Journal articles on the topic 'Nuclear magnetic resonance; rock mechanics'
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1
Tai, Yanzhi. "Study on Prediction Model of Mechanical Parameters of Rock Frozen-Thawed Damage based on NMR Technology." Geofluids 2022 (August 10, 2022): 1–8. http://dx.doi.org/10.1155/2022/5046892.
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In order to establish prediction models for the mechanical parameters of rock freeze-thaw damage based on nuclear magnetic resonance (NMR) technology, with reference to the laboratory test of rock mechanical parameters after freeze-thaw, combined with low-field NMR and multivariate analysis methods, PLSR and PCR prediction models for the peak stress, peak strain, and elastic modulus of frozen-thawed rocks were established. The results show that the correlation coefficient of calibration set ( R 2 cal ) and validation set ( R 2 val ) of the PLSR and PCR prediction models are both greater than 0.9, and the residual prediction deviation (RPD) of each model is greater than 3, indicating that the established prediction models have good stability, small relative error, and high prediction accuracy. The application evaluation results show that the peak stress and peak strain of frozen-thawed rocks can be accurately predicted using these models. In this paper, only the NMR tests are performed on the frozen-thawed rocks, and no rock mechanics experiments are performed. The research results provide a new method for the research of rock freeze-thaw damage.
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Chu, Fujiao, Dunwen Liu, Xiaojun Zhang, Hui Yu, and Guangli Zhu. "Dynamic Response and Damage Regularity of Sandstone with Different Moisture States under Cyclic Loading." Fractal and Fractional 6, no. 4 (April 18, 2022): 226. http://dx.doi.org/10.3390/fractalfract6040226.
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In the process of geotechnical engineering excavation, wet and water-filled rock masses are inevitable. To obtain the mechanical properties of these rocks, indoor tests are required, and most of the rock tests rock tests are dry or nearly dry. They cannot really reflect the true nature of the rock, let alone its nature under a dynamic load. The rock was repeatedly impacted during the blasting excavation process. To determine the mechanical response characteristics and damage evolution of rocks with different moisture states under cyclic dynamic loads, rock samples with three saturation levels were prepared. In the experiment, the Hopkinson pressure bar equipment was utilized to perform five cycles of impact with the same incident energy, and the dynamic response of rocks with different impact times was recorded. Nuclear magnetic resonance technology was employed to obtain the change law of the pores of rock specimens after impact, and the cumulative damage rules of rock were combined with the fractal theory. From the experiments, it can be observed that the stress-strain curves of all rock samples are similar, in that they all have stress addition and unloading stages. The peak stress is proportional to the impact time and moisture content, whereas the opposite is true for the peak strain. After the impact, the small and large pores closed and increased, respectively. The porosity and porosity change rate increased with an increase in the impact time. With an increase in moisture content, this trend is more obvious. It can be observed via magnetic resonance imaging that the internal fractures of the water-bearing rock are obvious after multiple impacts. In particular, the saturated rock specimens exhibited severe damage. Fractal analysis of the NMR figures revealed that after three impact times, the fractal dimension change in the water-bearing rock samples was not obvious. This phenomenon indicated that a macro gap appeared. The fractal dimensions of the dry rock samples continued to increase, and the internal damage was less obvious.
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Li, Hao, Zuliang Zhong, Kenneth Imo-Imo Eshiet, Yong Sheng, Xinrong Liu, and Dongmin Yang. "Experimental Investigation of the Permeability and Mechanical Behaviours of Chemically Corroded Limestone Under Different Unloading Conditions." Rock Mechanics and Rock Engineering 53, no. 4 (November 4, 2019): 1587–603. http://dx.doi.org/10.1007/s00603-019-01961-y.
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Abstract This paper investigates the mechanical properties and permeability of chemically corroded rock during deep underground tunneling. Nuclear magnetic resonance tests are carried out to quantify the chemical damage of limestone samples at the microscopic scale. Coupled hydrostatic pressure-unloading tests at different unloading rates are also conducted on these chemically corroded limestone samples to investigate permeability changes and chemical effects on mechanical behaviours. Magnetic resonance imaging, T2 spectrum distribution and porosity of the samples are obtained, and the chemical micro damage is visualized and quantified. The relationship between permeability and mechanical behaviors of the rock under hydrochemical–mechanical coupled effects is investigated. The results show that the permeability development process of the chemical corroded samples can be divided into three stages: at the first stage, the permeability initially decreases, and the second stage starts at the inflection point of the permeability curve, from where the permeability begins to increase slightly. At the third stage, the permeability of the limestone increases dramatically until the sample is ruptured. Chemical corrosion and unloading rates have a combined and significant influence on the development of micro cracks in rocks, which is the root cause of the permeability changes. A stress-permeability model is proposed to describe the permeability and stresses in chemical-corroded limestone; this can be adopted for other sedimentary rocks.
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Deng, Hong Wei, Chun Fang Dong, Jie Lin Li, Ke Ping Zhou, Wei Gang Tian, and Jian Zhang. "Experimental Study on Sandstone Freezing-Thawing Damage Properties under Condition of Water Chemistry." Applied Mechanics and Materials 608-609 (October 2014): 726–31. http://dx.doi.org/10.4028/www.scientific.net/amm.608-609.726.
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For the purpose of researching the freezing-thawing cycle pHysical mechanics properties of sandstone in various chemical solutions, taking the red sandstones from Shandong as the example, freezing-thawing cycles experiments under the condition of H2SO4 solution (pH≈1.5), NaOH solution (pH≈12.5), NaCl solution (pH≈7, mass fraction is 4%) and water were conducted. The nuclear magnetic resonance (NMR) technique was used to test the porosity of rock samples after freezing-thawing cycles. Brazilian splitting test was also conducted to test the samples with different times of freezing-thawing cycles and soaking solutions. Results show that the quality change of samples in various solutions is different. The mass of sample in water increased, however, the mass change of the sample in other three solutions showed a firstly increasing and then decreasing tendency. The porosity distribution in rock changed obviously after different time’s freezing-thawing cycles. After 30 times freezing-thawing cycles, the porosity in H2SO4 solution, NaOH solution, NaCl solution and water has increased by 151.1%, 85.443%, 39.388%, and 17.976% respectively. With the increase of freezing-thawing cycle’s times, tensile strength of the rock reduced, but the damage properties were different in various solutions. The research can provide some mechanical parameters basis to physical mechanics properties of sandstones.
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Deng, Hong Wei, Chun Fang Dong, Jie Lin Li, Ke Ping Zhou, Wei Gang Tian, and Jian Zhang. "Experimental Study on Sandstone Freezing-Thawing Damage Properties under Condition of Water Chemistry." Applied Mechanics and Materials 556-562 (May 2014): 826–32. http://dx.doi.org/10.4028/www.scientific.net/amm.556-562.826.
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For the purpose of researching the freezing-thawing cycle physical mechanics properties of sandstone in various chemical solutions, taking the red sandstones from Shandong as the example, freezing-thawing cycles experiments under the condition of H2SO4solution (pH≈1.5), NaOH solution (pH≈12.5), NaCl solution (pH≈7, mass fraction is 4%) and water were conducted. The nuclear magnetic resonance (NMR) technique was used to test the porosity of rock samples after freezing-thawing cycles. Brazilian splitting test was also conducted to test the samples with different times of freezing-thawing cycles and soaking solutions. Results show that the quality change of samples in various solutions is different. The mass of sample in water increased, however, the mass change of the sample in other three solutions showed a firstly increasing and then decreasing tendency. The porosity distribution in rock changed obviously after different time’s freezing-thawing cycles. After 30 times freezing-thawing cycles, the porosity in H2SO4solution, NaOH solution, NaCl solution and water has increased by 151.1%, 85.443%, 39.388%, and 17.976% respectively. With the increase of freezing-thawing cycle’s times, tensile strength of the rock reduced, but the damage properties were different in various solutions. The research can provide some mechanical parameters basis to physical mechanics properties of sandstones.
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Zhang, Xiang, Manke Wei, Zhen Lei, and Ying Chen. "A Multi-Scale Study on the Property Degradationof High-Temperature Treated Beishan Granite." Minerals 13, no. 1 (December 23, 2022): 27. http://dx.doi.org/10.3390/min13010027.
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Granite is the main host rock for the underground storage of nuclear waste in Beishan, China. Heat is continuously generated during the long-term disposal of nuclear waste; therefore, it is important to investigate the influence of high temperature on the physical and mechanical properties and the constitutive relation of Beishan granite. In this study, laboratory experiments on heat-treated (25 ∘C, 200 ∘C, 400 ∘C, 600 ∘C and 800 ∘C) Beishan granite samples were performed in combination with nuclear magnetic resonance (NMR) analysis and regular physical-mechanical tests. The results show that the elastic modulus tends to decline faster at the temperature ranges of 25–200 ∘C and 600–800 ∘C by approximately 26.767% and 66.996%, respectively. Compared with the results at 25 ∘C, the peak stress decreases by 72.664% at 800 ∘C. The peak strain increases gradually from 25 ∘C to 600 ∘C and abruptly from 600 ∘C to 800 ∘C. The peak strain at 800 ∘C is 2.303× greater than that at 25 ∘C. Based on the damage theory, the Weibull distribution, the rock damage threshold point, and the residual strength, this study corrected the Drucker–Prager (D–P) criterion to consider the damage stress and then to establish the constitutive model of thermally damaged Beishan granite. The parameters required for the model are conventional mechanical parameters that can be calculated from the uniaxial test results, thus making the model convenient to apply. Meanwhile, the mechanical behavior of thermally damaged Beishan granite under uniaxial compression was simulated using the Particle Flow Code (PFC) to explore the development of cracks from the microscopic scale. The research results can provide theoretical support for the calculation and numerical simulation related to the mechanics of high-temperature treated rocks.
