Application of Low-Field Nuclear Magnetic Resonance (LFNMR) in Characterizing the Dissociation of Gas Hydrate in a Porous Media
Yongchao Zhang, Lele Liu, Daigang Wang, Pengfei Chen, Zhun Zhang, Qingguo Meng, Changling Liu
Abstract
Clear understandings of the dissociation behaviors and characteristics of a gas hydrate are essential for the exploitation of hydrate-bearing reservoirs. To study the dissociation characteristics of a gas hydrate in porous media, measurements using the low-field nuclear magnetic resonance (LFNMR) method on three different sand samples are conducted in this work. The changes of pore radius and phase saturation during the dissociation are determined based on the transverse relaxation time (T2) spectra. The fractal dimension is employed to depict the distributions of pore spaces occupied by water in the media, which shows a decreasing function with the decreasing hydrate saturation. Predictions of water permeability during the hydrate dissociation are comparably conducted using a fractal model and the widely used Schlumberger-Doll Research model. The fractal model performs better in showing the influences of pore-structure factors on the water permeability. The changes of specific reaction surface areas during the dissociation are estimated and preliminarily analyzed based on the results of LFNMR measurements. Results in this work may provide valuable insights for the related researches including the mechanical, acoustic, and electrical properties of the hydrate-bearing sediments.