辽河坳陷东部凹陷低熟气地球化学特征  

Geochemistry of Low Maturity Gases from the Eastern Sag of Liaohe Depression,China

作　　者：李孝甫 王晓锋[1] 郑建京[1] 刘鹏[1,2] 孟强[1,2] 史宝光[1] 

机构地区：[1]甘肃省油气资源研究重点实验室/中国科学院油气资源研究重点实验室,甘肃兰州730000 [2]中国科学院大学,北京100049 [3]页岩气评价与开采四川省重点实验室,四川省煤田地质局,四川成都610072

出　　处：《天然气地球科学》2015年第7期1365-1375,共11页Natural Gas Geoscience

基　　金：中国科学院西部行动计划项目“准噶尔盆地东部低熟气资源潜力与有利勘探区预测”(编号:KZCX2-XB3-12);国家重点基础研究发展计划(编号:2012CB214801);中国科学院“西部之光”人才培养计划项目“准东地区侏罗系各类烃源岩的生排烃特征及生烃潜力评价”(编号:Y404RC1);甘肃省重点实验室专项(编号:1309RTSA041)联合资助

摘　　要：通过分析辽河坳陷东部凹陷29个天然气样品的地质和地球化学特征,探讨了研究区天然气成因类型的新认识。研究区主要烃源岩为古近系沙河街组和东营组,母质类型以偏腐殖型为主,热演化程度主体处于0.5%~1.0%之间。天然气组分以烃类气体占绝对优势,干气、湿气并存;δ13 C1值为-46‰^-38‰、δ13C2值为-30‰^-25‰、δ2 HCH4值为-250‰^-210‰;C5-7轻烃化合物中富含异构烷烃,庚烷值和异庚烷值均落在低演化区。对比分析吐哈低熟气特征,指出研究区探明天然气的主体属于低熟气范畴,满足其2个本质属性:母质为偏腐殖型、成熟度处于低演化阶段。气源对比表明,天然气主要来源于古近系沙三段(Es3)陆相湖盆偏腐殖型源岩,它的成熟度(RO)与基于"δ13C1—RO"计算得出的天然气RO值(0.50%~0.90%)在空间分布特征上相吻合。此外,微生物活动对气藏后期的改造作用也不容忽视:大部分C2+烃类被微生物消耗而使天然气组分变干;C2、C3含量降低至一定程度时,δ13C2值、δ13C3值呈现异常高,甚至达到正值,而δ13C1值受微生物活动影响较小;正庚烷容易被降解而使研究区天然气庚烷值相比吐哈低熟气更低。A suite of natural gases from the Eastern Sag of Liaohe Depression were characterized by their molecular and isotopic composition. The gas samples are largely gaseous hydrocarbons, together with high dryness（C1/C1-5 from 0.85 to 1. 00）,313Ci （-46%0 to -38%0）,313C2 （-30% to --25%）,δ2 HCH4 （--250% to --210%）. Isoparaffin is enriched in light hydrocarbons and heptane value（H） ~ isoheptane value（1） both display a low maturity feature. In contrast with the geochemical characteristics of low maturity gases in the Turpan-Hami Basin,the natural gas in this region mainly belong to low maturity gas because of hu- mic source rock and low maturity. The source rock in the study area is mainly developed in the Eocene Sha- hejie Formation（Es） and Dongying Formation（Ed）. The organic matter of the source rock is humic-type and its vitrinite reflectance（Ro） ranges from 0.5% to 1.0%. The Ro of source rocks which were calculated by the empirical relationship between the measured 31aC1 and Ro ranges from 0.57% to 0. 90% ,which is in agreement with the actual Ro of source rocks in this region, suggesting that the natural gases are derived from the source rock of the third Member of the Eocene Shahejie Formation（Es3）. Additionally, most gas samples display clear geochemical evidence of biodegradation alteration. The majority of gases contain over 90 % methane and small quantities of C2＋ alkanes, carbon isotopic composition of C2 and C3 in two samples from shallow reservoirs are especially positive when the contents of them microbially decreased to a certain degree. High susceptibility to biodegradation of n-heptane leads to a lower heptane value（H） than the low maturity gas from Turpan-Hami Basin.

关 键 词：低熟气 地球化学 生物降解 偏腐殖型 辽河坳陷 

分 类 号：TE122.1[石油与天然气工程—油气勘探]