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Tan, Maojin, Hongliang Wu, Jinyan Zhang, Kewen Wang, Keyu Mao, Bo Li, and Chenglin Li. "Influencing mechanics and correction method of nuclear magnetic resonance measurement in igneous rocks reservoir." Journal of Petroleum Science and Engineering 208 (January 2022): 109648. http://dx.doi.org/10.1016/j.petrol.2021.109648.
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Dang, Chen, Zhili Sui, Xiuyuan Yang, and Zhenlong Ge. "Pore Changes in Purple Mudstone Based on the Analysis of Dry-Wet Cycles Using Nuclear Magnetic Resonance." Shock and Vibration 2022 (January 25, 2022): 1–13. http://dx.doi.org/10.1155/2022/5578401.
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The study on the change of rock pore structure during the weathering of purple mudstone is of guiding significance to the stability of the bank slope of the three gorges reservoir. In this paper, the pore changes in the wet and dry circulation of purple mudstone in the three gorges reservoir area are studied by means of nuclear magnetic resonance (NMR). The results show that the simulated weathering of wet and dry circulation has a great influence on the purple mudstone. With an increase in the number of dry-wet cycles, the purple mudstone pore volume ratio significantly changed. Originally, it consisted of a small pore structure with a single pore diameter of 0.01–0.1 µm and changed to a variety of pore structures with various pore diameters of 0.001–100 µm. With the increase in the number of dry-wet cycles, the micropores (0.001–0.1 µm) were transformed into macropores (0.1–1 µm). The area of the second peak of the three samples (large pores 0.1–1 µm) increased from 0.9413, 0.9974, and 0.6779 to 0.9871, 1.1498, and 0.9901, respectively.
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Liu, Fujun, Liu Yang, and Hailiang Jia. "Variation in Anisotropy with Dehydration in Layered Sandstone." Water 13, no. 16 (August 16, 2021): 2224. http://dx.doi.org/10.3390/w13162224.
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Anisotropy in rock could significantly affect the stability and safety of rock engineering by differing physical and mechanical properties of rock in different directions. Another major factor for physical and mechanical properties of rock is moisture state, however, whether anisotropy can be altered by it remains unclear. This study investigated variation in anisotropy (by conduct-ing ultrasonic tests) with moisture state (measured by nuclear magnetic resonance) in layered sandstones, and interpreted the phenomenon from the perspective of linking dehydration with pore structure of rock. The results show that (1) sandstone with more obvious bedding bears stronger anisotropy, the P-wave velocity in the perpendicular direction is much lower than that in the parallel direction. (2) The anisotropy index fluctuates around 1 with dehydration of sandstone without obvious bedding, while the anisotropy in sandstone with obvious bedding was significantly enhanced be dehydration. (3) During dehydration bulk water escaped firstly then capillary water and bound water. (4) Dehydration is controlled by the bedding structure. The different dehydration rates of pore water in different directions inevitably lead to heterogeneity in moisture state that change the anisotropy of the rock, which is reflected by the non-synchronous changes in P-wave velocities in different directions.
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Che, Yongxin, Yongjun Song, Jianxi Ren, Jiaxing Chen, Xixi Guo, Hao Tan, and Mengling Hu. "Creep Characteristics of Different Saturated States of Red Sandstone after Freeze-Thaw Cycles." Geofluids 2021 (September 9, 2021): 1–13. http://dx.doi.org/10.1155/2021/6622380.
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To investigate the creep mechanical characteristics of rocks in different saturated states after freeze-thaw cycles, samples with different saturations (30%, 50%, 70%, 90%, and 100%) were selected for nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and uniaxial compression creep tests. The internal microscopic damage of the rock sample and mechanical characteristics under long-term loading are analyzed after the action of freeze-thaw cycles. The test results show that, as the saturation increases, the T2 spectrum distribution shifts to the right. The spectrum area gradually increases as the porosity increases. The critical saturation of freeze-thaw damage occurs when the saturation increases from 70% to 90%. It can be seen from the SEM image that the number of pores inside the rock samples gradually increases with increases in saturation, leading to the appearance of cracks. Under long-term loading, the saturation has a significant influence on the time-efficiency characteristics of sandstone freeze-thaw. As the saturation increases, the creep deformation gradually increases. After reaching 70%, the axial creep strain increases significantly. The rate of creep is accelerated, the creep failure stress is reduced, and the creep time under the last level of stress is significantly increased. A modified viscous-plastic body is connected in series to the basic Burgers model, the freeze-thaw-damage viscous element is introduced, and the creep parameters are fitted using test data. The results will provide a reference for long-term antifreeze design for rock engineering in cold areas.
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Deng, Hongwei, Guanglin Tian, Songtao Yu, Zhen Jiang, Zhiming Zhong, and Yanan Zhang. "Research on Strength Prediction Model of Sand-like Material Based on Nuclear Magnetic Resonance and Fractal Theory." Applied Sciences 10, no. 18 (September 21, 2020): 6601. http://dx.doi.org/10.3390/app10186601.
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Micro-pore structure has a decisive effect on the physical and mechanical properties of porous materials. To further improve the composition of rock-like materials, the internal relationship between microscopic characteristics (porosity, pore size distribution) and macroscopic mechanical properties of materials needs to be studied. This study selects portland cement, quartz sand, silica fume, and water-reducing agent as raw materials to simulate sandstone. Based on the Nuclear magnetic resonance (NMR) theory and fractal theory, the study explores the internal relationship between pore structure and mechanical properties of sandstone-like materials, building a compressive strength prediction model by adopting the proportion of macropores and the dimension of macropore pore size as dependent variables. Test results show that internal pores of the material are mainly macropores, and micropores account for the least. The aperture fractal dimension, the correlation coefficient of mesopores and macropores are quite different from those of micropores. Fractal characteristics of mesopores and macropores are obvious. The macropore pore volume ratio has a good linear correlation with fractal dimension and strength, and it has a higher correlation coefficient with pore volume ratio, pore fractal dimension and other variable factors. The compressive strength increases with the growth of pore size fractal dimension, but decreases with the growth of macropore pore volume ratio. The strength prediction model has a high correlation coefficient, credibility and prediction accuracy, and the predicted strength is basically close to the measured strength.
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Kan, Jiaguang, Guichen Li, Nong Zhang, Peng Wang, Changliang Han, and Shun Wang. "Changing Characteristics of Sandstone Pore Size under Cyclic Loading." Geofluids 2021 (March 3, 2021): 1–9. http://dx.doi.org/10.1155/2021/6664925.
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The size and distribution of pores in rocks are closely related to their physical and mechanical properties. It is important to study the structure and distribution of pore size inside the rock to assess the risk of damage to a given rock volume. These characteristics were studied under different pressures, pore diameters, and pore throat size distribution laws using a UTM5540 electronic universal testing machine, magnetic resonance imaging scanning, and low field nuclear magnetic resonance spectroscopy with cyclic loading on yellow sandstone. We found the following. (1) Under 0–10 MPa load, the peaks of the sandstone T 2 spectrum move left as load increases, and the porosity of the sandstone decreases. The peak area of the middle relaxation spectrum increases as pressure increases from 10 to 20 MPa, and a peak for the long relaxation time spectrum appears. (2) Under 0–10 MPa load, the spectral peak associated with a large pore moves left and decreases in area as pressure increases. Under 10–20 MPa load, the large-pore spectral peak moves right and increases in area as pressure increases. (3) Under the applied 0–10 MPa load, the porosity of water-saturated sandstone gradually decreases, and the sandstone NMR images darken with increasing load. The porosity of saturated sandstone gradually increases under 10–20 MPa pressure, and its NMR image brightens. (4) The number of small pore throats increases with increasing load, but the number of large- and medium-sized pore throats decreases. From 0 to 15 MPa, crack (>1 micron) abundance decreases, and fractures are generated by compaction under a 20 MPa load. The pore interconnectivity is enhanced, as are the number and size of pores in the sandstone. With continuing increasing pressure, the numbers of pores and penetration of cracks increase, which damages the sandstone.
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Pan, Zheng, Keping Zhou, Rugao Gao, Zhen Jiang, Chun Yang, and Feng Gao. "Research on the Pore Evolution of Sandstone in Cold Regions under Freeze-Thaw Weathering Cycles Based on NMR." Geofluids 2020 (November 20, 2020): 1–12. http://dx.doi.org/10.1155/2020/8849444.
