Conceptualizing leakage and storage contributions from long open interval wells in regional deep basin flow models

Deep basin aquifers are increasingly used in water‐stressed areas, though their potential for sustainable development is inhibited by overlying aquitards and limited recharge rates. Long open interval wells (LOIWs)—wells uncased through multiple hydrostratigraphic units—are present in many confined aquifer systems and can be an important mechanism for deep basin aquifers to receive flow across aquitards. LOIWs are a major control on flow in the deep Cambrian–Ordovician sandstone aquifers of the upper Midwest, USA, providing a source of artificial leakage from shallow bedrock aquifers and equilibrating head within the sandstone aquifers despite differential pumpage. Conceptualizing and quantifying this anthropogenic flow has long been a challenge for groundwater flow modellers, particularly on a regional scale. Synoptic measurements of active production wells and well completion data for northeast Illinois form the basis for a transient, head‐specified MODFLOW model that determines mass balance contributions to the region and estimates LOIW leakage to the aquifers. Using this insight, transient LOIW leakage was simulated using transiently changing K_V zones in a traditional, Q‐specified MODFLOW‐USG model, a novel approach that allows the K_V in a cell containing a LOIW to change transiently by use of the time‐variant materials (TVM) package. With this modification, we achieved a consistent calibration through time, averaging 19.9 m root mean squared error. This model indicates that artificial leakage via LOIWs contributed a minimum of 10–13% of total flow to the sandstone aquifers through the entire history of pumping, up to 50% of flow around 1930. Removal from storage exceeds 40% of flow during peak withdrawals, much of this flow sourced from units other than the primary sandstone aquifers via LOIWs. As such, understanding the timing and magnitude of LOIW leakage is essential for predicting future water availability in deep basin aquifers.     

Influence of diaphragm wall installation on the numerical analysis of deep excavation

This paper presents a numerical analysis of the influence of initial stress state on the response of deep excavation supported by retaining wall. Indeed, the influence of diaphragm wall installation prior to excavation works may affect the soil response and lateral wall deflection induced by excavation process. The first part of this paper gives a short review of the numerical methods aimed to reproduce the retaining wall installation. Numerical analysis of a deep excavation in two‐dimensional and three‐dimensional conditions is then performed according to the methods previously presented. In three‐dimensional conditions, diaphragm wall installation is performed considering a sequence of panels, described by their number and length. Results of three‐dimensional calculations confirm that stress state is disturbed by wall installation, which has a sensitive effect on the ground response induced by soil excavation. It is also noted that these results are not easily reproduced in two‐dimensional conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Log evaluation of fractured igneous reservoirs in Songliao Basin

The petrophysical parameters are bad in most igneous reservoirs of Songliao Basin because of the very low porosity and permeability. The evaluation of igneous reservoirs has not been fully studied so far. The current technique of formation evaluation and interpretation used in sedimentary formations face a series of prob- lems and difficulties. In this study, The PCA was used to identify lithology, a multi-mineral model “QAPM” was proposed. “Surface effect” must be considered when evaluating saturation. A software “SIMPLE” was developed and was used to deal with the logging data in over 70 wells with good results were achieved.     

Hydraulic redistribution by deeply rooted grasses and its ecohydrologic implications in the southern Great Plains of North America

Perennial bioenergy crops with deep (>1 m) rooting systems, such as switchgrass (Panicum virgatum L.), are hypothesized to increase carbon storage in deep soil. Deeply rooted plants may also affect soil hydrology by accessing deep soil water for transpiration, which can affect soil water content and infiltration in deep soil layers, thereby affecting groundwater recharge. Using stable H and O isotope (δ²H and δ¹⁸O) and ³H values, we studied the soil water conditions at 20–30 cm intervals to depths of 2.4–3.6 m in paired fields of switchgrass and shallow rooted crops at three sites in the southern Great Plains of North America. We found that soil under switchgrass had consistently higher soil water content than nearby soil under shallow-rooted annual crops by a margin of 15%–100%. Soil water content and isotopic depth profiles indicated that hydraulic redistribution of deep soil water by switchgrass roots explained these observed soil water differences. To our knowledge, these are the first observations of hydraulic redistribution in deeply rooted grasses, and complement earlier observations of dynamic soil water fluxes under shallow-rooted grasses. Hydraulic redistribution by switchgrass may be a strategy for drought avoidance, wherein the plant may actively prevent water limitation. This raises the possibility that deeply rooted grasses may be used to passively subsidize soil water to more shallow-rooted species in inter-cropping arrangements.     

