丙烷分子内碳同位素示踪作用  

Intramolecular 13C isotope distributions in propane from natural gases and produced in the laboratory

作　　者：帅燕华[1] 彭平安[2] 陶小晚[1] 李剑[1] 李芸[2] 熊永强[2] Yanhua Shuai;Ping’an Peng;Xiaowan Tao;Jian Li;Yun Li;Yongqiang Xiong(Research Institute of Petroleum Exploration and Development(PetroChina),Beijing 100083,China;State Key Laboratory of Organic Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 264400,China)

机构地区：[1]中国石油勘探开发研究院,北京100083 [2]中国科学院广州地球化学研究所,有机地球化学国家重点实验室,广州264400

出　　处：《科学通报》2023年第36期4995-5008,共14页Chinese Science Bulletin

基　　金：国家自然科学基金(41772135,42272139);中国石油天然气集团有限公司科技项目(2021DJ0604,YGJ2019-04-029)资助。

摘　　要：分子内同位素可标定物质来源、形成机理与路径.通过对比世界不同层系/类型天然气丙烷与有机质(Ⅰ~Ⅲ型干酪根、原油、nC_(25))热模拟产生的丙烷分子内碳同位素特征发现:(1)实验条件下丙烷演化模式与自然条件下区别极大,源于实验条件下能够全面再现各阶段特征,而自然条件下部分阶段不出现,尤其是油型气丙烷.(2)地质盆地油型气丙烷分子内碳同位素相对稳定,与母质类型、源岩时代、沉积环境等相关,受成熟度影响较小(<3‰),可做绝佳源岩示踪剂.煤成气丙烷由于煤富含支链结构而具有两阶段演化模式,阶段I随成熟度增加中位碳快速变重、边位碳轻微变重,阶段Ⅱ趋近于丙烷理论生成线.(3)丙烷分子内同位素受多种次生/后生作用影响显著,化学氧化致中位碳比边位碳变重幅度快1倍.(4)受Fe2O3等金属氧化物氧化影响,塔里木盆地克深8气藏中的丙烷中位碳明显偏重;而克深13气藏中丙烷被氧化程度弱,源于成藏晚;台盆区塔中45、轮古东、吉拉克、富满等油气藏奥陶系天然气来源一致,但与和田河天然气区别明显.丙烷分子内同位素示踪效应强大,将为深层与复杂构造区油气来源与成藏过程研究提供强有力支撑.Position-specific isotope analysis of propane provides novel information to understand its sources and sinks.However,little is known about the overall evolution trends because limited data are available.Here,we compared the positionspecific isotope values of propane from natural gases with a wide maturity range(reflectance of 1.0%to 3.0%)from China,America,and Brazil,and from simulated gases produced by various types of organic precursors(e.g.,type I–III kerogen,crude oil,and nC_(25))in the laboratory.We found that the evolution trends of intramolecular isotope compositions of propane from laboratory-simulated gases differed greatly from those of natural gases.This is likely associated with the fact that intramolecular isotopes of propane in the early maturity phase are observed clearly in laboratory experiments but not in geological basins,especially for propane from oil-type gases.Theδ^(13)C values at both central and terminal carbon positions in propane from natural oil-type gases showed little variation(within 2‰–3‰)during maturation.Thus,intramolecular isotopes of propane are a reliable indicator of gas origin.For propane from coal-type gases,there were two stages of evolution.With increasing maturity,theδ^(13)C value first increased rapidly at the central carbon position but remained stable at the terminal carbons.Then the intramolecular isotope compositions approached the theoretical values for propane generated from the cracking of long chain alkanes.This was attributed to a large contribution of isoprenoid organic precursor to propane generation in coal at maturity before the dry gas window stage.The intramolecular isotopes of propane were clearly affected by post-generation processes.With chemical oxidation degradation by high-valence Fe(Mn)oxide and thermal sulfate reduction,the carbon in the central position became heavier twice as fast as that in the terminal positions.Natural gases from the Keshen 8 gas field in the Kuche Depression of the Tarim Basin have been strongly oxidized by high-va

关 键 词：分子内同位素 成藏示踪 塔里木盆地 煤型气 油型气 化学氧化 

分 类 号：P618.13[天文地球—矿床学]