致密油储层CO_2驱核磁共振实验研究

Nuclear Magnetic Resonance( NMR) Experimental Study of CO_2 Flooding in Tight Reservoir

针对致密油储层动用困难问题本研究以CO_2为注入介质,对致密油注气开发效果进行评价,并借助核磁共振技术,从微观角度阐述了致密油储层注CO_2的驱替特征。实验结果表明,CO_2驱可以有效启动赋存在致密孔隙中的原油,非混相压力下(10 MPa),CO_2突破快,小孔隙中原油未动用,驱替后原油饱和度分布不均匀,驱替效率低;而在混相压力之上(24 MPa),CO_2突破明显变慢,驱替后原油饱和度均匀下降,大小孔隙中的原油均被启动,采出程度较高。此外从采出原油组成可以看出,高压下CO_2抽提作用非常明显,原油组分以C7~C29为主,几乎不合C30+组分,这表明CO_2会导致原油中重质组分在孔隙中沉积。

Regarding the difficulty in tight oil recovery,the effect of CO2 flooding technique was investigated in the development of tight oil reservoirs,in addition,the characteristics of CO2 flooding in displacing tight oil were also studied using nuclear magnetic resonance（NMR） from the micro-scale view.The experimental results indicated the CO2 flooding is capable of recovering the oil reserved in tight formation.Below the minimum miscibility pressure（10 MPa）,CO2 was found to breakthrough early,and the oil trapped in the small pores was not mobilized.The residual oil was heterogeneously distributed along the core and the overall displacement efficiency was relatively lower.On the contrary,above the minimum miscibility pressure（24 MPa）,CO2 showed a later breakthrough,and the residual oil profile exhibited a homogeneous dropping compared to the initial stage.Moreover,the oil trapped in large and small pores was both mobilized and accordingly the overall recovery efficiency was improved.Furthermore,CO2 presented a significant extraction effect at high pressure,and thus the produced oil was mainly composed of C7 ～ C29,C30 ＋ components were not observed.In other words,CO2flooding would lead to heavy component precipitation and deposition in porous media.