地下热-水动力-力学耦合过程数值模拟:以CO_2地质储存为例

在地下流动系统问题的研究中,热-水动力-力学(THM)耦合过程是研究的热点问题。在地下多相非等温数值模拟软件TOUGH2的框架内,基于Biot固结理论和摩尔-库仑破坏判定准则,建立了THM耦合模型;采用积分有限差和有限元联合的空间离散方法,开发了THM模拟器TOUGH2Biot。该模拟器中热和水动力过程是全耦合,力学过程是部分耦合。通过与解析解的对比,验证了其正确性。基于鄂尔多斯盆地CCS示范工程,采用TOUGH2Biot研究了CO2注入地层后的THM响应。结果显示CO2的注入引起流体压力急剧增加,地层有效应力减小,地表隆起,隆起大小在几十个厘米,同时孔渗增加,利于CO2注入引起的压力上升向外消散。CO2注入最有可能导致剪切破坏的位置位于最大速率注入点上部盖层,其次为靠近地表的位置。     

Natural and industrial analogues for leakage of CO2 from storage reservoirs: identification of features, events, and processes and lessons learned

Instances of gas leakage from naturally occurring CO₂ reservoirs and natural gas storage sites serve as analogues for the potential release of CO₂ from geologic storage sites. This paper summarizes and compares the features, events, and processes that can be identified from these analogues, which include both naturally occurring releases and those associated with industrial processes. The following conclusions are drawn: (1) carbon dioxide can accumulate beneath, and be released from, primary and secondary shallower reservoirs with capping units located at a wide range of depths; (2) many natural releases of CO₂ are correlated with a specific event that triggered the release; (3) unsealed fault and fracture zones may act as conduits for CO₂ flow from depth to the surface; (4) improperly constructed or abandoned wells can rapidly release large quantities of CO₂; (5) the types of CO₂ release at the surface vary widely between and within different leakage sites; (6) the hazard to human health was small in most cases, possibly because of implementation of post-leakage public education and monitoring programs; (7) while changes in groundwater chemistry were related to CO₂ leakage, waters often remained potable. Lessons learned for risk assessment associated with geologic carbon sequestration are discussed. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Review: Some low-frequency electrical methods for subsurface characterization and monitoring in hydrogeology

Low-frequency geoelectrical methods include mainly self-potential, resistivity, and induced polarization techniques, which have potential in many environmental and hydrogeological applications. They provide complementary information to each other and to in-situ measurements. The self-potential method is a passive measurement of the electrical response associated with the in-situ generation of electrical current due to the flow of pore water in porous media, a salinity gradient, and/or the concentration of redox-active species. Under some conditions, this method can be used to visualize groundwater flow, to determine permeability, and to detect preferential flow paths. Electrical resistivity is dependent on the water content, the temperature, the salinity of the pore water, and the clay content and mineralogy. Time-lapse resistivity can be used to assess the permeability and dispersivity distributions and to monitor contaminant plumes. Induced polarization characterizes the ability of rocks to reversibly store electrical energy. It can be used to image permeability and to monitor chemistry of the pore water–minerals interface. These geophysical methods, reviewed in this paper, should always be used in concert with additional in-situ measurements (e.g. in-situ pumping tests, chemical measurements of the pore water), for instance through joint inversion schemes, which is an area of fertile on-going research.     

International conference on novel methods for subsurface characterization and monitoring: from theory to practice: NovCare 2017

The NovCare 2017 International Conference (Novel Methods for Subsurface Characterization and Monitoring: From Theory to Practice) took place in June 2017 and was the fifth conference in a series that has proven to be an excellent forum for exchanging ideas and experiences related to the challenges of subsurface characterization and monitoring. Some of the presented work is included in this Thematic issue NovCare 2017.     

Modeling, parameterization and evaluation of monitoring methods for CO2 storage in deep saline formations: the CO2-MoPa project

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.     

An integrative hierarchical monitoring approach applied at a natural analogue site to monitor CO2 degassing areas

This paper introduces an integrative hierarchical monitoring concept allowing for the detection and assessment of possible leakages from geological storage formations into the shallow subsurface or atmosphere. The concept introduced in this paper combines various investigation methods working at different scales and with varying resolutions. This approach will allow large spatial areas to be consistently covered, to enable efficient monitoring. Experience gained from the adoption of these tools for naturally occurring CO₂ deposits (analogue sites) is helpful for the evaluation and adoption of the methods to the requirements of storage projects.     

