南黄海中部海底沉积物烃类气体地球化学特征及成因类型

Geochemistry and Genetic Types of Hydrocarbon Gases from Seabed Sediments in the Center of South Yellow Sea

南黄海中部海底沉积物顶空烃类气体以顶空甲烷(WC1)为主,除去3个WC1特高值样品后,余下样品WC1总体体积分数偏低并显示单峰分布,峰值为19.46μl/L。南黄海中部海底沉积物酸解烃甲烷(AC1)、乙烷(AC2)和丙烷(AC3)的频率分布图揭示了其频率分布特征。AC1频率分布显示明显的双峰特征,一个峰值为160μl/kg,另一个峰值为650μl/kg,而AC2和AC3频率分布显示单峰分布特征,峰值分别为3.5μl/kg和1.8μl/kg。AC1与重烃气体AC2+之间显示弱的正相关,而重烃气体AC2和AC3之间则显示明显的正相关关系,表明南黄海中部海底沉积物AC1与重烃气体AC2和AC3具有不同演化特征。海底沉积物烃类气体组合、湿度比、乙烷/乙烯比值,以及甲烷碳同位素组成指示,顶空烃类气体属于典型生物成因类型,而酸解烃类气体则属于热成因类型。顶空烃类气体的高值区与海底浅层气的分布区对应,而酸解烃类气体的异常区则主要受构造控制,可能代表了深部油气沿构造交接部位向海底表面渗漏的产物,预示着在南黄海中部区,特别是酸解烃类气体异常区的深部可能有油气存在。

The composition of headspace hydrocarbon gases was mainly of methane and miner heavy hydrocarbon gases in the central South Yellow Sea.The frequency chart of headspace methane(WC1) indicated a uni-modal distribution with a peak of 19.46μ l/L after eliminating three special high values.The frequency charts demonstrated the distributive characteristics of acid methane(AC1),ethane(AC2) and propane(AC3) from seabed sediments in the central South Yellow Sea.The frequency chart of AC1 indicated a bimodal distribution with a median of 160μl/kg and a median of 650μl/kg,and the frequency charts of AC2 and AC3 showed a uni-model distribution of with a peak of 3.5μl/kg and a peak of 1.8μl/kg respectively.It represented the different genetic characterizations and evolutions between AC1 with AC2 and AC3,where AC1 was a weak positive correlation with heavy hydrocarbon gases(AC+2),and AC2 was a strong positive correlation with AC3.The hydrocarbon gas association,wetness ratio,ethane/ethene ratio,and stable methane carbon isotopic compositions from seabed sediment in the central South Yellow Sea indicated that headspace hydrocarbon gases belonged to bacterial type and acid hydrocarbon gases belonged to thermogenetic type.The high value sites of headspace methane are suited with rich area of shallow bacterial gas in the central South Yellow Sea.The anomaly area of acid methane is controlled by tectonic and probably represents the product of hydrocarbon seepage from deep oil and gas source to surface along boundary faults of different tectonic units,and it is suggested that there may exist the oil and gas below the anomaly area of acid hydrocarbon gases in the central South Yellow Sea.