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The evolution of the rock pore structure is an important factor influencing rock mechanical properties in cold regions. To study the mesoscopic evolution law of the rock pore structure under freeze-thaw weathering cycles, a freeze-thaw weathering cycle experiment was performed on red sandstone from the cold region of western China with temperatures ranging from -20°C to +20°C. The porosity, T2 spectral distribution, and magnetic resonance imaging (MRI) characteristics of the red sandstone after 0, 20, 40, 60, 80, 100, and 120 freeze-thaw weathering cycles were measured by the nondestructive detection technique nuclear magnetic resonance (NMR). The results show that the porosity of sandstone decreases first and then increases with the increase of the freeze-thaw weathering cycles and reaches the minimum at 60 of freeze-thaw weathering cycles. The evolution characteristics of porosity can be divided into three stages, namely, the abrupt decrease in porosity, the slow decrease in porosity, and the steady increase in porosity. The evolution characteristics of the T2 spectrum distribution, movable fluid porosity (MFP), and MRI images in response to the freeze-thaw weathering process are positively correlated with the porosity. Analysis of the experimental data reveals that the decrease in the porosity of the red sandstone is mainly governed by mesopores, which is related to the water swelling phenomenon of montmorillonite. Hence, the pore connectivity decreases. As the number of freeze-thaw cycles increases, the effect of the hydrophysical reaction on the porosity gradually disappears, and the frost heaving effect caused by the water-ice phase transition gradually dominates the pore evolution law of red sandstone.
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Sun, Qian-Cheng, Can Wei, Xi-Man Sha, Bing-Hao Zhou, Guo-Dong Zhang, Zhi-Hua Xu, and Ling Cao. "Study on the Influence of Water–Rock Interaction on the Stability of Schist Slope." Sustainability 12, no. 17 (September 1, 2020): 7141. http://dx.doi.org/10.3390/su12177141.
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(1) The studies on the influence of rainfall on slope stability mainly focus on rainfall characteristics and the variation of strength parameters. Few studies pay attention to the micro structure changes of rock mass under long-term rainfall conditions, and the influence of failure mode. (2) Based on nuclear magnetic resonance (NMR) and electron microscopic imaging (Emmi) technology, the micro structure changes and macro deformation characteristics of the schist, under long-term immersion in different liquids are analyzed. (3) After soaking in the deionized water, the uniaxial compression strength of the intact specimen is slightly lower than that of the untreated specimens, but the test process in the elastic compression stage is considerably prolonged, and the failure modes show both shear and slip at the same time. While after soaking in acid solution, the fracture of rock samples with initial cracks can be obviously reduced and healed, which is consistent with the change of micro pore structure. The uniaxial strength and modulus of the intact samples are significantly lower, and only slip failure mode occurred. (4) It shows that water–rock interaction is an important factor influencing the stability of slope besides the external rainfall force, which affects the structural characteristics and mechanical properties of rock.
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Yu, Songtao, Junren Deng, Hongwei Deng, Feng Gao, and Jielin Li. "Brittle Characteristic and Microstructure of Sandstone under Freezing-Thawing Weathering." Advances in Civil Engineering 2020 (September 21, 2020): 1–12. http://dx.doi.org/10.1155/2020/8893278.
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As an important property of rock material, brittleness plays a vital role in rock engineering. This paper raised the concept of elastic strain energy release rate and proposed an elastic strain energy release rate based brittleness index based on the most acceptable definition of brittleness. Mechanical and Nuclear Magnetic Resonance parameters of sandstone under various Freezing-Thawing (F-T) cycles are also acquired and analyzed. Then, the proposed brittleness index is used to compare with two recently proposed brittleness indices to verify its correctness and applicability. Finally, the brittleness index is applied to evaluate the brittle behavior of F-T cycles treated sandstone under uniaxial compression. The results show that elastic modulus, value of the postpeak modulus, and peak stress decrease with F-T cycles, and the porosity and microstructure develop with F-T cycles. The proposed brittleness index is highly related to F-T cycles, peak stress, porosity, and elastic modulus of sandstone that suffered recurrent F-T cycles. It declines exponentially with F-T cycles and porosity increase while growing exponentially with peak stress and elastic modulus increase.
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Lin, Yun, Keping Zhou, Rugao Gao, Jielin Li, and Jian Zhang. "Influence of Chemical Corrosion on Pore Structure and Mechanical Properties of Sandstone." Geofluids 2019 (January 15, 2019): 1–15. http://dx.doi.org/10.1155/2019/7320536.
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Chemical corrosion plays a significant role in affecting the properties of rock materials. To understand the effects of chemical corrosion on the pore structure and mechanical properties of sandstones, porosity, T2 spectrum distribution, and NMR images of sandstone specimens were measured after every 10 days of immersion in chemical solutions using the nuclear magnetic resonance (NMR) technique. Static uniaxial compressive tests and dynamic compressive tests were conducted using a conventional servo-controlled testing machine and a split Hopkinson pressure bar (SHPB) system for specimens treated with chemical corrosion. The test results showed that after being treated with chemical corrosion, the porosity of a specimen increased, the T2 spectrum distribution would successively shift towards the right, and the distribution of pores tended to become more irregular. Additionally, all of the compressive strength and elastic modulus of sandstone treated with chemical corrosion under static and dynamic loads decreased, and the peak strain increased. The effect order of a chemical solution on the pore structure and mechanical properties of sandstone was H2SO4>NaOH>distilled water, which would be related to the different mechanisms of a water-rock reaction. According to the experimental results, the correlations between the mechanical properties and porosity were established. The results can serve as a reference for research in related fields.
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Feng, Yujie, Haijian Su, Qian Yin, Liyuan Yu, and Yingchao Wang. "Experimental Study on Mechanical Property and Pore Distribution of Limestone Specimens after Heat Treatment under Different Heating Conditions." Advances in Materials Science and Engineering 2021 (June 17, 2021): 1–14. http://dx.doi.org/10.1155/2021/9957330.
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The thermal effect of rocks not only depends on the temperature level but also may be influenced by the factors including heating environment, heating rate, and cooling method. In this study, approximate vacuum (V) and air circulation (A) heating condition are, respectively, applied on the limestone specimens in the whole heating process. Then, physical, mechanical, and nuclear magnetic resonance (NMR) tests were carried out to investigate the effect of heating conditions on the rock properties. The results show that heating conditions have significant effects on mechanical properties of limestone specimens (including peak strength, elasticity modulus, secant modulus, and crack initiation stress), which are due to the interference effect on the oxidation and thermal decomposition. It is worth noting that the significant temperature range of the heating condition is 450 ∼ 750°C, during which the mechanical performances of heat-treated specimens under V condition obviously outperform those under A condition. Combining the NMR results and the microstructure images from scanning electron microscope (SEM) technology, the evolution of pore distribution was revealed. As temperature increases from room temperature to 900°C, porosity increases gradually. However, pore distribution changes from small and medium pores dominating to large pore dominating and then to medium pore dominating. For limestone specimens after high-temperature treatment above 450°C, mineral crystals may melt and reconsolidate, filling in some of the previously large pores generated by thermal decomposition.
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Wu, Chao, Shengquan Wang, Delu Li, and Xiaokang Wang. "NMR Experimental Study on Dynamic Process of Pore Structure and Damage Mechanism of Sandstones with Different Grain Sizes under Acid Erosion." Shock and Vibration 2020 (January 8, 2020): 1–13. http://dx.doi.org/10.1155/2020/3819507.
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In many engineering projects, it is critical to consider the acid erosion of rock. This study investigates dynamic changes in pore structure and damage mechanisms in sandstones subjected to acid erosion. Specimens with three grain sizes were immersed in acid solution and tested by the nuclear magnetic resonance technique. Changes in solution pH, specimen mass and porosity, T2 spectrum distribution, and area were analyzed. Damage mechanisms are discussed, and relationships between porosity and acid erosion damage variables are established. The results show that acid erosion has significant effects on pore structure and erosion damage in sandstone. With increasing soaking time, new micropores formed in sandstone, while existing micropores and mesopores gradually expanded into macropores, causing the T2 spectrum distributions to change greatly. The porosity, acid erosion damage, and T2 spectral areas of sandstones with different grain sizes all increased gradually. Under acid erosion, sandstones became gradually weakened, but the effects varied greatly according to grain size. Pore structure changes and acid erosion damage were greatest in coarse-grained sandstone, followed by medium- and fine-grained sandstone.
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Li, Jielin, Liu Hong, Keping Zhou, Caichu Xia, and Longyin Zhu. "Mechanical Characteristics and Mesostructural Damage of Saturated Limestone under Different Load and Unload Paths." Advances in Civil Engineering 2021 (January 15, 2021): 1–16. http://dx.doi.org/10.1155/2021/8831247.
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To study the evolutionary characteristics of mesostructural damage to saturated limestone under different loading and unloading paths, three types of loading and unloading tests involving three different loading rates and initial peak stresses were performed. Nuclear magnetic resonance technology and scanning electron microscopy were used to investigate the evolutionary characteristics of pore water during the loading and unloading of the limestone. The results indicated that, with an increase in the initial peak stress, the rock viscoplasticity gradually decreased, and the variation of pore radius and the reduction of bound water decreased. With an increasing loading rate, the mesostructure evolution law under disturbance-increasing amplitude (DIA) cycling was opposite to those under increasing amplitude (IA) and repeated-increasing amplitude (RIA) cycling. With the increasing loading stress level, the porosity decreased and then increased. Under increasing amplitude cycling, a larger initial porosity resulted in higher pore compaction and expansion limits. Reducing the initial peak stress inhibited the pore expansion, whereas it had the opposite effect under RIA and DIA cycling. During loading and unloading, bound water exists in pores of organic matter and mesopores, and free water exists in macropores of intergranular and transgranular fractures. These changes indicate certain laws under different loading and unloading paths. The results of this study indicate that the mesostructure characteristics of rock depend on the loading and unloading paths.
