羌塘北缘开心岭—乌丽冻土区水溶烃组分及甲烷碳、氢同位素特征研究

doi:10.19657/j.geoscience.1000-8527.2019.06.16

摘要/Abstract

摘要：

羌塘北缘开心岭—乌丽冻土区沿隐伏断层发育多处冷泉含水溶解烷烃,采用水溶烃组分和甲烷的稳定碳、氢同位素特征对其成因开展了分析研究。结果表明,开心岭—乌丽冻土区水溶烃组分中甲烷含量比例高达99.83%~99.96%,同时伴随有少量乙烷、丙烷,另含微量的乙烯和丙烯。开心岭一带水溶烃甲烷δ¹³C_PDB值介于-46.5‰~-55.1‰,δD_VSMOW值为-281.0‰~-342.0‰;乌丽一带水溶烃甲烷δ¹³C_PDB值介于-47.8‰~-58.9‰,δD_VSMOW值为-339.0‰~-346.0‰,指示水溶烃甲烷为有机成因,但气源较复杂,利用δ¹³C_CH₄-δD_CH₄、δ¹³C₁-C₁/(C₂+C₃)等成因图解判别,得出甲烷主要属微生物气,次之为热解成因气,混有少量原油伴生气。推断甲烷主要为有机质在微生物作用下分解的烃类气体或次生生物气,与晚二叠世那益雄组含煤烃源岩有关,气源条件暗示该地区冻土带200~500 m深度内有利于微生物成因气为主的甲烷天然气水合物形成。

关键词: 水溶烃组分, 甲烷碳、氢同位素, 成因, 天然气水合物, 开心岭—乌丽冻土区, 羌塘北缘

Abstract:

Several cold springs bear water soluble alkanes along the concealed faults in the Kaixinling-Wuli permafrost region on the northern margin of Qiangtang area. Based on analyses of the water soluble hydrocarbon components, stable carbon-hydrogen isotopes of methane, the genesis of the water soluble alkanes was studied. The results showed that the methane (CH₄) volume fraction ratio in the water soluble hydrocarbon components reached as high as 99.83%-99.96% in the Kaixinling-Wuli permafrost region, accompanied by a small amount of ethane (C₂H₆), propane (C₃H₈), trace amounts of ethylene (C₂H₄) and propylene (C₃H₆). In water soluble hydrocarbon, methane δ ¹³C_PDB values range in -46.5‰ to -55.1‰ with δD_VSMOW values of -281.0‰ to -342.0‰ in the Kaixinling permafrost area. In water soluble hydrocarbon, methane δ ¹³C_PDB values are -47.8‰ to -58.9‰, and δD_VSMOW values are -339.0‰ to -346.0‰ in the Wuli permafrost area. These features indicate that in water soluble hydrocarbon, methane is of organic origin, but the gas origin is relatively complex. Methane mainly belongs to microbial gas, secondarily pyrolysis gas, mixed with a small amount of oil-associated gas, discriminated by the genesis diagrams of δ¹³C_CH₄-δD_CH₄ vs. δD_CH₄ and δ¹³C₁ vs. C₁/ (C₂+C₃). It is inferred that methane is mainly originated from the hydrocarbon gases or sub-microbial gases, decomposed from the organic matters under the action of microorganisms, in connection with the coal-bearing hydrocarbon source rocks in Nayixiong Formation of the Late Permian. Gas condition implies that at depths from 200 to 500 meters, it is conducive to form methane hydrate with microbial gas in this permafrost region.

Key words: water soluble hydrocarbon component, methane carbon-hydrogen isotope, genesis, gas hydrate, Kaixinling-Wuli permafrost region, northern margin of Qiangtang area

中图分类号:

王进寿, 卢振权, 王富春, 陈静, 薛万文, 张志清. 羌塘北缘开心岭—乌丽冻土区水溶烃组分及甲烷碳、氢同位素特征研究[J]. 现代地质, 2019, 33(06): 1306-1313.

WANG Jinshou, LU Zhenquan, WANG Fuchun, CHEN Jing, XUE Wanwen, ZHANG Zhiqing. Study on Features of Water Soluble Hydrocarbon Components and Carbon-hydrogen Isotopes of Methane in the Kaixinling-Wuli Permafrost Region on the Northern Margin of Qiangtang Area[J]. Geoscience, 2019, 33(06): 1306-1313.

