气压式振荡试验确定地层渗透系数适宜性

为评价滨海地区海（咸）水入侵区不同类型地层渗透性,提出振荡试验适宜模型选择方法。利用Geoprobe系统对不同平面位置地层实施了气压式振荡试验,部分点位进行了分层测试;利用配线法计算地层渗透系数。结果表明:当试验目标层为承压含水层时,利用Butler模型分析欠阻尼振荡试验,KGS模型分析过阻尼振荡试验,均可获得良好的计算结果;当试验目标层为弱透水层时,KGS模型可用于过阻尼振荡试验的数据分析,但计算结果会受到相邻高渗透性含水层以及钻孔编录不准确的影响。地层渗透性等级未知条件下,需根据地层类型、介质岩性、测试井结构和水位恢复过程曲线特征选择适宜的振荡试验分析模型,以准确获取地层渗透系数值。     

Determining the optimal pumping duration of transient pumping tests for estimating hydraulic properties of leaky aquifers using global curve-fitting method: a simulation approach

Global curve-fitting method (GCFM) is regarded as an effective approach in hydrogeological parameter estimation, as it integrates and uses pumping data and water recovery data of a transient pumping test for parameter estimation. The impacts of pumping duration on hydrogeological parameter estimation by GCFM were investigated in the present study using 2 in situ pumping tests and 24 simulated transient pumping tests. Empirical formulas for determining the optimal pumping duration were derived. The study results suggest that pumping duration will have impacts on the accuracy of hydrogeological parameter estimation. When pumping duration is longer than a certain period, relative errors of hydrogeological parameter estimation keep relatively stable within an acceptable limit. Therefore, it is unnecessary to continue the pumping for a very long time after the groundwater level has become stable. When the change rate of drawdown over time (γ) in an observation well located within a distance of 100 m to the pumping well reaches 0.134, the pumping can be stopped. If there are more than one observation wells in a pumping test, the smallest γ value should be selected to determine the optimal pumping duration. This research is meaningful in the instruction of pumping tests, and will reduce test costs greatly.     

埋置基础扭转振动的实用化计算与试验的对比

根据弹性半空间理论及基础振动试验和数值计算的最新成果,采用方程对等法推演出埋置块体基础扭转振动的实用化计算公式。在20 m×10 m×4 m土坑内采用摆锤分别对底面尺寸为0.5 m×0.5 m和1.0 m×0.5 m的埋置块体基础施加冲击荷载,使其发生扭转自由振动,并对其振动响应进行采集,将试验结果与采用实用化计算公式的计算结果进行了比较。该公式具有概念明确,计算简单的优点,对于任意形状,任意埋置状况的动力设备块体基础都适用,其结果对于结构工程的地震响应计算具有参考意义。     

一种用于水压致裂试验的水压供给装置研制及应用

为研究水压致裂过程中水力裂缝的起裂、扩展规律及机制,研制了一种新型水压供给控制装置。该装置由水泵、增压泵、空气压缩机和导水钢垫板等组成。该装置的主要特点是易于与目前广泛存在的压力伺服机相配合,共同完成水压致裂试验,具有操作简便、效率高、成本低、组装方便等优点,使水压致裂试验更易大面积推广。利用该试验装置对类岩石试块进行了水压致裂试验,研究了不同围压下含预置裂隙试件的水力裂缝扩展规律,并与无预置裂隙试件水力裂缝扩展规律进行了对比。试验结果表明,对于含预置裂隙试块,当水平应力差较小时,预置裂隙裂尖对水力裂缝扩展影响较大,水力裂缝起裂后向预置裂隙裂尖方向扩展;随着水平应力差的增大,水力裂缝向最大水平应力方向偏转。试验证明该装置可靠性高,试验过程稳定。该研究对水压致裂试验具有促进意义。     