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Ke, Bo, Keping Zhou, Hongwei Deng, and Feng Bin. "NMR Pore Structure and Dynamic Characteristics of Sandstone Caused by Ambient Freeze-Thaw Action." Shock and Vibration 2017 (2017): 1–10. http://dx.doi.org/10.1155/2017/9728630.
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For a deeper understanding of the freeze-thaw weathering effects on the microstructure evolution and deterioration of dynamic mechanical properties of rock, the present paper conducted the nuclear magnetic resonance (NMR) tests and impact loading experiments on sandstone under different freeze-thaw cycles. The results of NMR test show that, with the increase of freeze-thaw cycles, the pores expand and pores size tends to be uniform. The experimental results show that the stress-strain curves all go through four stages, namely, densification, elasticity, yielding, and failure. The densification curve is shorter, and the slope of elasticity curve decreases as the freeze-thaw cycles increase. With increasing freeze-thaw cycles, the dynamic peak stress decreases and energy absorption of sandstone increases. The dynamic failure form is an axial splitting failure, and the fragments increase and the size diminishes with increasing freeze-thaw cycles. The higher the porosity is, the more severe the degradation of dynamic characteristics is. An increase model for the relationships between the porosity or energy absorption and freeze-thaw cycles number was built to reveal the increasing trend with the freeze-thaw cycles increase; meanwhile, a decay model was built to predict the dynamic compressive strength degradation of rock after repeated freeze-thaw cycles.
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Cui, Lizhuang, Nan Qin, Shuai Wang, and Xuezhi Feng. "Experimental Study on the Mechanical Properties of Sandstone under the Action of Chemical Erosion and Freeze-Thaw Cycles." Advances in Civil Engineering 2021 (March 1, 2021): 1–14. http://dx.doi.org/10.1155/2021/8884079.
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In order to study the mechanical properties of sandstone under the coupling action of chemical erosion and freeze-thaw cycles, the fine-grained yellow sandstone in a mining area in Zigong, China, is collected as the research object. The changes in mechanical properties of yellow sandstone under the coupling action of chemical solution erosion and freeze-thaw cycles are analyzed based on uniaxial compression tests (UCTs) and triaxial compression tests (TCTs). The results show that, with the increase in freeze-thaw cycles, the compressive strength, elastic modulus, and cohesion of the sandstone samples decrease with varying degrees. Under constant freeze-thaw cycles, the most serious mechanical properties of degradation are observed in acidic solution, followed by alkaline solution and neutral solution. Under different confining pressures, the compressive strength and elastic modulus of the sandstone samples decrease exponentially with the increase in freeze-thaw cycles. Under the action of the chemical solution erosion and freeze-thaw cycles, the internal friction angle fluctuates around 30°. For the cohesion degradation, 35.4%, 29.3%, and 27.2% degradation are observed under acidic, alkaline, and neutral solutions. Nuclear magnetic resonance imaging shows that the chemical erosion and freeze-thaw cycles both promote the degradation of rock properties from surface to interior; after 45 freeze-thaw cycles, the mechanical properties drop sharply. To properly design rock tunneling support and long-term protection in the cold region, the impact of both freeze-thaw cycles and chemical erosion should be considered.
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Li, Dongfeng, Zhanyou He, Rui Wang, Le Zhang, Heng Fan, Hailiang Nie, and Zixiong Mo. "Research on the Effect of Shale Core Mechanical Behavior on Casing Deformation." Processes 11, no. 1 (January 14, 2023): 274. http://dx.doi.org/10.3390/pr11010274.
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As an unconventional, high-quality, efficient, and clean low-carbon energy, shale gas has become a new bright spot in the exploration and development of global oil and gas resources. However, with the increasing development of shale gas in recent years, the anisotropic load of the shale reservoir during the mining process has caused the casing to be deformed or damaged more and more seriously. In this paper, the mechanical behavior of shale core shear, triaxial and radial compression are studied using rock true compression tests, shear tests and nuclear magnetic resonance (NMR) technology. The process of macroscopic and microscopic changes of shale fractures during the tests were analyzed to predict the effect of the fracture-state changes and stress-state changes of different shale reservoirs on the casing deformation. The results show that after the shale core is damaged, the overall pore structure changes, resulting in the decrease or increase in shale porosity. During the process of triaxial pressurization, as the pressure continues to increase, there will be a critical pressure value from elastic deformation to plastic deformation. When the pressure value exceeds the critical pressure value, the shale reservoir will have strong stress sensitivity, which can easily cause wellbore collapse. The research results have important guiding significance for determining the casing deformation under shale reservoir load and preventing casing deformation failure.
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Lai, Bitao, Hui Li, Jilin Zhang, David Jacobi, and Dan Georgi. "Water-Content Effects on Dynamic Elastic Properties of Organic-Rich Shale." SPE Journal 21, no. 02 (April 14, 2016): 635–47. http://dx.doi.org/10.2118/175040-pa.
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Summary Acoustic-velocity measurements are an important nondestructive way to investigate dynamic rock-mechanical properties. Water content and bedding-plane-induced anisotropy are reported to significantly affect the acoustic velocities of siliciclastic sandstones and laminated carbonates. This relationship in organic-rich shales, however, is not well-understood and has yet to be investigated. The mechanical properties of organic-rich shales are affected by changes in water content, laminations, total organic content (TOC), and microstructures. In particular, kerogen density that accompanies changes in the composition of the TOC during maturity can significantly influence the acoustic responses within source rocks. To understand how these variables influence acoustic responses in organic shales, two sets of cores from the Eagle Ford shale were investigated: one set cut parallel to bedding and the other perpendicular to bedding. Textures of the samples from each set were characterized by use of computed-tomography (CT) scanning. Nuclear magnetic resonance (NMR) was used to measure the water content, and X-ray diffraction (XRD) to analyze the mineralogy. Scanning electron microscope (SEM) was also used to characterize the microstucture. Acoustic-velocity measurements were then made on each set at various confining pressures with the ultrasonic pulse-transmission technique. The results show that confining pressure, water content, and laminations have significant impact on both compressional-wave (P-wave) and shear-wave (S-wave) velocity. Both velocities increase as confining pressure increases. Velocities measured from cores cut parallel to bedding are, on average, 20% higher than those cut perpendicular to bedding. Increasing water content decreases both velocities. The impact of water content on shear velocity was found to be significant compared with the response with compressional velocity. As a result, the water content was found to lower both Young's modulus and shear modulus, which is opposite to the reported results in conventional reservoir lithology. In addition, both P- and S-wave velocities show a linear decrease as TOC increases, and they both decrease with increasing of clay content. The mechanisms that lead to water-content alteration of rock-mechanical properties might be a combined result of the clay/water interaction, the chemical reaction, and the capillary pressure changes.
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Perry, Stephanie. "Technology Focus: Formation Evaluation (August 2021)." Journal of Petroleum Technology 73, no. 08 (August 1, 2021): 41. http://dx.doi.org/10.2118/0821-0041-jpt.
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Leading into the third quarter of this year, I am honored to be able to highlight and share three impactful SPE papers that demonstrate integration at its best. In reviewing the papers, five main technical themes emerged. These include * Machine learning and artificial intelligence as applied to formation evaluation * Production analysis methodologies and their effect on understanding rock characterization and behavior * Subsurface characterization primarily focused on rock typing and permeability * Tool advancements (openhole, cased-hole, or laboratory-based tools) * Subsurface-to-production integration across subdisciplines (e.g., geology, geochemistry, petrophysics, and engineering) The latter is the common thread between the three papers recommended and discussed here. In this new decade, the prevalence of integration is at the forefront of the scientific community. Every discipline, scientist, or company has a way in which they define the term “integration.” Regardless of how you define the effort that links disciplines quantitatively, the importance of constraining subsurface characterization to link it to production results and drive toward a predictive model is a critical accomplishment for our industry. As such, I’d like to highlight three papers in this feature (OTC 30644, SPE 201417, and SPE 202683) and the knowledge and workflow applications they define and demonstrate. Sharing these integrated work flows with the community aids in teaching and leads to best-practice components of integrative studies. These efforts also share and demonstrate how to bridge the gap between in-situ characterization and wellhead performance prediction and results—in other words, the static-to-dynamic link between rock and fluid properties as quantified and how they will inevitably produce hydrocarbon through the rock and fluid interactions. Recommended additional reading at OnePetro: www.onepetro.org. SPE 201334 Combined Experimental and Well-Log Evaluation of Anisotropic Mechanical Properties of Shales: An Application to Wellbore Stability in the Bakken Formation by Saeed Rafieepour, The University of Tulsa, et al. SPE 201486 A New Safe and Cost-Effective Approach to Large-Scale Formation Testing by Fluid Injection on a Wireline Formation Tester by Christopher Michael Jones, Halliburton, et al. SPE 201735 Integrated Reservoir Characterization With Spectroscopy, Dielectric, and Nuclear Magnetic Resonance T1-T2 Maps in a Freshwater Environment: Case Studies From Alaska by ZhanGuo Shi, Schlumberger, et al.
