Visual observation of dissociation of methane hydrate crystals in a glass micro model: Production and transfer of methane

Dissociation of methane hydrate crystals in pore space caused by temperature increase or depressurization, which is one of the main concerns in developing techniques to exploit natural gases in clathrate hydrate in sediments, was observed by using a glass mimic of sediments. Hydrate crystals were formed at a system temperature of T = 274.0 K and system pressure of p = 12.5 MPa or T = 279.6 K and p = 10.1 MPa and then decomposed by increasing the system temperature to 289 or 290 K, respectively. Two experimental runs of depressurization were also conducted. Hydrate crystals formed at T = 282.9 K and p = 10.1 MPa or T = 274.0 K and p = 12.5 MPa were decomposed by depressurization to 1.7 or 0.5 MPa at a system temperature of 285.5 or 274.3 K. The glass mimic of sediments (glass micromodel) was composed of a quartz glass plate on which straight microchannels were carved and another quartz glass plate covering the microchannels. The microchannels were approximately rectangular in cross section with a top width of 1.0 x 10(2) mu m and were arranged in a grid pattern at regular intervals of 2.0 x 10(2) mu m. Methane gas released from dissociating methane hydrate crystals was commonly observed to form slugs that completely occupy the pores in all experiment runs. The mechanism of the dissociation of the methane hydrate crystals was discussed considering the heat and mass transfer of methane around the dissociating methane hydrate crystals. (c) 2008 American Institute of Physics.