Marek Marciniak

A method for the estimation of dual transmissivities from slug tests

Aquifer homogeneity is usually assumed when interpreting the results of pumping and slug tests, although aquifers are essentially heterogeneous. The aim of this study is to present a method of determining the transmissivities of dual-permeability water-bearing formations based on slug tests such as the pressure-induced permeability test. A bi-exponential rate-of-rise curve is typically observed during many of these tests conducted in heterogeneous formations. The work involved analyzing curves deviating from the exponential rise recorded at the Belchatow Lignite Mine in central Poland, where a significant number of permeability tests have been conducted. In most cases, bi-exponential movement was observed in piezometers with a screen installed in layered sediments, each with a different hydraulic conductivity, or in fissured rock. The possibility to identify the flow properties of these geological formations was analyzed. For each piezometer installed in such formations, a set of two transmissivity values was calculated piecewise based on the interpretation algorithm of the pressure-induced permeability test—one value for the first (steeper) part of the obtained rate-of-rise curve, and a second value for the latter part of the curve. The results of transmissivity estimation for each piezometer are shown. The discussion presents the limitations of the interpretational method and suggests future modeling plans.RésuméLors de l’interprétation de tests d’infiltration et d’essais de pompage, l’homogénéité de l’aquifère est. communément supposée, bien que les aquifères soient essentiellement hétérogènes. L’objectif de cette étude est. de présenter une méthode de détermination des transmissivités de formations aquifères à double perméabilité sur la base de tests d’infiltration, tels que des essais de perméabilité induits par des variations de pression. Une courbe avec un taux de croissance bi-exponentiel est. typiquement observée au cours de nombreux de ces essais réalisés dans des formations hétérogènes. Le travail a compris l’analyze de courbes déviant de l’augmentation exponentielle enregistrées à la mine de lignite de Belchatow en Pologne centrale, où un nombre significatif d’essais de perméabilité ont été réalisés. Dans la plupart des cas, une évolution bi-exponentielle a été observée dans les piézomètres comprenant un intervalle crépiné en face de sédiments stratifiés, chaque horizon ayant une perméabilité différente, ou dans des roches fissurées. La possibilité d’identifier les propriétés d’écoulement de ces formations géologiques a été analysée. Pour chaque piézomètre captant de telles formations, un jeu de deux valeurs de transmissivité a été calculé par tronçon sur la base de l’algorithme d’interprétation de l’essai de perméabilité par variation de pression—une valeur pour la première partie (plus pentue) de la courbe de taux de croissance obtenue et une seconde valeur pour la partie terminale de la courbe. Les résultats de l’estimation de la transmissivité pour chaque piézomètre sont présentés. La discussion présente les limites de la méthode d’interprétation et suggère de futurs projets de modélisation.ResumenLa homogeneidad del acuífero se suele asumir cuando se interpretan los resultados de los ensayos de bombeo y “slug”, aunque los acuíferos son esencialmente heterogéneos. El objetivo de este estudio es presentar un método de determinación de transmisividades de las formaciones acuíferas de doble permeabilidad basadas en ensayos “slug”, tales como los ensayos de permeabilidad inducidos por presión. Normalmente se observa una curva de tasa de crecimiento bi-exponencial durante muchos de estos ensayos realizados en formaciones heterogéneas. El trabajo implicó el análisis de curvas que se desvían del aumento exponencial registrado en la mina de Belchatow Lignite en el centro de Polonia, donde se han realizado un número significativo de pruebas de permeabilidad. En la mayoría de los casos se observó movimiento bi-exponencial en piezómetros con una pantalla instalada en sedimentos estratificados, cada uno con una conductividad hidráulica diferente o en roca fisurada. Se analizó la posibilidad de identificar las propiedades de flujo de estas formaciones geológicas. Para cada piezómetro instalado en tales formaciones, se calculó un conjunto de dos valores de transmisividad basado en el algoritmo de interpretación de los ensayos de permeabilidad inducidos por presión—un valor para la primera parte (más pronunciada) de la curva de tasa de crecimiento obtenida y un segundo valor para la última parte de la curva. Se muestran los resultados de la estimación de la transmisividad para cada piezómetro. La discusión presenta las limitaciones del método interpretativo y sugiere futuros programas de modelado.摘要尽管含水层本质上是非均质的,但在解译抽水和段塞流试验结果中,通常假定含水层是均质的。本研究的目的就是介绍一种根据段塞流试验诸如压力诱导渗透性试验确定多重透水性含水地层的导水系数。在非均质地层中进行的许多这种试验基本上都观测到了双指数上升率曲线。工作涉及到分析波兰中部Belchatow 褐煤矿记载的偏离指数上升的曲线,在这里进行了大量的渗透性试验。多数情况下,通过安装在分层的沉积物中带滤水管的测压计可以观测到双指数运移,每一沉积层具有不同的水力传导率,或在裂隙岩中。分析了确定这些地层水流特性的可能性。针对安装在这样地层的 每一个测压计,根据压力诱导透水性试验的解译算法计算了一套两个导水率值—一个值是获取的上升率曲线的第一(较陡峭的)部分,一个是曲线的后半部分。显示了每个测压计的导水系数估算结果。论述展示了解译方法的局限性及提出了未来的模拟规划。ResumoA homogeneidade dos aquíferos é geralmente adotada ao interpretar os resultados de ensaios de bombeamento e instantâneos (slug), embora aquíferos sejam essencialmente heterogêneos. O objetivo deste estudo é apresentar um método de determinação de transmissividades de formações armazenadoras de água de permeabilidade dupla, baseado em ensaios instantâneos (slug tests), tal como o ensaio de permeabilidade de pressão induzida. Uma curva de taxa de crescimento biexponencial é tipicamente observada durante muitos desses ensaios conduzidos em formações heterogêneas. O trabalho envolveu a análise de curvas que se desviam do crescimento exponencial registradas na Mina Belchatow Lignite, na Polônia central, onde números significativos de ensaios de permeabilidade têm sido conduzidos. Na maioria dos casos, o movimento biexponencial foi observado nos piezômetros com filtro instalado em camadas de sedimentos com diferentes condutividades hidráulicas, ou em rochas fissuradas. A possibilidade de identificar as propriedades do escoamento dessas formações geológicas foi analisada. Para cada piezômetro instalado em tais formações, um conjunto de dois valores de transmissividade foi calculado definido em trechos (piecewise), baseado em um algoritmo de interpretação de ensaio de permeabilidade de pressão induzida—um valor para a primeira parte (mais inclinada) da curva da taxa de crescimento obtida, e um segundo valor para a última parte da curva. Os resultados da estimativa de transmissividade para cada piezômetro são mostrados. A discussão apresenta as limitações do método de interpretação e sugere futuros planos de modelagem.

