中国南方海相页岩气中氮气成因及其指示意义

doi:10.11743/ogg20190603

摘要/Abstract

摘要： 中国南方海相页岩气资源丰富，部分页岩气气体组分中氮气（N₂）含量所占比例较大。依据川西南地区、长江三峡地区和贵州省岑巩地区页岩气地质、地球化学特征，结合黄金管热模拟实验，系统研究了页岩气中N₂的成因及其指示意义。结果表明，页岩气中N₂为典型壳源有机成因，高氮页岩气主要来源于干酪根的晚期热解，高氮含量是早期生成的原油裂解气未运聚成藏或成藏后受到破坏的体现。因此，页岩气资源量有限，主要证据有以下3个方面。首先，页岩中的干酪根类型是典型腐泥型，保存条件良好的情况下页岩气应以原油裂解气为主，但页岩气类型的识别表明高N₂含量的页岩气属干酪根热解气或原油裂解气和干酪根热解气的混合气。其次，通过对寒武系来源的原油样品进行黄金管热模拟实验，发现高氮页岩气碳同位素值比热模拟实验测得的原油二次裂解气碳同位素值明显偏重。最后，随着有机质演化程度的升高，N₂含量升高，而且保存条件较好的页岩气井，氮气含量较低，含气性较好，氮气含量对保存条件具有指示意义。

关键词: 氮气, 壳源有机成因, 干酪根热解, 黄金管热模拟实验, 海相页岩气, 中国南方

Abstract: Marine shale gas resources are abundant in Southern China,and nitrogen (N₂) content accounts for a larger proportion in the composition of some shale gas.Analytical data of the geological and geochemical characteristics of shale gas in southeastern Sichuan,Three Gorges Region of Yangtze River,and Cengong in Guizhou Province,and the thermal simulation experiment of gold tube,are integrated in the study of the origin of nitrogen in shale gas and its indicative significance.The results show that N₂ in shale gas is typically of organic crustal origin,shale gas with higher N₂ content is mainly derived from the late pyrolysis of kerogen,and the higher content of N₂ is just an embodiment of the early gene-ration of crude oil cracking gas under no migration and accumulation or under destruction after accumulation.Therefore,the fact that shale gas resources are limited may be verified by the following three aspects.First of all,the shale kerogen is typically of saprolite.Under good preservation conditions,the shale gas is supposed to be dominated by crude oil cracking gas.However,the identification of shale gas types indicates that the shale gas with higher N₂ content belongs to the kerogen pyrolysis gas or a mixture of crude oil cracking gas and kerogen pyrolysis gas.Secondly,the carbon isotope value of shale gas with higher N₂ content is significantly heavier than that of the secondary cracking gas of crude oil obtained by thermal simulation experiment,through the gold tube thermal simulation experiment of the crude oil samples taken from the Cambrian.Finally,with the growth of organic matter evolution,the N₂ content keeps increasing,and the shale gas wells with better preservation conditions are usually lower in N₂ content but better in gas-bearing properties.Therefore,the N₂ content is of indicative significance to the preservation conditions.

Key words: nitrogen (N₂), organic crustal origin, kerogen pyrolysis, gold tube thermal simulation experiment, marine shale gas, Southern China

中图分类号:

TE122.1

苏越,王伟明,李吉君,等. 中国南方海相页岩气中氮气成因及其指示意义[J]. 石油与天然气地质, 2019, 40(6): 1185-1196. doi: 10.11743/ogg20190603 Su Yue,Wang Weiming,Li Jijun,et al. Origin of nitrogen in marine shale gas in Southern China and its significance as an indicator[J]. Oil & Gas Geology, 2019, 40(6): 1185-1196. doi: 10.11743/ogg20190603

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