Vertical Distribution Of Hydraulic Conductivity Research Articles

Dipole Flow Tracer Test Models for Identifying Skin Properties and Ambient Groundwater Flow Effects.

As a special single-well test with dual-screened configuration, dipole flow test with a tracer (DFTT) has been an efficient tool for aquifer parameter interpretation. The tool is excellent for characterizing the vertical distribution of hydraulic conductivity, dispersivity and in situ reaction rate in aquifers. It is noteworthy that the effects of skin and ambient groundwater flow (AGF) on the solute transport, which have been widely investigated in terms of conventional tracer tests, have not been comprehensively studied with respect to DFTT. Meanwhile, it is important to elucidate the potentials of DFTT in identifying the primary skin properties as well as the methods to avoid the AGF effects on DFTT. Consequently, we developed a mathematical model for DFTT accounting for skin and AGF. The results show that a negative skin acts as a preferential pathway for tracer transport and the AGF effects on breakthrough curves (BTCs) can be easily mistaken for reaction. Through extensive mathematical model-based experiments, the BTCs calculated from the DFTT models with skin effects were categorized into four types, each of which is able to imply a specific kind of skin. Additionally, a new dimensionless parameter , composed of injection/extraction rate, hydraulic conductivity, hydraulic gradient of AGF and screen parameters, was defined to quantitatively indicate the AGF effects on the overestimation degree of the in situ first-order reaction, implying that one can adjust the field parameters of DFTT to keep less than 3.7% to achieve an overestimation error of reaction rate below 50%.

Analytical modeling of mine water rebound: Three case studies in closed hard-coal mines in Germany

Purpose.In this paper we present and validate an analytical model of water inflow and rising level in a flooded mine and examine the model robustness and sensitivity to variations of input data considering the examples of three closed hard-coal mines in Germany. Methods. We used the analytical solution to a boundary value problem of radial ground water flow to the shaft, treated as a big well, and water balance relations for the series of successive stationary positions of a depression cone to simulate a mine water rebound in the mine taking into account vertical distribution of hydraulic conductivity, residual volume of underground workings, and natural pores. Findings. The modeling demonstrated very good agreement with the measured data for all the studied mines. The maximum relative deviation for the mine water level during the measurement period did not exceed 2.1%; the deviation for the inflow rate to a mine before its flooding did not exceed 0.8%. Sensitivity analysis revealed the higher significance of the residual working volume and hydraulic conductivity for mine water rebound in the case of thick overburden and the growing significance of the infiltration rate and the flooded area size in the case of lower overburden thickness. Originality.The developed analytical model allows realistic prediction of transient mine water rebound and inflow into a mine with layered heterogeneity of rocks, irregular form of the drained area, and with the inflow/outflow to a neighboring mine and the volume of voids as a distributed parameter without gridding the flow domain performed in numerical models. Practical implications.The study demonstrated the advantages of analytical modeling as a tool for preliminary evaluation and prediction of flooding indicators and parameters of mined out disturbed rocks. In case of uncertain input data, modeling can be considered as an attractive alternative to usually applied numerical methods of modeling ground and mine water flow.

Fracture controlled permeability of ultramafic basement aquifers. Inferences from the Koniambo massif, New Caledonia

We study the relationship between fracture distribution and permeability in weathered peridotites exposed to tropical climate using the data from the Koniambo massif (New Caledonia, South Pacific). The vertical distribution of hydraulic conductivity is obtained from packer tests performed on four 200-m-deep boreholes. A positive correlation is observed between the cumulated width of weathered fractures and the hydraulic conductivity in a given depth-interval. Therefore, a two-scale model of weathered fractures is developed with small fractures (5 m radius) deduced from outcrop data and large fractures (50 m radius) from a remote sensing analysis. Hydraulic conductivity is 10−5 m/s in the fractures and 10−8 m/s in the matrix. Permeability fields are computed for the synthetic fractures network models, either from flow along the three axes of a periodic cube or from injection through a slit. Then, results are compared to packer tests and show that when both sets of large and small fractures are included, the proposed model reproduces reasonably in situ measured data. Analytical formulae are proposed for computing an approximate permeability from field data. The decrease of hydraulic conductivity with depth is also discussed. We show that the proposed model for peridotites aquifers is similar to the one currently admitted for granitic rock aquifers. It relies on weathering of a pre-existing serpentine-bearing fractures network which controls permeability in the weathering profile itself, but also deeper in the fresh and non-weathered rock. The proposed conceptual model allows deriving quantitative estimate of hydraulic conductivity from field data which are of primary interest for managing the groundwater resource of peridotite aquifers, particularly where mining operations impact groundwater flow.

