The thermal properties of the Mercia Mudstone Group

The Mercia Mudstone Group (MMG) crops-out extensively across England and Wales and its thermal properties are required for the design of infrastructure such as ground source heating and cooling schemes and electrical cable conduits. Data from the literature and new data from a borehole core have been compiled to generate an updated range of thermal conductivities related to rock type and the lithostratigraphy. These indicate a total range in saturated vertical thermal conductivity of 1.67–3.24 W m-1 K-1, comprising 1.67–2.81 W m-1 K-1 for mudstones, 2.12–2.41 W m-1 K-1 for siltstones and 2.3–3.24 W m-1 K-1 for sandstones. These data are all from measurements on samples and there will be uncertainty when considering the thermal properties of the rock mass due to micro and macro structural features. Geometric mean modelling of thermal conductivity based on mineralogy has overestimated the thermal conductivity. Correction factors for the modelled thermal conductivities have been calculated to enable a first estimate of MMG thermal conductivities when only mineralogical data are available. Measured thermal diffusivities from the borehole core were in the range of 0.63–3.07 x10-6 m2s-1 and are the first measured, thermal diffusivities to be reported for the MMG

Simulation of a geothermal aquifer storage in Brussels showing the need for a better balanced system with regards to the local hydrogeological conditions

An Aquifer Thermal Energy Storage (ATES) system was started in 2014 in the center of Brussels using the Landenian confined aquifer for heat and cold needs of an administrative building. Unfortunately, the imbalance between the injection of warm and cold water combined with the local hydrogeological conditions, has led rapidly to thermal interferences between the heat plume and the cold wells. A second ATES system located nearby started to operate around August 2017 for the heat and cold needs of another large administrative building. In the scope of the MUSE project (GeoERA/ERA-NET program), a numerical model was built using FEFLOW® to simulate groundwater flow and heat transport in the confined aquifer. After calibration on the available piezometric and temperature data, realistic scenarios were simulated to determine possible interferences and to image the year after year persisting and growing heat plume in the aquifer. Results show that even if the heat plumes of the two systems had come into contact, the influence of the second system on the first one was negligible during the first two years of joint operation. Indeed, for a longer period, simulated results pointed out that due to the thermal imbalance and the limited advection in the aquifer, the groundwater temperature would rise inexorably in the warm and cold wells of both systems. A business as usual scenario will lead to a decrease in efficiency for both systems. This case-study is showing how it could be difficult to find an optimum with regards to the local hydrogeological conditions. If advection is very important, thermal energy cannot actually be stored locally as heat and cold plumes are transported far away from the wells. On the contrary, if advection is limited, a global thermal balance is required for hot and cold injections. If advection is moderate (as in this case study), a detailed simulation of the groundwater flow and heat transport in the aquifer is required to find out if the annual imbalance can be managed in relation to the specific local hydrogeological conditions

Spring Water Geochemistry: A Geothermal Exploration Tool in the Rhenohercynian Fold-and-Thrust Belt in Belgium

peer reviewedSpring water geochemistry is applied here to evaluate the geothermal potential in Rhenohercynian fold and thrust belt around the deepest borehole in Belgium (Havelange borehole: 5648 m MD). Fifty springs and (few) wells around Havelange borehole were chosen according to a multicriteria approach including the hydrothermal source of “Chaudfontaine” (T ≈ 36 ◦C) taken as a reference for the area. The waters sampled, except Chaudfontaine present an in-situ T range of 3.66–14.04 ◦C (mean 9.83 ◦C) and a TDS (dry residue) salinity range of 46–498 mg/L. The processing methods applied to the results are: hierarchical clustering, Piper and Stiff diagrams, TIS, heat map, boxplots, and geothermometry. Seven clusters are found and allow us to define three main water types. The first type, locally called “pouhon”, is rich in Fe and Mn. The second type contains an interesting concentration of the geothermal indicators: Li, Sr, Rb. Chaudfontaine and Moressée (≈5 km East from the borehole) belong to this group. This last locality is identified as a geothermal target for further investigations. The third group represents superficial waters with frequently high NO3 concentration. The application of conventional geothermometers in this context indicates very different reservoir temperatures. The field of applications of these geothermometers need to be review in these geological conditions.MEE

Policy combinations to navigate between private and public monopolies in emerging technological sectors

