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Deep geothermal energy has become widely exploited in recent years through the use of closed loop systems for building heating. Intended to meet high heating demand in densely populated neighbourhoods, an enhanced U-tube borehole heat exchanger (EUBHE) system, in which a deviated deep borehole is connected with another vertical one to form a closed loop, is introduced in this work. For capacity and efficiency analysis of applying EUBHE systems to extract deep geothermal energy, a 3D numerical model is implemented and established based on the OpenGeoSys software. Through evaluation by thermal performance tests and thermal response tests on the EUBHE system, the maximum sustainable heat extraction rate is found to be 1.2 MW in a single heating season and 1.1 MW in 10 years, which can provide heating to more than 35,000 m2 of residential buildings located in northern China. Moreover, the 10-year system thermal performance and efficiency are evaluated when coupled with a ground source heat pump (GSHP), and compared with the two deep borehole heat exchanger (2-DBHE) array system that has the same total borehole length as the EUBHE system. Results show that GSHP-coupled EUBHE system is more efficient than the 2-DBHE array system, as it consumes 27% less electricity.

With the development of remote sensing and large-scale environmental modelling, large amount of environmental data are continuously becoming available. An intuitive and comprehensive visualization of these data could facilitate data exploration, communication and collaboration between the stakeholders for informed decisions making. In Poyang lake basin regions, we demonstrate how to develop a software platform that can visualize three-dimensionally environmental data layers including terrain, weather, river net, water level, land use changes and interrelations between these data layers for environmental system monitoring and decision supporting. The tool is built by combining several prevailing projects including Unity, Paraview, and hydrological models, etc. We develop an open standardized framework for the software tool to host environmental data layers permitting the application of the tool, which could be employed for the intuitive and comprehensive data visualization in other regions facing environmental challenges.

By its very nature, research into multi-physical processes occurring in porous and fractured media requires a collaborative approach. An interdisciplinary approach has led to the adoption of collaborative software development paradigms in this field relying on software for scientific computing as research infrastructures. The development of open-source software has become a cornerstone of computational approaches in academia and has even spawned successful business models in the commercial world. This article is geared toward readers who want to learn more about potential benefits of open-source software in porous media research and who want to familiarize themselves with typical workflows required to become an active contributor to or user of open-source solutions for porous media simulation. The article puts general principles, motivations and concepts into the specific context of experiences and lessons learned from the authors developing the open-source software projects OpenGeoSys and DuMu $$^{\text {x}}$$ .

Nowadays, utilizing shallow geothermal energy for heating and cooling buildings has received increased interest in the energy market. Among different technologies, large borehole heat exchanger (BHE) arrays are widely employed to supply heat to various types of buildings and districts. Recently, a 16-BHE array was constructed to extract shallow geothermal energy to provide heat to the newly-developed public building in Berlin. According to the previous geological survey, different non-homogeneous sedimentary layers exist in the subsurface, with variating groundwater permeabilities and thermal parameters. To estimate the performance of the BHE array system, and its sensitivity to different subsurface conditions, as well as to determine its thermal impact to the surrounding area, a comprehensive 3D numerical model has been set up according to the Berlin BHE array project. The model is simulated for 25 years with two finite element simulators, the open source code software OpenGeoSys (OGS) and the well-known commercial software FEFLOW. In the model, an annual thermal load curve is assigned to each BHE according to the real monthly heating demand. Although the way of the implementing parameters in the two programs differs from each other and some assumptions had to be made in the model comparison, the comparison result shows that both OpenGeoSys and FEFLOW produce in good agreement. Different parameters, e.g. the Darcy velocity, the thermal dispersivity of the aquifer, the surface temperature and the geothermal heat flux are investigated with respect to their impact on the underground and BHE circulation temperature. At last, the computed underground temperature and the brine fluid temperature evolution from OGS is benchmarked with the results from the model simulated in FEFLOW. The numerical experiments show that the the ground water field has the strongest influence on the brine fluid temperature within the BHEs. When the thermal dispersivity of the aquifer is considered, the mixing effect in the aquifer leads to a higher brine fluid temperature in the BHE, indicating a better thermal recharge of the system.

We present a new model for fast and efficient simulation of long-term concrete degradation due to alkali-silica reaction (ASR) and carbonation. The novel model provides an alternative coupling solution of reactive transport and multiphase multi-component flow by approximating the complex chemical reactions into a quickly calculating look-up table, which can further be integrated into a two-phase multi-component transport model via source/sink terms. The complex dynamic interplay between chemistry and multi-phase transport are well addressed in this approach. A 1-D reactive transport benchmark is proposed by taking into account the two main chemical reactions which drive the concrete degradation: ASR and carbonation caused by transport of CO2 in a gas phase. We contrast three different sets of simulations to explore the pattern of competition between ASR and carbonation in the long-term degradation of concrete. The numerical model derived from the look-up table approach is compared to a full reactive transport code to validate its accuracy and efficiency. It is shown that the look-up table approach and the full reactive transport code produce very similar results for degradation of concrete even for the case of competition between ASR and carbonation. However, in terms of performance, it is observed that the look-up table approach leads to a considerable reduction in calculation time. Future work will be focused on incorporating the proposed model with a geo-mechanical model for multi-chemo-physics analysis of the concrete evolution.

Ground source heat pump (GSHP) systems have been considered to be a low-carbon technology to provide heating and cooling for buildings in urban environments. This study focuses on the short-and long-term evolution of groundwater temperature induced by high-density GSHP installations in an urban residential area in Cologne, Germany. Specifically, a 2D heat transport model considering both thermal convection and conduction has been constructed using the finite element simulator OpenGeoSys. The simulated temperature changes within the initial few years were compared to the monitored dataset, while the GSHP heating load and thermal conductivity were calibrated. Subsequently, the validated model was run for 25 years to evaluate the long-term trend of the subsurface temperature. Also, effects of model uncertainties were explored with different simulated scenarios. Results indicate that sufficiently large groundwater flow and a high cooling ratio can effectively mitigate ground cooling. Based on these findings, best and worst-case scenarios were formulated for the studied case and the sustainability of GSHP operation were evaluated accordingly. As an outcome, specific design and operation criteria were proposed for the sustainable utilization of shallow geothermal energy for the heating and cooling of buildings in urban areas.

