Coupled hydraulic and mechanical model of surface uplift due to mine water rebound: implications for mine water heating and cooling schemes

Abstract

In order to establish sustainable heat loading (heat removal and storage) in abandoned flooded mine workings it is important to understand the geomechanical impact of the cyclical heat loading caused by fluid injection and extraction. This is particularly important where significantly more thermal loading is planned than naturally occurs. A simple calculation shows that the sustainable geothermal heat flux from abandoned coal mines can provide less than a tenth of Scotland's annual domestic heating demand. Any heat removal greater than the natural heat flux will lead to heat mining unless heat storage options are also considered.As a first step, a steady-state, fully saturated, 2D coupled hydromechanical model of a generalized section of pillar-and-stall workings has been created. Mine water rebound was modelled by increasing the hydrostatic pressure sequentially, in line with monitored mine water-level data from Midlothian, Scotland. The modelled uplift to water-level rise ratio of 1.4 mm m −1 is of the same order of magnitude (1 mm m −1 ) as that observed through interferometric synthetic aperture radar (InSAR) data in the coalfield due to mine water rebound. The modelled magnitude of shear stress at the pillar corners, as a result of horizontal and vertical displacement, is shown to increase linearly with water level. Mine heat systems are expected to cause smaller changes in pressure than those modelled but the results provide initial implications on the potential geomechanical impacts of mine water heat schemes which abstract or inject water and heat into pillar-and-stall coal mine workings.

A Review of the Performance of Minewater Heating and Cooling Systems

“…Rapid fluid pressure changes or elevated flow rates, especially in shallow mine workings, may theoretically lead to risk of geotechnical instability or erosion of unworked pillars [115]. A thorough assessment of geotechnical risk should be undertaken on evaluating any mine water thermal scheme (and is usually required by the Coal Authority in the UK).…”

Drilling into mines for heat: geological synthesis of the UK Geoenergy Observatory in Glasgow and implications for mine water heat resources

“…Preene and Younger 2014 'environmental and regulatory risk'). For example, on the groundwater and surface water chemistry impacts (Banks et al 2009;Burnside et al 2016 a,b), stability of mine workings (Younger 2014, Todd et al 2019 or potential movement of mine gas (Younger 2014). As an infrastructure designed for these kinds of mine energy challenges, the Glasgow Observatory comprises 12 boreholes, 4 research compounds, surface monitoring equipment and open data (Monaghan et al 2019).…”

The temperature of Britain's coalfields

“…At the time of writing, eleven feasibility studies are in progress funded by HNDU (Heat Networks Delivery Unit) and several academic and commercial studies have been published both regionally and at a site scale (e.g. White Young Green, 2007;Gillespie et al 2013;Harnmeijer et al 2017;Bailey et al 2016;Farr et al 2016;Brabham et al 2019;Todd et al 2019). Many cities and towns in Britain are located upon disused coalfields, and could provide a significant potential customer base for renewable energy schemes utilising abandoned coal mines.…”