| When formation pressure deplete to the dew point pressure, retrograde condensate phenomenon occurred during the development of condensate gas reservoir, before the gas condensate saturation gradually increasing at the critical flow saturation, gas condensate will not flow, 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. So researching the reasonable development way and removing the condensation pollution and producing the condensate oil as much as possible are of great significance for the effective development of condensate gas reservoir, at the same time it is an important trend of the development of condensate gas reservoir. The QD condensate gas reservoir belongs to low permeability gas reservoir which containing middle condensate oil. Currently formation energy of the gas reservoir is insufficient, and the gas condensate accumulated near the wellbore area, resulting the condensation pollution seriously. Appointed by TH oilfield, the project named "the theory and technology feasibility on improve oil and gas recovery of condensate gas reservoir in the middle and late development period" was conducted by our group members, and the research results would aid to provide theoretical reference for the further determination of technology policy.In this paper, using the gas reservoir engineering method we analyze the development present situation of QD condensate gas reservoir, including the analysis of the gas reservoir capacity and the classification or evaluation of46wells and the initial or present absolute open flow potential of33wells, the diminishing law analysis of13wells, J2X gas reservoir’s pressure system analysis, the calculation of the retrograde condensation saturation, the instability analysis of gas well test. On the basis of this, studying the feasibility analysis of gas injection about QD gas reservoir combined with retrograde condensation pollution experiment and remove condensate pollution, at the same time going the gas reservoir engineering research aimed at6injection gas wells so that determining the reasonable gas injection. After that, through the numerical simulation, establishing the single well gas huff and puff stimulation of QD condensate gas reservoir and the typical symmetry cyclic gas injection stimulation and the typical symmetry huff and puff stimulation. Designed28kinds of prediction scheme to optimize the total gas injection amount, injection rate, soak time, production rate, and the huff and puff cycle of the single well gas huff and puff parameters. Designing14kinds of prediction scheme to optimize the recirculating ratio and the production rate of the cyclic gas injection parameters. Finally to carry out the typical well group gas huff and puff prediction and then study the feasibility of enhancing recovery.Research results show that: In the middle-late period of QD gas condensate reservoir development, the absolute open flow potential of gas well decline seriously, the present average open flow potential of gas reservoir comparing to the initial fell by69.86%, the average decline rate was0.1639mon-1,and the retrograde condensate pollution is serious, but the gas well connectivity is better. The QD retrograde condensation pollution experiment of core prove that the biggest permeability reduction of gas reservoir was28.79%, and the removing retrograde condensation pollution experimental by gas injection prove that the recovery increased by9.48%comparing to the deplete production. Meanwhile, the injection gas well of QD reservoir can select the reasonable gas injection between the wellhead pressure of8MPa-20MPa, that proves the feasibility of gas injection for QD reservoir is higher, for the actual QD7gas condensate well, the optimal parameters of gas injection huff and puff are:the total gas injection amount200x104m3,injection rate12.5×104m3/d, soak time10days, production rate15×104m3/d, huff and puff cycle1time; condensate oil and gas recovery can be increased0.1904%and1.239%respectively. And when the optimal reinjection ratio of the typical well group is0.7, the cyclic gas injection restricted by injection volume, injection gas front scope is limited, not spread to the production wells, the degree of contact of the retrograde condensation pollution about production well bottom is limited, lead to the continuous gas injection effective is not obvious, which improving the recovery lowly. Finally combining with gas injection huff and puff and cyclic gas injection’s researching results, carried out the feasibility studying about the gas injection huff and puff for the same all gas wells, which proving the recovery of natural gas and condensate are better and the output input ratio is higher. Therefore it is feasible. |
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