青海祁连山冻土区天然气水合物的气体成因研究

在祁连山冻土区发现天然气水合物之后,其气体成因或来源便成为一个重要的科学问题。开展了气体组成和同位素特征及δ13C1-1/n、C1/(C2+C3)-δ13C1、δDCH4-δ13CCH4、(δ13C2-δ13C3)-ln(C2/C3)、ln(C2/C3)-ln(C1/C2)等关系图解的综合研究,结果显示:祁连山冻土区天然气水合物的气体以轻烃为主,具湿气特征,其同位素表现为正碳同位素系列特征。研究区天然气水合物的气体为有机成因,且以热解成因为主,夹少量微生物成因(醋酸根发酵),其中,热解成因气主要与原油裂解气、原油伴生气有关,少部分与凝析油伴生气、煤成气、干酪根裂解气有关。这一分析结果可能意味着研究区天然气水合物的气体来源与油型气密切相关,而与煤型气关系不大。

Study on Genesis of Gases from Gas Hydrate in the Qilian Mountain Permafrost, Qinghai

The genesis or origin of gases from gas hydrate becomes an important scientific issue after gas hydrate is discovered in the Qilian mountain permafrost,Qinghai.The composition and isotope of gases from gas hydrate and the relevant diagrams of δ13C1-1/n,C1/(C2+C3)-δ13C1,δDCH4-δ13CCH4,(δ 13C2-δ13C3)-ln(C2/C3),ln(C2/C3)-ln(C1/C2) are studied in this paper.Conclusions are drawn out: In the Qilian mountain permafrost,Qinghai,gases from gas hydrate are mainly composed of light hydrocarbons with features of wet gas;The isotopes are characteristic of normal carbon isotopic series.In the study area,gases from gas hydrate are organic and preferably of thermal genesis with secondarily of microbial genesis(acetate fermentation);Gases of thermal genesis are predominantly from crude oil cracking or in association with crude oil generation,and minor or trace of them are associated with condensate gases,coal-typed gases,kerogen cracking gases.This analytical result probably implies that gas source of gas hydrate is closely related to oil-typed gases rather than coal-typed gases in the study area.