Experimental study on methane hydrate formation in a partially saturated sandstone using low-field NMR technique

Fuel ◽  
2019 ◽  
Vol 251 ◽  
pp. 82-90 ◽  
Author(s):  
Yunkai Ji ◽  
Jian Hou ◽  
Guodong Cui ◽  
Nu Lu ◽  
Ermeng Zhao ◽  
...  
Keyword(s):  
Experimental Study ◽  
Methane Hydrate ◽  
Hydrate Formation ◽  
Partially Saturated ◽  
Low Field ◽  
Low Field Nmr

Study on Formation and Dissociation of Methane Hydrate in Sandstone Using Low-Field Nuclear Magnetic Resonance Technology

2020 ◽  
Author(s):  
Yunkai Ji ◽  
Jian Hou ◽  
Yongge Liu ◽  
Qingjun Du
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Signal Intensity ◽  
Methane Hydrate ◽  
Hydrate Formation ◽  
Hydrate Dissociation ◽  
Short T2 ◽  
Low Field ◽  
Excess Water ◽  
Lf Nmr

Abstract Natural gas hydrate, as an unconventional resource, has been attracting increasing attention. Understanding the characteristics of methane hydrate formation and dissociation in porous media is important for developing gas hydrate-bearing reservoirs. This work discusses the use of low-field nuclear magnetic resonance (LF-NMR) technology to investigate the formation and dissociation of methane hydrate in the sandstone. In this work, an experimental assembly wherein methane hydrate can form and dissociate, is used to conduct LF-NMR measurements. LF-NMR, as a noninvasive measurement technology, combines the transverse relaxation time (T2) measurement with the magnetic resonance imaging (MRI). T2 measurements can explore the characteristics of methane hydrate formation and dissociation in core samples from a pore-scale perspective. MRI can display the spatial distribution of water from a core-scale perspective. The excess-gas method and the excess-water method are successively applied to form methane hydrate, and depressurization is applied to dissociate methane hydrate in the laboratory. The characteristics of methane hydrate formation and dissociation is studied in the sandstone. Experimental results show that the signal intensity of short T2 and long T2 decreases simultaneously in the process of the methane hydrate formation using the excess-gas method, indicating that methane hydrate is formed in both small and large pores. When using the excess-water method, the signal intensity of long T2 decreases, and the signal intensity of short T2 increases in the process of the methane hydrate formation, indicating that methane hydrate is mainly formed in large pores. Methane hydrate is dissociated simultaneously in both small and large pores when using the depressurization method. Water content in small pores gradually increases. Capillary pressure causes some water to remain in the core samples following dissociation. Water content in large pores decreases initially and then increases during depressurization. In the early stages of depressurization, more water leaves large pores than is generated by hydrate dissociation. In the later stages of depressurization, less water leaves the large pores than is generated by hydrate dissociation. This study may inspire the new understanding on distribution of fluid in sediments during the process of accumulation and exploitation of natural gas hydrates.

Experimental Study on Gas Production from Methane Hydrate Bearing Sand by Depressurization

2013 ◽  
Vol 310 ◽  
pp. 28-32
Author(s):  
Jian Ye Sun ◽  
Yu Guang Ye ◽  
Chang Ling Liu ◽  
Jian Zhang
Keyword(s):  
Experimental Study ◽  
Methane Hydrate ◽  
Hydrate Formation ◽  
Gas Production ◽  
Decomposition Kinetics ◽  
Dissociation Process ◽  
Hydrate Dissociation ◽  
Gas Hydrate Formation ◽  
Experimental Apparatus ◽  
Hydrate Saturation

