The exclusive economic zone (EEZ) of Japan has a very wide area due to a lot of islands in the Japanese Archipelago. Among the several natural resources in the EEZ, methane hydrate has been found below the seafloor off the coasts of Japan in a large amount so that it is expected to be exploited as future energy resource.The exploration in the Japan’s EEZ revealed that there are two different types of accumulations: (i) within turbiditic reservoirs (hereinafter,&nbsp;called&nbsp;the stratigraphic-type deposit) and (ii) as shallow accumulation. In the former type, fine particles of methane hydrate are mainly contained in the sandy reservoirs, and in the latter type, the massive methane hydrate accumulation is buried below the seafloor of a mud layer with thickness less than 100m.In Japan, several researchers have investigated different methods for the exploitation of these methane hydrate accumulations. JOGMEC (Japan Oil, Gas and Metals National Corporation) conducted, in 2013 and 2017, two offshore gas production tests from stratigraphic-type deposits off the Atsumi and Shima peninsulas of the Honshu Island, Japan.On the other hand, for the shallow accumulation, the massive or granular methane hydrate excavated on seafloor shall be conveyed up to the production platform as a slurry, a mixture of the methane hydrate particles and seawater. During this transportation, the initial two-phase flow (methane hydrate and seawater) may be developed into a three-phase flow (methane hydrate, methane gas, and seawater) by partial dissociation of the hydrate due to a change in temperature-pressure condition in the riser or flowline. Moreover, there is a lack in the literature regarding the flow assurance within these two- and three-phases flows. For example, the dissociated methane gas conveyed upward could re-form into methane hydrate depending on the thermodynamic and operational conditions inside the riser or flowline resulting in formation of hydrate plugs.The dissociation and re-formation kinetics of methane hydrate are mainly controlled by temperature, pressure and methane concentration in the system; however, it is difficult to predict these factors in multiphase flow because they are affected by flow dynamics and heat transfer. To gather experimental data of dissociation kinetics, the authors developed a closed-loop experimental apparatus consisting of jacketed tubing, which was used as heat exchangers, acrylic window to observe the flow, and a slurry pump. In addition, the flow rate, salinity, temperature, and pressure in the apparatus were continuously measured in circulation experiments. For safety regulation, methane hydrate was replaced by ice including carbon dioxide, hereafter carbonated ice, in the experiments. In addition, synthetic seawater was used to circulate the ice. In this article, we show some experimental data of several cases including those conducted under freezing conditions. The main parameters were the flow rate and temperature of the seawater controlled by the cooling fluid that circulated through the annulus of the jacketed tubing.These experimental data can be expected to support our works attempted to address the flow assurance issue of multiphase flow containing methane hydrate.

Experimental Study on Plugging Inside a Pipe Using Carbonated Ice as a Substitute for Methane Hydrate

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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