Abstract
Permeability is one of the key factors that determine the fluids flow capacity and production potential of hydrate deposits. In this study, an experimental setup is developed to investigate the flow properties of the porous media, and the permeabilities to water are measured in the unconsolidated porous media with or without hydrate deposition in the pores. A specialized method of precisely controlling the amount of injected methane gas is employed to form methane hydrate in the core sample, and the hydrate formation process is described by the change characteristics of the gas and hydrate saturations. It is found that the residual gas plays an obstructive role in the water flow and it tends to slightly reduce the water permeability in the porous media, especially under high pressure conditions. After hydrate formation in the core sample, relatively steady flow state can be obtained under suitable water injection rate Q at which hydrate dissociation rate is very slow. The absolute permeability of the porous sample is reduced from 49.2 to 1.2 Darcies when the hydrate saturation increases from 0 to 9.3% in this study, indicating a strong dependence of k on the hydrate saturation.
Highlights
Natural gas hydrates (NGHs) are crystalline solid compounds formed by gas and water molecules combined in a clathrate structure [1]
We investigated the relationship between the effective water permeability and the hydrate saturation in unconsolidated hydrate-bearing sediments using a novel and more accurate method
The hydrate formation process is described by the change characteristics of the gas and hydrate saturations
Summary
Natural gas hydrates (NGHs) are crystalline solid compounds formed by gas and water molecules combined in a clathrate structure [1]. Under specific geologic conditions (high pressure and low temperature) in Nature, gas hydrates can be formed in huge amounts when the gas and water resources are adequate. Through scientific drilling projects and field-scale research projects, many countries have confirmed the extensive occurrence of gas hydrates in marine sediments and permafrost areas where the geologic conditions are favorable for their formation and stability. It is estimated that the total amount of natural gas trapped in gas hydrates is huge, and it is worth further exploring as a kind of new and challenging energy resource in the future [2,3]
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