[1] A series of triaxial compression tests were conducted in order to investigate the mechanical behavior of gas-saturated methane hydrate-bearing sediments, and a comparison was made between gas-saturated and water-saturated specimens. Measurements on gas-saturated specimens indicate that (1) the larger the methane hydrate saturation, the larger the failure strength and the more apparent the shear dilation behavior; (2) failure strength and stiffness increase with increasing effective confining stress and pore pressure applied during compression, though the specimen becomes less dilative under higher effective confining stress; (3) lower temperatures lead to an increase of the stiffness and failure strength; (4) stiffness of specimens formed under lower pore pressure is higher than that of specimens formed under higher pore pressure but at the same effective stress; (5) stiffness and failure strength of gas-saturated specimens are higher than those of watersaturated specimens; (6) gas-saturated specimens show more apparent strain-softening behavior and larger volumetric strain than that of water-saturated specimens.

The ambiguity of contact angle experimental measurements due to surface chemistry changes resulted from sample contamination and/or the degrees of reaction with supercritical CO 2 has resulted great difficulties to precisely understand the wetting behavior of CO 2 under the geological carbon sequestration (GCS) conditions. In this study, water contact angles on quartz surface under GCS conditions were investigated through the combined experimental and molecular dynamics simulation (MDS) methods. The experimental results show that water contact angles increases as ionic strength increases. The effects of pressure and temperature are very weak. The dependence of ionic strength, pressure and temperature is same for monovalent and divalent ions solutions. In the MDS, a hydroxylated quartz surface was used as the base point. A good agreement between the MDS and experimental results were obtained. Using the MDS method, a clean mineral surface with a desired surface chemistry can be constructed, which is difficult in experiments. So by comparing MDS and experimental results, the mechanisms of the reservoir wettability can be better understood. Further investigation can be made on quartz surface with different functional groups to better understand wettability alteration caused by contamination and/or CO 2 reaction.

No abstract

No abstract

This paper introduces the research advances on replacement of CH 4 in Natural Gas Hydrates (NGHs) by use of CO 2 and discusses the advantages and disadvantages of the method on the natural gas production from such hydrates. Firstly, the feasibility of replacement is proven from the points of view of kinetics and thermodynamics, and confirmed by experiments. Then, the latest progress in CH 4 replacement experiments with gaseous CO 2 , liquid CO 2 and CO 2 emulsion are presented Moreover, the superiority of CO 2 emulsion for replacement of CH 4 is emphasized. The latest experiment progress on preparation of CO 2 emulsions are introduced. Finally, the advancements in simulation research on replacement is introduced, and the deficiencies of the simulations are pointed. The factors influencing on the replacement with different forms of CO 2 are analyzed and the optimum conditions for the replacement of CH 4 in hydrated with different forms of CO 2 is suggested. Keywords: gas hydrate; replacement; carbon dioxide; feasibility; emulsion; simulation OPEN ACCESSEnergies 2012, 5 400 Nomenclature: t = time, s X CH 4 /X CO 2 = ratio of CH 4 and CO 2 in the vapor phase (X CH 4 /X CO 2 ) 0 = initial ratio of CH 4 and CO 2 in the vapor phase α = fitting parameter related to the a condensation rate of CH 4 molecules from the vapor phase n CH 4 .H = remaining amount of CH 4 in the hydrate phase, mol n CO 2 .H = amount of CO 2 in the hydrate phase, mol f = fugacity, MPa k Dec = overall rate constant of the decomposition, mol/s·m·MPa k Dec.R = reaction rate constant of decomposition, mol/s·m·MPa k Dec.D = decomposition rate constant of mass transfer in the hydrate phase, mol/s·m·MPa k Form = overall rate constant of the formation, mol/s·m·MPa k Form.R = reaction rate constant of formation, mol/s·m·MPa k Form.D = formation rate constant of mass transfer in the hydrate phase, mol/s·m·MPa A = surface area between the gas and the hydrate phase, m 2 H = hydrate phase G = gas phase

No abstract

No abstract

No abstract