The Su Tu Den-South West (STD-SW) field is located in the Cuu Long basin. The basement reservoir contained 450 MMstb oil initial in place. The current oil recovery after 7 years of production is about 87 MMstb. The area was produced by water injection with support of bottom aquifer. The producers, located at the crest of the high relief structure are exhibiting a high water cut. Since 2007, some producers with high water cut have been side tract to optimize the oil production of the reservoir that consists of granite. A kaolinezed weathered zone ranging in thickness from 4 to 55m covers the fresh granite. A Black Oil model was used to simulate the flow in the both weathered and granite zones. The main recovery mechanisms for this reservoir are imbibition and water/oil gravity drainage. The study results show that an economical attractive option for the field development is establishing an underground CO2 storage after using EOR-CO2 technique. The CO2 injection lead to CO2/oil gravity drainage of the oil and water present in the micro fractures of reservoir. The oil collected by the horizontal producers, resutling in incremental oil recovery of up to 15% of oil in place. To increase the amount of CO2, that can be used for underground, water (and more oil) have to be withdrawn from the reservoir.
