Analysis of hydrogeolgical characteristics and water environmental impact pathway of typical shale gas exploration and development zones in Sichuan Basin,China

Studying the influence of shale gas exploration and development on groundwater environment is the basis of guiding water environment protection in the process of shale gas exploration and development.Groundwater environmental pollution is concealed,complex and persistent.Once it is difficult to control the pollution,the current commercial shale gas development zones in Sichuan Basin that are mostly located in karst areas and highly sensitive to groundwater will be vulnerable to the impact of shale gas exploration and development.Based on the hydrogeological conditions of shale gas exploration and development area and combined with engineering analysis of exploration and development,various risk pathways that may affect the groundwater environment during process of shale gas exploration,mining well construction,mining operations and other stages were identified in this paper.Some existing risk pathways were proved by verification of typical areas and should not be ignored.Based on the actual situation of typical areas,the countermeasures of groundwater environmental protection in the process of shale gas exploration and development in karst areas were discussed.It is believed that the groundwater environment can be better protected by strengthening administration,research and application of new technologies,precise design,hydrogeological conditions,and research and feedback of groundwater environmental protection.     

Fragmentation of magma during Plinian volcanic eruptions

 The ratio of the volume of vesicles (gas) to that of glass (liquid) in pumice clasts (V _G /V _L ) reflects the degassing and dynamic history experienced by a magma during an explosive eruption. V _G /V _L in pumices from a large number of Plinian eruption deposits is shown here to vary by two orders of magnitude, even between pumices at a given level in a deposit. These variations in V _G /V _L do not correlate with crystallinity or initial water content of the magmas or their eruptive intensities, despite large ranges in these variables. Gas volume ratios of pumices do, however, vary systematically with magma viscosity estimated at the point of fragmentation, and we infer that pumices do not quench at the level of fragmentation but undergo some post-fragmentary evolution. On the timescale of Plinian eruptions, pumices with viscosities <10⁹ Pa s can expand after fragmentation, as long as their bubbles retain gas, at a rate inversely proportional to their viscosity. Once the bubbles connect to form a permeable network and lose their gas, expansion halts and pumices with viscosities <10⁵ Pa s can collapse under the action of surface tension. Textural evidence from bubble sizes and shapes in pumices indicates that both expansion and collapse have taken place. The magnitudes of expansion and collapse, therefore, depend critically on the timing of bubble connectivity relative to the final moment of quenching. We propose that bubbles in different pumices become connected at different times throughout the time span between fragmentation and quenching. After accounting for these effects, we derive new information on the fragmentation process from two characteristics of pumices. The most important is a relatively constant minimum value of V _G /V _L of ∼1.78 (64 vol.% vesicularity) in all samples with viscosities >10⁵ Pa s. This value is independent of magma composition and thus reflects a property of the eruptive mechanism. The other characteristic is that highly expanded pumices (>85 vol.% vesicularities) are common, which argues against overpressure in bubbles as a mechanism for fragmenting magma. We suggest that magma fragments when it reaches a vesicularity of ∼64 vol.%, but only if sheared sufficiently strongly. The intensity of shear varies as a function of velocity in the conduit, which is related to overpressure in the chamber, so that changes in overpressure with time are important in controlling the common progression from explosive to effusive activity at volcanoes. Received: 19 April 1995 / Accepted: 3 April 1996     

岩石圈内的流体通道研究概述

强震孕震环境是一个非常复杂的物质体系，它决定了地震前兆的形成机制，因此，在地震预报基础理论研究中，与强震孕震环境有关的深部物质的物理化学性质的研究具有重要的意义。深部地下流体在地震的孕育和前兆的形成过程中起了极其重要的作用，要研究深部地下流体的活动规律，首先必须研究岩石圈内的流体通道问题。同时，岩石圈内的流体通道也是火山研究中必须面对的一个重要问题。文章在全于流体通道网研究的基础上，简要介绍了岩石圈内流体通道的形成机制、主要特征、研究方法、科学意义和研究展望。     

Network properties of a two-dimensional natural fracture pattern

The influence that fractures exert on the permeability of a fractured rock is, to a large extent, controlled by the nature of the network formed by the fracture system. Here, the network properties of a two-dimensional natural pattern, mapped from the surface of a sandstone layer, are investigated and compared to those of realizations of spatially randomly distributed line segments with similar orientation and length distributions and line segment density (line length per unit area) to the natural pattern. These patterns are composed of clusters of varying size and shape, made up of interconnected fracture traces or line segments. Comparing the natural pattern with the realizations, the natural pattern was found to contain roughly half the number of clusters while the mass (total line length) of the largest cluster is approximately double that of the realizations. The size of the largest cluster controls the connectivity of the patterns, as can be seen by comparing the largest cluster of the natural pattern, which connects all four sides of the region, with those of the realizations, which are unconnected or connect only two sides. Cluster scaling characteristics were found to be similar in the natural pattern and the realizations and show a crossover from a dimension of one (their topological dimension) to two (the dimension of the embedding medium) at a point that corresponds to the fracture spacing. An investigation of the self-similarity dimension, using the box-counting method, showed similar characteristics with a broad transition zone between one- and two-dimensional behaviour at smaller box sizes. The patterns are therefore found to be non-fractal. The effect of the spatial distribution shown by the natural pattern is thus to modify the manner in which fractures are distributed among clusters, increasing connectivity (and permeability in the case of open fractures), but does not affect the cluster scaling characteristics or the self-similarity dimension of the fracture patterns.     