振荡试验确定倾斜承压含水层水文地质参数

为评价振荡试验在获取倾斜承压含水层水文地质参数过程中含水层倾角对计算结果的影响,基于Kipp模型推导了考虑承压含水层倾角的振荡试验解析解模型。倾斜承压含水层量纲一贮水系数和量纲一导水系数不变条件下,测试井-含水层系统的量纲一阻尼系数随着倾角的增加而增加。修正模型计算的量纲一阻尼系数与Kipp模型计算的量纲一阻尼系数偏差10%以上时,必须考虑倾角的影响并且承压含水层倾角对水头响应曲线造成影响临界角度约为34°。修正模型和Kipp模型对现场振荡试验水头响应曲线分析结果的差异表明,忽略含水层倾角会对倾斜承压含水层导水系数和贮水系数的计算结果产生较大误差。     

Numerical simulations for effects of anisotropy and heterogeneity on well responses to slug tests

Because of their simplicity, assumptions of isotropy and homogeneity are often applied to slug test analyses, determining hydraulic conductivity of heterogeneous and anisotropic formations, in spite of their inherent unfitness. In this study, it was examined how anisotropy and heterogeneity of the formation affect well recovery curves and therefore estimates of hydraulic conductivity in slug tests. Using a finite element method (FEM) slug test model, several hypothetical slug tests in anisotropic and heterogeneous formations with known hydraulic parameters and actual formations of unknown parameters were analyzed. Error factors as a result of the assumptions of isotropy and homogeneity were quantified through sensitivity analyses of well recovery curves. Results of slug tests analyzed in this study indicate that: (1) the well recovery curves in slug tests do not show unique shape or signs reflecting the anisotropy and heterogeneity of the tested formation; (2) the assumption of isotropy does not deviate estimates of hydraulic conductivity significantly when the radial hydraulic conductivity is larger than the vertical one in the formation; (3) the assumption of homogeneity in a layered heterogeneous system has a high potential for errors in hydraulic conductivity estimation, however it can be avoided by placing the screened section apart from the adjacent layers; (4) a low permeability well skin skews the hydraulic conductivity of the original formation, depending on the size and hydraulic conductivity of the skin.     

基于水力层析法的某煤矿承压含水层叠加放水试验分析

水文地质参数是衡量含水层富水性的重要指标,其空间分布特征的准确推算,对于矿井突水灾害预报与防治具有积极意义。传统放水试验分析方法得到的是等效水文地质参数,不能准确刻画含水层的空间异质性。基于随时间变化的水头数据与水文地质参数的互相关分析,将水力层析法应用在陕西榆林柠条塔煤矿井下承压含水层叠加放水试验数据分析中,获得了研究区水文地质参数的空间分布特征。结果表明,工作面南北富水性差异大,涌水区位于强导水带上;从涌水区往北,导水系数和储水系数整体上逐渐减小;南部导水系数和储水系数均较大,属于富水异常区。研究表明,水力层析法是一种有效的非均质含水层参数识别的新技术,将井下放水视为针对含水层的刺激源,结合水头与水文地质参数的互相关分析,联合多个观测孔的水头响应数据,反演刻画研究区域的主要地质结构特征。在矿井水文地质条件分析中,预先采用水力层析法识别富水异常区域,可以有效降低突水事故风险。     

抽水试验确定承压含水层参数方法探讨

地下水资源评价与地下水可开采量计算,需要对地下含水层组参数进行分析确定。本文结合鲁北地区两个地下水水源地采用抽水试验确定承压含水层水文地质参数的实践,探讨定流量(单孔或多孔)抽水试验确定含水层参数的可行性,并对定降深抽水试验确定水文地质参数方法进行了探索。     

基于单孔稳定流抽水试验观测值的非稳定流求参方法

在分析单孔稳定流抽水试验求参方法优缺点的基础上,介绍了一种基于多段降深单孔抽水试验观测值的非稳定流求参方法.在刘庄西区风井的应用实例表明,该方法不仅求参精度较高,而且还可利用稳定流抽水试验的观测值定性地评价含水层的储量性质,因此比常用的非稳定流求参法具有更多的优点.     

