Evaluation of CO2-EOR and Sequestration in Alaska West Sak Reservoir Using Four-Phase Simulation Model
- Vahid Nourpour Aghbash (U. of Alaska - Fairbanks) | Mohabbat Ahmadi (U Of Alaska Fairbanks)
- Document ID
- Society of Petroleum Engineers
- SPE Western Regional Meeting, 21-23 March, Bakersfield, California, USA
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.4.2 Gas Injection Methods, 6.5.7 Climate Change, 2 Well Completion, 5.4 Enhanced Recovery, 5.2.2 Fluid Modeling, Equations of State, 5.4.1 Waterflooding, 5.8.2 Shale Gas, 5.7.2 Recovery Factors, 6.5.1 Air Emissions, 5.10.1 CO2 Capture and Sequestration
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Injection of CO2 into West Sak reservoir of Alaska was studied. The study was conducted with the objective to store CO2 and enhance the oil recovery. Due to low reservoir temperature, mixing of possible injected mixtures, including pure CO2 and HC-enriched CO2, and the in-place hydrocarbon will result in development of three hydrocarbon phases, gas, oil-rich and CO2-rich phases, at certain pressures encountered in reservoir. Commercially available simulators are incapable of appropriate identification of this new phase and using them will result in unrealistic results and wrong predictions.
A compositional EOS simulator, capable of handling up to four phases, including two HC liquid phases, was used. A three dimensional simplified model of the reservoir was built, based on reservoir core data, to study the oil displacement by various injected fluids including pure CO2. Sensitivity of the results to the relative permeability parameters of the second liquid phase was studied. Effect of using WAG with different water to gas ratios on the oil recovery and CO2 sequestration was also investigated. Various simulations runs resulting from combining different water-CO2 injection plans, well completion schemes, well spacing and production constraint were conducted to propose an injection-production strategy that can optimize the oil recovery and CO2 storage.
Results show that the second liquid phase significantly affects both breakthrough time and total oil recovery. The sensitivity analysis of relative permeability parameters shows its profound effect on the results, emphasizes the need to use accurately measured relative permeability data to produce accurate results.WAG scheme improves the sweep efficiency but decreases the amount of stored CO2.Within the range investigated, 880 -1240 ft, we found higher recovery rate for smaller well spacing but negligible change in ultimate recovery.
West Sak contains 7 to 9 billion barrels of original oil in place. Its high viscosity makes the primary recovery scheme inefficient. Although waterflooding was successful to a certain degree but CO2 injection can be a successful option to increase recovery and store considerable mass of CO2 that might be produced from coal-bed gasification in Alaska. Although CO2 cannot develop full miscibility with West Sak oil; however, it causes the oil to swell, oil viscosity to decrease, and recovery to increase.
Industrialization and population growth have increased our energy needs considerably compared to past century. With exception of a small fraction, almost all of it comes from fossil resources such as coal, oil and gas. The process of burning, mainly for electricity generation, and processing of these resources, for purification and producing new products, generates considerable mass of undesirable components mostly in gaseous form. Those gaseous components, including CO2 which is mainly accounted for global warming, are emitted into atmosphere. Different approaches have been proposed to decrease CO2 emission. Among all the options, subsurface injection of CO2 into geological formations is considered as the best and possibly safest method, in the long-term, to store large quantities of CO2 (Bachu 2000).For a successful underground sequestration, presence of an upper seal, cap rock, with reliable integrity and also sufficient and connected pore volume inside formation, are the requirements. In line with this approach are injections into:
- Deep saline aquifers
- Mature oil reservoirs as Enhanced Oil Recovery (EOR)
- Depleted oil and gas reservoirs
- Enhanced coal bed methane
- Shale gas
- Basalt formations
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