A low-dimensional subsurface model for saturated and unsaturated flow processes: ability to address heterogeneity

A low-dimensional model that describes both saturated and unsaturated flow processes in a single equation is presented. Subsurface flow processes in the groundwater, the vadose zone, and the capillary fringe are accounted for through the computation of aggregated hydrodynamic parameters that result from the integration of the governing flow equations from the bedrock to the land surface. The three-dimensional subsurface flow dynamics are thus described by a two-dimensional equation, allowing for a drastic reduction of model unknowns and simplification of the model parameterizations. This approach is compared with a full resolution of the Richards equation in different synthetic test cases. Because the model reduction stems from the vertical integration of the flow equations, the test cases all use different configurations of heterogeneity for vertical cross-sections of a soil-aquifer system. The low-dimensional flow model shows strong consistency with results from a complete resolution of the Richards equation for both the water table and fluxes. The proposed approach is therefore well suited to the accurate reproduction of complex subsurface flow processes.     

A model for developing best practice volcano monitoring: a combined threat assessment,consultation and network effectiveness approach

This paper presents a combined approach to achieving best practice volcano monitoring through a review of New Zealand’s volcano-monitoring capability as established under the GeoNet project. A series of benchmark, consultation and network performance studies were undertaken to provide a comprehensive review of volcano monitoring in New Zealand and to establish plans for future improvements in capability. The United States Geological Survey National Volcano Early Warning System method was applied to benchmark the established monitoring networks against recommendations for instrumentation based on a volcano’s threat level. Next, a consultative study of New Zealand’s volcanology research community was undertaken to canvass opinions on what future directions GeoNet volcano monitoring should take. Once the seismic network infrastructure had been built, a noise floor analysis was conducted to identify stations with poor site noise characteristics. Noise remediation for poor sites has been implemented by either re-locating the site or placing sensors in boreholes. Quality control of Global Navigation Satellite System networks is undertaken through the use of multipath parameters derived from routine processing. Finally, the performance of the monitoring networks is assessed against two recent eruptions at Mount Tongariro and White Island. This combined approach can be used as a model to assess the need for future monitoring levels on any volcano.     

Analyses of pre-injection reservoir data for stable carbon isotope trend predictions in CO2 monitoring: preparing for CO2 injection

Baseline monitoring at the proposed enhanced gas recovery site in Altmark (Germany) was carried out in combination with theoretical and laboratory investigations to describe and predict the principles of expected stable carbon isotope and dissolved inorganic carbon (DIC) trends during CO₂ injection in reservoirs. This provides fundamental data for site-specific characterisation for monitoring purposes. Baseline ??¹³C values at the Altmark site ranged between ?1.8 and ?11.5??? and DIC values were about 2?mmol?L^?1. These baseline values form the basis for a theoretical study on the influences of the ambient reservoir conditions on the state of geochemical and isotope equilibrium of the reservoir fluids. Transferring this theoretical study to the Altmark site enables predictions on geochemical trends during potential injection. Assuming that CO₂ would be injected at the Altmark site to pCO₂?=?100?bar and with a ??¹³C of ?30???, at isotopic and geochemical equilibrium, ??¹³C_DIC values would approach this end-member, and DIC concentrations of 1,000?mmol L^?1 would be expected. Laboratory experiments were conducted at low pCO₂ levels (4?C35?bars) to mimic the approach of a CO₂ plume at a monitoring well. These results support field investigations from other sites: that ??¹³C_DIC is a sensitive tool for monitoring CO₂ migration in the subsurface and simultaneously allows quantification of geochemical trapping of CO₂.     

Laboratory experiments and field study for the detection and monitoring of potential seepage from CO2 storage sites

Potential CO₂ seepages from geological storage sites or from the injection rig may affect the surrounding environment. To develop reliable detection techniques for such seepages a laboratory rig was designed that is composed of three vertical Plexiglas columns. The columns can be filled with sediments and water; CO₂ can be injected from the bottom. Two columns are used to simulate the impact of CO₂ on soils; while the third one, which is larger in size, simulates CO₂ seepage in aquatic environments. The main results of the laboratory experiments indicate that increased levels of CO₂ generate a quick drop in pH. Once the seepage is stopped, a partial recovery towards the initial values of pH is recorded. The outcomes of the laboratory experiments on the aquatic seepage are compared with observations from a submarine natural emission of CO₂. In this natural underwater seepage multi-parametric probes and laboratory analysis were used to analyze the composition and the chemical effects of the emitted gas; basic acoustic techniques were tested as tools for the prompt detection of CO₂ bubbles in water.     

