Abstract: Based on near miscible flooding mechanism, the miscible phase can be achieved with the increase of miscible pressure, even though there is little middle molecular weight of crude oil. High miscible pressure of this kind of crude oil is required, which is hard to be achieved for reservoir gas injection engineering. However, based on nearmiscible flooding mechanism, the nearmiscible flooding of vaporcondensate double mass transportation action under lowest miscible pressure may be formed with wet gas or enriched gas produced by proper choose of composition of gas injected. Its character is the creation of low interface, which can reduce the injection pressure and arrive at the miscible flooding efficiency. Based on a practical reservoir in offshore oil field, the associated rich gas in the reservoir is rejected, through the simulation and experiment of multiplecontact PVT phase behavior and intermiscibility swelling between gas injected and formation oil, the change laws of PVT high pressure physical property and the change characteristic between the formation oil and gas injected during nearmiscible multiplecontact process are described and the near miscible flooding mechanism of associated rich gas injection of marine oil field are explored.
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Key words: rich gas flooding, nearmiscible, multiplecontact, flooding, gas injection