International audience; The growing demand for energy, natural resources and urban expansion during the last two centuries increased human interference with the geosphere far beyond geothermal usage. The increasing number of large-scale projects intervening the area of life of communities raised public concerns related to their environmental and social impact. Integration of public concerns into such projects should therefore go beyond outreach and communication measures. It requires an open approach to inclusive governance structures with respect to designing research and development processes and to modify technological options. Geoethical concepts emphasize that geoscientific knowledge may assist society in decision making as well as in dealing with risks, user conflicts and environmental threats on local, regional and global scale in order to support more sustainable practices at the intersection of human beings and the geosphere.In the present article, we analyse the social response to recent geothermal development and identify the precondition for public acceptability of geothermal projects. On this basis, the potential contribution of a GeoLaB, a Geothermal Laboratory in the crystalline Basement, to a geoethic approach in geothermal research and technology development is discussed. The underground research laboratory is planned as an infrastructure to answer scientific challenges and to offer the necessary transparency to interact with the public. The GeoLaB approach aims on transparent, tangible science and can serve to enhance mutual understanding of stakeholder groups. It may increase public awareness on geothermal research and potentially enhance the opportunity for public approval of planned activities. As a generic site, GeoLaB can develop scientific-technological solutions for a responsible exploitation of geothermal energy accompanied by sociological studies. The underground research laboratory will serve as a platform for science communication, participation and dialogue of stakeholders from industry, politics, administration and society. This complies with the comprehension of responsible research in a geoethical sense.

Implicit numerical integration of viscoplastic LUBBY2 and Minkley models of rock salt.Implementation into open-source software OpenGeoSys.Thermomechanical benchmark solutions for code verification.Demonstration of convergence properties and example simulations. The mechanical behavior of rock salt formations is not only of interest due to mining of salt but also because of its increasing relevance for geotechnical applications, e.g., for the storage of strategic oil and gas reserves, for hosting nuclear waste repositories, for compressed air energy storage (CAES) or the cavern storage of hydrogen. The safety assessment of geotechnical installations as well as long-term convergence predictions of salt caverns require models capturing the inelastic behavior of rock salt under thermomechanical loading. Many models have been derived for uniaxial or triaxial experimental setups and some are inadequately presented to fully describe three-dimensional scenarios. Here, a tensorial representation is chosen to avoid such inconsistencies and their possible consequences on commonly used material parameters are discussed. Two very commonly used material models, the LUBBY2 and Minkley formulations, have been primarily implemented into software relying on explicit time integration schemes. Here, their implicit implementation with analytical Jacobians into a scientific open-source finite element framework is described in detail. The implementations are verified by comparison to suitable analytical solutions for coupled thermomechanical loadings and their convergence behavior is analyzed.

In densely inhabited urban areas, deep borehole heat exchangers (DBHE) have been proposed to be integrated with the heat pump in order to utilize geothermal energy for building heating purposes. In this work, a comprehensive numerical model was constructed with the OpenGeoSys (OGS) software applying the dual-continuum approach. The model was verified against analytical solution, as well as by comparing with the integrated heat flux distribution. A series of modeling scenarios were designed and simulated in this study to perform the DBHE system analysis and to investigate the influence of pipe materials, grout thermal conductivity, geothermal gradient, soil thermal conductivity, and groundwater flow. It was found that the soil thermal conductivity is the most important parameter for the DBHE system performance. Both thermally enhanced grout and the thermally insulated inner pipe will elevate the outflow temperature of the DBHE. With an elevated geothermal gradient of 0.04 °C m−1, the short-term sustainable specific heat extraction rate imposed on the DBHE can be increased to 150–200 W m−1. The quantification of maximum heat extraction rate was conducted based on the modeling of 30-year-long operation scenarios. With a standard geothermal gradient of 0.03 °C m−1, the extraction rate has to be kept below 125 W m−1 in the long-term operation. To reflect the electricity consumption by circulating pump, the coefficient of system performance (CSP) was proposed in this work to better quantify the system efficiency. With the typical pipe structure and flow rate specified in this study, it is found that the lower limit of the DBHE system is at a CSP value of 3.7. The extended numerical model presented in this study can be applied to the design and optimization of DBHE-coupled ground source heat pump systems.

The use of clean and renewable energy and the abandoning of fossil energy have become goals of many national and international energy policies. But even when once accomplished, mankind has to take charge of the relics of the current energy supply system. For example, due to its harmful effects, nuclear waste has to be isolated from the biosphere safely and for sufficiently long times. The geological subsurface is considered as a promising option for the deposition of such by-or end products. In order to investigate the long-term evolution of a repository system, a multiphysics simulation was performed. It combines the structural mechanics of the host rock, the fluid dynamics of formation fluids, and the thermodynamics of all materials resulting in a highly multivariate data set. A visualization of such multiphysics data challenges the current methodology. In this article, we demonstrate how an analysis of a carefully selected subset of the variables in attribute space allows to visualize and interpret the simulation data. We apply a fiber surface extraction algorithm to explore the relationships between these variables. Studying the temporal evolution in attribute space, we found a regionally bulge that could be identified as an effect of the nuclear waste repository because it can be clearly separated from the natural geophysical state prior to waste disposal. Furthermore, we used the extracted fiber surface as a starting point to examine the distribution of other variables inside this area of the physical domain. We conclude this case study with lessons learned from the visualization as well as the geotechnical side.

In the context of reducing carbon emission, Deep Borehole Heat Exchanger (DBHE) array has a large potential in extracting geothermal energy to provide building heating in densely populated urban areas. To investigate the thermal interaction among the DBHE, a comprehensive numerical model has been built with the OpenGeoSys software, and it is validated by monitoring data from a pilot project in Xi’an, China. The long-term simulations manifest that the outlet temperature of the DBHE array has a noticeable draw-down of 4.70 ° C over 20 years in comparison to the single borehole setup. The maximum difference of outlet temperature among individual DBHE can reach up to 0.88 ° C over 20 years, which will lead to a shifted thermal load of 23.35 kW (12.25 % of the designed average value). Based on the predicted subsurface temperature distribution, a non-linear correlation can be established between the drawdown in working fluid temperature and the accumulated amount of extracted heat. The finding of work implies that the thermal interaction among individual DBHE is of significance for the sustainability of the system, and comprehensive numerical modeling should be considered in the designing procedure.

