Note Huff And Puff To Lift The Gas Condensate Wells Near Well Bore Formation Of Retrograde Condensate, Anti-clogging Mechanism Of Imbibition And Applied Research

The gas condensate reservoir is a sort of special gas reservoir. Due to the condensate exists in the form of gas in gas condensate reservoir, the retrograde phenomena would appear when pressure drop under dew point during the recovery process. Retrograde condensed liquid accumulation in the near wellbore formation will lead to blockage of the permeable passages and the decrease of gas wells productivities. Meanwhile, reverse imbibitions water blockage effect would be appeared to further damage the near the wellbore formation, especially in the low permeability and low productivity condensate gas wells. Therefore, describing the pollution mechanism of retrograde condensate and reverse imbibitions, developing the technical methods for decreasing and removing the formation damages caused by retrograde condensate and reverse imbibitions are problems that should be emphasized for the effective recover)' of low permeability condensate gas reservoir. In this paper, we summarized internal and external mechanisms and methods that reduce and remove the pollutions caused by retrograde condensate and reverse imbibitions, directing at single well gas injection huff and puff of low permeability gas condensate reservoir, we should study a more effective technical methods of removing these pollutions to enhance gas well productivities.This paper develops a phase equilibrium mathematical model based on oil-gas phase's equilibrium theory basis in gas injection process and simulates and calculates P-T and P-X phase diagram. In addition, a phase equilibrium model of a gas injection multicontact process is developed on the basis of studying mechanism of gas injection displacement and phase behavior of multicontact near miscible displacement is studied by simulation. These provide the theory of gas injection huff and puff methods.It is found that cumulative gas injection capacity has quite great influence on oil saturation of retrograde condensed liquid and gas relative permeability in the near wellbore formation through the numerical simulation research on a single well gas injection huff and puff of WD7 well. The more the cumulative gas injection capacity is, the larger extraction and evaporation of retrograde condensed liquid is, and the better effect of removing blockage is. The main mechanism of removing retrograde condensation blockage of pure dry gas injection single well huff and puff is implemented by the effect of extraction and evaporation of part of retrograde condensed liquid. Therefore, this method can only be used to remove retrograde condensed liquid blockage.Using the experiment to stimulate water blockage effect after building the critical flow saturation of retrograde condensed liquid in the long core. The water blockage effect is caused by the wellbore liquid accumulation reverse imbibitions before dry gas injection huff and puff. The pressure differential varying experimental process is described which followed by building the reverse imbibitions water blockage effect and injecting methanol solution for removing reverseimbibitions water blockage. The result indicate that methanol solution slug can break the water obstacle caused by water blockage and can push the formation water injected from injection side of core to far away. It can also effectively reduce the water blockage caused by formation water injected from injection side of core and decrease starting pressure of injecting process. By this method, a slug of methanol (or other surfactants) solution is injected before huff and puff to more effectively remove reverse imbibitions water blockage effect and enhance the condensate gas wells productivities.