Repurposing the Knutsford-1 borehole as a deep borehole heat exchanger with consideration of palaeoclimate corrections to heat flow in the Cheshire Basin

Abstract

Subsurface thermal data from UK boreholes typically lack palaeoclimatic corrections, leading to underestimations in heat flow. This can significantly affect predicted geothermal resources and system performance, creating a false perception of energy limitations. This study evaluates the impact of palaeoclimate corrections on geothermal performance in an onshore setting; focusing on the potential for a well to be re-entered and repurposed as a deep borehole heat exchanger (DBHE). Using the Knutsford-1 borehole, this re-evaluation for palaeoclimatic impacts on heat flow shows that corrected heat flows (52 mW/m²) exceed uncorrected values (46 mW/m²). In a steady state conductive model, temperature predictions based on the corrected heat flow align more closely to the recorded temperature data. Moreover, transient DBHE simulations using OpenGeoSys software over 25 years reveal a minimum 17 kW increase in thermal yield, highlighting the operational implications and benefits of these corrections. With thousands of legacy boreholes worldwide, integrating palaeoclimate corrections into geothermal assessments could reveal substantial untapped energy potential. By unlocking previously overlooked geothermal potential, this research highlights how accurate subsurface (re)assessments can transform legacy infrastructure into a cost-effective, sustainable energy source - demonstrating that with better data and a more holistic approach, existing wells can support low-carbon heat production.

Keywords: Borehole heat exchanger; Groundwater flow; Knutsford-1 borehole; Palaeoclimate corrections.

Fig. 1

Schematic of deep borehole heat exchanger (DBHE) operating with (a) conductive and (b) advective (forced through groundwater flow) heat transfer in the subsurface.

Fig. 2

(a) map showing the ice margin evolution through the last glacial cycle in relation to the location of the borehole studied here. Blue margin positions characterise the advance of the ice sheet from 27 ka to 26 ka, while red margins capture the retreat from the maximum position, 25 ka to 21 ka. The small inset in the lower left shows the location of the map at the national scale. On the key, MASL means Metres Above Sea Level and capture the elevation of the topography. (b) Graph showing modelled ice thickness in metres over the borehole study site for different timestamps of the last glacial cycle. These thicknesses estimates have been derived from the outputs of Clark et al..

Fig. 3

Assumed temperature history (also tabulated in Tables 3 and 4), representative of conditions in the Cheshire Basin during the Late Pleistocene. Present day taken as the year in which the Knutsford borehole was drilled, 1976, with T_o as 9.6 °C representing the annual mean surface air temperature for this year.

Fig. 4

(a) Example of the plan view domain (i.e., at the top of the model) and (b) fully discretised mesh and domain size. Note the varying colours represent the varying lithological layers highlighted in Table 5.

Fig. 5

Temperature variations with depth generated from the static setup using corrected and uncorrected heat flows. Note a linear gradient of 17 °C/ km is also shown for comparison and a newly released re-equilibrated bottom hole temperature (BHT) is shown. Data points from Plant et al. and Wright.

Fig. 6

(a) Outlet temperature and (b) thermal power change with time for both corrected and uncorrected scenarios. Note that the inlet temperature is fixed at 5 °C.

Fig. 7

(a) Outlet temperature and (b) thermal power change with time for cases of conductive heat transfer only (corrected scenario) and advective groundwater flow. Note that the inlet temperature is fixed at 5 °C.

Fig. 8

(a) 3D advective scenario with plan view plots at (b) 900 m through the Helsby Sandstone Formation, (c) 1300 m through the Wilmslow Sandstone Formation (un-silicified) and (d) 2200 m through the Manchester Marls Formation.

Fig. 9

(a) Outlet temperature, (b) thermal power, (c) building power and (d) pressure drop recorded at the end of the simulation for varying engineering parameters. Recorded at the end of the simulation.

Fig. 10

(a) Heat pump power, (b) circulation pump power, (c) coefficient of performance (COP) and (d) coefficient of system performance (CSP) recorded at the end of the simulation for varying engineering parameters.

Fig. 11

(a) Coefficient of system performance plotted with an overlay of thermal power (kW) and (b) pressure ddrop with an overlay of circulation pump power (kW) for varying flow rates and inlet temperatures recorded at the end of the simulation.