Methods and Parameters of Intensive Methane Extraction from the Coal Seams

Hydraulic fracturing is an effective technology for enhancing the extraction of reservoir methane, as proved by field experience and laboratory experiments. However, unlike conventional reservoirs, coal seams had high stress sensitivity and high anisotropy. Therefore, the efficiency of hydraulic fracturing in coal seams needs to be investigated. In this study, hydraulic fracturing was performed at Nantong mine in the southeast Sichuan basin, China. The field investigation indicated that the hydraulic fracturing could significantly enhance the methane extraction rate of boreholes ten times higher than that of normal boreholes in one of the minable coal seams (named #5 coal seam). The performance of hydraulic fracturing in three districts revealed that compared with south flank, the fluid pressure was higher and the injection rate was lower in north flank. The methane extraction rate of south flank was inferior to that of north flank. It indicated hydraulic fracturing had less effect on #5 coal seam in south flank. Moreover, the injection of high-pressure water in coal seams could also drive methane away from boreholes. The methane extraction rate of the test boreholes demonstrated the existence of methane enrichment circles after hydraulic fracturing. It indicated that hydraulic fracturing did act on #5 coal seam in south flank. However, due to the high stress sensitivity of coal seams and the high geo-stress of south flank, the induced artificial fractures in #5 coal seam might close with the decline of the fluid pressure that led to a sharp decline of the methane extraction rate.

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Numerical simulation of sectional hydraulic reaming for methane extraction from coal seams

Journal of Natural Gas Science and Engineering ◽

10.1016/j.jngse.2021.104180 ◽

2021 ◽

pp. 104180

Author(s):

Yongpeng Fan ◽

Longyong Shu ◽

Zhonggang Huo ◽

Jinwei Hao ◽

Yang Li

Keyword(s):

Numerical Simulation ◽

Coal Seams ◽

Methane Extraction

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Research in the Propping Agent for the Hydraulic Fracturing Cracks for the Methane Extraction from the Massive Coal Seams

Proceedings of the 8th Russian-Chinese Symposium "Coal in the 21st Century: Mining, Processing, Safety" ◽

10.2991/coal-16.2016.62 ◽

2016 ◽

Author(s):

Mikhail Baev ◽

Veniamin Khyamyalyaynen

Keyword(s):

Hydraulic Fracturing ◽

Coal Seams ◽

Methane Extraction

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Features of Borehole Degassing of the Outburst-prone Coal Seams

Occupational Safety in Industry ◽

10.24000/0409-2961-2020-12-74-78 ◽

2020 ◽

pp. 74-78

Author(s):

V.S. Zaburdayev ◽

◽

Yu.А. Filippov ◽

Keyword(s):

Coal Seams ◽

Strength Factor ◽

Mining Areas ◽

Coal Layer ◽

Methane Extraction ◽

Working Face ◽

Underground Workings ◽

Coal Reserves ◽

Gas Bearing ◽

Coal Strength

The conditions and features are given concerning the degassing of outburst-prone coal seams by wells drilled from the underground workings in the plane of the mined seam. Technological schemes for the location of wells in the mining areas during the preparation and development of the coal seams prone to sudden outbursts of coal and gas were substantiated taking into account the coal strength determined using the method of M.M. Protodyakonov. The scheme of coal seams degassing by wells oriented to the working face line is recommended with a coal strength factor f ≥ 1.3, the degassing scheme with crossed wells — at f < 1.3. The wells are drilled parallel to the working face line and oriented to it. The schemes are implemented in the shallow mines of Karaganda (Kazakhstan), Ukraine and China. Degassing of coal seams not unloaded from the rock pressure by crossing wells ensured an increase in methane production from 1 ton of coal by 0.4–4.8 m3 in the conditions of seams with different coal strength. The highest indicators were achieved in the powerful outburst-prone seams with a coal strength factor of f = 0.3–0.8 in the conditions of the mines of Karaganda Basin, where the volumes of methane extraction by crossing wells were 5.0–5.6 m3 per ton of the degassed coal reserves in the working areas. In the conditions of the outburst-prone shallow seams of Ukraine, the volumes of methane extraction from 1 ton of the degassed coal reserves on the medium density seams amounted to 2.5–4.4 m3 with a coal strength factor of f = 0.6–1.1. 2-2.3 m3 of methane was removed from 1 ton of coal at the Dziulishan mine (China) at a strongly crushed coal layer II1 with a strength factor f = 0.3–0.6. The use of degassing schemes for gas-bearing and outburst-prone coal seams ensures an increase in the productivity of working faces and, as a result, high economic indicators.

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