More than four billion barrels of heavy oil remain in the oil fields of Trinidad. If these oil fields are exploited, the country's total oil production can increase significantly. However, heavy oil is difficult to produce, due to its high viscosity, and only a small fraction is recovered after primary recovery. Therefore, it is necessary to implement enhanced oil recovery (EOR) techniques to increase heavy oil production. Two of the most commonly used EOR techniques are cyclic steam stimulation (CSS) and cyclic CO2 stimulation (CCO2S). These processes have a long history of successful heavy oil recovery in Trinidad and Tobago when applied individually. However, very little research was found regarding the combination of both processes which was the basis for this study
A test reservoir, located in the southern basin on land Trinidad was selected and a computer simulation model was built, using the Computer Modelling Group (CMG) software to determine the production analysis. Sand, structure and pay maps were obtained and digitized, using the Didger Five software and then uploaded into the CMG software. Reservoir properties and production data were also uploaded. Wells were then added to the model at the exact location indicated on the structure map. Simulations were conducted using varying injection rates, slug size and soak times for CSS, CCO2S and combined CSS and CCO2S to determine optimal EOR performance and production.
The combination of CSS and CCO2S show an increase in recovery by 8.6% and to be profitable at oil prices higher than USD 14/bbl. It is also best used as a first step for other enhanced oil recovery techniques to further increase recovery. In addition, the results show that 8 out of 17 wells were more responsive to CSS and CCO2S when applied individually than when combined.