Impact of fracture network geometry on free convective flow patterns

The effect of fracture network geometry on free convection in fractured rock is studied using numerical simulations. We examine the structural properties of fracture networks that control the onset and strength of free convection and the patterns of density-dependent flow. Applicability of the equivalent porous medium approach (EPM) is also tested, and recommendations are given, for which situations the EPM approach is valid. To date, the structural properties of fracture networks that determine free convective flow are examined only in few, predominantly simplified regular fracture networks. We consider fracture networks containing continuous, discontinuous, orthogonal and/or inclined discrete fractures embedded in a low-permeability rock matrix. The results indicate that bulk permeability is not adequate to infer the occurrence and magnitude of free convection in fractured rock. Fracture networks can inhibit or promote convection depending on the fracture network geometry. Continuous fracture circuits are the crucial geometrical feature of fracture networks, because large continuous fracture circuits with a large vertical extent promote convection. The likelihood of continuous fracture circuits and thus of free convection increases with increasing fracture density and fracture length, but individual fracture locations may result in great deviances in strength of convection between statistically equivalent fracture networks such that prediction remains subject to large uncertainty.     

Monitoring land subsidence and fault deformation using the small baseline subset InSAR technique: A case study in the Datong Basin,China

The Datong Basin is located to the north of the Fenwei Graben Basin, where ground fissures and subsidence are common geological hazards. The Datong Basin is also one of China's main energy bases and is known as “the hometown of coal”. In this study, the small baseline subset InSAR technique was used to process 40 scenes of Envisat ASAR images that cover this area. The magnitude and distribution of subsidence in the Datong Basin were obtained. Additionally, the relationships among the regional land subsidence, ground fissures and fault activity were addressed. The results reveal that Datong ground subsidence is affected by the groundwater exploitation and the nearby faults. The Datong ground fissures are controlled by regional fault activity (e.g., seismic activity) and its interaction with the ground subsidence. Meanwhile, the influence of surface precipitation on ground fissure activity was analyzed. The differential subsidence on both sides of the ground fissures was also studied.     

经验模态分解法在安徽省南部地下流体分析中的应用

首次引进经验模态分解法（EMD）对安徽省南部地下流体进行分析。通过对地下流体数据的分解与重构,发现该方法能提取不同尺度的水位动态,效果较好。通过对震例的总结发现：显著地震前、后安徽省南部地下流体EMD重构结果均出现异常,且存在某些地震前兆敏感点。同时,还对地震前地下流体的变化原因进行了初步分析。     

Hydrodynamic regime as a major control on localization of uranium mineralization in sedimentary basins

Uranium deposits in sedimentary basins can be formed at various depths,from near surface to the basement.While many factors may have played a role in controlling the location of mineralization,examination of various examples in the world,coupled with numerical modeling of fluid flow,indicates that the hydrodynamic regime of a basin may have exerted a major control on the localization of uranium deposits.If a basin is strongly overpressured,due to rapid sedimentation,abundance of low-permeability sediments or generation of hydrocarbons,fluid flow is dominantly upward and uranium mineralization is likely limited at shallow depths.If a basin is moderately overpressured,upward moving fluids carrying reducing agents may meet downward moving,oxidizing,uranium-bearing fluids in the middle of the basin,forming uranium deposits at moderate depths.If a basin is weakly or not overpressured,either due to slow sedimentation or dominance of high-permeability lithologies,minor topographic disturbance or density variation may drive oxidizing fluids to the bottom of the basin,leaching uranium either from the basin or the basement,forming unconformity-type uranium deposits.It is therefore important to analyze the hydrodynamic regime of a basin in order to predict the most likely type and location of uranium deposits in the basin.     

Characteristics-based classification research on typical petroleum contaminants of groundwater

Petroleum pollution has become an important factor to threaten the groundwater environment, and the classification of its typical characteristics will contribute to pollution assessment and environmental management. Under the same hydrogeological features con?dition, the reaction of typical petroleum pollutants in groundwater depends on the charac?teristics. This paper takes the typical toxicity, oil pollutant migration, degradation, water-soluble etc. as evaluation indexes, and with AHP method the typical petroleum pollut?ants in groundwater are divided into four classifications according to comprehensive calculated values: comprehensive value≥2.5, Class I hazardous pollutant; 2.0≤comprehensive value＜2.5, Class II hazardous pollutant; 1.5≤comprehensive value＜2.0, Class III hazardous po?llutant; comprehensive value＜1.5, Class IV hazardous pollutant. The pollutant group shall be managed according to the classification, and obtained classification list will provide technical support for priority monitoring and priority repair of groundwater environmental management.     

