缓解凝析气井反凝析污染的非平衡压降法

Non-equilibrium pressure drop method for alleviating retrograde condensate effect on gas condensate well deliverability

凝析气藏衰竭开采出现反凝析污染,如果衰竭速度控制不当,将严重影响气井生产。采用非平衡压降“雾状”反凝析控制技术可以缓解这种影响。该技术利用凝析油析出之初、其呈雾状的非稳态状态时,通过提高天然气流速使反凝析油即时形成即时采出,实现地层压力低于露点压力时反凝析油始终无法形成连续相,保持高的凝析油传输能力,并通过延长雾状流压力窗口实现反凝析污染的有效控制。首先通过Мирзажанзаде的非平衡压降理论结合非平衡定容衰竭相态实验,揭示了衰竭速度与“雾状”反凝析的内在规律;然后开展不同压降速度(1 MPa/h、2 MPa/h、3 MPa/h和4 MPa/h)下的长岩心反凝析伤害实验及衰竭开采实验,综合分析不同衰竭速度下的雾状流压力窗口和反凝析控制效果。结果表明,压降速度越大,反凝析出的“雾状”凝析油颜色越深,在凝析气中悬浮时间越长,随高速气流产出量越多;当压降速度为4 MPa/h时,雾状流压力窗口为10.5 MPa(46.5~36.0 MPa),储层反凝析污染改善效果最好,凝析油采收率最高,但对天然气采收率影响不明显。因此,综合考虑气井出砂和气窜情况,适当增大衰竭速度,有利于缓解近井地带反凝析污染,提高凝析油采收率。

Retrograde condensatedamage occurs during the depletion development of gas condensate reservoirs,and it will significantly affect the production of gas wells if the depletion rate is not well controlled.This effect can be inhibited to some extent by using a retrograde condensate control technology with a non-equilibrium pressure drop.The mechanism of the retrograde condensate control technology is that the retrograde condensate formed at the beginning is timely produced with the natural gas by increasing the flow velocity,and the retrograde condensate in the non-equilibrium state does not form a continuous phase and possesses a high transport capacity even if the formation pressure is smaller than the dew point pressure,moreover,and the retrograde condensate could be well controlled by extending the fog flow pressure window.In this paper,firstly,an inner relationship for depletion rate and“fog”retrograde condensate control is described by using the non-equilibrium pressure drop theory proposed by A.X.Мирзажанзадеcombined with phase state experiments of non-equilibrium constant volume depletion.Then damage test and depletion test of the long core at different pressure drop rates,including 1 MPa/h,2 MPa/h,3 MPa/h,and 4 MPa/h,are conducted and the effect of the retrograde condensate with a fog state in porous media at different depletion rates was evaluated.The results show that the greater the pressure drop,the darker the retrograde condensate with the fog state looks,and the longer the time of the retrograde condensate suspended in the natural gas,the more the retrograde condensate is producedby the high-pressure drop rate.When the pressure drop rate is 4 MPa/h,the pressure window keeping the fog flow of the retrograde condensate is large with agap of 10.5 MPa(ranging from 46.5 MPa to 36.0 MPa),and the reservoir damage caused by the retrograde condensate is most inhibitedwith the highest condensate recovery,but the natural gas recovery keeps unchanged.Therefore,appropriately increasing the depletion rate,but preventing the sand production and gas channeling in gas condensate wells,is conducive toinhibiting the retrograde condensate damage near the zone of gas condensate wellbores and improving the condensate recovery.