Branch of SDS-Gold Holding Company, Moscow, Russia:

V. I. Efimov, Deputy Director of Strategic Development, Professor, Doctor of Engineering Sciences, v.efimov@sds-ugol.ru

National University of Science and Technology—MISIS, Moscow, Russia:
S. M. Popov, Professor, Doctor of Economic Sciences

Moscow State Institute of International Relations (University), Moscow, Russia:
N. V. Efimova, Associate Professor, Candidate of Engineering Sciences

Siberian Institute of Mining, Kemerovo, Russia:
T. V. Korchagina, Deputy Director, Candidate of Engineering Sciences

Methane never stops releasing from closed mines to the ground surface. The release has a random and unpredictable nature. Such gas emission constitutes a threat as methane migrates in various states and at different degrees of solubility, inflammability and explosibility. Toxic gas poisoning hazard also grows. The risk is of particular concern if a gas emission source lies nearby residential and industrial buildings, considering housing density. It is noteworthy that despite the decades-long studies and monitoring of gas emission after closure of a number of mines in Europe and Russia, the problem connected with methane release and migration from flooded coal beds yet remains to be better investigated. The in situ observations in flooded mines show that the presence of water and the related hydrostatic pressure induce methane desorption and migration from flooded underground excavations. Nonetheless, scientific literature lacks information to be of essential scientific weight to describe such processes. The international practice and theory on methane emission to the ground surface after suspension (closure) of mines is extremely significant to getting an insight into processes subsequent to closure and flooding of mines in Russia. A closed mine can be either assumed a source of ecological hazard due to methane emission in the air, or a potential source of the nonconventional fuel and feed stock. The review of literature and the analysis of the results of test works devoted to the mentioned problem allows drawing conclusions that:
– after mine flooding methane migrates to residual voids, pores and cracks, which results in the increased pressure of free gas in excavations above water level;
– as groundwater level rises, methane desorption rate lowers under the influence of the hydrostatic pressure, and in this case, methane emission is 9 times higher from flooded coal than from dry beds;
– the value of the hydrostatic pressure has an insignificant effect on gas emission kinetics that becomes stabilized in 14–30 days.
The increase in the mine gas pressure creates conditions for methane migration through cracks toward ground surface. The complex process of methane emission is governed by many factors connected, among other things, with the structure and permeability of upper layers of rock mass and with the methane desorption rate from broken coal pillars and from coal left in mined-out voids of the flooded mines. These conclusions are supported by the data obtained after comparison of methane concentrations measured at the mouths of preventive holes drilled from the ground surface to the rock cavities in closed Voroshilov Mine, Prokopyevsk, Kemerovo Region, Russia.

1. Trubetskoy K. N., Guryanov V. S. Some aspects of development of resources of methane of the closed collieries. Ugol. 2007. No. 2. pp. 27–30.
2. Burrell R., Kerto S. Utilization of methane from the closed collieries: experience of Siberia and Great Britan. Reduction of methane emission: report for the II International conference. Novosibirsk : SO RAN, 2000. p. 518.
3. Puchkov L. A., Slastunov S. V. System approach to the coal methane problem solving. Proceedings of the VII International scientific and practical conference. Kemerovo : ZAO KVK «Ekspo-Sibir», 2005. pp. 8–15.
4. Feng G., Hu S., Li Z., Jiang H., Zhang Y. et al. Distribution of methane enrichment zone in abandoned coal mine and methane drainage by surface vertical boreholes: A case study from China. Journal of Natural Gas Science and Engineering. 2016. Vol. 34. pp. 767–778.
5. Karacan C. Ö. Modeling and analysis of gas capture from sealed sections of abandoned coal mines. International Journal of Coal Geology. 2015. Vol. 138. pp. 30–41.
6. Shi J.-Q., Rubio R. M., Durucan S. An improved void-resistance model for abandoned coal mine gas reservoirs. International Journal of Coal Geology. 2016. Vol. 165. pp. 257–264.
7. Vorobev S. A., Kachurin N. M. International experience of studies into integrated coal mining with underground method. Gornyi Zhurnal. 2016. No. 5. pp. 78–85. DOI: 10.17580/gzh.2016.05.11
8. Krause E., Pokryszka Z. Investigations on Methane Emission from Flooded Workings of Closed Coal Mines. Journal of Sustainable Mining. 2013. Vol. 12, Iss. 2. pp. 40–45.
9. Bekbasarov Sh. Sh., Karibaev E. G., Nurpeisova M. B. Provision of ecological safety of soil mastering. Gornyy zhurnal Kazakhstana. 2013. No. 7. pp. 37–40.
10. Magda Ya. To be or not to be? Ecological-geological consequences of mass closing of Donbass mines. Energeticheskaya politika Ukrainy. 2005. No. 2. Available at: http://masters.donntu.org/2009/ggeo/rybyantseva/library/article8.htm (accessed: 25.05.2017).
11. Shimotyuk V. D., Timofeenkov V. Yu. Monitoring of closed coal mines: British know-how in Kuzbass. EKO-byulleten InEkA. 2000. No. 5(52). Available at: http://ineca.ru/?dr=bulletin/arhiv/0052&pg=002 (accessed: 15.07.2017).
12. Efimov V. I., Lermontov Yu. S., Sidorov R. V., Korchagina T. V. Monitoring Liquidated Mines The Kuznetsk Coal Basin. Ugol. 2015. No. 9. pp. 79–84.
13. Efimov V. I., Sidorov R. V., Korchagina T. V. Problems of designing conservation (elimination) of mines Prokopevsko-Kiselevskogo district of Kemerovo oblast. Izvestiya Tulskogo gosudarstvennogo universiteta. Nauki o Zemle. 2016. No. 4. pp. 18–24.
14. Efimov V. I., Sidorov R. V., Mitichkin S. I. Prospects of mining and utilization of mine methane of closed mines of Prokopievsko-Kiselevskoe deposit in Kuzbass. Nauka i tekhnika v gazovoy promyshlennosti. 2015. No. 2. pp. 12–17.