scholarly journals Effect of Mineral Composition on Transverse Relaxation Time Distributions and MR Imaging of Tight Rocks from Offshore Ireland

Minerals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 232
Author(s):  
Stian Almenningen ◽  
Srikumar Roy ◽  
Arif Hussain ◽  
John Georg Seland ◽  
Geir Ersland

In this paper, we investigate the effect of magnetic field strength on the transverse relaxation time constant (T2) in six distinct core plugs from four different rock types (three sandstones, one basalt, one volcanic tuff and one siltstone), retrieved from offshore Ireland. The CPMG pulse-sequence was used at two different magnetic field strengths: high-field at 4.70 T and low-field at 0.28 T. Axial images of the core plugs were also acquired with the RAREst sequence at high magnetic field strength. Thin-sections of the core plugs were prepared for optical imaging and SEM analysis, and provided qualitative information on the porosity and quantification of the elemental composition of the rock material. The content of iron varied from 4 wt. % to close to zero in the rock samples. Nevertheless, the effective T2 distributions obtained at low-field were used to successfully predict the porosity of the core plugs. Severe signal attenuations from internal magnetic gradients resulted in an underestimation of the porosity at high-field. No definitive trend was identified on the evolution of discrete relaxation time components between magnetic field strengths. The low-field measurements demonstrate that NMR is a powerful quantitative tool for petrophysical rock analysis as compared to thin-section analysis. The results of this study are of interest to the research community who characterizes natural gas hydrates in tight heterogeneous core plugs, and who typically relies on MR imaging to distinguish between solid hydrates and fluid phases. It further exemplifies the importance of selecting appropriate magnetic field strengths when employing NMR/MRI for porosity calculation in tight rock.

Radiology ◽  
1991 ◽  
Vol 181 (1) ◽  
pp. 121-127 ◽  
Author(s):  
W W Orrison ◽  
G K Stimac ◽  
E A Stevens ◽  
D L LaMasters ◽  
M C Espinosa ◽  
...  

2019 ◽  
Vol 956 ◽  
pp. 117-124
Author(s):  
Yong Qiang Du ◽  
Jian Zheng ◽  
Jian Zhuang Zhi ◽  
Xiao Zhang

During the storage process, the HTPB (hydroxyl-terminated polybutadiene) coating is continuously affected by the strain, and the microstructure and mechanical properties will be degraded, which will seriously affect the performance of composite solid propellant and solid rocket motor and cause great harm. In order to analyze the microstructure and transverse relaxation characteristics of HTPB coating under different strains, low-field 1H NMR tests was carried out under 0%, 5%, 10% and 15% strain conditions, and the crosslinking density and transverse relaxation parameters of HTPB coating were analyzed. The results show that, the transverse relaxation decay can be divided into two segmental mobilities corresponding to two distinct transverse relaxation times. With the increase of strain, the crosslinking density shows a decline tendency, the transverse relaxation decay amplitude slows down, and the inversion curve has a tendency to move to the right. The ratio of the fast transverse relaxation time and the peak area are much larger than the slow transverse relaxation time, and the proportion of the fast relaxation time and the peak area enlarge with the increase of the strain, while the proportion of slow transverse relaxation time is reduced. With the increase of strain, there is a transition from slow transverse relaxation to fast transverse relaxation, and there is an inverse linear relationship between crosslinking density and transverse relaxation time.


2003 ◽  
Vol 181 (5) ◽  
pp. 1211-1215 ◽  
Author(s):  
Thomas Magee ◽  
Marc Shapiro ◽  
David Williams

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