In today's industrialized world, the generation and emission of greenhouse gases, more specifically CO2 and flue gas, are likely to continue. One of the solutions to the reduction of the emission is to store those gases permanently inunderground reservoirs. Sequestration of CO2 and/or flue gas is not cheap, however, the injection of those gases into oil or gas reservoirs to enhance production may offset some of the associated costs of doing this.
The use of CO2 for purely enhanced oil recovery purpose versus injection of CO2 primarily for sequestration aretechnically two different problems. In conventional CO2 EOR projects, the main purpose is to increase the amount of oil roduced per amount of CO2 injected. In this particular case, i.e., injection of CO2 for sequestration, the optimization problem turns out to be produce maximum oil with the highest amount of CO2 storage.
In this paper we investigated the optimality of CO2 storage process into oil fields using field scale numerical modeling.The amount of greenhouse gas sequestered during tertiary oil recovery for a West Texas reservoir using a commercial compositional simulator (CMG-GEM) was studied. Differentinjection strategies such as (1) miscible flooding, (2) immiscible flooding, 3) water altering gas (WAG) flood and 4) flue gas injection were considered. The influences of operational parameters such as injection pressure, composition of the gas (pure CO2 or flue gas), WAG ratios, injection rate, injection and production well constraints (completion), vertical heterogeneity, and injector location on maximum oil production with maximized gas storage were analyzed. Also considered were the effect of the amount ofwater in reservoir (history of production) and the relative permeabilities. The evaluations were performed at two points:
the breakthrough of CO2, and
abandonment gas-oil ratio.
Optimum injection strategies yielding maximum oil recovery and maximum CO2 storage were evaluated. The evaluation was performed not only for the amounts of oil recovery and CO2 storage but also the economics of the process. We provided a calculation procedure to estimate the cut-off point at which the governmental incentives become more critical compared to the revenue obtained from incremental oil recovery.
Fossil fuels are likely to remain a major primary source of world's energy supply in today's industrialized world becauseof their inherent advantages such as availability, competitive cost, ease of transportation and storage, and well-advanced technology over other energy sources [1,2].
The combustion of fossil fuels for energy is the major source of anthropogenic CO2 and will likely continue over the next century. The concentrations of CO2 in the atmospherehave increased by 31 percent since 1750 [3]. Of the total CO2 emissions in the United States in 2002, approximately 98% resulted from the combustion of fossil fuels (coal, petroleum, and natural gas). Industrial processes, including gas flaring and cement production, accounted for the other 2 percent [4].
Fossil fuel combustion for electricity generation is the largest contributor to CO2 emissions in the United States followed by fossil fuel combustion for transportation.
