Assessment of the resource base for engineered geothermal systems in Great Britain

An assessment of the engineered geothermal system (EGS) resource base that might be available for the generation of electricity for Great Britain has been undertaken by adopting a globally self-consistent protocol that if universally adopted, would allow estimates of EGS made for different countries and regions to be comparable. Maximum estimated temperatures at depths of 5 and 7 km are greater than 200 and 300 °C respectively, a considerable increase over previous estimates. The total heat in place in the basement, to a depth of 9.5 km that is theoretically available for EGS is 357,197 EJ. If it were possible to develop just 2% of this resource, this would be equivalent to 1242 times the final UK energy consumption in 2015. The theoretical and technical potential power has been calculated from the available heat in place. The total technical potential power, to a depth of 6.5 km, is 222,393 MWe and represents just 0.4% of the theoretical potential power. Current EGS exploitation is more likely to be restricted to a depths of around 4.5 km and reservoir temperatures greater than 175 °C. In which case technical potential power is mainly restricted to regions of high heat producing granites and represents a total technical potential power of 2280 MWe. However, improvements in drilling technology are expected to enable economic drilling to depths of 7 km or greater that will enable EGS exploitation in all regions of Great Britain

3D ground-use optimisation for sustainable urban development planning: a case-study from Earls Court, London, UK

Cities provide opportunities for economic growth, cultural and social development and scientific and technological innovation. Yet they have often developed without coordination and integration of the mutual benefits that could be provided by using urban underground space (UUS), often to the detriment or exclusion of other potential city functions (Parriaux et al., 2004). Given that 60% of the area expected to be urbanised by 2030 has yet to be built (World Economic Forum, 2016) there is significant opportunity to influence future city planning and design using subsurface engineering geological ground models as a component part of a UUS management system. For future city development to be sustainable and resilient to change, an integrated approach that crosses disciplines and facilitates desirable urban futures while minimising the likelihood of undesirable ones is required (Lombardi et al., 2012; Price et al., 2016).University of Cambridge Future Cities Fellowshi

The need for improved management of the subsurface

The subsurface is used intensively to support economic stability and growth. Human interaction with the shallow subsurface ranges from exploitation of resources, accommodation of utilities, harnessing of energy (ground source heat pumps) and storage of waste. Current practice of managing these shallow subsurface zones is far from ideal. Many subsurface interventions are preceded by feasibility studies, predictive models or investigative measures to mitigate risks or predict the impacts of the work. However, the complex interactions between the anthropogenic structures and natural processes mean that a holistic impact assessment is often not achievable. By integrating these subsurface infrastructures within three dimensional framework models, a comprehensive assessment of the potential hazards in these shallow subsurface environments may be made. Some Geological Survey Organizations (GSOs) are currently developing subsurface management systems that will aid decision making in the shallow subsurface [1]. The British Geological Survey (BGS) is developing an open Environmental Modeling Platform [2] to provide the data standards and applications to link models, numerical simulations and ultimately socio-economic models so as to generate predictive responses to questions concerning sustainable us of the subsurface

Influence of geology and hydrogeology on heat rejection from residential basements in urban areas

Urbanization and limited land availability have resulted in the increased utilization of underground structures including residential basements in largely populated cities such as London, with an average addition of 200 basements per year in some boroughs. Residential basements kept at a comfortable temperature level throughout the year significantly contribute to heat fluxes in the subsurface as well as an increase in ground temperature. Understanding the ground thermal status is crucial in managing the significant geothermal energy potential in urban areas as well as the sustainable development of the urban underground, and in maintaining the energy efficiency of underground structures. In this proof-of-concept study, a 3D finite element approach accounting for coupled heat transfer and groundwater flow in the ground was used to investigate the influence of ground conditions on the heat rejection rate from basements. A detailed analysis was made of ground, above ground and underground built environment characteristics. This study demonstrates that the amount of heat from basements rejected to the ground constitutes a significant percentage of the total heat loss from buildings, particularly in the presence of groundwater flow. The extent of thermal disturbance in the ground varies depending on the ground characteristics. The volume of thermally disturbance ground inversely correlates with the groundwater flow rate in ground mainly consisting of highly permeable material. However, a direct correlation exists when the thickness of permeable soil layer decreases. A larger horizontal to vertical ratio of ground thermal disturbance is observed when the thickness of permeable soil layer increases

Large-scale urban underground hydro-thermal modelling - A case study of the Royal Borough of Kensington and Chelsea, London.

