Selection of an EOR technique for the matured EOR 33 reservoir in Southern Trinidad using adsorption and simulation studies

Steadily decreasing oil production due to the maturation of oil fields and generally low energy commodity prices in Trinidad and Tobago (TT) have highlighted the need for more economical methods of enhanced oil recovery. These factors have also stimulated advances in research on the possible utilization of Enhanced Oil Recovery (EOR) technologies in TT. Estimates have shown that there is in excess of 1 billion barrels of oil in place (OIP) in reserves located in South West Trinidad where suitable EOR techniques can be employed to produce oil from these reserves. This study evaluated the outcomes after the application of various EOR techniques including CO2, waterflood (low and high salinity), Xanthan gum (XG) polymer slug, and polymer gel slug (low and high salinity) on the matured EOR 33 reservoir located in the lower Forest sands in Southern Trinidad. The simulated performance characteristics were obtained digitally utilizing the compositional reservoir simulation modelling (CMG-GEM) software where values of oil recovery %, reservoir pressure, and water cut % were obtained for each EOR technique. A comparison of the performance attributes was used to determine the best EOR option for the EOR 33 reservoir. A novel experimental and simulation approach was employed. The nature of the adsorption interaction between XG and gravel packed sand was studied in the laboratory and the Langmuir coefficients were generated for interactions at different salinities which were then incorporated into the simulation protocols to produce enhanced EOR projections. The results indicated that all the EOR strategies applied to EOR 33 resulted in an improvement in the oil recovery % (ranging between 28 and 54%). Compared to the CO2, water flood, and polymer flood strategies, the gel slug polymer flooding strategy resulted in the highest oil recovery factors with a maximum value of approximately 54% occurring at 1000 ppm NaCl. This strategy also yielded an associated water cut of 97% and a pressure of 617 psi demonstrating that this combination is the best EOR strategy for use in the EOR 33 reservoir and is an appropriate choice for process of optimizing oil recovery within these fields. This study also highlights the significant potential for the use EOR methods in heavy oil reserves located in South West Trinidad.