Borehole measurements of adsorbed gas content in coals using stimulated diffusion nuclear magnetic resonance

O’Neill, Keelan; Birt, Benjamin; Hopper, Timothy

doi:10.1016/j.coal.2021.103845

Cited by 13 publications

(12 citation statements)

References 56 publications

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“…Thus, the conversion factor could be determined, and the relaxation time could be converted into pore size by multiplying with the conversion factor. This approach has been previously described in the literature …”

Section: Resultsmentioning

confidence: 99%

“…This enables intuitive and quantitative identification of different fluid components. The decay of the echo signal is governed by the exponential decay and the influence of the planning factor and is expressed by the following decay law − b i normals = ∑ r = 1 p ∑ j = 1 m f italicir false[ 1 − exp ( − T w , s ) / T 1 r false] exp ( − t i / T 2 j ) + ε i normals The above equation describes the decay of the echo signal and includes various parameters such as the amplitude of the i th echo at T w,s denoted by b i s , the number of protons at quantitative relaxation time represented by f jr , and the number of equally spaced T 1 , T 2 values denoted by m and P , respectively. Additionally, ε i s represents the noise.…”

Section: Methodsmentioning

confidence: 99%

“…This approach has been previously described in the literature. 37 Since the mercury intrusion capillary pressure method would inevitably destroy the microstructure of the sample, the conversion coefficient was obtained by the low-temperature liquid nitrogen adsorption method. 42,43 The values obtained are 1.62 × 10 −8 for high-rank coal, 3.54 × 10 −8 for mediumrank coal, and 3.54 × 10 −8 for low-rank coal.…”

Section: Analysis Of Pore Structurementioning

confidence: 99%

“…In contrast, the 2D NMR T 1 −T 2 spectrum provides two-dimensional information, such as the internal rotational magnetic field G, diffusion coefficient D, and longitudinal relaxation time T 1 , which enhances the sensitivity to measured components, resulting in accurate and quantitative identification of different fluid components in the reservoir. 37,39,45 The relaxation time of different forms of water varies, leading to shorter relaxation times and smaller diffusion coefficients for components with restricted motion, while freemoving water exhibits relatively longer relaxation times and higher diffusion coefficients. 2D spectroscopy can characterize different phases of the same hydrogen-containing fraction and the intrinsic connection between different hydrogen-containing fractions, surpassing single-dimensional NMR in accurately studying fluid transport processes of the fractions.…”

Section: Spontaneous Imbibition Characteristicsmentioning

confidence: 99%

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Experimental Study on Spontaneous Imbibition of Coal Samples of Different Ranks Based on the NMR Relaxation Spectrum

Wang,

Du,

et al. 2023

ACS Omega

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The comprehension of the mechanisms governing spontaneous water imbibition in gas–water systems plays a significant role in the operation of hydraulic fracturing and the development of coalbed methane (CBM). In this study, nuclear magnetic resonance (NMR) techniques were used to investigate the pore structure and fluid behavior of different rank coal samples during spontaneous imbibition. Analyses were conducted on the 1D NMR T 2 spectrum, 2D NMR T 1–T 2 spectrum, and layer division T 2 spectra to achieve accurate and detailed information about the internal pore structure of coal and the characteristics of fluid transport during spontaneous imbibition. Low-rank coal exhibits good pore connectivity and favorable pore sorting characteristics, indicating favorable reservoir conditions. High-rank coal has larger pore spaces and highly developed micropores, which are highly beneficial for gas adsorption. However, its poor pore sorting characteristics and connectivity limit the migration and diffusion of fluids within the reservoir. The imbibition capacity follows a specific order of contribution, with small pores (10–50 nm) having the most significant role, followed by micropores (2–10 nm), ultramicropores (r < 2 nm), mesopores (50–1000 nm), macropores (1000–10,000 nm), and microfractures (r ≥ 10,000 nm). Low-rank coal stands out due to the restricted development of ultramicropores and small pores, leading to a different contribution of imbibition capacity compared to other samples, where macropores and microfractures dominate over all pore types. The coal reservoirs with favorable pore sorting characteristics and pore connectivity tend to exhibit a tendency toward rapid saturation and attainment of a prompt stable state during the hydraulic fracturing process. Finally, the mechanism of the late retreat effect of imbibition and the laws governing different coal ranks, pore structures, and fluid transport were discussed. This study offers comprehensive analyses of the mechanism of coal spontaneous imbibition and the characteristic laws of fluid seepage, providing insights into the optimization of CBM recovery and reservoir management.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Analysis Of Pore Structurementioning

confidence: 99%

Section: Spontaneous Imbibition Characteristicsmentioning

confidence: 99%

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Experimental Study on Spontaneous Imbibition of Coal Samples of Different Ranks Based on the NMR Relaxation Spectrum

Wang,

Du,

et al. 2023

ACS Omega

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“…Current research on gas content determination technology focuses on in situ determination. Scholars have put forward a method to determine technologies such as nuclear magnetic resonance without interfering with the coal seam itself 5 and explored the influence of gas components, atmospheric desorption, desorption after crushing, and other factors on gas content. 6 The coal seam gas content consists of three parts: loss, desorption, and residual.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on Gas Loss Derived from Positive Pressure

Wang

Yuan

et al. 2022

ACS Omega

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Positive pressure sampling enables the fixed-point and rapid acquisition of coal samples, but the derivation of loss volume during sampling is usually based on the law of gas desorption from granular coal at atmospheric pressure, which seriously affects the reasonableness of loss amounts under positive pressure and thus leads to errors in gas content determination. The gas loss under positive pressure is the key to the accurate determination of the gas content of coal seams. To obtain reliable loss data, under different positive pressures, we tested the gas desorption process of anthracite coal samples with different adsorption equilibrium pressures, analyzed the effect of positive pressure on gas desorption, studied the changes in the gas desorption rate caused by positive pressure, recorded the fluctuation of the amount of gas loss, and compared the values of loss under different conditions. The results show that the positive pressure is the main factor affecting gas desorption compared to the adsorption equilibrium pressure. The positive pressure has an inhibitory influence on gas desorption. Under the same positive pressure, the gas desorption rate shows a decreasing trend over time, and at the same time, the gas desorption rate gradually decreases accompanied by the increasing positive pressure. The gas loss error rate increases with increasing adsorption pressure under the same positive pressure. However, under the same adsorption pressure, the error rate of loss quantity presents a significant increase with positive pressure. The relative error of gas loss under different positive pressures can reach 63–180%, and the positive pressure has an obvious influence on gas loss. This study has experimentally confirmed that positive pressure has a greater effect on gas desorption than adsorption pressure, which will theoretically improve the method of deriving the amount of gas loss and will provide a basis for the accurate determination of gas content under positive pressure in engineering terms.

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Evaluating gas quantities

Flores,

Moore

2024

Coal and Coalbed Gas

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Borehole measurements of adsorbed gas content in coals using stimulated diffusion nuclear magnetic resonance

Cited by 13 publications

References 56 publications

Experimental Study on Spontaneous Imbibition of Coal Samples of Different Ranks Based on the NMR Relaxation Spectrum

Experimental Study on Spontaneous Imbibition of Coal Samples of Different Ranks Based on the NMR Relaxation Spectrum

Experimental Study on Gas Loss Derived from Positive Pressure

Evaluating gas quantities

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