Adaptive state estimation of groundwater contaminant boundary input flux in a 2-dimensional aquifer

In many circumstances involving heat and mass transfer issues,it is considered impractical to measure the input flux and the resulting state distribution in the domain.Therefore,the need to develop techniques to provide solutions for such problems and estimate the inverse mass flux becomes imperative.Adaptive state estimator(ASE)is increasingly becoming a popular inverse estimation technique which resolves inverse problems by incorporating the semi-Markovian concept into a Bayesian estimation technique,thereby developing an inverse input and state estimator consisting of a bank of parallel adaptively weighted Kalman filters.The ASE is particularly designed for a system that encompasses independent unknowns and/or random switching of input and measurement biases.The present study describes the scheme to estimate the groundwater input contaminant flux and its transient distribution in a conjectural two-dimensional aquifer by means of ASE,which in particular is because of its unique ability to efficiently handle the process noise giving an estimation of keeping the relative error range within 10%in 2-dimensional problems.Numerical simulation results show that the proposed estimator presents decent estimation performance for both smoothly and abruptly varying input flux scenarios.Results also show that ASE enjoys a better estimation performance than its competitor,Recursive Least Square Estimator(RLSE)due to its larger error tolerance in greater process noise regimes.ASE's inherent deficiency of being slower than the RLSE,resulting from the complexity of algorithm,was also noticed.The chosen input scenarios are tested to calculate the effect of input area and both estimators show improved results with an increase in input flux area especially as sensors are moved closer to the assumed input location.     

鄂尔多斯盆地北部深埋区“地貌—沉积”控水关键要素研究

鄂尔多斯盆地北部深埋煤田区地表主要有沙漠、基岩台地和黄土沟壑等地貌类型,沙漠区工作面涌水量比其他地貌区大1~2个数量级。为了查清煤层顶板直接充水含水层补给水源、导水通道和充水强度的控制要素,从地形地貌和地质沉积方面开展了研究,结果表明:沙漠地貌地势平缓,降水入渗系数大,第四系厚度大、富水性强,为下伏含水层提供了丰富的补给水源;基岩台地和黄土沟壑地貌,地形起伏大,降水入渗系数极小,浅部地层富水性极弱,是下伏含水层补给能力较弱的水源。陆相沉积形成的砂泥岩互层结构,不存在区域性稳定隔水层,各层段均属于弱-中等富水性含水层,3个矿井的白垩系含水层水位下降了20~130 m,证明浅部与深部含水层存在较密切的水力联系。煤层顶板主要发育七里镇砂岩和真武洞砂岩含水层,为厚度较大的中粗砂岩段,直接充水含水层地质沉积条件相似,但是沙漠区工作面顶板钻孔水量、累计预疏放水量和采空区涌水量均远大于其他地貌区,直接充水含水层富水性主要受地貌控制,深部含水层的水源为大气降水和第四系含水层。沙漠地貌区的不同矿井,工作面顶板钻孔水量、累计预疏放水量、采空区涌水量也存在较大差异,该差异与直接充水含水层厚度和岩性等有关,反映了地质沉积条件也是控制含水层富水性的重要因素。地形地貌和地质沉积是控制直接充水含水层富水性和工作面涌水量的关键要素。     

Groundwater Sustainability in Arid and Semi-arid Environments: A Review2

Groundwater is an important part of the global hydrological cycle. Sustainable utilization of groundwater is related to regional ecological security and food security, especially in arid and semi-arid environments. This paper reviewed the important achievements of the research on groundwater sustainability in arid and semi-arid environments during the past 30 years, and summarized the research progress in groundwater sustainability of arid and semi-arid environments from the conception evolution of groundwater sustainability, evaluation methods, influencing factors, sustainable management, and research frontiers. Our analysis suggests that groundwater in water limited environments around the world has shown unsustainable characteristics both in terms of quantity and quality. However, the existing research focuses more on the quantitative characteristics than the quality characteristics of groundwater, and thus the seriousness of the decline in groundwater sustainability is potentially underestimated. It is pointed out that more research efforts need to be done in the future in balancing the groundwater resources for human and nature, clarifying the impacts of human disturbance and climate change on groundwater sustainability, and strengthening groundwater sustainability through transboundary watershed management. We argued that the difficulty remains how to quantify the sustainable yield of a groundwater basin, and how to assess the groundwater sustainability. Further investigations are required in improving the theoretical framework of groundwater sustainability, modeling the impacts of the various alternative groundwater development scenarios, developing more flexible and efficient indicator frameworks for sustainability evaluation of groundwater system, and deploying more sophisticated groundwater monitoring network for real-time data acquisition. Finally, awareness should also be raised towards ground water sustainability both at the legal level and in the sphere of political action.     

铁在含水层介质中的沉积行为研究

为分析铁在含水层介质中的沉积行为,以石英砂为实验材料,研究了铁在石英砂表面的吸附规律,并对接触时间、铁浓度、腐植酸、钙离子等对沉积过程的影响进行了探讨。结果表明:铁在石英砂上的沉积是单分子层沉积,且沉积过程符合准一级动力学模型。低浓度腐殖酸会促进铁在石英砂上的沉积,但受络合作用影响,增加腐植酸浓度会减少铁在石英砂上的沉积。当水中存在阳离子Ca2+和阴离子SO42-时,会促进铁的沉积,NO3-离子的影响较小,而高浓度F-离子会阻碍铁的沉积。