Abstract
CO2-EOR application to the offshore oilfield in Vietnam has been investigated through an international joint study between Vietnam and Japan since 2007. Preliminary studies: laboratory experiments, screening study for CO2 recovery and simulation study indicated the feasibility. To reduce and mitigate uncertainties and risks in the field scale EOR implementation, the first offshore CO2-EOR pilot test was executed in Rang Dong oilfield, May 2011.
The test was conducted in the method of “Huff ‘n’ Puff” in Lower Miocene sandstone of Rang Dong oilfield, where oil has been produced since 1998. The test was designed to optimize CO2 injection volume, soaking time, production duration and monitoring plan. Operational risks were also assessed because of unpracticed CO2 handling and the uncertainties of the reservoir performance, then contingency plan was prepared as countermeasure against the risk.
In the actual test, over 110 tons of CO2 were successfully injected into the target reservoir. No safety and environmental issues were observed throughout the test operation. Bottom-hole pressure was kept higher than Minimum Miscibility Pressure (MMP) during the injection period, thus miscible condition was considered to be achieved near the wellbore. The intervals where CO2 injected were identified from oil saturation changes measured by several saturation logs and production log. Oil increment and water cut reduction from original pre-CO2 injection flow were clearly observed during post-CO2 injection flow (Puff) period, and oil composition change of fluid samples indicated oil vaporization and CO2 condensation into oil. CO2-EOR effects were clearly observed based on the monitored data and experimental results, such as production/injection performance, bottom-hole pressure, wireline logs, on-site fluid analysis and laboratory experiments after the test. The simulation model that integrated these data showed good agreement with the actual behavior and quantitatively evaluated the incremental oil.
