Pressure redistribution and free phase gas formation during and after undrained unloading of dissolved gas-charged sediment

Jason M. Abboud, M. Cathryn Ryan, Jocelyn L. Hayley, Rachel M. Lauer

In the proceedings of: GeoEdmonton 2018: 71st Canadian Geotechnical Conference; 13th joint with IAH-CNC

Session: Rock Mechanics and Engineering Geology II

ABSTRACT: Free-phase gas (FPG) formation and mobility in gas-saturated waters in the subsurface have geological and engineering implications, including topics as diverse as hydraulic fracturing and slope stability. FPG can form in submarine slopes and in groundwater where thermogenic or biogenic gasses are produced. Gas exsolution occurs when total dissolved gas pressure (PTGD) exceeds pore water pressure (PW), forming FPG (bubbles). We measured the responses of PTGD, PW, and volumetric water content during stepwise unloading of gas-charged sediment in a uniaxial cell filled with glass beads with varying grain sizes (2000 µm, 500 µm, 300 µm, 150 µm, 65 µm) to create FPG-water characteristic curves during FPG production of initially dissolved gas- and water-saturated materials. The transition from discrete FPG bubbles to gas mobilization occurred at higher saturation values in smaller grain size material.

RÉSUMÉ: La formation de gaz à phase libre (FPG) et leur mobilité dans les eaux saturées avec des gaz dans les eaux souterraines hydraulique et la stabilité de pente. Les FPG peuvent se former dans des pentes sous-marines et dans les eaux souterraines où sont produits des gaz thermogéniques ou biogéniques. Il y a dégagement de gaz quand la pression totale de gaz dissous (PTGD) est supérieure à la pressinterstitielle (PW), formant les FPG. Nous avons mesuré la réponse du contenu du PTGD, PW et la teneur en eau volumique pendant le déchargement progressif de sédiments chargés de gaz dans une cellule uniaxiale remplie de billes de granulométries variables (2000 µm, 500 µm, 300 µm, 150 µm, 65 µ-FPG pendant la production de FPG à partir de matériaux initiaux saturés en eau et en gaz dissouts. La transition de FPG à la mobilisation de gaz se déroule à des valeurs de saturation plus élevées dans des matières avec des plus petites grains.

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