Due to extensive water pollution in Chinese rivers and lakes, large efforts have to be made to improve the quality of drinking water and manage the sewage water treatment process. We propose a gene...

In previous studies, the amount of exploitable shallow geothermal energy was estimated by assuming a uniform temperature drop of 2–6 °C in the aquifer. In this work, a more comprehensive numerical model has been employed to evaluate the available amount of shallow geothermal energy by using Borehole Heat Exchanger coupled Ground Source Heat Pump systems. Numerical experiments have been performed by simulating the long-term evolution of the subsurface temperature field, which is subject to the operation of borehole heat exchangers and varying parameters like subsurface thermal conductivity and groundwater flow velocity. The concept of equivalent temperature drop is proposed as an auxiliary quantity for the subsurface. With the help of this parameter, a procedure has been established to quantify the amount of shallow geothermal potential. Following this approach, a realistic equivalent temperature reduction is found to be from −1.8 to −4.4 °C in the subsurface over a period of 30 years. This can be translated to an annual extractable geothermal energy value in a unit surface area, and it ranges from 3.5 to 8.6 kW h m−2 a−1. The exact value is site specific and heavily depends on the soil thermal conductivity, groundwater velocity, and borehole arrangement.

Current climate, environmental and energy policies aim at a decarbonisation of the energy sector by a transition to renewable energies on the one hand and at an increased energy efficiency on the other hand. Thereby they stimulate the interest in space-, cost-, and energy-efficient heat storage technologies. Thermochemical conversion is an attractive candidate technology for heat storage fulfilling these efficiency requirements. The design of practically any complex engineered system is accompanied by theoretical analyses based on model representations. Thus, numerical modelling is particularly important for thermochemical heat storage systems to help realise their potential and to advance the technology from the laboratory to a commercial setting. This article reviews modelling work in the context of heat storage and transformation aimed at capturing the coupled multi-physical processes that are relevant to the simulation of thermochemical heat storage in a space- and time-resolved manner.

To utilize the shallow geothermal energy, heat pumps are often coupled with borehole heat exchangers (BHE) to provide heating and cooling for buildings. In cold regions, soil freezing around the BHE is a potential problem which will dramatically influence the underground soil temperature distribution, subsequently the inlet and outlet circulating fluid temperature of the BHE, and finally the efficiency of the heat pump. In this study, a numerical model has been developed to simulate the coupled temperature evolution both inside the BHE, and the propagating freezing front in the surrounding soil. The coupled model was validated against analytical solutions and experimental data. The influence of the freezing process on the overall system performance is investigated by comparing one long BHE configuration without freezing and another short one with latent heat from the frozen groundwater. It is found that when freezing happens, the coefficient of performance (COP) of the heat pump will decrease by around 0.5, leading to more electricity consumption. Furthermore, analysis of the simulation result reveals that the exploitation of latent heat through groundwater freezing is only economically attractive if electricity price is low and interest rate high, and it is not the case is most European countries.

To utilize shallow geothermal energy, ground source heat pump systems (GSHPS) are often coupled with borehole heat exchangers (BHE). In recent years, some GSHPSs are experiencing a gradual decrease in BHE outflow temperatures and thus have to be shut down. In this work, a comprehensive numerical model was constructed to include flow and heat transport processes, together with the dynamics of heat pump efficiency. The model parameters are based on local conditions in the Leipzig area. Different scenarios were simulated to observe the evolution of BHE outflow and soil temperatures subject to various factors of influence. In the first year, the recovery of shallow geothermal energy only accounts for about 89% of the energy extracted. Over the following years, outflow and soil temperature will gradually drop until they reach a quasi-steady-state. It was also found that groundwater flow and using BHE for cooling will be beneficial to the energy recovery and efficiency of the heat pump. In comparison to other factors, the soil heat capacity and thermal conductivity are considered to have a minor impact on the sustainability of the system. In contrast, it is very likely that undersized systems are the cause of strong system degradation.

In the context of geotechnical and geological barriers, a thorough analysis of uncertainty and sensitivity is a crucial aspect of any physics-based performance assessment. While experimental data are scarce in actual waste repositories, large-scale experiments in underground research laboratories (URLs) provide such data that can be used to not only qualify THMC process models but also uncertainty assessment methodologies. In this paper, we adopt a Design of Experiments (DoE)-based history matching workflow – an approach popular in the oil and gas industry – and scrutinize its applicability for multiphysical analyses of nuclear waste disposal-related processes using synthetic experimental data. Based on an analytical solution of a coupled thermo-hydro-mechanical (THM) problem of a heat source embedded in a fluid-saturated porous medium mimicking a disposal cell in an argillaceous host formation, we discuss the adaptability of the workflow as a way to address parameter and model uncertainties for barrier integrity assessment. We thereby put particular focus on the relative importance of providing defined input parameter distributions for quantities generally afflicted with epistemic uncertainty and the constraints imposed by experimental (URL) or monitoring (repository) data. We found that once constraining data is available, the particular a priori distribution plays only a minor role for the outcome, such that we can conclude that the often unknown distributions can be substituted by uniform priors under such conditions. However, detailed knowledge of parameter distributions can increase the efficiency of the workflow significantly. We conclude that the presented workflow is particularly suitable for performing uncertainty quantification and sensitivity analysis for geotechnical applications where monitoring or other experimental data are available, as it allows us to deal with models of great complexity, epistemic uncertainty and it incorporates canonically to use of measured data in order to reduce uncertainty.

Lakes are important ecosystems that provide a number of ecosystem services including provision of drinking water, flood control, fisheries and in general a high natural, cultural and aesthetic value. Provisioning services from lakes are particularly relevant in regions where lakes supply drinking water. In these water bodies, a high water quality is of utmost importance in order to produce drinking water at required quantities and at affordable prices. High nutrient loading, eutrophication, and toxicant pollution, however, are growing stressors in many places, driving severe water quality deteriorations that harm domestic water supply, quality of life and social welfare. Fast growing urban areas are particularly vulnerable to these deteriorations in surface water resources, because waste, waste water, and chemical pollutants (heavy metals, pesticides, etc.) are affecting nearby aquatic ecosystems. While in river ecosystems these pollution pressures only affect water users further downstream, i.e. not directly the pollution producer responsible for the water quality deterioration, standing water bodies like lakes or reservoirs directly and often negatively feed back to the adjacent urban communities.