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Cui, Hengtao, Zhonghu Wu, Liping Li, Jing Wang, Shuguang Song, Shangqu Sun, Yujun Zuo, Hao Liu, and Yili Lou. "Numerical Test Study of the Microscale Failure Modes and Fractal Analysis of Lower Cambrian Shale Based on Digital Images." Advances in Civil Engineering 2020 (December 27, 2020): 1–16. http://dx.doi.org/10.1155/2020/8819711.
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To reveal the effect of confining pressure on the mechanical properties and rupture modes of quartz-bearing shale, the shale core of the no. 3 block of Fenggang, Guizhou Province, China, was analyzed by nuclear magnetic resonance, polarized light microscope thin section observation and identification, and core X-ray whole-rock minerals diffraction analysis to determine the distribution of shale minerals in the Niutitang Formation. On the microscale, based on digital image processing technology, this paper characterizes the nonuniformity of minerals in shale, a numerical model that can reflect the true microstructure of shale. Then, the failure process of shale under different confining pressures was simulated. The results show that when the shale is loaded with vertical displacement under different confining pressures, the compressive strength and elastic modulus of the sample change significantly. The failure mode can be roughly divided into three types: the inverted V-shaped (0 MPa, 2 MPa, and 4 MPa), V-shaped (6 MPa and 8 MPa), and inverted Z-shaped (10 MPa). Since the development of fractal theory provides a new space for studying the damage and fracture of rocks, the damage evolution and failure process of shale can also be regarded as the fractal process of cracks, in which the fractal dimension is the core parameter. The calculation is different under different stress levels. The fractal dimension under the condition of confining pressure shows that the value of the fractal dimension is greatly affected by the effect of confining pressure. When the fractal dimension is higher, the fracture mode is more complicated, and the internal damage degree is more serious. The research results provide important theoretical guidance for shale gas fracturing production.
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Xu, Junce, Hai Pu, and Ziheng Sha. "Dynamic Mechanical Behavior of the Frozen Red Sandstone under Coupling of Saturation and Impact Loading." Applied Sciences 12, no. 15 (August 2, 2022): 7767. http://dx.doi.org/10.3390/app12157767.
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Saturation is one of the critical factors causing frost damage to rock masses in alpine regions, and dynamic stress perturbations further complicate the damage process. Therefore, the effects of water content and loadings should be considered in the construction and maintenance of rock structures during winter in cold regions. In this study, the effects of saturation and impact loading on the dynamic mechanical behavior of frozen red sandstone were investigated using a low-temperature split Hopkinson pressure bar system (LT-SHPB). By combining low-field nuclear magnetic resonance (LF-NMR) and scanning electron microscopy (SEM), the dynamic evolution of the microstructure of the frozen sandstone due to changes in saturation was investigated. The results indicated that the increase of saturation reshapes the pore structure of the frozen sandstone and promotes the expansion of pores of different sizes during freezing, while at complete saturation the frozen samples are mainly developed with meso- and macropores. The dynamic strength, elastic modulus, and brittleness index of the frozen sandstone under impact loading, which are limited by the critical saturation Src, tend to increase and then decrease with saturation. For the four impact loads, the dynamic strength of the samples increased by 21.2%, 27.1%, 32.5%, and 34.3% when the saturation was increased from 0 to 50%, corresponding to 1.38, 1.43, 1.51, and 1.56 times the dynamic strength of the fully saturated samples, respectively. In contrast, the ultimate deformation capacity of the frozen sandstone showed an opposite trend with saturation. As the impact load increases, the dynamic strength, elastic modulus, and peak strain of the frozen sandstone show a significant strengthening effect due to the increase in strain rate, while its brittleness index gradually decreases, dropping by 11.2% at full saturation. In addition, the energy dissipation capacity of the frozen sample first increases and then decreases with increasing saturation, with the enhancement effect of saturation on energy dissipation smaller than the weakening effect.
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Tong, Rong-Chen, He-Juan Liu, Yu-Jia Song, Li-Huan Xie, and Sheng-Nan Ban. "Permeability and Mechanical Response of Granite after Thermal and CO2 Bearing Fluid Hydro-Chemical Stimulation." Energies 15, no. 21 (November 5, 2022): 8280. http://dx.doi.org/10.3390/en15218280.
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The large scale extraction of geothermal energy can reduce CO2 emissions. For hot dry rocks, the key to successful utilization depends on the efficiency of reservoir reconstruction. The chemical and thermal stimulation methods are always used in geothermal reservoir reconstruction except in hydraulic fracturing with high fluid injection pressure, which is believed to reduce the seismic hazard by applying before the high-pressure hydraulic fracturing stimulation. However, at the laboratory scale, there are still very limited experimental studies illustrating the combined effects of chemical and thermal stimulation on the permeability and mechanical properties of granite, which is regarded as the main type of hot dry rock. In this paper, comparative stimulation experiments were carried out, including thermal/cold stimulation, CO2 bearing solution hydro-chemical stimulation, combined thermal and CO2 bearing fluid stimulation. By means of nuclear magnetic resonance analysis, permeability test and triaxial compression test, the changes of the micro-structure, permeability and mechanical properties of granite under various stimulation conditions were analyzed. The experimental results show that, compared with the single thermal stimulation and CO2 bearing fluid hydro-chemical stimulation, the superposition effect of thermal and CO2 bearing fluid hydro-chemical stimulation can increase the number of micro-fractures in granite more effectively, thus increasing the permeability, while the elastic modulus and compressive strength decrease. Moreover, the cooling mode on the granite also has a certain influence on the stimulation effect. After water-cooling on the heated granite (300 °C), combined with the CO2 bearing fluid stimulation (240 °C, 20 MPa), the permeability of granite is the highest, increasing by 17 times that of the initial state, and the porosity also increases by 144.4%, while the elastic modulus and compressive strength decrease by 14.3% and 18.4%, respectively. This implies that the deterioration of mechanical properties due to the micro-fractures increased by the thermal and chemical stimulation can enhance the fluid conductivity and heat extraction of granite. The methods in this paper can provide a reference for the combined application of thermal and chemical stimulation technology in artificial reservoir reconstruction of hot dry rocks.
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Ma, Maoyan, Min You, Shuguang Peng, Biao Zhang, and Yuan Lin. "Macro-Micro Study on Mechanical Properties of Frozen Fine Sandstone Based on DEM Mathematical Model." Journal of Function Spaces 2022 (May 16, 2022): 1–10. http://dx.doi.org/10.1155/2022/7176665.
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The study of freezing rock mechanical properties is getting more and more urgent because of coal mine construction in western China. Particle discrete element method (DEM) can describe discontinuous medium problem mathematically. In order to reveal the mechanical failure mechanism of frozen fine sandstone, the uniaxial compressive strength test of frozen fine sandstone was carried out, and then, DEM was used to simulate the uniaxial test of frozen fine sandstone. Furthermore, the nuclear magnetic resonance (NMR) technology was used to obtain pore distribution of the freezing sandstone. Finally, the results of NMR test and discrete element simulation were combined to reveal the microscopic mechanism of mechanical change in freezing fine sandstone. The DEM results show that the strength of frozen fine sandstone increases with the decrease of temperature. With the decrease of temperatures, strain softening occurs in frozen sandstone, which indicates that the discrete element simulation results are in good agreement with the uniaxial test results. Therefore, DEM can be used to simulate the mechanical behavior of frozen fine sandstone. At the same time, the DEM results also indicate that the formation and development of the shear band are the precursor of the failure of the sample. Furthermore, the NMR test confirms that temperature has a great impact on the pore distribution of sandstone. With the decrease of temperature, the pore ice content increases greatly, which induces a great decrease in NMR porosity and a vast decrease in the proportion of large and medium pores in all pores. Meanwhile, with the growth of the cohesion induced by increasing ice content, the uniaxial compressive strength increases macroscopically.
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Wang, Haijing, Boqin Sun, Zheng Yang, Scott J. Seltzer, and Marcus O. Wigand. "Accurate Rock Mineral Characterization With Nuclear Magnetic Resonance." Petrophysics – The SPWLA Journal of Formation Evaluation and Reservoir Description 63, no. 3 (June 1, 2022): 405–17. http://dx.doi.org/10.30632/pjv63n3-2022a8.