In-situ identification of groundwater drainage conditions in a selected section within the Parsęta River valley

Drainage of groundwater by surface water, i.e. groundwater inflow into a stream or lake, is an essential component of the water balance. Moreover, the drainage and its spatial distribution determine geomorphological processes taking place in the riverbed. In order to identify the spatial distribution of groundwater inflow into the river, prototypes of two new meters filtrometer and gradientmeter) were designed and developed. The filtrometer allows to directly measure the groundwater-surface water seepage through bottom sediments at the place where the meter is embedded into the riverbed. The gradientmeter allows to measure hydraulic gradient within bottom sediments between groundwater and the river. Both parameters measured directly in the riverbed allow to specify the conditions of groundwater flow through bottom sediments. The field research studies conducted by means of the specified meters (filtrometer and gradientmeter) within the Parseta River valley at Storkowo were aimed to investigate the drainage of groundwater and its conditions. A section of the Parseta River with a length of 1600 meters and having no tributaries was selected. Three series of field measurements: spring, summer and autumn ones were conducted. During each series approximately 30 measurements were made by means of the filtrometer and the gradientmeter. The conducted measurements made it possible to calculate flow rates of the drainage of groundwater within the examined section of the Parseta. The obtained results were verified on the basis of control measurements with the application of the differential river flow method. Moreover, it was possible to assess the spatial distribution of specific discharge, hydraulic gradient and hydraulic conductivity in bottom sediments of the Parseta. On an annual basis, the largest drainage of groundwater was found within meander erosive areas where it reached nearly 150% of the average value for the examined section within the Parseta valley. Within meander accumulative areas, the drainage level was at approximately 110% of the average value. At straight sections the drainage of groundwater was the lowest and amounted about 66% of the average value. The research studies conducted in the Parseta valley confirmed the usefulness of the new method to assess the drainage of groundwater and its conditions within the river.