Neutron imaging method for natural gas hydrate sediment triaxial mechanical test

Abstract

The invention provides a method capable of carrying out high-precision imaging on an internal structure of a natural gas hydrate sediment triaxial mechanical test. The method is characterized in thatthe distinction degree of natural gas hydrate, natural gas and water molecules is enhanced, the imaging resolution of the internal structure of natural gas hydrate sediment is improved and high-precision imaging of the structure in the natural gas hydrate triaxial mechanical test process is achieved by reducing the energy of neutron beams and improving the mass attenuation coefficient of neutron beams based on the fact that the molecular structure size of hydrate is close to the wavelength of cold neutrons. By means of the method, the creep and relaxation rules in the natural gas hydrate sample forming and decomposing process can be obtained, and the dynamic response process of reservoir stability after natural gas hydrate development can be known easily. The method is characterized in that the distinction degree of natural gas hydrate, natural gas and water molecules is enhanced, the imaging resolution is improved and high-precision imaging of the natural gas hydrate dynamic gatheringand dispersing process is realized by reducing the energy of neutron beams and improving the mass attenuation coefficient of neutron beams based on the fact that the molecular structure size of hydrate is close to the wavelength of cold neutrons.

Description

technical field [0001] The invention designs a neutron imaging method for a triaxial mechanical test of natural gas hydrate deposits, and belongs to the technical field of natural gas hydrate exploitation. Background technique [0002] The exploration and development of gas hydrates have achieved certain results, but the formation, decomposition and secondary generation of gas hydrates in sediments, the existence forms and behaviors in sediment pores, and the formation and decomposition of hydrates have great impact on sediment physical properties. Key basic scientific issues such as the influence of (permeability, acoustic wave velocity, heat conduction, electrical conductivity, etc.), gas-liquid multiphase flow in production systems, hydrate stability in reservoir sediments, and secondary generation in production strings are unclear The commercial development of gas hydrate is limited. The formation and decomposition of gas hydrate in reservoir pores and the microscopic m...

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Problems solved by technology

X-ray diffraction can determine the crystal structure type of gas hydrate through diffraction peaks, but it cannot realize the imaging of the dynamic aggregation and dispersion process of gas hydrate; X-ray CT imaging technology depends on the density difference of the object to be measured, and hydrate is mainly composed of natural gas (mainly methane molecules) and water molecules, the molecular weight of the two is close, and it is difficult to distinguish them by X-ray CT, so the phase state imaging accuracy of gas hydrate is extremely limited

Indoor triaxial mechanical test is an important means to study the structural stability of natural gas hydrate deposits, but the ability of X-rays to penetrate high-pressure chambers is limited, so it is difficult to apply when detecting the kinetic and thermodynamic processes of hydrate formation and decomposition

Therefore, the current X-ray diffraction and X-ray CT technologies cannot meet the needs of triaxial mechanical test imaging of gas hydrate deposits

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