Abstract: In Pearl River Mouth Basin, Kaiping sag is located in the deep-water continental slope area beyond the existing continental shelf slope break zone, where oil and gas resources are less explored. It is of great significance to carry out source rock evaluation and clarify its crude oil source for deepening the understandings of oil and gas accumulation in Kaiping sag and guiding the next step of oil and gas exploration. Based on the test data including TOC content, rock pyrolysis, source rock and crude oil biomarker characteristics, the paper systematically analyzes the geochemical characteristics of source rocks of Wenchang Formation and Enping Formation, and conducts the oil-source correlation. The results show that:(1) The argillaceous source rocks of the Lower and Upper Wenchang Formation and Lower Enping Formation tend to be thick in the core area of Kaiping sag and gradually thinned towards the peripheral slope zone, of which the medium to high organic matter abundance and Type Ⅱ₁-Ⅱ₂ kerogen demonstrate that they are in the mature stage as a whole. (2) The source rocks of Wenchang Formation has the low values of Pr/Ph, C₁₉₊₂₀TT/C₂₃TT and low to medium OL/C₃₀H. C₂₇-C₂₈-C₂₉ regular steranes on the gas chromatography-mass spectrum present "V" shape, and C₃₀ 4-methylsteranes have high abundance. The source rocks of Enping Formation have high values of Pr/Ph and C₁₉₊₂₀TT/C₂₃TT, as well as low values of OL/C₃₀H and low C₃₀ 4-methylsterane content, and the distribution of C₂₇-C₂₈-C₂₉ regular steranes shows an inverted "L" shaped pattern. (3) There are two types of crude oil produced from Kaiping sag. As for Type A oil, the Pr/Ph values are within the range of 1.13 and 1.82, the C₁₉₊₂₀TT/C₂₃TT values range from 0.32 to 0.89, the OL/C₃₀H values are between 0.03 and 1.02, and the average relative content of C₂₇ and C₂₉ regular steranes is 26.20% and 46.44%, respectively. The C₃₀ 4-methylsteranes have high abundance. As for Type B oil, the Pr/Ph values are greater than 2.00, the C₁₉₊₂₀TT/C₂₃TT values are between 1.00 and 2.28, the OL/C₃₀H values range from 0.04 to 0.13, and the average relative content of C₂₇ and C₂₉ regular steranes is 9.92% and 65.54%, respectively. The content of C₃₀ 4-methylsteranes is extremely low. (4) Oil-source correlation analysis shows that Type A oil is originated from the hybrid organic matters of Type Ⅱ and Ⅲ formed by plankton and terrestrial plants in lacustrine source rock of Wenchang Formation; Type B oil comes from the deltaic swamp mudstone of Enping Formation in the background of oxidation sedimentation, and the hydrocarbon generation parent material is dominated by Type Ⅲ organic matter formed by terrestrial higher plants. In conclusion, the research has clarified the sources of oil and gas in Kaiping sag, which is of theoretical guiding significance for future oil and gas exploration.

Key words: source rock, geochemical characteristics, oil-source correlation, Kaiping sag, Pearl River Mouth Basin

摘要： 珠江口盆地开平凹陷位于现今陆架坡折带以外的深水陆坡区，油气勘探程度较低。通过开展烃源岩评价、明确其原油来源，对深化开平凹陷油气成藏认识和指导下一步油气勘探具有重要意义。综合总有机碳含量、岩石热解及烃源岩和原油生物标志化合物特征等测试资料，系统分析文昌组和恩平组烃源岩的地球化学特征，进行油源对比。结果表明：①文昌组下段、上段和恩平组下段的泥质烃源岩均表现为"开平主洼中心厚、向周缘斜坡带依次减薄"，有机质丰度中等—好，干酪根类型为Ⅱ₁型、Ⅱ₂型，整体处于成熟阶段。②文昌组烃源岩具有低Pr/Ph值、低C₁₉₊₂₀TT/C₂₃TT值、低—中等OL/C₃₀H值，气相色谱-质谱图上C₂₇-C₂₈-C₂₉规则甾烷呈"V"型，C₃₀ 4-甲基甾烷丰度高；恩平组烃源岩具有较高的Pr/Ph值和C₁₉₊₂₀TT/C₂₃TT值，较低的OL/C₃₀H值、C₃₀ 4-甲基甾烷含量，C₂₇-C₂₈-C₂₉规则甾烷分布呈反"L"型。③开平凹陷产出两类原油，A类原油的Pr/Ph值为1.13~1.82，C₁₉₊₂₀TT/C₂₃TT值为0.32~0.89，OL/C₃₀H值为0.03~1.02，C₂₇和C₂₉规则甾烷平均相对含量分别为26.20%、46.44%，C₃₀ 4-甲基甾烷丰度高；B类原油Pr/Ph值大于2.00，C₁₉₊₂₀TT/C₂₃TT值为1.00~2.28，OL/C₃₀H值为0.04~0.13，C₂₇和C₂₉规则甾烷平均相对含量分别为9.92%、65.54%，C₃₀ 4-甲基甾烷含量极低。④油源对比分析显示，A类原油来源于文昌组湖相烃源岩中浮游生物和陆源植物混合形成的Ⅱ型、Ⅲ型混合有机质；B类原油来源于氧化沉积背景的恩平组三角洲—沼泽相泥岩，生烃母质以陆源高等植物形成的Ⅲ型有机质为主。研究认识明确了开平凹陷油气来源，对未来油气勘探具有理论指导意义。

关键词: 烃源岩, 地球化学特征, 油源对比, 开平凹陷, 珠江口盆地