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

Objectives  A better understanding of formation kinetics and thermodynamics of CH 4, CO 2, and CH 4 -CO 2 mixed gas hydrates in porous media  To study CO 2 injection dynamics in gas hydrate bearing sediments  Build an analytical model in order to calculate hydrate equilibrium in porous medium

Tasks  Conduct the proof-of-principle experiments  Injection Dynamics of CO 2 in Gas Hydrate Bearing Sediments  Reservoir Modeling

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 CO 2 concentration in CO 2 -H 2 O micro- emulsion

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

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

Hydrate Saturation Prediction Results  Prediction of CH 4 hydrate saturation

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

Results for CH 4 hydrate equilibrium in pore of radius 300 A o

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

Results  Capillary pressure profile in reservoir

Results  CH 4 recovery after thermal stimulation

Reservoir Simulation  Objective  To study injection dynamics of CO 2 in hydrate bearing sediments  To study effect of concentration of CO 2- microemulsion on hydrate recovery at various injection temperatures  To study the feasibility of injection of CO 2 -microemulsion for CH 4 recovery from hydrate reservoir on Alaska North Slope (Mt. Elbert site located within Milne Point Unit )

Numerical Simulations: 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 = 4 0 C Pressure in the System = 6 MPa

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

Effect of injection temperature and CO 2 slurry concentration on CH 4 recovery: Surface Plot

Energy Efficiency Calculations  Analyze the effectiveness of CO 2 - microemulsion injection technique vs. Thermal Stimulation method.  Calculate the total energy requirement  Calculate the energy efficiency

Heat added to reservoir for producing 1 kg of CH 4 under different production schemes

Energy efficiency ratios for different production scenarios

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% CO 2 concentration will be a good choice for reservoirs with hydrate saturation < 50%

Conclusions  If the initial hydrate saturation is in the range of 55% to 75%, a 50% CO 2 micro-emulsion injection may be a good choice.  CO 2 -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 CO 2 microemulsion injection is about 1/10 th of that required by thermal stimulation method.

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

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