Investigation of enhancing coal permeability with high-temperature treatment

Liu, Jiang; Kang, Yili; Chen, Mingjun; You, Lijun; Zhang, Tingshan; Gao, Xinping; Chen, Zhangxin

doi:10.1016/j.fuel.2020.120082

Cited by 25 publications

(4 citation statements)

References 47 publications

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“…As temperature increases, permeability gradually decreases when thermal expansion deformation predominates, and conversely, it increases when desorption deformation becomes dominant. 6 Liu et al 7 argue that at high temperatures (50–200 °C), the increase in temperature of coal samples enhances gas pathways and initiates microfractures, forming a fracture network, which leads to increased permeability. Conversely, Wu et al 8 suggest that at lower temperatures, elevated temperatures induce expansion within the coal framework.…”

Section: Introductionmentioning

confidence: 99%

Study on the Mechanical Parameters and Permeability of Coal Reservoirs at Different Temperatures

Qi,

Fu,

Kang

et al. 2024

ACS Omega

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Deep coal reservoirs, as opposed to their shallower counterparts, exhibit characteristics of higher temperatures and pressures. These conditions affect the fracture structure and mechanical properties of coal, which in turn controls permeability. Substantial studies have been conducted to determine the effects of overburden pressure on permeability, but the correlation between the temperature and mechanical parameters/permeability of coal remains unclear. This study focused on low-rank bituminous coal from the southern edge of the Junggar Basin in Xinjiang. Using experiments conducted on seepage and mechanics at different depths (considering effective stress and temperature), the study investigated how temperature affects the mechanical parameters and permeability of coal column samples. A permeability prediction model was established incorporating temperature, mechanical parameters, and effective stress. The results show that from 20 to 80 °C, the elastic modulus of coal column samples decreases by 31.0%, and the Poisson ratio increases by 72.0%. Permeability decreases between 48.37 and 90.12% under different depths. The stress sensitivity coefficient under various temperature conditions decreased exponentially as the effective stress increased, and the temperature sensitivity coefficient under various effective stress conditions decreased with increasing temperature. The permeability was more sensitive to a temperature below 40 °C. In the permeability prediction model, the fracture compressibility coefficient is bifurcated into two coefficients, each controlled by temperature and effective stress. The permeability prediction error of the model was 12.7% under constant effective stress and 17.2% under varying effective stress and temperature conditions. The study could provide guidance for fracturing and coalbed methane production in deep coal reservoirs.

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Section: Introductionmentioning

confidence: 99%

Study on the Mechanical Parameters and Permeability of Coal Reservoirs at Different Temperatures

Qi,

Fu,

Kang

et al. 2024

ACS Omega

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“…Yin (Yin et al, 2013) pointed out that the increase in temperature can effectively reduce the compressive strength of coal; and the higher the temperature is, the lower the permeability becomes before the yielding stage. Liu (J. Liu et al, 2021) put the water‐bearing coal samples into helium at different temperatures and found that this can effectively remove a large amount of water and improve permeability before 200°C, while coal will undergo thermal cracking to expand the primary pore‐fissures and further improve its permeability at the temperature of 400–600°C. At present, researchers have proposed different mechanisms to explain the effect of temperature on permeability.…”

Section: Introductionmentioning

confidence: 99%

“…Liu (J. Liu et al, 2021) put the water-bearing coal samples into helium at different temperatures and found that this can effectively remove a large amount of water and improve permeability before 200°C, while coal will undergo thermal cracking to expand the primary pore-fissures and further improve its permeability at the temperature of 400-600°C. At present, researchers have proposed different mechanisms to explain the effect of temperature on permeability.…”

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confidence: 99%

The mechanism of inward and outward expansion of multiscale dynamic permeability of coalbed methane at different temperatures

