Gas Production from Hydrate-Bearing Sediments: The Role of Fine Particles

摘要

Even a small traction of fine particles can have a significant effect on gas production from hydrate-bearing sediments and sediment stability. Experiments were conducted to investigate the role of fine particles on gas production using a soil chamber that allows for the application of an effective stress to the sediment This chamber was instrumented to monitor shear-wave velocity, temperature, pressure, and volume change during CO_2 hydrate formation and gas production. The instrumented chamber was placed inside the Oak Ridge National Laboratory Seafloor Process Simulator (SPS), which was used to control the fluid pressure and temperature. Experiments were conducted with different sediment types and pressure-temperature histories. Fines migrated within the sediment in the direction of fluid flow. A vuggy structure formed in the sand; these small cavities or vuggs were precursors to the development of gas-driven fractures during depressurization under a constant effective stress boundary condition. We define the critical fines fraction as the day-to-sand mass ratio when days fill the pore space in the sand. Fines migration, clogging, vugs, and gas-driven fracture formation developed even when the fines content was significantly fewer than the critical fines traction. These results show the importance of fines in gas production from hydrate-bearing sediments, even when the fines content is relatively low.