莺歌海盆地高温超压大型优质气田天然气成因与成藏模式——以东方13-2优质整装大气田为例

Natural gas origin and accumulation model in major and excellent gas fields with high temperature and overpressure in Yinggehai basin:a case of DF13-2 gasfield

针对莺歌海盆地东方13-2大型优质高温超压气田天然气成藏特征存在认识不清等问题,开展了天然气成因、来源及成藏过程与成藏模式的系统分析。研究认为,东方13-2气田天然气以烃类气为主,CO2含量低;甲烷、乙烷及CO2碳同位素特征表明天然气为高成熟煤型气,CO2为有机和无机混合成因;天然气轻烃C6、C7系列中环烷烃含量最高,且环己烷占优,生源母质以陆源高等植物为主。东方13-2优质大气田分布于DF底辟外围区,具有"上中新统黄流组一段大型海底扇储层、优质浅海相泥岩封盖和断裂(裂隙)输导"三元时空耦合控藏特征。DF底辟外围区主要聚集了早期充注的烃类气,CO2含量低,且烷烃气碳同位素组成表明天然气呈"高效运聚"成藏特点,是今后莺歌海盆地天然气勘探主要方向。

As a major and excellent gasfield with high temperature and overpressure in Yinggehai basin, DF13-2 is still poor in the knowledge of gas accumulation characteristics, thus its gas origin, sources and accumulation process and model were systematically analyzed. By some researches, it has been recognized that. （1） the natural gas in DF13-2 is predominated by hydrocarbon gas, with its content of CO2 quite lower; （2） the hydrocar bon gas can be considered as a coal - type gas with high maturity, and CO2 may be in organic-inorgan ic hybrid origin from the carbon isotope of meth- ane, ethane and CO2 ; （3） C6 and C7 components of light hydrocarbon in gas are dominated by cyclo paraffinic hydrocarbon, especially cyclohexane, in- dicating that the organic matter in source rocks is mainly from terrestrial higher plant. Situated in the peripheral area of DF despair, DF13-2 is char- acterized by a ternary accumulation control of ＂ma- jor reservoir of submarine fans in Member 1 of Up- per Miocene Huangliu Formation, excellent seals of neritic-facies mudstone and fault （fracture） transportation＂. As a location where there is early- filled hydrocarbon gas, lower CO2 and a gas reser- voiring mechanism of ＂efficient migration-accumu- lation＂ indicated by the carbon isotope composition of hydrocarbon gas, this peripheral area will be one of the main targets of future gas exploration in Yinggehai basin.