Evaluation of CO₂ sequestration through enhanced oil recovery in West Sak reservoir

Nourpour Aghbash, Vahid

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Abstract

CO₂ enhanced oil recovery (EOR) has been proposed as a method of sequestering CO₂. This study evaluates using CO₂ as an EOR agent in the West Sak reservoir. The injected CO₂ mixes with the oil and reduces the oil viscosity, enhancing its recovery. A considerable amount of CO₂ is left in the reservoir and 'sequestered'. Due to low reservoir temperature, this process can lead to formation of three hydrocarbon phases in the reservoir. An equation of state was tuned to simulate the West Sak oil and complex phase behavior of the CO₂-oil mixtures. A compositional simulator capable of handling three-phase flash calculation and four-phase flow was used to simulate CO₂ injection into a three-dimensional heterogeneous pattern model. The results showed that CO₂ EOR in the West Sak reservoir increases oil recovery by 4.5% of original oil in place and 48 million metric tons of CO₂ could be sequestered. Ignoring four-phase flow underestimated oil recovery and sequestered CO₂ volume. Enriching the CO₂ with natural gas liquid decreased sequestered CO₂ volume without a significant increase in oil recovery. Dissolution of CO₂ in the water phase and different water/CO₂ slug sizes and ratios did not change the sequestered CO₂ volume and oil recovery.

Description

Thesis (M.S.) University of Alaska Fairbanks, 2013

Chapter one: Introduction -- 1.1. Overview -- 1.2. Objective -- Chapter two: Literature review -- 2.1. Description of West Sak reservoir -- 2.2. West Sak development -- 2.3. Gas injection mechanisms -- 2.4. Carbon dioxide EOR -- 2.4.1. CO₂ sequestration through EOR -- 2.5. Water alternating gas (WAG) -- 2.6. Dissolution of CO₂ in the aqueous phase -- 2.7. Injection of CO₂ in West Sak reservoir -- 2.8. Fluid characterization -- 2.9. Simulator description -- Chapter three: Methodology and model construction -- 3.1. The 1D model -- 3.2. The 3D pattern model -- 3.3. Tuning of EOS -- 3.4. Relative permeability -- 3.5. Production/injection options -- Chapter four: Results and discussion -- 4.1. Waterflooding -- 4.1.1. The 1D models -- 4.1.2. The 3D pattern model -- 4.2. CO₂ injection -- 4.2.1. The 1D model -- 4.2.2. The 3D pattern model -- 4.3. Effect of ignoring the second HC liquid phase -- 4.4. Effect of CO₂ dissolution in aqueous phase -- 4.4.1. The 1D model -- 4.4.2. The 2D pattern model -- 4.5. Effect of enriching CO₂ with natural gas liquid (NGL) -- 4.5.1. The 1D model -- 4.5.2. The 3D pattern model -- 4.6. WAG parameters -- Chapter five: Conclusions and recommendations -- 5.1. Conclusions -- 5.2. Recommendations -- References -- Appendix.

Date

2013-05

Type

Thesis

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Engineering