Traditional heating using non-renewable energy resources contributes up to 50% of current carbon emission level. Different sources of renewable energy are being exploited and developed to lower the carbon emission level for continuity of healthy living environment. It is found that thermal energy is stored in minewater flooding abandoned mines. The minewater can be extracted through newly drilled boreholes or existing mineshafts. To ensure successful and sustainable operation, mineshafts have to be structurally stable. When the mines are abandoned, the water level tends to recover. Some of the configurations of the minewater heat recovery may change the temperature of part of the shaft wall. This research aims to provide some insight on the stability of mineshafts for minewater heat recovery through numerical sensitivity analyses on: (a) water level, (b) temperature fluctuations. In the presented research work, rock masses with different properties have been analyzed. Change in temperature is found to mainly change the static Young's Modulus of intact rock and the joint roughness. However, the joint roughness is expressed indirectly using the Geological Strength Index, which has direct relationship with joint roughness and is used in stability analysis. It is found that an increase in water level reduces the integrity of the whole shaft. The degrees of stability deterioration are different at different depths and depend on the in situ stress state. Findings of this analyses can be assist in making a decision on the selection of the appropriate configuration for minewater heat recovery.

The Earth’s subsurface not only provides a wide range of natural resources but also contains large pore volume that can be used for storing both anthropogenic waste and energy. For example, geothermal energy may be extracted from hot water contained or injected into deep reservoirs and disused coal mines; CO2 may be stored within depleted petroleum reservoirs and deep saline aquifers; nuclear waste may be disposed of within mechanically stable impermeable strata; surplus heat may be stored within shallow aquifers or disused coal mines. Using the subsurface in a safe manner requires a fundamental understanding of the physiochemical processes which occur when decarbonising technologies are implemented and operated. Here, thermal, hydrological, mechanical and chemical perturbations and their dynamics need to be considered. Consequently, geoscience will play a central role in Society’s quest to reduce greenhouse gas emissions. This contribution provides a review of the physiochemical processes related to key technologies that utilize the subsurface for reducing greenhouse gas emissions and the resultant challenges associated with these technologies. Dynamic links between the geomechanical, geochemical and hydrological processes differ between technologies and the geology of the locations in which such technologies are deployed. We particularly focus on processes occurring within the lithologies most commonly considered for decarbonisation technologies. Therefore, we provide a brief comparison between the lithologies, highlighting the main advantages and disadvantages of each, and provide a list of key parameters and properties which have first order effects on the performance of specific rock types, and consequently should be considered during reservoir evaluation for decarbonising technology installation. The review identifies several key knowledge gaps that need to be filled to improve reservoir evaluation and performance prediction to be able to utilize the subsurface efficiently and sustainably. Most importantly, the biggest uncertainties emerge in prediction of fracture pattern development and understanding the extent and timescales of chemical reactions that occur within the decarbonising applications where external fluid or gas is cyclically injected and invariably causes disequilibrium within the system. Furthermore, it is clear that whilst geoscience can show us the opportunities to decarbonise our cities and industries, an interdisciplinary approach is needed to realize these opportunities, also involving social science, end-users and stakeholders.