils varies greatly in space, and high-freezing-point crude oils have been found in many structural belts. The freezing point of crude oils in the Dongying Sag is generally high, ranging from -40 to 80 °C. The distribution of high-freezing-point crude oils in the Dongying Sag is scattered, and they have been found at different depths, layers, and structural belts, with relatively more occurrences in specific areas. Based on the relationship between the wax content and the resin + asphaltene content, the high-freezing-point crude oils in the Dongying Sag can be classified into three types (type A, type B, and type C). Type A, type B, and type C high-freezing-point crude oils are mainly found in the gentle slope zone, depression zone, and uplift zone, respectively. The contents of wax and resins + asphaltenes in crude oils are the key factors controlling the freezing point of crude oils in the Dongying Sag. Oil source correlation using biomarkers and -alkane carbon isotopes demonstrates that different types of high-freezing-point crude oils are generated from different source rocks, indicating that the source of crude oils is not the only factor controlling the freezing point of crude oils. The hydrocarbon-generating parent material of hydrocarbon source rocks developed in different depositional environments of the Dongying Sag is generally characterized by the dominance of bacteria and algae and is supplemented by terrestrial higher plants. This lays the material foundation for the formation of waxes during the maturation of hydrocarbon source rocks. The change of temperature and pressure conditions during the process of oil expulsion from source rocks and migration in the carrier bed will lead to phase fractionation and composition changes of oils, thus forming type A freezing point crude oils in the slope zone and type B freezing point oils in the depression zone. The increase in resin and asphaltene content caused by biodegradation and water washing in shallower buried oil reservoirs is the reason for the formation of type C high-freezing-point crude oils. The research results indicate that the organic matter composition and hydrocarbon alteration during migration and accumulation jointly control the formation of high-freezing-point crude oils in lacustrine basins. The extensive input of terrestrial organic matter into the source rocks of the lacustrine basin laid the foundation for the formation of high-freezing-point crude oils, and the migration fractionation and biodegradation of the crude oils further promoted the formation of high-freezing-point crude oils.
原油凝固点是影响原油勘探、开发及运输过程的一个重要因素。在东营凹陷，原油凝固点在空间上变化很大，在许多构造带都发现了高凝固点原油。东营凹陷原油的凝固点普遍较高，范围在-40至80℃之间。东营凹陷高凝固点原油分布分散，在不同深度、层位及构造带均有发现，在特定区域出现的次数相对较多。根据蜡含量与树脂+沥青质含量之间的关系，东营凹陷的高凝固点原油可分为三种类型（A型、B型和C型）。A型、B型和C型高凝固点原油分别主要分布在缓坡带、洼陷带和隆起带。原油中蜡和树脂+沥青质的含量是控制东营凹陷原油凝固点的关键因素。利用生物标志物和正构烷烃碳同位素进行油源对比表明，不同类型的高凝固点原油产自不同的烃源岩，这表明原油的来源并非控制原油凝固点的唯一因素。东营凹陷不同沉积环境发育的烃源岩的生烃母质一般以细菌和藻类为主，并有陆源高等植物补充。这为烃源岩成熟过程中蜡的形成奠定了物质基础。烃源岩排油及在运载层中运移过程中温度和压力条件的变化会导致原油的相分离和组成变化，从而在斜坡带形成A型凝固点原油，在洼陷带形成B型凝固点原油。浅埋油藏中生物降解和水洗导致树脂和沥青质含量增加是形成C型高凝固点原油的原因。研究结果表明，运移聚集过程中的有机质组成及烃类改造共同控制了湖相盆地高凝固点原油的形成。陆源有机质大量输入湖相盆地烃源岩为高凝固点原油的形成奠定了基础，原油的运移分馏和生物降解进一步促进了高凝固点原油的形成。
