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Injection of CO 2 for Recovery of Methane from Gas Hydrate Reservoirs

Injection of CO 2 for Recovery of Methane from Gas Hydrate Reservoirs. Jan – Dec, 2006 University of Alaska – Fairbanks Pacific Northwest National Laboratory British Petroleum Exploration Alaska. Objectives.

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Injection of CO 2 for Recovery of Methane from Gas Hydrate Reservoirs

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  1. Injection of CO2 for Recovery of Methane from Gas Hydrate Reservoirs Jan – Dec, 2006 University of Alaska – Fairbanks Pacific Northwest National Laboratory British Petroleum Exploration Alaska

  2. Objectives • A better understanding of formation kinetics and thermodynamics of CH4, CO2, and CH4-CO2 mixed gas hydrates in porous media • To study CO2 injection dynamics in gas hydrate bearing sediments • Build an analytical model in order to calculate hydrate equilibrium in porous medium

  3. Tasks • Conduct the proof-of-principle experiments • Injection Dynamics of CO2 in Gas Hydrate Bearing Sediments • Reservoir Modeling

  4. Tasks Completed • Development of Pore Freezing Model to predict hydrate saturation in porous medium • Extension of Pore Freezing Model to predict mixed hydrate saturation in porous medium • Extension of UAF-HYD module to predict hydrate equilibrium in the porous medium • Simulation study to determine the role of capillary pressure in producing methane from hydrates • Simulation study to determine the optimum CO2 concentration in CO2-H2O micro-emulsion

  5. Tasks Completed • 5 conference papers presented • 1 Poster presented at 2006 AADE conference, Houston, Texas (April’06) • 1 journal paper submitted • 5 MS thesis defended

  6. Reservoir Modeling • Pore freezing model • Predicts Hydrate Saturation • Main feature- Consideration of salting out phenomenon • Involves calculation of equilibrium conditions for hydrates

  7. Hydrate Saturation Prediction Results • Prediction of CH4 hydrate saturation

  8. Hydrate Equilibrium Prediction • Hydrate Equilibrium in porous medium • Far different from that in bulk hydrate equilibrium • Changes due to interaction of chemical components with pore walls and due to energy required to maintain capillary equilibrium • Important to predict for any study involving hydrates in natural sediments

  9. Results for CH4 hydrate equilibrium in pore of radius 300 Ao

  10. Effect of Capillary Pressure on Hydrate Recovery • Contradictory opinions on its role in hydrate recovery • Function of wetting phase saturation • Calculated by van Genuchten principle • STOMP simulator used for studying the effect for various reservoirs with different soil characteristics • sandstone, sand, loam, silt loam and clay reservoirs considered

  11. Results • Capillary pressure profile in reservoir

  12. Results • CH4 recovery after thermal stimulation

  13. Reservoir Simulation • Objective • To study injection dynamics of CO2 in hydrate bearing sediments • To study effect of concentration of CO2-microemulsion on hydrate recovery at various injection temperatures • To study the feasibility of injection of CO2-microemulsion for CH4 recovery from hydrate reservoir on Alaska North Slope (Mt. Elbert site located within Milne Point Unit )

  14. Numerical Simulations: 2-D Horizontal System: 10 x 10 x 1 Grid Schematic representation of 2-D Reservoir Model • System Parameters: • Effective Porosity = 36% • Permeability: • x-direction = 400 md • y-direction = 200 md • Initial Conditions: • Hydrate Saturation (variable) System Temperature = 40C • Pressure in the System = 6 MPa

  15. Methane recovery as a function of Micro-emulsion temperature at different concentrations

  16. Effect of injection temperature and CO2 slurry concentration on CH4 recovery: Surface Plot

  17. Energy Efficiency Calculations • Analyze the effectiveness of CO2-microemulsion injection technique vs. Thermal Stimulation method. • Calculate the total energy requirement • Calculate the energy efficiency

  18. Heat added to reservoir for producing 1 kg of CH4 under different production schemes

  19. Energy efficiency ratios for different production scenarios

  20. Conclusions • The hydrates are formed at higher pressure in porous medium for a given temperature and at lower temperature for a given pressure than those in bulk medium • Capillary pressure has significant effect on methane recovery for different soils and it should be considered in hydrate recovery • The simulation study showed that a micro-emulsion with 30% CO2 concentration will be a good choice for reservoirs with hydrate saturation < 50%

  21. Conclusions • If the initial hydrate saturation is in the range of 55% to 75%, a 50% CO2 micro-emulsion injection may be a good choice . • CO2-microemulsion injection for methane recovery from a reservoir with high hydrate saturation may not be a good choice due to the low effective permeability. • It is found that the energy requirement for a gas hydrate reservoir by CO2 microemulsion injection is about 1/10th of that required by thermal stimulation method.

  22. Acknowledgement We gratefully acknowledge the financial support from AEDTL/NETL/DOE

  23. Questions …. ???

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