渤海海域烃源岩三峰接力生气特征及意义

Characteristics and Significance of Triple Natural Gas Peak Relay Generation of Source Rocks in Bohai Sea Area

渤海海域是当前和未来海上领域天然气勘探的重要方向,明确渤海海域天然气的生气机制、潜力和成藏机理,将有助于发展天然气成因理论和指导渤海海域油气勘探。通过渤海海域辽中凹陷典型烃源岩模拟实验,研究渤海海域主力烃源岩生气特征,建立渤海海域主力烃源岩生气模式;结合典型油气藏成藏机理解剖,识别不同类型天然气成藏规律,探讨天然气潜力和方向。研究认为:渤海海域沙三段II1型和II2型烃源岩具有三峰接力生气的特征,三期生气高峰分别对应Ro为1.0%(①)、1.5%(②)、2.7%(③),三个生气高峰呈现一种间歇式接力生气的特征,三个生气高峰对应的总产气量具有峰③≈峰②>峰①;渤海海域辽中凹陷普遍发育峰①、峰②阶段生成的天然气藏,其中峰①主要呈常压油气藏聚集于靠近烃源岩的斜坡带,峰②主要呈超压凝析气藏聚集于凸起带等构造高部,峰③形成的天然气只在局部井点有所发现,表明辽中凹陷深部烃源岩已经进入峰③阶段,具备形成大型过成熟气藏的潜力。

The Bohai Sea area of the Bohai Bay Basin is an important direction in oil and gas exploration at present and in the future.Understanding of the generation pathway,mechanism,and potential of natural gas at Bohai Sea area is beneficial for developing the natural gas generation theory and guideing petroleum exploration in the Bohai Bay Basin.Through the simulation experiment of typical source rocks in Liaozhong Sag of the Bohai Sea area,the generation characteristics of main source rocks in the Bohai Sea area are studied,and the generation model of main source rocks in the Bohai Sea area is established.Based on the analysis of typical hydrocarbon accumulation mechanism,the accumulation regularity of different types of natural gas is identified,and the potential and direction of natural gas are discussed.The results show that Type II1 and Type II2 hydrocarbon source rocks of the third member of the Shahe Formation in the Bohai Sea area have the characteristics of triple peak relay gas generation.The Ro of the three gas generation peaks is 1.0%(①),1.5%(②)and 2.7%(③),respectively.The three gas generation peaks show intermittent relay gas generation characteristics.The total gas production of the three gas generation stages has a Peak③≈Peak②>Peak①;Natural gas reservoirs generated at Peak①and Peak②stages are generally developed in Liaozhong Sag of the Bohai Sea area,among them,Peak①mainly shows atmospheric pressure oil and gas accumulation in the slope zone close to the source rock,and Peak②mainly shows overpressure condensate gas accumulation in the uplift zone.The natural gas formed by Peak③is only found at local well points.It shows that the deep source rocks in Liaozhong Sag have entered Peak③stage and have the potential to form large over-mature gas reservoirs.