Geochemical Characteristics of the Upper Triassic Xujiahe Formation in Sichuan Basin, China and its Significance for Hydrocarbon Accumulation  

作　　者：XIE Zengye LI Jian LI Zhisheng GUO Jianying LI Jin ZHANG Lu DONG Caiyuan 

机构地区：[1]Petrochina Research Institute of Petroleum Exploration and Development,Langfang 065007,Hebei,China [2]Key Laboratory of Gas Reservoir Formation and Development,CNPC,Langfang 065007,Hebei,China

出　　处：《Acta Geologica Sinica(English Edition)》2017年第5期1836-1854,共19页地质学报（英文版）

基　　金：funded by the National Science&Technology Major Project(grant No.2016ZX05007-003);the China Petroleum Science and Technology Project(grants No.2014B-0608 and 2016B-0602)

摘　　要：The alternative development of coal-bearing hydrocarbon source rocks and low-porosity and low-permeability tight sandstone reservoirs of the Triassic Xujiahe Formation in the Sichuan Basin is favorable for near-source hydrocarbon accumulation. The natural gas composition of the Xujiahe Formation in the Sichuan Basin is dominated by hydrocarbon gases, of which the methane content is80.16%-98.67%. Typically, the C2^＋ content is larger than 5% in main wet gas. The dry gas is mainly distributed in the western and northern regions of the basin. The non-hydrocarbon gases mainly contain nitrogen, carbon dioxide, hydrogen, and helium, with a total content of 〈2%. The carbon isotope ranges of methane and its homologues in natural gas are： δ^13C1 of-43.8‰ to-29.6‰, δ^13C2 of-35.4‰ to-21.5‰, δ^13C3 of-27.6‰ to-19.8‰,and δ^13C4 of-27.7‰ to-18.8‰. δ^13C3〉δ^13C4 occurs in some natural gas with a low evolution degree; such gas is mainly coal-related gas from humic-type source rocks of the Xujiahe Formation. As for the natural gas, δ^2 HCH4 values ranged from-195‰ to-161‰,δ^2 HC2H6 values ranged from-154‰ to-120‰, and δ^2 HC2H8 values ranged from-151‰ to-108‰. The dry coefficient,δ^13C and δ^2 HC2H4 are all positively correlated with the maturity of source rocks. The higher the maturity of source rocks is, the larger the natural gas dry coefficient is and the larger the δ^13C and δ^2 HC2H4 values are, indicative of the characteristic of near-source accumulation. The δ^2 HC2H6 value of natural gas is influenced by paleosalinity to a relatively large extent; the higher the paleosalinity is, the larger the δ^2 HC2H4 value is. The Pr/Ph value of the condensate oil ranged from 1.60 to 3.43, illustrating light oxidization-light reduction and partial-oxidization characteristics of the depositional environment of coal-bearing source rocks of the Xujiahe Formation. The natural gas light hydrocarbon（C5-C7） from the Xujiahe Formation presented two characteristics： the first was the rThe alternative development of coal-bearing hydrocarbon source rocks and low-porosity and low-permeability tight sandstone reservoirs of the Triassic Xujiahe Formation in the Sichuan Basin is favorable for near-source hydrocarbon accumulation. The natural gas composition of the Xujiahe Formation in the Sichuan Basin is dominated by hydrocarbon gases, of which the methane content is80.16%-98.67%. Typically, the C2^＋ content is larger than 5% in main wet gas. The dry gas is mainly distributed in the western and northern regions of the basin. The non-hydrocarbon gases mainly contain nitrogen, carbon dioxide, hydrogen, and helium, with a total content of 〈2%. The carbon isotope ranges of methane and its homologues in natural gas are： δ^13C1 of-43.8‰ to-29.6‰, δ^13C2 of-35.4‰ to-21.5‰, δ^13C3 of-27.6‰ to-19.8‰,and δ^13C4 of-27.7‰ to-18.8‰. δ^13C3〉δ^13C4 occurs in some natural gas with a low evolution degree; such gas is mainly coal-related gas from humic-type source rocks of the Xujiahe Formation. As for the natural gas, δ^2 HCH4 values ranged from-195‰ to-161‰,δ^2 HC2H6 values ranged from-154‰ to-120‰, and δ^2 HC2H8 values ranged from-151‰ to-108‰. The dry coefficient,δ^13C and δ^2 HC2H4 are all positively correlated with the maturity of source rocks. The higher the maturity of source rocks is, the larger the natural gas dry coefficient is and the larger the δ^13C and δ^2 HC2H4 values are, indicative of the characteristic of near-source accumulation. The δ^2 HC2H6 value of natural gas is influenced by paleosalinity to a relatively large extent; the higher the paleosalinity is, the larger the δ^2 HC2H4 value is. The Pr/Ph value of the condensate oil ranged from 1.60 to 3.43, illustrating light oxidization-light reduction and partial-oxidization characteristics of the depositional environment of coal-bearing source rocks of the Xujiahe Formation. The natural gas light hydrocarbon（C5-C7） from the Xujiahe Formation presented two characteristics： the first was the r

关 键 词：natural gas GEOCHEMISTRY ISOTOPES light hydrocarbon Xujiahe Formation Sichuan Basin 

分 类 号：P534.51[天文地球—古生物学与地层学] P618.13[天文地球—地质学]