Study On Mechanism And Remediation Of Condensate Oil In Low Permeability Sandstone Condensate Gas Reservoir

In the process of gas condensate reservoir’s depletion development, retrograde condensation phenomenon inevitably appears in the formation when layer pressure drops below the dew point. Condensate oil accumulates in near wellbore zone, which reduces the gas effective permeability significantly and results in decline of gas production or even shutting down of gas well, so the retrograde condensation damage occurs. Especially for the tight low permeability gas condensate reservoir which has poor reservoir property and high decline rate of productivity, the impact of retrograde condensation damage on the development effect is particularly hard. Therefore, it’s necessary to correctly assess the impact of condensate oil pollution on gas well production and find out mechanism of condensate oil pollution as well as developing effective method to remove that pollution, so that the condensate oil is produced as much as possible and better development effect of low permeability gas condensate reservoir is obtained.In this paper, experimental research on mechanism of condensation oil pollution for two kinds of condensate oil and gas system is conducted using two methods through indoor physical simulation approach, and gas permeability of different fluids in different retrograde condensation region is compared; after that, experimental research on removing condensate oil pollution for the condensate oil and gas system which has higher damage degree is conducted, and condensate oil recovery under different ways of removing pollution is compared so that the optimal way of removing pollution is obtained combining with the practice; finally, single well model of gas injection huff and puff is established by using numerical simulation software so that the case study is made for a specific low permeability gas condensate reservoir and the optimal parameters of huff and puff is obtained.Research results show that:under the same depletion pressure and for the same kind of fluid, the damage degree of condensate oil in near wellbore region is higher than that in far wellbore region; in the same retrograde region, the condensate gas with higher condensate oil content has more serious damage degree; compared with depletion development, cyclic gas injection on dew point pressure has the best effect to remove condensate oil pollution, however, combining with the practice and the technological requirement, the mode of early depletion development and injecting dry gas to huff and puff in the late is more appropriate for the research object in this paper (condensate oil and gas system with medium condensate oil content in low permeability sandstone reservoir with no fracture); for the actual AY gas condensate reservoir, the optimal parameters of gas injection huff and puff are:the total gas injection amount90×104m3, injection rate4×104m3/d, soak time10days, production rate2×104m3/d, huff and puff cycle1time; condensate oil and gas recovery can be increased0.468%and2.794%respectively.The research results in this paper can intensify the understanding of mechanism of condensate oil pollution and remove method. The gas injection huff and puff scheme optimized has been already implemented at the scene, and the permeability environment of gas is improved effectively and the production pressure difference is reduced significantly, which show that the development of similar gas reservoir has been guided by the research results.