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Nuclear magnetic resonance (NMR) logging is a powerful formation evaluation technology that provides mineralogy-independent porosity and helps distinguish clay-bound water, capillary-bound water, and free fluids. NMR logging tool generally operates at 1H NMR frequency of 2 MHz (magnetic field, B0 ~ 470 Gauss) or lower. At this magnetic field, it is only feasible to detect 1H signal from fluids in pores and rely on the relaxation time variation to characterize fluid and pore types. As magnetic field strength increases, NMR sensitivity increases very dramatically, and NMR signals from solid matrix become easier to be detected in high field. For example, NMR at 600 MHz is about 5,000 times more sensitive than the NMR at 2 MHz. Meanwhile, the spectral resolution of high-field NMR is also greatly increased, and high-field NMR spectrum can resolve the detailed differences between molecule types. Therefore, the high sensitivity and spectral resolution of high-field NMR open a totally new horizon for the characterization of geological samples, especially in organic shale reservoirs, in which organic matter and complex mineralogy remain challenging to be accurately characterized. In this work, we report high-field NMR applications for mineral characterization using a 600-MHz NMR spectrometer equipped with a multichannel and Magic-Angle Spinning (MAS) probe. Compared to X-ray diffraction (XRD), which is the primary tool for identifying and quantifying the mineralogy of crystalline compounds in geological samples based on Bragg’s diffraction, NMR can provide more compositional and structural information for noncrystalline compounds due to its sensitivity to local electronic binding structures. Here we demonstrate such an application of high-resolution 27Al NMR to determine the composition and bonding chemistry of 27Al as a fingerprint for a wide range of minerals. The ratio of 27Al at tetrahedral and octahedral binding sites is quantitative and essential to differentiate the dioctahedral and trioctahedral phases. 27Al NMR can also distinguish plagioclase series members ranging from albite to anorthite end members, where Na and Ca atoms can substitute for each other. 27Al NMR can be further combined with 1H, 13C, 29Si, 25Mg, 23Na, and 31P for more detailed mineral determination and clay typing. Our results show that, combined with XRD, this group of high-field NMR spectroscopic methods can greatly improve the accuracy of rock mineral and formation clay characterization in tight-rock and unconventional reservoirs.
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Looyestijn, Wim J., and Jan Hofman. "Wettability-Index Determination by Nuclear Magnetic Resonance." SPE Reservoir Evaluation & Engineering 9, no. 02 (April 1, 2006): 146–53. http://dx.doi.org/10.2118/93624-pa.
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Summary Knowing the wetting condition of a reservoir at an early stage is crucial for selecting optimum field-development options. Paying insufficient attention to the wetting condition (e.g., assuming water-wet behavior) may result in incorrect oil-in-place estimates and in unexpected dynamic behavior (e.g., under-waterflooding). A novel method is presented to determine the wettability of rocks from nuclear-magnetic-resonance (NMR) data. The method is based on the additional nuclear relaxation that fluids experience when in direct contact with the rock surface. Reduction of oil relaxation time away from its bulk value is generally known as a qualitative wettability indicator, assuming external factors to be negligible and/or invariant from one experiment to another. Through detailed modeling of the NMR response, this concept has been developed further to provide a quantitative wettability index. It is based on a model for the microscopic distribution of the crude oil and the wetting state of the rock at any given overall saturation. The method requires an NMR measurement on a sample containing two reservoir fluids (i.e., brine and crude oil). Multiacquisition schemes including diffusion effects make the interpretation more robust, but a normal NMR acquisition suffices as can be made with all available NMR tools (wireline and while-drilling). The new NMR-based method has been verified extensively on core data against standard wettability tests. Application to NMR logs is in progress. Introduction Importance of Wettability Determination. Wettability relates to the relative attraction of the rock to either water or oil and, thus, has a strong impact on the dynamic properties of the rock. Wettability ranges from pure water-wet (through intermediate-wet, or neutral) to oil-wet. Sandstone reservoirs have a tendency toward being water-wet to neutral, whereas carbonates are often neutral to oil-wet. However, there are too many exceptions to make reliable assumptions. Moreover, the wettability is likely to vary over the reservoir, and possibly also over time as a result of changing saturations during production. In current practice, wettability is poorly known; if identified at all, it is determined on a few core samples, and variation in 3D is hardly known. The purpose of the NMR wettability research is to take a first step toward alleviating these shortcomings by developing the results of recent work into a practical tool for use in reservoir studies. Wettability is rated as one of the critical uncertainties in many fields, particularly the Middle East carbonate fields. The ability to obtain wettability information at an early stage of field development is a significant improvement over current practices.
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Zhang, Fan, and Chi Zhang. "Probing water partitioning in unsaturated weathered rock using nuclear magnetic resonance." GEOPHYSICS 86, no. 5 (August 5, 2021): WB189—WB205. http://dx.doi.org/10.1190/geo2020-0591.1.
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”Rock moisture” (exchangeable water stored in weathered bedrock beneath the soil) is a key and yet overlooked component in hydrologic cycles. It can be partitioned to free water and capillary-bound water. Determining dynamic partitioning of rock moisture is crucial for conceptualizing critical zone functions and climate and hydrologic modeling. However, the quantification of rock moisture partitioning is challenging, especially in rocks with complex pore structures and weathering patterns. Laboratory nuclear magnetic resonance (NMR) measurements are performed on heterogeneous bedrock samples from a merokarst vadose zone to quantify the dynamics of rock moisture partitioning during the drying process. By fitting a multi-Gaussian function, NMR [Formula: see text] distributions are autodecomposed into multiple [Formula: see text] peaks representing different pore sizes and environments. This spectral analysis enables us to track the change of position, width, and area of peaks at any given saturation stage, shedding light on water depletion rates and patterns, water residence time, and partitioning and redistribution of the water in drying rocks. The changes in [Formula: see text] peaks associated with drying among our samples show strong correspondence with mineralogy, and [Formula: see text]-[Formula: see text] measurements indicate that rock moisture depletion and redistribution are closely related to the pore structures. Limestone with well-connected macropores shows a sequential water loss from large to small pores, whereas limestone with poorly connected macropores simultaneously loses water from all pore sizes. The [Formula: see text] peak decomposition analysis can be extended to the field scale to track rock moisture partitioning in the pore network. This capability has implications for documenting critical zone processes, including quantifying water storage dynamics, estimating plant available water, and monitoring weathering processes.
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Poonoosamy, Jenna, Martina Klinkenberg, Mara Lönartz, Yuankai Yang, Guido Deissmann, Felix Brandt, and Dirk Bosbach. "Combining innovative experimental approaches and cross-scale reactive transport modelling for assessing coupled hydrogeochemical processes at interfaces in deep geological repositories for radioactive waste." Safety of Nuclear Waste Disposal 1 (November 10, 2021): 105–7. http://dx.doi.org/10.5194/sand-1-105-2021.
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Abstract. Deep geological repositories with a multi-barrier concept are foreseen by various countries for the disposal of high-level radioactive waste. A reliable and consistent assessment of the safety of these repositories over time scales of some hundred thousand years requires an advancement of process understanding. Simulation tools need to be developed for a close-to-reality description of repository evolution scenarios. This is especially required to resolve the challenging task of comparing and assessing the safety of different repository concepts in different host rocks within the German site-selection process. The construction of underground galleries and geotechnical barriers in the host rock formation and the emplacement of nuclear waste packages will create perturbations induced by chemical, thermal and pressure gradients at the interfaces of the different barriers, leading to mineral dissolution and precipitation to achieve re-equilibration. Such coupled hydrogeochemical processes generate non-linear responses in transport and mechanical properties of barrier materials and host rocks, which have to be taken into account for a more rigorous assessment of repository system evolution. Reactive transport modeling (RTM) can be applied to investigate these perturbations and processes across temporal and spatial scales, from the micro-scale at interfaces via the repository near field to the entire repository system – information not accessible through experiments alone. Although RTM is capable of addressing highly complex hydrogeochemical phenomena, the application of RTM codes to real systems is impeded by the often simplified description of coupled processes. To enhance the predictive capabilities of reactive transport models and to gain fundamental insights into the coupling between solute and radionuclide transport properties (e.g., permeability and diffusivity) of porous media and dissolution/precipitation processes, we conducted experiments on “simplified” chemical systems combined with pore-scale and continuum-scale reactive transport modelling to study processes in isolation, with the final aim of improving conceptual approaches for process couplings implemented in reactive transport codes. In this context, we investigated the effects of coupled mineral dissolution and precipitation in porous media on changes in permeability using flow-through experiments conducted in a magnetic resonance imaging scanner, which enabled the in situ investigation of porosity evolution in combination with monitoring changes in permeability and mineralogy. Our observations showed that classical implementations in reactive transport codes such as the Kozeny–Carman equation (Carman, 1937) failed to reproduce the changes in permeability and that more sophisticated approaches are required (Poonoosamy et al., 2020a, b). Moreover, we developed a novel “lab-on-a-chip” setup, i.e., micronized counter diffusion reactors with in operando 3D Raman tomography (Poonoosamy et al., 2019, 2020c), which enables evaluation of the alteration in pore architecture and study of the effect of coupled mineral dissolution and precipitation on the diffusive transport of solutes and radionuclides in porous media. Our approach enables the development of process-based theoretical models which allow for improvements in RTM codes and for predicting the evolution of perturbed interfaces in waste repositories, thus building confidence in the predictive capabilities of reactive transport models and reducing uncertainties with respect to future repository evolution.
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Tong, Rongchen, Hejuan Liu, Jianfeng Liu, Yingkun Shi, Lihuan Xie, and Shengnan Ban. "Meso-Mechanical Characteristics of Granite with Natural Cracks after Mud Acid Corrosion." Energies 15, no. 3 (January 19, 2022): 721. http://dx.doi.org/10.3390/en15030721.
