Haibing Shao

OpenGeoSys: an open-source initiative for numerical simulation of thermo-hydro-mechanical/chemical (THM/C) processes in porous media

In this paper we describe the OpenGeoSys (OGS) project, which is a scientific open-source initiative for numerical simulation of thermo-hydro-mechanical-chemical processes in porous media. The basic concept is to provide a flexible numerical framework (using primarily the Finite Element Method (FEM)) for solving multifield problems in porous and fractured media for applications in geoscience and hydrology. To this purpose OGS is based on an object-oriented FEM concept including a broad spectrum of interfaces for pre- and postprocessing. The OGS idea has been in development since the mid-eighties. We provide a short historical note about the continuous process of concept and software development having evolved through Fortran, C, and C++ implementations. The idea behind OGS is to provide an open platform to the community, outfitted with professional software-engineering tools such as platform-independent compiling and automated benchmarking. A comprehensive benchmarking book has been prepared for publication. Benchmarking has been proven to be a valuable tool for cooperation between different developer teams, for example, for code comparison and validation purposes (DEVOVALEX and CO2 BENCH projects). On one hand, object-orientation (OO) provides a suitable framework for distributed code development; however, the parallelization of OO codes still lacks efficiency. High-performance-computing efficiency of OO codes is subject to future research.

Reactive transport codes for subsurface environmental simulation

A general description of the mathematical and numerical formulations used in modern numerical reactive transport codes relevant for subsurface environmental simulations is presented. The formulations are followed by short descriptions of commonly used and available subsurface simulators that consider continuum representations of flow, transport, and reactions in porous media. These formulations are applicable to most of the subsurface environmental benchmark problems included in this special issue. The list of codes described briefly here includes PHREEQC, HPx, PHT3D, OpenGeoSys (OGS), HYTEC, ORCHESTRA, TOUGHREACT, eSTOMP, HYDROGEOCHEM, CrunchFlow, MIN3P, and PFLOTRAN. The descriptions include a high-level list of capabilities for each of the codes, along with a selective list of applications that highlight their capabilities and historical development.

The IWAS-ToolBox: Software coupling for an integrated water resources management

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.

GeoSysBRNS-A flexible multidimensional reactive transport model for simulating biogeochemical subsurface processes

The description of reactive transport processes in subsurface environments requires a sound understanding of both the biogeochemical complexity of the system and the spatially resolved transport of reactive species. However, most existing reactive transport models, for example in the field of contaminant hydrology, are specialized either in the simulation of the reactive or of the flow and transport processes. In this paper, we present and test the coupling of two highly flexible codes for the simulation of reactive transport processes in the subsurface: the Biogeochemical Reaction Network Simulator (BRNS), which contains a solver for kinetically and thermodynamically constrained biogeochemical reactions, and GeoSys/RockFlow, a multidimensional finite element subsurface flow and transport simulator. The new model, named GeoSysBRNS, maintains the full flexibility of the original models. The coupling is handled using an operator splitting scheme, which allows the reactive solver to be compiled into a problem specific library that is accessed by the transport simulator at runtime. The accuracy of the code coupling within GeoSysBRNS is demonstrated using two benchmark problems from the literature: a laboratory experiment on organic carbon degradation in a sand column via multiple microbial degradation pathways, and a dispersive mixing controlled bioreactive transport problem in aquifers, assuming three different reaction kinetics.

Mechanism insights into enhanced trichloroethylene removal using xanthan gum-modified microscale zero-valent iron particles

This report focuses on the enhancement in trichloroethylene (TCE) removal from contaminated groundwater using xanthan gum (XG)-modified, microscale, zero-valent iron (mZVI). Compared with bare mZVI, XG-coated mZVI increased the TCE removal efficiency by 30.37% over a 480-h experimental period. Because the TCE removal is attributed to both sorption and reduction processes, the contributions from sorption and reduction were separately investigated to determine the mechanism of XG on TCE removal using mZVI. The results showed that the TCE sorption capacity of mZVI was lower in the presence of XG, whereas the TCE reduction capacity was significantly increased. The FTIR spectra confirmed that XG, which is rich in hydrophilic functional groups, was adsorbed onto the iron surface through intermolecular hydrogen bonds, which competitively repelled the sorption and mass transfer of TCE toward reactive sites. The variations in the pH, Eh, and Fe(2+) concentration as functions of the reaction time were recorded and indicated that XG buffered the solution pH, inhibited surface passivation, and promoted TCE reduction by mZVI. Overall, the XG-modified mZVI was considered to be potentially effective for the in-situ remediation of TCE contaminated groundwater due to its high stability and dechlorination reactivity.

Recent studies on hydrothermal systems in China: a review

This paper reviews the state-of-the-art in hydrothermal systems in China with emphasis on current studies of potential and reservoir engineering. Three hydrothermal systems, namely, Yangbajing, Xianyang, and Xiongxian, are used as case studies to represent high temperature granite reservoirs, medium-to-low temperature sandstone reservoirs, and medium-to-low temperature carbonate reservoirs, respectively. There is a huge potential of hydrothermal resources in China that have not been fully studied for possible exploitation. The study reveals that the potential of developing hydrothermal resources is preferable to exploitation of hot-dry-rock (HDR) systems in the near future. In order to enhance the utilization efficiency and prolong the economic lifetime of a geothermal field, reinjection needs to be increased, including treated wastewater as an option. In this regard, deep karstic aquifers containing hot water are the most ideal targets for development due to their favorable characteristics including high single-well yield, low salinity, easy reinjection, and fewer environmental impacts when exploited. The next challenge lies in the geothermal reservoir management for sustainable production. Numerical models describing the full complexity of coupled physicochemical thermodynamic processes such as the open source OpenGeoSys modeling platform are powerful tools for production planning as well as for assessing the possible environmental impacts. Comprehensive reservoir simulation should be employed to provide an optimal fluid production scheme and to maximize the sustainability in the development of a hydrothermal field.

