Multi-scale characterization for pore systems of hydrate-bearing reservoir

By using X-ray computeted tomography(XCT), low-field nuclear magnetic resonance(NMR), N₂ gas adsorption(N₂GA) method, the microscopic pore system of hydrate-bearing sediments in  KG Basin was comprehensively characterized. Results shown that the pore types are complex, with diverse pore geometry, poor connectivity, foraminiferal shells provide certain pores, 4-20μm micropores contribute the most to permeability. For the lacking of measuring closed pores by N₂GA leads to a significant difference in the total pore volume compared with NMR results.

Through monitoring the phase transition process in pores under temperature changes through NMR, the intensity value of the first peak signal of CPMG is collected, meanwhile the pure water signal is calibrated to calculate the unfrozen water content and pore size distribution. The results indicate that the water signal inside the macropores is constantly increasing, significantly weaker than in the micropores; the middle peak values corresponding to the mesopores are disorferly. Analysis shows that water migration occurs within the mesopores, the process of ice melting into water initial occurs in smaller pores.