The previous chapters gave detailed insight into the collection of environmental data and the use of that data for purposes such as determining and improving water quality, dealing with extreme weather events, or the planning of waste water management systems. However, adequate visualisation techniques are required to communicate the significance of this work and the consequences of research results to stakeholders or laymen. In addition, sustainable management of water resources requires well-engineered software solutions that can be operated by regional authorities and operating companies. To this end, the “Urban Catchments”-project includes the adaption and adjustment of software frameworks for the region around Chao Lake.

The overall objective of the project was the development of water management system solutions for a sustainable improvement of water quality in the city of Chaohu and in the Chao Lake. The Urban Water Resources Management (UWRM) concept is the innovative approach, which includes both efficient urban water management in urban and suburban areas, as well as interaction with aquatic ecosystems. Data and models for planning purposes and regional water management are made available by using a comprehensive online environmental information system for authorities and water suppliers. The Chao Lake plays a central role as an ecological and economic protection and raw water supplier for the drinking water supply of the population of the city of Chaohu. The research and development project (R&D Project) thus makes an important contribution to the sustainable development of the Chaohu region as part of the Masterplan Ecological Seascape Chaohu of the Anhui Provincial Government. The scientific and technical solutions are implemented in demonstration projects.

The Research Centre for Environmental Information Science (RCEIS) was established in March 2014. In the long-term vision RCEIS shall become a Sino-German competence centre and research platform for Earth systems observation and modelling by combining expertise in the fields of environmental and information sciences using modern information technology. As a scientific goal, RCEIS will develop novel concepts by using infrastructures for Earth system observation and analysis in order to better understand the evolution and dynamics of environmental systems under global change and globalization (anthropogenic pressure). An important methodology is the further development and combination of different infrastructures for Earth system observation, e.g. combining information from remote sensing (satellites and airborne) and “ground-truth” measurements. Moreover, monitoring (remote sensing and monitoring) and modelling platforms (multi-sphere/compartment, cycle-oriented) need to be combined.

It has been over 15 years since the concept of Virtual Geographic Environments (VGEs) was formally proposed (Lin and Gong 2001). Although the thinking about VGEs never stops since it was born, and the continued development of VGEs has brought about significant achievements resulting from this concept (e.g., Goodchild 2009; Gong et al. 2010; Konecny 2011; Lu 2011; Priestnall et al. 2012; Lin et al. 2013a, b, 2015) as well as related technologies and implementations (e.g., Xu et al. 2011, 2013; Chen et al. 2012, 2013a, b; Zhang et al. 2015a, b; Zhu et al. 2015), there are still some misunderstandings about this ‘new’ branch of Geoscience. Questions generally are related to two concepts: the first concerns the differences between VGEs and game-like virtual worlds, similar virtual communities and cities, and digital earth; the second asks how VGEs can contribute to geographic research beyond traditional Geographic Information Systems (GIS) and Maps (Aydi et al. 2013; Tung et al. 2013). The answer to the first question may be found in the term ‘geographic environment’ which refers not only to the natural surface of the earth, space, or a place, but also involves the social behaviors that interact with natural factors; it is the sphere of direct interaction between nature and society (Kalesnik 1979). An important feature of geographic environments is that they change continuously with time. Although some objects in geographic environments have relatively stable shapes (such as a rock or soils), many exist in constantly changing forms (such as vegetation, air and water), and human beings (both in groups or individual) are active throughout their ‘lives’. Given this definition, to build a virtual mirror that can reflect the real geographic environment, only considering the physical part would result only in a one-sided perspective. Moreover, dynamic geographic phenomena and processes require careful attention, a fact often overlooked by traditional systems. Thus, an ideal virtual environment

This paper presents the design and integration of a GIS-based data model for the regional hydrologic simulation in the Meijiang watershed, China. Hydrologic systems (HS) require integration of data and models simulating different processes. Here, an object-oriented approach using Unified Modeling Language (UML) is introduced, which supports the development of GIS-based Geodatabase model—GeoHydro/DataBase (GH/DB). Spatial data, such as basins, stream network, and observation stations are stored in the feature classes. The time series and their attributes are included in the tables. Relationship classes are used to link associated objects. The new development within the scientific program OpenGeoSys (OGS) is the integration of GH/DB into the numerical simulations. The graphical user interface is implemented for the pre- and post-processing of the simulation. As for the case study, a regional hydrologic model is developed in the Meijiang watershed area for the understanding of water infiltration from surface into groundwater via soil layer with various time scales. The integration of databases and modeling tool represents the comprehensive hydrosystems and thus it is a useful tool to understand the different processes and interactions between the related hydrological compartments.

Thermal energy storage technologies are of current interest in order to improve the integration of renewable energy sources as well as energy efficiency. Numerical simulations of thermochemical heat storage are especially challenging and time consuming due to the complexity of the mathematical description of the strongly coupled and highly nonlinear processes characteristic for such systems. These difficulties are exacerbated once practically relevant complex or large geometries are considered as they can occur around heat exchangers or due to internal heterogeneities of the reactive bed. To allow a computationally efficient simulation of such applications, an existing finite element implementation of a thermochemical heat storage model was parallelised using PETSc routines. Input/output, global assembly and the linear solver all work in a distributed fashion. The approach is implemented into the open source framework OpenGeoSys. The performance of the present parallelisation approach is tested by simulating the discharge of a heat store based on calcium-oxide and water as a benchmark problem. The computational time required for the simulation could be reduced significantly.