Finance is one of the main critical issues for the development of a low carbon society especially during times of economic recession. Closing this green investment gap will require policy intervention. This paper is part of a larger research project – the ALPI project – which aims at analysing and designing relevant instruments to accelerate the transition towards a low carbon society. As a showcase of emerging technologies in Belgium, the Hasselt University, the University of Liège and the Geological Survey of Belgium are investigating the regional potential for geothermal electricity production. Deep geothermal energy appears to be currently on the edge of a take-off. But the actual emergence of this technology is subject to developments in legislation and incentives from regional governments. Different risk/return expectations across stages of the investment continuum exist and the financial structures that are employed at each stage may require different types of public support. Considering the particularities of the development of geothermal energy in Belgium, we present different combinations of incentives to support geothermal energy, and we review different sector evolutions through a broad stakeholder consultation (policy makers, sector federations, industry, researchers, banking sector, investors, etc.). However, a review of the learning effects shows that neither of the two combinations can prevent a regional monopolisation of the underground as a natural resource either by a private first-mover, or a public investor. Therefore, intermediary solutions are proposed to provide a balance between the two extremes, and to ensure an improved sector growth and a continuous open market.Assessment of Low Carbon Society Policy Instruments (ALPI) http://www.alpi.ugent.be/index.htm

Modelling interactions between three Aquifer Thermal Energy Storage (ATES) systems in Brussels (Belgium)

peer reviewedShallow open-loop geothermal systems function by creating heat and cold reserves in an aquifer, via doublets of pumping and reinjection wells. Three adjacent buildings in the center of Brussels have adopted this type of aquifer thermal energy storage (ATES) system. Two of them exploit the same aquifer consisting of Cenozoic sands, and started operation in 2014 and 2017, respectively. A previous hydrogeological model developed by Bulté et al. (2021) has shown how the thermal imbalance of one of the systems jeopardizes the thermal state of this upper aquifer. Here, the interactions with a more recent third ATES system located in the deep aquifer of the Palaeozoic bedrock are studied and modelled. After being calibrated on groundwater flow conditions in both aquifers, a 3D hydrogeological model was used to simulate the cumulative effect of the three geothermal installations in the two exploited aquifers. The results of the simulations showed that although the hydraulic interactions between the two aquifers are very weak (as shown by the different observed potentiometric heads), heat exchanges occur between the two aquifers through the aquitard. Fortunately, these heat exchanges are not sufficient to have a significant impact on the efficiency of the individual geothermal systems. Additionally, this study shows clearly that adding a third system in the lower aquifer with a mean power of 286 kW for heating between October and March and an equivalent mean cooling power between April and September is efficient.7. Affordable and clean energ

Ostracods, rock facies and magnetic susceptibility records from the stratotype of the Terres d'Haurs Formation (Givetian) at the Mont d'Haurs Givet France)

More than 5,500 carapaces, valves and fragments of ostracods, were extracted from 48 samples collected in the stratotype of the Terres d'Haurs Formation (= Fm) and in the very base of the stratotype of the Mont d'Haurs Fm, at the Mont d'Haurs, close to Givet. Fiftytwo species belonging to several assemblages of the Eifelian MegaAssemblage have been identified. They are generally indicative of neritic marine environments below fair-weather wave base, some even below storm wave base. Ostracods indicative of semi-restricted environments are also present but the sedimentological analysis displays that these ostracods have been mainly transported from these shallow settings. Close to the boundary of the Terres d'Haurs Fm and the Mont d'Haurs Fm, thick-shelled ostracods indicate that the energy of the environment increased. The richness in ostracods and their great diversity in the two studied sections prove that the living conditions were particularly favourable for these crustaceans. Ten microfacies are recognized, the succession of which (from 1 to 10) constitutes a standard shallowing upward sequence, with environments ranging from open marine, near storm wave base, to coastal, close to subaerial exposure. The microfacies analysis points to a carbonate ramp system with oolitic shoals and algal shoals separating semi-restricted and coastal areas from the open marine environment. Storm events and those related to the wave activity redistributed many organisms, which formed diversified communities with abundant echinoderms, bryozoans, molluscs and brachiopods in the peri-shoal environments. The lithological curve reflects a progessive and transgressive evolution in two phases marked by two parasequence sets: the first set records the destabilization of the overlain carbonate platform (Trois-Fontaines Fm) leading to the establishment of a shallow "open lagoon" in the inner ramp, the second set corresponds to the development of several shoals at the inner-mid ramp zones. No important reefal episode is present and shoals are of modest relief. The salinity and energy were the key parameters controlling the zonation of the organisms and the distribution of the environments. Low-field magnetic susceptibility (XLF) values are weak and eight magnetic susceptibility evolutions are reported along the lithological column. The magnetic susceptibility and microfacies curves are more or less mimetic in the lower half of the section and opposite in the upper part of the Terres d'Haurs Fm. A significant decreasing trend of the low-field magnetic susceptibility values across the boundary between the Terres d'Haurs Fm and the Mont d'Haurs Fm is presented. Two linear regression models show a moderately positive correlation between XLF values and microfacies in the lower half of the section and a moderately strong negative correlation between these two parameters in the upper part of the Terres d'Haurs Fm. The water agitation is highest in the mid and inner ramp, associated to the oolite and algal shoal environments and corresponds to the lowest mean XLF values presented in the models. The lower half of the section corresponds more to a carbonate platform profile in opposition to the second model, which confirm the carbonate ramp morphology. The average XLF values in the upper part of the Terres d'Haurs Fm are more homogeneous compared to those reported in the lower half of the Terres d'Haurs Fm. High-resolution stratigraphie correlation for the base of the Mont d'Haurs Fm in Belgium and France is proposed due to similar XLFdata established in the "Les Monts de Baileux" section 40 km distant from the stratotype area.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Ostracods and rock facies across the Givetian/Frasnian boundary interval in the Sourd d'Ave section at Ave-et-Auffe (Dinant Synclinorium, Belgium)

