134 / 2021-10-04 16:46:00

Application of long-reach directional drilling for gas drainage of adjacent seams in coal mines with severe geological conditions

LRDD,gas hazards,methane drainage,drainage strategy

Coal mine methane (CMM) released during mining operations is a severe safety hazard worldwide, being one of the major causes of mine gas explosions and gas outburst incidents with many fatalities each year. In order to reduce gas content in gassy and tight coal seams a special drainage strategy is required.

The development of such a strategy is not only affected by geological factors but also engineering ones such as artificial fracturing and mining technical criteria (Skiba et al. 2013, Bojarski et al. 2014, Yan, 2020, ).



The study aimed to demonstrate the application of Long Reach underground Directional Drilling boreholes (LRDD) for gas drainage of adjacent seams before and during the longwall face operations.

This paper presents proposed workflow for the proper placement of long reach underground directional boreholes (LRDD) which consists of geomechanical, petrophisical and coal-gas characteristic based on which modelling and simulation processes are developed and boreholes trajectories are proposed. Such approach was confronted with the trial of workflow implementation performed within DD-MET project to low permeability-high gas content coals of Staszic-Wujek hard coal mine (Upper Silesia Coal Basin – Poland).



Five LRDD boreholes (TM1-TM5) with a length of 300 and 400 m were located over coal seam #501 in the fracture zone (mainly composed of sandstones) and monitored over five months of longwall face operations. The LRDD boreholes were drilled parallel to the longwall face what was forced by the mining plans and operation movement. The drilling operation was performed using Epiroc® Diamec PHC 8 underground core drilling rig with the nonmagnetic DeviFlex type inclinometer, which provided boreholes of a diameter of 95 mm. The results from the drainage were supported by the laboratory measurements of coals and barren rocks (sandstones and mudstones) and detailed information about key features controlling methane content, which were also used for calibration of developed geological and geomechanical numerical models.

The results from petrophysical measurements revealed low porosity-permeability features with complicated pore structure of coal samples and two types of sandstones of moderate and good filtration and reservoir properties. The efficiency of CH₄ intake of directional boreholes was on the ca. 70% level, while conventional boreholes only 30%.

The drainage efficiency significantly increased in the destressed zone around the advancing longwall face due to the developed fractures and stress relief. The average concentration of methane in the directional wells was ca. 89% while average methane intake was in the range of 5-4 m³/min. Moreover, post-exploitation drainage was observed from some boreholes with a cumulative flow rate of 3.0 m³/min from TM2 and TM4 boreholes and 0.2 m³/min from TM2 boreholes. The methane concentration was in the range of 50% for TM2 borehole to 74% for TM4 borehole. The total methane intake from the boreholes drilled in part I-C was nearly 1.8 million m³CH₄.



The obtained results proved the efficiency of this new in Europe LRDD boreholes technology as a feasible-one for gas control in coal mines characterized by severe geological conditions, what brings valuable environmental benefits and assure the effectiveness of the coal production process.



Acknowledgement

This project is financially supported by the European Commission Research Fund for Coal and Steel (RFCS) project “Advanced methane drainage strategy employing underground directional drilling technology for major risk prevention and greenhouse gases emission mitigation” GA: 847338-DD-MET-RFCS-2018/RFCS-2018, which is co-founded by the programme of The Minister of Science and Higher Education entitled PMW in 2019-2022, Agreement no. 5038/FBWiS/2019/2. The authors would like to express their gratitude to the research partners at PGG S.A. and Central Mining Institute for their contribution to the project.



References

YAN, X., ZHANG S., TANG S., LI Z., ZHANG Q., WANG J., DENG Z. 2020. Quantitative optimization of drainage strategy of coalbed methane well based on the dynamic behavior of coal reservoir permeability. Scientific Reports, 10, 20306, 701–709, https://doi.org/10.1038/s.41598-020-77148-1.

BOJARSKI, P., KOT-NIEWIADOMSKA, A. 2014. Directional drilling as a new tool to identify geological disturbances in coal seams. Zeszyty Naukowe Instytutu Gospodarki Surowcami Mineralnymi i Energi Polskiej Akademii Nauk 88, 29-41.

BRUNNER D.J, SCHWOEBEL J.J, THOMSON S. Directional drilling for methane drainage and exploration in advance of mining. Online: http://www.reidrilling.com.

KARACAN C.O., RUIZ F.A., COTE M., PHIPPS S. 2011. Coal mine methane: A review of capture and utilization practices with benefits to mining safety and to greenhouse gas reduction. International Int J Coal Geol.86 (2–3), 121-156.

SKIBA J., JURA B., KRAUSE E., WIERZBIŃSKI K., Directional CBM Drillings Ahead of Mining - New Chance for Reduction of CMM Emissions in Poland. Proceedings of METHANE EXPO 2013, March, 14, 2013, Vancouver, Canada.