Stress and strain fields for overdamped slug tests in aquifer materials,and resulting conservation equation

Two theories may be used to analyze overdamped variable‐head (slug) tests in aquifer materials. The first theory assumes that the solid matrix strain has a negligible influence. The second theory takes into account some elastic and immediate strain. Something is wrong with these theories because they yield different hydraulic conductivity values. This paper explains what is wrong after establishing the strain‐stress elastic equations for a slug test in 2 ideal conditions: plane strain and spherical symmetry. The equations show that the radial contraction (or elongation) and tangential elongation (or contraction) yield a null volumetric strain. As a result, the conservation is described by the Laplace equation, which is used by the first theory. This first theory is the only one to yield correct solutions. The diffusion equation, with storativity, which is used by the second theory, is physically ill founded for slug tests in aquifers. This new proof scientifically confirms previously raised doubts and experimental proofs that the second theory is ill founded.     

A practical approach for the interpretation of flowing well tests

Flowing well test is one of the tools employed to identify transmissivity and storage coefficient of a confined aquifer where the potentiometric surface is located above the ground surface, so that the groundwater flows naturally from the well without pumping. During a flowing well test, constant hydraulic head is preserved at the well while the discharge from the well decreases with time and the temporal variation of discharge provides significant information about aquifer characteristics. In this study, a simple and straightforward approach is presented as an alternative to a number of graphical or error minimization-based techniques available in the literature for analyzing data from flowing well tests. The proposed method employs a polynomial regression equation to establish a link between observed discharge and the theoretical dimensionless discharge that is introduced in the analytical solution, so as to retrieve the aquifer parameters. The method is tested with a vast number of synthetically generated data sets as well as a real data set reported in the literature. Besides its simplicity, the present method is seen to produce highly accurate and reliable estimations.     

How to conduct variable-density sand tank experiments: practical hints and tips

Sand tank experiments are a powerful tool for the investigation and visualization of groundwater flow dynamics. Especially when studying coastal aquifers, where the presence of both fresh and saline water induces complex variable-density flow and transport processes, the controlled laboratory settings of tank experiments help scientists to identify general patterns and features. This technical note provides practical information on planning, conducting and evaluating sand tank experiments, with a focus on application to coastal hydrogeology. Materials, e.g. the sand tank itself, liquids and porous media, are discussed, as well as their handling and auxiliary equipment. The collation of hints and tips is intended to guide novices, as well as experienced researchers, and possibly prevent them from repeating the errors that have been encountered during a long history of experimental work conducted by the authors and researchers associated with many other published studies.

     

承压完整井非稳定流抽水试验的观测时间要求

文章针对无界承压含水层中完整井的非稳定流抽水试验,将Theis公式描述的水位降深与时间的变化关系作为观测井外水位变化的理论真值,考虑观测井内外达到水力平衡所引起的滞后时间因素,推导了观测井内水位变化的理论测量值,分析了测量值与真值之间的相对误差以及测量值接近真值所需要的观测时间。     

压完整井非稳定流抽水试验的观测时间要求

文章针对无界承压含水层中完整井的非稳定流抽水试验,将Theis公式描述的水位降深与时间的变化关系作为观测井外水位变化的理论真值,考虑观测井内外达到水力平衡所引起的滞后时间因素,推导了观测井内水位变化的理论测量值,分析了测量值与真值之间的相对误差以及测量值接近真值所需要的观测时间.     

流量对水力压裂破裂压力和增压率的影响研究

水力压裂现场原位测试试验的破裂压力是计算构造地应力的重要参数。为了探究流量对水力压裂破裂压力和增压率的影响,设计4种不同恒定流量情况的低渗透硬脆灰岩室内大型水力压裂试验,结合声发射监测技术分析不同流量下水力裂缝破裂压力、破坏模式和缝网复杂程度的规律以及流量与增压率的内在关系。试验结果表明：流量越大,破裂压力越高,缝网复杂程度越低;典型压力?时间曲线分为缓慢增压段、急速增压段、稳定增压段和突然下降段;稳定增压段增压率保持不变,压力随时间线性增长,其增压率的大小和流量存在明显的线性关系;基于流量与稳定增压段增压率的线性关系,考虑流量因素的Ito理论可以很好地定量解释流量对破裂压力的影响,试验结果与理论预测吻合度较高。     

