Variable frequency of pulse hydraulic fracturing for improving permeability in coal seam

Li, Quangui; Lin, Baiquan; Zhai, Cheng; Guanhua, Ni; Peng, Shen; Sun, Chao; Cheng, Yanying

doi:10.1016/j.ijmst.2013.10.011

Cited by 60 publications

(15 citation statements)

References 2 publications

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“…To reuse this abandoned well, drilling should continue until the well penetrates coal seams #9 and #15 located below coal seam #3. A hydraulic fracturing method [25][26][27] could then be used to increase the original permeability of the three coal seams and allow the abandoned well to be reused.…”

Section: Location Of the Well Bottommentioning

confidence: 99%

Methane Extraction from Abandoned Mines by Surface Vertical Wells: A Case Study in China

Zhang

Feng

et al. 2018

Geofluids

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Considerable methane resources exist in abandoned coal mines. However, methane extraction from abandoned mines in China is still in the exploratory stage. This study presents technologies and engineering practices suitable for the extraction of gob methane from abandoned mines using surface vertical wells, including methane drainage systems, well bottom locations, and an intermittent drainage method. Seven surface wells in the Yongan abandoned mine in China were selected for gob methane extraction. Field results showed that the methane volumetric flow rate of a well whose bottom was close to the gob bottom was 2.5 times greater than that of a well with a bottom located in the gob fractured zone. Moreover, intermittent extraction can enable a well to extract methane cyclically at a high volumetric flow rate. A well drilled mistakenly into a coal pillar can be reused through hydraulic fracturing. The overall maximum methane volumetric flow rate, average concentration, and extraction span were 210 m3/h, 83%, and 1100 days, respectively.

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Section: Location Of the Well Bottommentioning

confidence: 99%

Methane Extraction from Abandoned Mines by Surface Vertical Wells: A Case Study in China

Zhang

Feng

et al. 2018

Geofluids

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“…Eventually, due to the influence of cyclic loads at different frequencies, the fatigue failure of pores and cracks in coal gradually becomes more obvious, thus promoting the formation of new pores and cracks. Li et al [20] investigated the mechanism of crack propagation during pulse hydraulic fracturing by utilizing the triaxial mechanical test system and acoustic emission. Similarly, Li et al [21] carried out field testing at Yuwu Coal Mine (Shanxi Province, China) with pulse hydraulic fracturing.…”

Section: Introductionmentioning

confidence: 99%

Effects of Cyclic Loading on the Pore Structure of Anthracite Coal

Wang

Cheng

2021

Advances in Civil Engineering

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In the process of improving coalbed permeability through pulse hydraulic fracturing, the cyclic loading effect influences the characteristics of micropores in coal matrix, thus affecting the process of gas migration. Therefore, it is essential to investigate the effect of cyclic loading on the pore structure of coal. Seven groups of loading tests at different frequencies and amplitudes were conducted on anthracite coal obtained from Shanxi Province, China, using a fatigue-testing machine. Subsequently, using a PoreMaster GT-60 Mercury-intrusion apparatus, the influence of the frequency and amplitude on the structural characteristics (including mercury-injection and mercury-ejection curves, pore size distribution, porosity, and specific surface area) of pores in coal samples was analyzed. Finally, the law and mechanism of action of the loading frequency and amplitude on pores in coal samples were comprehensively analyzed. The test results showed that, in the case of maintaining the sine-wave amplitude unchanged during loading while altering the loading frequency, the overall porosity and pore volume rise at different degrees. The growth of the loading frequency presents a more significant promotive effect on the initiation and development of pores and fractures. Moreover, it drives the transformation of micropores and transition pores into mesopores and macropores, thus increasing the proportion of seepage pores. Under the condition of large sine-wave amplitude during loading, macropores and mesopores are subjected to the repeated action of the external force, thereby reducing the overall porosity. In addition, the volume of the seepage pores declines, and the number of the coalesced pores decreases. Finally, in light of these results, the implications of frequency and amplitude selection in the process of pulse hydraulic fracturing are discussed. Therefore, the results of this research will provide an important theoretical basis for the field application of pulse hydraulic fracturing technology in coal mines.

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“…Furthermore, borehole sealing is a vital factor to the gas extraction efficiency. e borehole-sealing quality is closely related to the solidified sealing material [19]. e mining team of coal and methane has developed a new type of solidified material for sealing ( Figure 1), it can optimize the deficiencies of traditional materials in terms of initial setting time, fluidity, and expansion, however, the porosity and mechanical properties of the material during sealing are still to be studied.…”

Section: Introductionmentioning

confidence: 99%

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

Zhang

Jin

Liu

et al. 2020

Advances in Polymer Technology

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

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Variable frequency of pulse hydraulic fracturing for improving permeability in coal seam

Cited by 60 publications

References 2 publications

Methane Extraction from Abandoned Mines by Surface Vertical Wells: A Case Study in China

Methane Extraction from Abandoned Mines by Surface Vertical Wells: A Case Study in China

Effects of Cyclic Loading on the Pore Structure of Anthracite Coal

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

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