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Most of the discovered high-temperature geothermal energy systems are often related with granite that is characterized by natural faults, fractures and cracks of different size. However, the porosity and permeability of the granite matrix is very low, greatly limiting the efficiency of heat extraction in granitic rock. Chemical stimulation, which is regarded as one of the most important means of reservoir stimulation, has consequently received more and more attention. In this paper, a Triassic granite obtained from the eastern region of Liaoning Province in China was reacted with three different concentration of mud acid solution (8% HCl + 1% HF, 10% HCl + 2% HF, 12% HCl + 3% HF) and the resulting microstructure changes studied by scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR). The experimental results show that the number of micropores in the granite increases after chemical corrosion by mud acid solution. A higher mud acid solution concentration results in a much higher pore volume. Triaxial compression tests on the granite before and after chemical corrosion were carried out to study the effect of acidification on the mechanical characteristics of granite, showing that the peak stress and elastic modulus of granite decreases 25.7% and 16.5%, respectively, after exposure to mud acid solution (12% HCl + 3% HF) corrosion for three weeks at room temperature. The particle flow program PFC2D based on discrete element method was used to investigate the mechanical response before and after the chemical corrosion. Considering that the granite is rich in microcracks, the study is simplified by considering them all grouped into one main closed fracture. The influences of main crack inclination angle, crack length, friction coefficient and confining pressure on the mechanical response were investigated. Under the triaxial compression loading state, wing cracks appear at the initial crack tip, then secondary cracks begin to appear. The sensitivity analysis shows that three characteristic strengths (crack initiation strength, damage strength and peak strength) are strongly correlated with crack length, crack inclination angle, crack surface friction coefficient and confining pressure. These three characteristic strengths decrease 60%, 59% and 53%, respectively, compared with their initial values with the increase of main crack length from 6 mm to 22 mm, while they present positive correlation with the fracture friction coefficient from 0 to 1.0 and confining pressure from 10 to 50 MPa. There is a critical inclination angle of the main crack (i.e., 45°), meaning that these three characteristic strengths of granite decrease with inclination angles smaller than 45°, while they increase with an inclination angle larger than 45°. After the corrosion effect of mud acid solution on granite, the pore structure was changed and mechanical properties was damaged, which further affect the failure mode and failure process of granite samples affected by mud acid solutions. This paper provides a theoretical reference for evaluating the effect of chemical stimulation technology on the mechanical characteristics of granite, serving for the continuous hydraulic stimulation design after the chemical stimulation.
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Arns, Christoph H., Tariq AlGhamdi, and Ji-Youn Arns. "Numerical analysis of nuclear magnetic resonance relaxation–diffusion responses of sedimentary rock." New Journal of Physics 13, no. 1 (January 28, 2011): 015004. http://dx.doi.org/10.1088/1367-2630/13/1/015004.
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Lambert, R. K., R. J. Pack, Y. Xia, C. D. Eccles, and P. T. Callaghan. "In vitro tracheal mechanics by nuclear magnetic resonance imaging." Journal of Applied Physiology 65, no. 4 (October 1, 1988): 1872–79. http://dx.doi.org/10.1152/jappl.1988.65.4.1872.
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Images of rabbit tracheal cross sections were obtained at a series of transmural pressures ranging from 22 to -95 cmH2O by use of a nuclear magnetic resonance imaging microscope. The excised, washed tracheas were immersed in a solution of phosphate-buffered saline made up in deuterium oxide (D2O, pH 7.3). The images are maps of proton density in the image slice (2.5 mm thick). All but one series of images showed a collapse process in which the trachealis muscle invaginated asymmetrically, i.e., the muscle appeared to favor one side of the cartilage ring system more than the other. The connecting tissue between the cartilage rings appeared to be more compliant than the rings themselves, thus suggesting that the tracheal lumen became corrugated at negative pressures. In the plane of a cartilage ring, the lumen appeared to remain patent at pressures as low as -95 cmH2O. However, between rings, where the tracheal wall was more compliant, the lumen appeared to be totally occluded at -53 cmH2O. Lumen areas in both the plane of the cartilage rings and in a plane between rings were measured from each series of printed images for six tracheas. These measurements, when normalized, averaged, and plotted against transmural pressure gave asymptotic logarithmic compliances (n1 in the model of Lambert et al., J. Appl. Physiol. 52: 44-56, 1982) of 1.2 +/- 0.4 and 20 +/- 7 for the interring and ring regions, respectively. These values are greater than the critical value of 0.5 (J. Appl. Physiol. 62: 2426-2435, 1987) and are thus consistent with wave speed flow limitation being possible anywhere in the trachea during forced expiration.
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Li, Xin, Li Zhi Xiao, and Tian Lin An. "Nuclear Magnetic Resonance Logging Evaluation of Natural Gas Hydrate Reservoir." Advanced Materials Research 482-484 (February 2012): 1017–20. http://dx.doi.org/10.4028/www.scientific.net/amr.482-484.1017.
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Natural gas hydrate in ocean bottom and permafrost is a great potential energy resource. Compared to fluids hydrocarbons (oil, water and gas) in conventional reservoir evaluation, natural gas hydrate exists in sedimentary formations in solid form, which should be reconsidered in its reservoir evaluation and global reserves assessment. Nuclear magnetic resonance (NMR) technique plays an important role in natural gas hydrate reservoir evaluation. The recent applications of NMR logging in natural gas hydrate reservoir evaluation including formation porosity-permeability estimation, gas hydrate saturation estimation and growth habits prediction in rock pores are introduced. Finally, the potential combination application of downhole NMR 1H relaxation and 13C spectroscopy in natural gas hydrate reservoir evaluation model is also discussed.
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d’Entremont, Agnes G., and David R. Wilson. "Joint Mechanics Measurement Using Magnetic Resonance Imaging." Topics in Magnetic Resonance Imaging 21, no. 5 (October 2010): 325–34. http://dx.doi.org/10.1097/rmr.0b013e31823fb2b9.
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SUEKANE, Tetsuya, Naoto FURUKAWA, Asuka MIZUMOTO, Shoji TSUSHIMA, and Shuichiro HIRAI. "Imaging of Migration and Dissolution of CO2 in Rock by Nuclear Magnetic Resonance." Journal of the Visualization Society of Japan 26, Supplement1 (2006): 295–98. http://dx.doi.org/10.3154/jvs.26.supplement1_295.
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Ramia, M. E., and C. A. Martín. "Sedimentary rock porosity studied by electromagnetic techniques: nuclear magnetic resonance and dielectric permittivity." Applied Physics A 118, no. 2 (November 7, 2014): 769–77. http://dx.doi.org/10.1007/s00339-014-8798-0.
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Liu, Taoying, Chaoyang Zhang, Ping Cao, and Keping Zhou. "Freeze-thaw damage evolution of fractured rock mass using nuclear magnetic resonance technology." Cold Regions Science and Technology 170 (February 2020): 102951. http://dx.doi.org/10.1016/j.coldregions.2019.102951.
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Tchistiakov, Alexei A., Elizaveta V. Shvalyuk, and Alexandr A. Kalugin. "The rock typing of complex clastic formation by means of computed tomography and nuclear magnetic resonance." Georesursy 24, no. 4 (December 20, 2022): 102–16. http://dx.doi.org/10.18599/grs.2022.4.9.
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This study provides a new rock-typing approach for low-resistive and low-permeable clastic rocks. The approach includes integrated interpretation of routine core analysis data with microstructural characteristics, acquired from computed tomography (CT) and nuclear-magnetic resonance (NMR) data. The studied formation comprises siltstones in its bottom, which are replaced by sandstones in its top. Sandstones form the main part of the oil reservoir, whereas siltstones were originally considered as water-saturated. The reserves calculation was performed based on a single Archie equation for the whole formation. Despite on apparent water saturation and low permeability of the siltstones, incidental perforation showed considerable oil inflow from them as well. In order to delineate missed productive intervals within the low-resistive siltstones, we had to develop a new rock-typing approach, acknowledging rock multimineral composition, diversity of microstructures, a wide range of porosity, permeability, and residual water saturation values. Designed laboratory program included porosity, permeability, electrical resistivity measurements, capillary, NMR and CT tests. The experiments were performed on the same core samples that enabled reliable correlation between measured parameters. The joint interpretation of flow zone indicator, calculated as a function of porosity and residual water saturation, together with the results of petrophysical and microstructural measurements allowed reliable rock-typing of the clastic formation. It will serve as a petrophysical basis for identification of the missed productive intervals. The developed laboratory program and rock-typing algorithm can be implemented in other oilfields.
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Ding, Shun, Hailiang Jia, Fan Zi, Yuanhong Dong, and Yuan Yao. "Frost Damage in Tight Sandstone: Experimental Evaluation and Interpretation of Damage Mechanisms." Materials 13, no. 20 (October 16, 2020): 4617. http://dx.doi.org/10.3390/ma13204617.
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Low-porosity tight rocks are widely used as building and engineering materials. The freeze–thaw cycle is a common weathering effect that damages building materials in cold climates. Tight rocks are generally supposed to be highly frost-resistant; thus, studies on frost damage in tight sandstone are rare. In this study, we investigated the deterioration in mechanical properties and changes in P-wave velocity with freeze–thaw cycles in a tight sandstone. We also studied changes to its pore structure using nuclear magnetic resonance (NMR) technology. The results demonstrate that, with increasing freeze–thaw cycles, (1) the mechanical strength (uniaxial compressive, tensile, shear strengths) exhibits a similar decreasing trend, while (2) the P-wave velocity and total pore volume do not obviously increase or decrease. (3) Nanopores account for >70% of the pores in tight sandstone but do not change greatly with freeze–thaw cycles; however, the micropore volume has a continuously increasing trend that corresponds to the decay in mechanical properties. We calculated the pressure-dependent freezing points in pores of different diameters, finding that water in nanopores (diameter <5.9 nm) remains unfrozen at –20 °C, and micropores >5.9 nm control the evolution of frost damage in tight sandstone. We suggest that pore ice grows from larger pores into smaller ones, generating excess pressure that causes frost damage in micropores and then nanopores, which is manifested in the decrease in mechanical properties.
