Multiple contact miscibility test for both forward and backward technique was conducted on light live reservoir crude with the API value of 41.5°. The experiment was conducted in four stages. At each stage of the experiment, a small amount of liquid and gas were sampled out from the PVT cell for compositional analysis.The multiple contact miscibility test simulate the continuous multiple contact process when the injection gas Carbon Dioxide (CO2) is injected into the reservoir fluid. In this study, the injection gas was mixed with the crude oil to achieve equilibrium at reservoir pressure and temperature. Dynamic miscibility between oil and Carbon Dioxide, which was not miscible on first contact was achieved by in-situ mass transfer of components between phases. This mass transfer phenomena, however, is not the same for forward and backward method of multiple contact miscibility test. At each stages of the test, different component has been transferred between phases with different amount and rate.
The results indicate that the amount of methane in vapour phase had increased significantly, as the number of contacts increases for both forward and backward multiple contact tests. The intermediate fraction became lighter and lighter as the contact progress. While the heavier component that was left out in the liquid phase susceptible to flocculate and produce heavy deposit such as asphaltenes. The phase envelope for liquid phase was generated using PVTi software with compositional data as an input. The change in the phase envelope shape explained the process that happened at each stages of the experiment. Ternary diagram was build to explain the difference in extraction process between forward and backward multiple contact test.
In conclusion, for CO2, some period of immiscible displacement must occur before mass transfer between reservoir oil and the advancing gas front establishes dynamic miscibility. This phenomenon was observed for both backward and forwards multiple contact experiment.