Within the next decade, the potential for application of gas miscible flooding process can be enormous, particularly, in those reservoirs currently under waterflood. In general, reservoir pressures of these oil fields are maintained at relatively high pressure, which is favourable for application of gas miscible flooding. We conducted a feasibility study to investigate the application of hydrocarbon gas miscible flooding in an oil field in Middle East offshore area. This oil field has a plan to utilise the high pressure hydrocarbon gas produced from deeper gas formation beneath the target oil reservoir, as the injection gas. A series of laboratory tests, comprising of: (1) Phase behaviour tests, (2) Slim tube displacement tests and (3) Composite core displacement tests, were conducted to characterise the miscible process in the crude oil-injection gas system. With the help of phase behaviour tests such as swelling test and multiple-contact test, the equation of state (EOS) parameters were fine-tuned. The minimum miscibility pressure (MMP) was determined by the slim tube displacement tests and also a set of representative EOS parameters were successfully verified by simulating slim tube displacement performance. As the MMP is still below the current reservoir pressure, the composite core displacement tests were conducted to evaluate the displacement efficiency at the current reservoir pressure as the tertiary oil recovery after water flooding. The test results showed that more than 80% of residual oil after water flooding could be recovered. Finally, the compositional reservoir simulation studies for the sector model of the target oil reservoir were conducted and it too, indicated that hydrocarbon gas miscible flooding could be feasible in such a high water-saturation oil reservoir.

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