Mechanisms of Shale Gas Generation from Typically Organic-Rich Marine Shales
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摘要: 目前页岩生烃的评价体系主要停留在静态条件下，忽略了成烃的动态过程，不能正确评价页岩原始的生烃潜力.采用生烃动力学模拟实验方法，分别对一个相对低成熟的典型海相富有机质页岩及其干酪根样品开展封闭体系和半开放体系下的人工熟化，并对熟化后的两个系列样品进行黄金管生气动力学模拟实验.对裂解产物中气态烃化合物、轻烃类化合物以及碳同位素开展了定量分析，结果表明，甲烷生成过程被划分为4个阶段，即生油（小于1.0% EayRo）、凝析油生成（1.0%~1.% EayRo）、湿气生成（1.%~2.2% EayRo）和干气生成阶段（大于2.2% EayRo）；页岩中甲烷的最大产率主要来自干酪根的初次裂解（占22.7%）、可排沥青（占7.6%）和残余沥青（占19.6%）的二次裂解；经过早期排烃作用的页岩样品仍有大量的可溶沥青，在高-过成熟阶段其可以与干酪根、不可溶沥青相互作用，成为晚期主要的页岩生气母质.Abstract: The evaluation system of shale hydrocarbon generation is mainly addressed in the static condition at present, ignoring the dynamic process of hydrocarbon generation. Consequently, the original hydrocarbon generation potential of the shale cannot be properly evaluated. In this study, a typically marine shale sample with relatively low maturity and its kerogen were artificially matured by a half closed pyrolysis system and a closed pyrolysis system. Samples with different maturity levels obtained from the two systems were then pyrolyzed for gas generation in sealed gold tubes (i. e., pyrolysis experiment in sealed gold tubes). The quantitative analysis based on the products of C1-C5 gases, C6-C12 light hydrocarbons and carbon isotopes of gases from the simulation experiments indicates that the generation process of methane in kerogen can be divided into four stages:oil-generation ( < 1.0% EasyRo), condensate-generation (1.0%-1.5% EasyRo), wet-gas-generation (1.5%-2.2% EasyRo) and dry-gas-stage (>2.2% EasyRo). Kerogen, expelled bitumen and residue bitumen contributes 22.7%, 57.6% and 19.6% of maximum yield of methane in shale, respectively. Abundant soluble bitumen still exists in the shale matrix after the hydrocarbon expulsion, which becomes the major source of shale gas by interacting with kerogen and insoluble bitumen at high maturity levels.
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Key words:
- organic-rich shale /
- kinetics of hydrocarbon generation /
- hydrocarbon expulsion /
- kerogen /
- bitumen /
- geochemistry
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图 3 黄金管热模拟实验中全岩与干酪根的C6~C12轻烃产率
a.正构烷烃；b.异构烷烃；c.环烷烃；d.芳烃
Fig. 3. Yield curves of C6-C12 light hydrocarbons generated from the organic-rich shale and kerogen by pyrolysis experiments in sealed gold tubes
图 1 黄金管热模拟实验中全岩与干酪根的气态烃产率
a.甲烷；b.乙烷；c.丙烷
Fig. 1. Yield curves of gaseous hydrocarbons from the organic-rich shale (whole rock) and kerogen by pyrolysis experiments in sealed gold tubes
图 2 黄金管热模拟实验中气态烃的碳同位素组成
a.甲烷；b.乙烷；c.丙烷
Fig. 2. Carbon isotope composition of gaseous hydrocarbons by pyrolysis experiments in sealed gold tubes
图 4 半开放体系下页岩熟化过程中气态烃产率(a)与碳同位素δ13C (b)
C1=CH4；C2=C2H6；C3=C3H8
Fig. 4. Yield (a) and carbon isotope curves (b) of gaseous hydrocarbons generated from artificially matured samples in a half closed pyrolysis system
图 5 半开放体系下模拟实验样品在黄金管生烃模拟中的气态烃产率
a.甲烷；b.乙烷；c.丙烷
Fig. 5. Yield curves of gaseous hydrocarbons generated from artificially maturated shale samples by pyrolysis experiments in sealed gold tubes
图 6 半开放体系下模拟实验样品在黄金管生烃模拟中的碳同位素变化特征
a.甲烷；b.乙烷；c.CO2
Fig. 6. Carbon isotope curves of artificially maturated shale samples by pyrolysis experiments in sealed gold tubes
图 7 干酪根样品在热成熟过程中的气态烃产率
a.甲烷；b.乙烷；c.丙烷
Fig. 7. Yield curves of gaseous hydrocarbons generated from artificially maturated kerogen samples
图 8 热模拟实验中不同成熟度干酪根气态烃产率
a.甲烷；b.乙烷；c.丙烷
Fig. 8. Yield curves of gaseous hydrocarbons of kerogen samples with different maturity by pyrolysis experiments
图 9 不同成熟度干酪根的碳同位素特征
a.甲烷；b.乙烷；c.丙烷
Fig. 9. Carbon isotope curves of kerogen samples with different maturity
图 10 干酪根样品K1在热成熟过程中产生甲烷的来源
Fig. 10. Possible origins of methane during the maturation of original kerogen sample K1
图 11 页岩样品S1在热成熟过程中产生甲烷的来源
Fig. 11. Possible origins of methane during the maturation of shale sample S1
图 12 黄金管封闭体系中不同热模拟样品的甲烷产率对比
Fig. 12. Yield curves of methane generated from different samples in an anhydrous closed pyrolysis system
图 13 黄金管封闭体系中不同热模拟样品的甲烷产率曲线
图a、b中K′成熟度分别为0.7% EasyRo、1.0% EasyRo
Fig. 13. Yield curves of methane generated from samples by pyrolysis experiments in sealed gold tubes
图 14 黄金管封闭体系中样品的气态重烃(C2~C5)产率曲线
Fig. 14. Yield curves of gaseous hydrocarbons (C2-C5) generated from samples by pyrolysis experiments in sealed gold tubes
表 1 封闭体系模拟样品的成熟度与TOC含量
Table 1. Maturity and TOC content of the whole rock and kerogen samples obtained from the closed pyrolysis system
样品代号 样品类型 成熟度(%) TOC(%) R 全岩(未抽提) 0.57 6.78 K0 干酪根(未抽提) 0.57 67.12 K1 干酪根(抽提过) 0.57 68.12 K2 干酪根(抽提过) 0.8 69.07 K3 干酪根(抽提过) 1.0 69.92 K4 干酪根(抽提过) 1.3 72.56 
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表 2 半封闭体系人工熟化实验条件与样品基本参数
Table 2. Experimental condition of artificially matured samples and basic parameters of samples with different maturity level in a half closed pyrolysis system
样品代号 成熟度(%) 温度(℃) 压力(MPa) 时间(h) 残余固体TOC(%) S1 0.7 300 50 66 4.55 S2 1.0 343 50 72 5.07 S3 1.3 370 50 65 3.56 S4 2.0 415 50 72 3.42 S5 2.5 442 50 72 2.86 S6 3.0 467 50 72 2.99
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