川东北元坝—通南巴地区二叠系—三叠系天然气地球化学特征及成因  

Geochemical characteristics and origin of Permian and Triassic natural gas in Yuanba-Tongnanba area,northeastern Sichuan Basin

作　　者：刘景东[1,2] 刘光祥[2] 王良书[3] 吴小奇[2] 

机构地区：[1]中国石油大学地球科学与技术学院,山东青岛266580 [2]中国石油化工股份有限公司石油勘探开发研究院无锡石油地质研究所,江苏无锡214126 [3]南京大学地球科学系,江苏南京210093

出　　处：《石油学报》2014年第3期417-428,共12页Acta Petrolei Sinica

基　　金：国家重大科技专项(2011ZX05005);国家自然科学基金项目(No.41302118);中央高校基本科研业务费专项资金项目(14CX02116A)资助

摘　　要：依据天然气组分、碳同位素和稀有气体等资料对川东北元坝—通南巴地区二叠系—三叠系天然气地球化学特征及成因进行了系统研究。结果表明,(H_2S+CO_2)与(H_2S+CO_2+∑C_n)比值可以作为表征热化学硫酸盐还原作用(TSR)程度的参数。元坝地区长兴组至须家河组二段、通南巴地区飞仙关组至须家河组四段天然气δ^(13)C_2变化幅度大于δ^(13)C_1,且δ^(13)C_2值介于-24.4%。^-36.7‰,表明存在油型气和煤型气混合,理论上各层系天然气碳同位素均应呈倒序分布,但元坝地区长兴组、飞仙关组和通南巴地区嘉陵江组天然气受TSR影响,仍表现为δ^(13)C_1<δ^(13)C_2或δ^(13)C_1<δ^(13)C_2<δ^(13)C_3的正序分布。元坝地区须家河组三段、四段天然气δ^(13)C_2值大多重于-28%。,以煤型气为主,表现为δ^(13)C_1<δ^(13)C_2<δ^(13)C_3的正序分布。天然气稀有气体氦同位素R/R_a值分布于0.00881~0.02510,表现出典型的壳源特征,源于TSR的酸性气体和源于烃源岩热演化的有机酸对碳酸盐岩的溶蚀是该地区二氧化碳形成以及δ^(13)C_(CO_2)变重的主要原因。气-气及气-源综合对比表明,元坝—通南巴地区天然气成因类型可以划分为龙潭型(A1型)、混合型(A2型)和须家河型(B型),龙潭型和混合型主要来源于上二叠统龙潭组烃源岩,其中混合型混有少量须家河组来源气,须家河型主要来源于其自身层系的烃源岩。Based on the data of gas composition,carbon isotope and noble gas,a systematic study is conducted on geochemical charac teristics and origin of Permian and Triassic natural gas in Yuanba-Tongnanba area of northeastern Sichuan Basin.The results indicate that the ratio of （H2S＋ CO2） and （H2S＋ CO2 ＋ ΣCn） can be used as a parameter for representing thermochemical sulfate reduction （TSR） level.The variation range of δ13C2 is wider than that of δ13C1 for gas from Changxing Formation to Member Ⅱ of Xujiahe For mation in Yuanba area,as well as Feixianguan Formation to Member Ⅳ of Xujiahe Formation in Tongnanba area.δ3 C2 values range from-24.4‰ to-36.7‰,indicating that there exists a mixture of oil-type gas and coal-type gas.On a theoretical level,the distri bution of carbon isotopes in all strata series shows a reverse sequence.However,affected by TSR,gas from Changxing and Feixian guan Formations in Yuanba area and Jialingjiang Formation in Tongnanba area has a positive sequence of δ13 C1 〈δ^13 C2 and δ^13 C1 〈δ^13 C2 〈δ^13C3.δ^13C2 values are always greater than-28‰ for gas from Members Ⅲ and Ⅳ of Xujiahe Formation in Yuanba area,mainly indicating coal-type gas with the positive sequence of δ^13 C1 〈δ^13 C2 〈δ^13 C3.According to the helium isotope analysis of gas and noble gas,R/Ra values range from 0.00881 to 0.025 10,showing a typical crust source type.Carbonate dissolution by acid gases and organic acids respectively though TSR and thermal evolution of source rock plays a main role in causing CO2 generation and increased δ13Cco2.Based on a comprehensive comparison analysis of gas gas and gas source rock data,origin types of gas in Yuanba-Tongnanba area can be divided into Longtan （A1）,mixed （A2） and Xujiahe （B）.Of these,A1 and A2 mainly originate from source rock in the Upper Permian Longtan Formation,and A2 is mixed with some gas from source rock of the Xujiahe Formation; B is mainly from source rock in the Xujiahe Formation.

关 键 词：天然气成因 碳同位素 热化学硫酸盐还原作用(TSR) 二叠系—三叠系 元坝—通南巴地区 

分 类 号：TE122[石油与天然气工程—油气勘探]