Ostracods from the Sourd d'Ave section have been collected in the Moulin Boreux and Fort Hulobiet Members (Fromelennes Fm. Givet Group) and in the Pont d'Avignon Member (Nismes Fm. Frasnes Group). Ostracods collected in the Fromelennes Fm. by Milhau (1983a) and in the Nismes Fm. by Casier (1987a) have been also reviewed. Forty-four ostracod species are identified in the Fromelennes Fm. and 25 in the Nismes Fm. They belong exclusively to the Eifelian Mega-Assemblage, and several assemblages indicative of restricted and shallow marine, sometimes agitated, environments are recognized in the Fromelennes Fm. The great rarity of ostracods in the upper part of this formation provides evidence for less favourable lagoonal conditions probably related to increasing aridity at the end of the Givetian. In the Frasnes Group, assemblages are exclusively open marine and indicative of increasing water depth. The majority of ostracod species recognized in the Givet Group are missing in the base of the Frasnes Group as a consequence of the Frasnes Event. A systematic list of ostracods identified in the Fromelennes Fm. at Sourd d'Ave is published as an annex. Systematic sampling has been carried out in order to establish the sedimentological evolution of the environments and to detail the Givetian-Frasnian (G/F) transition. This allowed recognition of 13 microfacies types that replicate the standard sequence of Préat & Mamet (1989) from open marine shallow subtidal to restricted supratidal near emersion. The Boreux Member and the Fort Hulobiet Member display restricted facies (Amphipora, spongiostromid and algal bafflestones and bindstones, loferites with desiccation lumps) with poorly fossiliferous beds interbedded with higher energy peloidal and sometimes oolitic grainstone facies. Laminite horizons, sometimes with small-sized lateral linked hemispheroid stromatolites are uncommon, and are associated with dolomicrites showing pseudomorphs of evaporite minerals. These evaporitic facies become common in the upper part of the Fort Hulobiet Member suggesting the palaeoclimate became more arid at the G/F transition. Metre-scale cyclicity is pervasive throughout the Givetian part of the section. The boundary between the Givet Group and the Frasnes Group is very distinctive in the field, and is characterized by a transition from restricted evaporative lagoonal facies to open marine interbedded marly shales and nodular limestones. The upper part of the Fort Hulobiet Member consists of interbedded biostromes (semi-restricted stromatoporoid boundstones) followed by Amphipora floatstones, then fossil-poor units and restricted supratidal laminites with well-developed fenestral fabrics. The Frasnian Pont d'Avignon Member contains a rich faunal assemblage (bryozoans brachiopods, molluscs, nautiloids, tentaculitids) suggesting an abrupt drowning from the marginal Givetian carbonate platform into a Frasnian distal ramp or deep basinal environment below or near storm wave base.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Numerical modeling of the interference of thermally unbalanced Aquifer Thermal Energy Storage systems in Brussels (Belgium)

A numerical model was built using FEFLOW® to simulate groundwater flow and heat transport in a confined aquifer in Brussels where two Aquifer Thermal Energy Storage (ATES) systems were installed. These systems are operating in adjacent buildings and exploit the same aquifer made up of mixed sandy and silty sublayers. The model was calibrated for groundwater flow and partially for heat transport. Several scenarios were considered to determine if the two ATES systems were interfering. The results showed that a significant imbalance between the injection of warm and cold water in the first installed ATES system led to the occurrence of a heat plume spreading more and more over the years. This plume eventually reached the cold wells of the same installation. The temperature, therefore, increased in warm and cold wells and the efficiency of the building’s cooling system decreased. When the second ATES system began to be operational, the simulated results showed that, even if the heat plumes of the two systems had come into contact, the influence of the second system on the first one was negligible during the first two years of joint operation. For a longer modeled period, simulated results pointed out that the joint operation of the two ATES systems was not adapted to balance, in the long term, the quantity of warm and cold water injected in the aquifer. The groundwater temperature would rise inexorably in the warm and cold wells of both systems. The heat plumes would spread more and more over the years at the expense of the efficiency of both systems, especially concerning building’s cooling with stored cold groundwater