Correction to: Uncertainty in the prediction and management of CO2 emissions: a robust minimum entropy approach

Natural Hazards - The Mahi—one of the major rivers in Western India—is subject to frequent major flooding, which severely affects the local economy and infrastructure. Little has been...     

Natural hazards in the Bavarian Alps: a historical approach to risk assessment

The Bavarian Alps region is strongly affected by various natural hazards, mainly hydrological events (floods, debris flows), geomorphic/geological events (landslides, rock falls), and avalanches. Extraordinary floods, like in 2002 or in the summer of 2005 in south Bavaria, have again posed the question of the possible extent and frequency of recurrence of catastrophic events. To put risk assessment on a broader basis historical data about all kinds of past natural hazards were detected in the archives of local authorities and administrative offices for water management. More than 10,000 sources (written accounts, maps, and photographs) were collated in a database. The majority of this information reaches back to the middle of the 19th century. In addition, many documents referring to events dating back even as far as the middle age were found. The Historische Analyse von NaturGefahren (HANG, historical analysis of natural hazards) project at the University of Eichstaett mainly focuses on a small-scale examination of the data. Initial results of the data analysis show that most catastrophic events in the Bavarian Alps only affect parts of the area, but not the whole region. Therefore it is necessary to assess the risk potential on a local scale like valleys, the catchment areas of mountain streams, or even single streams. Firstly the presented data is aimed to help engineers in future planning of hazard-protection measures. Secondly the information can form a vital component to enhance our knowledge of hydrological and geomorphic/geological dynamics in the Alps.     

Tales of transformation: The potential of a narrative approach to pro-environmental practices

Individual lifestyles and practices play an important part in governmental strategies to improve environmental outcomes, both in the UK (DEFRA, 2008) and elsewhere. This often involves promoting actions deliberately aimed at reducing one’s environmental impact, or pro-environmental practices. However, our understanding of these practices has weaknesses; notably regarding the “Value-Action Gap” and the conditions promoting enduring change. This article explores how narrative methods could further our knowledge of pro-environmental practice. It illustrates the utility of the approach using the example of moments of sudden change, or “transformative moments”, in the lives of individuals who take action to address climate change. Drawing on three cases from an ongoing study, it uses narrative tools to explore the nature of these transformations, including the inter-related roles of context, information, emotions and relationships with other people. The discussion highlights tentative conclusions regarding these moments of sudden change, and offers suggestions for future research. Finally, it evaluates the utility of narrative approaches to pro-environmental practice, suggesting that despite some limitations, this method has significant potential to address unresolved issues in the field.     

Uncertainty in the prediction and management of CO2 emissions: a robust minimum entropy approach

Natural Hazards - CO2 emission control is one of the most vital parts of environment management. China owns the largest CO2 emission in the world. For the sake of clarifying China’s emission...     

A preliminary design of a radon potential map for Canada: a multi-tier approach

Canada is a vast country with most of the population living on a small portion of the land. However, for a national radon potential map, it is mandatory to cover the entire country including sparsely populated areas. Because of these characteristics, the radon map development for Canada is challenging. After briefly reviewing of radon map development in the world, this study considers a multi-tier approach to best use available however limited resources and to generate a national radon map in a timely fashion. In summary, radon potential maps for highly populated areas should be determined by direct indoor radon measurements where enough indoor radon data are available. In areas where indoor radon measurements are limited or not yet available, the radon potential maps could be developed from various data sources with a multi-factor scoring system including geological information on soil permeability, soil gas radon concentration and ground uranium concentration. In sparsely populated areas, radon potential maps can only be generated with geological predictive tools, especially in those areas where no houses have yet been built. Because indoor radon measurement data and geological information relevant to radon are very limited in Canada, a multi-step strategy is also worth considering in addition to the multi-tier approach.