Productivity and development model of source rock of the Liushagang Formation in the Weixinan Sag
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摘要: 涠西南凹陷是中国近海北部湾盆地已证实的富烃凹陷,始新统流沙港组是该凹陷主要烃源岩层系。为深入认识涠西南凹陷流沙港组烃源岩的生产力和发育特征,采用有机地球化学与地球生物学相结合、定性分析与定量计算相结合的方法正演恢复了涠西南凹陷不同次洼流沙港组不同层段烃源岩的古生产力、有机质埋藏效率和有机碳埋藏生产力,进而建立了研究区流沙港组烃源岩形成的地球生物学模式。结果表明,涠西南凹陷流沙港组烃源岩的古生产力、有机质埋藏效率及有机碳埋藏生产力在横向不同次洼和纵向不同层段上均存在差异,横向上以B次洼最优,纵向上以流二段最高;涠西南凹陷流沙港组烃源岩发育超营养湖高埋藏效率高埋藏生产力、富营养湖中等埋藏效率中等埋藏生产力及富营养湖低埋藏效率低埋藏生产力3种代表性的地球生物学模式。Abstract: The Weixinan Sag is a proven hydrocarbon-rich sag with the Eocene Liushagang Formation as main source rock system in the Beibuwan Basin, offshore China.In order to deepen the understanding of the productivity and development characteristics of the Liushagang Formation source rock, the paleo-productivity, organic matter burial efficiency and organic carbon burial productivity of each sub-sag in the Weixinan Sag and each member in the Liushagang Formation are restored forward by using the methods of organic geochemistry combined with geobiology and qualitative analysis combined with quantitative calculation, and the geobiological development models of the Liushagang Formation source rock are further established.The results show that there are differences in paleo-productivity, organic matter burial efficiency and organic carbon burial productivity among different sub-sags in lateral and vertical directions.The B sub-sag is the best in plane and the E2L2 is the highest in vertical sequence.Three representative geobiological development models of the Liushagang Formation source rocks can be summarized as the hypertrophic lake with high burial efficiency and burial productivity, the eutrophic lake with medium burial efficiency and burial productivity, and the eutrophic lake with low burial efficiency and burial productivity.
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Key words:
- paleo-productivity /
- burial efficiency /
- burial productivity /
- geobiological model /
- Weixinan Sag
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表 1 涠西南凹陷流沙港组烃源岩主峰碳、姥鲛烷/植烷、CPI、w(TOC)统计
Table 1. Statistics of the main peak carbon, pristane/phytane, CPI、w(TOC) of the Liushagang Formation source rock in Weixinan Sag
烃源岩层段 主峰碳 姥鲛烷/植烷 CPI/% w(TOC)/% 流一段 C29~C32 区间值 2.47~3.2 0.92~2.34 1.13~2.84 平均值 2.86 1.48 2.07 流二段 C17~C 19 区间值 1.18~2.41 0.97~3.27 1.81~3.28 平均值 1.98 1.67 3.06 流三段 C19~C 31 区间值 2.08~3.54 0.99~3.63 1.00~2.55 平均值 2.9 1.41 1.95 表 2 涠西南凹陷流沙港组湖泊古生产力、有机质埋藏效率、有机碳埋藏生产力计算参数、计算结果一览
Table 2. Calculation parameters and results of the lake paleo-productivity, organic matter burial efficiency and organic carbon burial productivity of the Liushagang Formation in Weixinan Sag
井位 洼
陷层
段沉积速率/
(m·Ma-1)w(TOC)/
%孔隙度φ/
%沉积物密度ρ/
(g·cm-3)湖泊古生产力/
(g·m-2·
a-1)湖泊古生产
力平均值/
(g·m-2·
a-1)有机质
埋藏
效率/%有机质埋
藏效率平均值/
%有机碳埋藏
生产力/
(g·m-2·
a-1)有机碳埋
藏生产力
平均值/
(g·m-2·
a-1)A7-1 A
次
洼流一
段82.70 1.79 0.11 2.47 785 944 17.78 15.64 140 147 A1-2 35.56 2.34 0.18 2.43 995 9.21 92 A1-1 102.34 2.69 0.15 2.35 1 053 19.94 210 A2 流二
段154.84 2.60 0.12 2.47 1 069 927 24.15 24.61 258 220 A7-1 90.40 2.30 0.09 2.51 1 040 18.68 194 A1-1 303.46 1.80 0.12 2.37 673 30.99 208 A2 流三
段86.13 2.32 0.11 2.49 1 023 890 18.19 15.89 186 144 A1-1 54.71 1.71 0.10 2.38 756 13.58 103 B3-1B B
次
洼流
一
段113.05 3.13 0.16 2.43 1 242 761 20.96 23.00 260 173 B1-2 165.00 2.45 0.10 2.52 1 045 24.80 259 B2-1 156.78 0.73 0.13 2.46 297 24.28 72 B2-2 125.10 1.14 0.14 2.44 461 21.98 101 B3-1 流
二
段273.16 3.39 0.18 2.47 1 240 1 070 29.92 32.11 371 346 B3-1B 539.47 3.41 0.11 2.47 1 279 36.83 471 B1-2 320.00 2.41 0.08 2.47 975 31.53 308 B2-1 282.00 1.67 0.11 2.51 673 30.24 2.30 B2-2 335.73 2.98 0.11 2.51 1 183 32.01 379 B3-1 流
三
段46.97 2.23 0.15 2.49 987 1 056 12.03 7.59 119 80 B2-1 27.71 2.45 0.10 2.54 1 220 6.67 81 B2-2 21.47 1.9 0.11 2.55 962 4.08 39 C7-1 C
次
洼流
一
段266.94 2.52 0.15 2.34 908 792 29.68 31.70 269 249 C8-1 319.09 2.73 0.14 2.43 1 018 31.50 320 C4-1 368.97 1.69 0.14 2.43 623 32.97 205 C4-3 357.14 1.65 0.14 2.47 620 32.64 202 C8-1 流
二
段282.95 3.12 0.12 2.47 1 220 1 022 30.28 29.93 369 308 C4-1 224.43 1.94 0.12 2.47 773 27.92 216 C4-3 322.06 2.7 0.11 2.50 1 0.10 31.59 338 C7-1 流
三
段38.52 1.34 0.12 2.48 619 762 10.02 6.42 62 34 C8-1 20.41 2.63 0.11 2.49 1 306 3.57 47 C4-1 16.10 1.96 0.12 2.49 982 1.16 11 C4-3 42.22 0.30 0.10 2.51 143 10.95 16 -
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