An experimental study on microscopic characteristics of gas-bearing sediments under different gas reservoir pressures
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Abstract: Gas-bearing sediments are widely distributed in five continents all over the world. Most of the gases exist in the soil skeleton in the form of discrete large bubbles. The existence of gas-phase may increase or decrease the strength of the soil skeleton. So far, bubbles’ structural morphology and evolution characteristics in soil skeleton lack research, and the influence of different gas reservoir pressures on bubbles are still unclear. The micro characteristics of bubbles in the same sediment sample were studied using an industrial CT scanning test system to solve these problems. Using the image processing software, the micro variation characteristics of gas-bearing sediments in gas reservoir pressure change are obtained. The results show that the number and volume of bubbles in different equivalent radius ranges will change regularly under different gas reservoir pressure. With the increase of gas reservoir pressure, the number and volume of tiny bubbles decrease. In contrast, the number and volume of large bubbles increase, and the gas content in different positions increases and occupies a dominant position, driving the reduction of pore water and soil skeleton movement.
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Table 1. Basic properties parameters of test soil
Feature parameter Value Water content (ω) 40.0% Density (ρ) 2.82 g/cm3 Dry density (ρd) 1.95 g/cm3 Gravity specific (Gs) 2.7 Void ratio (e) 0.71 Porosity (n) 43% Table 2. Bubble volume of each equivalent radius range under different gas reservoir pressures (mm3)
Radius range/μm Reservoir pressures/MPa 0 2 4 6 3 <20 0.064 0.090 0.057 0.058 0.100 20–40 0.304 0.753 0.338 0.497 0.491 40–60 0.545 1.196 0.650 0.931 0.549 60–80 1.067 1.288 1.131 1.211 0.888 80–100 2.000 1.384 1.491 1.718 1.392 100–200 22.302 7.574 8.933 10.096 9.137 200–300 24.447 5.450 11.176 9.535 11.389 300–400 16.269 7.115 10.188 13.503 11.609 400–500 12.142 6.988 9.849 9.482 9.945 >500 120.636 160.066 157.064 188.412 174.696 Summary 199.776 191.905 200.877 235.442 220.196 -
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