ALBERT

Description: Convective, intrusive geothermal plays: what about tectonics? A. Santilano, A. Manzella, G. Gianelli, A. Donato, G. Gola, I. Nardini, E. Trumpy, and S. Botteghi Geoth. Energ. Sci., 3, 51-59, https://doi.org/10.5194/gtes-3-51-2015, 2015 We revised the concept of convective geothermal plays by analysing four case studies: Larderello and Mt. Amiata (Italy), The Geysers (USA), and Kizildere (Turkey). We suggest a classification based on the age and nature of the heat source and the related hydrothermal circulation, considering that the tectonic setting is not a discriminant parameter suitable for a classification. Finally we propose to distinguish the convective geothermal plays as volcanic, young intrusive and amagmatic.

Description: Geochemical study on hot-spring water in West New Britain Province, Papua New Guinea M. M. Lahan, R. T. Verave, and P. Y. Irarue Geoth. Energ. Sci., 3, 61-67, https://doi.org/10.5194/gtes-3-61-2015, 2015 West New Britain Province, which occupies the western part of New Britain Island in Papua New Guinea, is ideally located within an active tectonic region that influences volcanism creating an environment favourable for geothermal activity. Geothermal mapping of surface manifestations reveals high temperature geothermal prospects along the northern coastline of West New Britain Province that are further confirmed by geochemical analysis. The occurrence of geothermal features is confined to the Quaternary Kimbe Volcanics and alluvium in the lowland areas. The features in Talasea appear to be controlled by deep-seated northerly trending faults while structures in Hoskins also appear to be deep seated but have not been identified. The geothermal systems in West New Britain Province have not been drilled, but preliminary reconnaissance geothermal mapping and geochemical analysis reveals four high temperature geothermal prospects suitable for further investigation and development of geothermal energy. These are the Pangalu (Rabili) and Talasea Station geothermal prospects in Talasea and Kasiloli (Magouru) and Silanga (Bakama and Sakalu) geothermal prospects in Hoskins. The calculated reservoir temperatures for these fields are in the range of 245–310 °C. Recommendations are made for further follow-up exploratory investigations.

Description: Rearrangement of stresses in fault zones – detecting major issues of coupled hydraulic–mechanical processes with relevance to geothermal applications G. Ziefle Geoth. Energ. Sci., 2, 39-48, https://doi.org/10.5194/gtes-2-39-2014, 2014 The South German Molasse Basin provides favourable conditions for geothermal plants. Nevertheless, micro-seismic events occur in the vicinity of the geothermal Unterhaching Gt2 well and seem to be caused by the geothermal plant. The injection and production are located in an existing fault system. The majority of seismic events takes place at a horizontal distance of 500 m or less of the borehole. However, none of the seismic events are located in the injection reservoir but in fact at a significantly greater depth. A deeper process understanding of the interacting thermal–hydraulic–mechanical effects in the vicinity of the well is desired. This article presents a significantly simplified 2-D model, investigating interactions of the stress field in the vicinity of the geothermal well and movements in the fault system. This might be of special interest, as the operation of the geothermal plant might lead to changes in the material and fracture properties on the one hand and in the equilibrium state on the other. A detailed description of the model, as well as various parameter studies, is presented. It can be seen that boundary conditions such as direction of the stress field in relation to the fault system, geometry of the fault system and parameters of the fractures have a significant influence on stresses in the proximity of the geothermal well. A variation in the spatial stress field in some parts of the fault system is to be expected. For the chosen assumptions the dimension of this variation is about 25% of the assumed stresses. Future work on this model might focus on the characteristics of the fault system, as well as on the influence of the coupled thermal–hydraulic–mechanical effects.

