CO2 retention values in enhanced oil recovery

Carbon dioxide (CO2) retention is the fraction of the injected volume trapped in the subsurface as a result of enhanced oil recovery (EOR). CO2 retention is determined by multiple factors acting generally in combinations varying according to the geology of the reservoir and the implementation of the recovery. Primarily, the factors are the amount of CO2 remaining in the pore space connected to injection wells but not to the producer; dissolution into the formation water, subjacent aquifer, or both; accumulation in the pore space vacated by produced oil; chemical reaction with the minerals in the matrix; and loss to a thief zone. Accurate modeling of retention is important in the evaluation of the economics of reservoir development and in the assessment of potential CO2 sequestration. This contribution deals with 23 units containing information relating retention rates to the amount of CO2 injected in EOR operations. For all but two units, the flooding is miscible and all but two units are in the United States. Compilation of values reported in the literature shows a tendency for higher values of retention for carbonate than for siliciclastic reservoirs.