The shallow subsurface of dense cities is increasingly exploited for various purposes due to the significant rise in urban populations. Past research has shown that underground activities have a significant impact on local subsurface temperatures. However, the resulting spatial variability of ground temperature elevations on a city-scale is not well understood due to the lack of sufficient information and modelling complexity at such large scales. Resilient and sustainable planning of underground developments and geothermal exploitation in the short and long-term necessitate more detailed, more reliable knowledge of subsurface thermal status. This paper investigates the impact of some common underground heat sources such as train tunnels and residential basements on subsurface temperature elevation on a large scale and highlights the influence of local geology, hydrogeology, density, and type and arrangement of the heat sources on ground thermal disturbance. To tackle the size issues and computational expenses of such a large-scale problem, a semi-3D hydro-thermal numerical approach is presented to capture the combined influence of underground built environment characteristics coupled with ground properties on ground temperature elevation within the Royals Borough of Kensington and Chelsea (RBKC), London. Numerical results show that the extent of ground thermal disturbance is mostly affected by geological and hydrogeological characteristics in permeable ground (River Terrace Deposits). Density and spatial distribution of heat sources, however, are critical parameters in ground temperature evaluation in highly impermeable ground such as London Clay Formation. The locality of temperature rise and potential ground energy within immediate impermeable ground surrounding heat sources versus significantly large extent of ground thermal disturbance in permeable ground, highlights the significant dependency of ground thermal state and geothermal potential at the studied site to the ground and underground built environment characteristics and necessitates a better understanding of shallow subsurface thermal state for a sustainable and resilient urban underground development.This work was funded under the Global University Alliance (Cambridge Centre for Smart Infrastructure and Construction, University of California, Berkeley, and National University of Singapore) and in collaboration with the British Geological Survey (BGS) (EPSRC reference: EP/N021614/1)

Trends in heavy metals, polychlorinated biphenyls and toxicity from sediment cores of the inner River Thames estuary, London, UK

River islands (Ait or Eyot) within the inner tidal Thames serve as unique recorders of current and historical estuarine chemical pollution. Sediment cores from Chiswick Ait were assessed for contamination using Microtox® solid phase bioassay, stable isotopes (δ13C, δ15N), heavy metals and polychlorinated biphenyls (PCBs). Microtox® classified these sediments as non-toxic to moderately toxic and bulk isotopes identified a change in organic input. Metals Cu, Zn, Cr, Ni, Cd, Hg and Ag showed parallel rise, peak and fall profiles which when allied to a 207/208Pb and 137Cs based chronology supported major changes in trace metal contributions corresponding to approximate input times of 1940 (rise), 1963 (peak) and 1985 (fall). Metals ranged from Cu 15 to 373 mg kg−1 (mean 141 mg kg−1), Zn 137 to 1331 mg kg−1 (mean 576 mg kg−1), Cr 14–351 mg kg−1 (mean 156 mg kg−1), Pb 10 to 1506 mg kg−1 (mean 402 mg kg−1), As 1 to 107 (mean 38 mg kg−1), Ni 11 to 113 mg kg−1 (mean 63 mg kg−1), Cd 0.2 to 53 mg kg−1 (mean 9 mg kg−1), Hg 1 to 8 mg kg−1 (mean 4.6 mg kg−1) and Ag from 0.7 to 50 mg kg−1 (mean 7.5 mg kg−1). Down core total PCBs ranged from 10.5 to 121 μg kg−1 and mean of 39 μg kg−1. The rise, peak and fall of Cu, Zn, Cr, Ni, Cd and Ag pollution matched local sewage works' treatment discharge records. Whereas the Hg, Pb and As profiles were disconnected, reflecting alternative historic sources and or partitioning behaviour. Comparison to marine sediment quality guidelines indicate that Zn, Pb, Ni, Cd and Hg exceed action level 2, whereas sedimentary Cu, Cr and As concentrations were above action level 1 (no action) but below action level 2 (further investigation required). The river islands of the tidal Thames capture a unique contaminant chemistry record due in part to their location in the tidal frame (salinity minimum) and close proximity to west London

Development of unified geological model surfaces from legacy 3D models in the Thames basin catchment area

A proliferation of 3D geological models has been created by the British Geological Survey (BGS) over the last 15 years, following significant developments in software, hardware and modelling methodology. Modelling of the subsurface by the BGS has been widespread, ranging in depth from 1m to 15000m, and covering areas in the orders of 0.1 km2 to 100 km2. These models have been produced to increase our understanding of the subsurface environment and to help us communicate issues pertaining to it, such as geological hazards, water protection and resource management. For these reasons, particular focus has been drawn to the major urban areas of the UK such as the Lower Mersey Corridor (Liverpool to Manchester), the Clyde basin (Glasgow and surrounding region) and Thames basin (London and surrounding region). This has led to the development of a number of overlapping models in these regions and, since these models have been created for specific purposes and at varying scales, there has been little consideration given to ensuring that the individual geological surfaces within them are consistent from one model to another. Methodology has now been developed through the Thames Basin Cross- Cutting Project to amalgamate multiple versions of individual geological surfaces taken from existing 3D models, some of them overlapping, into a series of unified surfaces that represent the preferred geological interpretation at any given set of coordinates. The methodology alleviates some of the issues that have arisen with the existing models, such as different scales of overlapping surfaces (expressed as cell or mesh size), and the use of different subsets of the available records (boreholes/seismic reflection profiles/geological maps), commonly with different interpretations. This methodology has been tested on four key horizons within the Thames basin catchment area which are the stratigraphic tops and bases of the Lambeth Group and Chalk Group. The unified surfaces will provide a consistent representation of the subsurface for use by other modelling disciplines, including groundwater science. They will contribute to a whole-systems approach to climate change research, structural modelling, process modelling and palaeoclimate studies. They will also provide a starting point for future geological modelling that takes account of the work already done for existing 3D models, rather than one that goes back to the original data