济阳坳陷深层裂解气成因鉴别及其成藏差异性

济阳坳陷深层裂解气藏成因较为复杂，影响了深层天然气的认识和勘探。利用天然气组分和碳同位素等鉴别了原油裂解气和干酪根裂解气，进一步分析了2类成因的成藏差异性。原油裂解气表现为Ln(C₂/C₃)值随Ln(C₁/C₂)值增大而增大；干酪根裂解气随Ln(C₁/C₂)值的增大，Ln(C₂/C₃)值基本不变。在有机质类型和热演化程度大致相当的情况下，原油裂解气δ¹³C₁值、δ¹³C₂值、δ¹³C₃值与相应的干酪根裂解气的最大差值分别为-12.4‰、-8.8‰和7.5‰；随着δ¹³C₁值或(δ¹³C₁-δ¹³C₂)值的增大，干酪根裂解气(δ¹³C₂-δ¹³C₃)值快速减小，而裂解气(δ¹³C₂-δ¹³C₃)值变化微弱。干酪根裂解气藏表现为早期油气扩散、断裂活动停止和后期天然气充注，原油裂解气藏体现为早期油气充注、岩性侧向封堵和后期古油藏裂解的成藏规律。2种裂解气成因开启了深层天然气勘探的新思路，并指出了其勘探方向，对深层勘探具有重要的指导意义。

Origin and Accumulation of Cracking Gas in the Deep Buried Horizons in Jiyang Depression

The origin of cracking gas in the deep buried horizons is very complicated,and it is one of the main limits for gas exploration in Jiyang Depression.Based on gas component and carbon isotope analysis,it is possible to distinguish between oil cracking gas and kerogen cracking gas.Oil cracking gas is featured by ln(C₂/C₃) increasing with ln(C₁/C₂);but as for kerogen cracking gas,ln(C₂/C₃) was almost constant despite of the increase of ln(C₁/C₂).When the organic matter type is the same and thermal maturity is similar,the difference ofδ¹³C₁,δ¹³C₂,and δ¹³C₃ between oil cracking gas and kerogen cracking gas can be up to -12.4‰,-8.8‰ and 7.5‰,respectively.With the increase ofδ¹³C₁or (δ¹³C₁-δ¹³C₂),(δ¹³C₂-δ¹³C₃) of kerogen cracking gas decreased rapidly,while that value of oil cracking gas are almost constant.This study also demonstrated the differences in gas accumulation between these two kinds of gas reservoir.As for kerogen cracking gas,fault activities damaged oil and gas reservoir that formed in early period,and gas reservoir formed in lithologic traps in low lying structural belt during late period when fault activity stopped.As for oil cracking gas,oil and gas accumulated in early period sealed by lithology difference,and oil cracked in late period to form cracking gas reservoir.Understanding in the origin of the two kinds of cracking gas reservoir opened a new concept in gas exploration,and this is significant for exploration in deep buried horizons.