Post-fire management effects on sediment (dis)connectivity in Mediterranean forest ecosystems: Channel and catchment response

Forest fires and post-fire practices influence sediment connectivity (SC). In this study, we use the ‘aggregated index of connectivity’ (AIC) to assess SC in five Mediterranean catchments (198–1090 ha) affected by a wildfire in 2012 in south-eastern Spain. Two temporal scenarios were considered, immediately after the fire and before post-fire management, and 2 years after the fire including all practices (hillslope barriers, check-dams, afforestation, salvage logging and skid trails). One LiDAR (light detection and ranging)-derived digital elevation model (DEM, 2 m × 2 m resolution) was generated, per scenario. The five catchment outlets were established as the computation target (AIC_OUT), and structural and functional SC were calculated. Index outputs were normalized to make the results of the non-nested catchments comparable (AIC_N-OUT). The output analysis includes the SC distribution along the catchments and at local scale (929 sub-catchments, 677 in the burned area), the hillslope and channel measures' effect on SC, and a sedimentological analysis using observed area-specific sediment yield (SSY) at 10 new (built after post-fire practices) concrete check-dams located in the catchments (SSY = 1.94 Mg ha⁻¹ yr⁻¹; σ = 1.22). The catchments with more circular shapes and steeper slopes were those with higher AIC_N-OUT. The structural SC maps – removing the rainfall erosivity influence – allowed evaluating the actual role played by the post-fire practices that reduced SC ( $\overline{x}$= − 1.19%; σ = 0.41); while functional SC was linked to the actual change of SC ( $\overline{x}$= + 5.32%; σ = 0.62). Hillslope treatments resulted in significant changes on AIC_N-OUT at sub-catchment scale with certain disconnectivity. A good and positive correlation was found between the SSY and the changes of AIC_N-OUT. However, the coarse DEM resolution explained the lack of effect of the rock check-dams – located on the secondary channels – on AIC_N-OUT. AIC_N-OUT proved to be a useful tool for decision making in post-fire restoration, but an optimal input data is still necessary to refine calculations.     

Effect of depression storage capacity on overland‐flow generation for rough horizontal surfaces: water transfer distance and scaling

Overland‐flow triggering on rough surfaces was investigated using an understanding‐oriented model. The model was based on conditioned‐walker technique and developed to simulate and analyse the evolution of puddle connection on numerically generated rough surfaces. The percolation theory gave a theoretical framework to formalize model outputs and to study overland‐flow scaling. Overland‐flow triggering appeared consistent with a percolation process. A scale‐change exponent was suggested. New insights based on the concept of transfer distance of water were emphasized. Transfer distance enabled us to analyse the water redistribution inside a field and helped to define rainfall efficiency when infiltration occurred. Copyright © 2002 John Wiley & Sons, Ltd.     

吲哚类杂环芳香族有机物在好氧和厌氧条件下的微生物降解途径

用红树林的底泥通过富集培养得到在好氧或厌氧条件下能完全矿化吲哚的细菌，并对降解过程及中间代谢产物进行了鉴定。此研究中，吲哚化合物是培养液中的唯一碳和能量来源，而厌氧条件包括有产甲烷和硫酸盐还原。结果表明，不论在哪种条件下，吲哚噪降解过程分二步敖基化反应，分别发生在2和3位上，形成氧化吲哚和靛红。同时，1、2或3位上的甲基替代使1—甲基吲哚，2—甲基吲哚和3—甲基吲哚的降解受到严重抑制。显然，杂环类芳香族化合物的代谢有其共同点，同时不同替代会完全改变有机物的可降解程度。     

Describing the Geometry of 3D Fracture Systems by Correcting for Linear Sampling Bias

Analyzing the geometric bias inherent to linear sampling of natural fracture systems is a prerequisite to any attempt of structural modeling. In this paper, the basic parameters of 1D-sampled fracture sets, i.e. orientation, density, and size, are interpreted in terms of geometric probabilities. Weighting factors are derived which allow the 3D restitution of a moderately variable fracture network from a single borehole. The proposed method is applied to well core data from a granitic rock mass, and the efficiency of the proposed corrections is illustrated through random disc simulations tested by virtual scanlines analogous to the real borehole. This approach aims to reduce the prospecting effort in exploration, and to criticize assumption of structural homogeneity by rigorously comparing fracture populations collected from nonparallel boreholes. Then a parametric study of fracture size is performed and a range of mean size leading to fully connected networks is identified.     

A two-dimensional fuzzy random model of soil pore structure

A new conceptual model for soil poresolid structure is formalized. Soil poresolid structure is proposed to comprise spatially abutting elements each with a value which is its membership to the fuzzy set “pore, ” termed porosity. These values have a range between zero (all solid) and unity (all pore). Images are used to represent structures in which the elements are pixels and the value of each is a porosity. Twodimensional random fields are generated by allocating each pixel a porosity by independently sampling a statistical distribution. These random fields are reorganized into other poresolid structural types by selecting parent points which have a specified local region of influence. Pixels of larger or smaller porosity are aggregated about the parent points and within the region of interest by controlled swapping of pixels in the image. This creates local regions of homogeneity within the random field. This is similar to the process known as simulated annealing. The resulting structures are characterized using one and twodimensional variograms and functions describing their connectivity. A variety of examples of structures created by the model is presented and compared. Extension to three dimensions presents no theoretical difficulties and is currently under development.     

区际联系──区域地理学的近期前沿

本文首先指出５０年代以来区域地理学发展滞缓的问题所在，结合实例，阐述６０年代以来区域地理学研究中关于空间关系与空间组织、功能区和优化地域组合的研究进展，认为现阶段区域地理学的前沿在向区际联系的研究方向转移。区域地理学的研究领域从特定区域的独特性，转向地域分异，现阶段又在上述基础上向区际联系方面发展。