Study on the Effects of Heterogeneous Distribution of Methane Hydrate on Permeability of Porous Media Using Low‐Field NMR Technique

Abstract

The permeability of sediments is an important parameter that effects flow characteristics of the gas and water in the process of natural gas hydrates development. The distribution of gas hydrate is generally heterogeneous in porous media. It poses a great challenge to the permeability measurement of hydrate‐bearing sediments. To study the effect of heterogeneous distribution of methane hydrate on the permeability of porous media, methane hydrate formation in the sandstone and permeability measurement was carried out using a low‐field nuclear magnetic resonance (NMR) measurement system in situ conditions. The spatial distribution of methane hydrate in the core samples was determined by combining the T2 distribution with magnetic resonance imaging. The results show that the distribution of methane hydrate is heterogeneous in the core samples. The temporal and spatial variation of permeability happens in the process of hydrate dissociation. The heterogeneity of methane hydrate distribution severely affects the analysis of permeability change. Considering the heterogeneity of methane hydrate distribution, a new method was proposed to obtain the quantitative relationship between hydrate saturation and relative permeability based on magnetic resonance imaging and the equivalent seepage capacity method. The results show that the relative permeability models obtained by this method agree better with experimental results. The optimum coefficients of relative permeability models obtained by equivalent seepage capacity method change significantly in contrast with the direct fitting method. The variation of the optimum coefficient is up to 300% in this study. The model coefficients are related to the pore characteristic of hydrate‐free porous media.

Pore‐Scale 3D Morphological Modeling and Physical Characterization of Hydrate‐Bearing Sediment Based on Computed Tomography

“…From Figure 9, the absolute permeabilities K h calculated via the FVM methods and PNM methods are quite similar in sediments with the same hydrate saturation, showing that both methods were equally reliable. Moreover, Figures 9a and 9b show that the absolute permeability K h decreases exponentially with increasing hydrate saturation for both models, which is similar to the results of previous experimental studies (Ji et al, 2020; Kuang et al, 2019; Wu et al, 2018) and simulation studies (Chen et al, 2018; Dai & Seol, 2014; Li, Liu, et al, 2019). This is primarily because the generation of hydrate blocks the flow channels.…”

“…Thus, many studies have also been conducted on remolded specimens in the laboratory, and the heat and mass transfer processes have been evaluated widely, which is directly related to NGH exploitation efficiency. Minagawa et al (2008), using proton nuclear magnetic resonance measurement, found that the permeability decreased exponentially with increasing hydrate saturation, and other researchers found a similar phenomenon (Ji et al, 2020;Kang et al, 2016;Zhang et al, 2020). Jin et al (2007) proposed that the X-ray computed tomography (CT) technique could be used to obtain the pore structure and free gas distribution of HBS, where the permeability could be calculated and analyzed.…”

“…Journal of Geophysical Research: Solid Earth (Ji et al, 2020;Kuang et al, 2019;Wu et al, 2018) and simulation studies (Chen et al, 2018;Dai & Seol, 2014;. This is primarily because the generation of hydrate blocks the flow channels.…”

Advances in Characterizing Gas Hydrate Formation in Sediments with NMR Transverse Relaxation Time

“…The NMR T 2 method is used to determine the petrophysical characteristics of conventional and unconventional porous media in oil and gas fields, such as porosity, pore geometry, pore connectivity, permeability, and even the fluid saturation in reservoirs [37][38][39][40][41][42][43][44]. Therefore, the NMR T 2 method is also widely used for monitoring the pore structure and the formation process of gas hydrate in sediments [45][46][47][48][49][50][51][52][53]. NMR T 2 is an effective method for microscopic detection of hydrate-bearing sediments with considerable advantages (e.g., fast response, high resolution, and no damage) in the quantitative analysis of gas hydrate in sediments by low-field NMR (LF-NMR) [54][55][56].…”

Mechanical behaviors of hydrate-bearing sediment with different cementation spatial distributions at microscales

“…Nevertheless, the vast majority of studies did not consider the hydrate cementation spatial distribution influence on the mechanical behavior of hydrate-bearing sediments due to the lack of an effective nondestructive technique. Moreover, in nature, the hydrate cementation pore habit was reported to be heterogeneous affected by the effective stress, pore-size-dependent capillary pressure, and hydrocarbon accumulation history, which has been assessed directly by X-ray computed tomography (CT) (Lei et al, 2019;Le et al, 2020) or magnetic resonance imaging (MRI) (Ji et al, 2020;Song et al, 2015;Zhang et al, 2020b) and indirectly by comparing the measured seismic velocities and those calculated via elasticity models (Dvorkin et al, 2000). Luo et al (2015) studied the effect of a heterogeneous distribution of the hydrates on the wave velocity of the sediment and found that the compressional wave velocity increases with the hydrate saturation, while the heterogeneous distribution of the hydrates can have a remarkable influence on the results, especially in the low-saturation condition.…”