The Thematic Issue is dedicated to different aspects of using the potential of the geologic subsurface as a resource for energy production (e.g., hydrothermal and petrothermal resources), energy storage as well as for safe deposition of energy waste, and energy conversion (e.g., as biochemical reactors to convert hydrogen and carbon dioxide into methane). Figure 1 shows an overview map of hydrothermal systems in China including a classification to high-, midand low-temperature reservoirs and basins (Kong et al. 2014). Current research efforts concerning hydrothermal resources focus on the sustainable development of large-scale geothermal fields. Pang et al. (2012) designed a roadmap of geothermal energy development in China and reported the recent progress in geothermal research in China (Pang et al. 2014). Recently, Pang et al. (2015) presented a new classification of geothermal resources based on the type of heat source and followed by the mechanisms of heat transfer. The present Thematic Issue is focusing on petrothermal resources and particularly enhanced geothermal systems. Some of the basins indicated in Fig. 1 are also of interest for unconventional gas resources which is discussed in a separate Thematic Issue in Environmental Earth Sciences (Hou et al. 2015a). Geothermal energy resources are considered to provide a significant contribution to renewable energy supply from both shallow and deep systems (Arola et al. 2014; Huenges et al. 2013; Kolditz et al. 2013; Scheck-Wenderoth et al. 2013). Understanding the thermally induced coupled processes is important for reservoir operations (McDermott et al. 2006; Kolditz and Diersch 1993). Breede et al. (2014) provide a systematic review of enhanced or engineered geothermal systems (EGS). Ramos et al. (2015) provide a systematic review of projects implemented worldwide and a methodology for screening geothermal projects. Geothermal shallow surface systems based on ground source heat pumps have already proved to be a feasible option for the heating and cooling of buildings. The present work studies the concept of using abandoned mines for geothermal heat recovery in various countries such as Germany, the Netherlands, Norway, Russia, Spain, UK and United States. De Filippis et al. (2015) are discussing the geothermal potential of the Salento peninsula in southern Italy. They propose a simple methodology for the assessment of low-enthalpy geothermal energy systems based on stochastic approaches. They found that coastal areas might lower potential due to saltwater intrusion problems. Hou et al. (2015b) introduce the first & Hongwei Zhou zhw@cumtb.edu.cn

Coalbed methane, tight and shale gas are three important unconventional gas resources in China. ‘‘According to data from the Ministry of Land and Resources, at the end of 2013, China had 11, 12 and 25 trillion cubic meters, respectively of remaining technically recoverable resources of coalbed methane, tight gas and shale gas which are still in the early stage of development’’. (Source CNPC and ARA International Limited). China is developing its shale gas exploration and exploitation strategies for economic reasons and social aspects (so-called ‘‘shale gas revolution’’). Huge shale gas reserves provide a reliable source for sustaining China’s economic development and contributing to China’s ‘‘Energiewende’’. Zhao et al. (2015a) analyze the strategic measures and advantages for a safe and vigorous development of shale gas in China and review the developments of hydraulic fracturing technologies in China. Economic exploitation for shale gas is highly dependent on the complexity of the fracture network caused by hydraulic fracturing technology, so it is necessary to accurately assess the effect of the fracture network on gas flow behavior and productivity (Li et al. 2015c). This thematic issue is particularly dedicated to recent researches in unconventional gas resources in China related to the reservoirs indicated in Fig. 1 in order to substitute coal by ‘‘clean’’ gas energy resources as a transitional technology towards renewable energy resources. The thematic issue compiles theoretical, experimental as well as field studies in China. Different reservoir types are under investigation such as tight and shale gas reservoirs as well as coal mines with coalbed methane resources. Fundamental aspects on process understanding in unconventional gas reservoirs as well as the international context of research and technology deployment are discussed in this volume. Tight gas reservoirs have become an important resource for the world’s gas supply. Such reservoirs have very low permeability (usually below 0.1 mD) and show a strong stress sensitivity to fluid transport properties and a considerable productivity decline during the production process due to decreasing reservoir pressure as well as increasing effective stress. In an experimental study by Albrecht and Reitenbach (2015) several measurement series were performed on plugs from the North-German Rotliegend tight gas reservoirs to determine the effects of changing stress and pore pressure conditions on reservoir & Olaf Kolditz olaf.kolditz@ufz.de

Numerical modelling of coupled physical processes in bentonite–sand mixtures under the geological conditions is significant for designing and constructing sealing systems in deep underground repositories for highly radioactive nuclear waste. Within the framework of DECOVALEX 2015, Task A, this work presents the model validation of OpenGeoSys by numerical modelling of coupled hydromechanical (HM) processes in bentonite–sand mixtures. Parameters used in the HM model were determined by modelling the laboratory tests of the sealing experiment (SEALEX). Afterwards these parameters were applied for the modelling of a small-scale mock-up test considering the influence of technological gap and incidental fail of the seal in the sealing system. In order to investigate the availability of employing these HM parameters and numerical models directly to field predictions, the modelling results and measured data of an in situ SEALEX experiment were analysed comparatively. The modelling results reproduced well the main features in HM behaviour of the compacted bentonite–sand mixture, which denotes that the adopted HM models and parameters are adequate for describing the HM processes in the sealing system. It is necessary to take the elastoplastic behaviour and evolution of the permeability of bentonite–sand mixtures into account when using the adopted models to reproduce the HM processes of a sealing system.

In large scale Ground Source Heat Pump (GSHP) systems, multiple Borehole Heat Exchangers (BHEs) are often connected with the pipe network array to extract shallow geothermal energy. In this study a comprehensive numerical model was developed. The heat transport within and around the BHEs and the pipe network is explicitly quantified in a coupled manner. The model allows a dynamic heat extraction calculation on the individual BHE that is determined by the hydro-thermal processes in the pipe network. The model is thus capable of capturing the long-term thermal interference among BHEs. The model was verified against analytical solution with respect to its hydraulic and thermal balances. Based on it, a series of numerical experiments have been performed to quantitatively investigate the amount of shifted thermal extraction rate in large BHEs array. It is found that, the heat extraction rate on the central BHEs was gradually shifted towards those located at the edge in the long-term operation. Over different seasons, the strongest shifting phenomenon was observed in the month with the lowest thermal load. The shift becomes significant with the increasing number of BHEs installed. The result of numerical study suggests that traditional super-positioned based infinite line source approach with a constant heat flux is not accurate enough for long-term prognosis since it does not fully consider the thermal recharge and the thermal interference effects.

