Stress sensitivity characterization and heterogeneous variation of the pore-fracture system in middle-high rank coals reservoir based on NMR experiments

Zhang, Junjian; Wei, Chongtao; Ju, Wei; Gao, Yan; Lu, Guanwen; Hou, Xiaowei; Zheng, Kai

doi:10.1016/j.fuel.2018.10.127

Cited by 120 publications

(94 citation statements)

References 42 publications

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“… 12 , 38 , 39 Coal maturity in this region varies from bituminous to anthracite coal, and the coal reservoirs have undergone several stages of evolution including deep metamorphism during the early Yanshanian period and structural–thermal metamorphism during the Yanshanian period. 40 , 41 …”

Section: Materials and Methodsmentioning

confidence: 99%

Multifractal Analysis in Characterizing Adsorption Pore Heterogeneity of Middle- and High-Rank Coal Reservoirs

et al. 2020

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Nanopore heterogeneity has a significant effect on adsorption, desorption, and diffusion processes of coalbed methane. The adsorption pore size distribution heterogeneity was calculated by combining N 2 with CO 2 adsorption data, and factors affecting multifractal and single-fractal dimensions were studied. The results indicate that pore size distribution of micropores (with pore diameters smaller than 2 nm) and meso–macro-pores (with pore diameters between 2 and 100 nm) in coal samples exhibit typical multifractal behavior. The overall heterogeneity of micropores in high-rank coal samples is higher than that in the middle-rank coal samples. The low-probability measure areas control the overall heterogeneity of pores with diameters of 0.40–1.50 nm. The high-probability measure area heterogeneity and spectral width ratio have a higher linear correlation with coal rank and pore structure parameters than those of low-probability measure areas. Heterogeneity of high-probability measure areas and overall pore size distribution are controlled by pores with diameters of 0.72–0.94 nm. Multifractal parameters of meso–macro-pores have no clear relationship with coal rank. The pore volume of 2–10 nm diameter shows a good linear correlation with heterogeneity of low-probability measure areas, and pores of this diameter range are the key interval that affected pore size distribution heterogeneity. The single-fractal dimension obtained using the Frenkel–Halsey–Hill (FHH) model shows a positive linear correlation with heterogeneity of the low-probability measure areas. It indicates that this parameter can effectively characterize the pore size distribution heterogeneity of low-probability measure areas in meso–macro-pores.

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Section: Materials and Methodsmentioning

confidence: 99%

Multifractal Analysis in Characterizing Adsorption Pore Heterogeneity of Middle- and High-Rank Coal Reservoirs

et al. 2020

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“…One of the meanings of low magnetic field NMR T 2 spectrum in fluid physics is the pore size distribution of the rocks (the ratio of the volume of pores of different sizes to the total pore volume). In rock pores, the T 2 relaxation time of a fluid can be expressed as 58

{(\frac{1}{T_{2}})}_{t} = {(\frac{1}{T_{2}})}_{s} + {(\frac{1}{T_{2}})}_{D} + {(\frac{1}{T_{2}})}_{B}

where

{(\frac{1}{T_{2}})}_{t}

is the total relaxation time,

{(\frac{1}{T_{2}})}_{S}

is the lateral relaxation time of the fluid due to surface relaxation,

{(\frac{1}{T_{2}})}_{D}

is the lateral relaxation time of the fluid due to diffusion relaxation under a gradient magnetic field and

{(\frac{1}{T_{2}})}_{B}

is the lateral relaxation time of the free state fluid.…”

Section: Resultsmentioning

confidence: 99%

Damage analysis of sandstone during the creep stage under the different levels of uniaxial stress using NMR measurements

