The water flow velocity distribution characteristics in sediments with nature hydrate dissociation

Abstract

The nature gas hydrates (NGHs) are a kind of clean and new type energy with huge reserves, which has a great exploitation potential. Water flow velocity distribution characteristic is a key parameter for revealing fluid migration mechanism in hydrate sediments during the hydrate exploitation process. At present, there are few experimental studies on the water flow velocity distribution in hydrate sedimentary layers by using magnetic resonance imaging (MRI). Meanwhile, there is still a blank for the application of MRI in hydrate seepage characteristics research. The constant volume method for methane hydrate formation with the initial pressure of 6 MPa and the temperature of 274.15 K were used in this paper. And a method which used a constant step of 0.5 K in the temperature-increasing process to control hydrate dissociation was used to research the water phase velocity distribution. A standard spin echo pulse sequence was chosen to obtain the 2D proton density weighted images in this study. The results showed that there are two different water velocity areas with plus velocity and minus velocity in the cross section of the hydrate-saturated sediment core. The distribution of the hydrate in the hydrate-saturated sediment core influenced the two different velocity area (plus velocity and minus velocity). The plus water phase velocity area will gradually increasing along the surface of the hydrate enrichment area to the interior with the temperature increase process. There is a certain weakening effect of the presence of hydrate for the flow of water. And the greater the flow velocity, the more obvious the weakening effect.