The rapid and controllable generation of gas hydrates is one of the key core technologies in the fields of energy extraction, natural gas storage and transportation, and carbon dioxide sequestration. The research and application of hydrate accelerators aim to significantly improve the generation rate and storage density of hydrates, but their regulation process is extremely complex, involving dynamic changes in microstructure, water distribution, and pore structure. How to monitor this dynamic process in real-time, non destructively, and accurately has become an urgent need for scientific research and engineering practice. In this context, low field nuclear magnetic resonance technology, with its unique advantages, has become an indispensable and powerful tool in the monitoring and research of hydrate promoter regulation processes.

Introduction to the principle of low field nuclear magnetic resonance technology

The physical basis of this technology is the spin properties of atomic nuclei. In a constant main magnetic field, hydrogen nuclei (protons) in the sample undergo energy level splitting. After applying a specific frequency of radio frequency pulse, protons undergo resonance absorption of energy. When the pulse stops, the proton releases energy and returns to equilibrium, a process called "relaxation", which includes longitudinal relaxation (T1) and transverse relaxation (T2). There are significant differences in the proton relaxation time of water molecules in different states (free, bound, solid). By measuring and analyzing the relaxation time and its distribution, the internal moisture content, occurrence state, and dynamic migration information of the sample can be inferred without invading or damaging the sample.

Application of Low Field Nuclear Magnetic Resonance Technology in the Study of Hydrate Promoters

In the process of exploring the effectiveness of hydrate accelerators, the core is to clarify how they affect the interaction, nucleation kinetics, and growth process of water molecules and gas molecules. Low field nuclear magnetic resonance technology can directly and in situ reflect changes in the physical and chemical environment of water molecules by detecting the relaxation signals (T1, T2 relaxation times) of hydrogen atoms (protons) in water.

In specific applications, researchers can use this technology to monitor in real-time:

1) Water phase transition: When free water transforms into cage type hydrate crystals, the motion state of hydrogen atoms undergoes a drastic change, resulting in a significant reduction in their relaxation time. By tracking the changes in T2 spectral distribution, the signal peaks of free water, bound water, and water in hydrates can be clearly identified, allowing for quantitative calculation of hydrate generation and conversion rates.

2) The influence mechanism of accelerators: Different types and concentrations of accelerators (such as surfactants, nanoparticles, etc.) can change the properties of the water gas interface and water distribution. LF-NMR can sensitively capture these microscopic changes, revealing whether the promoter accelerates the mass transfer process or changes the nucleation pathway.

3) Process inside porous media: In simulated porous media such as sandstone, technology can non destructively detect the spatial distribution and growth patterns of hydrates at the pore scale, and evaluate the actual effectiveness of accelerators under complex geological conditions.

Figure 1: Nuclear magnetic signals at different stages of hydrate formation

Figure 2: Layered NMR signals at different stages of hydrate formation

Figure 3: T2 spectrum during hydrate formation process

Comparative advantages of low field nuclear magnetic resonance technology and traditional detection methods

Compared to traditional monitoring methods used for hydrate research, such as differential pressure method, gas chromatography, visual observation, or thermal analysis, low field nuclear magnetic resonance technology exhibits multidimensional advantages:

Non destructive and in-situ monitoring: LF-NMR completely eliminates the need to invade the sample, enabling true in-situ and continuous monitoring without interfering with the formation/decomposition process of hydrates, obtaining continuous dynamic data, and fully recording the reaction process.

High resolution and quantitative capability: It can effectively distinguish water in different phases (free water, bound water, water in hydrates) and provide accurate quantitative information, such as hydrate saturation and water conversion rate, which is difficult to directly achieve with many traditional methods.

Suitable for complex systems: particularly adept at analyzing the internal processes of opaque systems (such as porous media, emulsions, and systems containing solid particles), breaking through the limitations of visual observation methods.

Rich information dimensions: In addition to content, it can also provide various information about pore structure, fluid fluidity, and other aspects, which helps to understand the regulatory mechanism of accelerators from multiple perspectives.

Relatively easy and safe to operate: Low field equipment has low magnetic field strength, does not require liquid helium cooling, has low maintenance costs, operates safely and stably, and is more convenient for long-term and frequent laboratory use.

In summary, applying low field nuclear magnetic resonance technology to monitor the regulation process of hydrate accelerators provides an unprecedented micro perspective and precise data support for a deeper understanding of the mechanism of action of accelerators and optimizing their performance. It is driving a profound transformation of hydrate technology from macroscopic phenomenon description to microscopic mechanism analysis, and will play a more central role in the development of efficient and controllable hydrate technology in the future.