Assessing risks related to stimulation of firedamp drainage boreholes in order to recommend prevention measures and monitoring methods to help early risk management during design of future drainage projects

Coal mining in Europe is extending to deeper and deeper levels, facing ever increasing coal seam methane contents and much higher methane emissions at production districts. Methane emissions raise a serious safety problem but also limit production advancement rates. Current drainage and pre-drainage methods applied in European coal mines are not sufficiently effective to face growing risks related to methane emissions. Therefore, in order to improve safety and increase production rates, it is essential to develop new gas control and drainage techniques. The Research fund for coal and steel of the European commission funds the GASDRAIN project between July 2014 and June 2018. The main objective of this project is to investigate stimulation techniques to improve drainage efficiency by increasing the permeability in the vicinity of firedamp drainage boreholes. As all stimulation techniques cannot be appropriate to all coal seams and mining conditions, 4 techniques are investigated by GASDRAIN partners. They are: hydraulic fracturing, open or cased hole cavitation, high pressure water jet slotting and use of explosives. Application of these stimulation techniques induces risks during stimulation process but also later during mining of stimulated/fractured coal seams or rock strata. For instance, self-heating of coal and spontaneous combustion are possible risks due to penetration of oxygenated air within coal seams or rock strata through fractures created by stimulation. Thus, a detailed risk analysis related to the use of the 4 stimulation techniques has thus been carried out. Firstly, all relevant incidents associated with stimulation of firedamp drainage boreholes have been identified through a bibliographical review and by collecting feedback from partners of the project through a questionnaire. Then, a core set of relevant risk scenarios has been defined and was represented with a bow-tie diagram (or event tree). Best practice measures to prevent and mitigate the risks (i.e. safety barriers) have also been selected. Authors will detail results from the detailed risk analysis (relevant incidents, bow-tie diagram) and present recommendations on prevention measures or monitoring methods which can help early risk management during design of future drainage projects in European coal mines