四川盆地合川地区致密砂岩气藏特征与分布预测

Characteristics and Distribution Predicting of Tight Sandstone Gas Reservoir in Hechuan Area,Sichuan Basin

四川盆地合川地区须二段气藏具有低孔、特低渗的特点,属于典型的致密砂岩气藏。盆地模拟结果显示:须二段经历了快速埋深、抬升、再埋深和再抬升4个阶段;在白垩纪之前须二段已完成压实成岩阶段;其下须一段开始生气时间为侏罗纪末,大量生气时间为白垩纪,进入新生代后不再生气;主要成藏期为白垩纪中后期,即天然气主要成藏事件发生在砂岩致密之后。根据先致密、后成藏的地质模型和致密砂岩气藏非浮力驱动的特点,建立数值模型,并采用该模型定量模拟致密砂岩气资源丰度的分布,模拟结果发现:在已发现的合川1块和潼南2块,预测结果符合率达到88%,说明预测模型是合理的;该区还有约一半的天然气资源未发现,主要分布在合川东北部、潼南北部和东南部。

T3x2 gas reservoir is a typical 'tight sandstone gas' reservoir,which features in low porosity and ultra-low permeability.The basin modeling results shows that T3x2 gas reservoir has gone through four processes:burial,uplift,re-burial and re-uplift.T3x2 was compacted and became tight sandstone before the Cretaceous.T3x1,which lies beneath T3x2,started to generate gas in late Jurassic.The peak of gas generation started in late Cretaceous and ended in Paleocene.The critical moment of gas migration and accumulation was in late Cretaceous,that is early than the age when T3x2 became tight sandstone.Based on the geological models and the characteristics that the buoyancy of gas in water is not the main drive of gas flow in tight sandstone,this paper proposes the method of modeling gas migration and accumulation,and then uses it to predict the gas distribution in T3x2.As a result,the modeling is consistent 88 percent with the actual data of the discovered resources at Hechuan1 Block and Tongnan2 Block.It confirms the predicting model is rational.Furthermore,the modeling results show there are half of natural gas undiscovered in the Hechuan area,located at the northeast of Hechuan,and north and southeast of Tongnan.