Hydraulic conductivity explored by factor analysis of borehole geophysical data

A multivariate statistical method is presented for providing hydrogeological information on groundwater formations. Factor analysis is applied to borehole logs in Hungary and the USA to estimate the vertical distribution of hydraulic conductivity of rocks intersected by the borehole. Earlier studies showed a strong correlation between a statistical variable extracted by factor analysis and shale volume in primary porosity rocks. Hydraulic conductivity as a related quantity can be derived directly by factor analysis. In the first step, electric and nuclear logs are transformed into factor logs, which are then correlated to hydraulic properties of aquifers. It is shown that a factor explaining the major part of variance of the measured variables is inversely proportional to hydraulic conductivity. By revealing the regression relation between the above quantities, an estimate for hydraulic conductivity can be given along the entire length of the borehole. Synthetic modeling experiments and field cases demonstrate the feasibility of the method, which can be applied both in primary and secondary porosity aquifers. The results of factor analysis show consistence with those of the Kozeny-Carman method and hydraulic aquifer tests. The application of the statistical analysis of well logs together with independent ground geophysical and hydrogeological methods serves a more efficient exploration of groundwater resources.

An auger tool to estimate hydraulic conductivity using a resistivity analogy

A field instrument and analysis method was developed to estimate the vertical distribution of hydraulic conductivity, K, in shallow unconsolidated aquifers. The field method uses fluid injection ports and four pressure transducers in a hollow auger that measure the hydraulic head outside the auger at several distances from the injection point. A constant injection rate is maintained for a duration time sufficient for the system to become steady state. The novelty of this method lies in the fact that K is determined while the drill string is in the ground and the change in hydraulic head is monitored in the same drill stem. Dense vertical sampling and the application of four transducer offsets provide a detailed resolution of the vertical variability in hydraulic conductivity. Exploiting the analogy between electrical resistivity in geophysics and hydraulic flow, data are processed with a 1-D inversion algorithm for the pole-pole resistivity method resulting in models consistent with the known geology. The injection methodology, conducted in three separate drilling operations, was investigated for repeatability, reproducibility, linearity, and for different injection sources. Repeatability tests, conducted at ten levels, demonstrated spreads of generally less than 10%. Reproducibility tests conducted in three closely spaced drilling operations showed a spread of less than 20%, which may be due to lateral variations in hydraulic conductivity. Linearity tests, made to determine dependency on flow rates, showed no indication that the applied flow rate biased the measurements given the uncertainty of repeated measurements. In order to obtain estimates of the hydraulic conductivity by an independent means, a series of measurements were made by injecting water through screens installed at two separate depths in a monitoring pipe near the measurement site.

A method to estimate hydraulic conductivity while drilling

A field test and analysis method has been developed to estimate the vertical distribution of hydraulic conductivity in shallow unconsolidated aquifers. The field method uses fluid injection ports and pressure transducers in a hollow auger that measure the hydraulic head outside the auger at several distances from the injection point. A constant injection rate is maintained for a duration time sufficient for the system to become steady state. Exploiting the analogy between electrical resistivity in geophysics and hydraulic flow two methods are used to estimate conductivity with depth: a half-space model based on spherical flow from a point injection at each measurement site, and a one-dimensional inversion of an entire dataset. The injection methodology, conducted in three separate drilling operations, was investigated for repeatability, reproducibility, linearity, and for different injection sources. Repeatability tests, conducted at 10 levels, demonstrated standard deviations of generally less than 10%. Reproducibility tests conducted in three, closely spaced drilling operations generally showed a standard deviation of less than 20%, which is probably due to lateral variations in hydraulic conductivity. Linearity tests, made to determine dependency on flow rates, showed no indication of a flow rate bias. In order to obtain estimates of the hydraulic conductivity by an independent means, a series of measurements were made by injecting water through screens installed at two separate depths in a monitoring pipe near the measurement site. These estimates differed from the corresponding estimates obtained by injection in the hollow auger by a factor of less than 3.5, which can be attributed to variations in geology and the inaccurate estimates of the distance between the measurement and the injection sites at depth.

