柴达木盆地东部涩北一号叠置气藏的两种成藏模式

柴达木盆地东部涩北一号气田由7个纵向叠置的气藏组成,各气藏中生物气的富集程度相差悬殊。为了查明生物气富集的控制因素,首先以单储系数、储量丰度和试气产量为依据,将7个气藏划分为高富集与低富集两类;然后对两类气藏的成藏条件进行了对比分析。研究认为,埋深大于950 m的第四-第七气藏为高富集气藏,这些气藏处于最大生气带,能同时接受本区及中央凹陷生物气的供给,加上其储盖组合、圈闭及后期保存条件优越,有利于生物气富集成藏;浅部的第一-第三气藏为低富集气藏,它们埋藏所处层段还未达到生气高峰,主要由下部气藏扩散散失生物气充注成藏,且保存条件较差,生物气难以富集。在成藏条件分析的基础上,将高、低富集气藏的形成分别归结为气源充注和扩散充注成藏模式。

Two pooling patterns of superimposed reservoirs in Sebei-1 gas field, the eastern Qaidam Basin

The Sebei-1 field consists of seven vertically superimposed gas reservoirs with various biogas enrichments.These reservoirs are divided into high-enrichment reservoirs(HER) and low-enrichment reservoirs(LER) based on such data as reserves per unit volume,abundance of gas reserves,and flow rate tested.The pooling conditions for these two types of reservoirs are compared and analyzed.The results are used to define the controlling factors for the biogas enrichment in the field.The lower four deeper reservoirs with burial depth greater than 950 meters are the HER type,while the upper three shallow ones belong to the LER type.The former ones are favorable for gas pooling and enrichment as they are located in the central of a gas-generation zone with biogas charging both from the local area and central depression,and apart from that,they also have favorable re-servoir-seal assemblage,trapping and preservation conditions.In contrast,the later ones are unfavorable for gas pooling and enrichment as the source rocks have not reached peak gas generation,the biogas are mainly sourced from the lower gas reservoirs through diffusion,and the preservation conditions are relatively poor.Based on the analysis of pooling conditions,the paper suggests that the pooling patterns for the HER and LER reservoirs be described as source-charged and dispersion-charged respectively.