Description: Assessing the prospective resource base for enhanced geothermal systems in Europe J. Limberger, P. Calcagno, A. Manzella, E. Trumpy, T. Boxem, M. P. D. Pluymaekers, and J.-D. van Wees Geoth. Energ. Sci., 2, 55-71, https://doi.org/10.5194/gtes-2-55-2014, 2014 In this study the resource base for EGS (enhanced geothermal systems) in Europe was quantified and economically constrained, applying a discounted cash-flow model to different techno-economic scenarios for future EGS in 2020, 2030, and 2050. Temperature is a critical parameter that controls the amount of thermal energy available in the subsurface. Therefore, the first step in assessing the European resource base for EGS is the construction of a subsurface temperature model of onshore Europe. Subsurface temperatures were computed to a depth of 10 km below ground level for a regular 3-D hexahedral grid with a horizontal resolution of 10 km and a vertical resolution of 250 m. Vertical conductive heat transport was considered as the main heat transfer mechanism. Surface temperature and basal heat flow were used as boundary conditions for the top and bottom of the model, respectively. If publicly available, the most recent and comprehensive regional temperature models, based on data from wells, were incorporated. With the modeled subsurface temperatures and future technical and economic scenarios, the technical potential and minimum levelized cost of energy (LCOE) were calculated for each grid cell of the temperature model. Calculations for a typical EGS scenario yield costs of EUR 215 MWh −1 in 2020, EUR 127 MWh −1 in 2030, and EUR 70 MWh −1 in 2050. Cutoff values of EUR 200 MWh −1 in 2020, EUR 150 MWh −1 in 2030, and EUR 100 MWh −1 in 2050 are imposed to the calculated LCOE values in each grid cell to limit the technical potential, resulting in an economic potential for Europe of 19 GW e in 2020, 22 GW e in 2030, and 522 GW e in 2050. The results of our approach do not only provide an indication of prospective areas for future EGS in Europe, but also show a more realistic cost determined and depth-dependent distribution of the technical potential by applying different well cost models for 2020, 2030, and 2050.

Description: Classification of geothermal resources by potential L. Rybach Geoth. Energ. Sci., 3, 13-17, https://doi.org/10.5194/gtes-3-13-2015, 2015 A new resource classification scheme is described, based on different geothermal potentials: theoretical, technical, economic, sustainable, developable – decreasing successively in size. In converting theoretical to technical potential, the recovery factor (the ratio extractable heat/heat present at depth) is of key importance. The proposed classification of potentials provides a useful template for standardizing the future reporting of geothermal energy resources worldwide.

Description: Influence of major fault zones on 3-D coupled fluid and heat transport for the Brandenburg region (NE German Basin) Y. Cherubini, M. Cacace, M. Scheck-Wenderoth, and V. Noack Geoth. Energ. Sci., 2, 1-20, https://doi.org/10.5194/gtes-2-1-2014, 2014 To quantify the influence of major fault zones on the groundwater and thermal field, 3-D finite-element simulations are carried out. Two fault zones – the Gardelegen and Lausitz escarpments – have been integrated into an existing 3-D structure of the Brandenburg region in northeastern Germany. Different geological scenarios in terms of modelled fault permeability have been considered, of which two end-member models are discussed in detail. In addition, results from these end-member simulations are compared to a reference case in which no faults are considered. The study provides interesting results with respect to the interaction between faults and surrounding sediments and how it affects the regional groundwater circulation system and thermal field. Impermeable fault zones seem to induce no remarkable effects on the temperature distribution; that is, the thermal field is similar to the no-fault model. In addition, tight faults have only a local impact on the fluid circulation within a domain of limited spatial extent centred on the fault zone. Fluid flow from the surrounding aquifers is deviated in close proximity of the fault zones acting as hydraulic barriers that prevent lateral fluid inflow into the fault zones. Permeable fault zones induce a pronounced thermal signature with alternating up- and downward flow along the same structures. Fluid flow along the plane of the faults is principally driven by existing hydraulic head gradients, but may be further enhanced by buoyancy forces. Within recharge domains, fluid advection induces a strong cooling in the fault zones. Discharge domains at shallow depth levels (~

