CO2提高天然气采收率的重力效应与气藏压力影响模拟

利用TOGUH2开展均质天然气藏模型中实施CO2提高天然气采收率的模拟研究,分析重力效应作用机制和气藏压力对CO2运移和CH 4采收率变化规律的影响,为CO2提高天然气采收率的工程应用提供指导。模拟结果表明:重力效应抑制CO2向上运移,减缓了CO2与天然气纵向方向的混相,间接促进水平方向运移,导致气藏内CO2水平运移速率显著大于纵向运移速率,但是CH 4采收率曲线不仅受重力效应影响,也受CO2注入流速和气藏压力的综合影响;气藏内的CH 4生产时间及最终采收率随气藏压力降低而增加,在枯竭状态的低气藏压力条件下实施CO2提高天然气采收率能够获得更好的CH4采收率,但生产时间相对较长;较高气藏压力条件下,CO2为超临界状态,重力效应作用明显,CO2快速沉降并优先驱替气藏底层CH4,但是容易从生产井底部自下而上突破至生产井,提高天然气采收率效果不佳。

Simulation on gravity effect and reservoir pressure influence analysis in CO2 enhanced gas recovery

In this study,TOGUH2 simulator was applied to simulate CO2 enhanced natural gas recovery(CO2-EGR)with a homogeneous natural gas reservoir model,in which the gravity effect and influence of reservoir pressure on CO2 migration and CH 4 recovery were studied in order to provide theoretical support for the application of the CO2-EGR technique.The simulation results show that the gravity effect can inhibit upward migration of CO2 and slow down the vertical mixing of CO2 and CH 4,which can indirectly promote the horizontal migration and make the horizontal displacing rate significantly greater than the vertical one.However,the produced curve of CH 4 is not only determined by gravity effect,but also affected by CO2 injection rate and reservoir pressure.The CH 4 production time and final recovery efficiency increase with the decrease of reservoir pressure,and better CH 4 recovery efficiency can be achieved at the depleted reservoir pressure than other operation conditions,while the production duration can be relatively longer.When CO2 is in a supercritical state at relatively high reservoir pressure,the gravity effect can have relatively significant effect on the displacement process.CO2 can rapidly sink and preferentially displace CH 4 in the bottom layer of the gas reservoir,but it can break through vertically from the bottom of the production well,resulting in a poor natural gas recovery.