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烷烃碳同位素对页岩含气性的指示意义 ——以四川盆地及周缘龙马溪组为例

作    者:廖 芸1,2,郭艳琴1,2 ,陈志鹏1,2 ,王 芳3 ,王高成4 ,邹 辰4 ,马 瑶1,2 ,陈志鹏1,2 ,王 芳3 ,王高成4 ,邹 辰4 ,马 瑶1,2
单    位:1 西安石油大学地球科学与工程学院;2 陕西省油气成藏地质学重点实验室; 3 中国石油长庆油田勘探开发研究院;4 中国石油浙江油田公司
基金项目:本文受国家自然科学基金“热水沉积过程中热流体演化对有机质富集的控制作用”等资助
摘    要:
以四川盆地及周缘龙马溪组为例,分析了烷烃碳同位素平面分布特征以及倒转情况,定量研究了烷烃碳同 位素值与热演化程度、埋藏深度及含气量之间的关系,并探讨了造成不同区块烷烃碳同位素倒转程度差异的主要 原因。结果表明:①龙马溪组页岩气组分具有典型的干气特征:CH4含量介于 95.32%~99.59%,平均为 98.44%; C2H6含量较少,介于 0.09%~0.74%,平均为 0.52%;C3H8含量普遍很低。②烷烃碳同位素表现为自盆地边缘向盆地 中心逐渐变轻的特征,δ13C1值介于-36.9‰~-26.7‰,平均为-30.27‰;δ13C2值介于-42.8‰~-31‰,平均为-34.9‰; δ13C3值介于-50.5‰~-33.1‰,平均为-37.28‰。③整体上,四川盆地及周缘龙马溪组页岩气烷烃碳同位素具有完全 倒转(δ13C1>δ13C2>δ13C3)的特征,页岩气成藏过程中干酪根裂解气与滞留烃裂解气的混合可能是导致其烷烃碳同位 素发生倒转的主要原因。④同位素定量分馏模型显示滞留烃裂解气在页岩气中的占比多大于60%,指示两种裂解气 混合比不同是造成烷烃碳同位素倒转程度差异的主要原因;整体上,随滞留烃裂解气含量的增多,δ13C2值减小,烷烃 碳同位素倒转程度增大,页岩的含气量也逐渐增加。
关键词:碳同位素倒转;滞留烃裂解;页岩含气量;龙马溪组;四川盆地

Indicative significance of alkane carbon isotope to shale gas content: taking Longmaxi Formation in Sichuan Basin and its surrounding areas as example

Author's Name: LIAO Yun, GUO Yanqin, CHEN Zhipeng, WANG Fang, WANG Gaocheng, ZOU Chen, MA Yao
Institution: 
Abstract:
Taking Longmaxi Formation in Sichuan Basin and its surrounding areas as an example, this paper analyzes the plane distribution characteristics and reversal of alkane carbon isotopes, quantitatively studies the relationship between alkane carbon isotope value and thermal evolution degree, burial depth and gas content, and also discusses the main reasons for the difference of alkane carbon isotope reversal degree in different blocks. The results show that: (1) Longmaxi shale gas has typical dry gas characteristics: the content of CH4 ranges from 95.32% to 99.59%, with an average of 98.44%; the content of C2H6 is relatively low, ranging from 0.09% to 0.74%, with an average of 0.52%; the content of C3H8 is generally very low. (2) The carbon isotopes of alkanes gradually lighten from the edge to the center of the basin, with δ13C1 value ranging from -36.9‰ to -26.7 ‰ with an average of -30.27 ‰, δ13C2 value ranging from -42.8‰ to -31‰ with an average of -34.9 ‰, and δ13C3 value ranging from -50.5‰ to -33.1‰ with an average of -37.28 ‰. (3)The Longmaxi shale gas is characterized by complete reversal of alkane carbon isotopes (δ13C1>δ13C2>δ13C3), which is mainly caused by the mixing of kerogen pyrolysis gas and residue hydrocarbon pyrolysis gas. (4) The isotope quantitative fractionation model shows that the proportion of residue hydrocarbon pyrolysis gas in shale gas is more than 60% in most blocks. It indicates that the difference of mixing ratio of two kinds gas is the main reason for the difference of alkane carbon isotope reversal degree. With the increase of content of residue hydrocarbon pyrolysis gas, the δ13C2 value decreases, the alkane carbon isotope reversal degree increases, and the gas content of shale increases gradually.
Keywords: carbon isotope reversal; shale gas content; residual hydrocarbon pyrolysis; Longmaxi Formation; Sichuan Basin
投稿时间:2021-03-17  
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