Estimation of the In-Situ Permeabilities of Nankai Trough Hydrate Bearing Sediments from Pressure Temparature Core Samplar (PTCS) Core Measurements

摘要

As permeability is important for every hydrocarbon production, it will be important for natural gas production from methane hydrate bearing layers. Also, it is very important to design the tools for future production when we are going to apply depressurization method on methane hydrate bearing sediments. Several samples of Nankai Trough methane hydrate zone were sampled using pressure temperature core sampler. A few of them were not disturbed so that they were enough to measure relationship between permeability and porosity, and the others had given enough information of methane hydrate bearing layers. Features of Nankai Trough methane hydrate bearing layers are that methane hydrate is as a pore-filling matrix of sediments, host sediments consist with turbiditie and they are member of sand and mud layers which are not consolidated. Every samples had been compressed as K_0 condition until overburden pressure before permeability measurement. For natural sediments, each sample was trimmed by a lathe from frozen core, which had been stored in liquid nitrogen to prevent methane hydrate dissociation, was settled in tri-axial compression apparatus. Also, permeability of several artificial samples which grain size distribution and mineral composition were simulated for Tb section of Nankai Trough natural turbidite were measured. Result of measurements, permeability of turbidite Tb section has correlation with void percentage, which is defined as true void volume percentage within sediments, not but only porosity of host sediments. Moreover, permeability is influenced by grain size distributions of sample intervals. These results imply that permeability is influenced by not only hydrate saturation nor porosity, but also by grain size distribution of each layer. The results will help to estimate permeability from interpreted well logging data.