The International Water Research Alliance Saxony (IWAS) is addressing the global challenges concerning water quality in the areas of drinking water and sanitation, agricultural irrigation and the quality of surface and ground waters, as well as developing specific ecosystem-relevant services to be implemented on an exemplary basis in selected model regions. Locations (model regions) have been selected in Eastern Europe (R1), Central and Southeast Asia (R2 and R3), the Middle East (R4) and Latin America (R5) that are representative international regions with respect to climate, land use and demographic change (Ibisch et al., Helmholtz Centre for Environmental Research—UFZ, Department of Aquatic Ecosystem analysis and management, 2013). The causes of water problems and the relevant boundary conditions vary from region to region (Borchardt and Ibisch, Integrated water resources management in a changing world : lessons learnt and innovative perspectives, pp 225, 2013). Mongolia and Vietnam were selected model regions in the first IWAS phase; the research was transferred and continued in one of the cross-cutting projects in IWAS II (Vietnam → capacity development) or in the frame of related project activities in Central Asia (R2 Mongolia, Karthe et al., Environ Earth Sci, doi: 10.1007/s12665-014-3789-1 , 2014). The IWAS consortium exists on scientific institutions like the Technische Universitat Dresden and the Helmholtz Centre for Environmental Research—UFZ, Leipzig, as well as partners from industry like the Stadtentwasserung Dresden GmbH (SE-DD), DREBERIS—Dresden consulting for international strategies, and itwh—institute for technical-scientific Hydrology, Hanover. This thematic issue compiles the most important scientific results of the second phase of the IWAS project. The project itself and findings of the first phase were already introduced in a previous special issue by Kalbus et al. (Environ Earth Sci 65:1363–1366, 2012). Main results: The IWAS project is structured by the model regions (R) as well as by cross-cutting activities scenario analysis (Q1), technology development (Q2), governance (Q3) and capacity development (Q4).

Current visualization techniques for computational fluid dynamics applications are sophisticated and work well in simple geometries. For complex geometries such as pore spaces, multiple domain boundaries obstruct the view and make the studying of fluid flow fields difficult. To overcome these deficiencies, we use two-sided materials to render the domain boundaries. Using this technique, it is possible to place the camera inside the domain and have a non-obstructed view of the surrounding flow field without losing spatial reference to the domain boundaries. As a result, a larger part of fluid flow visualization is visible. Two-sided material rendering was successfully applied to display still images with Blender Cycles renderer, in a virtual reality environment, and several implementation techniques were explored for using the Visualization Toolkit.

In the future, climate change will strongly influence our environment and living conditions. Weather and Climate simulations that predict possible changes produce big data sets. The combination of various variables of climate models with spatial data from different sources helps to identify correlations and to study key processes. In this paper, the results of the Weather Research and Forecasting model are visualized for two regions. For this purpose, a continuous workflow that leads from the integration of heterogeneous raw data to 3D visualizations that can be displayed on a desktop computer or in an interactive virtual reality environment is developed. These easy-to-understand visualizations of complex data are the basis for scientific communication and for the evaluation and verification of models as well as for interdisciplinary discussions of the research results.

New methods and technologies for energy storage are required to make a transitionto renewable energy sources; in Germany this transition is termed “Energiewende”. Subsurface georeservoirs, such as salt caverns for hydrogen, compressed air, and methane storage or porous formations for heat and gas storage, offer the possibility of hosting large amounts of energy. When employing these geological storage facilities, an adequate system and process understanding is essential in order to characterize and to predict the complex and interacting effects on other types of subsurface use and on protected entities. In order to make optimal use of georeservoirs, a comprehensive use planning of the subsurface is required that allocates specific uses to appropriate subsurface locations. This paper presents a generic methodology on how subsurface use planning can be conducted and how its scientific basis can be developed. Although synthetic, realistic scenarios for the use of the geological underground for energy storage are parameterized and numerically simulated, accounting for other kinds of subsurface use already in place. From these scenario analyses, the imposed coupled hydraulic, thermal, mechanical and chemical processes, as well as mutual effects and influences on protected entities are assessed and generalized. Based on these, a first methodology for large-scale planning of the geological subsurface considering different surface and subsurface usage scenarios may also be derived.

Reinjection of geothermal water into reservoirs could help maintain the reservoir pressure but may lead to thermal breakthrough. Therefore, the calculation of an optimal distance between the production and reinjection wells is required to balance the changes of pressure and temperature in the reservoir. In this work, a procedure has been designed to optimize well-doublet placement by integrating numerical simulations and economic analyses. The procedure is composed of two subsequent steps, which makes the method more flexible. The first step is the numerical simulation, which incorporates the geological and physical processes. The second step is to optimize the cost by varying the well distance. An example shows that it is better to place the reinjection well in the downstream of the production well. A distance of 400 m between the wells was found to be optimal for the given scenario. Through a further comparison with economic parameters in different countries, the optimal distance was found to be more relevant to the ratio of heat price over electricity than a single parameter for heat or electricity prices.

International audience; In this paper, a comparative modelling exercise from the DECOVALEX-2015 project is presented. The exercise is based on in situ experiments, performed at the Tournemire Underground Research Laboratory (URL), run by the IRSN (Institut de Radioprotection et de Sûreté Nucléaire), in France. These experiments aim at identifying conditions (e.g. technical specifications, design, construction, and defects) that will affect the long-term performance of swelling clay-based sealing systems, which is of key importance for the safety of underground nuclear waste disposal facilities. A number of materials are being considered as seals; the current work focusses on a 70/30 MX80 bentonite–sand mixture initially compacted at a dry density of 1.94 Mg/m3. The performance of the sealing plug involves at least three different important components, which are the hydro-mechanical behaviour of the bentonite–sand core, the overall permeability of the surrounding argillite, and the influence of the technological gap between the core and the argillite. Two particular tests have been selected for a comparative modelling exercise the WT-1 test, which was designed to study the rock mass permeability, and the PT-A1 test, which aimed at quantifying the evolution of the hydro-mechanical field within the bentonite–sand core. A number of independent teams have worked towards modelling these experiments, using different codes and input parameters calibrated on additional small-scale laboratory experiments. Their results are compared and discussed. © 2017, Springer-Verlag Berlin Heidelberg.

Salt caverns are artificial cavities in salt formations, which are usually used for long-term storage of hydrocarbons such as black oil or natural gas. At least two facilities, located in MacIntosh, USA (PowerSouth Energy Cooperative) and in Huntorf, Germany (Crotogino and Quast 1981), employ salt caverns in combination with compressed air energy storage (CAES).

