Abstract
In May 1991 an immiscible carbon dioxide injection project began in the Sergi-C reservoir in the Main Block of Buracica Field. The injection has been performed in seven wells located in the upper part of the reservoir. Some time after the beginning of CO2 injection, the reservoir pressure increased and an increment of the oil production was attained. But, later on, the producing wells in the upper rows, beyond being the most productive wells, were also those that experienced the higher producing rates of CO2. This obliged for the shutting in of some wells and also the creation of a gathering system for the CO2 being produced, with the connection of the annular space of some wells to their pipelines. It was verified that the producing rate of gas and CO2 followed close upon the CO2 injection rate. Production data and simulation results have shown that the interruption or reduction of the CO2 injection would cause a significant reduction of the oil production. Due to the great demand for CO2 by new projects it was considered which would be the best way for ceasing the CO2 injection in the field, aiming at an increase in the supply of CO2 for other projects, but reducing its detrimental effect on the oil production. The adopted solution consisted in the creation of a water barrier for isolation of the CO2 cap. For this, seven wells closer to the gas-oil contact were chosen for water injection of a total rate of 2400 m3/day. The plan considers the interruption of CO2 injection when the water barrier is completely formed, which will take about 4 to 5 years after the beginning of the water injection. At that time the CO2 injection can be interrupted without impairing the project profitability. The water injection began in January 2002 and since then the project has been showing to be a success. The success can be seen by the increase in the oil rates and reservoir pressure and also reduction of CO2 production. The paper presents the main features of the project, as well as the results attained so far.
