Geochemical Characteristics and Oil-Source Rock Correlation of Crude Oil in Wushi Sag, Beibuwan Basin, South China Sea
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摘要: 为了探究乌石凹陷的油气来源,对原油及烃源岩样品进行地球化学分析.研究结果表明,乌石凹陷原油可分为3类:Ⅰ类原油分布在深洼带的涠洲组和流沙港组一段储层,成熟度整体偏高,C19三环萜烷、C24四环萜烷、奥利烷丰度均相对较高,C23三环萜烷、C30 4-甲基甾烷丰度相对较低,体现出水生低等生物与陆源高等植物双重输入的特征.Ⅱ类和Ⅲ类原油主要分布在反转构造带和缓坡带的流沙港组二段、三段储层中,成熟度整体低于Ⅰ类原油,C19三环萜烷、C24四环萜烷、奥利烷丰度均较低,C23三环萜烷、C30 4-甲基甾烷丰度相对较高,表明其母质来源以低等水生生物为主.相对Ⅱ类原油,Ⅲ类原油的Pr/Ph值更低,全油稳定碳同位素偏轻.油源对比表明,Ⅰ类原油主要来源于流沙港组二上亚段烃源岩;Ⅱ类及Ⅲ类原油均来自流沙港组二下亚段烃源岩.Abstract: To study the genetic relationship between oil and source rock in Wushi sag, geochemical analyses of crude oil and source rock samples were carried out in this paper. The results show that crude oils in Wushi sag can be classified into three groups: group Ⅰ crude oil is distributed in the Weizhou Formation and 1-member of Liushagang Formation reservoir in the deep sag belt. The maturity of this crude oil is relatively high, and the abundances of C19 tricyclic terpenes, C24 tetracyclic terpenes, and oleanane are relatively high, while the abundances of C23 tricyclic terpenes and C30 4-methylsteranes are relatively low, which reflects the characteristics of double input of lower aquatic organisms and terrigenous higher plants. Group Ⅱ and group Ⅲ crude oil is mainly distributed in the 2-member and 3-member of the Liushagang Formation reservoir in the reversal tectonic belt and gentle slope belt, and their maturity is overall lower than that of group Ⅰ crude oil. The abundances of C19 tricyclic terpanes, C24 tetracyclic terpanes, and oleanane of these oils are relatively low, and the abundances of C23 tricyclic terpanes and 4-methylsteranes are relatively high, indicating their parent material is mainly from lower aquatic organisms. The difference between the two groups of crude oils mainly lies in the Pr/Ph value and the stable carbon isotope characteristics of whole oil. Compared with group Ⅱ crude oil, group Ⅲ crude oil has a lower Pr/Ph value and lighter stable carbon isotope. The oil-source rock correlation shows that the group Ⅰ crude oil mainly comes from the upper sub-member of 2-member of Liushagang Formation source rock. Both group Ⅱ and group Ⅲ oils are derived from the lower sub-member of the 2-member of Liushagang Formation source rock.
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表 1 乌石凹陷不同构造带原油物性及族组分统计
Table 1. Statistical data of physical properties and group components of crude oil in different structural belts of Wushi sag
构造带 密度(g/cm3) 粘度(mPa·s) 含硫量(%) 含蜡量(%) 胶质+沥青质(%) 饱和烃(%) 芳烃(%) 非烃+沥青质(%) 原油类型 深洼带 0.797~0.862 1.30~16.09 0.03~0.25 6.93~21.1 2.38~6.90 72.72~88.68 7.66~18.55 3.06~11.95 轻质油 0.828(16) 4.416(16) 0.1(16) 14.068(16) 4.66(14) 80.66(16) 12.66(16) 6.68(16) 反转构造带 0.806~0.850 3.31~8.96 0.03~0.14 11.7~19.1 1.70~6.91 75.92~86.16 3.86~14.91 3.94~12.77 0.822(8) 5.09(8) 0.06(8) 9.91(8) 3.26(7) 81.32(8) 11.08(8) 7.60(8) 缓坡带 0.852~0.935 14.31~491.1 0.14~0.35 4.83~31.9 4.68~32.7 46.83~79.35 11.80~28.07 8.67~32.62 中质‒重质油 0.899(13) 168.31(11) 0.23(12) 16.1(13) 15.33(13) 63.4(13) 18.8(13) 17.8(13) 注:0.797~0.862分别表示最小值、最大值;0.828(16)分别表示平均值、样品数. 表 2 乌石凹陷不同构造带原油生物标志物参数及稳定碳同位素值
Table 2. Biomarker parameters and stable carbon isotopes of crude oil in different structural belts of Wushi sag
