Numerical simulation of Water-alternating-gas Process for Optimizing EOR and Carbon Storage

As concerns around global warming increase, carbon capture, utilization and geological storage (CCUS) is a promising way to reduce the emissions of the anthropogenic CO2 into the atmosphere. Of those, sequestering the CO2 into depleted hydrocarbon reservoirs with associated enhanced oil recovery is the most achievable approach under current economic constraints since it increases recovery of existing oil reserves, and bridges the gap between regional-scale CO2 capture and geologic sequestration. The Upper Devonian fluvial sandstone reservoirs in Jacksonburg-Stringtown oil field in West Virginia, which have produced over 22 million barrels of oil since 1895, is an ideal candidate for CO2 sequestration coupled with EOR. This work illustrates an example of CCUS, in which CO2 is simultaneously sequestered and oil recovery enhanced in a depleted oil reservoir by water alternating gas (WAG) method. Three mechanisms for CO2 storage including structural/stratigraphic trapping, dissolution trapping and residual trapping are considered. This model is based on a highly detailed geological model constructed based on existing legacy geological data from the field. A composition model of 0.4 PVI of water injected before WAG process is considered as a benchmark for this study. The results of numerical simulation show that over 26 years of WAG injection, oil recovery increased from 0.16% to 1.9% due to various injection strategies. WAG injection rate, injection time ratio and cycle period play important roles in the storage CO2. As a conclusion, this research constructs and validates a basic workflow for CO2 storage and CO2-EOR that can be applied to other super-mature oil fields, which have abundant conventional legacy data and limited high-quality data.