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Feng, Ziyan, Cheng Feng, Yuntao Zhong, Zhijun Qin, Rui Mao, Lei Zhao, and Xianghua Zong. "TOC estimation of shale oil reservoir by combining nuclear magnetic resonance logging and nuclear physics logging." Journal of Geophysics and Engineering 19, no. 4 (August 2022): 833–45. http://dx.doi.org/10.1093/jge/gxac052.
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Abstract The evaluation of source rock properties has become a vital step in logging interpretation. Total organic carbon (TOC) content is the key to estimating the quality and hydrocarbon generation potential of source rocks. In the shale oilfield of the Junggar Basin, the conventional method of calculating the TOC of hydrocarbon source rocks cannot satisfy logging evaluation requirements. This paper predominantly deals with a method for the quantitative estimation of TOC in source rocks via nuclear physics and nuclear magnetic resonance (NMR) logs. According to this method, the total hydrogen index of the source rock is the sum of the response of kerogen, clay minerals and fluid, expressed by corrected neutron porosity. The hydrogen index of fluid and clay minerals is indicated by the effective porosity of NMR and the estimated clay content, respectively. To eliminate the hydrogen index of fluid, the effective NMR porosity is subtracted from the corrected neutron porosity. On this basis, a new and overlapping method suitable for clay-rich rocks and oil reservoirs is proposed. This method was developed by overlaying the scaled clay content curve on the hydrogen index curve. In non-source rocks, the two curves regularly overlap. However, in organic-rich rocks the two curves will separate. The separation distance between the two curves was used to estimate TOC continuously. Possessing sound application and benefiting from the measured results of sweet spots, this method provides new insights for TOC quantitative prediction in shale oil reservoirs.
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Krebs, M., B. Lungwitz, A. Souza, A. Pépin, S. Montoya, P. Schlicht, A. Boyd, E. Vidoto, R. Polli, and T. Bonagamba. "The First Visualization of Acid Treatments on Carbonates With 3D Nuclear-Magnetic-Resonance Imaging." SPE Journal 20, no. 04 (August 20, 2015): 678–88. http://dx.doi.org/10.2118/168198-pa.
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Summary Carbonate reservoirs often show great heterogeneity in their inner rock structure, and stimulation treatments are often necessary to maintain or establish fluid production. Therefore, core-flow tests are usually conducted to test and model stimulation treatments within a laboratory scale to predict their performance. The visualization of wormholes that were created within core-flow tests requires novel technologies for evaluation and pathway-prediction purposes. Unfortunately, past visualization techniques were always associated with the destruction of the core sample, creating a demand for nondestructive methods. Nuclear-magnetic-resonance imaging (NMRI) is such a method that fulfills the approach of being nondestructive. The technology is widely known by medical applications, and this study developed a procedure on how to use the NMRI technology to visualize wormholes with NMRI in 3D. The study was started by initially choosing and obtaining various core samples that have different contents of calcite and dolomite. These core samples were imaged with the NMRI and microfocus-computed-tomography (µCT) technology in their unchanged state, and basic petrophysical experiments were conducted for initial experiments. The μCT technology was used as a reference visualization technique, because it provides a very high resolution with a corresponding high level of detail. Afterward, core-flow tests were conducted on the core samples with various acid systems and wormholes generated. Finally, the core samples with wormholes were imaged again with the NMRI and μCT technology, whereby the NMRI acquisition technique was improved toward imaging of rock samples, and the results were compared with the μCT results. The NMRI results showed moderate imaging achievements for the unchanged rock samples and high-quality imaging achievements for the extracted wormholes.
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Chen, Jinhong, Stacey Althaus, Houzhu Zhang, and Mohammed Boudjatit. "Automatic High-Spatial-Resolution Nuclear-Magnetic-Resonance Spectroscopy and Imaging System for Rock Cores." Microscopy and Microanalysis 27, S1 (July 30, 2021): 3286–89. http://dx.doi.org/10.1017/s1431927621011314.
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Dijk, Peter, Brian Berkowitz, and Peter Bendel. "Investigation of flow in water-saturated rock fractures using nuclear magnetic resonance imaging (NMRI)." Water Resources Research 35, no. 2 (February 1999): 347–60. http://dx.doi.org/10.1029/1998wr900044.
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Hollingsworth, K. G., and M. L. Johns. "Rheo-nuclear magnetic resonance of emulsion systems." Journal of Rheology 48, no. 4 (July 2004): 787–803. http://dx.doi.org/10.1122/1.1753277.
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Luo, Zhi-Xiang, Jeffrey Paulsen, M. Vembusubramanian, and Yi-Qiao Song. "Restricted diffusion effects on nuclear magnetic resonance DT2 maps." GEOPHYSICS 80, no. 2 (March 1, 2015): E41—E47. http://dx.doi.org/10.1190/geo2014-0206.1.
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The 2D nuclear magnetic resonance diffusion-relaxation experiment (NMR [Formula: see text]) has proven to be a powerful method to characterize complex fluids. Molecular components with distinct diffusion coefficients are shown on [Formula: see text] maps as separate peaks. In porous media such as reservoir rocks, molecular diffusion is restricted such that the apparent diffusion coefficient is time dependent and the diffusion behavior is non-Gaussian. Such restricted diffusion effects can manifest on the [Formula: see text] maps and complicate the interpretation of the results, but so far, they have not been systematically investigated. We used controlled laboratory experiments to demonstrate the influence of non-Gaussian restricted diffusion on NMR [Formula: see text] maps under various conditions and to show how restricted diffusion effects on [Formula: see text] maps can be distinguished from multiphase fluids. NMR [Formula: see text] experiments were carried out on a series of water-saturated packs of glass beads and two rock cores. The results revealed the important role of two critical length scales controlling the restricted diffusion effects on NMR [Formula: see text] maps: the molecular diffusion length [Formula: see text] during the NMR diffusion encoding time and the characteristic pore size [Formula: see text]. For [Formula: see text], the effect of non-Gaussian diffusion was negligible and the NMR [Formula: see text] map showed only one peak. As [Formula: see text] approaches [Formula: see text], an additional peak with a smaller diffusion coefficient emerged (resembling the [Formula: see text] map of an unrestricted two molecular components fluid), and its relative intensity was maximized (to [Formula: see text]), when [Formula: see text]. As [Formula: see text] further increased, the relative intensity of the additional peak started decreasing, in contrast to the scenario of [Formula: see text] maps of multiphase fluids. We determined the extent and influence of restricted diffusion on NMR [Formula: see text] maps, and we informed the interpretation of NMR [Formula: see text] measurements, which are commonly used to quantify gas, water, and oil signals in reservoir rocks.
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Shen, Rui, and Zhi Ming Hu. "Study of Nuclear Magnetic Resonance on Imbibition Mechanics of Conglomeratic Cores." Applied Mechanics and Materials 110-116 (October 2011): 4128–32. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.4128.
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In order to deeply study the imbibition mechanism of conglomerate reservoir, the law that fluid flows in different sizes of pores in the process of imbibition was researched by nuclear magnetic resonance. First, the conglomerate core was saturated by the simulated formation water, and then was saturated by polyfluoroethylene oil to form the irreducible water. During the experiment of imbibition, several time points were selected and the conglomerate core was tested by NMR. According to the relaxation time T2, pores were divided into large, middle and small three size ranges. As the imbibition time increases, the available rate of middle and small pores increase faster than large pores. The available rate of middle and small pores both exceed 50%, but the one of large pores is lower than 35%. The difference of mechanism between imbibition and waterflooding is explained by their NMR test results.
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Zhao, Yuan, Jiangteng Li, and Gang Ma. "Experimental Study on the Damage and Degradation Characteristics of Red Sandstone after Dry and Wet Cycling by Low Magnetic Field Nuclear Magnetic Resonance (NMR) Technique." Geofluids 2021 (April 12, 2021): 1–8. http://dx.doi.org/10.1155/2021/8866028.
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To study the damage evolution of rocks under the action of wet and dry cycles, nuclear magnetic resonance (NMR) technology was used to test red sandstone under different times of wet and dry cycles. The T 2 spectral distribution curve, porosity, spectral peak area, and damage distribution curve of the rock were obtained, and the quantitative relationship between porosity, damage degree, and number of cycles was established. The results show that with the increase of the number of wet and dry cycles, the T 2 spectral curve of rock gradually moves to the right, but the moving amplitude gradually decreases. The porosity and spectral area increase with the increase of the number of wet and dry cycles, coupled with a declining growth rate, and the maximum increase in porosity is 18.789%. The damage degree of rock increase with the increase of the number of cycles, but with the continuous increase of the number of cycles, the damage rate decreases, and finally the damage degree of rock tends to be a constant value.