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通过对徐家围子断陷天然气藏盖层分布及封闭能力的研究,得到徐家围子断陷天然气藏主要有泥岩、高声波时差火山岩、低声波时差火山岩和泥质砾岩4种盖层。泥岩主要分布在登二段以上地层中,为区域性盖层。高声波时差火山岩盖层主要分布在营一段顶部,为局部盖层。低声波时差火山岩盖层分布在营一段和营三段内部,泥质砾岩盖层分布在营四段,二者均为夹层。泥岩、高声波时差火山岩和泥质砾岩盖层封闭能力强,低声波时差火山岩盖层封闭能力弱。通过盖层与天然气分布之间的关系研究得到,徐家围子断陷盖层对天然气成藏与分布的控制作用主要表现在以下3个方面:①登二段和营一段顶部盖层控制着天然气的纵向分布;②盖层分布层位差异造成断陷南北具有不同的天然气储盖组合,天然气富集程度不同;③高声波时差与低声波时差火山岩盖层之间的差异造成天然气主要分布在火山岩体顶部。
Through the study on the cover distribution and sealing ability of natural gas reservoir in the Xujiaweizi Fault Depression, the natural gas reservoirs in the Xujiaweizi Fault Depression are mainly mudstone, high acoustic time lag volcanic rock, low acoustic lava volcanic rock and argillaceous conglomerate. Mudstone is mainly distributed in the strata above Deng 2, which is a regional cap rock. High acoustic wave time lag volcanic cap rocks are mainly distributed in the top of the camp, as a partial cap layer. Low acoustic wave time lapse volcanic rocks are distributed in the first battalion and the third battalion, muddy conglomerate cap rocks are distributed in Ying 4, both of which are mezzanine. Mudstone, high acoustic wave time lag volcanic and argillaceous conglomerate cap sealing ability, low acoustic wave time lag volcanic cap closure weak. Through the study of the relation between caprock and gas distribution, the controlling function of Xujiaweizi fault caprock on gas accumulation and distribution is mainly manifested in the following three aspects: ① The top cover of Deng 2 Member and Ying 1 Member controls natural gas ; (2) the distribution of caprock layers resulted in different natural gas cap-rock assemblages in the north and south of the fault depression and different degree of natural gas enrichment; (3) the differences between the high acoustic wave time lag and the low acoustic wave lava volcanic cap rocks resulted in the distribution of natural gas Volcanic rock top.