This paper is based on laboratory research which is focused on the potential applications of CO2 gas, existing in different reservoirs in Indonesia, especially in the D-Alpha Gas Reservoir in Natuna Sea. CO2 gas as an injection fluid into oil reservoirs has been a well recognized and well tested Enhanced Oil Recovery (EOR) method, because CO2 dissolves easily into oil, it reduces oil viscosity, and it can extract the light components in oil at sufficiently high pressures. The technical contributions that can be derived from this paper are: first, the cost of disposal of CO2 produced with natural gas can be saved, second, CO2 injected into nearby Natuna oil reservoirs will increase oil recovery of those reservoirs, third, the best method among several alternatives offered in this paper to maximize the benefit in recovering more oil can be selected. There were three objectives we wanted to achieve in these laboratory experiments. The objectives are to obtain oil recovery performance and to identify the interactions between fluids as a result of, first, CO2 dissolved in Water (carbonated water) Injection, second, CO2 slug and chase fluid injection, and third, CO2 injection with the addition of a surfactant slug and water into oil reservoir. The results showed that the cemented sand core delivered consistent results during the whole series of experiments. The sandpack has apparently altered during the experiments. The scaling coefficient calculations have shown that all displacement fronts are stable. All displacements have shown that oil recoveries with these methods are higher than with waterflood only. The observations on different displacement angle have shown that gravity plays an important role in the recovery process, so does CO2 gas concentration in injection water, CO2 slug size and surfactant concentration. It has been observed also that there are optimum values for those parameters, meaning that above those optimal, there is no increase in oil recovery. We conclude that these methods could offer alternatives in improving oil recovery, even after waterflood, also that the operation parameters should be optimized to maximize the benefit.

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