松辽盆地杏山凹陷深层天然气地球化学特征及富集规律

Geochemical characteristics and enrichment regularity of deep gas in Xingshan Sag,Songliao Basin

为明确松辽盆地杏山凹陷深层天然气成因和富集规律,综合利用76口井天然气组分和碳同位素对深层天然气地球化学特征进行了系统分析。结果表明:火石岭组具有埋深大、甲烷含量低、重烃含量高、碳同位素组成最轻的特征;登娄库组埋藏浅、甲烷含量高、重烃含量低、碳同位素组成最重;营城组介于二者之间。各层位天然气成因类型不完全一致,火石岭组为油型气、煤型气的混合气;营城组以煤型气为主,少量油型气的混入导致天然气中δ^(13)C1、δ^(13)C_(2)倒转;登娄库组全部为煤型气,不同成熟阶段煤型气混合造成天然气中δ^(13)C_(2)、δ^(13)C_(3)倒转。断裂构成的输导通道是深层不同成因气聚集、混合的必要条件;暗色泥岩和煤的分布影响深层不同成因气藏和高产气井分布,烃源岩和断层的联合作用控制了深层天然气富集。

In order to make clear the generation and enrichment regularity of deep gas in Xingshan Sag of Songliao Basin,we systematically analysed the geochemical characteristic of deep gas,based on comprehensive data such as chemical components and carbon isotope composition in 76 wells. The results show that the gas in Huoshiling Formation is short of methane and enrichment of heavy hydrocarbon,and carbon isotope is the lightest. While the gas in Denglouku Formation is characterized by enrichment of methane and short of heavy hydrocarbon,carbon isotope is the greatest. Gas in Yingcheng Formation is somewhere in between. The generation of deep gas in different layers are not exactly corresponding to each other,the gas in Huoshiling Formation is a mixture of coal-formed gas and oil-related gas,while gas in Yingcheng Formation is mainly coal-formed gas with little amount of oil-related gas. Mixing of oil-related gas with coal-formed gas is the reason for δ^(13) C1 andδ^(13) C_(2) partial reversal. The gas in Denglouku Formation is all coal-formed gas,the mixture of coal-formed gas with different maturity stages is the reason for δ^(13) C_(2) and δ^(13) C_(3) partial reversal. The fault is the necessary pathway for gas migration and accumulation among different genetic types,while gas of different genetic types and highyielding gas wells are all affected by the distribution of mudstone and coal,the enrichment of deep gas is controlled by the combined effect of source and fault.