A multistep constant-head borehole test to determine field saturated hydraulic conductivity of layered soils

Although most field soils are heterogeneous, existing analytical solutions to estimate field saturated hydraulic conductivity K fs in unsaturated systems assume that the soil is homogeneous. To overcome the limitations of existing analytical solutions we propose a multistep constant head borehole test to evaluate the field saturated hydraulic conductivity of layered media. The field test consists of conducting constant head borehole tests at different depths that correspond to the different layers in the soil. Measurements of water level and the stable flow rate are then used to compute the hydraulic conductivity of each layer. Equations for evaluating the saturated conductivity of each layer are derived. To determine the flow contribution of each layer, a new pressure solution is also presented. One of the assumptions of the proposed analytical solution is that the pressure gradient on the borehole wall of each layer is independent of the hydraulic conductivity of the layer. Comparison of analytical results with numerical simulation results show that this assumption is reasonable. The proposed analytical procedure can be used to calculate both the saturated and unsaturated flow components. For deep boreholes with large H a ratios (≥ 20; H constant depth of water; a borehole radius) the effect of unsaturated flow on the estimated field saturated hydraulic conductivity can be neglected and only one borehole is required. However, for shallow boreholes ( H a < 20 ), the unsaturated flow component is not negligible and can be estimated by drilling two nearby boreholes of different radii. Field test results are provided to demonstrate the application of the proposed method using deep boreholes in an arid setting. Constant-head borehole tests were repeated at different depths, depending on the number of layers in the system. This test provides a method to determine the vertical distribution of hydraulic conductivity for layered soils which is important for acçurate evaluation of subsurface flow and contaminant transport.

A Test of the In Situ Permeable Flow Sensor at Savannah River, SC

AbstractA test of the In Situ Permeable Flow Sensor was conducted in which ground‐water flow velocity measurements made by the flow sensors were directly compared to velocity estimates obtained using standard hydrologic techniques. Two flow sensors were deployed in a confined aquifer in close proximity to a well which was screened over the entire vertical extent of the aquifer. When the well was pumped at four different pumping rates, the horizontal component of the flow velocity measured by the flow sensors was directed toward the pumping well, within the uncertainty in the measurements, and the magnitude of the horizontal component of the velocity increased linearly with pumping rate, as predicted by theoretical considerations. The measured magnitudes differed from predicted values, calculated with the assumption that the hydraulic properties of the aquifer were homogeneous and isotropic, by less than a factor of two. Vertical components of ground‐water flow observed with the flow sensors are qualitatively consistent with the vertical distribution of hydraulic conductivity estimated from grain‐size analysis but are significantly larger in magnitude than predicted. This is likely due to the creation of a vertical conduit of increased hydraulic conductivity during emplacement of the probes. The results suggest that while the flow sensors measured the local ground‐water flow velocity vector during the test quite accurately, care must be exercised to disturb the formation as little as possible during emplacement. The technology has many potential uses, particularly in the area of environmental site characterization and remediation process monitoring.

Combined Use of Flowmeter and Time‐Drawdown Data to Estimate Hydraulic Conductivities in Layered Aquifer Systems

AbstractThe vertical distribution of hydraulic conductivity in layered aquifer systems commonly is needed for model simulations of ground‐water flow and transport. In previous studies, time‐drawdown data or flowmeter data were used individually, but not in combination, to estimate hydraulic conductivity. In this study, flowmeter data and time‐drawdown data collected from a long‐screened production well and nearby monitoring wells are combined to estimate the vertical distribution of hydraulic conductivity in a complex multilayer coastal aquifer system. Flowmeter measurements recorded as a function of depth delineate nonuniform inflow to the wellbore, and this information is used to better discretize the vertical distribution of hydraulic conductivity using analytical and numerical methods. The time‐drawdown data complement the flowmeter data by giving insight into the hydraulic response of aquitards when flow rates within the wellbore are below the detection limit of the flowmeter. The combination of these field data allows for the testing of alternative conceptual models of radial flow to the wellbore.

