A risk-based method for the design of monitoring networks for surface gas emanations from abandoned underground coal mines

摘要

In this paper, a risk-based method implemented within a geographic information system is proposed to locate monitoring points near zones of lower hydraulic resistance for the detection of gas leaks from underground gas storage sites installed in former underground coal mines. Risk assessment is conducted considering (1) the location and extent of the mined areas and of the former underground mining infrastructures, (2) damage induced by the mining works on the upper geological formations and their associated increase in hydraulic conductivity, and (3) potential impacts on humans, based on a proxy for population density. A new physically based method is proposed to compute the damage induced by the mining activities on upper geological layers, based on a 3D reconstruction of the geometry of the voids of the upper part of the former mine and a computation of the associated ground movements using influence functions. A new type of influence function applicable to inclined coal seam is proposed. The whole methodology is applied to the former underground gas storage site of Peronnes-lez-Binche, in Belgium. Three locations are identified for the installation of new piezometers to complement the existing monitoring network.