The Geothermal Potential of Low Enthalpy Deep Sedimentary Basins in the UK

Abstract

Low enthalpy geothermal resources located within deep Permian and post-Permian sedimentary basins across the UK are estimated to contain at least 300 EJ (x1018 J) of heat, sufficient if fully developed to supply all heating needs in the UK for the next century. The geothermal heat estimate is based on data held within the Geothermal Catalogue (Busby, 2010). A source of deep well data not included in the Geothermal Catalogue is held by the oil and gas industry; access to this data has allowed new geothermal research to be undertaken to re-evaluate and constrain an existing geothermal resource (the Cheshire Basin), and to evaluate a previously un-quantified resource (the East Midlands). These areas were determined based on the availability of oil and gas well data. Data relating to the East Midlands indicate the total available extractable heat from produced oil and co-produced water located in Carboniferous sediments totals 2.64 MWt. In the Welton Field water from non-oil bearing horizons are factored in; the extractable heat increases from 0.91 MWt to 1.6 MWt. The Cheshire Basin uses the offshore East Irish Sea Basin as an analogue to better constrain the aquifer properties of the Triassic Sherwood Sandstone Group (SSG) and Permian Collyhurst Sandstone Group (CS). It also assesses the connectivity of these Groups across the basin. The Helsby Sandstone Formation (part of the SSG) will likely exhibit a minimum transmissivity of 4.26 D m alone. Data for the CS were inconclusive due to diverging porosity trends between the basins; transmissivity could be on average 0.13 D m or 3.85 D m with resulting flow rates of 47.7 m3 d-1 or 1431 m3 d-1. Factoring in reservoir stimulation is deemed necessary if the CS is to be targeted. The connectivity of the basin is restricted by large N-S orientated largely cemented faults, restricting flow in an E W orientation. In addition the connectivity is further affected by facies heterogeneity and diagenesis; this increases tortuosity that may be advantageous in a geothermal context.

The work is pertinent given the UK’s commitment to the Kyoto Protocol and Renewable Energy Directive. Geothermal technologies are low CO2 emitters, are non-intermittent, unobtrusive, do not attract large emission-based taxes, have long (~25 year) lifespans and have minimal post-use clean up costs. The uptake of geothermal resource within the UK still remains low, however, indicating barriers to uptake exist. Technical barriers (i.e. those relating to drilling of the well, geology, flow rates and temperature) are not limiting uptake. Non-technical barriers relating to lack of risk insurance schemes and longer payback times owing to the relative value of hot water versus petroleum are identified as restricting factors to the uptake of geothermal resources.

Geothermal energy development in the UK is still in its infancy and work such as this only strengthens the case for investment. The potential for geothermal resource exploitation to offset the conventional energy consumed to produce heat is sizeable; no other renewable technology has the capacity to deliver heat that low enthalpy geothermal offers.