Deep crustal source of gneiss dome revealed by eclogite in migmatite (Montagne Noire,French Massif Central)

In orogens worldwide and throughout geologic time, large volumes of deep continental crust have been exhumed in domal structures. Extension-driven ascent of bodies of deep, hot crust is a very efficient mechanism for rapid heat and mass transfer from deep to shallow crustal levels and is therefore an important mechanism in the evolution of continents. The dominant rock type in exhumed domes is quartzofeldspathic gneiss (typically migmatitic) that does not record its former high-pressure (HP) conditions in its equilibrium mineral assemblage; rather, it records the conditions of emplacement and cooling in the mid/shallow crust. Mafic rocks included in gneiss may, however, contain a fragmentary record of a HP history, and are evidence that their host rocks were also deeply sourced. An excellent example of exhumed deep crust that retains a partial HP record is in the Montagne Noire dome, French Massif Central, which contains well-preserved eclogite (garnet+omphacite+rutile+quartz) in migmatite in two locations: one in the dome core and the other at the dome margin. Both eclogites record P ~ 1.5 ± 0.2 GPa at T  ~  700 ± 20°C, but differ from each other in whole-rock and mineral composition, deformation features (shape and crystallographic preferred orientation, CPO), extent of record of prograde metamorphism in garnet and zircon, and degree of preservation of inherited zircon. Rim ages of zircon in both eclogites overlap with the oldest crystallization ages of host gneiss at c. 310 Ma, interpreted based on zircon rare earth element abundance in eclogite zircon as the age of HP metamorphism. Dome-margin eclogite zircon retains a widespread record of protolith age (c. 470–450 Ma, the same as host gneiss protolith age), whereas dome-core eclogite zircon has more scarce preservation of inherited zircon. Possible explanations for differences in the two eclogites relate to differences in the protolith mafic magma composition and history and/or the duration of metamorphic heating and extent of interaction with aqueous fluid, affecting zircon crystallization. Differences in HP deformation fabrics may relate to the position of the eclogite facies rocks relative to zones of transpression and transtension at an early stage of dome development. Regardless of differences, both eclogites experienced HP metamorphism and deformation in the deep crust at c. 310 Ma and were exhumed by lithospheric extension—with their host migmatite—near the end of the Variscan orogeny. The deep crust in this region was rapidly exhumed from ~50 to <10 km, where it equilibrated under low-P/high-T conditions, leaving a sparse but compelling record of the deep origin of most of the crust now exposed in the dome.     

Evaporation from boreal reservoirs: A comparison between eddy covariance observations and estimates relying on limited data

Hydrological models used for reservoir management typically lack an accurate representation of open-water evaporation and must be run in a scarce data context. This study aims to identify an accurate means to estimate reservoir evaporation with simple meteorological inputs during the open-water season, using long-term eddy covariance observations from two boreal hydropower reservoirs with contrasting morphometry as reference. Unlike the temperate water bodies on which the majority of other studies have focused, northern reservoirs are governed by three distinct periods: ice cover in the cold season, warming in the summer and energy release in the fall. The reservoirs of interest are Eastmain-1 (52°N, mean depth of 11 m) and Romaine-2 (51°N, mean depth of 42 m), both located in eastern Canada. Four approaches are analysed herein: a combination approach, a radiation-based approach, a mass-transfer approach, and empirical methods. Of all the approaches, the bulk transfer equation with a constant Dalton number of 1.2 x 10⁻³ gave the most accurate estimation of evaporation at hourly time steps, compared with the eddy covariance observations (RMSE of 0.06 mm h⁻¹ at Eastmain-1 and RMSE of 0.04 mm h⁻¹ at Romaine-2). The daily series also showed good accuracy (RMSE of 1.38 mm day⁻¹ at Eastmain-1 and RMSE of 0.62 mm day⁻¹ at Romaine-2) both in the warming and energy release phases of the open-water season. The bulk transfer equation, on the other hand, was incapable of reproducing condensation episodes that occurred soon after ice breakup. Basic and variance-based sensitivity analyses were conducted, in particular to measure the variation in performance when the bulk transfer equation was applied with meteorological observations collected at a certain distance (~10–30 km) from the reservoir. This exercise illustrated that accurate estimates of open water evaporation require representative measurements of wind speed and water surface temperature.     

