Analytical Estimation of CO2 Storage Capacity in Depleted Oil and Gas Reservoirs Based on Thermodynamic State Functions
- Ernesto Valbuena (Texas A&M University) | Maria Barrufet (Texas A&M U.) | Gioia Falcone (TU Clausthal)
- Document ID
- Society of Petroleum Engineers
- SPE Latin America and Caribbean Petroleum Engineering Conference, 16-18 April, Mexico City, Mexico
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.6.4 Drillstem/Well Testing, 5.8.8 Gas-condensate reservoirs, 5.4 Enhanced Recovery, 4.1.5 Processing Equipment, 5.2.2 Fluid Modeling, Equations of State, 6.5.3 Waste Management, 4.5 Offshore Facilities and Subsea Systems, 6.5.1 Air Emissions, 5.5 Reservoir Simulation, 4.1.2 Separation and Treating, 5.2 Reservoir Fluid Dynamics, 6.6.2 Environmental and Social Impact Assessments, 5.4.2 Gas Injection Methods, 6.5.7 Climate Change
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Numerical simulation has been used, as common practice, to estimate the CO2 storage capacity in depleted reservoirs. However, this method is time consuming, expensive, and requires detailed input data. This investigation proposes an analytical method to estimate the ultimate CO2 storage in depleted oil and gas reservoirs by implementing a volume- constrained thermodynamic equation of state (EOS) given average reservoir pressure and fluid composition.
This method was implemented in an algorithm which allows fast and accurate estimations of final storage, which can be used to select target storage reservoirs and design the injection scheme and surface facilities. Impurities such as nitrogen and carbon monoxide, usually contained in power plant flue gases, are considered in the injection stream and can be handled correctly in the proposed algorithm by using their thermodynamic properties in the EOS.
Results from analytical method presented excellent agreement with those from reservoir simulation. Ultimate CO2 storage capacity was predicted with an average difference of 1.26 wt% between analytical and numerical methods; average oil, gas, and water saturations were also matched. Additionally, the analytical algorithm performed several orders of magnitude faster than numerical simulation, with an average of 5 seconds per run.
Greenhouse gas (GHG) emissions have been continuously increasing in the past 3 decades. More than 70% of these emissions are composed of CO2, which reached 30 Gt in 2009 (EIA 2011). Several environmental agencies and governments have shown concern about this statistic and its potential relation with global warming.
Coal consumption accounted for the release of nearly 14 Gt of CO2 during 2009, almost 45% of worldwide carbon dioxide emissions (EIA 2011). Given that coal is mainly used in power plants to generate electricity, these locations are large sources of CO2 and become the most important target for carbon capture and sequestration (CCS) processes. A large coal-fired power plant, generating 500 MW, emits approximately 2.9 Mt-CO2 per year or 55.2 BSCF of CO2 per year.
Metz et al. (2005), Dooley et al. (2006), and EPA (2011) defined carbon capture as a process consisting first of removing the impurities from a CO2-based stream to increase the CO2 concentration and improve the efficiency of the final storage process; and secondly, compressing the gas stream to transport it to a storage location, which can be geologic formations such as aquifers and depleted oil and gas reservoirs, to achieve long-term isolation from the atmosphere.
Geological storage of CO2 in aquifers and depleted oil and gas reservoirs represent an attractive option to reduce carbon emissions to the atmosphere, as it has been studied in the oil and gas industry for several years. Particularly, interest now exists in using depleted reservoirs taking advantage of the higher storage density in comparison with aquifers; additionally, extensive knowledge of the reservoir's static and dynamic properties, acquired during the developing phase, are available to optimize the efficiency of the project and increase the final storage capacity and profits.
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