Drilling into coal mine workings: overview and experience from Britain’s coalfields

Underground coal mining in Britain spanned several centuries, in multiple different seams, and at depths ranging from near surface to greater than 1 km below surface. Due to this complexity, drilling into abandoned mine workings and especially mine voids is frequently considered challenging and risky. Increasing interest in open loop mine water heat schemes and the need to drill new boreholes for the abstraction and recharge of mine water has highlighted a need to understand the successes and failures of previous operational boreholes in order to de-risk mine water heat schemes. Analysis of 564 boreholes purposely drilled to encounter specific mining targets has enabled the success rates for monitoring and operational boreholes across Great Britain to be assessed for the first time. 87% of boreholes are suitable for their original purpose and, of those planned to hit underground mine voids, there is a good success rate, >75% encountering mine voids. This analysis should provide confidence to those planning to drill boreholes for mine water heating, cooling or storage schemes that, when the correct qualified people are used, hitting targets in abandoned coal mine workings is possible.