Hao

Liu

et al. 2023

Deep Underground Science and Engineering

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The multiscale micro‐nano pores in coal can result in the ultra‐low permeability of coal, which restricts the efficiency of gas extraction. It is difficult for the conventional seepage‐enhancement measures to affect the nanoscale pores within the coal matrix. Thermal stimulation can reach deep into the micro‐nano pores within coal matrix to improve the permeability. Therefore, it is important to study the diffusivity and permeability of the multiscale micro‐nano pores at different temperatures. In this study, the experiments of diffusion‐seepage measured by the methods of GRI (Gas Research Institution) and steady‐state were conducted using a cylindrical coal at different temperatures and pressures. The experimental results show that the apparent diffusion coefficient of cylindrical coal is not constant but variable dynamically; and the classical diffusion model fails to describe the full‐time process of gas flow accurately. On this basis, a model of multiscale dynamic apparent diffusion‐seepage that can accurately describe the full‐time flow process was proposed. As is observed, the apparent permeability attenuates dynamically with time without stress loading, and the initial apparent permeability and the attenuation coefficient increase monotonically with the rise of temperature. Under the stress constraint, the steady‐state permeability increases after a decrease as the temperature rises, displaying a “U‐shaped” pattern. Without stress constraint, the increasing temperature causes the exterior multiscale pores to expand outward by different degrees so as to increase permeability, while the interior micro‐nano pores show three inward and outward expansion mechanisms. Under stress constraint, at low temperature and high effective stress, the increasing temperature causes pores to expand inward and the permeability decreases accordingly. When temperature continues to increase, coal expands outward because the effective stress is counteracted by the thermal stress, leading to an increase in permeability. This study is of significance for thermal gas extraction engineering.

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“…Numerous CBM development practices show that the current technology, mainly focusing on increasing permeability, cannot meet the needs of efficient CBM extraction. − External load stress technologies, such as hydraulic fracturing, high-energy gas fracturing, and detonation fracturing, increase the permeability of coal seams and improve the CBM extraction efficiency. , However, these technologies also have certain disadvantages. Water will hinder the desorption and migration of CBM. , Therefore, the improvement effect of methods such as hydraulic fracturing on CBM extraction is not ideal.…”

Section: Introductionmentioning

confidence: 99%

Theory and Engineering Practice of Intermittent Heat Injection-Enhanced Coalbed Methane Extraction

Hu,

Feng,

Zhou

2023

ACS Omega

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Because of the strong adsorption characteristics of methane and the low permeability of coal seams, the extraction efficiency of coalbed methane (CBM) is very low. Here, based on the energy conservation equation, we propose the theory of heat injection-enhanced CBM extraction. We developed a device for heat injection-enhanced CBM extraction and performed an on-site heat injection test in the Chengzhuang coal mine. The results showed that when the water injection rate was 0.5 m3/h, the heat injection temperature was 145 °C, with two heat injections, yielding the best CBM extraction effect. This could fully utilize the heat injection equipment and achieve a fast, safe, and efficient extraction. The gas production law of the intermittent heat injection-enhanced CBM extraction method had obvious stages; the CBM concentration and daily gas production were very low during the heat injection stage but were greatly improved during the extraction stage after heat injection. The highest CBM concentration reached 100%, and the maximum daily gas production of CBM increased by 1269 times. The variation law of the cumulative gas production with time was fitted using Wang’s empirical formula. Comparative analysis showed that, compared to traditional extraction, intermittent heat injection shortened the extraction time by 6.6 years. Compared with other enhanced CBM extraction methods, the intermittent heat injection method had obvious technical advantages and greater improvements in concentration and CBM extraction speed. Therefore, the results are of great significance for improving the recovery rate of CBM and for reducing greenhouse gas emissions.

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Investigation of enhancing coal permeability with high-temperature treatment

Cited by 25 publications

References 47 publications

Study on the Mechanical Parameters and Permeability of Coal Reservoirs at Different Temperatures

Study on the Mechanical Parameters and Permeability of Coal Reservoirs at Different Temperatures

The mechanism of inward and outward expansion of multiscale dynamic permeability of coalbed methane at different temperatures

Theory and Engineering Practice of Intermittent Heat Injection-Enhanced Coalbed Methane Extraction

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