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Evaluating the Response of Geothermal Reservoirs in the Cheshire Basin: A Parameter Sensitivity Analysis


Deep geothermal reservoirs (>2 km) from both low- to medium-enthalpy resources are considered as an alternative energy source to fossil fuels in the UK. Geothermal energy can be explored using existing technology from the oil industry and, unlike other renewable sources, is weather independent with the ability to deliver a reliable base load of energy. With an emerging need for a carbon-free economy, future alternative fuels must be developed. The Collyhurst formation, located within the Permo-Triassic Cheshire Basin of the UK, is investigated as a potential reservoir capable of producing a sustainable energy source equivalent to 2.8 billion barrels of oil. Numerical simulations are conducted to study the effects of a sensitivity analysis, designed to identify the most influential engineering and physical parameters on a system. The Collyhurst formation is an extensive, 700 m thick aeolian- to fluvial- sandstone body with high outcrop porosities and hydraulic conductivities (ranging from 3.7 x 10-5 to 10 m/day). Modelled at depths of 2.8 - 3.5 km for the central part of the basin, the reservoir temperature is expected to be ~80 °C. The finite-difference method is used to model the thermal and hydraulic interactions in the wellbore and reservoir, with both depletion and recharge phases being investigated. Numerical simulations are used to determine the key parameters responsible for affecting the productivity of the proposed geothermal scheme. The study concluded, both engineering and physical parameters, including the thermal gradient, hydraulic conductivity, production rate and the length of the well screen are the most important to determine the economic viability. Engineering parameters, such as production rate and the length of the well screen, can also be used to mitigate localised geological problems such as low-hydraulic conductivities. Seasonal changes in the consumption of energy are also considered, investigating the effect of natural recharge in-between peak times of demand. The results of this study can be used as a guide for decision makers who are proposing to exploit the energy using a single-well geothermal scheme for the basin. Key geological risks are also identified from the model, enabling all risks to be mitigated against and alternative engineering solutions planned for. The research shows that engineering parameters must be accounted for prior to the development of single-well, low-enthalpy schemes in thick sedimentary reservoirs.