图/表 7

图1 开心岭—乌丽冻土区地质简图 1.全新统;2.晚更新统;3.渐新统—中新统;4.古近系;5.下白垩统;6.上白垩统;7.上三叠统火山岩建造;8.上三叠统碳酸盐岩建造;9.上三叠统碎屑岩建造;10.上二叠统碳酸盐岩建造;11.上二叠统含煤碎屑岩建造;12.中二叠统礁灰岩;13.下二叠统火山岩夹碎屑岩建造;14.地质界线;15.角度不整合界线;16.主要断层;17.隐伏断层;18.三级构造分界线;19.烃源岩;20.煤矿点;21.水流方向;22.查错断陷;23.乌丽断隆;24.沱沱河断陷;25.开心岭断隆;26.水溶烃采样点及编号;27.地体结合带及编号。

Fig.1 Geological diagram of Kaixinling-Wuli permafrost region

表1 开心岭—乌丽冻土区冷泉水溶烃烷烃气成分分析结果

Table 1 Results of water soluble hydrocarbon alkane gas composition in frozen cold spring from Kaixinling-Wuli permafrost region

样号	采样地	烃类气体成分和含量/(μL/L)						碳数比例/%
样号	采样地	CH₄	C₂H₆	C₂H₄	C₃H₈	C₃H₆	总烃	C₁	C₂	C₃
D603S3	乌丽	629.16	0.25	0.08	0.00	0.10	629.60	99.93	0.05	0.02
D767S1^*	乌丽	834.23	0.15	0.04	0.02	0.13	834.58	99.96	0.02	0.02
D773S3^*	乌丽	1 113.21	1.38	0.17	0.06	0.13	1 114.95	99.84	0.14	0.02
D774S3	开心岭	583.22	0.79	0.17	0.01	0.04	584.24	99.83	0.17	0.01
D777S2	开心岭	743.76	0.18	0.05	0.02	0.04	744.05	99.96	0.03	0.01
D778S1	开心岭	667.91	0.19	0.04	0.02	0.04	668.20	99.96	0.03	0.01
D780S6	开心岭	342.23	0.08	0.02	0.01	0.02	342.36	99.96	0.03	0.01
平均值		701.96	0.43	0.08	0.02	0.07	702.57	99.92	0.07	0.01

表2 开心岭—乌丽冻土区冷泉水水溶烃烷烃气碳、氢同位素测试结果

Table 2 Results of carbon, hydrogen isotope tests of water soluble hydrocarbon gas from frozen cold spring

样号	δ¹³C_PDB/‰			δ $D V SMOW$ /‰		C₁/ (C₂+C₃)
样号	CH₄	C₂H₆	C₃H₈	H₂	CH₄	C₁/ (C₂+C₃)
D603S3	-58.9	未检出	未检出	未检出	-339.0	1 463
D767S1	-55.6	未检出	未检出	未检出	-342.0	2 453
D773S3	-47.8	未检出	未检出	未检出	-346.0	640
D774S3	-48.4	未检出	未检出	未检出	-342.0	578
D777S2	-53.6	未检出	未检出	未检出	-340.0	2 565
D778S1	-55.1	未检出	未检出	未检出	-334.0	2 303
D780S6	-46.5	未检出	未检出	未检出	-281.0	2 633
平均值	-52.3				-331.9	1 805

表2 开心岭—乌丽冻土区冷泉水水溶烃烷烃气碳、氢同位素测试结果

Table 2 Results of carbon, hydrogen isotope tests of water soluble hydrocarbon gas from frozen cold spring

样号	δ¹³C_PDB/‰			δ $D V SMOW$ /‰		C₁/ (C₂+C₃)
样号	CH₄	C₂H₆	C₃H₈	H₂	CH₄	C₁/ (C₂+C₃)
D603S3	-58.9	未检出	未检出	未检出	-339.0	1 463
D767S1	-55.6	未检出	未检出	未检出	-342.0	2 453
D773S3	-47.8	未检出	未检出	未检出	-346.0	640
D774S3	-48.4	未检出	未检出	未检出	-342.0	578
D777S2	-53.6	未检出	未检出	未检出	-340.0	2 565
D778S1	-55.1	未检出	未检出	未检出	-334.0	2 303
D780S6	-46.5	未检出	未检出	未检出	-281.0	2 633
平均值	-52.3				-331.9	1 805

图2 水溶烃甲烷碳同位素与C1/(C2+C3)关系图解(底图据文献[33,34])

Fig.2 Relationships of methane carbon isotope vs.C1/(C2+C3) of water soluble hydrocarbon (after references[33-34] )

图3 水溶烃烃类气体成因δ13CCH4-δDCH4图解(底图据文献[29,35])

Fig.3 Genetic diagram of water soluble hydrocarbon gas (after reference [29,35] )

图4 水溶烃甲烷碳同位素与组分关系图解(底图据文献[34]) Ⅰ1.生物气;Ⅰ2.生物和亚生物混合气;Ⅰ3.亚生物气;Ⅱ1.原油伴生气;Ⅱ2.油型裂解气;Ⅲ1.油型裂解和煤成混合气;Ⅲ2.凝析油伴生和煤成混合气;Ⅳ.煤成气;Ⅴ1.无机气;Ⅴ2.无机和煤成混合气。

Fig.4 Diagram of carbon isotope and composition of water soluble hydrocarbon methane (after reference [34]])

图5 水溶烃气体δ13CCH4-δDCH4成因判别图解(底图据文献[35]) A.生物成因气;B.生物与热催化过渡气;C.石油伴生气;D.凝析油伴生气;E.煤型气;F.海相过熟气。

Fig.5 δ13CCH4-δDCH4 genetic discrimination diagram of water soluble hydrocarbon gas (after reference [35] )

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