深盆气藏的主要特征及形成机制

在国外深盆气地质理论的基础上 ,结合我国深盆气勘探开发实际 ,对深盆气的主要特征进行了分析 ,深盆气藏位于向斜盆地轴部或坳陷深处 ,分布规模巨大 ,气水关系倒置 ,多具异常压力 ;主要储层虽为致密砂岩 ,但多含饱和气的渗透性储层 ;海陆交互相的煤系地层是深盆气藏的主要气源岩 ,储层与成熟气源岩的接触是深盆气形成的必要条件 .在分析国外深盆气形成的动态圈闭机理和扩散运移方式存在问题的同时 ,提出了对深盆气藏形成机制的新认识 .我国鄂尔多斯盆地和四川盆地都存在丰富的深盆气资源 ,其它类似结构的盆地都有可能存在深盆气 ,应进行勘探潜力分析 .

Basic Characteristics of Deep Basin Gas Traps

Abundant geological data from the deep basin gas productive regions reveal the basic characteristics of deep basin gas traps. Gas is trapped in the deepest part of the basin. The gas/water contact occurs at the updip end of the accumulation. Most deep basin gas accumulations have original gas pressures that lie abnormally. The gas accumulation is extensive. It occupies low permeability reservoirs incorporated locally with high permeability beds. The intimate association of reservoir rocks with thick, rich, mature source rocks is a key factor. Our model experiments suggest that the existence in a dynamic state of updip gas migration is not a prerequisite for the deep basin gas accumulation. The examples for illustrating the features of deep basin gas entrapment are found in the widespread Upper Paleozoic tight gas reservoirs of Ordos Basin and in the Upper Triassic productive zones of Sichuan Basin. These regions provide some of the best available information on the trapping mechanisms of deep basin gas.