| The reservoir heterogeneity of KeKeYa X41condensate gas reservoir is serious, whose edge water energy is weak. After years of natural depletion, the present formation pressure is below the maximum retrograde condensation pressure, reservoir energy is insufficient, productivity declines obviously, retrograde condensation is serious, producing gas-oil ratio increases sharply, the recovery of the reservoir is low, and the remaining reserves are large. Thus, based on this real condensate gas reservoir, the indoor experiments and combined with numerical simulation method was run to study the EOR mechanism by injecting CO2and natural gas respectively. The effect evaluation of condensate oil recovery by CO2and natural gas injection were carried out. Finally, an optimal scheme was obtained for the development of KeKeYa X41condensate gas reservoir, which can provide technical support for secondary development of KeKeYa condensate gas reservoir.In this paper, the research includes:the phase behavior of original reservoir fluids in initial development phase; phase behavior of residual oil system and formation balance gas by CO2and natural gas injection; tubule experiment of present residual oil system by CO2and natural gas injection; long core displacement efficiency experiment; the mechanism of gas injection by the numerical simulation research. The conclusions obtained from the above research are as follows:(1) X41condensate gas reservoir belongs to the type that the content of C7+is less and is rich. The dew point of K401well is the original formation pressure. When the formation pressure drops to15.68MPa, it can get maximum condensate saturation,9.58%. With the loss of the formation pressure, the contents of C7+in the produced fluids has been a declining trend.(2) After injecting CO2or hydrocarbon gas into remaining condensate oil system, it can make saturation pressure, expansion factor and the dissolved gas oil ratio increasing. And compared with hydrocarbon gas injection, CO2injection can cause greater decline in density difference, viscosity difference and interfacial tension between oil and gas. So compared with hydrocarbon gas, CO2can make it easier to change properties of gas condensate, thus it can narrow the property difference between oil and gas, and create more favorable conditions for miscible. Injecting CO2or hydrocarbon gas into remaining condensate oil system belong to multiple contact miscible displacement. And the miscible pressure of CO2injection is less than hydrocarbon gas injection. (3) Injecting CO2or hydrocarbon gas into balance gas can reduce its dew point, so as to reduce the amount of retrograde condensate fluid. Under the same pressure and with the same amount of gas injection, the reducing amount of retrograde condensate resulted by CO2injection is two times than hydrocarbon gas injection.(4) The tube experiment have shown that when the formation pressure was above17.8MPa, CO2injection can realize miscible flooding, and hydrocarbon gas is27.1MPa miscible flooding. Tube simulation results show that:the injecting gas can constantly extract the intermediate hydrocarbon and heavy components of gas condensate. It also can dissolve in condensate oil unceasingly, in order to increase the volume of a gas condensate, enhance the expansion of condensate, reduce the viscosity of gas condensate. The higher the gas injection pressure and the greater the injection volume, the less the rest of the condensate in the tube and the closer the piston displacement.(5) From the long core experiment, we can know that when bringing pressure from10.34MPa to15MPa and25MPa, respectively, the displacement efficiency by CO2injection is higher than hydrocarbon gas injection. For the same kind of injected gas, the condensate recovery degree in25MPa is always higher than that in15MPa. It can show that the higher the injection pressure, especially when it is above the miscible pressure, it can get higher condensate oil recovery.(6) By utilizing compositional model of CMG, numerical simulation model of gas(CO2〠hydrocarbon gas) flooding for enhancing condensate oil recovery has been established. In this model, some sensitive factors are taken into consideration, such as injection-production well pattern, injection rate, injection pressure (maintaining level of reservoir pressure). As a result, the reasonable injection-production pattern, injection fluid, injection rate and injection pressure are optimized to be2:3, CO2,50000m3/day and20MPa, respectively. |
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