The simulate experiments of gas production from methane hydrates reservoirs was proceeded with an experimental apparatus. Especially, TDR technique was applied to represent the change of hydrate saturation in real time during gas hydrate formation and dissociation. In this paper, we discussed and explained material transformation during hydrate formation and dissociation. The hydrates form and grow on the top of the sediments where the sediments and gas connect firstly. During hydrates dissociation by depressurization, the temperatures and hydrate saturation presented variously in different locations of sediments, which shows that hydrates dissociate earlier on the surface and outer layer of the sediments than those of in inner. The regulation of hydrates dissociation is consistent with the law of decomposition kinetics. Furthermore, we investigated the depressurizing range influence on hydrate dissociation process.

scholarly journals Experimental Study on Mechanical Properties of Hydrate-Bearing Sand: The Influence of Sand-Water Mixing Methods

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2554
Author(s):  
Weiguo Liu ◽  
Dedong Pan ◽  
Shi Shen ◽  
Zeshao You ◽  
Yuechao Zhao ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Experimental Study ◽  
Water Distribution ◽  
Hydrate Formation ◽  
Triaxial Tests ◽  
Water Mixture ◽  
Water Mixing ◽  
Low Field ◽  
Seeding Method ◽  
Hydrate Bearing Sediments

Laboratory-synthesized specimens are employed for an experimental study on the mechanical properties of hydrate-bearing sediments (HBS) due to the difficulty of field coring. A representative synthesized sample for the analysis of the mechanical properties of HBS in the experimental study requires evenly distributed hydrates in the pores of the sample. However, a specimen made with an improper sand–water mixing method might have an uneven water distribution, resulting in an uneven hydrate distribution when applying the ice-seeding method for hydrate formation. This study adopted three kinds of methods to mix sand and water before forming hydrates and applied the low-field nuclear magnetic resonance (NMR) technique to investigate how these methods affect the hydrate distribution, further affecting the mechanical properties. To analyze the mechanical properties of HBS, we conducted drained triaxial tests. As shown in low-field NMR, when we compacted a sample of the sand–water mixture and froze it upside-down before hydrate formation, a sample with an even water distribution was obtained. Subsequently, the hydrate in HBS distributed also evenly. The stress-strain curves present different strain softening and hardening patterns due to the different hydrate distributions. Moreover, the samples with the evenly distributed hydrates have higher initial elastic modulus and strength than the ones made with other methods.

scholarly journals Gas hydrate in-situ formation and dissociation in clayey-silt sediments: An investigation by low-field NMR

2020 ◽  
pp. 014459872097415
Author(s):  
Xiaoxiao Sun ◽  
Xuwen Qin ◽  
Hongfeng Lu ◽  
Jingli Wang ◽  
Jianchun Xu ◽  
...  
Keyword(s):  
Gas Hydrate ◽  
Hydrate Formation ◽  
Dissociation Process ◽  
Hydrate Dissociation ◽  
Hydrate Reservoir ◽  
Low Field ◽  
Gas Hydrate Formation ◽  
Clayey Silt ◽  
Hydrate Saturation ◽  
Low Field Nmr

The hydrate reservoir in the Shenhu Area of the South China Sea is a typical clayey-silt porous media with high clay mineral content and poor cementation, in which gas hydrate formation and dissociation characteristics are unclear. In this study, the CO2 hydrate saturation, growth rate, and permeability were studied in sandstone, artificial samples, and clayey-silt sediments using a custom-built measurement apparatus based on the low-field NMR technique. Results show that the T2 spectra amplitudes decrease with the hydrate formation and increase with the dissociation process. For the artificial samples and Shenhu sediments, the CO2 hydrate occupies larger pores first and the homogeneity of the sandstone pores becomes poor. Meanwhile, compared with the clayey-silt sediments, CO2 hydrate is easier to form and with higher hydrate saturation for the sandstone and artificial samples. In hydrate dissociation process, there exists a protection mechanism, i.e. the dissociation near the center of hydrates grain is suppressed when gas pressure drops suddenly and quickly. For permeability of those samples, it decreased with hydrate forms, and increases with hydrate dissociation. Meanwhile, with the same hydrate saturation, permeability is higher in hydrate formation than in dissociation.

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