Abstract
In the shallow methane hydrate (MH) mining project, it is planned to discharge the mud water into a deep-sea depression at the drilling site. In this study, to understand the turbidity during the discharge into the sea, experiments were conducted using a simulated deep-sea bottom mud (chinese kaolin) and deep-sea bottom mud collected from the seafloor of the MH existence site in the Japan Sea to simulate continuous long-term mud injection using a water tank that reproduces a depression. Numerical analysis using a density-flow model was also conducted to understand the behavior of the input mud water.
As a result, it was confirmed that the density flow spreading tended to be dominant in the case of continuous long-term injection. In addition, it was confirmed that the flow velocity at the time of injection was higher in the mud from the deep-sea bottom at the MH existence site under the same concentration conditions, and that the turbidity due to muddy water tended to be prolonged after the injection. It is suggested that these characteristics are affected by the clay minerals contained in the mud and the organic content in the mud as seen in the strong thermal loss.
