北部湾盆地流二段不同类型烃源岩生排烃效率与成藏贡献对比

Comparison on the efficiency of hydrocarbon generation&expulsion and the contribution to hydrocarbon accumulation of different source rocks in Liu 2 Member,Beibuwan basin

北部湾盆地目前的油气储量发现主要集中在涠西南和乌石凹陷这两个勘探成熟区,钻井揭示其主力烃源岩为流二段半深湖—深湖相烃源岩,包括泥岩、页岩和油页岩等3种类型。本文主要针对这两个成熟区14口井的3种类型烃源岩的岩心、岩屑及13个典型油田的原油共计173个样品进行了系统采集和分析测试,利用生排烃热模拟实验和混源油人工配比实验等手段,开展了3种类型烃源岩的生排烃效率及其对13个典型油田的成藏贡献定量对比分析。结果表明,流二段油页岩有机质丰度高、类型好,生烃潜力明显优于泥岩和页岩,是该盆地最优质的烃源岩;3种类型烃源岩的生排烃效率由高到低依次为油页岩、页岩和泥岩,其中油页岩的生油效率和排油效率最高,分别是泥岩的5.2倍和3.4倍;流二段油页岩对该盆地成熟区13个典型油田的油源贡献率超过70%,是油气成藏的主力烃源岩,因此在新区勘探潜力评价中应高度重视油页岩的分布预测及资源潜力评价。

The oil reserves found in Beibuwan basin are mainly concentrated in the two exploration mature areas of Weixinan sag and Wushi sag.Drilling revealed that the main source rocks are the semi-deep to deep lacustrine facies source rocks in Liu 2 Member,which include the mudstone,shale and oil shale.A total of 173 samples including cores and cuttings samples of 3 types of source rocks in 14 wells of those two mature areas,as well as the crude oil samples of 13 typical oilfields were collected and analyzed systematically.The hydrocarbon generation and expulsion efficiency of 3 types of source rocks and their contribution to the hydrocarbon accumulation of 13 typical oilfields were quantitatively analyzed by means of the thermal simulation experiment of hydrocarbon generation and expulsion and the experiment on artificial mixing ratio of mixed source oil.The results show that the oil shale has higher organic matter abundance,better organic matter type and larger hydrocarbon generation potential than mudstone and shale,and it is the best source rock in Beibuwan basin.From top to bottom,the hydrocarbon generation and expulsion efficiencies of 3 types of source rocks are successively the oil shale,shale and mudstone.Among them,the oil shale has the highest hydrocarbon generation and expulsion efficiencies that are 5.2 times and 3.4 times of those of mudstone,respectively.The oil source contribution rate of oil shale in the Liu 2 Member exceeds 70% among those 13 typical oilfields in this basin,which is the main source rock for hydrocarbon accumulation.In the evaluation of exploration potential in the new area,more attentions shall be paid to the distribution prediction and the resource potential evaluation of oil shale.