Characterization of hydrogeologic properties for a multi-layered alluvial aquifer using hydraulic and tracer tests and electrical resistivity survey

A multi-layered aquifer, typical of riverbank alluvial deposits in Korea, was studied to determine the hydrologic properties. The geologic logging showed that the subsurface of the study site was comprised of four distinctive hydrogeologic units: silt, sand, highly weathered and fresh bedrock layers. The electrical resistivity survey supplied information on lateral extension of hydrogeologic strata only partially identified by a limited number of the geologic loggings. The laboratory column tracer test for the recovered core of the sand layer resulted in a hydraulic conductivity of 5.00×10⁻² cm/s. The slug tests performed in the weathered rock layer yielded hydraulic conductivities of 4.32–7.72×10⁻⁴ cm/s. Hydraulic conductivities for the sand layer calculated from the breakthrough curves of bromide ranged between 2.08×10⁻³ and 2.44×10⁻² cm/s with a geometric mean of 6.89×10⁻³ cm/s, which is 7 times smaller than that from the laboratory column experiment. The trend of increasing hydraulic conductivity with an increase in tracer travel length is likely a result of the increased likelihood of encountering a high conductivity zone as more of the aquifer is tested. The combined hydrogeologic site characterization using hydraulic tests, tracer tests, and column test with geologic loggings and geophysical survey greatly enhanced the understanding of the hydrologic properties of the multi-layered alluvial aquifer.     

Study on the hydraulic parameter differences between pumping and recharge in a confined aquifer of a soft soil area

Artificial recharge is an effective remediation measure for controlling groundwater level and subsidence in many coastal cities in China. Hydraulic parameters estimated by pumping tests are often used in the design of both pumping and recharge systems. However, the hydraulic parameters in the recharge process have been found to differ from those in the pumping process and should be studied in greater detail. Eight single-well pumping and recharge tests were conducted within a confined aquifer in a soft soil area in the city of Tianjin, and the differences in wellbore storage influences and well losses between the recharge and pumping processes were examined. Furthermore, based on the Hantush and Jacob model, an algorithm combining the Levenberg–Marquardt algorithm (LMA) and genetic algorithm (GA) was employed for estimation of the hydraulic parameters. The results illustrated that the combined algorithm eliminating wellbore storage influences could provide hydraulic parameters from which the groundwater level variation could be accurately simulated. The hydraulic conductivity and specific storage values obtained in the pumping tests were higher than those obtained in the recharge tests. In addition to slight plugging of the recharge well, the specific storage differences could be explained by the compression and rebound deformation characteristics of sand in the confined aquifer. The specific storage estimated by pumping tests should be adjusted when applied in groundwater recharge calculation.

     

无观测孔双井干扰抽水求取承压含水层导水系数方法探讨

煤矿疏降水工程需要以含水层组参数为基础进行合理布设。结合某矿区内的非稳定流双孔干扰抽水试验,在无观测孔情况下,根据抽水井资料分别利用通用直线法、水位恢复法、解析法及优化拟合四种方法确定承压含水层的导水系数,并利用后期疏降水孔资料对上述方法进行验证,结果表明通用直线法和水位恢复法计算结果可靠。     

Comparison of pumping at constant head and at a constant rate for determining the sustainable yield of a well

Determining the yield of a production well remains one of the main problems in hydrogeological studies. Starting from the results of a 3-year-long monitoring of a continuously exploited well functioning at constant head (i.e., at a variable discharge rate), a new pumping style has been examined using numerical models. The objective is to control the impact of pumping on the aquifer in accordance with the principle of sustainability. Different models were developed in a transient state and were calibrated using discharge data of the well during the recession periods. Successively, the trends of the residual outflow from the aquifer system with the well operating at variable discharge and at constant discharge were simulated. The results indicate that the ratio of the volume of water pumped from the well to the volume of residual outflow is a significant indicator of the sustainability of groundwater withdrawals. Modeling confirms that a constant discharge rate can be derived from the information gained through a preliminary production phase of a well at constant head. This approach appears to be particularly useful when the problem is determining the sustainable yield of a single well from aquifers with low hydraulic diffusivity.