Spatial variability of soil salinity in Bohai Sea coastal wetlands, China: Partition into four management zones

Soil salinization constitutes an environmental hazard worldwide. The Bohai Sea coastal wetland area is experiencing dramatic soil salinization, which is affecting its economic development. This study focused on the spatial variation and distribution characteristics of soil salinity in this area using geostatistical analysis combined with the kriging interpolation method, based on a large-scale field investigation and layered soil sampling (0–30, 30–60 and 60–100 cm). The results revealed that soil salinity in these layers demonstrated strong variability, obvious spatial structure characteristics and strong spatial autocorrelation. Soil salinity displayed a significant zonal distribution, gradually decreasing with increasing distance from the coastline. Apart from the northern part of the study area, which appeared to be not affected by soil salinization, there were varying degrees of soil salinization in nearly 70% of the total area. With increasing soil depth, the areas of non-salinized and mild salinized soil gradually decreased, while those of moderate salinized and strong salinized soils increased. The area of saline soil first decreased and then increased. The study area could be divided into four management zones according to soil salinities in the top 1-m soil body, and utilization measures, adapted to local conditions, were proposed for each zone. The results of our study present an important theoretical basis for the improvement of saline soils, for wetland re-vegetation and for the sustainable utilization of soil resources in the Bohai Sea coastal wetland.

Salt dynamics in soil profiles during long-term evaporation under different groundwater conditions

To study salt dynamics in soil profiles under different groundwater conditions, a 3-year indoor experiment was carried out under conditions of open-air evaporation. Silt loam soil was treated under three groundwater table depths (0.85, 1.05, and 1.55 m) combined with three groundwater salinities: 0.40 dS m− 1 (2 g l− 1), 0.80 dS m− 1 (4 g l− 1), and 1.60 dS m− 1 (8 g l− 1). A total of nine soil columns (0.14 m internal diameter) were used to simulate different combinations of groundwater depths and salinities. The results obtained showed that salt first accumulated at the bottom of the soil column, and only when soil salinity in this layer had remained relatively stable with time, salt began to accumulate in the adjacent upper soil layers. When all subsoil layers had reached dynamic salinity equilibrium, electrical conductivity (EC) of soils in the surface layer began to increase drastically. With increasing salt accumulation in the surface soil, EC of the subsoil began to rise tardily. The further up the soil layer, the earlier EC started to increase, although the redistribution of salts in the soil profile tended to be homogenous. Groundwater depth did not significantly change subsoil EC values at the same depth; however, it distinctly affected the time needed for the subsoil to reach dynamic salinity equilibrium. Groundwater salinity, on the other hand, did not significantly alter the time point at which soil salinity at the same depth began to increase rapidly or the time period needed to reach dynamic salinity equilibrium. This study explored salt transport processes in the soil profile through a long-term experiment, enabling us to reveal some general laws governing salt dynamics that will be very important to understand the mechanism of soil salinization. The results could be further used to set up strategies to prevent salinization or to improve salt-affected soils.

On the importance of a coordinated site characterization for the sustainable intensive thermal use of the shallow subsurface in urban areas: a case study

Shallow geothermal applications have become standard solutions for heating and cooling in many newly built or redeveloped residential neighborhoods, but current urban development practices do not yet consider the new demands that result from the intensive thermal use of the shallow subsurface. A coordinated site characterization is of great importance as a sound basis for an optimized planning of geothermal systems that brings together user requirements (heating, cooling, and/or seasonal energy storage) and (hydro)geological subsurface conditions. The aim of this study is to raise awareness and to demonstrate the relevance of a coordinated site characterization. Therefore, this study quantifies the advantages of a site-specific over a desktop-based site characterization in reducing uncertainty for calculation of borehole heat exchanger length and predicted induced temperature changes in the subsurface for a newly developed residential neighborhood in the city of Taucha, Germany. Results show that savings of over EUR 1850 per house (EUR 98,050 for the entire neighborhood) can be achieved by a coordinated exploration and prediction accuracy of temperature plume development was substantially improved. Although being more cost intensive, exploration costs for this case study are <3% of the assumed individual geothermal system costs of EUR 16,000 if divided equally among geothermal users. Three different options are presented to implement coordinated exploration concepts into site development practice.

Calibration of water–granite interaction with pressure solution in a flow-through fracture under confining pressure

Fluid–mineral interaction has an irreversible impact on the fracture permeability evolution in the life span of deep geological reservoirs. To investigate the impact, a preliminary study on water–granite interaction in an undeformable fracture under confining pressure is conducted. A 1-D flow and reactive transport model is therefore developed and validated against the experimental data in Yasuhara et al. (Appl Geochem 26(12):2074–2088, 2011). The model takes free-face dissolution on pore walls as well as enhanced dissolution at asperity contacts into account, together with a nested well-equipped geochemical system. The simulation is implemented by FEM-based simulator OpenGeoSys with a plugin module of IPhreeqc for speciation calculation. After calibration, the predictions of effluent element concentrations are in good agreement with the measurements. The study indicates the high effluent concentrations arise from enhanced mineral dissolution at asperity contacts. Pressure solution at anorthite contacts may not take effect under experimental conditions because of the high-level energy barrier to interpenetration, and Al-bearing secondary minerals such as gibbsite may be formed in the current near-equilibrium aqueous system. The sensitivity analysis suggests that contact area ratio is a paramount parameter in determining the surface reactivity and reactive surface area at contacts.