歧口凹陷古近系天然气藏主要特征

歧口凹陷已发现板桥和千米桥两个中型凝析气田,通过近两年的预探,在埕海潜山和歧口古近系深层天然气勘探又取得了重要突破,显示出歧口凹陷天然气具有良好的勘探前景。从生储盖等成藏要素方面对歧口凹陷古近系天然气藏进行了系统的解剖,明确了歧口凹陷古近系天然气藏的主要特征。研究表明,歧口凹陷天然气主要分布在沙河街组中深层,浅层次生气藏主要位于构造圈闭中,中深层气藏位于构造岩性圈闭中;天然气成因类型以偏腐殖型气为主;储层类型以孔隙型为主,中深层裂缝发育,双重孔隙介质特征明显;两套最大湖泛期形成的区域盖层发育异常超压,天然气保存条件好;气藏主要位于高生气强度区,以晚期成藏为主,平面上具有"南油北气"、纵向上具有"上油下气"的分布特征。

Characteristics of the Paleogene gas reservoirs in Qikou Sag

Two condensate gas fields,i.e,Banqiao and Qianmiqiao,have been discovered in Qikou Sag.In addition,exploration breakthrough was also made in the Chenghai buried hill and the deep Paleogene in Qikou Sag,indicating good exploration prospect.This paper systematically analyzed the Paleogene natural gas reservoirs in Qikou Sag in terms of petroleum factors including source rocks,reservoirs and cap rocks,and described the key characte-ristics of the gas reservoirs.The result indicates that the natural gas mainly accumulate in the mid-deep strata of Shahejie Formation.The shallow secondary gas reservoirs mainly occur in structural traps.In contrast,the mid-deep gas reservoirs mainly occur in structural-lithologic compound traps.The genetic type of gas is dominated by humus type.The pore space of the reservoir is dominated by pores,with fractures occurring in the mid-deep layers,indicating dual porosity reservoir.Two regional cap rocks developed during the maximum flooding are overpressured and provide favorable preservation condition for gas reservoirs.The gas reservoirs mainly occur in areas with high gas generation intensity and are characterized by late hydrocarbon charging.The hydrocarbon distribution is characteri-zed by"gas in the north and oil in the south"and"oil in the upper interval and gas in the lower interval".