Experimental Study of Low-Temperature Shale Combustion and Pyrolysis Under Inert and Noninert Environments

Chen, Wei; Zhou, Yu; Yu, Weigang; Yang, Leilei

doi:10.2118/194507-pa

Cited by 7 publications

(14 citation statements)

References 28 publications

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“…As shown in Figures a and b, the surface conditions for the raw and CS1 samples are similar, which is consistent with the similar pore volume and diameter. Because only the moisture and a small amount of volatile are released, there are no obvious pores and fractures observed on the surfaces of raw and CS1 samples . Some pores and fractures generated on the surfaces of CS2 and CS3 samples were observed (Figure c and d).…”

Section: Results and Discussionmentioning

confidence: 97%

“…The pore structures generated in the CS2 sample also prompted the spreading of the water droplet. In addition, many oxygen-containing functional groups were added on the shale surface during combustion, 51 which effectively increased the affinity of shale to water molecules. The water droplets were observed to completely spread over the surface of the CS3 sample and did not maintain certain shapes because of the generation of large fractures.…”

Section: Results and Discussionmentioning

confidence: 99%

“…The cleaning method for the contact angle measurement used in this study is consistent with the one developed by Yuan et al 30 The weight-loss curve for the Wenjiaba shale samples showed that weight was lost rapidly when the temperature was increased to 400 °C and that the weight tended to be stable when the shale sample was heated up to 800 °C. 51 Thus, temperatures of 200, 400, and 800 °C were selected as combustion temperatures to investigate the effect of combustion on the shale wettability. Finally, the shale samples (CS1, CS2, and CS3) were combusted in a tube furnace with a constant air flow at 200, 400, and 800 °C for 30 min, respectively.…”

Section: Samples and Experimentsmentioning

confidence: 99%

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Experimental Study of the Wettability Characteristic of Thermally Treated Shale

Yang

Gu²,

Chen

et al. 2020

ACS Omega

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Extraction of shale gas from shale reservoirs is significantly affected by shale wettability. Recently, thermal recovery technologies (e.g., combustion) have been tested for shale gas recovery. This requires an understanding of the wettability change mechanism for thermally treated shale samples. In this study, the effect of combustion on shale wettability was investigated. Shale samples were first processed to obtain smooth surfaces and then combusted at temperatures of 200, 400, and 800 °C. The initial contact angles and dynamic behavior of water droplets on shale surfaces were recorded using the sessile drop method. It was found that pores and fractures were generated on the shale surfaces following high-temperature combustion. The pore volume and diameter increased with increasing combustion temperature, which improved the connectivity of hydrophilic pore networks. Compared to a raw shale sample, the shale sample combusted at 400 °C showed a smaller initial water contact angle and a more rapid decrease in the contact angle because of the oxidation of organic matter and generation of pore structures. Water droplets were found to completely spread over the surface of the shale sample combusted at 800 °C because of the generation of fractures. Moreover, the van der Waals potential between water droplets and combusted shale samples was determined to be stronger. However, the initial contact angle and dynamic behavior of water droplets did not show a significant change for the shale sample combusted at 200 °C. As a result, high-temperature combustion (≥400 °C) can be used to significantly improve the hydrophilicity of shale.

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Section: Results and Discussionmentioning

confidence: 97%

Section: Results and Discussionmentioning

confidence: 99%

Section: Samples and Experimentsmentioning

confidence: 99%

See 1 more Smart Citation

Experimental Study of the Wettability Characteristic of Thermally Treated Shale

Yang

Gu²,

Chen

et al. 2020

ACS Omega

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“…According to the TGA-FTIR results of shale sample from Wenjiaba in previous studies (Chen et al 2019d), the rapid weight loss occurred when the shale samples were heated up to 400 °C, and the weight loss rate was maximum at around 450 °C and 580 °C. Therefore, the temperatures 400 °C and 450 °C were selected to study structure characteristic changes.…”

