柴达木盆地三湖坳陷盐壳遮挡型生物气成藏模式  

Hydrocarbon accumulation patterns of salt crust covered biogenic gas reservoirs in the Sanhu Depression, Qaidam Basin

作　　者：单俊峰[1] 鞠俊成[1] 张文伟[1] 韩宏伟[1] 周铁锁[1] 王宇斯 杨时杰[1] 曹宇森 Shan Junfeng;Ju Juncheng;Zhang Wenwei;Han Hongwei;Zhou Tiesuo;Wang Yusi;Yang Shijie;Cao Yusen(Exploration and Development Research Institute,PetroChina Liaohe Oilfield Company,Panjin,Liaoning 124010,China)

机构地区：[1]中国石油辽河油田公司勘探开发研究院

出　　处：《天然气工业》2019年第8期25-32,共8页Natural Gas Industry

基　　金：中国石油天然气股份有限公司重大科技专项“辽河油田千万吨稳产关键技术研究与应用”（编号：2017E-16）

摘　　要：柴达木盆地三湖坳陷广泛发育第四系生物气藏,已建成目前我国最大的生物气生产基地,但近年来,该区的生物气勘探遇到了“地震真假异常识别、微幅度构造落实、岩性圈闭识别刻画”等诸多难题,成为制约其勘探突破的瓶颈。为此,开展了生物气成藏模式研究,在分析精细构造解释成果的基础上,结合室内实验探讨了盐壳的封盖能力、分布范围、形成时间及成因,提出了盐壳遮挡型生物气成藏模式,并结合烃源、储层等条件,预测了盐壳遮挡型生物气藏的勘探前景。研究结果表明:①三湖坳陷第四系为滨浅湖相砂泥岩互层,烃源岩及储集条件优越,纵向上形成多套生储盖组合,生物气具有持续运移、聚集、散失、再聚集的动态成藏特征;②三湖坳陷受喜马拉雅运动的影响,气候变化频繁,形成古湖水盐度分带,南部河流注入端形成淡水区,北部形成卤水区,受蒸发作用的影响,北部潜水不断咸化,在陵间断层东段形成一套分布面积广、厚度稳定、封盖能力强的盐壳;③凹陷中心湖相泥岩生成生物气通过横向及纵向运移至陵间断裂带,遇盐壳有效遮挡聚集成藏。结论认为,三湖坳陷发育优质的烃源岩和储层、强封闭性的有效遮挡层——盐壳,形成良好的生储盖时空配置关系,可形成盐壳遮挡型生物气藏,天然气资源规模大、勘探前景广阔。Quaternary biogenic gas reservoirs are extensively developed in the Sanhu Depression of the Qaidam Basin,where the largest domestic biogenic gas production base has been built up.In recent years,however,the exploration of biogenic gas there encounters a variety of difficulties,such as the identification of true and false seismic abnormality,the determination of micro-relief structure and the identification and description of lithologic traps,which are the bottlenecks restricting its exploration breakthrough.In this paper,hydrocarbon accumulation patterns of biogenic gas were studied.Then,based on fine structure interpretation results,combined with laboratory experiments,the sealing ability,distribution range,formation time and genesis of salt crust were discussed,and the salt crust covered hydrocarbon accumulation pattern of biogenic gas was put forward.Finally,combined with the conditions of source rocks and reservoirs,the exploration prospect of salt crust covered biogenic gas reservoirs was predicted.And the following research results were obtained.First,the Quaternary in the Sanhu Depression is composed of sandstone–mudstone interbeds of shore-shallow lake facies,with superior conditions of source rocks and reservoirs.Many source–reservoir–caprock assemblages are vertically formed.The biogenic gas has the characteristics of dynamic hydrocarbon accumulation,i.e.,continuous migration,accumulation,diffusion and re-accumulation.Second,under the effect of Himalayan movement,the climate changes frequently and the salinity of the ancient lake is zoned in the Sanhu Depression.A freshwater area is formed at the inlet of the river in the south and a brine area is formed in the north.Under the influence of evaporation,the phreatic water in the north is salinized continuously,and a set of extensively distributed salt crust with steady thickness and a strong sealing ability is formed at the eastern part of Lingjian fault.Third,the biogenic gas generated by dark mudstone of lacustrine facies in the depression center

关 键 词：柴达木盆地 三湖坳陷 第四纪 生物气 成藏条件 生储盖组合 盐壳遮挡 勘探潜力 

分 类 号：P61[天文地球—矿床学]