Experimental study on the sensitivity of hydraulic permeability of fine-grained sediments sampled from a gas hydrate distribution area in the northern South China Sea

doi:10.13745/j.esf.sf.2024.4.25

Abstract

Abstract:

Natural gas hydrates are mainly distributed in fine-grained marine sediments containing clay minerals. For instance, the sediments in the northern region of the South China Sea contain a large amount of illite. Understanding the changes in permeability during the depressurization extraction process is crucial for effectively regulating the production of gas from hydrates. This study utilized remolded soil samples taken from the target hydrate test-production area in the northern South China Sea and conducted limit water content tests, drained consolidation tests, and steady-state seepage tests under different pore fluid concentration conditions. Data on the liquid limit, plastic limit, plasticity index, permeability coefficient, and permeability were obtained. The stress sensitivity and chemical sensitivity of the permeability of South China Sea sediments were analyzed. The results indicated that the limit water content parameters of the South China Sea sediments decreased as the pore fluid concentration increased. The permeability of the sediments increased with the pore fluid concentration, while it decreased with increasing stress. Moreover, the degree of stress sensitivity increased as the pore fluid concentration rose, whereas the degree of chemical sensitivity diminished with increasing stress. The fitting relationship of the permeability coefficient obtained using the normalized void ratio was found to be unaffected by pore fluid concentration, making it convenient for engineering applications.

Key words: hydraulic permeability, hydraulic conductivity, water ratio limit, sensitivity index, depressurization

CLC Number:

SONG Dekun, LIU Lele, WANG Dong. Experimental study on the sensitivity of hydraulic permeability of fine-grained sediments sampled from a gas hydrate distribution area in the northern South China Sea[J]. Earth Science Frontiers, 2024, 31(6): 405-414.

Figures/Tables 12

Fig.1 Grain size distribution of marine sediments sampled from the northern South China Sea

Fig.2 Mineral composition of marine sediments sampled from the northern South China Sea

Fig.3 Three phase diagram of hydrate-bearing sediments

Fig.4 The schematic diagram of apparatuses for hydraulic permeability and conductivity measurements

Fig.5 Water ratio limits of the samples under different salinities of solution

Fig.6 Schematic diagram of the effect of pore fluid salinity on clay fabric

Fig.7 Vertical stress dependent hydraulic conductivity under different salinities of pore fluid

Fig.8 Linear relationship between normalized void ratio and normalized hydraulic conductivity

Fig.9 Vertical stress dependent hydraulic permeability under different salinities of pore fluid

Fig.10 Pore fluid salinity dependent hydraulic permeability under different vertical stresses

Fig.11 Relationship between normalized sensitivity coefficient of hydraulic permeability and normalized vertical stress

Fig.12 Relationship between void ratio and normalized hydraulic conductivity

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