Section: Shale Sample Preparationmentioning

confidence: 93%

“…Proximate analysis, ultimate analysis and vitrinite reflectance of shale sample, adapted fromChen et al (2019d) …”

mentioning

confidence: 99%

Thermally enhanced shale gas recovery: microstructure characteristics of combusted shale

et al. 2020

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Recently, thermal recovery technologies such as combustion have been studied for shale gas recovery. Thus, understanding of the microstructure of combusted shale is essential for evaluating the effects of thermal treatment on shale gas transport capacity. In this study, the effect of combustion on shale microstructure changes was investigated. Firstly, different-sized shale samples were combusted at 450 °C for 30 min. Afterward, shale microstructure properties including surface topographies, porosity and permeability of the raw and combusted shale samples were measured and compared. It was found that the pore volume and specific surface area increased after combustion, especially for small pulverized samples. According to surface topography obtained from atomic force microscope, more rough surfaces were obtained for the combusted shale due to larger pores and generation of thermal fractures caused by the removal of organic matter. Based on the mercury intrusion porosimetry measurements, the porosity of the shale samples increased from 2.79% to 5.32% after combustion. In addition, the permeability was greatly improved from 0.0019 to 0.6759 mD, with the effective tortuosity decreased from 1075.40 to 49.27. As a result, combustion treatment can significantly improve the gas transport capacity.

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Heating-Induced Enhancement of Shale Gas Transport and Its Application for Improving Hydraulic Fracturing Performance

et al. 2022

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Enhancing the gas transport capacity of shale is essential to obtain economical gas production. Thermal stimulation has been theoretically and experimentally proven as a feasible technology for improving shale gas extraction. In this work, Longmaxi organic-rich shale samples were heated at 200−1000 °C for 240 h to investigate the feasibility of heating-induced generation of additional gas transport pathways and improvement of gas transport capacity (diffusivity and permeability) within the shale matrix. Results show that the mass loss of shale samples is basically unchanged after 200 °C, while a significant mass loss ranging from 3.5 to 14.4% can be observed in the heat treatment at 400−1000 °C. Decomposition (e.g., organic matter, calcite, and dolomite) and clay dehydration are the primary causes of shale mass loss. The organic matter in the shale remained unchanged after 200 °C heat treatment but greatly reduced, until almost disappeared, after 400 and 600 °C heat treatments, and the content of carbonate minerals dropped sharply, until almost disappeared, after 600−1000 °C heat treatment. Nitrogen adsorption experiments and in situ scanning electron microscopy observations show a significant improvement of pore volume and pore size after 400−600 °C heat treatment. However, the mineral melt and recrystallization after the heat treatment at 800 and 1000 °C can cause pore destruction and densification, resulting in pore volume decrease, indicating that the best heating temperature in Longmaxi shale samples is around 600 °C to enhance the pore volume and connectivity in the shale matrix. The methane adsorption decreased by 63.0%, the effective diffusion coefficient in the macropore increased by 263 times after 600 °C, and the permeability increased by 212.8 times at 5 MPa confining pressure. The newly formed transport pathways derived from 600 °C heat treatment may also improve shale matrix permeability at a high effective stress ranging from 30 to 65 MPa, which is a typical stress condition in the shale formations 2000−4500 m in depth. Based on the experimental results in this study, we proposed the heat treatment to improve hydraulic fracturing performance by mitigating fracturing-induced formation damage (e.g., water blockage, clay swelling, and secondary precipitation) within the fracture−matrix interface. In situ combustion of shale gas in hydraulic fractures may be a possible method to heat the shale formations and generate heating-induced transport pathways on the wall surfaces of hydraulic fractures.

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Experimental Study of Low-Temperature Shale Combustion and Pyrolysis Under Inert and Noninert Environments

Cited by 7 publications

References 28 publications

Experimental Study of the Wettability Characteristic of Thermally Treated Shale

Experimental Study of the Wettability Characteristic of Thermally Treated Shale

Thermally enhanced shale gas recovery: microstructure characteristics of combusted shale

Heating-Induced Enhancement of Shale Gas Transport and Its Application for Improving Hydraulic Fracturing Performance

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