徐家围子断陷营城组火山岩裂缝与天然气成藏

徐家围子断陷营城组火山岩储层虽然发育大量气孔和原生裂缝,但是其连通性差,构造裂缝的发育程度决定了储层的优劣和成藏概率。为了阐明裂缝与天然气成藏之间的关系,首先,利用岩心、成像测井以及实验分析等资料对徐家围子断陷营城组火山岩储层裂缝的成因类型与特征、控制因素、分布规律及形成期次进行了研究,然后结合研究区烃源岩演化、气源断裂活动期次以及盖层封闭能力演化,讨论了构造裂缝与天然气成藏的关系。研究结果显示,徐家围子断陷营城组火山岩发育原生裂缝和次生裂缝,以次生构造裂缝为主。在平面上构造裂缝受断裂、岩性和岩相控制,在纵向上受不整合面控制,具有旋回性分布的特点。构造裂缝主要分三期形成,其中第二期形成时期(泉头组沉积末期-青山口组沉积时期)与烃源岩生烃高峰期相吻合,并且气源断裂处于活动期,盖层也具有很好的封气能力,为研究区主要成藏期。

Natural Gas Accumulation and Fractures in Volcanic Rocks of Yingcheng Formation in Xujiaweizi Fault Depression

Thevolcanic rocks of Yingcheng Formation in the Xujiaweizi Fault Depression contain abundant but poorly connected pores and primary fractures. The degree of tectonic fracturing determines the reservoir quality and probability of hydrocarbon accumulation. In order to illustrate the relationship between fractures and natural gas accumulation, we carried out analyses of cores, image logs and experimental study and discussed firstly the fracture genetic types, characteristics, controlling factors, distribution and sequences. And then, combined with the evolution of source rocks, the gas source fault activity period analysis and the evolution of caprock sealing ability, the relationship between fractures and natural gas accumulation was discussed. The fractures consist of primary and secondary fracture types, and the latter is the predominant type. The distribution of tectonic fractures is controlled by the lithology, lithofacies, fault and unconformity. Tectonic fractures formed mainly in three periods. The second period of tectonic fracturing (Late Quantou?QingshankouPeriod) is contemporary with the peak of hydrocarbon generation, when the gas source faults were active and the caprock had a good gas sealing capacity. So, the Late Quantou?QingshankouPeriod was the mainly natural gas accumulation period.