构造带 井号 储层 Pr/Ph CPI C19TT/C23TT C24TeT/C23TT Ts/(Ts+Tm) C29Ts/(C29Ts+C29H) Ol/C30H Ga/C30H 4-MSI δ13C全油(‰) 原油族群 深洼带 WA71 流一段 2.10 1.08 1.36 1.38 0.77 0.59 0.12 0.09 0.29 ‒25.98 Ⅰ WA73 涠洲组 2.38 1.08 0.69 0.77 0.64 0.43 0.09 0.03 0.35 ‒26.56 Ⅰ WA92 流一段 2.53 1.11 1.16 0.86 0.79 0.55 0.18 0.09 0.41 ‒26.04 Ⅰ WA82 流一段 2.61 1.14 0.83 1.45 0.79 0.56 0.10 0.07 0.62 ‒27.25 Ⅰ WA14 涠洲组 2.72 1.10 0.71 0.85 0.62 0.32 0.11 0.05 0.37 ‒26.26 Ⅰ WA51 流一段 2.84 1.18 0.97 1.89 0.62 0.37 0.11 0.03 0.57 ‒27.72 Ⅰ WA52 流一段 2.28 1.12 0.89 1.55 0.66 0.38 0.11 0.07 0.66 ‒27.57 Ⅰ WA53 流一段 2.99 1.16 0.96 1.65 0.68 0.40 0.14 0.07 0.56 ‒27.62 Ⅰ 反转构造带 WB21 流三段 1.87 1.03 0.61 0.35 0.67 0.38 0.09 0.08 0.97 ‒22.97 Ⅱ WB22 流三段 1.97 1.07 0.57 0.40 0.59 0.38 0.07 0.05 1.01 ‒23.02 Ⅱ WB28 流三段 2.10 1.08 0.49 0.45 0.63 0.40 0.07 0.04 0.99 ‒23.96 Ⅱ WB29 流三段 1.75 1.12 0.56 0.33 0.60 0.36 0.06 0.06 1.04 ‒23.80 Ⅱ 缓坡带北部 WC16 流二段 1.60 1.12 0.34 0.52 0.60 0.30 0.04 0.04 1.56 ‒23.53 Ⅱ WC92 流二段 1.77 1.15 0.45 0.53 0.51 0.26 0.06 0.04 1.12 ‒24.18 Ⅱ WC93 流二段 1.91 1.15 0.47 0.79 0.46 0.25 0.05 0.06 0.98 ‒23.43 Ⅱ WC94 流二段 1.95 1.11 0.51 0.70 0.52 0.29 0.07 0.03 1.09 ‒24.52 Ⅱ WC95 流二段 1.97 1.10 0.60 0.53 0.58 0.31 0.09 0.04 1.05 ‒24.08 Ⅱ 缓坡带南部 WD93 涠洲组 0.94 1.08 0.16 0.53 0.62 0.34 0.07 0.03 0.91 ‒27.24 Ⅲ WD93 流一段 1.26 1.06 0.16 0.57 0.64 0.35 0.06 0.04 0.83 ‒27.38 Ⅲ WD17 流二段 0.95 1.08 0.22 0.51 0.55 0.28 0.08 0.03 1.09 ‒26.19 Ⅲ WD81 流二段 1.30 1.16 0.18 0.66 0.47 0.30 0.05 0.03 0.98 ‒26.34 Ⅲ 表 3 乌石凹陷流沙港组烃源岩总有机碳含量、热解参数、镜质体反射率统计
Table 3. Total organic carbon content, pyrolysis parameters and vitrinite reflectance of source rocks in Liushagang Formation, Wushi sag
烃源岩层 总有机碳(%) 产油潜率 S1+S2(mg/g) 热解最大峰温 Tmax(℃) 氢指数HI(mg/g) 镜质体反射率 Ro(%) 流一段 0.52~4.04 0.82~17.74 426~450 104~360 0.52~0.73 1.71(27) 5.06 (27) 438 (27) 250 (27) 流二上亚段 1.00~4.45 3.00~24.91 430~449 231~579 0.47~0.89 2.30 (68) 10.52 (68) 440 (68) 396 (68) 流二下亚段 2.56~11.8 11.58~81.4 430~452 311~796 0.49~0.88 5.50 (29) 31.08 (29) 440 (29) 510 (29) 流三段 0.50~2.72 1.38~12.18 434~456 181~505 0.46~0.92 1.61 (30) 6.24 (30) 445 (30) 342 (30) 注:1.71(27)分别表示平均值、样品数. 表 4 乌石凹陷流沙港组烃源岩生物标志物参数及干酪根稳定碳同位素统计
Table 4. Biomarker parameters and stable carbon isotopes of source rock of Liushagang Formation in Wushi sag
井号 烃源岩层 Pr/Ph Ga/C30H Ol/C30H C19TT/C23TT C24TeT/C23TT 4-MSI δ13C干酪根(‰) WA51 流一段 2.40 0.05 0.11 0.87 1.23 0.22 ‒26.96 WA51 流一段 2.53 0.07 0.17 0.66 1.56 0.32 ‒27.67 WA53 流一段 4.12 0.07 0.15 1.14 2.41 0.46 ‒27.56 WA71 流一段 2.46 0.06 0.08 1.19 1.70 0.53 ‒27.20 WA25 流二上亚段 3.14 0.01 0.21 1.48 1.47 0.27 ‒27.20 WA51 流二上亚段 2.66 0.06 0.12 0.75 2.13 0.52 ‒26.99 WA73 流二上亚段 2.27 0.14 0.22 1.55 1.67 0.27 ‒27.10 WA91 流二上亚段 4.48 0.09 0.66 2.40 1.73 0.61 ‒26.68 WA92 流二上亚段 2.63 0.18 0.12 1.11 1.55 0.46 ‒27.46 WB11 流二下亚段 1.93 0.11 0.08 0.63 0.55 0.89 ‒26.85 WB22 流二下亚段 1.74 0.01 0.02 0.15 0.96 1.09 ‒25.80 WB22 流二下亚段 1.62 0.03 0.06 0.21 0.11 1.60 ‒23.50 WC61 流二下亚段 1.88 0.05 0.04 0.17 0.98 0.77 ‒27.45 WC91 流二下亚段 1.95 0.03 0.05 0.16 0.66 1.02 ‒23.45 WB24 流三段 2.04 0.04 0.07 0.54 1.28 0.83 ‒26.15 WC41 流三段 2.87 0.06 0.10 0.89 0.97 0.75 ‒25.77 WC41 流三段 2.66 0.09 0.04 0.92 1.08 0.77 ‒25.54 WC91 流三段 1.99 0.06 0.05 1.25 1.11 0.91 ‒25.21 -
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