Optimisation of doublet well spacing in low-enthalpy geothermal systems is addressed by defining a novel objective function that is based on the Coefficient of Performance (CoP) and energy sweep efficiency. The definition of objective function that separates performance-based criteria from economic factors, allows us to better observe the effects of heterogeneity on optimisation. A checkerboard pattern of two doublets (two injection wells diagonally placed and two production wells diagonally placed over corners of a rectangle) is considered for a range of homogeneous to heterogeneous (spatially correlated and fluvial) synthetic low enthalpy reservoirs. Optimal length and width of this rectangle are sought in order to (a) maximise heat recovery from a conventionally-chosen licence area around the rectangular domain, (b) minimise heat recovery from outside this licence area, and (c) maximise CoP. We define fixed (15 years and 30 years) and varying life times of operation (between 15 and 30 years). For optimisation, in addition to a simple-search procedure of optimisation across a mesh of simulation nodes, we also utilise a surrogate response surface model to computationally solve the optimisation problem. Our results consistently show that for a fixed life time of 15 years and a discharge rate of 250 m3/hr, 400 m is the optimal well/doublet spacing. Increasing the life time and the discharge rate will increase the optimal well/doublet spacing. The results show while CoP is sensitive to the heterogeneity, adding energy sweep to the objective function makes the distances found for the homogeneous cases also consistent solutions for the heterogeneous cases.

The Geothermal industry is increasingly exploring the adoption of advanced completion technologies in High-Pressure, High Temperature (HPHT) environments. This paper outlines applications for Swellable Elastomeric Technologies, are their benefits, in Geothermal Wells.

The technologies discussed in this paper offer reliable isolation, without mechanical packers and may offer reduce use of grout (cement).

The compounds discussed – Super Absorbent Polymers (SAP) – offer improved performance in high salinity environments when compared to conventional, osmotic-swell elastomers. These characteristics may also prove well suited to wells where the production of elements, such a Lithium, is desired.

Swelling in water, SAP compounds offer enhanced zonal isolation reliability when compared to grout (cement), conforming to borehole irregularities, negating potential for micro annuli formation.

Designs for Geothermal usage can offer:

• Cable feedthroughs to facilitate succinct Pressure-Temperature (P-T) measurement above and/or below isolations.
• Reduced well count and subsequent topside infrastructure – dual string completions.
• Improved HSE performance, through a reduction to hazard exposure during drilling and completion operations.
• Improved environmental performance
  • Reduced reliance on grout (cement) which may be considered as high energy consuming and high carbon emitting during its production.
  • Elastomer is inert and stable – removal of potential for grout (cement) contamination of formation water.
• More straightforward well recovery when compared to well completions, which have been fixed with grout (cement).

This paper concludes that Swellable Elastomeric Technologies offer a resilient solution for Geothermal Wells and may offer enhanced isolation performance, improved health and safety metrics and reduced environmental impact.

The Durham Geothermal Cogeneration Project targets the radiogenic Weardale Granite and overlying sediments along the Sharnberry–Deerness fault in northeast England. A geothermal gradient of 32-38°C/km yields surface production temperatures of 210-250°C at 6.5km and 160-190°C at 5km, well above the 85°C required for current third generation district heating, and technically suitable for fourth generation operation with customer-side temperature reductions.

A four-gate phased reservoir strategy mitigates risk and maximises flexibility. Gate 1 drills a 2.5km slim-hole to test fault transmissivity and temperature. If artesian flow or sufficient gradient is confirmed, Gate 2 advances to a 6.5km appraisal well with a 500m lateral. A successful outcome (≥210°C, ~50kg/s) enables a six-lateral fault-based development yielding ~39MWₜ and up to 37MWₑ. If flow is inadequate, a trial stimulation for a nine-lateral Enhanced Geothermal System (EGS) is attempted. Gate 3 provides a 5km sidetrack for EGS fallback, while Gate 4 targets sedimentary rock at 3km as a heat-only contingency. Each gate reuses the existing wellbore, limiting sunk cost and abandonment liability while ensuring delivery of the 39MWₜ base case.

Surface infrastructure includes a 16.9km network delivering approximately 101GWh/year to anchor loads including Durham University, the hospital, and civic buildings (achieving ~5.95 MWh/m linear heat density). A central energy centre includes twin heat exchangers, a 900 m³ thermal buffer, SCADA controls, and variable-speed pumps. An Organic Rankine Cycle unit enables flexible operation between cogeneration and heat only modes. Built-in geothermal redundancy avoids reliance on fossil backup or high-cost low-carbon alternatives, ensuring a resilient, low-carbon supply.

The “Advanced Computing Facility” is a high-performance data centre at the University of Edinburgh with a 6 MW maximum capacity. It will host the national supercomputer, funded by the UK government, which will increase the facility’s IT power demand to over 25 MW. The "Galleries to Calories" project investigates the techno-economic feasibility of using mine water from a nearby flooded coal mine as a heat sink to support the cooling requirements. The first exploration well encountered several unmapped voids and a mine water temperature of 16 °C – temperatures that must remain low to minimise future pumping costs in a potential cooling system. A preliminary well-field design proposes three well-doublet pairs with a combined abstraction rate exceeding 100 L/s for the existing 6 MW system. A 3D numerical groundwater model, calibrated with well test data, predicts a manageable drawdown within the 0.1 km² site. However, modelling also highlights a significant risk of thermal feedback from reinjection wells, along with induced advection from deeper, warmer mine workings. Modelling results indicate that maintaining a temperature increase below 1 °C is achievable through strategic well placement. This requires consideration of the regional groundwater flow direction, the high transmissivity of mine workings and host rock, and the potential use of hydraulically isolated mine panels. The discussed well configuration is designed to also optimise heat recovery approximately 500 m downgradient from the injection site, where a potential district heating network — delivering over 20 GWh/year — could be supported by the Geobattery system.