Single Well Tracer Tests in Aquifer Characterization

AbstractWhen the purpose of aquifer testing is to yield data for modeling aqueous mass transport, pumping tests and gradient measurement can only partially satisfy characterization requirements. Effective porosity, ground water flow velocity, and the vertical distribution of hydraulic conductivity within the aquifer are left as unknowns. Single well tracer methods, when added to the testing program, can be used to estimate these parameters. A drift, and pumpback test yields porosity and velocity, and point‐dilution testing yields depth‐discrete hydraulic information, A single emplacement of tracer into a test well is sufficient to conduct both tests. The tracer tests are facilitated by a simple method for injecting and evenly distributing the tracer solution into a wellbore, and by new ion‐selective electrode instrumentation, specifically designed for submersible service, for monitoring the concentration of tracers such as bromide.

Evaluation of methods for determining the vertical distribution of hydraulic conductivity : Taylor, K; Wheatcraft, S; Hess, J; Hayworth, J; Molz, F Ground WaterV28, N1, Jan-Feb 1990, P88–98

Evaluation of methods for determining the vertical distribution of hydraulic conductivity : Taylor, K; Wheatcraft, S; Hess, J; Hayworth, J; Molz, F Ground WaterV28, N1, Jan-Feb 1990, P88–98

Evaluation of Methods for Determining the Vertical Distribution of Hydraulic Conductivity

ABSTRACTSix borehole methods for determining the vertical distribution of hydraulic conductivity in unconsolidated geologic formations are evaluated. Straddle packer tests are inappropriate if there is a hydraulic path around the packer on the outside of the well screen. Methods based on grain‐size analysis fail to incorporate the influence of small‐scale structure and packing. Methods based on relationships between electrical and hydraulic conductivity require special conditions and are site‐ and formation‐specific. Borehole effects invalidate methods based on the natural flow of fluid through a well bore. Stoneley wave attenuation methods are not effective in unconsolidated formations. A single‐well electrical tracer test is effective, but requires the injection of significant volumes of fluid.

Determining the Distribution of Hydraulic Conductivity in a Fractured Limestone Aquifer by Simultaneous Injection and Geophysical Logging

ABSTRACTA field technique for assessing the vertical distribution of hydraulic conductivity in an aquifer was applied to a fractured carbonate formation in southeastern Nevada. The technique combines the simultaneous use of fluid injection and geophysical logging to measure in situ vertical distributions of fluid velocity and hydraulic head down the borehole; these data subsequently are analyzed to arrive at quantitative estimates of hydraulic conductivity across discrete intervals in the aquifer. The diagnostic capabilities of the analysis were found to be constrained by the accuracy and resolution of the logging tools as well as by the hydraulic characteristics of the formation. Despite these limitations, this injection/logging technique appears to be practical and effective under the conditions encountered in this application. The results of this analysis identified the contact margin between the Anchor and Dawn Members of the Monte Cristo Limestone as being the dominant transmissive unit. This section is extensively fractured, and quantitative estimates of its hydraulic conductivity are at least two orders of magnitude larger than that of the surrounding competent rock matrix. This transmissive zone also correlates strongly with an interval where the drilling rate was reported to be quite rapid. Aquifer transmissivity was computed from the profile of hydraulic conductivity and found to be 7.6 × 105 ft2/day, a value that is in close agreement with that determined from a conventional constant‐discharge test. Discrepancies between the two estimates may be scale‐dependent, a function of the different formation volumes investigated by each method. The friction factor, a parameter derived from the differential pressure and velocity logs, appears to be a good indicator of borehole rugosity across intervals where fluid velocity remains virtually unchanged, and vertical flow is turbulent.