International audience; A comparative modelling exercise involving several independent teams from the DECOVALEX-2015 project is presented in this paper. The exercise is based on various laboratory experiments that have been carried out in the framework of a French research programme called SEALEX and conducted by the IRSN. The programme focuses on the long-term performance of swelling clay-based sealing systems that provide an important contribution to the safety of underground nuclear waste disposal facilities. A number of materials are being considered in the sealing systems; the current work focuses on a 70/30 MX80 bentonite–sand mixture compacted at dry densities between 1.67 and 1.97 Mg/m3. The improved understanding of the full set of hydro-mechanical processes affecting the behaviour of an in situ sealing system requires both experiments ranging from small-scale laboratory tests to full-scale field emplacement studies and coupled hydro-mechanical models that are able to explain the observations in the experiments. The approach was to build models of increasing complexity starting for the simplest laboratory experiments and building towards the full-scale in situ experiments. Following this approach, two sets of small-scale laboratory experiments have been performed and modelled. The first set of experiments involves characterizing the hydro-mechanical behaviour of the bentonite–sand mixture by means of (1) water retention tests under both constant volume and free swell conditions, (2) infiltration test under constant volume condition, and (3) swelling and compression tests under suction control conditions. The second, more complex, experiment is a 1/10th scale mock-up of a larger-scale in situ experiment. Modelling of the full-scale experiment is described in a companion paper. A number of independent teams have worked towards modelling these experiments using different conceptual models, codes, and input parameters. Their results are compared and discussed. This exercise has enabled an improved modelling of the bentonite–sand mixture behaviour, in particular accounting for the dependence of its retention curve on the dry density. Moreover, it has shown the importance of the technological voids on the short-term behaviour of the sealing system. © 2016, Springer-Verlag Berlin Heidelberg.

R&D project CLEAN in the context of CO 2 storage and enhanced gas recovery Michael Kuhn 1,* , Uwe-Jens Gorke 2 , Jens T Birkholzer 3 , Olaf Kolditz 2,4 Helmholtz Centre Potsdam, GFZ - German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany Helmholtz Centre for Environmental Research, Permoserstrase 15, 04318 Leipzig, Germany Lawrence Berkeley National Laboratory, Earth Sciences Division, One Cyclotron Road, Berkeley, CA 94720, USA TU Dresden, Helmholtzstrase 10, 01062 Dresden, Germany *corresponding author Email: michael.kuehn@gfz-potsdam.de Phone +49 331 288 1594 Fax +49 331 288 1502 Anthropogenic emissions of carbon dioxide (CO 2 ) into the atmosphere have a significant impact on the Earth's carbon cycle. While efforts are made to reduce the release of greenhouse gases via reduced energy consumption, more efficient energy production, and a shift to renewable energy supplies, it is generally expected that fossil fuels will continue to provide a major part of the world’s energy portfolio during the 21 st century (IPCC 2005). This is particularly true for coal which is relatively inexpensive and abundantly available in existing or emerging industrial power houses such as the United States, Brazil, Russia, India, and China. Carbon Capture and Storage (CCS) has been developed as an interim measure to allow energy production from coal without CO 2 emissions. This currently available technology entails capturing CO 2 from large-scale industrial sources such as coal-fired power plants or cement, steel and petrochemical factories. The captured CO 2 gas is then compressed to a smaller volume, hence higher density, transported in pipelines, and eventually injected for long-term storage into deep geologic formations, such as deep saltwater-bearing aquifers or depleted oil and gas fields (IPCC 2005). Extensive research is currently carried out to (1) improve the technology and efficiency of capturing CO 2 and (2) to ensure the long-term safety of storing CO 2 underground. This volume of “Environmental Earth Sciences” is a Thematic Issue (TI) focusing on the geologic storage aspect of CCS. The idea of a TI as a new type of publication within this series is to assemble manuscripts dealing with a specific topic comprising its state-of-the art, providing recent research results, and discussing future work from an international perspective. This TI is dedicated to the recent progress made in Germany’s CO 2 storage R&D programme GEOTECHNOLOGIEN funded by the Federal Ministry of Education and Research (BMBF) and the German Research Foundation (DFG)

The joint research project CLEAN was conducted in the years 2008–2011 by a German research and development (R&D) alliance of 16 partners from science and industry. The project was set-up as pilot project to investigate the processes relevant to enhanced gas recovery (EGR) by the injection of CO2 into a subfield of the almost depleted Altmark natural gas field. Despite the setback that permission for active injection was not issued by the mining authority during the period of the project, important results fostering the understanding of processes linked with EGR were achieved. Work carried out led to a comprehensive evaluation of the EGR potential of the Altmark field and the Altensalzwedel subfield in particular. The calculated safety margins emphasize that technical well integrity of the 12 examined boreholes is given for EGR without a need for any further intervention. The laboratory and field tests confirm that the Altensalzwedel subfield is suitable for the injection of 100,000 t of CO2. Numerical simulations provide sound predictions for the efficiency and safety of the EGR technology based on the CO2 injection. The development and testing of different monitoring techniques facilitate an improved surveying of CO2 storage sites in general. The CLEAN results provide the technological, logistic and conceptual prerequisites for implementing a CO2-based EGR project in the Altmark and provide a benchmark for similar projects in the world.

The paper presents a modeling strategy as well as simulation results of a designed conservative tracer test in the depleted Altensalzwedel natural gas reservoir in order to know the tracer concentration and breakthrough time at the production wells. Krypton is considered as a suitable tracer. The production wells are located in several hundred meters to a few kilometers away from the injection well. The numerical simulation has been performed by using the newly implemented compositional gas flow module of OpenGeoSys (OGS), a scientific open-source simulator for calculation of coupled geohydraulic (single and multiphase flow), transport (heat and mass transfer), geomechanical and geochemical processes. The tracer breakthrough curves at the production wells show that the breakthrough times vary between 2 and 3 years. The model verification is presented by comparing the OGS results with a one-dimensional analytical solution. The numerical results have been verified by code comparison, additionally.

Capture and geological sequestration of CO2 from large industrial sources is considered a measure for reducing anthropogenic emissions of CO2 and thus mitigating climate change. One of the main storage options proposed are deep saline formations, as they provide the largest potential storage capacities among the geologic options. A thorough assessment of this type of storage site therefore is required. The CO2-MoPa project aims at contributing to the dimensioning of CO2 storage projects and to evaluating monitoring methods for CO2 injection by an integrated approach. For this, virtual, but realistic test sites are designed geometrically and fully parameterized. Numerical process models are developed and then used to simulate the effects of a CO2 injection into the virtual test sites. Because the parameterization of the virtual sites is known completely, investigation as well as monitoring methods can be closely examined and evaluated by comparing the virtual monitoring result with the simulation. To this end, the monitoring or investigation method is also simulated, and the (virtual) measurements are recorded and evaluated like real data. Application to a synthetic site typical for the north German basin showed that pressure response has to be evaluated taking into account the layered structure of the storage system. Microgravimetric measurements are found to be promising for detecting the CO2 phase distribution. A combination of seismic and geoelectric measurements can be used to constrain the CO2 phase distribution for the anticline system used in the synthetic site.