岩性识别：方法、现状及智能化发展趋势

岩性识别是地质工作中一项基础而又重要的工作。传统的岩性识别方法过于依赖经验和地质专业知识积累,不仅耗时长、专业性强,还易受主观因素影响,导致准确率不理想。笔者等首先回顾了传统的岩性识别方法,之后总结了最新涌现的智能化识别方法,最后详细介绍了基于岩石图像、镜下图像、图像与元素信息融合等的智能识别方法。基于岩石图像的识别方法对于文中的岩石识别准确率可达90%以上,基于图像与元素融合的岩性识别方法可以缓解图像相似度高、风化破坏表观特征等因素对识别准确度的影响。笔者等认为当前岩性智能化识别研究仍处于初级阶段,无法满足工程需求。综合各类数据源的优势,利用机器学习深度挖掘岩石元素、矿物、光谱和表观特征间的内在关联性,有利于突破单源信息的局限性,实现岩性快速准确识别。     

安徽滁河断裂带温泉的水化学和同位素特征及成因分析

笔者等以安徽滁河断裂带内的6个温泉为主要研究对象,分析了水样的水化学特征,利用氢氧同位素对温泉的补给高程进行估算,并提出温泉的成因模式。研究区温泉阳离子以Ca2+和Mg2+为主,根据SO2-4和HCO-3的相对含量的不同,可以将水样分为两组,A组水样（富HCO-3）的主要离子的质量浓度均低于B组（富SO2-4）水样,A组水样的水化学类型为HCO-3—Ca2+·Mg2+; B组水样的（除AH14为SO2-4—Ca2+外）水化学类型为SO2-4—Ca2+·Mg2+。A组水样的稀土元素含量高于B组,二者均在NASC标准化图解上表现出平坦型的配分模式,且都表现出轻稀土富集和Eu正异常的特征。水样的氢氧稳定同位素组成表明温泉的补给来源都是大气降水,补给区温度约为13~15 ℃。A组温泉的补给高程为120~160 m低于B组温泉的200~260 m,且A组温泉的热储温度为45~70℃,低于B组温泉的热储温度70~105 ℃。地下水经历深循环获得大地热流加热后沿断裂带上升出地表。     

实时智能地震处理系统在2020年四川石渠M5.6地震序列中的应用

实时智能地震处理系统（RISP）是一套基于深度学习技术的新型地震实时处理系统,于2021年6月在四川开始试运行。为了评估该系统在四川台网稀疏区域的地震检测和处理能力,笔者等采用RISP系统对2020年4月1日四川甘孜州石渠县发生的M5.6级地震序列进行了回溯性分析,获得了较为可靠的自动处理地震序列目录,并与人工目录进行了对比分析。震后10d内,RISP系统自动处理获得了386个地震信号,地震数量是正式地震目录的1.98倍,匹配率为97.43%。分析显示,发震时刻偏差小于±1.0 s的地震占比71.05%,震中位置偏差小于10 km的地震占比96.31%,震级偏差小于±0.3级的地震占比99.47%。根据RISP系统检测地震序列分布特征和震源机制解,认为此次地震的发震断层为五道梁—长沙贡玛断裂北东侧的一条未发现的分支断层。研究结果表明,RISP系统的应用可以提升台网稀疏区域的地震检测能力,可快速产出地震序列目录,对大震应急、震后趋势判定和发震构造研究等具有重要意义。     

基于地球物理反演结果对沂沭断裂带中段深部结构再认识

沂沭断裂带为郯庐断裂带山东段的大断裂,其深度切穿莫霍面,把鲁中造山带与苏鲁造山带隔开,断裂带的活动情况影响山东地区大地构造的稳定性。以往的工作多集中在地表或近地表地质要素的调查和研究,局部也开展了一些地球物理探测工作,大多以剖面为主,对区内地质构造的认识比较局限。本文收集沂沭断裂带约14600 km2范围的区域重力数据,并对其进行了定性解释和三维定量反演,获得了区内地下30 km内的相对密度分布。综合研究了从诸葛镇到五连金矿的精测剖面,其中包括重力、磁法和大地电磁3种方法。由此得到以下几点结果：①揭示了区内东部地下存在一条巨大的隐伏隆起构造,深度约2 km到10 km,从南南西方向延伸到北北东,有3个局部核心区：分别是石桥子镇往西南约30 km范围、由桑园镇、五莲县金矿及许孟镇三者之间的区域、以湖头镇为中心向北向南各延伸约30 km范围。②地表观察的断裂F1和F2比由反演的相对密度确定的断裂F′1和F′2向东偏移,而且北部偏移比南部更大。③重力、磁法、大地电磁测深综合剖面S1—S2研究表明,沂沭断裂带北段内岩矿石具有较低的相对密度、较低的磁性和较低的电阻率特征,意味着断裂带在北部具有张性特点。综上所述,研究区内东部上地壳内存在隐伏隆起构造,昌邑—大店断裂和安丘—莒县断裂在北部具有张性断裂特征,在南部具有挤压特征,莒县以南小地震方式释放部分应力。