Description: Effectiveness of acidizing geothermal wells in the South German Molasse Basin S. Schumacher and R. Schulz Geoth. Energ. Sci., 1, 1-11, https://doi.org/10.5194/gtes-1-1-2013, 2013 In Germany, many hydro-geothermal plants have been constructed in recent years, primarily in the region of Munich. As the host formation here mainly consists of carbonates, nearly all recently drilled wells have been acidized in order to improve the well yield. In this study, the effectiveness of these acid treatments is analyzed with respect to the amount of acid used and the number of acid treatments carried out per well. The results show that the first acid treatment has the largest effect, while subsequent acidizing improves the well only marginally. Data also indicate that continued acidizing can lead to degradation of the well. These findings may not only be important for geothermal installations in Germany but also for projects, for example, in Austria, France or China where geothermal energy is produced from carbonate formations as well.

Description: Empirical relations of rock properties of outcrop and core samples from the Northwest German Basin for geothermal drilling D. Reyer and S. L. Philipp Geoth. Energ. Sci., 2, 21-37, https://doi.org/10.5194/gtes-2-21-2014, 2014 Information about geomechanical and physical rock properties, particularly uniaxial compressive strength (UCS), are needed for geomechanical model development and updating with logging-while-drilling methods to minimise costs and risks of the drilling process. The following parameters with importance at different stages of geothermal exploitation and drilling are presented for typical sedimentary and volcanic rocks of the Northwest German Basin (NWGB): physical ( P wave velocities, porosity, and bulk and grain density) and geomechanical parameters (UCS, static Young's modulus, destruction work and indirect tensile strength both perpendicular and parallel to bedding) for 35 rock samples from quarries and 14 core samples of sandstones and carbonate rocks. With regression analyses (linear- and non-linear) empirical relations are developed to predict UCS values from all other parameters. Analyses focus on sedimentary rocks and were repeated separately for clastic rock samples or carbonate rock samples as well as for outcrop samples or core samples. Empirical relations have high statistical significance for Young's modulus, tensile strength and destruction work; for physical properties, there is a wider scatter of data and prediction of UCS is less precise. For most relations, properties of core samples plot within the scatter of outcrop samples and lie within the 90% prediction bands of developed regression functions. The results indicate the applicability of empirical relations that are based on outcrop data on questions related to drilling operations when the database contains a sufficient number of samples with varying rock properties. The presented equations may help to predict UCS values for sedimentary rocks at depth, and thus develop suitable geomechanical models for the adaptation of the drilling strategy on rock mechanical conditions in the NWGB.

Description: The role of the legislative and regulatory branches in promoting the use of geothermal energy in Latvia I. Skapare, A. Kreslins, and A. Cers Geoth. Energ. Sci., 4, 23-27, https://doi.org/10.5194/gtes-4-23-2016, 2016 Latvia currently is self-sufficient in energy resources up to approximately 35 %. Annual fossil energy prices rise and risks of security of energy supply promote the development legislation in the matter of renewable resources. One of the Latvian Ministry of Economics' recent products is a new draft law called the "Renewable Energy Law", which has been created due to one of the European Union and Latvian national energy policy objectives: to increase the share of renewable energy up to 40 % by 2020 (Moore and Vanags, 2012). Currently, geothermal energy potential is assessed at 1 × 1013 kWh; nevertheless, it is difficult for geothermal energy to compete with other renewable energy resources in the Latvian energy market. A great job has been done in recent years at the legislative branch to choose the right methods for supporting the use of renewable energy resources. This paper aims is analysis of current situation and assessment of Latvian legislation possibilities to promote the use of geothermal energy.

Description: Geothermal heat pump system assisted by geothermal hot spring M. Nakagawa and Y. Koizumi Geoth. Energ. Sci., 4, 1-10, https://doi.org/10.5194/gtes-4-1-2016, 2016 Abandoned mines are usually nothing but problems. The author attempts to show that it is feasible to turn this local problem into an economic benefit by combining other locally available resources such as geothermal heat.