The idea of this paper is twofold. On one hand, we propose a general systematic for benchmarking of CO2 modelling. On the other hand, we integrate material from the CLEAN project into this framework to demonstrate its applicability (Kuhn et al. in Environ Earth Sci, this issue 2011). Benchmarks are an important instrument to gain a better understanding of interacting physico-chemical processes and they are a necessary tool to verify the algorithms and the software dedicated to simulate the separated and differently coupled thermo-hydro-mechanical/chemical processes during injecting and storing CO2 in the subsurface. In general we distinguish between process- and site-related test cases. Process-related benchmarks deal with the required complexity of process coupling as well as equations of state for fluids and constitutive laws for geologic formations. Site-specific benchmarks represent different geological settings for potential CO2 reservoirs, e.g., depleted gas and oil reservoirs as well as deep saline aquifers. The data basis for benchmarking mainly comes from experimental work in the CLEAN project as well as from literature. The benchmarking systematic is aimed at serving as basis for process studies, experimental design as well as for code inter-comparison purposes not only for numerical tools having used by the CLEAN partners but also for upcoming international benchmarking initiatives as well.

Numerical modeling of interacting flow and transport processes between different hydrological compartments, such as the atmosphere/land surface/vegetation/soil/groundwater systems, is essential for understanding the comprehensive processes, especially if quantity and quality of water resources are in acute danger, like e.g. in semi-arid areas and regions with environmental contaminations. The computational models used for system and scenario analysis in the framework of an integrated water resources management are rapidly developing instruments. In particular, advances in computational mathematics have revolutionized the variety and the nature of the problems that can be addressed by environmental scientists and engineers. It is certainly true that for each hydro-compartment, there exists many excellent simulation codes, but traditionally their development has been isolated within the different disciplines. A new generation of coupled tools based on the profound scientific background is needed for integrated modeling of hydrosystems. The objective of the IWAS-ToolBox is to develop innovative methods to combine and extend existing modeling software to address coupled processes in the hydrosphere, especially for the analysis of hydrological systems in sensitive regions. This involves, e.g. the provision of models for the prediction of water availability, water quality and/or the ecological situation under changing natural and socio-economic boundary conditions such as climate change, land use or population growth in the future.

In this paper, conceptual modeling and numerical simulation of two-phase flow during CO2 injection into deep saline aquifers is presented. The work focuses on isothermal transport and deformation processes in the vicinity of the injection well including hydromechanical failure analysis. Governing differential equations are based on balance laws for mass and momentum completed by constitutive relations for the fluid and solid phases as well as their interactions. Constraint conditions for the partial saturations and the pressure fractions of CO2 and brine are defined. To characterize the stress state in the solid matrix the effective stress principle is applied. The coupled problem is solved using an in-house scientific finite element code, and verified with benchmarks. In terms of application-oriented aspects, we examine the mechanical integrity of a deep saline aquifer during the injection of supercritical CO2. The analysis is conducted with a numerical scheme of the capillary pressure and non-wetting phase pressure for the two-phase flow process. In this study, unidirectional hydromechanical coupling is considered. Caprock stability is monitored in time, referenced to the potential for hydraulic fracture and shear slip along an optimally oriented shear plane for a suite of injection pressures. For reasonable parameter values and the chosen aquifer geometry, significant mechanical failure (and potential breach of integrity) is expected in the shale caprock for all but low injection rates. This indicates that the analysis of the hydromechanical response is crucial for proper selection of injection sites, injection rates, and total storage capacity.

In recent years, the amount of environmental data that is measured, collected and analysed has risen in staggering amounts. The reason for this is largely the desire and need of both science and politics to better understand the reasons, effects and possible consequences of climate change. This includes topics as diverse as the behaviour of groundwater regimes in arid regions, the migration of animal species, or the wide range of ecosystem services. In addition, this trend is reinforced by observation methods getting more and more refined: satellites can measure data in the sub-metre range, eddy covariance systems analyse high-frequency atmospheric data such as wind, heat or gas fluxes and weather surveillance radar creates high-resolution data of precipitation parameters every few minutes, to name just a few examples. Vital insight is gained from correlating such data or simulating certain processes based on the collected information. Examples range from devising water management schemes for arid and humid regions, feasible plans for the transition from fossil to renewable energy sources, finding adequate storage sites for nuclear waste, or the effects of chemicals discharged into the atmosphere by industry or into the water in the form of agricultural fertilisers. Developing effective visualisation techniques is the key to improving the understanding of complex data sets and communicate findings to the public in general and stakeholders in particular. This process requires collaboration of researchers from environmental sciences (geology, meteorology, hydrology, etc.) and computer scientists with experience in handling and visualising large amounts of heterogenous data. While this has previously worked well in other domains, e.g. for the visualisation of complex medical data (Preim and Botha 2013; Deserno 2011), in environmental sciences visualisation is often viewed as an addendum. Once the field work and simulations are done, results are visualised to show the results to other interested parties. The possibilities for visualisation in assisting scientists in their research for verification, integration and analysis of the data are often neglected outside of the established domains of timeseries analysis or cartographic data in geographic information systems. In addition, visualisation is an excellent means of communication between researchers from different disciplines and facilitating support for basic workflows such as model creation. This thematic issue includes expanded and new articles based on presentations of the workshop ‘‘Visualisation in Environmental Sciences’’, which took place as a co-located event of EuroVis 2013, the EuroGraphics conference on visualisation. Contributions included applications from the domains of biodiversity (Slingsby and van Loon 2013), migration ecology (Kolzsch et al. 2013), ecosystem restoration (Eligehausen et al. 2013), flood analysis (Schlegel et al. 2013), 3D geological modelling (Lidal et al. 2013) and urban climate simulation (Rober et al. 2013). The intent is to give readers a notion about the multitude of possibilities for visualisation in the scope of environmental sciences. K. Rink (&) O. Kolditz Department of Environmental Informatics, Helmholtz Centre for Environmental Research, Leipzig, Germany e-mail: karsten.rink@ufz.de