Experimental Study on the Evolution of Compressibility and Gas Permeability of Sediments after Hydrate Decomposition under Effective Stress

Abstract

The effective stress and types of particles significantly affect the permeability of hydrate sediments. In this study, effects of hydrate saturation, hydrate decomposition, effective stress, and particle type on gas permeability and sample deformation of montmorillonite samples and quartz-montmorillonite mixtures were investigated. The results showed that the gas phase permeability increased with hydrate formation. In addition, the decline of sample porosity is the fundamental factor determining the permeability failure rate under effective stress. During methane hydrate decomposition by depressurization, the compression coefficient of samples increases with decreasing pore pressure, which means that decomposing natural gas hydrate makes experimental samples more sensitive to stress. Furthermore, the addition of sand particles significantly affects the compressibility of sediments. In addition, because of the decline of sample porosity and the swelling of montmorillonite, the results of gas permeability show a downward trend when the pore pressure decreases during the decomposition of methane hydrate. Gas permeability of the sample ranges from a few millidarcies to several hundred millidarcies. Furthermore, the content of clay and the particle size in the sample are the key factors in determining the permeability damage rate when the stress increases during decomposition of methane hydrate. Therefore, the addition of quartz sand can reduce damage of gas permeability of sediments caused by effective stress and hydrate decomposition.

Gas and Water Relative Permeability in THF Hydrate-Bearing Berea Sandstone

“…The obtained effective permeability can equally represent the relative permeability by using the acquired data for mathematical calculations. Relative permeability is defined as the ratio of effective permeability to absolute permeability k eg = 2 p a q g μ g L A ( p 1 2 − p 2 2 ) × 10 2 k ew = q w μ w L A ( p 1 − p 2 ) × 10 2 where k eg and k ew are the gas effective permeability and the water effective permeability (mD), respectively, p a is the atmospheric pressure (MPa), q g and q w are the gas flow rate (standard cubic centimeter (sccm)) and water flow rate (mL/min), respectively, μ g and μ w are the dynamic viscosity of gas and water (mPa·s), respectively, L is the length of the sample (cm), A is the cross-section of the sample (cm 2 ), and p 1 and p 2 are the inlet pressure and outlet pressure (MPa), respectively.…”

“…Relative permeability is defined as the ratio of effective permeability to absolute permeability. 62 k…”

Experimental Study On the Effect of Hydrate Filling On the Mechanical Properties of Marine Sediments in the Shenhu Area, South China Sea

“…The above studies show that the mechanical properties of hydrate formations are the result of multiple factors, including formation type, hydrate saturation, and experimental conditions, 38,39 among which the formation type is the main factor affecting the mechanical response. 40 The formation skeletons used in previous studies were mostly manual configurations in the laboratory rather than actual samples from the South China Sea strata.…”

Experimental Study on Permeability of Methane Hydrate Clayey Interbedded Sediments Considering Effective Stress and Hydrate Dissociation

“…38,39 In addition, with the dissociation of methane hydrate, it is found that the permeability of clays (montmorillonite, illite, and kaolin) decreases, and the permeability damage degree of the three clays first and then decreases. 40,41 Liu et al achieved the reformation of methane hydrate in marine soil sediments and investigated the effect of the reformation of methane hydrate on the gas permeability of sediments, which is of great significance for methane hydrate exploitation in the South China Sea. 42 The above research results of hydrate permeability are summarized in Table 1.…”

“…The experimental results show that the relationship between permeability and effective stress of montmorillonite is more in line with exponential function. With the increase of methane hydrate saturation, the compressibility of montmorillonite sediments is gradually enhanced. , In addition, with the dissociation of methane hydrate, it is found that the permeability of clays (montmorillonite, illite, and kaolin) decreases, and the permeability damage degree of the three clays first and then decreases. , Liu et al achieved the reformation of methane hydrate in marine soil sediments and investigated the effect of the reformation of methane hydrate on the gas permeability of sediments, which is of great significance for methane hydrate exploitation in the South China Sea . The above research results of hydrate permeability are summarized in Table .…”