Hydrocarbon generation potential and oil source comparison of source rocks in the central and western regions of Xihu Depression
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摘要:
西湖凹陷作为中国东部油气勘探主战场,一直以来都受到油气地质学家们的广泛关注。前人对西湖凹陷油气资源的研究主要集中在深部地层(平湖组及其下伏层),而对中浅层系(花港组及其上覆层)烃源岩的关注度相对较少。近年来已有勘探发现西湖凹陷中浅层系具有规模成藏的潜力,针对西湖凹陷烃源岩开展研究,利用多项地球化学测试手段分别分析了西湖凹陷中西部地区的烃源岩生烃潜力和生物标志化合物特征。结果显示:西湖凹陷煤和炭质泥岩的生烃潜力好,而泥质烃源岩生烃潜力变化较大,深部地层的泥质烃源岩评价为好或极好烃源岩,中浅层系为差烃源岩。烃源岩有机质类型主要为Ⅱ2~Ⅲ型,热演化阶段可划分为开始生烃阶段(
R o>0.6%)和大量排烃阶段(R o>0.8%)。基于原油和各类烃源岩的生物标志化合物特征对比显示研究区泥质烃源岩为主要原油来源。本研究对西湖凹陷未来油气勘探与开发具有参考意义。Abstract:Objective The Xihu Depression, located in eastern China, is a significant area for oil and gas exploration. While previous studies have focused on deep strata, such as the Pinghu Formation, little research has been conducted on the middle and shallow strata, including the Huagang Formation. Recent findings suggest that these shallow and middle strata have hydrocarbon accumulation potential, but their hydrocarbon-generating capacity and the source of crude oil in the Xihu Depression remain uncertain.
Methods To address these gaps, we collected 203 source rock samples from 13 drilling boreholes in the western slope zone and central inversion tectonic zone of the Xihu Depression. These samples spanned from the Eocene Baoshi Formation to the Miocene Longjing Formation. Geochemical tests and analysis were conducted to assess the hydrocarbon potential and biomarker characteristics of the source rocks.
Results The results indicate that coal and carbonaceous mudstone in the Xihu Depression have excellent hydrocarbon generation potential, while the hydrocarbon generation potential of mudstone varies. Deep layer source rocks are evaluated as good or excellent sources of hydrocarbons, while the middle and shallow layers are considered poor sources. The organic matter in the source rocks mainly consists of types Ⅱ2-Ⅲ, and the thermal evolution stage can be divided into a hydrocarbon generation stage (
R o>0.6%) and a large hydrocarbon expulsion stage (R o>0.8%).Comparing the biomarkers of crude oil and different types of source rocks, we found that the argillaceous source rock in the study area is the primary source of crude oil.Conclusion This research provides valuable guidance for future oil and gas exploration in the Xihu Depression.
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Key words:
- source rock /
- hydrocarbon generation potential /
- geochemical feature /
- biomarker /
- Xihu Depression
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图 1 西湖凹陷构造单元划分(a)与地层综合柱状图(b) (据文献[6]修改)
图b中蓝底表示深部地层,黄底表示中浅层系
Figure 1. Structural units (a) and stratigraphic chart (b) of the Xihu Depression
图 9 西湖凹陷不同类型烃源岩饱和烃质量(质荷比m/z=191,217)色谱图
Ol为奥利烷;Dia为C27重柏甾烷;其余同图 7
Figure 9. Chromatograms of saturated hydrocarbon mass (m/z=191 and 217) in different source rocks in the Xihu Depression
表 1 未成熟烃源岩有机质丰度评价表(据文献[14]修改)
Table 1. Evaluation of organic matter abundance
有机质丰度 w(TOC)/% (S1+S2)/(mg·g-1) EOM/(μg·g-1) HC/(μg·g-1) 差烃源岩 [0, 0.5) [0, 3) [0, 500) [0, 300) 中等烃源岩 [0.5, 1.0) [3, 6) [500, 1 000) [300, 600) 好烃源岩 [1.0, 2.0] [6, 12] [1 000, 2 000] [600, 1 200] 极好烃源岩 >2.0 >12 >2 000 >1 200 表 2 西湖凹陷烃源岩有机质丰度统计
Table 2. Statistical analysis of the abundance of organic matter in the Xihu Depression
烃源岩 w(TOC)/% (S1+S2)/(mg·g-1) EOM/(μg·g-1) HC/(μg·g-1) 煤 $\frac{48.56 \sim 65.79}{55.16(4)}$ $\frac{166.30 \sim 253.33}{211.89(4)}$ $\frac{11\;439 \sim 30\;561}{18\;674(4)}$ $\frac{3\;768 \sim 8\;710}{5\;795(4)}$ 炭质泥岩 $\frac{6.55 \sim 31.69}{13.00(14)}$ $\frac{18.01 \sim 99.36}{43.31(14)}$ $\frac{181 \sim 1\;9330}{5\;301(4)}$ $\frac{81 \sim 8\;203}{2\;348(14)}$ 泥岩 $\frac{0.12 \sim 5.59}{1.27(185)}$ $\frac{0.10 \sim 21.11}{1.65(179)} $ $\frac{46 \sim 6\;240}{801(80)}$ $\frac{14 \sim 2\;884}{374(80)}$ 泥质烃源岩 龙井组 $\frac{0.35 \sim 2.35}{0.74(14)}$ $\frac{0.23 \sim 3.14}{1.07(14)}$ $\frac{118 \sim 704}{346(13)}$ $\frac{41 \sim 372}{170(13)}$ 花港组 $\frac{0.13 \sim 2.79}{0.59(57)}$ $\frac{0.10 \sim 4.85}{0.98(53)}$ $\frac{60 \sim 3\;131}{492(33)}$ $\frac{44 \sim 919}{234(33)}$ 平湖组 $\frac{0.12 \sim 5.59}{1.52(91)}$ $\frac{0.20 \sim 21.11}{3.25(89)} $ $\frac{46 \sim 19\;930}{2\;662(38)}$ $\frac{14 \sim 8\;203}{1\;294(38)}$ 宝石组 $\frac{0.32 \sim 5.43}{2.28(23)}$ $\frac{0.58 \sim 16.57}{4.78(23)}$ $\frac{324 \sim 2\;638}{1\;294(6)}$ $\frac{62 \sim 890}{286(6)}$ 注:横线上方表示最小值与最大值; 下方为平均值,括号内为样品数 表 3 西湖凹陷3类烃源岩典型生物标志化合物特征
Table 3. Biomarker characteristics of three main types of source rocks in the Xihu Depression
陆源输入 低等藻类 细菌改造 盐度分层 氧化还原 煤 高C19/C23 低C27/C29 低S/H高补身烷/升补身烷 低Gam/C30H 高Pr/Ph 高CPI 高TAR 高Pr/nC17 高二萜化合物 低C17/C31 低Ts/Tm 炭质泥岩 中C19/C23 中C27/C29 中S/H中补身烷/升补身烷 低Gam/C30H 中Pr/Ph 中CPI 低TAR 中Pr/nC17 中二萜化合物 中C17/C31 中Ts/Tm 泥岩 低C19/C23 高C27/C29 高S/H低补身烷/升补身烷 高Gam/C30H 低Pr/Ph 低CPI 中TAR 低Pr/nC17 低二萜化合物 高C17/C31 高Ts/Tm -
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