Cheng

Zhou

Pan

et al. 2020

Fatigue Fract Eng Mat Struct

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In this paper, the nuclear magnetic resonance (NMR) measurements are carried out to evaluate the micro‐cracking characteristics of sandstones during the creep stage under the different levels of creep stresses. The variations in the parameters, including transverse relaxation time (T2) spectra distribution, percentage of the pore distribution, incremental value of porosity and ultrasonic P wave velocity are analysed. The results show that, during the creep stage, small pores in the rocks gradually evolve into large pores, resulting in an increase in damage of rocks. With the increase of the loading ratio, the increasing rate of porosity increases sharply, implying that the damage degree becomes more serious under the high loading ratio. When the loading ratio is larger than 0.7, the increasing rate of porosity and the decreasing rate of the P wave velocity both increases rapidly. During the creep stage, the relationship between micro‐crack and macro‐creep characteristics of rocks is established based on the analysis of the deformation and the porosity evolution during creep. It is found that, as the loading ratio increases, the increasing rate of porosity is linear with the creep strain. The NMR method offers a feasible option to identify micro‐cracking process of rocks during the creep stage, which can directly reflect the damage mechanism of rock caused by creep. The porosity of rocks is an effective parameter to evaluate the damage of rocks. The damage evolution of the specimen is highly anisotropic and is heavily related to the loading ratio during the creep stage. The relationship between the damage parameter and the loading ratio is exponential.

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“…Sensitivity. It can be clearly seen from Figures 5-7 that there are three distinct peaks in the NMR spectra of the three samples, on the basis of previous studies, this paper divides the pore types into adsorption pore, seepage pore, and fracture according to the relaxation time of each peak in the T 2 spectrum [42,44]. It also can be seen in the T 2 spectrum of the three samples that the main peak area is much larger than the two subpeak areas, which indicates that the absorption pore content of the three samples is the largest.…”

Section: Analysis Of T 2 Spectrum and Stressmentioning

confidence: 93%

“…To better characterize the effect of pressure on various pores in the samples, a parameter of 푆 푖 /푆 0 is defined to characterize stress sensitivity of various pores. A dimensionless parameter of is defined as [29,42]:…”

Section: Analysis Of T 2 Spectrum and Stressmentioning

confidence: 99%

Sealing Performance of New Solidified Materials: Mechanical Properties and Stress Sensitivity Characterization of Pores

Zhang

Jin

Liu

et al. 2020

Advances in Polymer Technology

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Borehole-sealing solidified material plays a significant role in improving sealing quality and enhancing gas drainage performance. In this study, the MTS815 electro-hydraulic triaxial servo test system and MR-60 NMR test system were adopted to conduct triaxial compression control experiment on the coal sample material, concrete material, and new solidified sealing material, respectively. This paper aims to analyze the difference of support effects, porosity, and stress sensitivity between those materials. Experimental results show that under the same stress condition, the stiffness of traditional concrete solidified material is the largest, while the new solidified material is the second, and the coal sample material is the smallest. Compared with the traditional concrete solidified material, the new solidified sealing material has better strain-bearing capacity and volumetric expansion capacity under each confining pressure in the experiment. The axial strain and volume increment of new solidified material is higher than those of the traditional concrete solidified material at the peak stress. Meanwhile, the confining pressure has a certain hysteresis effect on the postpeak stress attenuation. Fracture has the strongest stress sensitivity in three pore types, and its T2 map relaxation area has a larger compression than adsorption pore and seepage pore under the same pressure. The relative content of seepage pore and fracture in the new solidified material is less than that of coal and concrete samples, and the stress sensitivity of the new solidified materials is weaker than that of coal and concrete materials, thence, new solidified material will have better performance in borehole sealing. Outcomes of this study could provide guidance on the selection of the most effective sealing materials for sealing-quality improvement.

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Stress sensitivity characterization and heterogeneous variation of the pore-fracture system in middle-high rank coals reservoir based on NMR experiments

Cited by 120 publications

References 42 publications

Multifractal Analysis in Characterizing Adsorption Pore Heterogeneity of Middle- and High-Rank Coal Reservoirs

Multifractal Analysis in Characterizing Adsorption Pore Heterogeneity of Middle- and High-Rank Coal Reservoirs

Damage analysis of sandstone during the creep stage under the different levels of uniaxial stress using NMR measurements

Sealing Performance of New Solidified Materials: Mechanical Properties and Stress Sensitivity Characterization of Pores

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