Effect of Water Saturation on Relative Permeability and Porosity in Hydrate Bearing Sand

Abstract

Abstract Large amounts of natural gas, predominantly methane are stored in gas hydrates in sediments below the seafloor and the permafrost. Gas hydrates are ice-like crystalline solids formed from mixtures of water and light natural gases at high pressure and low temperature condition. Vast quantities of methane hydrates have been discovered worldwide in sediments and sedimentary rock. During dissociation, 1 m3 of methane hydrates at reservoir condition could release 164 m3 of methane gas at standard conditions. Therefore, methane hydrate can be an affordable energy, alternative for fossils fuels. Production of natural gas from hydrate bearing sediments significantly influenced by geological conditions and petrophysical properties. The most valuable information needed to reliably predict are permeability and porosity reduction in the presence of gas hydrate as this parameters will influence the flow in the sediments for production. This present research examines the effect of water saturation on the permeability and porosity in unconsolidated quartz sand. Methane hydrate was formed in quartz sand in Hydrate Tubular Cell using deionized water at 276 K and 8 MPa. The system was pressurized and stabilized at 8 MPa after absolute permeability measurement. After stabilization, the system was cooled to 276 K to form methane hydrate. Relative permeability to gas was measured after methane hydrate formation. Water saturation varies from 10%, 35 %, 50 %, 75% and 100% in the sand pack with porosity of 40%. Absolute permeability was calculated using Darcy equation for permeability measurement using gas before hydrate formation at each water saturation. Average absolute permeability is 108.7 mD. Values of hydrate saturation was calculated at different water saturations. The results indicated that, variation of water saturation affect the relative permeability and porosity after hydrate formation. Relative permeability to gas decreased from 0.75 to 0.49 as water saturation decreased. This study found that porosity of the sample reduced drastically as the sample saturated with 35% of water. Porosity reduced from 40% to 37.4% due to increment of hydrate saturation. Water saturation affect formation of hydrate in pores, thus it affects the relative permeability and porosity of the sand pack. These data are essential for modelling and the development of commercial gas production technology for methane production for various field operating scenario.